Chevy Truck stalls after 30 seconds

[Geezer]

Some history: I have a 1994 Chevy K3500 crew cab with a little over 200k miles on it. Last year I replaced the engine, a 350 gas engine with TBI, with a known good used one from a 1992 Chevy van. I used the original fuel injection and alternator and other accessory stuff. The fuel gauge was not working properly, so I also replaced the sending unit and, since I had the tank out, put in a new fuel pump.

A few months ago the engine started but then quit after running for less than a minute. I pulled the fuel filter and some dirty fuel came out of it so I replaced it. The problem went away, but returned a week later. I replaced the filter again, but this time the filter seemed clear. Fuel was squirting through it no problem. It worked OK since then, but the problem still occurred once in a while. I was always able to restart it and it ran fine after that.

Yesterday it got much worse. It starts normally, runs for about 30 seconds, and quits. Every time.

I pulled the top half off of the throttle body and watched the injectors spray. They spray fine for the 30 seconds and then just quit, which is when the engine stops.

One thought I had was that the computer is switching off the fuel pump for some reason. I disconnected the battery to reset the computer, but that didn't solve the problem.

I know it's a long shot, but has anyone seen anything like this before? I am hoping to get some ideas before I start spending time and money on an Easter egg hunt.

Thanks,

Greg

 

[FJRONAMISSION]

I got nothin..........

 

[racer]

Geez.......ever hear of cash for clunkers?

 

[radman]

Oil pressure switch. It shuts the pump off if oil pressure drops as a safety roll-over device. The ecm runs the pump for 2 seconds, then shuts down until it receives a signal from the ignition module (which is also a suspect). Lacking this signal, pump quits, you run outta fuel. Chief symptom is if, upon a key cycling, it starts and quits again. Also check fuel pump relays.

Check fuses-if I recall, there are two for the FP, one initial and one running.

 

[Geezer]

Geez.......ever hear of cash for clunkers?

Yep. I had three clunkers and traded in the worst of the three, my '94 Ford Explorer, on a new Corolla. Now I am still nursing along a '92 Jeep Wrangler and the big pickup. B)

 

[Geezer]

Oil pressure switch. It shuts the pump off if oil pressure drops as a safety roll-over device. The ecm runs the pump for 2 seconds, then shuts down until it receives a signal from the ignition module (which is also a suspect). Lacking this signal, pump quits, you run outta fuel. Chief symptom is if, upon a key cycling, it starts and quits again. Also check fuel pump relays.Check fuses-if I recall, there are two for the FP, one initial and one running.

Thanks radman. I was hoping you'd have some words of wisdom for me. I'll start on your suggestions right after work today.

 

[lnewlf]

Ditto on the ignition module..sometimes a good beating will make it work for a while..If you do replace it go for the Goodwrench unit[ACDelco] from the dealer..don't forget to put the insulating grease under it..

You can test the fuel relay by jumping power to the G terminal [ could have the wrong letter on that] at the data link-if the pump is good it will run constantly and that would indicate a bad relay or oil pressure switch..

 

[Geezer]

Ditto on the ignition module..sometimes a good beating will make it work for a while..If you do replace it go for the Goodwrench unit[ACDelco] from the dealer..don't forget to put the insulating grease under it..You can test the fuel relay by jumping power to the G terminal [ could have the wrong letter on that] at the data link-if the pump is good it will run constantly and that would indicate a bad relay or oil pressure switch..

Thanks for the additional information. I did replace the ignition module a few years ago. When that went the engine would not start at all. Both the oil pressure switch and ignition module are fairly inexpensive, so I hope it's one of those. I don't want to drop that gas tank again unless I really have to. It is a 34 gallon tank.

 

[radman]

I don't want to drop that gas tank again unless I really have to. It is a 34 gallon tank.

Interesting you should mention that. The first thing the morons that work as drivers here do when their truck starts having possible fuel problems is, even though they have a half a tank, to fill it righ to the top, as if the extra weight will make that pump just sing. :blink: Then we have to deal with a 200lb bomb to slam a pump in.

 

[Mizz Bustanut]

..sometimes a good beating will make it work for a while..

Tried that with Bust . . . . . . didn't get anywhere.

