:confused: I have a 1998 Chevy Blazer with a 4.3 vortex 6 cyl. My problem is I am getting a very rough idle or stumble. I replaced plugs and wires and the problem still exist. I even went through the trouble of pulling the new plugs and check to see if I cracked one putting them in. I also cleaned the throttle body and connected my snap on MT2500 scanner. After going through the diagnostics there are no codes present. I even tapped on the MAF sensor and it does not affect the stumble at all.Any one ever have this happen to them???

Did you change the cap and rotor?

If you didn't replace the cap and rotor, that is probably your problem.

You can also try cleaning the EGR valve and running some Techron through the tank.

Replace the PCV valve also, it will cause a rough idle.

Fuel and air filter too.

At the risk of sounding like a total IDIOT I have to ask..... I thought this particular vehicle was distributorless?

Nope, it's got one. If you replaced the wires yourself, you plugged them right in the cap. That needs to be replaced as well as the rotor inside of it. You can get an AC Delco cap and rotor from rockauto.com for a decent price. (that's where I got the ones for my 98 Blazer.)

I see were the plugs wire go but I thought it was the coil assembly in a DIS system..... I am an IDIOT!!!!!!!!!!! LOL

I see were the plugs wire go but I thought it was the coil assembly in a DIS system..... I am an IDIOT!!!!!!!!!!! LOL

Don't feel bad a lot of people have come to this forum believing they didn't have a distributor.

The DIS is on the 2.2L S10s
Yours has EDI. (Enhanced Distributor Ignition)

:lol: Thanks.........Boy was I misled!!!!

You're welcome.

The screws have Torq heads. You will need a T-20 for the cap and a T-15 for the rotor.

You're welcome.

The screws have Torq heads. You will need a T-20 for the cap and a T-15 for the rotor.

And watch you don't overtighten them or you will strip the threads out of the distributor.

They are only plastic. Tighten till firm and snug ONLY.

I still have the rough idle after replacing the cap and rotor rechecked to make sure i did not screw anything up and it all looks good any have any ideas??

A rough idle has several common causes:

Some other routine maintenance items that can help are:

Air Filter
Fuel Filter
and PCV valve

Another common cause of a rough idle is carbon build up in the EGR valve:

Simply remove the valve, clean it, and reinstall with a new gasket.

In your other post you said you cleaned the throttle body. This may be another surprise to you...the throttle body only lets air in. You have an injector system located inside the intake manifold. It has six injectors one for each cylinder. The fuel enters the cylinder through a poppit valve. These valves are known to clog and cause a rough idle. The most effective way I know to clean them is to add a bottle of Techron to your fuel tank.

I still have the rough idle after replacing the cap and rotor rechecked to make sure i did not screw anything up and it all looks good any have any ideas??

What plugs are you using?

[QUOTE=freddie cosme]I still have the rough idle after replacing the cap and rotor rechecked to make sure i did not screw anything up and it all looks good any have any ideas??[

What do you recomend to clean the EGR?? Brakeclean??

TB Cleaner

Well replaced all that was mentioned before (major tune up) cap rotor wires pcv fuel filter air filter cleaned EGR and throttle body even added a 20 oz bottle of techron and still have a rough idle.I dont know whats next I have no codes and Im running out of patience.... Im ready to trade it in

Well replaced all that was mentioned before (major tune up) cap rotor wires pcv fuel filter air filter cleaned EGR and throttle body even added a 20 oz bottle of techron and still have a rough idle.I dont know whats next I have no codes and Im running out of patience.... Im ready to trade it in

just a thought... how were your plugs when you changed them? any glazing, burned deposits? How is your coolant level? Is it low, or is it where it should be? Any puddles under your vehicle?

When I removed the plugs they did not look that bad.The tip of the electrode of the plug was a little worn but I would chaulk that up to normal wear and tear. as for my coolant I have not checked it.Do you think that may cause the rough idlle? I am not running hot and I have no puddles under my car......

That covers all the normal maintenance items. If the rough idle persisted, that would indicate that you may have a real problem. I would check the fuel pressure. Your local Autozone should have a fuel pressure gauge as a loaner tool. You just pay for the tool, return it within 3 days and they give your money back.

