1995 Chevy 1500 1/2 Ton Truck (350, 5.7L)

[userpete1037]

Ok,

Last week my truck started to stall a little bit. As I drove it a little longer, it stalled all the way out. It started back up fine but when I gave it some gas, it cut off. This happened several times. I popped the hood and noticed the throttle body was a little loose. Thinking air may have gotten into the system,I tightened it back up. I started it up,put it in gear and it seemed to drive fine and it started stalling again. While I was on the interstate, it would cut off, cut back on,cut off and then cut back on. Finally it completely stalled out. I had to have it towed to my house. I hooked my code scanner up to it and it through code 44 (O2 sensor) and code 54 (Fuel pump relay or something like that). I have no idea what could be causing my truck to run this way. Does anyone have any suggestion as to what it might be causing this problem?

[MT-2500]

What is the engine code?

02 sensor is not you main problem.
Have you got good spark and fuel pressure when it acts up or quits?
Is it dead now or just acting up?

Pull the throtle body and replace the base gasket to start with.
Clear codes and see what comes back.

Check fuel pressure when it quits.
Post back fuel pressure readings.

Get some good repair info on the code for fuel pump relay and fuel pump and fuel pressure.
Let us know how it goes.

[userpete1037]

It's not dead. It actually starts up. As a matter of fact, I started it up yesterday and it ran fine. I gave it gas and it idled up with no problems. After about 15 min of running, I gave it some more gas it acted like it wanted to cut off when I gave it gas. Other than that, it runs fine when it idles by itself it's just when I press the accelerator,it wants to shut off.

[MT-2500]

Engine code?

Check the fuel pressure when it quits for being up to specs.

[userpete1037]

IT's been a while guys and I apologize for not getting back to with. Work has allowed me little time to troubleshoot my truck. Anyway, I tested the pressure and it was around 7-8lbs. I thought I might have a faulty fuel pump so I replaced it along with a sending unit and it still is doing the same thing. I've needed a new knock sensor for a couple of years but I know that isn't the problem. I think I will try replacing the MAP SENSOR unless anyone has anymore suggestions.

[MT-2500]

Proper testing before throwing parts at it.

What is your engine code? The 8th diget in vin?

What is the fuel pressure reading when it quits?
When it quits is it losing spark or fuel pressure or both or someting else?

[userpete1037]

The 8th digit is K. When it quits, it's loosing fuel pressure not spark.

[MT-2500]

Originally Posted by userpete1037

The 8th digit is K. When it quits, it's loosing fuel pressure not spark.

What is the fuel pressure reading when it quits?
When it quits is it losing spark or fuel pressure or both or someting else?

[userpete1037]

the reading is about a constant 8psi. What's happening is when I press the gas pedal very quickly, it stalls for a split second and idles back into place. If I press the pedal gently it idles fine without stalling. This is weird. I have no idea what's going on.

[MT-2500]

Originally Posted by userpete1037

the reading is about a constant 8psi. What's happening is when I press the gas pedal very quickly, it stalls for a split second and idles back into place. If I press the pedal gently it idles fine without stalling. This is weird. I have no idea what's going on.

8 lbs is low pressure.
Are you sure it is not losing fuel when it stalls?
Watch the gauge when it stalls or quits.

Any check engine lights or codes?

[jdmccright]

8 psi is definitely low. Should be 11-15 psi. I'd check the fuel pressure regulator...IAC, PCV, and EGR valves also while you're under there.

[userpete1037]

I got a t-fitting made that fits where the fuel filter goes and I'm getting a constant 13psi now. My truck will start with no problem but the problem I'm having now is that it's starting to idle rough and backfire. I changed the spark plugs because they were corroded some with what appears to be carbon deposits. Still doing the same thing. I took off the distributor cap and rotor button and it appears they need replacing but not sure if that will do the trick. I hooked my Actron Code Scanner up to it and it though a code 34 which references the MAss Air Flow (MAF) Sensor and Manifold Absolute Pressure (MAP) Sensor. I know mine doesn't have an MAF.

[2000CAYukon]

Check the vacuum hose to the MAP sensor which is at the back of the TBI and goes to the MAP sensor. If hose is bad or if the MAP sensor will not hold a vacuum, a code 34 will be set.

//2000CAYukon

[userpete1037]

I will check the hose and I believe I can perform a vacuum test on the MAP sensor. I be sort of busy through the week so it may take me a couple of days before I can respond. Thanks for the insight.

[CalifOkie]

Try a known good throttlebody on it... Here lately I have seen quite a few fuel pump and TBI failures. Which I believe is caused by the ethanol/ gas mixture deteriorating the fuel systems. As far as the TBIs go in the last 3 months I've had a 94 4.3L TBI, a 91 305 TBI, and a 94 350 TBI. All three developed internal vacuum leaks in the units themselves. This is evident from your code 34 MAP sensor stored. If the TBI can not hold a steady vacuum without it leaking off then the ECM will become aware of the vacuum loss by monitoring the MAP (manifold absolute pressure) sensor and seeing a gradual bleed off at that point it codes 34 thinking the Map is not holding the vacuum when infact it is it's vacuum source that is failing to hold the vacuum. Your original code 44 O2 sensor code was probaly triggered by extremely lean exhaust caused by airleaking around the TBI base gasket when it was loose. If you have been burning alot of ethanol/gas definately look hard at the throttlebody.