5.7 with stumble under light throttle

[Faded_blue_obs]

I recently joined the forum when I purchased a 1995 Chevy k 2500 (camper edition?) with 167 000 mile from my grandfather who took ok care of it (for a farm pickup) when I got the pickup it would start running rough a light throttle and would often die when cold unless above 1700 rpm’s so I did the typical tune up spark plug, wires, cap rotor, etc. help for a little bit but not really so started reading through forums and thought maybe the cts replaced it help for about a week and a half. So then I thought maybe the distributor, replaced it with like new used distributor help for a couple month and now it’s getting worse dies right after start up Dies under light throttle when backing up and trying to park. Also replaced the air fuel mixture solenoid and fuel filter. Also it has been getting crappy fuel mileage now like about 8 mpg on the highway. Don’t know what to do now replace tbi itself? Computer going bad? Need help

 

[Drunkcanuk]

What have you done in regards to the fuel system?
Last time the filter was changed?
What is your fuel pressure?

I had similar symptoms in my 91, 5.7.
Idled and revved fine, under load stumbled on itself.
Was the little chunk of hose connecting the pump to the fuel lines inside the tank. Enough to run, but not under load.

 

[Faded_blue_obs]

I have only replaced the fuel filter, had LOTS of black crap in the fuel filter but again it has been a farm truck almost it whole life. I have been planning on checking fuel pressure but just haven’t got around to it yet.

 

[Erik the Awful]

Check your fuel pressure and your O2 sensor cross-counts (swings from lean to rich and back).

Have you replaced the air filter?

 

[89RCLB]

That black crap in the fuel filter is from the short piece of hose that connects the fuel pump to the hard line that feeds the TBI. That piece of hose deteriorates, splits and results in low fuel pressure or lack of fuel pressure when it fails completely. And of course, the pump itself could be marginal.

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Fuel pressure check is in order. Should be 9-13 PSI, higher PSI's are better.

Replacing that piece of hose or the pump requires dropping the tank or lifting the bed to gain access.

Edit: This was on my GMC. Had the truck idling for a few minutes to warm up when it suddenly died. Had been running just fine prior to this.

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[Faded_blue_obs]

So I checked the fuel pressure had 11 psi of fuel pressure. So I scanned and had a distributor code so bought a new distributor didn’t fix it. Had a brand new throttle body on a truck that needs tranny so robbed the throttle body and fixed the problem. Other then right after start up for like 5-10 seconds it runs like it has a hog cam in it but then levels out and has more power and WAY better fuel mileage

 

[Schurkey]

So I checked the fuel pressure had 11 psi of fuel pressure.

Adequate. Not spectacular.

So I scanned and had a distributor code

WHICH ONE?

robbed the throttle body and fixed the problem.

Excellent. Why? Faulty TPS sensor? Faulty injector(s)?

Other then right after start up for like 5-10 seconds it runs like it has a hog cam in it

I have no idea what that means.

but then levels out and has more power and WAY better fuel mileage

That part sounds good.

 

[Faded_blue_obs]

For the code it I believe it was code 12 not a 100% sure that’s right. The reason I replaced the throttle body is because I was curious that the tps might be bad because it was a farm truck so it flagged for heavy equipment which means it was under light throttle a lot and that’s were it had the most problems and had a brand new throttle body not being used so just replaced the whole thing to eliminate tps injectors. So when I start my truck it sort of misses and surges but the best way I could describe it is it sounds like someone has installed an aftermarket cam shaft and makes it “chop” but only for like 10 seconds when I start but only when cold

 

[Drunkcanuk]

For the code it I believe it was code 12 not a 100% sure that’s right. The reason I replaced the throttle body is because I was curious that the tps might be bad because it was a farm truck so it flagged for heavy equipment which means it was under light throttle a lot and that’s were it had the most problems and had a brand new throttle body not being used so just replaced the whole thing to eliminate tps injectors. So when I start my truck it sort of misses and surges but the best way I could describe it is it sounds like someone has installed an aftermarket cam shaft and makes it “chop” but only for like 10 seconds when I start but only when cold

A code "1-2" is the system communicating with the ECM, basically saying I'm working. Anything AFTER the 1-2, is now the codes. It will flash 3 times.

 

[Faded_blue_obs]

Ohh ok thanks