89 Blazer Wouldn't Start Now Running Rich

My 89 S10 4.3L V6 Blazer wouldn't start when I was out shopping on Friday. I had it towed home and the engine fired up immediately on Saturday for a brief test. Thinking that it was an ignition problem I fitted a new disrtibutor cap, rotor arm and king lead on Sunday afternoon

It then started up easlily and as I ran the engine I saw that it was running very rich. I backed it out of the shop and when I put my hand in front the the tailpipe even though the mixture was sooty and rich, the exhaust gasses were so hot that it burnt the hairs off my hand - ouch.

When driving back into the shop the engine stalled and wouldn't start again - I only tried briefly to restart this time, since the failure to start a warm engine was the same as I had on Friday when I was out shopping.


Having a rich engine running so hot is strange - I don't know what to look at now. I imagine that some sensor is misbehaving - where do I go from here? I have the shop manuals and am pouring over them.

My service engine light doesn't seem to come on at all - maybe the bulb has blown - is there a way to read any engine diagnostic codes without using the service engine light to flash out these codes? I hate to have to strip out the dashboard to get at the service engine light.

thanks Mark

Going to try changing the MAP sensor first. A couple of brittle EGR control lines need replacing.

Has anyone had any experience with a good scan tool for this vehicle? I think that I need one to read the sensor outputs.

On the older 12 pin connecting OBD I systems there is no real need for a scan tool. Assuming your check engine light works you just need to jump the top right and the pin next to it for the computer to go into diagnostic mode. Don't start the truck, just turn the key to run

The check engine light doesn't work and I don't want to rip into the dashboard to fix it. I figured that a scan tool would be an easier way to go.

I should be able to read some sensor data with a scanner shouldn't I - the shop manual indicates that I can read quite a bit of sensor data. Got to beat changing random sensors.

I got a scan hooked up. I found two error codes - O2 sensor saying rich mixture and low voltage from MAP sensor. The low MAP sensor voltage is most likely from diagnostic tests when I ran the engine with the electrical connector disconnected from the MAP sensor. I have cleared the codes but now I can't get the engine to start at all.

I am monitoring the ecm values in real time with the scan tool. The MAP sensor is reading 4.80V and looks about right. The TPS runs from 0.70V with throttle closed and 4.28V with the throttle fully down - this looks a little low. The O2 sensor is reading around 450mV

I cannot get the ECM to go into the Clear Flood mode which might help me start the engine, despite holding the throttle down and cranking the engine the scan tool shows the Clear Flood mode as OFF. I am not seeing any RPM reading when cranking the engine - not sure if this is a real problem or an issue with the tool not reading the serial data correctly. It would help if I could get the engine to fire up but maybe the plugs are fouled from running so rich. I am going to wire in a remote starter so that I can monitor the injector body and spark while cranking.

Does anyone have any further thoughts. I haven't seen any obvious reason fro running so rich yet. Is isn't looking like a sensor to me right now.

Mark

Check for good hot blue spark to plugs.
Then check fuel pressure and watch for fast leak down.
Is it a tbi or mpi fuel injection.
To shut fuel off you can unplug fuel pump relay if it will not go into clear flood.
Plull a plug or two and see if it is has gas on it.
But no rpm reading and no check engine light kinda points to the computer.
Drop it down and give it the old tap or twist test and see what it does.
Good luck.
Mt

Reset your timing to zero.

Remember to disconnect the timing wire while doing so.

It's the Model 220 T Body.

I am trying to see where to connect a gauge to measure the fuel pressurre. A high fuel pressure would give me a running rich problem.

I don't know why it won't go into clear flood. It says that throttle must be greater than 80% for 20 secs with ignition on and rpm below 600rpm. The manual doesn't say anything about cranking the engine but I have tried both. The scan tool might not be reading right. I would hve to monitor the injector pusles to be sure. The max voltage on the TPS at 4.2V with the pedal top the metal is a little low - I disconnected the tps connector and jumpered across the tps connenctor to apply the full 5v refrence voltage to the tps input pin and the scan tool showed 5v on the tps signal but still I never could see a computer indication of flood mode. The tps is a little off I think too.

How do I reset the timing to zero. I have cleared all the codes in the ecm.

I am going to hook up a remote starter wire so that I can take a good look at the spark and injector patterns. The starter is buried below the exhaust manifold.

