96 K3500, cranks, no start...

green 788 · February 5, 2014

I have a 1996 GMC K3500 4 door dually that brought me home yesterday, but would not start this morning.

I put a new Bosch fuel pump in the tank about 30,000 miles back.. maybe more like 25,000 miles.

I cannot hear the pump do the 2 second prime... but the 34 gallon tank is pretty well full, and I'm told the Bosch pump is so quiet I may not be able to hear it like you do the Delphi... so I'm not sure.

There is voltage going to the pump, I get the 2 second prime voltage at the plug near the frame rail (I can't reach up on top of the tank, so that's as far as I can check it)...

I did the spark test... screwdriver in the plug wire, it does arc to ground while cranking, so I don't think it's a bad ignition issue.

Lastly... I sprayed some carb cleaner into the intake (just at the air cleaner port, with filter removed), and it will not hit a lick... I would think if it were a fuel issue the engine would at least try to sputter and run on carb cleaner... right?

Any ideas would be great. I don't have a fuel pressure gauge at this point, so I don't know about rail pressure... but again, I'd have thought the thing would hit and try to run on carb cleaner.

Thanks in advance for any help... I will hang with this thread, and not wander off leaving things in doubt as to what I end up doing. So if you're kind enough to help with some advice, I'll be kind enough to follow up and post back.

Dan

green 788 · February 5, 2014

Update...

I checked fuel rail pressure and found that nothing was there... no pressure, so no pump function.

Apparently, starting fluid and carb cleaner sprayed into the air intake tube is not a good way to diagnose a fuel pump failure. For some reason, this engine just seemed to ignore the carb cleaner and starting fluid... odd, but that's how it did.

Either that or I have some additional problem... but I do know I have spark, I did check that as mentioned earlier.

I dropped the tank today, and found that the locking ring that holds the pump airtight into position was LOOSE... the pump was just flopping around, for the most part.

I had noticed that the truck had been hard to start for a long time. I'm guessing that the pump was working practically all the time just trying to keep the pressure built up enough for proper running.

Anyway... I think the pump is warranted for life from Advance. It's a Bosch, as mentioned... maybe they'll replace it for me, I'll see tomorrow. As of now, I'm frozen darn near solid :o ... and it's gonna be colder tomorrow, but I have to get my truck going, so I'll be out in the weather again working on it...

green 788 · February 7, 2014

Hey Dan, how did the repair job go?

green 788 · February 7, 2014

Well, I'm glad you asked.

It was a fuel pump. Moral of this story for the archives is not to count on a spurt of carb cleaner to diagnose a bad fuel pump.

The best thing to do is check for fuel pressure on the rail at the schrader valve (where you hook up the pressure gauge)... if you don't have a gauge, a small screwdriver can be used to press the schrader valve in at fuel rail check point, and with the engine cranking you should get some fuel spurt. In my case... nothing. So there was no fuel pressure.

I dropped the tank and installed a new pump, and it's back on the road.

green 788 · February 7, 2014

Don't you know you're a moron for releasing fuel underneath the hood? Especially while cranking the engine!?? You're going to get someone killed with idiotic advice like that.

green 788 · February 7, 2014

I shoulda known some jack monkey would have some smart comment. But hey, we take greater risks all the time. Anyway, my fuel pump was bombed out... no fuel came out of the schrader valve. So we're gtg. :/

1997SierraSLT · February 7, 2014

I replaced my fuel pump at 140,000 miles. I had consistent 55-60 psi fuel pressure but the truck ran like crap and had no power above 65 mph. Changed out the fuel pump and it ran like a champ. Moral of the story......just because you have good fuel pressure doesn't mean you have fuel flow.

green 788 · February 8, 2014

97 Sierra... thanks for the reply. I had been getting hard starting for several weeks before my pump finally crapped out. It was a Bosch... and that model has been discontinued. When I switched it out, Advance Auto replaced it for free... but the Bosch was discontinued. The only thing they had at AA that they could swap it out with was an Airtex. I know that Airtex got a bad rep some time back... but they've changed a lot of things, presumably... they had a plug connection that would melt in the gas and mess up. That is supposed to be different now--hopefully? I did note that the Bosch plug adapter had melted a bit, and may have been the real reason that the Bosch quit...

The tank was clean, and the fuel filter (which I did replace) did not seem to be plugged up, so I don't know the reason for the failure. It's not real hard to swap out the fuel pump on this truck. It's not fun, but not hard with a friend or two to help out.

This truck of mine is geared 4:10, and weighs about 7100 pounds (I put it on a truck scale once) so it goes through fuel to the tune of 8 to 10 mpg, with about 9 being average. I pull a trailer with it pretty often, in my work... so when I say the Bosch pump lasted only 30k miles, I should note that the pump probably moved as much fuel in that 30k miles as most do in 90k. :o

Dan