:lol:

 

[Vesparado]

My dads truck '95 Chevy p/u with a V6 Vortec had the same issue. I replaced the coil wire because it was rotted. check your wires and distributor as well. Good luck.

 

[buf2phx]

I don't want to drop that gas tank again unless I really have to. It is a 34 gallon tank.

Interesting you should mention that. The first thing the morons that work as drivers here do when their truck starts having possible fuel problems is, even though they have a half a tank, to fill it righ to the top, as if the extra weight will make that pump just sing. :blink: Then we have to deal with a 200lb bomb to slam a pump in.

Customers do that all the time. Got a face full of gas pulling a Cavalier tank that was filled to the brim. Not the best way to start the morning. As far as pick ups go,unless you have a crazy custom box on it,pulling the box off is a much easier way to change a fuel pump. Back in the rusty NE that was sometimes the only chance you had to save the sending unit.

Mike

 

[jestal]

Did anyone mention checking for any trouble codes? Since the 30 seconds you describe sounds like it is fairly repeatable my guess would be something is sending bad info to the ECM and it is shutting the fuel pump off. That should set a code.

The first thing to do (after checking for codes) is to put a fuel pressure guage on the schraeder valve fitting at the TB.....So far we do not know if fuel pressure is dropping causing the problem so don't start replacing parts.

The silicon grease under the ignition module is actually conducting grease not insulating grease. It helps carry the heat from the ignition module away to the distributor housing to keep the module cool.

Those vehicles do not use an oil pressure switch interupt for stalling or rollover protection. To the best of my recollection the GM TBI systems of that era had a third terminal on the oil pressure switch that feeds the fuel pump but that is a redundant feed to provide voltage to the pump in case the fuel pump relay fails so as to keep the engine running and to enable the onboard diagnostics (for fuel pump voltage) to work. The ECM controls the fuel pump relay and will turn the pump off in the event of an engine stall for whatever reason.

 

[Hit the Road Jack]

I had a similar condition with my Grand Cherokee. The Fuel Pressure Regulator was the culprit.

Good luck!

 

[n1acguy]

Oil pressure switch. It shuts the pump off if oil pressure drops as a safety roll-over device. The ecm runs the pump for 2 seconds, then shuts down until it receives a signal from the ignition module (which is also a suspect). Lacking this signal, pump quits, you run outta fuel. Chief symptom is if, upon a key cycling, it starts and quits again. Also check fuel pump relays.Check fuses-if I recall, there are two for the FP, one initial and one running.

Does sound like an oil pressure issue or a problem with the sensor. Does it show good oil pressure before it shuts off? Thirty seconds is about the time of the delay.

If it is an oil pressure issue and it's just overall bearing wear and not a disintegrated bearing, you might try a heavier weight oil. I'd try 15/40 or 20/50, it might buy some time.

 

[lnewlf]

..sometimes a good beating will make it work for a while..

Tried that with Bust . . . . . . didn't get anywhere.

:lol:

Jestal is right-the grease under the module is a conductor-my duh.. Some guys create a "door" to access the fuel pump by cutting out a section of bed and repairing with a preformed bed repair panel.

Miz Bust-have you tried a goat and a pair of jumper cables?

 

[Geezer]

Jestal is right-

He usually is.

I'll have to dig out my fuel pressure gauge and see if that tells me anything, though I think it will read OK. It only calls for 9-13 PSI. My calibrated thumb tells me that I can spray the fuel far enough to be at least 9 PSI .

I don't have a code reader but I know where I can borrow one. I used to have instructions on how to read codes on my kids old Ford Probe by jumping out a couple of pins and counting flashes on one of the lights on the instrument cluster.

This is going to take a few days to get sorted out. I'll let you all know what I find.

 

[Geezer]

It took a while, but the truck is running again. :yahoo:

Well, it is a long story, but the bottom line is a corroded connection inside the fusible link that provides 12v to the fuel pump relay. After fooling around with that wiring bundle enough times it got bad enough to give me some voltage readings that were definitely bad. I jumped out the link and it runs fine. I'll get a new fusible link or inline fuse and call it fixed.

Thanks to all of you for sharing your ideas and experience.

 

[madmike2]

Thanks for reviving this and telling us what you found. It doesn't sound like finding the culprit was "fun", but at least you found it and it WAS a fuel pump interrupt, just not the one anticipated.