Jump to content
  • 0

2002 Suburban, 5.3L Vortec flex-fuel + 2003 Express 1500 (5.3L as well), ODD shutdown issue


Tickerguy

Question

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!

Link to comment
Share on other sites

Recommended Posts

  • 0

You've got a couple odd ones there!  Unfortunately the only way to pinpoint a severely intermittent and environmentally dependent problem like that is to recreate the problem while watching live data on a scan tool. If it ain't broke, it's impossible to fix.

 

Best to do this with someone else driving so you can focus on the scan tool 100%. It will take some time to go through all the parameters, but you can start with all the fuel parameters first. Once you figure out what you're losing (computer command, voltage dropping out as with a short, etc..) it will make troubleshooting 10,000x easier. You'll be able to tell if the fuel pump command is there, check pressure, etc..

 

Keep us posted on this one. This will be a good learning case study for everyone. These kinds of problems are super aggravating, even for seasoned techs. Hope you find the issue quickly.

Link to comment
Share on other sites

  • 0

More data -- I started with the cannister purge (vent) valve, on the assumption that if it was commanded closed but actually was not that it would result in a wildly-off mixture since that is *after* the MAF and thus anything that gets into the intake (usually fuel vapor, obviously), if unmetered could throw the mixture lean enough to result in a lean-out to the point of a stall (it's a pretty large hose coming into that valve!)  That is, I presume what the PCM usually does is to open the evap cannister intake to the manifold BUT at the same time make sure the cannister purge is closed (otherwise you get a wildly crazy flow through the system, all air, after the MAF.)  That could plausibly result in the engine having a mixture lean enough to not fire, and cycling the key would turn off whatever cycle the PCM uses to clear the cannister of vapor, thus an immediate restart.

 

Removed the valve, power off it's open as expected.  Applied BENCH power, it closes as expected and does not pass air, drawing 0.5A when closed.  HOWEVER, if I have mild (mouth) PRESSURE (positive) on the nipple simulating the canister and fuel system being above ambient pressure as would be the case if you increased altitude and drop power it does NOT open until the pressure goes to zero.  If I have vacuum on the nipple and drop power, it does open immediately.  Since the PCM wiring is two-wire it cannot sense the actual state of the valve, only where it *thinks* it is.

 

Next I turned the key on (NOT started), crawled under the truck, I see 12V across the connector pins with a DVM.  HOWEVER, plugging the valve in DOES NOT cause it to click shut (!!!).

 

My understanding is that "key on" but engine NOT running should cause the valve to close, and then it is regulated by the PCM as to when it is actually in operation as the vehicle is running.

 

I obviously have no way to know if there is CURRENT on those pins (and don't care to find out by shorting it for obvious reasons) but if I have +12V across that connector then the ground has to be presumed good as well; in addition I have +12V between one of the pins and the exhaust (bare metal right there), confirming that I DO have a good ground.

 

Is the PCM *monitoring* that to make sure its plugged in (e.g. a high-impedance DMM will show 12V, but no amps) but is not actually applying power to it?

 

I'm tempted to replace the valve since it's reasonably cheap and original and see if doing so alters the fuel trims.  I DID note that when coming down out of altitude that the long term fuel trim went from a consistent +3 to centered right on 0 with some excursions....

 

The actual purge valve (at the intake) operates as expected; closed with no power, open with power, will open and close irrespective of whether pressure or vacuum is on the cannister side.  The seals also look good there.

Edited by Tickerguy
Link to comment
Share on other sites

  • 0

Ok, further update... the NEW purge valve will open and close under both positive and negative (mouth) pressure, where the old one will NOT open if power is removed and the pressure is positive.  Guess what -- that's exactly what would happen if the valve was closed, you ascended in altitude (tank is now positive-pressure compared to the outside ambient) and then the PCM dropped power to it to command it open.

 

Aha, says the dude.  I'm about to install it but this fits exactly with what I observed and might well be a fix.  Now it will be fun to find a place where I can actually test the theory.

Link to comment
Share on other sites

  • 0

So new valve installed and drove it up to 6,500' altitude, no problems.  But -- it wasn't over 80F, which I can't do anything about and which makes the test questionable.  The long-term fuel trims did change with that new valve installed to some degree -- not a lot, but noticeable (positive deviation from what they were.)  I also checked the fuel pressure, which I can't do while driving as the hose I have is nowhere near long enough to snake it somewhere useful; just over 50psi with the key on but engine off, right around 40-45psi at idle and spikes higher (mid 50s) when I blip the throttle good.  That implies that the pump itself is delivering fuel at reasonable volume and the regulator is good.

