Car gurus, can you chime in?

In My Humble Opinion
1

Let me get the standard disclaimers out of the way: I will be taking it to a real mechanic (again!). This thread is purely for entertainment / informational purposes, you are not my mechanic, etc etc.

I bought a 2003 Chevy Suburban from carmax last year with about 80,000 miles on it. One day the missus drove it until well-after the fuel light had come on, and parked it. The next day, it would not start. I added about 10 gallons of gas to it, but it wouldn’t start. The starter would crank & crank & crank, but the engine would never catch. So we had it towed back to carmax, where the tow-truck guy started it without any problem and drove it off the truck. No problems were found - good fuel pressure, no engine codes, etc. Baffling, to say the least.

Not long after that, we were driving in unusually hot weather (about 102F) and going up-hill, when the truck stalled. Again, it would not start. We had it towed back to carmax, where again it started right up & the guy drove it off the truck. I had them replace the fuel filter & pressed the guy to give me some advice. He suggested a ‘top engine clean’ (not sure what that really means) & cleaning the throttle body assembly. I also read that ‘junk’ can accumulate in the fuel tank interfere with fuel flow sometimes, so we made a resolution to never let it get below 1/2 tank.

It’s been a while & no further problems, so we took it for a trip this past weekend. On our way home, while driving in the rain & cold (37F) through West Virginia, the truck stalled out while doing about 60 - 70MPH. (in the fast lane in the rain at night, with a concrete wall on my left & 18-wheeler on my right & my wife and kids in the car. SCARY!) I drifted over to the side of the road and came to a complete stop, and this time it started right back up. (WHEW!)

After another couple-hundred miles, about 3 miles from my driveway on a flat surface the truck stalled again. Again, I drifted over to the side of the road & came to a complete stop, after which it started up. Both of these stalls happened with about 3/4 of a tank of gas.

In all cases but the first one, it’s stalled out while accelerating. There haven’t been any symptoms leading up to the stall, we’re going one minute & the next it’s dead. There are no lights on the dash. The carmax guys’ have said the fuel pressure seems fine. I’ve searched the web & have found many other similar reports, with hints of everything from bad o2 sensors to leaking gaskets to faulty fuel injectors to bad fuel pumps. So I’m at a loss on where to begin. I’m going back to carmax, but I’m pretty sure they’re not going to be able to find anything, so I’d love to get any suggestions I can from you guys.

Thanks much!

2

It sounds like it’s running fine otherwise, right? If so, it shouldn’t be the injectors or the pump, those are terminal, not chronic, problems.

It sounds like the fuel cutoff is kicking in. Maybe the solenoid is bad, or maybe the manual switch got hit somehow. Some cars have a manual switch, in my old Escort it was in the trunk, though I have no idea where it is on my current car.

YMMV, I’m not a mechanic but I slept at a Holiday Inn Express, no warranties expressed or implied, etc.

3

Almost certainly, some electrical or electronic part of the fuel or ignition system has an intermittent glitch. Unfortunately, the list of possible suspects is a long one. Also unfortunately, it’s often impossible to pinpoint the problem without catching it in the act - if it’s presently working, it’s likely to show good when tested.

With the engine size (e.g. 4.8 liter) I can check for common pattern failures.

4

Yes, seems to fine otherwise. There was some post somewhere (now I’ll have to see if I can dig it back up) that suggested the fuel injectors were actually pushing too much fuel in some circumstances, which would cause it to stall. The fact that 3 out of 4 stalls have happened while I was accelerating seems significant, but I don’t know how. There was also a near-stall that I think I averted by letting up on the gas. That is to say, I thought it felt sluggish, so I let up on it, and then it was fine - all in the space of 1 second. It was also 2 AM and I was on a hair trigger so I might have hallucinated the sluggishness :wink:

It’s the standard Vortec 5300 (5.3 liter). I do tech support for a living, so I know it’s a PITA to guess at these intermittent problems. But, I’ve got to do something.

5

I assume that the fuel filter has been checked to make sure nothing’s clogging it?

Sometimes older fuel tanks have bits of gunk floating at the bottom. They don’t usually cause a problem until someone runs the tank down to empty (or nearly so). Then those bits of gunk could actually get sucked into the fuel intake and clog the filter.

6

I had a problem similar to this. Turned out to be a short on the cable to the fuel cut-off switch.

7

Check the ignition switch while you are at it. I’ve had two go out on me and both were after a series of episodes where the engine just quit and then started right up later.

8

Please, enough with the ‘gunk in the tank’ guesses.

Does this engine have a feature that enables it to switch to fewer than eight cylinders under certain conditions?

9

Not that I’m aware of. It’s a '03 Suburban LT, and has (as far as I can tell) the ‘standard’ generation III vortec LM7, which (again, near as I can tell) doesn’t have anything in the way of “Active Fuel Management”

10

Sounds like a classic case of fuel starvation. Marginal fuel delivery will show up under heavy load, and the engine may run like a top otherwise.

Guess #1, I’m pretty sure your truck has the fuel pump inside the tank. Believe it or not this pump is cooled and lubed by the fuel. The pump may have been hurt by getting run dry (ridiculous, eh?). This can cause fuel starvation under heavy load. In this case be careful, because before the engine dies it will run lean for a minute, and that can lead to detonation and/or very hot exhaust gas temps real fast. Extreme case; I’ve seen a highly supercharged engine actually break the block in half before the driver could get his foot off the gas. It turned out to be a loose power connection to the pump. That was one expensive wire.

Guess #2, check your gas cap. If it’s not venting properly it can cause these symptoms. After you rule out guess #1, go out and make it happen and then without delay open your gas cap. If the tank sucks in a bunch of air that’s probably your culprit. Fuel tanks vent in through the gas cap and out through the carcoal canister.

No trouble codes is odd. Low fuel pressure will usually show up. However some codes don’t get stored if they are intermittent. You might try buying or borrowing an OBD code reader and then give this a try.