Problem with my dads truck. No power

[joegreen]

My dad drives a 1988 chevy 2500 light duty. It has a brand new 700r4 and a 350 with almost 200,000 on it. This is his only vehicle and he needs it for work. He said the truck was fine driving to work but when he went to leave the truck started to run wierd. First off it seems like it has an rpm cap like it can only get to a certain low rpm. He can only do like 15-20 mph. The truck has no power. At idle it slows down then picks back up. It keeps doing this like a wave. If he revs up the motor slowly he can get it to rev highish but the second he puts his foot down the rpms drop and it runs bogs sort of. He tested the tps and the map sensor and they tested fine for voltage. He has a newer coil. I had him blink out any codes and it flashed 12 3 times then came back with a code 44. He replaced the o2 sensor although i think that that code only appeared because of how the engine was running. Tomorrow he is going to get the icm tested at the store. What are some things i can tell him to check? Does this sound like its in limp home mode. So it ran good when he arrived at work and instantly ran bad when he started it up to leave. Thanks

[steveo]

as far as i know, with that ecm if it was in limp home mode, it wouldn't blink codes.

i'd be looking carefully at the ignition system, but could also be low fuel pressure or something...

[joegreen]

ok. i will see if i can get a fuel pressure tester from the zone and have them test the icm.

[joegreen]

ok so the icm tested bad for low rpm. Also the connector into the back of the icm that has that big plastic ring attached to it was replaced because it was all old and melted looking. Anyway the truck is still doing the same thing. About to do a fuel pressure test.

[joegreen]

Ok, so the fuel pressure held steady at 9 psi. The truck seems to be running good so far but has only been driven a few miles since the repair. There is a code 15 set but the thermostat is also not working properly so the engine does not get up to operating temperature. I think those two may be related. I will report back with more info after the thermostat is replaced and some more miles rack up.

[fastacton]

9 psi is too low. It should be 12-14 psi.

[joegreen]

I know 9 psi is on the low side but these systems came 9-13 psi from the factory so i am ok with 9 psi for now as long as it holds steady. I may modify the fuel pressure regulator eventually and bump it up to 14 psi.

[gearhead1]

It could be a plugged or partially plugged cat.

[joegreen]

Ok, so the truck was just taken on a 60 mile drive and it drove without a hitch. Replaced the pick up coil and the icm. I dont know what one was the problem. Here are some picks so you can see how bad the pick up coil was. Sorry for the blurry picks.
83248325

[steveo]

it's always a good sign when looking for an ignition problem to find something burned to a friggn crisp, isn't it

anyway 9psi should be acceptable IF the pressure doesn't drop during heavy fueling (epsecially since your problem was under load, not resting.. you might want to load it up with the fuel pressure tester connected?)

you could check for a plugged cat with a vacuum gauge.

[joegreen]

it's always a good sign when looking for an ignition problem to find something burned to a friggn crisp, isn't it

anyway 9psi should be acceptable IF the pressure doesn't drop during heavy fueling (epsecially since your problem was under load, not resting.. you might want to load it up with the fuel pressure tester connected?)

you could check for a plugged cat with a vacuum gauge.

The problem did also happen i neutral without load. But i hope things stay ok. How do you test for a bad cat with a vacuum guage?

[tayto]

I've always had luck putting the stock regulator in a vise and breaking free the factory brazing. Some report to not do it this way, I have done ~6 this way with no issue. I then hook a fuel pressure gauge up and shoot for 13 or 14 psi. I have a very narrow set of slip joint pliers that fit inbetween the regulator and throttle body so I can adjust in situation. I like to do it with engine running. If you can't get 13/14 psi you can shim the spring with a washer. Also like to upgrade to the TPI fuel pump before doing this. Had to get my old caprice through emissions testing as part of the deal for selling it. I replaced injectors with used ones from the wrecker which fixed the code 43 set the regulator to 10 psi, it passed emissions with flying colours. Then cranked the fuel pressure up to 14 psi, car never had power like that in the 5 years I owned it. Sold it a week later.

http://www.binderplanet.com/forums/showthread.php?p=298293#post298293

[steveo]

How do you test for a bad cat with a vacuum guage?

if you rev up and hold the throttle in neutral, the needle drops, but then comes back up quickly, as there's no load on the engine. that is, unless exhaust is clogged, in which case it wont come back up much at all (or very slowly?)

vacuum gauges are great tools

of course someone good at reading datalogs can analyze rpm vs tps vs map on a graph and point towards a clogged exhaust too

[joegreen]

OK, so i got my laptop hooked up to the truck after we fixed the coolant temp sensor. We took it for a short drive and a took a data log. Maybe somebody can look at it and see what you think. The blm's seemed on the high side.

[Fast355]

OK, so i got my laptop hooked up to the truck after we fixed the coolant temp sensor. We took it for a short drive and a took a data log. Maybe somebody can look at it and see what you think. The blm's seemed on the high side.

Theres your sign! Low fuel pressure. Need to get it up to 13-14 psi to make it run right. Anything lower and you are shooting yourself in the foot driveability, power and efficiency wise.

[joegreen]

I will make the fuel pressure regulator adjustable and hopefully get up to 14 psi. Actually, should i just shim the pressure regulator instead?

[fastacton]

You may want to look at the pump as well, the regulator may already be set correctly and the pump just can't deliver.

[joegreen]

Yeah, i thought about that. Is their a way to test the max pump output.

[tayto]

Place pressure gauge where you can see it while driving. Drive up big hill at WOT, preferably so you can get to RPM redline. I've been told pressure shouldn't even drop by 1 psi. Infact at idle if you flick the throttle and the needle drops this is cause for concern at least for those of us running higher psi through the injectors. I have a feeling it's time to upgrade... Acdelco EP241 is the TPI pump (~50 psi), I recommend no other brand they seem to be the best. I have heard of guys running the vortec pump (60 psi) EP381 in place of the TBI pump. I have never done it and it might be over kill. I'd nearly go for which ever is cheaper. Might have an issue with to much fuel getting returned to tank tho... Make sure you use supplied hose (purple stripe) and clamps with new "high pressure" pump. Put a new sock and fuel filter on it. I'd also recommend getting injectors professionally cleaned. Adjust regulator, you might hit 13 you might not. If not shim the spring get a TBI gasket/rebuild kit as the old gaskets and packings will most likely rip on you.

[joegreen]

Some good news and the end to this thread. I bought a rebuild kit and rebuilt the throttle body. It has not been touched since probably new (1988). So while rebuilding i also made the fuel pressure regulator adjustable. When everything was put back together i retested the fuel pressure a few times while adjusting the regulator. The pressure stayed at 8 psi actually. I misread the gauge and thought it was 9 psi But it turns out every line was 2 psi not 1. So anyway i put in a new fuel pump and got the fuel pressure dialed in to 13-14 psi and the truck has never run better. The blm's stay right at 128 at idle and only deviate by a few numbers when revving up. Thanks everyone for your help.