 

The bodies of the relays that are energized when the truck is running are all equally warm (A/C, DRL and fuel pump) implying that there isn't a problem with the wiring under the relay block, and none of the terminals on the relays are burnt, so that isn't implicated either.

 

When I went to remove the gauge I pulled the relay and cranked to relieve the pressure so it wouldn't spray gas all over the place and got the exact behavior I get when it acts up.  So I'm back to....

 

1. The pump itself shut down even though the drive to it is present (relay is closed)

 

OR

 

2. The PCM (or another module that can) commanded it off.

 

So I'm back to "under what conditions will the pump shut down that are cleared by a power-cycle (key off and back on)", and does the pump have logic in it that can cause it to do that on its own (e.g. not thermally protected which will automatically reset, but which would reset only on a power cycle.)

Link to comment
Share on other sites

  • 0

Could very well be the relay heating up and failing. Wouldn't be the first time I've seen that happen. If it does happen again, leave the key on and swap that relay with the A/C relay (if it's the same). If it suddenly starts, that's more than likely the problem.

Link to comment
Share on other sites

  • 0

I've already swapped it with the DRL relay and it did it again (twice) after I did that.  But -- again -- only at altitude, and only when quite hot outside.  Even beyond 5k' all the way through from the Grand Tetons to Casper Wyoming in the evening, no problems.  It's heat and altitude that triggers it.

 

There's another piece of information -- several years ago I lent the truck to a friend to move.  She ran it out of fuel; it has long had a problem with the gauge sender in that when it shows 1/4 it's actually out.  Well, she ignored my warning and called me to tell me it wouldn't start, insisting she hadn't run out of gas.  I showed up with the mower can and before putting it in the tank, turned the key on -- it read just under 1/4 and the fuel pump did not do the usual "couple of seconds" thing, it came on and stayed running.

 

So that "prime" cycle does have some mechanism of feedback to the PCM, despite there being no sender on the fuel rail that I can find for pressure.  I don't know what it is looking at, but it clearly does, because with the tank empty it ran when the key was on until I turned the key off.  I stuck the mower can full of gas into the tank, the pump ran the usual 3 seconds or so when I turned it back on and it fired up instantly.  Yet when doing the usual startup thing the relay does cycle back off; I can hear it click with the cover off the relay box.

 

Anyone got a wiring diagram on this beast?

Edited by Tickerguy
Typo
Link to comment
Share on other sites

  • 0

The prime function is based off of the oil pressure sender. Key on and no oil pressure, it'll stop running after 2-3 seconds. Once oil pressure is detected, it stays running. That's how the prime works.

 

I had forgotten about this since my '07 is all failure-prone computer controlled now, with no return line. It's pulse-width modulated speed. So, when the magic box (above the spare no less, where all the road salt and sand goes) fails and leaves you for dead on the side of a busy highway, the new one won't even work when you plug it in. Needs to be programmed to the vehicle (MORE $$$ to GM  - nice racket they're running over there!), THEN it will work! 

 

Gotta love modern technology ...

Link to comment
Share on other sites

  • 0

Nice.....  yeah, as near as I can tell that's not the case with the '02; all I can find for regulation on that beast is a mechanical spill valve on the rail that has manifold vacuum as a control (an actual hose!) and that appears to be working properly.  I could see where a stuck-open regulator could screw you hard (dump all the pressure, have a nice day!) but that doesn't appear to be at play here.

 

One extremely annoying thing on these is no reasonable third-party scantools that can talk GM-ese.  Ford and Mazda have Forscan which, with an OBDLink-MX, can do basically anything the dealer tool can including getting at all the secondary modules.  I have VCDS which I bought for my VW years ago as well; same deal.  As near as I can tell there's no comparable software option (I'd pay a rational amount of money for it) for GM products.  If you wind up in module Hell you're paying a dealer, like it or not.  A couple hundred bucks on a non-locked-VIN basis (so I can use it on any GM product I own in the future), sure.  A grand or more?  Never.

 

I prefer GM products generally but I won't buy one of the newer ones for this reason.  I insist on being able to fix my own stuff and the lack of a comprehensive, reasonably priced means to get at the electronic side of things means it's a "no sale" for anything newer than what I own.  When this thing dies it's the end of the GM line for me until and unless that situation changes.  Hate it or love it I'll wind up with a Ford because I can actually fix it on my own.