Good luck , I got so fed up with my TBI on my 89 that I took the whole damn thing off . I beleive the tps calibrates itself when you reset the codes and drive it , but if it will not run that idea is useless .
You may have a problem with the idle air control solenoid . mine would not idle correctly and ran rich when it was above idle speed . I disconnected it and removed it and adjusted it to make it idle and left it loose.
Are the injectors leaking when it is pressurized ? Rob

What did you replace the TBI with on your 89. I have the 4.3l engine. I might consider this since this vehicles no longer requires smog testing in NC

I will check to see if the injectors are leaking and spatying properly. I am trying to figure out what fittings I need to connect up a fuel pressure gauge to monitor the pressure. Is the pump running when the ignition is turned. I have the shop manuals but sometimes it takes a lot of digging to find the right information.

There are 2 injectors in the TBI unit. Are they both on at low running or is one for acceleration. I think the one on the left - ie the passenger side was doing the most fuel injecting when it was last running.

I need to get the thing to start but everything is all sooted up now. Gone are the days when removing spark plugs was easy

I would like to test the fuel pressure - it looks like I have to open up the fuel line where it connects between the flexible lines and the steel line in the engine compartment. I will need some sort of T adapter. Has anyone done this and knows where I can get this adapter. I have a fuel line pressure gauge in the garage somewhere. I will dig it out and see if it has any adapters with it. Goodness knows what the threads are.


thanks Mark

I am just south of you in SC . I now have an Edelbrock carb and intake and cam . Power package as they call it . I replaced every sensor and component on the fuel and ignition systems with no success of solving my problem . The kit is listed for marine engines since it does not have EGR capability . Rob:devil:

I would like to test the fuel pressure - it looks like I have to open up the fuel line where it connects between the flexible lines and the steel line in the engine compartment. I will need some sort of T adapter. Has anyone done this and knows where I can get this adapter. I have a fuel line pressure gauge in the garage somewhere. I will dig it out and see if it has any adapters with it. Goodness knows what the threads are.


thanks Mark

The best place to test the fuel pressure on that one is at the fuel filter.
Special fitting on the line so you will need a adapter to fit them.
9-13 lbs of fuel pressure.
Good luck
MT

Thank you both,


I will see what fuel adapters I have got.

I need to remotely crank the engine from under the hood. There is no way to get at the terminals on the starter motor - I think I have followed the wires back - there is a thick bundle and a thin bundle. I am thinking that the solnoid line will be in the thin bundle that comes out in front of the engine (probably only as single wire in the thin bundle). I imagine that I can tap into this wire there. Is there any other place that techs use when they want to remotely crank this engine?

thanks Mark

Look for a purple wire a litter bigger than some.
I catch a lot of them around the brake booster are.
MT

I put a "T" in the fuel line where it come out of the frame between the front driver side tire and the exhaust manifold . On my 89 it has a two inch peice of rubber hose there . There are three lines there . The front one is the supply . I don't have the skirting material so it was really accessable especially with my lift kits . Rob

Also , there is a red insulated female blade connector which is located near the brake booster . You can supply 12 volts to it to run the fuel pump with the ignition off . I used that to prime my carb . Rob

I am suspicious of the fuel pressure and that needs to be measured next. I see the fuel filter. Do I need to remove it and put some sort of T adpater temporarily in it's place ? Any idea where I can order the right adapter/gauge to measure the pressure? MT-2000 have you done this before?


thanks Mark

Your local parts place or tool store should have some adapters.
Yes I do it 2-3 times a week for the over 20 years the tbi system without the fuel pressure test port has been out.
MT

I am not having much luck with finding an adapter - do I need to remove the fuel filter and put a T piece in it's place? Is that what you mean to do. I am not finding anything on the web. Any idea what the threads are?

I am not finding any ports on this vehicle for plugging in a pressure gauge. Most vehicles have a place to measure the pressure. They didn't seem to bother on this vehicle, making a simple procedure a PITA.



I have a pressure gauge. Myabe I need to modify a fuel filter and solder or braze in a pressure take off port to a new fuel filter.

thanks Mark

OK I think I see - I will have a look in Lowes - they keep all sorts of fittings.

I have to make something like this guy made


http://minimopar.knizefamily.net/quickfpg.html

My first step is to buy a fuel filter so I can match up the threads in the hardware store.


Mark

Do not try to jeery rig it up and mess up your fuel lines.