The gauge attaches to the schrader valve, it is at the back of the intake on the driver's side, it looks like a big tire valve with a black cap on it:

When you turn the key on, the pump runs for 2 seconds. While the pump is running the pressure should be 60-66psi.

When the pump primes and shuts off (engine still off) the pressure should hold steady between 55-60psi.

With the engine running the pressure should drop 3-10psi depending on engine speed due to vacuum on the regulator.

I have a fuel pressure guage and I will hook it up. Is it ajustable via a pressue regulator?

fuel pressure right on 55psi

:confused: Just a tidbit of info the vehicle runs good while normal driving....its when you come to a stop you feel the crappy idle.

does it shake like a dog would when you give them a bath and they want to shake water off? Mine does that since i bought it and it seems normal because my uncle's 91 does the same.

Just my99 :2cents:

just a thought... how were your plugs when you changed them? any glazing, burned deposits? How is your coolant level? Is it low, or is it where it should be? Any puddles under your vehicle?
I was just curious... Why would you ask about my coolant? I was checking it out & it needs to be changed (flushed).

I was checking to see if I was getting any voltage to my EGR. I put my test light to the connector and I got was a weak lit test light, I checked other sensors and my test light is brightly lit. I think I may have a EGR circut problem.

What was your fuel pressure for each of the following situations:

1)KEY ON, ENGINE OFF, PUMP RUNNING.

2)KEY ON, ENGINE OFF, PUMP OFF. (DOES IT REMAIN CONSTANT?)

3)KEY ON, ENGINE RUNNING.


He was probably asking about the coolant due to the notorious leaking Chevy intake gasket. Let's hope that isn't the problem. If it were leaking you should have seen deposits on the plugs and the idle would have improved briefly after changing the plugs.

I believe the EGR valve should only have voltage when it is being commanded to open and the voltage will depend on how far the ECM wants it open.

And no it isn't normal for these engines to shake like a mad dog.

After looking back over this thread, I just realized we didn't have you try cleaning the IAC valve. That would be another easy thing you could try.

What was your fuel pressure for each of the following situations:

1)KEY ON, ENGINE OFF, PUMP RUNNING.

2)KEY ON, ENGINE OFF, PUMP OFF. (DOES IT REMAIN CONSTANT?)

3)KEY ON, ENGINE RUNNING.


He was probably asking about the coolant due to the notorious leaking Chevy intake gasket. Let's hope that isn't the problem. If it were leaking you should have seen deposits on the plugs and the idle would have improved briefly after changing the plugs.

I believe the EGR valve should only have voltage when it is being commanded to open and the voltage will depend on how far the ECM wants it open.

And no it isn't normal for these engines to shake like a mad dog.

After looking back over this thread, I just realized we didn't have you try cleaning the IAC valve. That would be another easy thing you could try.
Key on engine off pump running 65psi
Key on engine running 57 psi
Key on engine off pump off 65psi for 2 sec and then drops to55psi

What was your fuel pressure for each of the following situations:

1)KEY ON, ENGINE OFF, PUMP RUNNING.

2)KEY ON, ENGINE OFF, PUMP OFF. (DOES IT REMAIN CONSTANT?)

3)KEY ON, ENGINE RUNNING.


He was probably asking about the coolant due to the notorious leaking Chevy intake gasket. Let's hope that isn't the problem. If it were leaking you should have seen deposits on the plugs and the idle would have improved briefly after changing the plugs.

I believe the EGR valve should only have voltage when it is being commanded to open and the voltage will depend on how far the ECM wants it open.

And no it isn't normal for these engines to shake like a mad dog.

After looking back over this thread, I just realized we didn't have you try cleaning the IAC valve. That would be another easy thing you could try.


Yes, blazee is correct, that was what I was asking about. And yes, you might have seen a brief improvement after putting in fresh plugs. plug # 6 and # 3 usually show first signs. Also, I wonder, did you try cleaning the MAF? Other common causes of missing at idle are all the things mentioned so far, plus faulty coil, bad spark plug wires ( I know you replaced them) vacumn leak, incorrect timing, faulty TPS (Throttle position Sensor) and fuel line / filter problem. Just out of curiousity, how was your oil when you changed it? does it smell of gas or coolant? blazee has you on the right track, tho, of using a system of elimination to check for cause / solution.