Edited by Tickerguy
Link to comment
Share on other sites

  • 0

Autel works real good on GM stuff. Breezes through it nice. Still have glitches, but you'll get that with a $12,000 Snap-On unit, too. No better bang-for-buck ratio than the Autel these days. I paid $1,600 for mine 5 years ago, when the Snappy unit was $10k. There's ones way cheaper than this that'll do the job, too. I needed bi-directional control because I have to fix these rolling toilets every day, lol. Makes troubleshooting ALOT easier, and we need all the help we can get in today's automotive world, where one system can fail literally in 500,000 different ways ...

 

For programming, you'd need a laptop, and a J-box. Set you back about $3,000 or better all told. Then you can get on Delco TDS like everyone else, pay GM for the software, and upload it to the vehicle through your link (J-box and laptop). You wouldn't be able to make keys though, or get certain security info without the locksmith license. You can program existing ones, however. 

 

That GMT-800 was built when GM still cared about quality, somewhat. The cheapout phase was long underway by then, but at least they limited that to all interior stuff - window regulators, cluster stepper motors, dash material, etc., and of course, the body, which they'll never keep from rusting away by year 10. I sure wish I had a simple vacuum dependent fuel pressure regulator instead of a $300 magic box that can fail at any time. '07 and up, quality dropped everywhere - not just the interior, but now drivelines and brakes are in play.

 

I'll never forget this one guy posting a video of his brand new 2009 Silverado, fogging out his garage so bad it was BILLOWING out the door, and you could hardly see his tail lights! That was oil smoke out the tailpipe with just 250 miles on the clock. Stuff like this was happening left and right around that time.

 

Thankfully my '07 wasn't quite that bad, but everything else has failed multiple times over it's 110k mile life so far. Brakes pulsating at FORTY miles (had 5 or 6 warranty brake jobs that never fixed it for long), trim falling off the door a week after delivery, more interior squeaks and rattles (at double-digit miles) than my 266k mile '94 K1500 (last well-built truck GM ever made) I was driving prior, lower ball joints failed at 38k, then at 40k right out of warranty, the 4x4 switch failed, uppers failed at 50k, along with 1 strut, weeping front axle seals, and engine oil burning, then the hub bearings failed not long after, then at 97k during a rear diff fluid change I found 80% of the spider gear's teeth in my drain pan, and at 103k miles, 3rd and 4th gear went up in smoke with no warning, like a light switch.

 

The truck is actually getting better with age, as I replace all the poorly engineered parts with much better, more robust parts as the years go by. After the engine fails (which should be soon - I'm at the early mile range for AFM failure and the #2 cam bearing walking out of its bore), she'll get a crate from an engine builder, then a supercharger. Then she'll be complete, and reliable ... except for the billion miles of crap wiring this thing has ...

Link to comment
Share on other sites

  • 0

Well, yeah, I know about the cylinder-deactivation garbage -- basically everyone who does it has had it blow up on people.  No thank you.  The shocker is that this thing has pretty-much stayed together, and my daughter's '03 Express is in pretty decent shape too.  Then there's the '03 Jetta TDI she has (used to mine) with roughly 300k on the clock and other than an A/C compressor and a set of struts, brakes and such, three timing belt kits and miscellaneous suspension bushing stuff is actually OEM -- yes, including the CLUTCH and even the alternator!  Next timing belt interval I'll swap the cam and lifters (reasonable; they were serviceable at 250k but showing signs of wear) and probably the oil pump just on principle, especially if the front main is leaking by then (it isn't so far.)

 

This is the first real stumper that I've had with the thing and the annoying part is that my kid's '03 does it too under identical circumstances.  No way I'm going anywhere near any of the newer GM stuff; I've seen plenty of "no thanks!" sort of problems with stuff 10 years newer and the "must have $3,000 tool AND subscription to work on it" nonsense is enough for me to say "nope!"

 

Being in FL until a year ago (now NE TN) rust isn't an issue but destroyed paint, well, on my '02, yeah.  Oh well.  It looks like crap but runs good.  And I *did* have to change a window regulator in West Yellowstone; amusingly, NAPA got one for me in one day.  I do appreciate being able to get the door card off these trucks in about 5 minutes without breaking a crap-ton of those push-in fasteners that all the newer stuff uses.

 

I may wind up painting this thing and, when the engine finally blows, buying a crate motor or yanking it out and rebuilding it so long as the body holds out.  Other than the leather looking like Hell (Katzkin can fix THAT it just takes money) I can't complain about the interior either, surprisingly.  It's not like a newer vehicle of the same size and towing capacity is going to do materially better than 18mpg on the highway unloaded and 10 with a 6k trailer behind it, plus I already have the brake controller and WD hitch so..... yeah.

