1992 Jimmy (W) Fuel/Air Problems

[z3r0]

Well, this is my first post here. I would like to start by saying hello.

My 1992 GMC Jimmy (S15) (VIN W) has a 4.3L vortec in it. (God bless those horrible spider injectors.)

I am a delivery driver/courier. My problem started after a delivery. When I got into my truck I placed the transmission in drive and it died. I had a heck of a time starting it back up. When I got it started, I had to 2 foot it back to my house.

Once there, I had my friend take a look at it on the following day. We began thinking that it wasn't getting the right fuel/air mixture. I can start it from a cold start, or after we unhook the power from the injector and start it, it seemed like i burnt excess fumes in the intake. Then, hooked the injector back up and it starts right up. Once warm I can rev it up in park and eventually it will choke itself out within ten minutes. After the truck chokes it will crank and crank ect... Until it either sits long enough or the injector power was cut and started again.

I have changed the TPS, IAC valve, fuel injector and the fuel pressure regulator. Still no luck, it has the same symptoms. I have also changed the plentum gasket and triple checked the torque on the the plentum bolts.
There seems to be no leaks on the gasket.

We have also checked the fuel pressure by removing the input on the fuel filter. The fuel pump is giving proper pressure forward. We have also tested the fuel pressure from the test port behind the intake. The pressure don't seem to hold like it should but has a very VERY slow release. (10 psi every half hour to an hour or so). I have not changed the entire spider itself.

I'm going a bit nutty trying to fix this problem. It seems like the intake is flooding... I am wondering if anyone has encountered this problem on this vortec engine. I would assume the Blazer and Sonoma engines would be the same. There are about 106k miles on this vehicle. I bought it 2 weeks ago for $1500. I really need this vehicle. My family depends on me to support them. If any good tech has any ideas, I will be happy to hear them. Any ???'s, just ask and I will be happy to answer.

Thanks,
Z3r0

[MT-2500]

Originally Posted by z3r0

Well, this is my first post here. I would like to start by saying hello.

My 1992 GMC Jimmy (S15) (VIN W) has a 4.3L vortec in it. (God bless those horrible spider injectors.)

I am a delivery driver/courier. My problem started after a delivery. When I got into my truck I placed the transmission in drive and it died. I had a heck of a time starting it back up. When I got it started, I had to 2 foot it back to my house.

Once there, I had my friend take a look at it on the following day. We began thinking that it wasn't getting the right fuel/air mixture. I can start it from a cold start, or after we unhook the power from the injector and start it, it seemed like i burnt excess fumes in the intake. Then, hooked the injector back up and it starts right up. Once warm I can rev it up in park and eventually it will choke itself out within ten minutes. After the truck chokes it will crank and crank ect... Until it either sits long enough or the injector power was cut and started again.

I have changed the TPS, IAC valve, fuel injector and the fuel pressure regulator. Still no luck, it has the same symptoms. I have also changed the plenum gasket and triple checked the torque on the the plenum bolts.
There seems to be no leaks on the gasket.

We have also checked the fuel pressure by removing the input on the fuel filter. The fuel pump is giving proper pressure forward. We have also tested the fuel pressure from the test port behind the intake. The pressure don't seem to hold like it should but has a very VERY slow release. (10 psi every half hour to an hour or so). I have not changed the entire spider itself.

I'm going a bit nutty trying to fix this problem. It seems like the intake is flooding... I am wondering if anyone has encountered this problem on this vortec engine. I would assume the Blazer and Sonoma engines would be the same. There are about 106k miles on this vehicle. I bought it 2 weeks ago for $1500. I really need this vehicle. My family depends on me to support them. If any good tech has any ideas, I will be happy to hear them. Any ???'s, just ask and I will be happy to answer.

Thanks,
Z3r0

Did you check for fuel leaks when you had the platinum off?
With upper platinum off prime up fuel pressure and look for fuel leakage.

There is a very good chance your nut kit the in and out fuel lines inside intake are leaking.

When you prime up fuel pressure what doe the pressure go to how fast does it leak down?

