GM 5.7/Full-size van problem

I'd mentioned it in another thread, but my '98 G3500 cargo van died on the interstate a couple weeks ago. The fuel sender isn't working right, so I initially suspected it was out of gas the 1st time it died(after driving for 200-miles non-stop). After filling the tank & priming/cranking about a dozen times, it ran fine for 54-miles, then died again, so I had it towed to our mechanic.

The mechanic isn't finding any problems w/it, and now I'm concerned it may be something else. I need to take it on another 1600-mile trip this weekend, so I'd like to make sure my guess diagnosis is correct.

Do late-90's 5.7L have any weird electrical problems that I should be considering instead of the fuel pump?

You're sure it isn't the fuel pump? Those are pretty classic fuel pump failure symptoms right there. Otherwise, I suppose it could be an electrical issue, dying crank sensor (vortecs have one, though it is quite basic), or something similar. The only other systemic issue I'm aware of is with the fuel spider, but that generally results in poor running rather than a dead engine.

Also check the ignition module, which tends to act up when warm when they are going out.

In reply to gearheadE30:

I thought I was a 100% sure it was the fuel pump, but since it's intermittent and I won't be able to put many miles on it before driving it 850-miles one-way, I want to make sure I'm not overlooking any other likely culprits.

In reply to 81cpcamaro:

The actual symptom was running absolutely great, followed by a sudden noticeable lack of power for a second or 2, then dead. The second time it happened, it sputtered once or twice before dying.

Does that still sound like a fuel pump? It seems to start after its cool, but I've never heard of a fuel pump doing that?

I had very similar symptoms in an Astro that turned out to be water in the tank. Everything worked fine, the engine just couldn't run on the stuff.

How difficult is swapping the ignition module? Napa lists them for $70 so I'm going to pick one up, I'm just not sure if it's an easy roadside repair?

I think it's still in the distributor housing if you have a Vortec 5.7, under the cap and rotor. Once you get the doghouse out of the way it should be simple, remove the distributor cap, two screws hold the module in place. But i'd replace it before the trip.

EDIT: Just checked, the module mounts on the intake next to the ignition coil, so it should be really easy with the doghouse off.

In the picture, coil is on the right and module on the left.

Before you drop the tank to replace the pump, be sure there isn't any breaks in the wire. My Suburban had a broken wire right where the wire came out of the main harness that was clipped to the frame rail. The wire wasn't completely broken so I got 12 volts but not enough amperage to run the pump properly.

There was a weird ground issue on the ecu' of those. Wiggle harness coming out of the ecu. It is on the driver side under the hood behind the headlight area.

petegossett wrote: In reply to 81cpcamaro: The actual symptom was running absolutely great, followed by a sudden noticeable lack of power for a second or 2, then dead. The second time it happened, it sputtered once or twice before dying. Does that still sound like a fuel pump? It seems to start after its cool, but I've never heard of a fuel pump doing that?

Hard to be sure, most fuel pumps seem to just give up and quit. Wouldn't hurt to try the ignition module, at least you would have a backup.

My fuzzy memory says that on those the pcm is right below the master cylinder. I remember one once that had a master cylinder leaking, and the brake fluid was seeping into the pcm which then fragged it. It was tough troubleshooting, not common, just something to keep in mind.

I'll vote fuel pump. Once they get good and hot is when they act up check with a presure guage, might be low (bit usable) when cold and get worse as it heats up. Low on fuel will make it worse. pump won't be sumbersed to stay cool.

I think fuel pump as well. Ignition modules tend to just shut off abruptly without warning. Of course you could take the ignition module to a advance/autozone and have it tested for free just for peace of mind.

A few years ago I was working on a mid ninties firebird that had a similar problem, including the fuel gauge malfunction, that was fuel pump related. The plug on top of the bracket that holds the pump and fuel level float was burned up. I think it was because the pump had been drawing a lot more amps than it should for a long time, the pump relay had obviously been over heated at some point too.

It wound up needing the whole fuel pump and level sender assembly to make it right again.

I would also replace the ignition module, if it's not bad now, and you don't know how old it is, it will be soon.

Ok, thanks for the advice everyone, it sounds like I'm on the right track. At this point I might as well consider the pump & ignition module "preventative maintenance", even though the van only has 82k on it.

I'd check the condition of the distributor and wires. My Dad's '97 extended cab with the 305 Vortec had similar symptoms and found that the ignition components were all original. The truck had just shy of 200k miles on it at that point. Replacing with new components solved the issue for him.

In answer to the intermittent fuel pump thing: they don't always just fail and be done. I've had a few that worked fine, then didn't work for awhile, then worked for about 40 miles, then didn't work, then worked for so long that I forgot I should be worried and then it died again. One had almost no brush material left in the motor, resulting in intermittent contact. The other had a ball bearing (gerotor style pump) and the bearing failed. It would occasionally lock up, but would sometimes release with a tap or just from turning off the pump briefly.

If it happens again hit the fuel tank with a piece of wood. If it starts up again it is defiantly the fuel pump. I don't remember you mentioning the filter, a plugged filter can over heat the fuel pump.

In reply to pjbgravely:

Thanks for the reply...I was meaning to post an update!

I had the pump & sending unit replaced, and made the 850-mile trip down to the coast fine. I noticed a difference between this trip & the last one though:

On the way down a few weeks ago, during the hottest part of the afternoon the temp gauge was just touching 210-degrees. This trip, despite the heat warning in effect, the gauge never rose above 200. I'm thinking this may have been due to it running leaner from lower fuel pressure due to the failing pump?