1998 GMC Suburban K1500 5.7 only starts with starter fluid. Is this the right forum?

[anothermark]

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.

 

 

[richard wysong]

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?

[PopeyeD]

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.

[anothermark]

"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?

[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.

[dna9656]

You have thought this through just about as well as anyone could. You could turn they headache over to a GM dealer, as they are supposed to have ALL the tech data and know the truck best. I know that sounds like hype but you got to give it some credence...

 You COULD have an obstructed fuel line but I have to doubt it, You didn't say if you have a filter or screen in the tank, unless your fuel line is deteriorating inside...do you use a lot of gas with alcohol in it? It's said that's hard on older fuel systems, corrosion being one of the problems. If you have a screen in the tank it should catch the larger stuff but again I have seen those screens have large corrosion issues and they let big stuff in, hopefully caught by an external filter, that would explain the frequent filter change. During my military service in vehicle maintenance fuel filters lasted seemingly forever, a result of clean gas and no crap in the tank. I bet your tank is plastic yes? If so that reduces the crap in the tank chances a lot.

Your injectors prolly need a pro cleaning job, most everybody's do because most everybody doesn't get them cleaned before there is a problem.

I had a '94 4.3 that  had issues it needed a fuel pressure regulator,the part was hugely expensive The mech I used is prolly one of if not the best mech in town, he could work at any shop but he has his own. He told me that the spec for the fuel pressure MUST be exactly X (I don't remember the number but the number was higher than the one you described) so if your fuel pressure isn't EXACTLY what's prescribed (my mech said it HAD to be exactly correct) it won't run right or at all.

Good luck and please post the fix once you find it.

 

[richard wysong]

the fuel pump module is in the tank and includes the pump, sending unit for the gauge, the float for the gauge, the strainer, all the wires and hoses all on the bracket that drops into the tank. it is possible to just change the pump itself but why would you unless to save a buck. its possible the strainer is not installed correctly and getting pinched under the pump which is spring loaded and sits firmly against the bottom of the tank

[asilverblazer]

Is it hard to start every time? Once it has started with starter fluid can you shut it of and restart it regularly?

 

It idles fine and purrs right along... what about driving, does it run and drive fine?

 

I'd think any kind of blockage would not allow it to drive without major drivability symptoms. 

[richard wysong]

have you burned a tank of fuel since the problem started? maybe u got bad gas