[z3r0]

I did not see any visual leaks inside the plenum. All the testing we did on the fuel pressure was with the plenum off.We spend about 4 hours trying to diagnose the problem.

We did prime up the fuel pressure. It went up to 67psi, then dropped about 5psi immediately. Then the pressure slowly dropped about 7-10psi after 30-45 minutes. Once the pressure guage reached 53psi or so, it held pretty solid.

I do have another spider handy. And my next step was to replace that with yet another plenum gasket and see what happens next... I am definately looking for someone who might have plenty experience with these engines as well as someone who thinks outside the box. I believe after all this, my mechanic frind and I are getting tunnel vision. There did seem to be slight fuel mixed with the carbon buildup inside the intake. But no visible leaks.

Maybe with the plenum on, the vaccum is causing it to leak?

[MT-2500]

Any codes or check engine lights?
Are plugs black or wet on end?
Does it have good hot blue spark to all plugs?
Good ac delco plugs?

[z3r0]

Plugs are in fact ac delco and are properly gapped. I always have an extra set of plugs on hand. I have switch them out. I never had a code blow while diagnosing the problem. The truck has been down for a week. 3 1/2 of those days I have attempted something new. Just yesterday I got my first code (lucky me) by putting a paper clip in a/b. The service engine soon light gave a CODE 22. Which has to do with an improper voltage in the TPS (So MOD said).

Last night I returned the TPS I had bought. Replaced with another new one. I did test the old one. But I wanted to take no chances. Cleared the trouble codes and started the vehicle at cold. Once warm and it wanted to bog down, it blew the code again.

Maybe something else is causing the tps to fail. I suppose I can clean the EGR (it probably needs it) and I do want to test the fuel pressure from the back drivers side of plenum while truck is running to see what the fuel pressure does when the truck attempts to bog down. I'll be away from home today but I will try tomorrow. I'll check back here to see any updates on this thread.

[gjwickline]

with pressure holding at 57 shouldnt be a leak, you should check fuel return line for a blockage if blocked fuel has no where else to go except for conbustion chambers. the individual fuel injector tubes do have a spesific cylinder they go to, check to make sure they are feeding the correct cylinders.

[z3r0]

So I notice the fuel filter is pretty old. I am replacing that since it's only $10 and may keep me more accurate while diagnosing.

When I got the vehicle it began to bog (or hold back) at 45-55 miles an hour. If I pressed the gas to the floor it would accelerate normally above that speed. I don't know if that will help with your diagnosis.

How could I check for an actual blockage in my fuel line? I can clamp it off and block in myself. But unaware of how to check for a blockage. My friend is busy so I cannot consult with him at the moment either.

The thing that keeps getting me is the fact that it will start after I unplug the injector and start then runs ok after I plug it back in. (until it "floods" again)

It seems like I'm drying up from a flood. Which tells me internal gas leak?! But I see none. I do have gas in the oil as well.

But I have no prior knowledge of the vortec engine. My mechanic friend says, and I quote "The vortec is my enemy. Why GM would put fuel components, like the spider inside the air intake is beyond me."

Oh, and the spider is in fact installed correctly.

[z3r0]

I have read under Technical Service Bulletin on MOD and for my year make model it says:

No start, Hard Start, Rough Idle: Clean poppet valves

how would I clean he poppet valves properly? MOD has no info for the poppet valve under "Repair".

[MT-2500]

Code 22 is low voltage on the TPS sensor circuit.

If sensor has been replaced the problem is with wiring or PCM.

Run a voltage check on TPS sensor and check the voltage all of the way to PCM.

The only true test on a TPS sensor is with a lab scope.

[z3r0]

Well, sorry bout the delay since my last post. I had a spare car I could use temporarily for work. Unfortunately, the clutch in the grand am went out tonight.

Most cars I have owned were fords. I know most people talk highly of GM since so many things usually go wrong with Fords. Maybe the with the fords it was nickle and dime, but the gm vehicles seem to be everything expensive when it fails. Please excuse me, as I am just venting. I now have no vehicle for work.

