Stalling and other abnormal behavior

[Sinners Saint]

Ok I'm back with another issue. I searched the forums but can't quit figure out if my issue is what I think it is. I noticed here about a week ago that the truck would stall when I got on it hard sometimes. Also every once in a while it would die shortly after start just idling in the driveway. I thought maybe the fuel filter needed changing, so I changed it. Its still acting up and has gotten slightly worse. I noticed that when I'm setting at lights or just parked idling that the SES light would come on, but if I tap the throttle it goes off. So the code is not storing and I don't know if you can hook up a dianostic with the engine running on OBD1 trucks.
I was thinking maybe the LP is going out, I jumped it and it is putting out fuel through the filter bleeder. Does not squirt it out all over the place like it did when I did it the first time I changed the filter, but it does pretty well. Do these symptoms sound like a failing LP to you guys?

 

[ak diesel driver]

possibly. Put a fuel pressure guage on the drain t with a long hose and tape the guage to the window and take it for a spin. Make sure the hose isn't pinched. Also put a piece of clear tubing on the return coming out of the IP so you can check for air.

 

[bk95td]

A plugged sock in the fuel tank is possible.

 

[buddy]

The first thing you did when you suspected an LP not functioning was to jump it. The problem there is you took the electronics out of the equation. You still run it off the OPS, or done a OPS relay mod yet? I use GMTDScanTech while driving all the time. And the truck stores all codes in history. If you even just jumper A and B on the DLC the SES will flash the codes it stored.

 

[Turbine Doc]

Sit down & have a read through this which can be found in our tech reference library http://www.thetruckstop.us/forum/sh...t-Pumps-amp-OPS-operation-and-troubleshooting

 

[Sinners Saint]

Thanks I did'nt think the codes stored if the SES light did'nt stay on. I checked them this evening.
34-injection timing stepper motor fault
49-service throttle soon lamp circuit fault
57-PCM 5 volt shorted
62-turbo boost sensor circuit low
I hav'nt been able to install a fuel pressure gauge yet or do much else. I did pick up a new lift pump, but I can't install it yet since my back is tweeked out on me.

 

[buddy]

Before replacing an LP, need to figure out if its getting power when its supposed to, or just wire it up to ignition so you arent wondering if the OPS is working.

You should clear the codes with the pedal method and check it again after a drive.

Could be bad OPS or could be an electrical gremlin from those codes

 

[Sinners Saint]

Lifted this from the stickies, sounds exactly how my truck is acting. I'm gonna attempt to do some work on it tomorrow, but depends on if my back will be bothering me to much or not.

Healthy IP is capable of pulling it's own fuel past a dead or weak lift provided it is GM flow on fail type lift pump, performance can suffer at higher rpm "fish biting" is common sign of dead lift or bad ops in OBD-I truck, "f-b" same feel one gets when fish 1st hits your line, jerking/tugging you feel in truck sort of similar to "miss" in gasser truck. In OBD-IIs lift power is from 2 places PCM & OPS you have to lose both for total no power to lift.

I have replaced the OPS recently with a new ac/delco part. But thats not to say it cant fail. Its been less than six months.

 

[buddy]

This is where testing stuff with a test light or multimeter eliminates or identifies the issue very quickly.

is power going into the OPS so it can go out of it, is power at the LP when engine is running?

 

[JMJNet]

That is easy. Just open the t-valve when engine is running, if you stall then you have LP and/or OPS issues.

Did the truck start when you put 12V source to the LP which essentially overriding the OPS? Open the t-valve also see if engine stall.
If the engine can start without stalling, you can then put a voltmeter on the LP connector from OPS which should not be connected now since you put 12V direct source.
Most of the time if the volt is low, you have a failing OPS. If volt is good then we have to measure the pressure of the LP.
Then you know how to continue. One thing though, your suspicion may be correct that the LP may be weak if it has not been changed for a while.
We suggest that you get a 93 model year LP.

The difficult part will be to figure out if this is one of the cause of your codes. May be or may be not. LP/OPS issue does not usually cause any code at least not at the early stage of problem. Then also, the cause of each code and how they interact with each other.

 

[knkreb]

Engine ground strap maybe? All of those maybe electrical things... it's a cheapy check.