Edited by Tickerguy
Link to comment
Share on other sites

  • 0

I may have found it.

 

So I'm emptying the tank to drop it; there's about 5 gallons or so in it.  Rigged my test gauge with a nice long hose into a 5 gallon can and jumpered the power terminals on the relay.

 

After about a gallon had come out of the tank I still had good fuel flow out the hose but the stream was full of fine air bubbles and I could hear the pump change its sound as well.  Of course you CAN'T hear the pump over the engine when its running.

 

Looks like the pump gets warm and wherever it draws from stops getting clean fuel; perhaps a seal expands or something similar and it starts getting air entrained into the fuel flow.  Maybe not a big deal at lower altitudes or when cool, but when hot, well..... insufficient clean fuel in the rail means you can easily be hosed.

 

New pump is on the way and the tank is coming out this afternoon.  Go figure.

 

Will report back once the job is complete.

Link to comment
Share on other sites

  • 0

Interesting. I would think that would be more of a problem on a cooler day at lower elevation, since heat and elevation both cause the engine to run rich, & the computer will dial back the pulse width on the fuel injectors (leaning it out) to compensate. Of course, going up a long, steep grade will negate any of that (even more so if towing), since the load will require more fuel.

 

Shouldn't be bubbles either way, so hopefully that fixes it. 

Link to comment
Share on other sites

  • 0

Well well now we got an interesting and new set of facts.

 

Dropped the tank.  Should have been empty.  When I got the jack under it and took the straps off, well, it was rather too heavy.

 

I got it out and.... there's a crap-ton of fuel in it.  But the pump was pumping... nothing.

 

So..... hypothesis (which I will confirm when I get the pump out after going to get a siphon to remove the fuel) is that there's a crack somewhere in the pump that lets air in intermittently but, it's not all THAT intermittent because here I am at sea level, I ran the pump until I got no fuel jumpering it, and the tank is nowhere NEAR empty.  We'll see exactly how much is in there when I get the siphon.  And I need a piece of 5/8" ID fuel line as I had to cut the vent line; it would NOT come off the nipple on the tank and that's plastic, so getting really aggressive was asking to buy a tank which I definitely did not want to do.

 

Surprisingly enough the area above and around the tank is in surprisingly good condition corrosion and such-wise.  No problems at all, which for 20 year old truck..... who can argue with that?

 

Pump is on the way.

 

For those who don't know there's an anti-siphon (and ignition) screen on the inlet and vent lines.  Stuff a hose down the filler attempting to siphon fuel and you'll get nothing.

Edited by Tickerguy
Link to comment
Share on other sites

  • 0

Well that's a good find. Sounds like that would be it. That will most definitely cause a lean condition and stall.

 

I had a '95 Volvo 940 wagon here several years ago for a complaint of, "Runs great until the first stop sign, then dies, and won't restart the rest of the day." I towed the thing here, and fired it up on my trailer when I got back. I let it idle 30 minutes - no problems at all. Then I figured I'd simulate a drive. I held the pedal down to 3k rpm, then let off to simulate a shift, then  let it go back down to idle. I did this twice when it finally stumbled and stalled. Now I could troubleshoot!  Threw my timing light on as a quick way to check spark - light blinked all the way down to stalling. Then I threw my fuel pressure gauge on - 0 psi ! Was the last thing I suspected, since the owner said he JUST replaced it months ago, and I could clearly hear it running when inside the car. Long story short, I yanked the pump out (super easy on these - go through a small removable hatch in the cargo area of a wagon, or trunk of a sedan, and remove the pump from the top of the tank. Why GM can never make life easy like this for techs, I'll never understand). Got the pump in a cup of acetone, connected power, and the pump torqued in my hand as it instantly spooled up to full RPM ... with not a DROP of fluid coming out the outlet!  The one-way check valve inside had failed in the WRONG direction. It's supposed to prevent drain back which results in long crank times. In this case it prevented fuel flow, lol! First time I'd ever seen that in my life. Was a Walbro pump too, so not a Chinese junk knockoff brand. Walbro is among the best there is! 

 

One thing I've learned over 40 years of playing around with cars and trucks, you never know what you're going to see with failures. Just when you think you've seen it all, one will come in and surprise the crap out of you.🤣 And that aspect has only got worse the past 15 years!

Edited by Jsdirt
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Answer this question...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.



×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.