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

[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!

[Tickerguy]

I'm going to tear it apart and figure out why it failed once I get a replacement and put the beast back together.  This is certainly an interesting one and since its original, and the kid's may be as well, I'm wondering if we share a common flaw in terms of design that may have been addressed down the road but neither was ever changed out.

[Tickerguy]

Who's the jackwad at GM who thought that tiny little feed hose from the tank bottom would be sufficient to keep the cup full under all load and environmental conditions?  Specifically the most pressure differential (and thus flow potential) you can ever have on the "suction" side of a pump is 14.7psi, and as you go up in altitude that decreases of course.  Run out of fuel in the cup if you consume it faster than the lift side can refill it and the high-pressure side sucks air - you're done.  The obvious debris all over the in-cup strainer -- but none polluting the tank-bottom one -- is almost-certainly what used to be internals of said lift pump.  The inside of the tank is completely clean; no debris of any sort.  There's what appears to be a silicone one-way valve on the bottom of the cup for it to fill as well; it's possible that second intake is only for cooling flow, but if it is then the disparity of debris in the two strainers still is a problem.

 

It appears, from the pictures I've seen of the replacement on the way, that this bit of stupidity has been corrected as there is no second thin line anymore.

 

One thing I get very, very annoyed with is obvious stupidity in design.  This qualifies.

 

Edited June 22, 2021 by Tickerguy

[Jsdirt]

Welcome to my world, lol. I deal with crap like this every day! Wait until you try to get a transmission out of one of these. The 800 series is MUCH easier than the 900 series, though. I swear the 900 series was engineered out of spite for mechanics. 

 

I do more Fords around here than anything, and there aren't too many 800 series trucks around, and even fewer 900 series. Been a LONG time since I've done a fuel pump in one. Most have long since rotted away to nothing, and got sent to the crusher. I don't even recall the cup, unless I just yanked the entire assembly out, tossed it in the trash, and threw the new one in. More than likely I was all fired up after dealing with the rusty tank straps and pump ring on top of the tank. I'd bet on that, lol. Pic jogs the memory a little. Nice illustrations.  

[Tickerguy]

Biggest bit of stupidity (other than the parking brake design which has been stupid on GM truck products for decades, simply because it never gets hot and thus turns into a ball of rust) is the impossibility of dropping the transmission pan without removing the shift cable bracket first (or the exhaust, which is even worse!)

 

That wouldn't be such a big deal EXCEPT the bolts are Torx and on the TOP of the gearbox, and on a 4x4 the front driveshaft is in the way, so you get to take that out first.  Turns what should be a 30 minute job to do trans fluid and filter into a couple of hours.  God help you if you strip those Torx bolts too; do that and you get to pull the transmission in order to get to them with a cutoff wheel on a dremel or similar.

 

First time I did one of these I ASSUMED there was clearance to get the pan off -- and wound up taking a transmission fluid bath as a consequence.

Edited June 22, 2021 by Tickerguy

[Jsdirt]

Yep! Then after all that, you get all the pan bolts out, start dropping the pan while ATF runs down your arms because there's no drain plug, and you realize the crossmember is in the way! By the time you're done wiggling the stupid pan around the crossmember, most of the ATF is now on YOU. That's how the 900 series is anyway. I can't remember if the 800 clears the crossmember or not. What a moronic design!

 

The first time I did my fluid & filter, I swapped those torx out for regular 12mm hex head bolts. I just knew down the road I'd have to deal with these all rusty. I did the fluid / filter change at 40k miles - the truck was basically still brand new then - no rust, and yet I STILL had to fight them! GM loves to torque crap like that to 10k foot-pounds. When I did the transmission swap this past fall, those 2 bolts I put in were solid rust. Sure was glad I used anti-seize compound. That was the one part of the entire job that didn't fight me tooth and nail! Whenever I do a 900 series for customers, I just bend the tab out, do the job, and bend it back. The transmission will fail anyway before the next service is due. They all do. 3 / 4 clutch pack goes up in smoke. More corners cut, more money for the consumer to spend ...

 

The way I do fluid changes now is, I'll pull a cooler line and let the pump suck all the fluid out of the pan. I shut it down at the first hint of bubbles - doesn't hurt anything. Now you can wrestle with the poorly engineered pan location without taking an ATF bath.

 

I know the feeling - you give the engineers the benefit of the doubt: "They must have left clearance here - would be STUPID not to!" Then you find, they left you NONE. A day in the life of 21st Century auto repair! 

Edited June 22, 2021 by Jsdirt

[Tickerguy]

Oh there's a drain plug in mine.  It was non-removable.  Once I got the pan off and could put REAL torque (and HEAT on it) I realized they likely loctite RED'd it in the hole.  Ain't coming out, no way, no how, and was obviously done at the factory to force you to drop the pan, which is ok generally in that you want to change the filter anyway.

