Our 99 Suburban (5.7 w/ 180k miles) has been acting up lately. It starts fine when cold, but if you drive it awhile, turn it off and try to restart it, it isn't getting fuel. It seems to act up more when it's hot outside. It will start and run on starting fluid, but dies as soon as the fluid goes away. It almost seems like a sensor or component or electrical connection is getting heat soaked.

I replaced the fuel filter yesterday and it was full of fine, black gunk. I captured some of the gas that came out of the line. It kinda look like piss, with the same fine black gunk in it and possibly some water in the bottom. I put 2 bottles of dry gas in it and drove it for about 20 miles with no problems. But as soon as I stopped it and tried to restart it 10 minutes later, it had the same symptoms, would only start/run on starting fluid. I tried it again this AM, and it started right up.

The fuel pump was replaced about 10,000 miles ago. New OEM spark plugs about 2,000 miles ago. I also replaced the battery as it was kinda weak.

I'm going to put on a new fuel filter this AM.

Anybody have any experience with this or any test proceedures / ideas?

It's FI? Electric fuel pump? Can you hear it run? If so, is it running when hot and

will not start? Do not assume that the fuel pump is good because you replaced it.

Fuel preasure gauge would eliminate it as a suspect. Good Luck.

Thanks!

Yes, it's FI (throttle body style aka TBI). I can hear the fuel pump cycling when the key is first turned on, even when it's not starting. The new pump was an OEM unit, as I was cautioned about crummy aftermarket units. My mechanic replaced it. Do new OEM pumps require a wiring splice? It seems like I read something like that on BB somewhere.

Haven't checked the fuel pressure yet. BTW, where is the fuel pressure check port on this engine?

No service engine lights, even when it won't start or stalls.

It's starting up and running fine now, but I'm hesitant to drive it anywhere. I've already used up 2 AAA tows in 2 days.

You may have more than 1 fuel filter.

You may have a leaky fuel line... so you're sucking air.

The "sock" on the end of the pickup inside the tank?? Have you checked that??

The seal on the top of the tank?? sometimes on sealed units, that can affect the performance.

You "should" get some kind of CEL if it were electrical. So I think you're headed in the right direction by hunting down mechanical issues... I would check those other things.

Um did you guiys miss the part about a " fine black gunk " being in the filter and fuel ?? Soiunds like to me you have something in the system breaking down. You need to determine what/where the gunk is coming from. Sounds like you're clogging the filter as it runs and once it has cooled, it has also had enough time for the gunk to settle in the bottom of the filter. Might need to drain your tank to get to the source. I have also heard of the pumps getting hot and deteriorating from the inside. Just another possibility.

Try unhooking the fuel line AT the outlet of the pump, see what comes out. THEN disconnect it BEFORE the pump and see what comes out. This will eliminate the pump

was the filter changed AT the time of the new pump? bigest mistake MANY people do when changing the pump is to NOT change the filter AT the time of pump repair. most pumps are killed to start with because of a plugged filter...

mike

Mechanically speaking, it could be a number of things. Pump, filter, etc... BUT- I would determine what the "fine black gunk" is first as it's likely the source of the problem. Unless your car's been sitting for some time, there shouldn't be any reason why a "fine black gunk" is in the feul.

If you can't reasonably determine where it came from, be it something your mechanic might've accidentally done or otherwise, try changing where you feul up. I don't know if anybody else on these boards is familiar with it, but there's a chain of convenience stores around the midwest called Casey's General Store, and they are notorious for having bad gas. I had a problem with it once, that being it plugged my carb to the point I needed a complete rebuild on it, and I haven't feuled with them since. Likewise I haven't had a problem with gas since. Quiktrip. Every trip. Gauranteed.

The first place to start is to check the fuel pressure. There is a schrader valve on the driver's side of the engine just forward of the distributor that you can connect your pressure gauge to.

You need something like ~65psi key on, engine off
~55psi running
Anything less and the poppets will not open.

The in-tank fuel pumps in the 96-99 (Vortec) Suburbans/Tahoe/Yukons are a known problem area especially if you run the tank down too low on a regular basis (the fuel helps to keep the pump cool). Also, a clogged fuel filter tends to shorten the life of the pump also by making it work harder than it normally should.

The Suburban die hards change their fuel filters every 25,000 miles or so and never let the tank drop below 1/4.

