94 Suburban problems

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dmc1953

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I have a 94 Chevy Suburban C1500 with a 5.7L, 350 Engine. It has 235,000 miles on it. I purchased it about 4 years ago with 191,000 miles in very good condition and obviously well maintained. I have continued to maintain it well.

For the past few months it has begun to start a little slower that before and when accelerating cold or warm there is a spot where it looses power. It doesn’t sputter or die it just looses power. I can press the accelerator farther and it will come back to life and do fine. After a 20 -30 minute drive if I park for a while, 20 – 30 minutes, when I start it up it dies. The only way to keep it running is to give it the gas and smooth it out at about 1500 rpm for 10 – 15 seconds. Then I can drive it with no problem most of the time though it still has the dead spot on acceleration.

There is a good spray pattern from the throttle body injectors. Plugs and wires are relatively new and plugs look good (AC Delco Rapidfire Platinum). When I turn on the ignition without going to start, the fuel pump builds pressure for 4 – 6 seconds. I haven’t checked the fuel pressure yet and am considering investing in the rig to do so. I recently replaced the fuel filter but that didn’t help.

The check engine light has not come on but many of the lights in the cluster are burned out and I haven't felt like going to the trouble to fix that so it is possible that the check engine bulb is bad.

Anybody have any ideas about this problem?
 
well normally when you first turn the key to the run position all your warning lights should come on so you know whether or not they work. I would definitely do a fuel pressure test, the tester can be rented. I assume you have checked the air filter.
 
Thanks Zora. My instrument panel has all gauges and they work so I"m thinking the only warning lights I would have would be the check engine Light and the brake warning light. I have a K&N air filter and it probably is getting on time to clean it though it looks ok. I spoke with a mechanic this afternoon who told me since it had so many miles on it to check the distributor for wear as well as some of the electronic parts in it might be going bad. I plan to do that tomorrow (Sunday) if I have a chance. I'll let you know how that goes. Thanks again Zora.
 
Haven't been able to get to the parts store yet so last night I pulled the distributor cap and cleaned the corrosion from the electrodes in the cap and cleaned the rotor button. Went for a short drive afterwards and it started and ran much better. When I get to the parts store I'll get a new cap and rotor button. I hope this is that simple to fix.

I did some reading on the K&N filter to refresh my memory and it's in good shape and I'm certain that it was not over oiled last time so that shouldn't be a problem. My Suburban has a MAP sensor.

I paid attention to the instrument display when I turned the key to the run position and the service engine light among others does come on. I haven't paid attention to that in a long time. Dumb I guess. I'll update when I know more. Thanks.
 
Just finished the fuel pressure test and the fuel pump is fine. Tested it cold and hot. I let it run for about 20 minutes to reach and run at operating temperature and then let it sit for about 30 minutes. When I tried to crank it the fuel pump responded with the proper psi and the engine caught and died for several tries. Usually when this happens I can give it the gas and pump the accelerator and keep it running to a point that it will smooth out. Then if I hold it at about 1500 rpms for 15 or 20 seconds I can drive it with little or no problem. This starting when it is warm and has been sitting for awhile is the major problem I've been experiencing. Since the distributor shows no sign of wobble or wear I'm thinking that the module in the distributor must be breaking down due to heat soak in the engine compartment. I'm thinking a dying module could also be the reason it takes a little longer to start than it used to. Does it sound like I'm on the right track?
 
1. After you turn it off and wait a few minutes if you look down the throat of the throttle body do you see any gas dripping?
2. Anything unusual about your temperature gauge readings?
3. Concerning the module, the fact that the engine clears up when holding it at 1,500 RPM doesn't sound like a module.
 
zora said:
1. After you turn it off and wait a few minutes if you look down the throat of the throttle body do you see any gas dripping?
2. Anything unusual about your temperature gauge readings?
3. Concerning the module, the fact that the engine clears up when holding it at 1,500 RPM doesn't sound like a module.
Click to expand...

1. After I turn it off and wait for a few minutes I don't see any gas dripping, however when I remove the air cleaner top I hear a sound from the Throttle body that is like a rapid gurgling of tiny bubbles. After 7 or 8 minutes the sound slows to a point of being intermittent short burst of slower gurgling. This sound can't be heard with the air cleaner in place. At this point when I started it, after allowing about 6 seconds for the fuel pump to pressurize the system, it started and ran poorly almost shutting down for 30 seconds to a minute (I didn't time it) and then it smoothed out. If I had waited 30 minutes I would expect to have play with the accelerator to keep it running.

2. When I turned the key to prime the fuel pump before starting the engine the temperature reading was normal, not hot or cold. When the engine started the temp was normal.

3. Understand what you're saying.
 
zora said:
I know this document is for slightly older vehicles but my apply to yours, there is a section on the symptoms you have
http://www.73-87chevytrucks.com/techinfo/TroubleshootingTBISystems.pdf
Click to expand...

Thanks Zora. I tested the ICM with a new spark tester today....on cold start up it throws plenty of fire. The major problem has been on hot start up after it has been sitting for 20 - 30 minutes. Now I see the ICM is throwing plenty of fire then too so I have to guess that it is not the problem. The injectors in the Throttle Body appear to be supplying adequate fuel hot or cold so I have to guess that is not the problem either.

I wish it would throw a code even if only for just a second!
 
Finally took my Suburban my trusted shop Mechanic. He tested the fuel pump more rigorously than I had and found that it would not hold the pressure under a load. Why didn't I do a load test? Anyway, he replaced the fuel pump and she runs like new. Thanks to everyone for all the input.
 
good to hear you got it resolved
 
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