87 V10 5.7 Runnin rough

[Bain1012]

Needin help here. I got an 87 v10 with a 5.7. She's runnin fine at idle but after it shifts to 2nd goin down the road she sputters and sounds like it's runnin on 4 cylinders. When that happened I mashed the throttle and it just cut out completely so I let off and it came alive. Tune up was done 4 weeks ago. New cap, rotor, wires, and plugs. I have good spark at all cylinders. Just changed the fuel filter figuring that's what was causing the issue. No change. Gonna check fuel pressure tomorrow. Any help is greatly appreciated.

 

[foamypirate]

Sounds like you are on the right track. Also, sometimes the fuel hose between the pump and sender, inside the tank, will split, causing low fuel pressure. It may be enough to idle, but not to cruise around, if that has happened.

 

[PrairieDrifter]

Check your fuel pump volume too not just the pressue

 

[Bain1012]

Checked my pressure I'm at a consistent 12 psi. I'm at a loss right now.

 

[HotRodPC]

Sounding like a fuel problem for certain. This is a TBI engine right? Someone else chime in to be certain, but isn't fuel pressure for TBI supposed to be up in the 18-22lb range? Maybe I'm getting confused with SFI on the Vortecs, but I think those even require more pressure.

Also, the fuel line in the tank that foamypirate mentioned is a known issue. If that little 1 inch hose is split, which is even more common these days due to Ethanol, it'll run but not very good until it progresses to a point it won't run at all. How much fuel is in your tank right now? Maybe you can put more fuel in the tank so the fuel level is over and above the hose so if it is split, then it'll be sucking fuel instead of air, and if it runs good after adding fuel, you can pretty much be certain that the little hose is the problem.

 

[Bain1012]

Tank is full so there was a split it wouldn't be an issue. And yes it's a TBI. I took a 97 vortec block and heads and did a full rebuild with a few upgrades and put the tbi on cause I couldn't afford the $2500 fuel system I was plannin on runnin

 

[Bain1012]

Pressure for tbi is 12-15 if I'm remembering properly.

 

[foamypirate]

Tank is full so there was a split it wouldn't be an issue. And yes it's a TBI. I took a 97 vortec block and heads and did a full rebuild with a few upgrades and put the tbi on cause I couldn't afford the $2500 fuel system I was plannin on runnin

Based on this, you likely need a tune. A factory stock Vortec makes 255hp vs 190 from the TBI 5.7L. You are probably short on fuel for the airflow you have.

 

[HotRodPC]

And I'd imagine it's safe to assume that you didn't use an OEM TBI intake on the Vortec heads? Honestly I don't even think it would run would it? It would have massive vac leaks in that case.

 

[PrairieDrifter]

tbi fuel pressure is 9-15 im pretty sure

 

[HotRodPC]

hmmm, someone else me out here, wasn't it a while ago a guy was having a similar issue and it turned out to be an EGR valve issue?

 

[HotRodPC]

And where is @89Suburban ? He's experienced some TBI issues. @Jims86 TBI Guru hasn't been here in awhile, but I'll call him in via FB.

 

[PrairieDrifter]

I think you should check your fuel volume still...you said it idles fine and can drive in first gear until you hit second, idle and first gear is what I would consider to be a light load and second gear would be a moderate load(imo) so the pump has enough volume to supply the fuel it needs at idle and in first but when you mashed you said it cut out and when you let off it ran fine again? So when you mashed it you weren't getting near the gas you needed so it basically died but once you let off it had enough fuel volume to keep it running at the lower rpm. Fuel volume is just as important, if not more important, as fuel pressure is. That's my theory of what's going on, but I could also see it being an egr problem possibly.

It depends what egr you have but theres a positive and a negative type, on the egr it should have some numbers and it will have either a (p) or an (n) I think its the negative egr that you cant use a hand vacuum pump to test it, I may be wrong I cant remember, but start the motor hook up your vacuum pump and start adding some vacuum and see if your engine will start dying that will let you know that the egr valve isn't locked up or leaking

 

[HotRodPC]

I certainly agree with the fuel volume issue too since it really mimics a fuel starvation problem. If it were a carbed engine, I'd be going directly for the accelerator pump. Reason I say that is because you mention mashing the gas and it falls flat on its face, then let up and it recovers.

Dumb Question, and not even sure it can be done, cuz I don't recall if the threads are different on both end or not, but you mention you replaced the fuel filter recently. Is it possible you may installed the fuel filter backwards? It would make sense to me that if the paper collapsed in the filter, it could still push the pressure but restrict the fuel volume. Did the old fuel filter seem to be restricted at all?

 

[Bain1012]

Fuel filter is in properly. And it's now turnin into an on/off problem I drove it a few times today and a couple of times it worked just fine no hesitation no stutter. But then the next time I'd jump in and go the problem would surface.