anothermark

" Richard Wrote: "have you scanned it and looked at the data stream? possibly bad coolant sensor or intake air temp, . have you checkedthe fuel flow? not just the pressure which is a little low but it should still start. a good fuel pressure gauge has a dump valve on it, with the truck running you should be able to open the dump valve and it should stay running if the pumps doing its job. it wouldn't be the first time they have shipped a whole batch of defective pumps. if they do change the pump again have them blow out the lines between the pump and the filter just to make sure theres no debris in that line. unlikely theres muck in the tank unless you run without a gas cap. was it doing this before you changed the filter? if so its unlikely theres anything in the line from the filter to the engine unless the filter was so old that the insides disintegrated. any water in the filter when you changed it? are you changing the fuel pump module or just the pump?" Thanks, Richard. The mechanic ran diagnostic checks but found no error codes, he said. I have a good fuel pressure gauge with a pump valve on it and will check fuel pressure flow when I dump the fuel, and hope it keeps running. My first thought was a bad batch of pumps from China or Vietnam or wherever. And yes, it was doing this before I had the filter changed which therefore means it's unlikely the line is blocked as you said? But I never checked the filter, which was quite old, for water myself. And, if the fuel pump module is under the hood, then he only changed the pump inside the tank. Thanks again for your advice.

"Have the tanks cleaned out! Your description points to a problem BEFORE the fuel pump (i.e. in the tank) that repeats AFTER the fuel pump has been replaced. If what you have written is true and accurate, there is no further question." Thanks. What I wrote was accurate, and very true. That was my thought, that there might be dirt or dust in the tank that worked its way in there over the dusty miles and it just took a short while to clog the intake filter on the new pump, if that's what it's called. The key being that it started up perfectly with a new pump, twice, and then went bad shortly thereafter both times. But that said, why does it keep running once started? Is it because enough fuel gets pumped through to run, but not to start? That once started the vacuum pressure from the manifold sucks the fuel in and less pump pressure is required? And if I have the tank flushed out do I need to replace the pump again or can that pump filter be cleaned?

I'm stumped and have run this problem by a half dozen mechanics who usually give me the expensive answer. I've got a GMC 1998 Suburban K1500 5.7 with 250,000 miles. It only starts with starter fluid now and then idles fine, maybe a bit rough, but purrs right along. So I replaced the fuel pump relay and the fuel filter but that didn't help. Then I had a mechanic replace the fuel pump and that fixed the problem. Started right up, all was good and well for a few hundred miles until it reverted back to its old self, not starting without starter fluid. (He never flushed the tanks to wash out any dirt or debris, I don't recall). As the pump was under warranty the mechanic replaced that pump and all was well again, fired right up and I was happy, for a few hundred miles when it happened once more. It's taking longer to start now even with the starter fluid. So, my fuel pressure gauge test measured the following. Key on, key off 50 psi where it held steady (It should be 60 - 62). At an idle it ran at 52 psi. I turned it off and pressure dropped to 48 where it held solid for 10 minutes. From what I've read, because pressure held steady at 48 psi after I turned it off the problem isn't a leaky spider fuel injector or a leaky fuel pressure regulator under the intake manifold - and a real pain to get to. Am I right? Or, can the pressure regulator be causing problems even if it does not leak? And how would I know? Is leakage the only problem that can arise with the regulator? With two brand new fuel pumps I find it unlikely that's the problem, but what else could it be? And, if it was the spider injector or pressure regulator leaking I would think it still wouldn't have started up even with those new fuel pumps. Opinions run the course. And what are the odds of two new fuel pumps being bad right out of the box? Maybe there's a clogged fuel line? Some obstruction? One fellow told me he had the same problem with a small piece of paper towel caught in the line. Now, here's a clue. I've driven this rig thousands and thousands of miles on dusty dirt roads in the Southwest deserts and off-road in the Rockies. Is it possible that dirt or dust or gunk is in the tank that is blocking something? I know clogged fuel filters and this isn't it. In my experience the truck usually sputters and bumps along if the filter is really clogged, but not this rig. And, I had the filter changed. Or, is there a valve of some kind in the line that might be stuck open or shut? I have no idea, but I don't want the mechanic to throw parts at it randomly, like replacing the spider injectors or the pressure regulator, expensive as that is. Any ideas? Thanks.