Key on engine off pump running 65psi
Key on engine running 57 psi
Key on engine off pump off 65psi for 2 sec and then drops to55psi
Im starting to wonder....My coolant resorvior is brown and my radiator is getting there. I think I will top them off and monitor them.

well I dont think its the intake manifold I put a pressure tester on it and it held pressure. I would think if it was an intake gasket it would leak down.

does anyone know how to test your injectors??

Key on engine off pump running 65psi
Key on engine running 57 psi
Key on engine off pump off 65psi for 2 sec and then drops to55psi

Sorry it took so long to get back to you, for some reason this didn't show up as new in my list of subscribed threads.

Your fuel pressure is within spec so it shouldn't be an issue. I don't know how you can test the injectors yourself.

Have you tried cleaning the IAC valve, yet? After cleaning it you need to disconnect the battery for about 10 minutes so the ECM will relearn the idle. Same thing with cleaning the MAF, like blazer94 suggested.

You should also look into the things that blazer94 suggested, except the timing. The ECM controls the timing on 96 and newer models, it can't be adjusted.

Im starting to wonder....My coolant resorvior is brown and my radiator is getting there. I think I will top them off and monitor them.

I know none of us are loaded with cash, but if your coolant is rusty colored and the rad is getting that way, I would NOT top off, I would flush and fill. Bad thing about flushing tho, is sometimes if your heater core has a small leak and a rust flake is blocking it, you discover after flushing that you now have a leak in your heater core. Not too bad of a job, couple hours if you've done it before, first time can be a real bitch-kitty, tho. Also, I erred, as blazee mentioned, I forgot 95+ have ecm controlled timing. :smokin:

fuel pressure right on 55psi

Fuel pressure is low, should be between 61-66psi with the key on.\

Also, you should have regapped the plugs properly and not just looked at them and put them back in.

BTW, what brand of plug are you using?

just curious to know how many injectors does a 98 chevy blazer have?? Is it one or is it 6

It has six

In your other post you said you cleaned the throttle body. This may be another surprise to you...the throttle body only lets air in. You have an injector system located inside the intake manifold. It has six injectors one for each cylinder. The fuel enters the cylinder through a poppit valve. These valves are known to clog and cause a rough idle. The most effective way I know to clean them is to add a bottle of Techron to your fuel tank.

Fuel pressure is low, should be between 61-66psi with the key on.\


His fuel pressure is fine:

Key on engine off pump running 65psi
Key on engine running 57 psi
Key on engine off pump off 65psi for 2 sec and then drops to55psi

well folks i have done and checked everthing that was mention to me and still have a rough idle (stumble). i have used original ac delco parts. No codes present, cooling system checked and flushed.Iam leaning towards fuel injectors but I want to be sure before I swap them out. Is there any tests or diagnostic procedure that i can do to detemine if they are bad???

Just as a recap, can you tell us what you replaced and did?

Just as a recap, can you tell us what you replaced and did?
sure........cap rotor wires fuel filter air filter plugs coolant flush cleaned iac maf egr reset coputer after doing this. i scanned for codes checked my fuel pressure

How about a new PCV valve?

What kind of plugs did you use and what gap did you set them to?

How about a new PCV valve?

What kind of plugs did you use and what gap did you set them to?
yes i did change the pcv valve, as for the plugs i dont remember the number on the plug but they are whats called for that vehicle.the gap was set at .035

yes i did change the pcv valve, as for the plugs i dont remember the number on the plug but they are whats called for that vehicle.the gap was set at .035

What brand name did you use?

For that engine, you use:

41-932 SPARK PLUG, AC DELCO PLATINUM PLUG GAP .054

or

#12 SPARK PLUG, AC DELCO RAPIDFIRE PLUG GAP .060

0.035 is WAAAAAAY to narrow of a gap for your truck engine.

Yep the plugs need to be regapped, there is a good chance they are causing your problem. You said the problem also existed before you changed plugs, hopefully with what you've done, you have fixed the original problem, too.

What brand name did you use?

