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2002 Suburban, 5.3L Vortec flex-fuel + 2003 Express 1500 (5.3L as well), ODD shutdown issue
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Question
Tickerguy
We have two vehicles in our family with the same issue; mine is the 2002 Suburban and my daughter's is the 1500 Express, 2003. Same engine.
BOTH exhibit the same odd behavior -- but only under certain circumstances. I thought this was limited to hers last year, but nope -- mine just did it in the last week.
Here's the symptomology:
At altitude (over 5k'), and when warm/hot (80F+) while driving the engine suddenly acts like it has no fuel pressure. Tooling along at whatever speed (it has happened on the highway and at lower speeds, 45mph in Grand Teton national park) you lose power w/o warning. There is very little (but not zero) throttle response, the dash remains active, the tach remains active (which would tend to rule out the crank sensor) and as you pull off the road the engine stalls. Voltage reading when it occurs is normal. The vehicle acts as if it is out of fuel (e.g. very low to zero fuel rail pressure) but obviously it is not out of fuel, but has no fuel delivery.
In each case where it has occurred -- no exceptions -- key off/on produces an immediate restart; the engine will stumble for a second or two and then returns to normal idle and you can continue. Attempting a restart without going through key-off produces nothing (as if out of gas.) I have swapped the fuel pump relay with the DRL relay in the power box (same relay number) on the theory that it was intermittently defective, no change. I have tried wiggling the key (thinking potentially bad ignition switch BUT with the dash up the PCM is clearly getting power and since the cut-off is not total it's also getting spark), no change. From what I can see the fuel pump relay output is protected by a fuse, so an overcurrent there should produce a hard shutdown and a blown fuse. The original incident with my truck (which has never done this before) was about an hour out of Denver on I-70 at ~5k feet; fuel was at roughly 3/4 tank at the time. Topped it off after the second incident, swapped the DRL and fuel pump relay, got to Denver and thought I had identified the problem and fixed it only to have it happen again in traffic coming down the freeway toward Pueblo (so, obviously, wrong guess.) After that temperatures were somewhat cooler into the evening and night and it did not do it again until in the Grand Tetons when we had one more incident. Again, nowhere near low on fuel and again, a restart was immediate on key off/on.
Power was normal through all of this other than the expected lower performance with higher altitude.
My daughter's 1500 Express also did the same thing under the same conditions! She had it happen out of Pueblo while heading to some out-of-the-way stuff (Sand Dunes) and turned around, since being stranded there would be bad. Then it occurred against near Taos, again, at elevation and moderately high temperatures. Same deal -- it acts like it's out of gas but isn't anywhere near actually being out of fuel.
Once we both left the higher altitudes it has not happened again. I ran across Kansas two days ago in 100F outside temperatures at 80MPH for hours, no problems. She went through NM and TX in similar heat and speeds, no problems. We both then continued to our homes, another 12+ hours (now more than a solid day of uninterrupted driving in hot weather), no problems.
Her check engine light is not on (she doesn't have a code scanner with her) and neither is mine; I have Torque and an OBDLink MX in the truck; there are no stored codes or freeze frames. Fuel trims look ok (neither short or long-term go beyond +/- 7) although as I came down in altitude the long term went from around +3-4 to right near zero. MAF looks ok as well; showing 6g/s at idle; in the mountains it was constrained (thinner air of course) but as I descended the range looks ok too as I get readings around 120-130 under hard acceleration. MAP sensor (vacuum) also looks good. Coolant was running a bit over where it usually does (190-195F) but expected for the higher elevations in high heat and relatively high load climbing hills and such (Torque again); about 5-7F over where it usually runs here in my local area in the evenings and such, so it's definitely not an overheat-related shutdown and the dash indicated no problems with anything.
There is no PID I can find for fuel pressure, unfortunately, so being able to ascertain that while driving means I can't rule in or out the obvious (e.g. no fuel pressure at the rail) problem that I expect is indeed what's going on.
Where do I start with this? I do not know whether her fuel pump is original, but mine is -- never been changed. When key-on I hear it run for a few seconds, then shut off as normal. The only thing I know is hosed is that the float is screwy in that when it reads 1/4 tank it is actually empty (as discovered the hard way.)
Anyone know under what conditions the PCM will command the fuel pump off? I'm assuming that's not happening and the pump itself is shutting down and power-cycling it resets whatever tripped it, but to have two vehicles do the exact same thing under the exact same circumstances, but intermittently and only when away from home (I live at about 1,000' elevation so testing a fix is going to be a problem) isn't nice. Heat itself is, I believe, eliminated since it was much hotter coming back through Kansas and Texas than it was when we had the issue occur.
Does anyone know if there are a set of conditions under which the fuel pump will shut itself off in a fashion that will only reset when power-cycled, since that is what appears to be going on here? Of note while elevated temperature appears to be required (we drove through the Tetons and Yellowstone for two days with temps in the 70s and less without problems) a near-empty tank is not; the shutdown in the Tetons and the one in Denver in traffic both happened with about 3/4 tank of fuel, and when my daughter's truck did it both times she had plenty of fuel (more than half a tank) as well.
Ideas on where to start on this would be great; the lack of codes, obviously, doesn't help a bit. I'm the original owner on the '02 and it's been quite trouble-free; it has had no electrical gremlins or other odd stuff during its lifetime, and has low mileage as it's a towing/hauling vehicle only really (~100k miles); it looks like crap as the paint is hosed from the sun but otherwise has been a pretty solid truck. The Express was bought used a bit over a year ago so we have no detailed history on it.
I'm tempted to drop the tank and replace the fuel pump but without knowing that there are a set of conditions that can cause it to shut down that would key off/on reset it throwing a $300 part at the problem without any indication that will fix it doesn't push my buttons for obvious reasons.
Thanks in advance!
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