So here is where I stand with the Jimmy:

1.) I could not get the fuel filter changed due to the nuts being rounded from the previous owner. I took it to the shop a day or so ago. They replaced 3ft of gas line with a new fitting installed and a new fuel filter. I can now have an accurate fuel reading. Still, having the same issue as posted above.

2.) Fuel pressure test was successful. Pressure is within the ideal operating range.

3.) Band on caty while attempting to start. (For the hell of it)

So. My next tests will be:

1.) Checking the wiring of PCM for correct voltage.

2.) Re-opening the plenum to check for any fuel inside.

3.) Checking for leakback by building pressure through the lines and separating pressure from the tank/plenum to see if there is a problem with either one.

4.) Replace/check plugs to looked for fouled plugs on cylinder #? ...

5.) Cheap oil change to see if there is still fuel getting into the oil and to protect engine from burning up due to insufficient lubrication.

To sum it up:

1.) New spider, injector, fuel pressure regulator, idle air control valve, fuel filter and throttle positioning sensor.

Problem: Vehicle starts then idle drops once running 10min or so. Cannot turn over vehicle unless I wait 30-60 min or if I:
unplug injector>start>dies>plug in injector>starts>dies again after short period of time

I'll let you know from here. Still open for ideas/suggestions. I'll never turn down reasonable advice.

Thanks MT and Old Master for input thus far.

[MT-2500]

Originally Posted by z3r0

Well, sorry bout the delay since my last post. I had a spare car I could use temporarily for work. Unfortunately, the clutch in the grand am went out tonight.

Most cars I have owned were fords. I know most people talk highly of GM since so many things usually go wrong with Fords. Maybe the with the fords it was nickle and dime, but the gm vehicles seem to be everything expensive when it fails. Please excuse me, as I am just venting. I now have no vehicle for work.

So here is where I stand with the Jimmy:

1.) I could not get the fuel filter changed due to the nuts being rounded from the previous owner. I took it to the shop a day or so ago. They replaced 3ft of gas line with a new fitting installed and a new fuel filter. I can now have an accurate fuel reading. Still, having the same issue as posted above.

2.) Fuel pressure test was successful. Pressure is within the ideal operating range.

3.) Band on caty while attempting to start. (For the hell of it)

So. My next tests will be:

1.) Checking the wiring of PCM for correct voltage.

2.) Re-opening the plenum to check for any fuel inside.

3.) Checking for leakback by building pressure through the lines and separating pressure from the tank/plenum to see if there is a problem with either one.

4.) Replace/check plugs to looked for fouled plugs on cylinder #? ...

5.) Cheap oil change to see if there is still fuel getting into the oil and to protect engine from burning up due to insufficient lubrication.

To sum it up:

1.) New spider, injector, fuel pressure regulator, idle air control valve, fuel filter and throttle positioning sensor.

Problem: Vehicle starts then idle drops once running 10min or so. Cannot turn over vehicle unless I wait 30-60 min or if I:
unplug injector>start>dies>plug in injector>starts>dies again after short period of time

I'll let you know from here. Still open for ideas/suggestions. I'll never turn down reasonable advice.

Thanks MT and Old Master for input thus far.

You are welcome.
Did you get the TPS problem fixed?
If not work on that first thing.

[z3r0]

I just got off work. I work at a pizza joint, I switch hit in kitchen/and driving on days and go st8 to driving for the night. Luckily I still have enough work to pay child support. But not really any money for my own bills. So I need a vehicle running asap. $250 for the clutch parts and $350 for labor on the grand am. So I am focusing on the Jimmy since this is all work I can do without the shop.

I was thinking you all would assume I was crazy for cleaning the poppet valves on the "new" spider. I wanted to add that I got the spider itself from a friend. He replaced the spider on his blazer, which turned out not to be his problem. ($300 learning experience for not properly diagnosing his problem first) DON'T LET THIS HAPPEN TO YOU!!

I am about to begin testing within the next hour or two. I'll keep you posted with my findings. Starting with the oil change and TPS test (PCM wiring). Once, I get rid of my DTC I'll go from there.