They are special o ring type fittings.
Hardware store does not have anything like it.
They are automotive type fuel line fittings.
Just get the right fittings from a parts place that sells or rents fuel pressure gauges.
But if you want to go to all of the trouble you can get some fittings off of a salvage yard car or take a fuel filter and take fitting off of it or hook/soder another hose fitting into it.
Up to you.
MT

Yes I would rather just buy the right part but I am not having any luck in finding anything suitable. I am looking on the web but not seeing anything other than aftermarket fuel gauges. Whre did you get your fittings?

The parts places in town don't seem to have anything suitable. GM didn't give much thought to this did they. The shop manual isn't much help and gives the wrong instructions but quotes a gauge J29658A/BT 8205 and adapter J2968A-85 to go between the steel line and flexible hose in the engine compartment. However the flexible hoose is crimped onto the steel hose so this is obviously not going to work.

As you say I don't want to mangle up my fuel line fitttings with the wrong fittings.

Mark

would any of these work for me

http://www.jegs.com/webapp/wcs/stores/servlet/CategoryDisplay?catalogId=10002&storeId=10001&categoryId=22703&parentCategoryId=10019&langId=-1

key man i had a similar probablem with mine same year it was the oxygen sensor but even having a leak in ur exhaust throws the voltage off and then makes it run richer so try that i guess!

Thanks for the Oxy sensor tip. Right now I am getting a reasonable reading from the o2 sensor but I haven't ruled it out yet. I can't start the engine right now. I am going to have to change the fouled plugs I expect before I can get it to start again. I don't want to run it too long with it running so rich. Before I do that, I just want to check the fuel pressure. it will probably be OK but that will be one less thing to worry about. After that I am going to have to tack in a wire form the starter solenoid so that I can remotely crank the engine while I am under the hood.


In the meantime I am going to add a fuel gauge like this guy did

http://www.rx7.org/Robinette/fuelp_gauge.htm

but I am going to put the gauge fitting near where the fuel filter fits. I can use the rubber hoses in that area. I may then remove the gauge but leave the T fitting there with the gauge port blanked off with a blanking bolt.


Seems like the best plan to me right now

Has the timing been reset and has the ignition module been checked?

I had a spark before and it was running but running really rich. Now it won't start but the plugs are probably fouled and I think that I will need new plugs before it will restart. I wanted to check the fuel pressure before I attempt a re-plug and restart. I will check for a spark at that time but I had one after the vehicle was towed home. I am not seeing any engine rpm on the scan tool when the engine is cranking which is a concern.

What is the procedure for resetting the timing? I am not sure if advanced or retarded tming can effect the mixture as much as it is. What do you think?

If it is overly retarded it can.

You will haqve to disconenct the timing wire from the PCM and set the timing to zero.

retarded timing - thank you. It didn't sound retarded but that might account for why the exhaust gasses were so hot.

PCM - what is that one? I will study the manual regarding ignition timing.


Something else to look at - may tie in with no rpm signal showing on the scan tool while cranking


Mark

retarded timing - thank you. It didn't sound retarded but that might account for why the exhaust gasses were so hot.

PCM - what is that one? I will study the manual regarding ignition timing.


Something else to look at - may tie in with no rpm signal showing on the scan tool while cranking


Mark

You can not tell by sound. You need to check it. Disconnect the timing bypass and check the base timing.
PCM = computer= Powertrain control module= engine and trans PC
Do you have any check engoine lights or codes?
MT

I am not sure if I have a PCM on this 89 vehicle. There is a separate ESC module that monitors a knock sensor and then sends an ESC (electronic spark control) signal to the ECM for timing control

The main ignition module feeds the ECM and there is an additional set-timing connector between the ignition module and ECM. I imagine that you would want to open this connector when strobing the timing.

I hooked up this scan tool

http://tradervar.zoovy.com/c=x7OZs8f36LavhFVFQzYJWsNNY/category/scantools/

It gave me two codes

MAP sensor voltage low

O2 sensor rich



The MAP sensor low voltage code was caused by me running the engine with the MAP sensor disconnected to see if this corrected the rich mixture it didn't. I have since reconnected the MAP sensor and I am reading 4.80V on the MAP sensor with the ignition turned on and the engine not running.

