94 Suburban problems

[dmc1953]

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?

[j cAT]

your info is lacking. so my guess would be a worn distributor bearing. so replace distributor. before that measure fuel pressures and compare to the vehicle spec. not sure on your vehicle what that would be. being this old replace the ECT and check for the connector wiring its in good shape. make sure the T stat is keeping the engine at around 190 deg F. the 350 distributors all fail when over 175K. gradual engine power starting issues.

[dmc1953]

Thank you j cAT for the info. I spoke with a mechanic this afternoon who also suggested that I check the distributor for wear and possible replacement. The fuel pressure on this one is supposed to be around 12 psi. Since I don't have the rig to check that now I will look at the distributor first and replace it if it is worn. I think the ECT is good and the T stat keeps the engine in the 170 deg range. That is lower than stock and probably was replaced by the former owner. The engine has always run great at that temp. FYI this one has the factory towing package which includes an oil cooler. I'll check the distributor tomorrow (Sunday) if I get a chance and proceed from there. I'll post back if I replace it and let you know if that solved the problem. Thanks again.

[j cAT]

Originally Posted by dmc1953

Thank you j cAT for the info. I spoke with a mechanic this afternoon who also suggested that I check the distributor for wear and possible replacement. The fuel pressure on this one is supposed to be around 12 psi. Since I don't have the rig to check that now I will look at the distributor first and replace it if it is worn. I think the ECT is good and the T stat keeps the engine in the 170 deg range. That is lower than stock and probably was replaced by the former owner. The engine has always run great at that temp. FYI this one has the factory towing package which includes an oil cooler. I'll check the distributor tomorrow (Sunday) if I get a chance and proceed from there. I'll post back if I replace it and let you know if that solved the problem. Thanks again.

170 deg f is too low . could cause timing problems, esp. in cold weather

[dmc1953]

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 ran much better. When I get to the parts store I'll get a new cap and rotor button and a new thermostat. I'll update when I know more. Thanks.

[j cAT]

Originally Posted by dmc1953

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 ran much better. When I get to the parts store I'll get a new cap and rotor button and a new thermostat. I'll update when I know more. Thanks.

now if the new cap rotor doe not hold up then the distributor is most likely having the bearing wobble rotor issue. replace the distributor .

[dmc1953]

I checked for wobble and didn't see or feel any so to be safe I decided to clean the old cap and rotor before investing in new ones just in case I do end up needing a new distributor. My guess is the previous owner had already replaced it.

[dmc1953]

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?

[j cAT]

with the fuel test the ICM being the problem would be a good guess .. also at this miles and the ICM original I would replace it.

just make sure you use the HEAT SINK THERMAL COMPOUND !!.

This helps reduce ICM failures this is same product used on , power transistors and computer microprocessors.

[ASJT3]

Originally Posted by j cAT

with the fuel test the ICM being the problem would be a good guess .. also at this miles and the ICM original I would replace it.

just make sure you use the HEAT SINK THERMAL COMPOUND !!.

This helps reduce ICM failures this is same product used on , power transistors and computer microprocessors.

Echo j_cat's comments, I've had a similar issue solved by replacement of ICM. You indicate problem occurs when starting warm engine and you say you think ECT is good...on what basis? Did you test it? Easy test to do, all you need is an ohmmeter/multimeter and a pot of hot water.

Originally Posted by dmc1953

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.

With the truck off, when you turn your key to the on position (prior to cranking the engine), the oil, brake, and service engine soon lights (among others) should illuminate. This is how you know which bulbs have gone bad. If you've never replaced dash lights on these models before, it's really not too bad. Should take about half hour.

[dmc1953]

Originally Posted by j cAT

with the fuel test the ICM being the problem would be a good guess .. also at this miles and the ICM original I would replace it.

just make sure you use the HEAT SINK THERMAL COMPOUND !!.

This helps reduce ICM failures this is same product used on , power transistors and computer microprocessors.

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!

[dmc1953]

Originally Posted by ASJT3

Echo j_cat's comments, I've had a similar issue solved by replacement of ICM. You indicate problem occurs when starting warm engine and you say you think ECT is good...on what basis? Did you test it? Easy test to do, all you need is an ohmmeter/multimeter and a pot of hot water.

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 tested the ECT yesterday and it's good. I had assumed it was because the temp gauge was working.


With the truck off, when you turn your key to the on position (prior to cranking the engine), the oil, brake, and service engine soon lights (among others) should illuminate. This is how you know which bulbs have gone bad. If you've never replaced dash lights on these models before, it's really not too bad. Should take about half hour.

I usually don't pay much attention to those but they are all working. I've pulled that instrument cluster before and as you say it's not too bad but not something I'd want to do unless it's absolutely necessary.

I wish the service engine light would come on and give me a code while driving so I could have something to hang my hat on!

[dmc1953]

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.