I hope the post about proper cleaning of poppet valves helps someone out there. That info was almost impossible to find therefore is worth its weight in gold IMO. I have a friend in a shop that has access to Mitchell OnDemand. He printed that out for me and I spend precious time typing in the info for you all.

[z3r0]

So, waiting for my friend to arrive... He is the muscle and brains. I am just the information mole with relatively good vehicle knowledge/experience.

I was thinking. (Watch out,stand back, put on fire resistant coveralls and wear eye protection)

When I removed the battery cable to get in the plenum and to prevent the vehicle from starting, the computer settings for my idle and TPS reset.

When I put in the new TPS, I did not do the computer relearn steps.

Mitchell says this can cause: Rough or unstable idle. Hesitation or stumble. Rich or lean running. Poor fuel mileage. Harsh or poor transmission shift quality.

Which is just awesome since these were my symptoms before I changed the TPS.

This is the procedure:
1. All service procedures must be complete. Reset minimum air, TPS and max ISC extend, if necessary.
2. Warm engine until operating temperature is reached. Coolant temperature must be greater than 176°F (80°C). This takes approximately 8 minutes (Up to 18 minutes on Allante).
3. Enter diagnostics. Turn ignition off. Allow approximately 20 seconds for the ISC motor to retract and perform a TPS learn.
4. Repeat Step 3).
5. Allow engine to idle in PARK with wheels straight ahead for at least 5 minutes, ensure coolant temperature is greater than 176°F (80°C).
6. With brake applied and Climate Control in the OFF position, place the transmission in "D" position and allow the engine to idle (foot off accelerator) for at least one minute.
7. Ensure outside air temperature reading is at least 50°F. While still in "D", with brakes applied and at idle, place Climate Control in the AUTO position and verify A/C clutch engagement. Allow engine to idle for at least one minute.
8. Place transmission in PARK and turn engine OFF. CAUTION: Because of the load differences on the engine with A/C ON versus OFF, it is VERY IMPORTANT that learning be procedure be performed under both conditions.

Now, I did not get my error code until I unplugged the battery to open plenum.

Would there be another way to reset the TPS? I cannot follow these steps since the vehicle does not properly stay running.

Another thing while I am waiting... The last thing I did before this problem occurred with my vehicle is, get gas. Could bad gas cause this problem?
Should I cyphen/drain the tank and refill? Or should I wait? Gas ain't cheap.

I also found a nasty leak in my exhaust at the muffler.
This just keeps getting better.
My FPR was definitely bad as I did have what appeared to be gasoline in the plenum and in my oil.

[z3r0]

Ok. Probed TPS with engine off and key turned to the on position.

Reading: .32 - .33

As I turn the throttle forward, the reading goes down. Not up.
It should (According to Mitchell) go smoothly up greater than 4.0.

When I place the ground directly to the vehicle, reading was 5.0

Mitchell tells me: TPS signal circuit open or shorted to ground or faulty ECM connection or faulty ECM.

Next step: Test pins on ECM. If reading is correct on ECM, I'll then search for a problem in the wire/ground and repair. If reading from pins on ECM is incorrect, then I should replace ECM.

Basically the ECM is telling injector to dump more fuel into the system. Creating flood. Currently diagnosing ECM now...

ECM price - $90 from O'Reilly
Just have to check OEM # to ensure that the proper part is ordered and replaced.

Thanks thus far MT for heads up on PCM and thank you Old Master for the understanding on these silly vortec intakes.

Very good leaders here. You should all listen to the advice given by these mods.
Don't get cocky. You may not be giving enough information for these people to help you properly. You are on the other side of a computer. They are not under your hood diagnosing your problem. You can't make sugar out of sh*t.

I did fail to mention that my heads up display was giving me incorrect cooling temps and oil pressure. That would probably have helped. Sorry guys.


Will re-post by tomorrow with results.

[z3r0]

The wire from TPS to ECM was good. Fault lies in ECM. Other problems lie in ECM also.

Question: There is another small computer box mounted to the same bracket on the ECM it's white/semi transparent. There is a 4 pin connector (male) and a 9 pin connector (male) both side by side. What is this little box?