 

Kid just had the 4L60E blowup happen to her; almost 200k miles, smoked the 3/4 clutch pack.  Limped it to a place in second.  Nice surprise when you're on the road and it blows up in your face; not much you can do about it though as I'd driven it recently and there was no hint of misbehavior first.  Mine is still behaving ok but eventually I'm expecting to have to drop and replace it.

[Tickerguy]

Observation: These fuel pumps ("Cup style") all appear to return fuel to the cup and not the tank "at large."

 

IMHO this is a generally-bad design because the fuel being returned (bypassed by the regulator) is going to be quite hot.  In fact, in adverse conditions (e.g. very hot day outside, engine is working, etc.) that fuel could be VERY hot.  Putting it back in the cup means it does not have the mass of the remaining fuel to dissipate the heat into, nor can it dissipate it through the tank wall; it will instead be immediately recirculated to the engine by the pump a second and subsequent time.

 

I can see where a return back to the tank generally could be trouble too in that the fill rate into the cup might be insufficient and if it is then you'd get starvation.  But without an external fuel cooler, which I know this truck does not have (my VW Jetta TDI does under the floor in the return line) this looks like it could be begging for serious trouble.  Gasoline has an initial boiling point (at atmospheric pressure) around 95F where the lighter fractions boil off; I've seen 150F IATs in the mountains with this engine on Torque which is MUCH higher than I see around here even under heavy operating conditions, and obviously the fuel rail is right near the exhaust manifolds which are plenty hot when the engine is running. 

 

Altitude would potentiate this materially by depressing the boiling point; at 6,000' the boiling temperature is lower by about 6% so now we're right around 90F for that initial fractionalization.

 

I have to wonder if the shutdowns are actually potentiated by fuel boil in the pump cup, which of course then winds up attempting to pump vapor and the rail pressure collapses even though the pump has power and is running.  The shutdown resets the condition since the boiled fraction would either wind up in the charcoal cannister or condense and then the fuel level in the cup would be made up by cooler fuel in the tank itself, which is liquid.  Key off/on, in short, would be enough time for the vapor in the pump to condense back to liquid and pumping is restored.  This also explains why when the tank is VERY full it doesn't happen; the cup does not go all the way to the top, so if the tank is full enough you get exchange with the fuel in the tank at-large.

 

If that's the case the only actual fix is an external fuel cooler since the cup design will always recycle the returned fuel and no new, cooler fuel will be admitted until the level drops, so you will always be able to provoke this under the right set of circumstances (altitude and heat.)  The other fix I can come up with would be to drill a few holes at about 1/4 of the way up the fuel cup; in this fashion if the tank is more than 1/4 full or thereabouts you will get circulation of the extremely hot fuel back into the tank at-large.  It won't prevent you from getting hosed if the fuel level is low, but otherwise it should.

 

Direct-draw, non-return pumps will not run into this as there's no circulation back to the tank of potentially heated fuel from the rail.

Edited June 23, 2021 by Tickerguy

[Tickerguy]

So the new pump is here and guess what -- the fine folks who make these things came to the same conclusion I did above some time in the last however many years.

 

Anyone with a vehicle in this age range that has a return line and the original fuel pump, or one of unknown vintage, if you have this sort of problem (high-altitude, high-temperature issues with fuel delivery) I'll bet its related.

 

The new pump I received today (Delphi) has *two* chambers in the cup.  The first admits fuel as the other one did with a silicone flapper at the bottom. The return also dumps into there.  The motor, however, is not in that chamber -- there is just a suction line all the way down at the bottom of that chamber in the cup.

 

The *second* chamber pulls the fuel in that chamber through the suction line into the pump/motor chamber and ejects it out toward the rail.  I presume as there is no visible connection for cooling flow there is a cooling flow bleed somewhere on the pump itself that bleeds a small amount of the ejected fuel into that chamber of the cup since I cannot imagine that chamber remains "dry" in operation.

 

This accomplishes several things that materially improve the pump and, I bet, prevent the problem.

 

1. The pump *itself* no longer contributes to the heat level in the cup, since the bleed is now a continually-exchanged flow of fuel for cooling purposes rather than the motor simply being submerged in the cup and relying on engine draw for turnover.  It also means the entire motor is submerged, which was not the case in the old design as the fuel level got lower in the tank   The continual bleed means that heat is effectively carried to and dissipated in the entire load of fuel in the tank, instead of just a small part of it.  That's a major improvement.