The TPS appears to be working OK. I get 0.70V with my foot off the gas peddle and 4.06V with the peddle fully down. This is a little low - I would like to see 4.5V or so with the peddle fully down but I don't think that this will give me my rich running problem. I may well change the TPS when I get the engine running again. The O2 sensor is giving me approx 440 to 480 mV with the ignition on which looks good I think.

There may be an issue with me not seeing any engine rpm signal from the ECM on the scan tool but I want to check this with a running engine and if it still appears as problem then I will check it on a working 89 S10 Blazer. I think I know someone who has one. I want to verify the correct operation of the scan tool.

The vehicle doesn't seem able to entire the Clear Flood mode but that may be an old problem which I can most likely work around.

Mark

I am not sure if I have a PCM on this 89 vehicle. There is a separate ESC module that monitors a knock sensor and then sends an ESC (electronic spark control) signal to the ECM for timing control

The main ignition module feeds the ECM and there is an additional set-timing connector between the ignition module and ECM. I imagine that you would want to open this connector when strobing the timing.

I hooked up this scan tool

http://tradervar.zoovy.com/c=x7OZs8f36LavhFVFQzYJWsNNY/category/scantools/

It gave me two codes

MAP sensor voltage low

O2 sensor rich



The MAP sensor low voltage code was caused by me running the engine with the MAP sensor disconnected to see if this corrected the rich mixture it didn't. I have since reconnected the MAP sensor and I am reading 4.80V on the MAP sensor with the ignition turned on and the engine not running.

The TPS appears to be working OK. I get 0.70V with my foot off the gas peddle and 4.06V with the peddle fully down. This is a little low - I would like to see 4.5V or so with the peddle fully down but I don't think that this will give me my rich running problem. I may well change the TPS when I get the engine running again. The O2 sensor is giving me approx 440 to 480 mV with the ignition on which looks good I think.

There may be an issue with me not seeing any engine rpm signal from the ECM on the scan tool but I want to check this with a running engine and if it still appears as problem then I will check it on a working 89 S10 Blazer. I think I know someone who has one. I want to verify the correct operation of the scan tool.

The vehicle doesn't seem able to entire the Clear Flood mode but that may be an old problem which I can most likely work around.

Mark

I am not sure if I have a PCM on this 89 vehicle. There is a separate ESC module that monitors a knock sensor and then sends an ESC (electronic spark control) signal to the ECM for timing control

The main ignition module feeds the ECM and there is an additional set-timing connector between the ignition module and ECM. I imagine that you would want to open this connector when strobing the timing.

I hooked up this scan tool

http://tradervar.zoovy.com/c=x7OZs8f36LavhFVFQzYJWsNNY/category/scantools/

It gave me two codes

MAP sensor voltage low

O2 sensor rich



The MAP sensor low voltage code was caused by me running the engine with the MAP sensor disconnected to see if this corrected the rich mixture it didn't. I have since reconnected the MAP sensor and I am reading 4.80V on the MAP sensor with the ignition turned on and the engine not running.

The TPS appears to be working OK. I get 0.70V with my foot off the gas peddle and 4.06V with the peddle fully down. This is a little low - I would like to see 4.5V or so with the peddle fully down but I don't think that this will give me my rich running problem. I may well change the TPS when I get the engine running again. The O2 sensor is giving me approx 440 to 480 mV with the ignition on which looks good I think.

There may be an issue with me not seeing any engine rpm signal from the ECM on the scan tool but I want to check this with a running engine and if it still appears as problem then I will check it on a working 89 S10 Blazer. I think I know someone who has one. I want to verify the correct operation of the scan tool.

The vehicle doesn't seem able to entire the Clear Flood mode but that may be an old problem which I can most likely work around.

Mark

Sorry that the system glitched and posted my message 3 times - well let's blame the system - makes me feel better

Mark

I do that too sometimes
I do that too sometimes
I do that too sometimes
Mark , you might be going to alot of trouble trying to check fuel pressure this way . There is an easier way . The fuel line comes out of the frame beside the steering shaft . The front one is the supply line . It probably has 4 clamps on it , mine did . Pull it off there and add your "T" . Rob

Thanks Rob,

I see the fuel line coming out of the frame where you say. The line comes up and then turns through 90 degrees towards the engine and then runs straight before being clamped to a steel line. I am thinking of adding the T part just before the pipe is clamped onto the steel pipe. It would be easier to see and work on there and shouldn't be in the way.

