New problem, Can't find the culprit.

[Jhm89]

Hey all. 1987 GMC V2500 here. 350 out of a 94 Chevy, with the TBI and accessories from the 87 motor. Original TH400 with a new control modulator, and accumulator piston. 115k miles on the body, and trans.

I'm real happy with the truck right now. To the point that I'm ready to start working on the cab rust. Except now after less then a year with this new to me motor, It's acting funky.

The truck runs fine the first trip of the day, short or long. Then after its been warmed up and whatnot, and only sometimes, When I get back in it, it will fall on it's face. Today it died in reverse when I was on my way home. After about a minute of it wanting to die, it just comes back and runs normal.

Coming to you guys, because I'm just frustrating myself with it. If it was a fuel pump problem, wouldnt it have trouble starting? The fuel filter is fairly new. Could it be rust in the tank?

And finally, I've been over the motor a few times and can't find a vacuum leak, adjusted the timing yesterday and it seems to idle fine. Vacuum gauge reading was perfect, IAC is functioning, plugs look awesome, wires are ok, dist and button likewise. Also, the AIR system was taken off the truck, and the TB vacuum port for it is covered.

Any tips tricks or ideas are greatly appreciated. I guess I should mention, when I bought it, the guy who had it sitting in his shop, he didnt drive it. Said that he thinks one of the fuel pumps dosent work. I've gotten it to start on both pumps, but only use the pass side. Afraid to put gas in the other just for it to **** out or something. Sorry to ramble. Thanks for your time.

TL;DR Truck falls on its face for about a minute, no vacuum leak. Has to be fuel amirite!?

 

[89Suburban]

Fuel pressure test should shed some light. No engine light coming on? Fuel pump to tank fitting hose inside the tank known to split and bleed pressure off. Try running on the other tank and see if it does the same thing. Maybe the selector valve acting up? Check the connections for corrosion. Just vomiting out random ideas here.

 

[chengny]

Could it be an electrical problem - that is causing a fuel delivery issue?

Like maybe something as simple as the power connections to the fuel pump, the signal from the distributor module to the ECM, etc.

Unlike the old days, when the fuel/air & ignition systems were independent, today it isn't so easy to know where to point the finger of blame.

If you have trouble with a power plant that incorporates TBI (and ECM, ESC and all the other electronic components), it's difficult to identify which of the two primary systems is the root cause. They both are interdependent to a certain extent - and the ECM is right in the middle.

Having said that; it does sound like a sudden loss of fuel availability at the TBI inlet. If you're up for it, maybe tee into the fuel pump discharge line before the TBI inlet and run a gauge into the cab where you can monitor the pressure. If you notice that the fuel pressure drops right before the engine dies. You can assume the fuel pump is cutting out. What you can't assume is whether it is being shutdown by the ECM or a simple loose connection for example.

As a first step, I would jump the fuel pump relay and see if the shut-downs stop. If you continue to stall, it is a straight forward wiring issue between the relay and the pump. On the other hand, if you no longer "lose the plant" with the relay jumped, then it is a situation where the ECM is commanding the pump to stop.


Also, similar to when you suggest rust in the tank, you may have some restrictions in the fuel line. Check like this:

FUEL PUMP FLOW TEST


1.Disconnect the EFI (TBI) fuel feed line, then connect suitable hose to line and direct end into suitable container.


2.Apply battery voltage to the fuel pump test terminal. The fuel pump should supply 1/2 pint or more fuel within 15 seconds.

3.If fuel flow is below minimum, check for fuel restrictions. If there is no restrictions, check pump vacuum and/or pressure.


Also, this bit of advice is included in the fuel flow/pressure test procedures:

Some 1985-90 engines equipped with 2.5L, 2.8L, 4.3L, 5.0L, 5.7L or 7.4L may experience a condition where fuel delivery is interrupted to the engine causing a "no start condition". This condition may be caused by deterioration of the in-tank fuel pump coupler hose located between the fuel pump sending unit and the fuel pump. This condition may be repaired by replacing the original coupler hose with a new VITON coupler hose kit P/N 25028041. The kit consist of a new VITON hose and two clamps.

I realize this is mostly theory and not anything specific you can check, but maybe someone else can give you a more concrete diagnosis.

 

[kleedus]

did you adjust the timing right

unhook the wire set to 0 then hook wire back up and shut truck off and restart the engine

 

[Jhm89]

Quick update. Yes, I set the timing properly. Saturday night we went to the county fair. After a few hours when It was time to go home, got in and fired it up. It ran like ****, so I let it sit for a minute, This was the first time it happened during the nighttime, I noticed the dash lights and cab light flickered a bit. Thought maybe the new speakers I put in were messing it up. Just took them back out for now, Didn't change. I didnt drive it Sunday, So today I went into town, ran okay but then like always on the second startup to go home, it was trying to die. One other symptom it did tonight, was idle crazy high after it comes back to life.

Put $5 in the drive side tank, it's currently peeing it all back out into a bucket...
Going to try to make some progress tomorrow.
Went through and cleaned up grounds, no difference.

I looked at the VITON coupler hose kit, is it really $51? This pump from Rockauto comes with a new house and clamps, and the whole deal is just $20. http://www.rockauto.com/catalog/moreinfo.php?pk=1400501&cc=1166048
The hose shown with this pump is the same part as the VITON one correct?

Thanks for the help everybody. Hopefully one of these local shops will hire me soon, It's hard to keep this beast going with no money.