Mystery problem...

Ok, I recently purchased a 1989 blazer with the 4.3 motor TBI for $75 in pieces. put it all together, and it's in great shape, no rust, new mufler, etc... (former owner was a mechanic who was about to finish restoring it, but was involves in an accident and died :S )

My problem is the motor is running like crap...

When you first start it it runs really rough and will not come close to idling without help using the gas pedal... It misses a lot and shakes like there's no tommorow. once it's been warmed up a bit it will idle, but roughly with the rpms going up and down and will stall after 10-20 seconds if not given gas. If I go for a short drive (I don't have it registered just yet so no long drives) it will not operate between 1/8 throtle and full throtle... if you just barely touch the gas pedal, it will slowly accelerate. If you floor it, it will hesitate for 1-2 seconds, then accelerate like it should. however, anything in between and there's no power. If you floor it a few times, this "dead" zone will be a little less noticible, though still there... Also after flooring it when you come to a stop it will for the most part idle just fine (even in gear), though there's a soft "poof" ever second or two, with the engline giving a soft shake when it happens. The check engine light does not come on at all... If I let the engine cool down, the problem gets worse again.

Here's what I've tried doing to fix it...

1) checked all the spark plugs... all were the same color, almost white with a bit of a tan.
2) tested all the spark plug wires resistance, all were under the 30,000 ohms limit stated in my manual
3) with the engine running, and IAC valve disconnected (as it said in the manual) disconnected one at a time each spark plug wire and listened for a rpm drop... heard a small drop in rpm on all cilynders (and shocked myself 5-6 times :P )
4) cleaned IAC vavle
5) cleaned and sealed with high temp silicone the EGR valve
6) checked the PCV (or PVC, can't remember what it's called, the one on the valve covers) valve, works fine
7)played with the timing, no effect one way or the other...
8)checked injectors, both giving a good spray (at idle anyway)

Also, I have a vent hose which I cannot figure out where it goes... it is on the right side of the engine (left if you're looking from the front of the truck) on the intake manifold in between the throtle body and the valve cover, see http://www.clubplus.net/~tommy/blazer/TBI.JPG for a picture... (not my pic, found on web) When this vent house is left open, the motor idles high and shakes a LOT, when plugged, idle is low but engine doesn't shake near as much. I've looked all around within reach of the hose (which is about a foot and a half long) and can't find anywhere where it could go...

I should also point out that this engine sat for 3-4 years... not sure if it effects anything...

Anyone have any ideas? I really need to get this truck running as my current car is heading for the scrap heap soon... Also, my friend can get me a carburator for the engine to replace the TBI setup for $120 CND, would this solve the problem? and would it be worth it?

Thanks a bunch, Thomas

i'm not sure where that goes but it probably has something to do with the front diff actuator. if you have any unplugged vacuum ports it will run like a bag of crap. there are many other things that might be causing your problems such as fuel pressure, incorrect timing sensors not working or not hooked up, exhaust restriction. the most important sensors are knock(side of block), tps(throttle position), and ect(engine coolant temp). since you got this thing as a pile of stuff you have no idea whats good and whats bad. with a good volt meter and manual you can check most of this stuff. does the check engine light come on?

Welcome to the forum. You may need to replace the fuel filter. It wouldn't hurt to flush the entire fuel system. If it sat for that long theres no telling what's in the tank, filter and lines. Good luck.

Welcome to the forum. You may need to replace the fuel filter. It wouldn't hurt to flush the entire fuel system. If it sat for that long theres no telling what's in the tank, filter and lines. Good luck.

I'm going to replace the fuel filter today, but I don't think that the problem is bad gas as the tank/sending unit is new (well, got it at a scrap yard, but it is super clean inside and out). Injectors as also "new used". Plus to be safe I put fuel stabilizer in the tank...