Here are the parts that I have ordered for the job

http://store.summitracing.com/default.asp?Ntt=fuel+pressure+gauge&x=16&y=9&searchinresults=false&Ntk=KeywordSearch&DDS=1&N=115&target=egnsearch.asp


http://store.summitracing.com/default.asp?Ntt=fuel+pressure+gauge&x=16&y=9&searchinresults=false&Ntk=KeywordSearch&DDS=1&N=115&target=egnsearch.asp



Mark

I found the purple starter solenoid wire - I got at it where the wiring harness crsooses the intake manifold from the front ogf the engine towards the passenger firewall side.

I am looking at the possible retarded ignition timing. Is this caused by a mechanical problem or can an electronic issue cause retarded timing to occur. I see that the knock sensor circuitry is designed to advance the timing until pinging occurs and then back off a tad but what can cause retarded ignition timing.

Reatrded timing would account for my hand getting burnt by the very hot exhaust gases at the rear tailpipe

Mark

Here's an update.

I installed a fuel pressure gauge - fuel pressure is 11 psi cranking and drops to zero quickly when cranking stops. Injectors are both spraying a nice pattern but way too much fuel. Cranking the engine with the electical connectors removed from the injectors and no fuel is leaking from them.

I removed a plug it was soot black and wet with fuel. I suspect the ecm now. I am not sure about not getting an rpm reading from the scan tool while cranking so I am changing the ignition module in the distributor and if that doesn't do any good then it must be the ecm as far as I can figure. Can't see what else is going to give such a rich starting mixture. The system is open loop then. The throttle body is awash with gas when cranking.

Where is the ecm located? Is it behind the glove box or behind the instrument panel. Any tips for getting to it.


thanks Mark

If I remember correctly, its behind the instrument panel, passenger side. You can get to it by removing the plastic shroud under the passenger side of the dashboard. I would defiently be looking at the ECM. They were a common problem. TPS values at .70 volts are right on. It should go in flood clear mode buy holding the pedal to the floor. If its a timing problem, (doubt it, but possible), find the EST timing bypasss wire, located under the dashboard passenger side, I think its a brown/tan wire, with the connector. Disconnecting this wire will bypass all timing control by EST and set the engine to its base timing. Assuming there is no mechanical problem with the engine, you should be close to "0" for base timing. Try starting it. If it starts and runs alright, you could be looking at a timing problem, which would indicate a ECM problem, or the EST module. Either way, I bet you have A bad ECM, but run through all your tests first, before throwing parts at it.

I am a little confused - the passenger side has the glove box and no instrument panel. Should I look below the glove box for the plastic shroud that you talk about? All of the instruments are on the drivers side. I haven't been able to find the bypass timing wire althought I can see it in the shop manual. It is brown and tan I found a single wire connector in the harness above the brake servo/booster is that the one or is it hidden under the dashboard as you mention?

I am not sure what further tests to run now apart from the timing tests that you talk about but I am skeptical of a timing problem causing such bad running and sooty exhaust gases. I think that I have seen all that I need to but I may be missing something else. As I mentioned earlier the scan tool shows that the ecm will not enter the clear flood mode nor am I seeing any engine revs when I am cranking which makes me suspect either the igniton module or ecm.

The engine won't start without a set of new plugs. The plugs in there now are so black and carboned up that starting is impossible. The new set will be fouled very quickly I fear as the engine is running so rich.

I went out and took a look at the dashboard setup. There is a glove box and below that is a parcel shelf and below that is the passenger footwell. Do I remove the covering in the passenger footwell and look up or is it behind the cover in the parcel shelf or maybe behind the glove box? The shop manual seems very vague on this subject and covers too many models.

thanks for your help


Mark

When I removed the EFI from mine I get a buzzing sound from the ECM behind the glove box . The one on right side if sitting in a left driver position . I was also confused by the last few post . Mark, are you getting spark now? before buying an ECM check the distributor . The shaft may be worn and allowing the timing to vary . Rob

Mark, The wire that you would disconnect to set the timing is in the passenger floor board at the top of the carpet . just pull the carpet down a little and it should be there .
The one above the brake booster shoulb be your fuel pump jumper . Mine is red though . Rob

[quote=Markgc] I am a little confused - the passenger side has the glove box and no instrument panel. Should I look below the glove box for the plastic shroud that you talk about? All of the instruments are on the drivers side. I haven't been able to find the bypass timing wire althought I can see it in the shop manual. [quote]

LOL, yes you are right, no instrument panel on the passenger side. Sorry, I wasn't quite right when I said instrument panel. What I meant to say is it is the plastic shroud on the passenger side of the dashboard, on the bottom, above where you put your feet.