This also lessens the sticker shock at the Gas Station. Your Suburban has a 42 Gallon tank. Filling a near empty Surban at $4.00 per gallon is hard on the pocket book.

I got mine for $7.00 on sale:
http://www.harborfreight.com/cpi/ctaf/disp...temnumber=92699
And it has the correct fitting for your Suburban.

I've had a 93 GMC Sierra with a 5.7 that my father bought new. This truck has been babied its whole life, still has original shocks at 150,000. I've had it 8 years and in 2004 it just shut down on me one day. I did the same thing with gas and starting fluid and like you it quit after using what was in the TBI. A supposedly reputable shop had the truck a month and after replacing the fuel pump, lines, straps, computer, plugs, wires, cap, rotor(fvcker stuck an old one in after I had just put in the new one) and various other parts he gave me back the truck, supposedly fixed, only to have it die on me after 8 miles. Only then did they trace it to a small electronic part under the distributor. A $1,500 bill for a mis-diagnosed $38 part.

Check that, it may work. I wish I remembered which exact part, but the experience is something I've been trying to block from memory.

Only my father's insistance the guy was a good wrench kept me from giving him one of these

In that case, it could be either the condenser or the module. Those are the only two things I can think of that would be "under" the distributor.

But I still insist that you figure out what the black gunk is. Whether its the source of the problem or not, it's not a good thing.

The 1999 does not have the module in the distributor like the 1993 does. In the 99, this is controlled by the ECM/PCM.

The "black gunk" could be either the short rubber hose that connects the tank to the steel fuel lines or fuel pump impeller disintegrating. Check your fuel pressure and also make sure your system is holding pressure for at least an hour (hint, run engine for a few seconds, wait an hour or two and depress the schrader valve to check for pressure. Caution, if it is still pressurized, it will be at 40+ psi or so. Use a rag to contain the spray).

g.m. have problems "zapping" their moduals in the distributor if the cap gets carboned up. the high voltage takes the path of least resistance eventually jumping to the modual. this is an on or off running thing though. sounds like your $38 part mel.

i second the hose thing, so if there is non-original hose in the line somewhere and sqeeze chech for bloated/spongy feel

Wow! Thanks for all the responses and ideas.

I replaced the filter again (about 30 miles) , and there very little, if any, black gunk. The fuel coming out of the line looked OK.

I asked my mechanic about the new fuel pump he installed about 20,000 miles ago. He stated that the tank was emptied and cleaned, there were no splices in the electrical connections to the pump (some require this?), the pump was OEM, and a new fuel filter was installed. This guy is very fair, honest and inexpensive. I trust him.

Last night he sampled the fuel from the tank, and it looks good. Fuel pressure checks out OK (58 psi) and doesn't bleed down. No fault codes found, no check engine lights. Checked temp of relays, OK. Fuses and electrical connections in general, OK. Coolant temp, OK. Let it idle for 40 minutes to get good n' warm. Let it sit 15 minutes. Restarts just fine.

He still has it, and I'm going to ask him about some of your suggestions.

GRRRRR! I did it again!!!!!!! Thought I had it licked. Why does it only malfunction on the hottest #$@% days?!!!

Changed the filter yet again, even cycled the fuel pump and let the fuel run out of the line while the filter was off...fuel looked great and pump appeared to have plenty of pressure and volume.

I did buy a fuel pressure guage and hooked it up after it stalled. Sure enough, it read way too low, 35 psi. Cycling the fuel pump several times without starting brought up the pressure to 50 psi. It would start and idle poorly, but not drive, at least not further than a few miles.

I think I have some crap in the tank that is clogging up the fuel sock on the pump. I literally jumped up and down on the rear bumper to slosh the fuel in the tank around. After a few pump cycles, the pressure was back up to 58 psi. Started and ran great...for about a mile. Same low 35 psi fuel pressure. Left the pressure guage hooked up. Had it towed home. Went out to start it about 1 hr. later, 58 psi and started right up.

All things seem to point to a fuel tank problem, unless somebody has any other ideas.

Scrap it and buy a new one, SUVs are super cheap now.

Has the fuel pressure regulator been changed? It solved my running problems years ago on the same vintage.
Good luck.
Jule

Thanks for the suggestion. No it hasn't. Did your 'burb have similar symptoms and was your regulator gunked up or just bad?