And thanks for the welcome :D


I'm not sure where that goes but it probably has something to do with the front diff actuator. if you have any unplugged vacuum ports it will run like a bag of crap. there are many other things that might be causing your problems such as fuel pressure, incorrect timing sensors not working or not hooked up, exhaust restriction. the most important sensors are knock(side of block), tps(throttle position), and ect(engine coolant temp). since you got this thing as a pile of stuff you have no idea whats good and whats bad. with a good volt meter and manual you can check most of this stuff. does the check engine light come on?

ok, forgot to mention in my first post that there is plenty of fuel reaching the injectors... I don't have the tool to actually test the pressure, but while in the middle of replacing the original injectors with test ones from a friend, I turned the key on, and the fuel pump pumped a LOT of gas all over the throtle body :P

Also, have tried 2 different tps's, and 3 different map sensors. I'll take a look at the ect and knock sensors in a bit...

And being a brand new exaust system front to back, I would assume it's not exaust restriction. And like I said in my first post ;) the service engine soon light does not come on at all...

Thanks again...

All the missing and shaking sounds like it could be a firing order or valve timing (or sticking) issue, maybe. The one at a time plug wire removal should have ruled out incorrect order, plus that doesn't sound like a mistake you'd make based on how well you described the issue and what you've done so far. Just shooting in the dark here, but I'd want to check the valve operation. I'm not sure if they're still the preferred method, but my dad used to have a vacuum gage that was marked to tell you if valve timing was off, and of course erratic movement of the needle would indicate a mechanical issue like sticking or other causes for poor compression which would then lead to a cylinder by cylinder compression check. Best of luck.

1.) Cap and Rotor?

2.) Did you disconnect the timing wire when setting the timing to zero?

1.) Cap and Rotor?

2.) Did you disconnect the timing wire when setting the timing to zero?

1) no money to buy new (I'm totally broke at this moment) but I have a second cap that I've tried, no change

2) yes I disconnected the wire (and reconnected afterwards)

Aside from that, I've checked the resistance of the ect sensor, it read 3,000 ohms at roughly 15 celcius. not sure what it should be, but given the manual saying 100,000 ohms at -40 and 70 ohms at somthing like 90 celcuis (not sure of the temp, don't have it beside me) 3000 doesn't seem absurd

I've also checked the tps, and it's working perfectly (0.5 volts at closed throttle going to near 5 volts at full throttle)

As for the knock sensors, can you show me in a picture of some kind where they are? the manual doesn't mention them and I've no idea where they are...

Fuel filter also had no change...

Just for the hell of it I also checked the firring order, no problem there.

Allbert, can you go into more detail on how one would check valve operation... I actually know less about car engines then one would assume :P (I know dirt bike mechanics inside and out, which has helped me, but cars are quite different)

Thanks again! :)

I would check all your vacuum hoses for leaks.

The IAC is probably trying hard to compensate for a vacuum leak somewhere in the system.

I would check all your vacuum hoses for leaks.

The IAC is probably trying hard to compensate for a vacuum leak somewhere in the system.
A) Do you know where that hose I have goes? (check first post)

B) would it run worse when cold then warm with a vacuum leak? because once mine is wamred up it idles (though still like a POS)

That would be your vacuum leak for sure.

Can you take some clearer shots of it, I can't really see it.

http://www.clubplus.net/~tommy/blazer/mytbi.jpg

the yellow hose on the right is just a short piece of hose that is blocked off that I use to cover the opening where the air filer plugs onto, the other yellow hose is to repair a broken plastic vent hose...

The hose that I don't know about is the one going up and resting on the air filter screw thing... It's been blocked this whole time... (it runs even crappier when unplugged)

Check you EGR valve and see if it should be inserted on it.

Check you EGR valve and see if it should be inserted on it.
Nope, egr valve has a hose comming from a seloniod monted beside he map sensor...

Thomas

PCV valve hose?

PCV valve hose?
Nope, it's hooked up porperly too... everything on the vacuum diagram on the label under the hood is hooked up properly,all of the vacuum ports on the throttle body are used... I've looked everywhere within reach of the hose and can't find anywhere :|

http://www.clubplus.net/~tommy/blazer/mytbi.jpg

Aight, I am stumped seeing I don't know the TBI engine as well as my CPI and the CSFI system.

Anyone know where the hose with the screw it in goes?