Also, like Rmbodie said, the timning bypass wire is just at the top of the carpet on the passenger side, pull the carpet off a little, and you'll see it.

Don't put new plugs in until you figure out your problem. Clean the current plugs with a little sandpaper between the electroid and tip, regap and reinstall.

I replaced the ignition module but I still see 0 rpm on the scan tool when cranking and the throttle body is flooding in gas just as before. I checked for a spark and I have one still.

I am trying to get at the ecm. I cannot get through the glove box but there is a small inspection panel and i can see a black and white wire there with a single in line connector. I can see the ecm hidden in there.

I started to remove the panel above the passengers feet - there seems to be a fan or something there that will obstruct access to the ecm - is this normal. The shop manual doesn't seem to help at all here - it isn't very well written. Do I have to remove this fan next - half the dashboard is apart now LOL. I am tired and calling it a day - I will tackle it again tomorrow.


Mark

Mark , Are you sure the plug wire are in the correct order . The 2.8 and 4.3 have different firing orders . My book has them on the same page . Rob

The HT leads (plug wires) should be right as I labelled each one with it's position on the distributor as I pulled each one off the old distributor cap. ie left front, left center, right back etc. I can double check. I will try and change the plugs tomorrow and go for a quick restart just to make sure that the rich running problem is still there.

I found this place - I think that I will send them my ecm for checking and repair next. That's if I can get it out LOL


http://www.autopart.com/ecc/Ecc.htm

Mark

When I removed the EFI from mine I get a buzzing sound from the ECM behind the glove box . The one on right side if sitting in a left driver position . I was also confused by the last few post . Mark, are you getting spark now? before buying an ECM check the distributor . The shaft may be worn and allowing the timing to vary . Rob

I have always had a spark but since I have just replaced the ignition module inside the distributor I just wanted to make sure that the new module was working OK. Just because it is new out of a box doesn't mean that it is working OK.

The distributor seemed OK mechanically. I noticed that part of the pickup stator core was broken but this looks like it has been like that for a long time and probably isn't connected with my present issue.

I changed the igniton module because I was concerned that I wasn't able to see an engine rpm reading when I am cranking the engine and a friend had a similar issue with a Fiero that wouldn't start. I am going to change the plugs and start the engine so that I can check for an rpm reading on the scan tool, see if the mixture is still rich and check the MAP sensor output voltage.

I didn't realise that getting to the ecm was going to be such a pig of a job. I haven't got it out yet. I want to check the ecm connectors too when I get it out. I will look for the timing bypass wire but I still think that the timing issue is a really long shot here but it won't hurt to put a strobe on the ignition as a quick check if I can keep the engine running long enough. You should see the state of the plugs right now. Blacker and more sooted up than I have ever seen plugs before. The tailpipe is full of black soot too.

Mark

I changed the plugs today and got the engine started up while monitoring the scan tool. I can see engine rpm's OK. The engine is still running very rich.

I monitored the O2 sensor and it was showing around 470 to 500 mV (0.5V) even though the engine was puffing out black smoke. This makes me think that the O2 sensor must be bad - I understood that the O2 sensor output range is around 0 to 1V - with the engine running so rich what should I be seeing? 1V ?

I think that the O2 sensor must be bad. Do you agree? Any tips on getting the thing out? Is it better done with a hot or cold exhaust system?


thanks Mark

I changed the plugs today and got the engine started up while monitoring the scan tool. I can see engine rpm's OK. The engine is still running very rich.

I monitored the O2 sensor and it was showing around 470 to 500 mV (0.5V) even though the engine was puffing out black smoke. This makes me think that the O2 sensor must be bad - I understood that the O2 sensor output range is around 0 to 1V - with the engine running so rich what should I be seeing? 1V ?