It is sounding so much like what mine was doing. The first time it stopped(very hot day) after getting it towed home there were 5 drunk GM techs accross the street. They all came over to help. Turned key and heard fuel pump working, cranked on it and it fired right up and ran fine. The jostling from the tow somehow made it better. Next day nothing. Replaced wires, cap, rotor, plugs, computer to no avail. Next stop was to the shop that ripped me off. After all they did it would run great for a time, sometimes a month then shut down. Same thing, get it towed, cleared up and ran.

A few months later a spring in the oil pump went bad and killed the lower half of the engine. Drove it for 25,000 miles until it gave out completely. Last June I put in a 350 from an older truck myself not using the old distributor or TBI unit, just what the replacement had. It has been 10,000 miles and over a year and it has not shut down once since. The problem is solved IMO.

I'm just saying it sounds like you're chasing the same ghosts I was.

how hot is the fuel?... vapor locking?

you may have a line collapsing internally, (earlier black gook). look for crimped, bent line. have you run e85/gasahol? that is real hard on earlier fuel lines/pumps etc...

you may have to pull the pump and check the boot/filter... he did install a NEW one, right?

I have a 95 4.3 V6. similiar problem last year. Fuel Pump. In the beginning same symptoms as yours. Then just completely failed with fine black gunk in the filter.

My mechanic said some trucks have had to replace pumps (OEM) at 35K miles. My truck had 150K at the time so I feel lucky. I would replace the pump again.

Jim

During my years with GM we say this problem over and over. The injection system uses eight poppet nozzles that must have a minimum of 47 PSI to open them. If the pressure leaks down they wont open. The fuel pump is located on a module in the tank, on this module is a small pressure pulsator that dampens the fuel pulsations from the pump. It is sealed to the outlet of the pump and module with weak "O" rings that over time leak and cause a slow drop in pressure. The next issue is the regulator located under the intake upper plenum. They will also bleed off pressure. To test this install the fuel pressure gauge at the test port, block the return line and monitor pressure for 4-5 hours. Finally there are the poppet nozzles, many design updates. They will also cause bleed off due to a stuck check ball, however this is usually present with the P0300 random harassment (I mean missfire) code. Hope this helps, Larry

Many thanks for all the responses and ideas!

Orange914: It seems to happen on REALLY hot days (92+ F), especially after we let it idle alot, so maybe fuel temp has something to do with it. I didn't think that FI vehicles could vapor lock, but maybe they do. I'm not running E85, but most of the stations around here have 10% (maybe more) Ethanol. Maybe I got some E85 by mistake?

Is that "line collapsing internally" you're referring to located in the tank with the fuel pump and is it included with the OEM pump assembly, or is it an extra part? I was going to pull the tank and inspect everything anyway. My mechanic didn't say anything about replacing the line/boot/filter when he replaced the pump, so maybe that's it.

Roadsterfan: I'm pulling the tank anyway, so maybe a new pump is in order. Kinda sucks, as the new OEM pump in it only has 40,000 mile on it!

LS6/914: I left the pressure guage hooked up, checked the pressure and it is zero after sitting 2 days. Turned the key to cycle the pump, and it built up to 55 psi immediately. Is the pressure supposed to stay up after sitting 2 days or is zero pressure normal? The pressure seems to be fine until the ambient gets above 92 AND we've been idling alot.

I'll do the pressure regulator test next, thanks for the tip!

Is the pressure pulsator included with a new OEM pump assembly, or do you have to get it and/or the O rings separately?

No codes, ever, so the poppets are less of a suspect.

Zero pressure is never 'normal' on any FI system. It should retain pressure for that long definitely. When it refuses to start, have you tried letting the pump 'prime' the system without cranking it? I seem to recall you saying in an earlier post that when the problem occurs your fuel pressure is down in the 30's, which would be bad.

A problem I've seen on many VORTEC V6's (Well, OK, two, but they're the only two I've had) is the fuel return lines that attach to the fuel distributor assembly. (The box that the poppet lines attach to) These lines apparently rub against something and eventually will not hold pressure. I've had to replace them on both of these engines, and I've heard that it's a common problem. Whether it applies to the VORTEC V8s is another question, but it's certainly worth checking.

We did, and it didn't help. Man, if I had a nickel for every time we 'primed' the fuel pump without starting, (waiting 2 hours for AAA to show up) we'd be rich! Learned that trick from driving teeners with hot start / vapor lock issues.

My GM FI when not running is not under pressure. You can undo any fuel line you need to when the key is off, no pressure. I will go with my first diagnosis...FUEL PUMP.

Jim