I can't be certain without looking at my other truck which isn't here right now, but according to my book it looks like the hose that goes to the temperature sensor in the air cleaner assembly that controls the damper in the pre heater.

Nope, that's the yellow one... (I put a blocked hose on it while the air cleaner is off so I don't have a vacuum leak...)

Where can you get a carb for that price . I have the samr year with similar problems and I am going to put a carb on it . Is that a used one ? how are you going to make it fit ? I finally have mine idling all the time but I have the IAC unplugged and the Mechanical adjust screw doing the job .

If it still might be some help, I found a web page with some info on how to use a vacuum gage: http://www.free-ed.net/sweethaven/MechTech/Automotive/Automotive02/lessonMain.asp?iNum=01030305

Rmbodie, a friend of a mechanic friend... heck, don't even know what the going rate is for carbs

Allbert, Thanks, I'll try and see if I can find a vacuum gage sometime tommorow (got a final exam for uni today :| )

I finally got a chance to look under the hood of my 91 blazer yesterday and that line goes to a small check valve then a T behind the distributer. One side goes to the vacuum ball, the other goes to another T with one line going along the firewall over to the drivers side the other going along the firewall to the passenger side. Sorry I couldn't be more specific I was pressed for time. I'll be going back next week and I'll try to take a picture if I can.

I finally got a chance to look under the hood of my 91 blazer yesterday and that line goes to a small check valve then a T behind the distributer. One side goes to the vacuum ball, the other goes to another T with one line going along the firewall over to the drivers side the other going along the firewall to the passenger side. Sorry I couldn't be more specific I was pressed for time. I'll be going back next week and I'll try to take a picture if I can.

That makes sense.

Thanks for the location... all hooked up now. However, still running like a bag of crap. once it's warm it will idle and for the most part will accelerate well enough, but will still hesitate at higher throttle openings. (such as highways) I've also run it enough now to notice an EXTREMELY low gas millage (I don't have an exact mesurement, but approximately 10 miles/gallon) In addition, when cold, it will search for idle (high/low, but mostly low), stall, and hesitate over 10% throttle. any thoughts?

Flipster , the hose plugged with the screw goes to a multidistribution vac near the distributer at the firewall . the peice of hard plastic tubing coming thru the firewall behind the transmission dipstick is supposed to be connected to it as well. Along with a line running to the back of your transmission , unless you have 2 wheel drive. I assume your vents don't change from floor to dash or windshield.
Your description of your problems sounds like what I have been fighting for six months now. I have my IAC solenoid unplugged and the plunger screwed out to close the hole and the mechanical idle set screw holding the idle . My 89 would randomly idle high/low, stumble, studder, stall, running hot ,and was getting bad gas mileage . I had no codes except lean O2 senser . Now I can drive it with no real problems except hills . It will surge or hesitate when starting on even low grade hills.With all new ignition and fuel components , The only thing not replaced is the computer.

ok, fixed the vacuum hose...

Also got a theory as to why it's running like crap... thought maybe you guys would know more...

When I got the truck, the fuel tank/sending unit was garbage, so I replaced them with scrap yard parts from a mid 90's one... now, according to my manual, the fuel pressure should test at 9-13 psi for my TBI, however, for the newer models it says 55-61psi, could it be the fuel pump I have is supplying too much fuel pressure? keeping in mind that my setup has a presure bleed off, and I don't know how that would affect fuel pressure. Basically, has there been a change in fuel pump since 89? And could this be the problem?

PS, I don't have access to a fuel pressure gauge (aside from bringing it to the garage, but I'd like to avoid that cause I'm broke)

Thanks, Thomas

That is most likely the problem.

what I'm wondering though, is is there a difference in the actual fuel pump from 89 to early-mid 90s? Also my TBI has a fuel presure regulator... and the pump I put in did look the same as the one that was in it before...

Check your intake gasket, and also your tbi gasket can of starting fluid sprayed at each engine should not speed up any, if it does tighten or replace.

your egr is sticking. it might be the solenoid that controls it or both. get a new egr and clean the passageway. also check your map sensor. my pickup acted similarly and it was both items acting up. The GM garage had too replace both eventually.