I think that the O2 sensor must be bad. Do you agree? Any tips on getting the thing out? Is it better done with a hot or cold exhaust system?


thanks Mark

In open lope your 02 senser may be at a fixed voltage.
Is it running in open or closed lope?
Check your map sensor and coolant sensors and air intake sensors first.
MT

I think that it was running in closed loop mode and the mixture display was jumping between rich and lean on the scan tool data display - so I am presuming that it was in closed loop as the engine had been running for a few minutes. The MAP sensor voltage was varying as I reved the engine. The coolant sensor seems correct. There is no air intake sensor on this vehicle as far as I know.


Mark

Unplug the 02 sensor and check the voltage with a volt/ohm meter.
The unplug PCV valve and see if it leans up.
MT

What kind of scan tool are you using that will give you this info on an 89 model ? Rob

I will check the O2 sensor with a meter this morning. It should weaken out the mixture a bit if the engine is running open loop right?

Did you mean PCV valve - do I unplug the vacuum line to it?


Rob - this is the scan tool that I bought

http://tradervar.zoovy.com/product/CP9110?META=nextag-CP9110


Thss guy also sells his stuff on ebay - you might save a little money that way


Mark

http://cgi.ebay.com/Scan-Tool-With-GM-FORD-Cartridges-CP9110-and-more_W0QQitemZ7606479835QQcategoryZ92078QQssPageNa meZWDVWQQrdZ1QQcmdZViewItem

Rob to answer your question directly - yes the tool works perfectly with my 89 Blazer. I have yet to try it on my 86 RS Cavalier and 89 Silverado but it should work on all 3 just fine - it is suppposed to work on any Ford or Chevy 84 thu 96. It comes with all the cables needed and runs off the cigarette lighter socket

It can read the fault codes, reset the ecm (sometimes) and read real time sensor data coming to the ecm.

Let me know if you have any specific questions


Mark

I will check the O2 sensor with a meter this morning. It should weaken out the mixture a bit if the engine is running open loop right?

Did you mean PCV valve - do I unplug the vacuum line to it?


Rob - this is the scan tool that I bought

http://tradervar.zoovy.com/product/CP9110?META=nextag-CP9110


Thss guy also sells his stuff on ebay - you might save a little money that way


Mark

http://cgi.ebay.com/Scan-Tool-With-GM-FORD-Cartridges-CP9110-and-more_W0QQitemZ7606479835QQcategoryZ92078QQssPageNa meZWDVWQQrdZ1QQcmdZViewItem


The 02 sensor should adjust mixture in closed loop.
In open loop the pcm may just us a fixed or subustute 02 sensor reading.

Yes I ment to say unplug the pcv vacume hose when you are checking 02 sensor with a volt/meter.
Unpluging the vacume hose on it should show a leaner mixture on 02 sensor reading.
Also the scan tool should say open or closed loop.
Some of them you will have to speed the engine up to get them to go into closed loop.
Is the engine getting up to 195 degrees tempture?
MT

I ran the engine with the O2 sensor disconnected and monitored it's output voltage. The engine was still running very rich and blowing out black smuts all over the garage floor - I ran the engine until it was warmed up- ran for about 10 minutes UI would say. The O2 voltage reached a max of 680 to 700 mV. I have a vacuum pipe disconnected - it is the port that goes to the air filter. It doesn't seem to help much with the rich running. I wouldn't have expected the engine to be so rich with the O2 sensor disconnected and rthe ecm using preprogrammed values. I am pressumomg that there is only one O2 sensor. There is an O2 CROSSCNTS value on the scan tool as well as a O2S readout.

The scan tool was showing open loop maybe because the O2 sensor was open circuit and the ecm was having to read open loop values without the O2 sensor input.

The engine rpm is reading OK but it jitters around a bit at higher revs and reads 6250 quite a bit on the scan tool readout.

Thanks for all your help on this one - at least I am learning the ins and outs of ecm control systems and how to work on them


Mark

When the exhaust cools down I will reconnect the O2 sensor. Not sure where to go now. I am leaning towards ecm (fuel control circuit) but not really sure anymore.

I haven't seen anything really obvious yet.

What should I try next. I guess rich open loop testing rules out the O2 sensor for now?

I ran the engine O2 sensor disconnected and pulled the pcv valve tube at the inlet manifold - to give a big vacuum leak - the O2 sensor voltage went up from 700mV to about 720mV as measured on my dvm - strange - it should have weakend the mixture and the voltage gone down but maybe with so much unburnt fuel it helped a bit more fuel burn??

Coolant temp around 170F.

Going to reconnect O2 sensor and see if ecm will enter closed loop mode OK


Mark