1988 suburban won't run

1988 Sub 350 4x4 3/4 ton 205K miles (30K on engine)
I drive this truck maybe 1 or 2 times a month. I had to get emissions tested today to get my new lic. Started great drove to test center and the idle was up to high 1400rpm and would not kick down. No test today.

On the way home, sub died when I tried to take off at a green light. Sub would only start if I hold the pedal to the floor. No codes when I use the jumper wire on the OBD.

Let it set for an hour and it fired right up. Drove it around for 15 minutes and it started stumbling and dying again.

I had the fuel pump and filter changed 6 years ago. New MAP sensor 1 year ago.

Any Ideas on where to start?

1988 Sub 350 4x4 3/4 ton 205K miles (30K on engine)
I drive this truck maybe 1 or 2 times a month. I had to get emissions tested today to get my new lic. Started great drove to test center and the idle was up to high 1400rpm and would not kick down. No test today.

On the way home, sub died when I tried to take off at a green light. Sub would only start if I hold the pedal to the floor. No codes when I use the jumper wire on the OBD.

Let it set for an hour and it fired right up. Drove it around for 15 minutes and it started stumbling and dying again.

I had the fuel pump and filter changed 6 years ago. New MAP sensor 1 year ago.

Any Ideas on where to start?

my guess is the fuel is bad. try some dry gas additive 2 bottles and put some fresh fuel in it.

with your useage I would use fuel stabilizer at each tank filling.

keep fuel at 3/4 mark to avoid excessive water/condesation build up.

you could also have rodent nests in stuff like air box etc..

my guess is the fuel is bad. try some dry gas additive 2 bottles and put some fresh fuel in it.

with your useage I would use fuel stabilizer at each tank filling.

keep fuel at 3/4 mark to avoid excessive water/condesation build up.

you could also have rodent nests in stuff like air box etc..

Would that cause the high idle?

Would that cause the high idle?


when too much fuel enters the engine the idle will increase with fuel injection or a TBI. fuel from the regulator or injectors leaking ..the fuel being contaminated with organic material growing in the alcohol fuel mix does this. or the regulator diaphram is ruptured.or both .

The high idle suggests to me that a vacuum line is off or corroded somwhere or plugged. Or it could be a sensor related issue like a IAC, if it has one, Idle Air Control valve, or another sensor, but I would think there would be a code for such. The hard starting suggests to me, that this is a fuel related issue, i.e. the fuel filter plugged. 6 years is a long time for that. Or it could be exhaust related, with the cat, possibly rodents clogging up things. First I'd check the vacuum lines, then take off the air filter and hoseway to make sure they are free of blockages, then if worse comes to worse, unhook the exhaust in front of the cat and verify it isn't clogging the exhaust. Hope this helps.

I found a vacuum line that came off when I pulled the air cleaner off. I hooked it back up, but nothing has changed.

How long should the fuel pump run when you turn the key on, but don't try to start the engine? I can hear the pump run for about 15-17 sec before it shuts off. This seems like a long time if it only needs to get to 12 PSI.

thanks for the help.

How long should the fuel pump run when you turn the key on, but don't try to start the engine? I can hear the pump run for about 15-17 sec before it shuts off. This seems like a long time if it only needs to get to 12 PSI.

thanks for the help.

The fuel pump should 'prime' for a few seconds. The extended period of time suggests that it is not building up pressure fast enough. I have a feeling it's the fuel filter being partially clogged that is causing this issue. I would change that first and because it is a usual maintenance item, it's not like it isn't worth changing.

If, by chance, you still have the same issue after replacing the fuel filter.... check the fuel pressure. It could be a faulty FPR, fuel pressure regulator.

I changed the fuel filter. Ran better for a little bit then back to the same thing.

Pulled the fuel pressure regulator and swapped it with the one I had on the old engine. Still runs bad and now I am getting fuel pooling on top of the injectors.

Any ideas what is next?

It's possible both FPR's are bad. If it has a vacuum hose on it, turn the key on/engine off, and see if there is raw fuel coming out of the hose. There shouldn't be.

So, I rebuilt the fuel pressure regulator and pulled the 2 injectors and cleaned them.

Put it back together, and it started ran good and then I tried to start it again.
Same story. It will start if I hold the throttle to the floor.

Any suggestion? :banghead:

Some more things to check, in no particular order...

- IAC valve (idle air control)
- check timing
- check fuel pressure at rail, KOEO (key on, engine off) and when starting
- check there is no restriction in the exhaust
- go around by hand and make sure the plug wires are all in place and snapped onto the plug and distr

Patience and precision is key, so nothing get's overlooked. Good luck.