For that engine, you use:

41-932 SPARK PLUG, AC DELCO PLATINUM PLUG GAP .054

or

#12 SPARK PLUG, AC DELCO RAPIDFIRE PLUG GAP .060

0.035 is WAAAAAAY to narrow of a gap for your truck engine.
I will pull them out and regap them..... keep your fingers crossed

I will pull them out and regap them..... keep your fingers crossed

Hold on there, what plugs are you using?

Hold on there, what plugs are you using?
41-932 is whats in the truck

ok, set the gap to 0.054.

Good luck.

ok, set the gap to 0.054.

Good luck.
I have been researching the S10 blazer This cpi unit keeps comming in to the picture.Is there any way to check this or is this a problem that pertains to early 1990's blazer? Or is this a characteristic of this vehicle regardless of the year as long as it has fuel injection??

I have been researching the S10 blazer This cpi unit keeps comming in to the picture.Is there any way to check this or is this a problem that pertains to early 1990's blazer? Or is this a characteristic of this vehicle regardless of the year as long as it has fuel injection??

You don't have a CPI. Don't worry about it.

You don't have a CPI. Don't worry about it.
Thats good to here.....but are injectors a common problem with blazers?

Thats good to here.....but are injectors a common problem with blazers?

Not really, we hear very few problems with the 1996+ CSFI system like what you have.

If you do have a problem, the check engine light will point you to the EXACT injector to replace.

CPI owners like me enjoy more power and torque, but we don't have the ability to diagnose an exact cylinder fuel problem.

The injectors aren't the problem with the CSFI systems we have, the problem is the poppit valves. They get clogged or stick and can cause rough idle and misfires.

CSFI owners enjoy better gas mileage. :)

The injectors aren't the problem with the CSFI systems we have, the problem is the poppit valves. They get clogged or stick and can cause rough idle and misfires.

CSFI owners enjoy better gas mileage. :)

Ouch....... low blow. Heheeh...

BUT!.......I have more power. ;)

nahnah........

Well I pulled the plugs and cleaned them up and regapped them, then reinstalled them..... not much of a change. But on the flip side I FINALLY got a SES light on. it gave me a code of P00300 cylinder misfire. I went and got new ac delco wires and RECHECKED my plugs just to be sure, cleared the codes and the light came back on again P00300. The more this things stumbles and idles rough it leads me to believe I have a fuel delivery problem (fuel injectors) I have checked the coil and output to the plugs via a sparktester. what do you think? Also...with the SES light is there a way to tell what cylinder it is? Also are the poppit valves part of the injector??

Also recheck the cap and rotor.

A guy recently had the same problem and it turned out to be a poorly made cap and rotor.

:disappoin Well I have done everything that has been dicussed... the maintence needed to be done no regrets there. But the time has come to make some serious choices. Buy the ford expedition or another chevy ?

:disappoin Well I have done everything that has been dicussed... the maintence needed to be done no regrets there. But the time has come to make some serious choices. Buy the ford expedition or another chevy ?

How about invest $50 and some patience and get your truck fixed.

No offense, but buying a new truck because of a rough idle is wasteful.

How about invest $50 and some patience and get your truck fixed.

No offense, but buying a new truck because of a rough idle is wasteful.
Ok I'll bite what can I spend 50.00 bucks on to correct the problem? I have done all the maint.

List what you have done to this point.

List what you have done to this point.
Cap rotor, wires, plugs, fuel filter, air filter cleaned the egr, iac, cleaned maf sensor

I would take it to the dealer and have them hook it up to a tech2 computer so they can monitor the sensors.

How many miles on it?

I would take it to the dealer and have them hook it up to a tech2 computer so they can monitor the sensors.

How many miles on it?
I have 85000 miles on it. I took it to a shop they said I need injectors after talking to the tech he said all I really needed were two but the shop wants to sell me all six. He told me its not hard to do but we were interupted (service manager) so we could not finish our conversation. I guess what Im trying to figure out is if the injectors are under the plenum or what?

Did they give you the codes to tell you which two were acting up?

Have you run a strong dose of fuel injector cleaner through it yet?

The injectors are inside the intake. Most of the time Techron will clear up injection problems. Usually the poppet valves are the problem not the injectors, but they are sold together so I don't think you can replace just the poppets.
If you do need to replace the injectors, I would recommend that you look into the new updated MFI system, it does away with the poppet valves and all the problems associated with them. I have a service bulletin with info about the MFI and installation instructions that I can email to you if you want it.

