27 replies to this topic

[jeb]

I've owned this truck since new. 86k on the clock, all maint up to date. The issue I have is the truck just mysteriously will do a cough and die or almost die thing. Once it does that, it's very hard to keep running. I have to feather/pump the pedal to keep it running. But it will stall quickly, so I have to get off the road NOW once it happens. Once it stalls, it will usually restart but runs very erratically for a while and won't hardly get out of it's own way. Once it cools down for 30 minutes or so, all is good. It's very disconcerting as it makes the truck hard to depend on.

I've had this issue 3, maybe 4 times over the years with this truck. Always pulling fairly heavy, always on a hot day. First time was pulling a U-Haul flat bed with our WRX on it. 600 mile trip, close to 100 degrees where the problem was, interstate driving. Truck ran fine after a 30 minute cool down and continued pulling the load fine for another 100 miles in even hotter temps. Had maybe 20K on the clock at that time. No code recorded. All gauges in normal ranges. No coolant loss, etc. Dealer could not find an issue.

The other times have been hauling my V-nosed, dual axle (19'x8.5' including V) dirt bike trailer. Never much weight in it and my truck has pulled this load since new many, many 1000's of miles with no issues. Even in very hot weather. Did it again today with temps near 90. Fortunately, I was close to home and my neighbor came to my rescue. I got a code out of this time, but it's just the P0300 misfire code. I didn't really need a code to tell me it was doing that as it was rough ideling and popping a bit, like it usually does. 20-30 minutes later, all seems well again, like normal. Seems like it happens every couple of years. Odd deal. Dealer is never able to find an issue.

I've hauled in hot weather quite a bit over the years with no issues, but it does seem heat related. I just can't figure out what could cause an issue like this. I just have a feeling it's going to really leave me high and dry someday far from home, and would really like to get it fixed before that happens. So any suggestions would be most welcome.

Thanks in advance.

[Chevyboy86]

Almost sounds like a bad fuel pump...or a stubborn one. My buddy had the same kinda thing happen to his 98 Sierra...turned out to be a fussy fuels pump. Random misfire code could be something g electrical too...maybe test fuel pressure??

[jeb]

Someone else suggested the fuel pump to me as well. But it seems odd it would only have an issue every couple of years like this. I may have to look into it more, though.

Ran it up the gas station this morning. It had more than 1/2 tank of fuel left, but wanted to test run it. Ran fine, like always happens after this.

[dewfpo]

In the old days (before fuel injection and 45+ psi fuel pressure systems) I'd say you were vapor locking but that's not supposed to happen nowadays for the reasons I mentioned. Vapor lock only happened sometimes and was not always repeatable. It's a shame you can't hook a fuel pressure gauge and run it all the time and see if it's any different when the symptoms come back.

DEWFPO

[99 2500]

Need to get it on a scanner to see how the o2 sensors are oscillating , also weak plug wires can cause strange issues like this.

[Shaners]

Maybe a fuel pressure regulator?

[jeb]

Waking this one up. I changed the plugs and wires on the truck, just to try something. But it messed up again today. And this was a bit different. I was not hauling at all. It was a hot day, in the upper 90's. We had taken an 1.5 hour each way trip early in the day, no problem. All twisty 2 lane highway stuff. Then after letting the truck sit for 2 hours or so, we went to a "drive through zoo". Then we idled around some back country roads around near where we're camped on Table Rock Lake. Just sight seeing. About 10 minutes or so before I had the problem show up again, I did kind of sense the tranny slipping a little. I have gauges for Tranny temp, oil temps and engine temp. None of them were beyond half way, and certainly no where near the hot zone. But it stalled on us in some really slow going. Same basic stuff as I described in the first post above.

Let it sit for 5 minutes or so, and it started up. We were only 3 miles or so from our camp spot, so we hustled back to the diesel pusher. Stalled just as we drifted into camp. Whew!

After an hour, I took it around the camp area and all seems fine again. No codes, no CEL's, etc. So the common items at this point are hot days running the AC hard. The one time the warranty did something on this, they replaced the torque converter. And I did sense the tranny slipping a bit today. But it's hard to draw a line between the tranny slipping and the motor stalling, given all the heat gauges being in range. And no lights. Tranny fluid and filter were changed within the last year.

I am getting really paranoid about this truck. I love it overall, but what a screwy problem. I need to get it figured out and fixed. So any more suggestions would be appeciated.

[8.1HD/ALLISON]

Check fuel pressure when acting up. Should be 55-62 psi I believe. Remove vacuum hose from fuel pressure regulator and make sure its not leaking. Get ahold of a scan tool and see what misfires, fuel trims, mass air flow, o2 sensors readings are doing when it acts up. If its not throwing a check engine light I would imagine its fuel or air related.

[jeb]

Thanks, but the problem is, you never know when it's going to act up. Usually, it's a LONG time between episodes. This time it was only about 3 months, which is by far the cloesest they've happened together. So kind of hard to borrow a scan tool for that long. I do have a code reader, but it shows nothing, which you'd expect with no CEL.

Where is the fuel pressure regulator? I can at least look at that and maybe replace the vaccum line.

It almost acts like an old carb'd car that has boiling fuel in the bowl. And it always happens on hot days.

[99 2500]

My vote goes toward the fuel pump. A weak pump will work normal at times and struggle to keep up under heavy load or long running times and sets no codes.

[jeb]

I've for sure thought about the fuel pump, too. But I just have trouble thinking it could be bad for a few reasons. First time it happened, I only had like 10k on the truck. Also, I pull my dirt bike trailer and boat all over the country and only rarely have this issue. You'd think a weak pump would show up more often. I also thought about the heat possibly impacting the pump performance, but this last time the tank was only down 5 gallons out of it's almost 40 gallon capacity. So it could not have been overly exposed to heat. I know the pumps do go bad, and I have 90k on the truck now. So maybe I should change it just to be safe.

Good point about it not throwing a CEL with a marginal pump, too.

Edited by jeb, 26 June 2012 - 03:29 PM.

[markw8]

Why not just do a proper fuel pump test and you'll know if thats it.

Mark

[jeb]

I didn't know you could do that. I assume it's a dealer thing? I'm very mechanically oriented. Can the tools to do that be rented?

[Chevyboy86]

Give it some injector cleaner, it will lubricate your fuel pump. My buddy had problems like yours, got another year out of the pump by putting in some injector cleaner a couple times.

[jeb]

Any particular brand of pump that everyone recommends? I don't mind buying OEM but, if that is the issue, it seems the OEM pump is not that great.

Any links to threads about what all is involved with changing one would be appreciated, too. I know I need to pull the tank, and that I need the fuel line connector tools.