 

2. The suction side from the first part of the cup is obviously a positive-displacement stage.  It has to be, otherwise the pump would never work at all (it would fail to prime) if the fuel level was lower than the hump in the hose, which it nearly-always is unless the tank is completely full.  This in turn means that *IF* vapor gets into that hose the vapor will be immediately pulled through and expelled, likely preferentially through the cooling bleed at the motor since it is of much lower density than liquid fuel, and thus the collapse of fuel rail pressure is averted.  The second stage (that pumps the fuel to the rail) cannot be positive displacement because if the pressure regulator at the engine were to fail closed the pump would dead-head, go locked-rotor and destroy itself almost immediately.  Thus this has to be a two-stage design -- the previous one may well not be (I may well rip it completely apart to find out.)

 

When I get the chance I'm going to see what's in my daughter's van -- I'll lay odds its the OEM fuel pump given what I've found here.

 

I think we can call this one resolved.

[Jsdirt]

Some great info and observations there. Makes sense. Plus a cooler motor = longer life to boot.

 

I remember when fuel injection was first starting to become widespread in the mid 80's, there was always that rumor going around to, "Never let your tank go below a 1/4, or the pump will burn up." The pumps in the 80's were overbuilt in most higher end vehicles, so I think that applies more to late 80's and 90's vehicles, especially late 90's.

 

I still have a '86 Grand Marquis, 5.0 multiport, that's still running on the OE fuel pump! 35 years, and almost 280,000 miles. They sure don't build stuff like that anymore, that's for sure! What's even more impressive is I had forgotten to change the fuel filter for the first 11 years of owning it! It was a Motorcraft filter, too, so it could have very well been original! That would have made it 28 years old at the time! When I cut the filter open, it looked like MUD inside the pleats! Still flowed fuel - never had any indications it was plugged up, but it was very difficult to blow through. This normally kills modern pumps (in last 20 years) real fast. Nope! This one is still running with zero signs of slowing down yet! I sure wish automakers still cared about customers enough to build something this good today. I'd be the first one in line to buy one.

[VanExpress]

A little late to the discussion, but glad I stumbled on this thread regarding in tank fuel pumps in GM products.  It seems that Tickerguy has done an in depth analysis of what seems to be parallels issues that I am having with my 2004 Chev., 1500 Express van with 5.3L vortec engine.  The van has about 185, 000 miles on it, and save for the normal wear and tear replacement things and a transmission o'haul about 5K miles ago has been a good running machine.  However, on a recent round trip from Austin, TX to Albuquerque, NM via southern Colorado and TX panhandle, and back, without warning engine begin to stumble and act if running out of gas, but with about 1/2 tank of gas, and finally just stopped running.

This occurred in Post, TX on a Sunday evening....talk about a bad places to have trouble...and with only a Zone about to close.  Based on past experiences as past owners of several late '90s Jimmys and Blazers, I immediately suspected the fuel pump, but had no way to verify as Zone didn't have a fuel pressure tester and even if they had one, getting to the test port in the van is impossible without dismantling part of the lower dash in order to remove the interior engine shroud. 

Anyway, after waiting a bit, and figuring how and where I was going to get towed and what would be involved in the fix,  I attempted to start the van and ta da, it started right up, idled OK and we eased around a bit and all seemed to be fine, so headed on down to Austin and van continued to run without a hiccup.

So, once at home base with tools and a fuel pressure tester, dismantled the dash and remove engine cover, attached tester to port and got these readings:

    Ignition on, no start - Pressure goes to 63 PSI and in few seconds drops to 53 PSI

    Ignition off - Pressure holds at 53 PSI and after about 15 minutes drops to 50 PSI

   Ignition on, start engine - Pressures goes to 60 PSI and varies between about 57 - 62 PSI, depending on throttle.

 

At the same time, I wanted to make some checks of the fuel pressure regulator and I searched hi and lo on each fuel rail in the area as is shown in OEM Helm manuals for this model Express van, and NO pressure regulator.  So where is it?

 

After much searching on line, I found some guy on U Tube that had the same experience with a Suburban and had found that it is now located in the fuel pumpin the gas tank.  I have since found some critic notes that in about '03, for certain models of GM (which apparently includes my van) they relocated the fuel regulator to the fuel pump assembly....great, now we have at least 3 functions buried in the damn fuel tank that can go wrong....fuel pump, pressure regulator, and stupid fuel tank pressure sensor, all requiring dropping of the fuel tank to fix. Geeezz. 

 

In the video on U tube of the guy I referred to earlier, he showed installing a fuel regulator module on to the pump assembly, that is identical to the one that used to be mounted on the driver side fuel rail of the engine. In his installation sequence he did not connect anything to the vacuum port on the regulator.....so how does this work without vacuum?