The injectors are inside the intake. Most of the time Techron will clear up injection problems. Usually the poppet valves are the problem not the injectors, but they are sold together so I don't think you can replace just the poppets.
If you do need to replace the injectors, I would recommend that you look into the new updated MFI system, it does away with the poppet valves and all the problems associated with them. I have a service bulletin with info about the MFI and installation instructions that I can email to you if you want it.

He needs to know which injectors to replace. There should be codes for each of them.

A whole injection system replacement would be a little expensive when compared to a couple injectors.

I only suggested that he look into it as an option. According to the prices I got from www.GMpartsdirect.com (http://www.gmpartsdirect.com/) it would cost $76.72 more to get the whole updated assembly. I would gladly pay that to not have to worry about it anymore. I'm not sure if that will be the total or not, but that is the price for everything listed in the procedure.

Price to replace 2 injectors
Replacement injector...$44.21
Replacement injector...$44.21
Total........................$88.42

Price of updated injector assembly
MFI assembly.............$147.98
MFI mounting bracket...$17.16
Total........................$165.14

He needs to know which injectors to replace. There should be codes for each of them.

A whole injection system replacement would be a little expensive when compared to a couple injectors.
injectors 2 and four

I only suggested that he look into it as an option. According to the prices I got from www.GMpartsdirect.com (http://www.gmpartsdirect.com/) it would cost $76.72 more to get the whole updated assembly. I would gladly pay that to not have to worry about it anymore. I'm not sure if that will be the total or not, but that is the price for everything listed in the procedure.

Price to replace 2 injectors
Replacement injector...$44.21
Replacement injector...$44.21
Total........................$88.42

Price of updated injector assembly
MFI assembly.............$147.98
MFI mounting bracket...$17.16
Total........................$165.14
Im very interested I will look into it!!!!!!!

I only suggested that he look into it as an option. According to the prices I got from www.GMpartsdirect.com (http://www.gmpartsdirect.com/) it would cost $76.72 more to get the whole updated assembly. I would gladly pay that to not have to worry about it anymore. I'm not sure if that will be the total or not, but that is the price for everything listed in the procedure.

Price to replace 2 injectors
Replacement injector...$44.21
Replacement injector...$44.21
Total........................$88.42

Price of updated injector assembly
MFI assembly.............$147.98
MFI mounting bracket...$17.16
Total........................$165.14
do you have a part number and foward me the tsb

do you have a part number and foward me the tsb I need your email address to send you the TSB. If you don't want to post it here, you can send it to me in a PM. The TSB has the part numbers.

I'm super curious as to what the outcome is. Mine is idling rough too! 98LT2WD with 120,000. I also have ticking/tapping under load and start-up. I'm doing an engine flush today!

I'm super curious as to what the outcome is. Mine is idling rough too! 98LT2WD with 120,000. I also have ticking/tapping under load and start-up. I'm doing an engine flush today!

Have you ever done a tuneup?

Changed your fuel filter?

Have you ever done a tuneup?

Changed your fuel filter?

Oh yeh, definitely. At around 100,000. Changed all spark related stuff, fuel filter and pcv. I also use fuel cleaners regularly. I have regretably extended a few oil changes so I figured that would be the best for the engine anyway and a good place to start. I also bought a new fuel filter just to see. This winter the ticking was pretty bad but not so much since it has warmed up. The engine cleaning is where I'll start!

Thanks LT!

what about the cap and rotor?

What plugs did you use?

What kind of oil filter are you using? Fram filters will cause noisy starts.

What kind of oil filter are you using? Fram filters will cause noisy starts.

Yes, cap & rotor. Plugs--i dunno. platinums. yes, fram oil filters. where the heck do you get something different? and what kind? I am flushing the motor now. I am using GUNK and I let it run for 10 minutes(twice what it said). I know someone said 30 minutes but I was too scared to let it go that long. castrol gtx oil.

I have K&N air filter and clean it & re-oil it often.

I prefer the Napa Gold oil filters you get them (of course) from Napa. They are made by WIX. WIX is a well known name, their filters are well made, very high quality and I have found them to give quieter start-ups than AC Delco. If the filters carrying the WIX name were available in my area, I would buy them, but they're not so I settle for the Napa version.


AC Delco is another good filter to use.

If you use a Fram filter get the X2, it is made better than the other Fram filters. I used to use these before I swtiched to Napa Gold. I also have quieter start-ups with the Napa than I did with the X2.

Never use fram oil filters.

FRAM is so huge! How can they be bad if they are so popular? What is it that makes them bad? I don't get it.

Thanks for the replies!

FRAM is so huge! How can they be bad if they are so popular? What is it that makes them bad? I don't get it.

Thanks for the replies!

This is the inside of a proper oil filter.

http://www.oilfilterstudy.com/wix60-e.jpg

And this is a Fram Extra Guard piece of shit.

http://www.oilfilterstudy.com/frameg-b.jpg

Only Fram you can instal is the Extended Guard.

All the rest is mass produced shit.

If you're going to sell me on something other than FRAM you're at least going to have to show me the same views of each. I still can't see why the other is better. Is it the inside (that I can't see)? Trust me, by no means am I trying to be an A$$ here but I truly don't see anything that makes FRAM that bad?! I appreciate your views and your thoroughness of trying to make me see what you do!!

Thanks Again!

If you're going to sell me on something other than FRAM you're at least going to have to show me the same views of each. I still can't see why the other is better. Is it the inside (that I can't see)? Trust me, by no means am I trying to be an A$$ here but I truly don't see anything that makes FRAM that bad?! I appreciate your views and your thoroughness of trying to make me see what you do!!

Thanks Again!

Here you go:
http://minimopar.knizefamily.net/oilfilterstudy.html

Don't see what makes it bad?? ......it's made out of cardboard.:eek7: All other filters are made of metal.

What you can't see.... is that the anti-drainback valve is shitty. The anti-drainback valve leaks. allowing oil to drain out of the top of the engine when you shut it off, this means that everytime you crank your engine while using a FRAM....it dry starts. The dry start causes tremendous wear and the tapping and rattling you hear at start-up.

Here you go:
http://minimopar.knizefamily.net/oilfilterstudy.html

Don't see what makes it bad?? ......it's made out of cardboard.:eek7: All other filters are made of metal.

What you can't see.... is that the anti-drainback valve is shitty. The anti-drainback valve leaks. allowing oil to drain out of the top of the engine when you shut it off, this means that everytime you crank your engine while using a FRAM....it dry starts. The dry start causes tremendous wear and the tapping and rattling you hear at start-up.

THANK YOU! That wasn't so hard. Are you a teacher? Well, you should be! That is just what I needed to hear. After this oil change I will find a replacement!

Again, Thank You blazee!!

You're welcome. :)

I suggest you go with the WIX or NAPA Gold. They have an awesome anti-drainback valve. You can read about all the different filters in the link that I posted. BTW that link says that WIX and AC Delco's By-Pass valves may possibly leak.....no worries there, the filters for our engines don't have the by-pass valve.

Fuxx.

I had my oil changed last week after I got my truck, and the filter they put on was a Pennzoil, which is apparently the same as one of those crappy FRAMs.

Now I get to have my filter changed again. >_<

Easy, just remove the Fram, replace it with a good one and top up the oil as needed.

Best to check the oil when hot and the engine has been turned off for 5 minutes to get the true level.

Im very interested I will look into it!!!!!!!
Any progress in the last week?

Any progress in the last week?


My ticking has seemed to stop. At least for now. The idle also seems to be smoother but there is still some roughness to it. I am happy of the outcome this far. The motor flush really helped! Now I have a leaky radiator. It seems to be at the top where the "plastic" is.

:grinno: :grinno: Sorry I have not updated..... (VACATION) I will be installing the new injector set up later today and I will let you know

:smokin: Just put in the new replacement fix injectors (courtesy of blazee recomendation) and I gotta tell you its the way to go!!! For the price of this kit you gotta be a fool not to go this route. THANKS!!!!!!!!We have been going back and forth on this issue and I feel we have covered alot and I have learned alot. My Thanks to all!!! Oh by the way kudos to blazerlt on that hood hinge thread that also was a concern of mine

I'm glad to hear that you got it fixed.

Did you have to get anything other than the bracket, assembly, and intake gasket in order to convert it?