 

Anyway, after several weeks of tooling around town and several hundred miles, van still running fine with no hicups. However am a bit leery of taking it on an extended road trip and having the fuel pump and associated parts go out in the middle of no where, and so am going to replace the fuel pump....after I chop a hole in the floor of the van over the fuel tank and fuel pump....no more dropping the tank for me!

And so am about to order a fuel pump from Rock xxxx and find that the fuel pump for my van doesn't have the regulator in, but regulator sold separately. So I'm still puzzled about the relocation of the regulator in to the pump, and how it works and what the pump part number is for the pump that has the integral regulator???? Someone in the thread, mentioned a Delphi pump with an improved return fuel cups and such.  Would welcome anyone with ideas, suggestions, etc. addressing  pump part number with regulator, brand (Delphi or AC Delco}, and how it works and if it will fix my problems.  So tnx in advance for any and all info.  

 

 

[Jsdirt]

Your pressures look good there. You could have a dead segment in the armature, or bearings that are beginning to fail causing intermittent low pressure. You'll want to check out ALL wiring to the pump first before replacing anything.

 

Either way, at the miles you're at, especially if that pump is OE original, I'd scrap it for a new one. Regulator is part of the pump assembly. I don't know where you're looking, but none of the pumps listed here mention a separate regulator: https://www.rockauto.com/en/catalog/chevrolet,2004,express+1500,5.3l+v8,1423954,fuel+&+air,fuel+pump+&+housing+assembly,10147

 

Always good practice to replace the ENTIRE assembly, not just the pump, since your fuel gauge relies on good contacts inside this unit as well.

 

Be glad you've got a 800 series truck instead of the newer 900 series and up. Those have no return line, and rely on a fuel pump module, conveniently located above the spare tire where all the road salt gets tossed from all 4 wheels. So when your spare winch rusts out and you have to cut the hanger & cable off, then spend $200+ on a new module, you'll find it DOESN'T WORK without J-box programming (GM gets more money selling you the programming info), costing you even more money and downtime!

 

Better hang on to that '04!

Edited June 1, 2022 by Jsdirt

[Tickerguy]

17 hours ago, VanExpress said:

A little late to the discussion, but glad I stumbled on this thread regarding in tank fuel pumps in GM products.  It seems that Tickerguy has done an in depth analysis of what seems to be parallels issues that I am having with my 2004 Chev., 1500 Express van with 5.3L vortec engine.  The van has about 185, 000 miles on it, and save for the normal wear and tear replacement things and a transmission o'haul about 5K miles ago has been a good running machine.  However, on a recent round trip from Austin, TX to Albuquerque, NM via southern Colorado and TX panhandle, and back, without warning engine begin to stumble and act if running out of gas, but with about 1/2 tank of gas, and finally just stopped running.

This occurred in Post, TX on a Sunday evening....talk about a bad places to have trouble...and with only a Zone about to close.  Based on past experiences as past owners of several late '90s Jimmys and Blazers, I immediately suspected the fuel pump, but had no way to verify as Zone didn't have a fuel pressure tester and even if they had one, getting to the test port in the van is impossible without dismantling part of the lower dash in order to remove the interior engine shroud. 

Anyway, after waiting a bit, and figuring how and where I was going to get towed and what would be involved in the fix,  I attempted to start the van and ta da, it started right up, idled OK and we eased around a bit and all seemed to be fine, so headed on down to Austin and van continued to run without a hiccup.

 

Welcome to the Hell my daughter had with her '03 Express.  Same deal.  It's especially great when it happens in the middle of traffic.  Oddly enough it has only happened to both her and I at altitude; at sea level, never.

 

Both her truck and mine are sporting new fuel pumps at this point and it has not yet recurred.  I dropped the tank to get to both of them; it's especially fun on the Express as the idgits at GM used captive nuts on a crap bracket that inevitably strips when you try to take them out, so you get to drill the bolt and then buy new captives (which are, fortunately, readily available and cheap.)

 

Oddly enough while Delphi redesigned the pump that goes in my '02 Suburban and should completely remedy the root of the issue the pump for the '03 Express was exactly the same was what came out of there.  It was clearly original and the fittings are different between the two so there's no possibility of using the Suburban's in the Express.  Oh, and for good measure on the van the tank design is such that you can easily wind up with a no-fuel situation with close to a quarter tank if you travel up an incline (you'll see once you drop it why; there's basically no sump which is Effing Stupid.)  That's not a factor on the 'Burban.

 

There IS a fuel pressure regulator at the rail; on some it has a vacuum connection (does on mine) and on others it does not.  Your pressures look good but so did mine -- right up until it died, of course.  I spent a LOT of time chasing potential electrical (e.g. swapping the fuel pump relay, etc) with no joy, but as far as I can tell it is actually fixed now (and I've been using it "in anger" since, including towing where the load is a LOT higher.)