*fixed* ANOTHER fuel pump/pressure question 03 Yukon Denali

[CBIII]

Sorry in advance.. I've chased everything I can at this point so here I am. bought the truck in January and no noticeable issues. A few weeks ago (after it had been running for ~2 hours from errands), I get a slight backfire, then it has no power and won't move. I shut it off and fired it back up and it was good for another ~10 minutes, then it did the same thing, ran like ass and could barely move. Whole vehicle shook, etc. Parked it and attempted to restart and no success. eventually had to tow it home, where it started after the tow. I let it be overnight, and it fired up again in the morning. I swapped fuel filter as a hail mary and strapped a fuel gauge to it. ~35psi. It made it about 45 minutes to a friend's place where it gave out entirely and would not start.
Took several seconds to start after cranking.
When it WOULD run, it would have 20-40psi, but it would vary.
When I would turn they key on, the gauge would make it to 30psi, a relay would click in the underhood panel and pressure would drop off.
Pressing the accelerator, pressure would fall off to ~20psi.
Pressure did not change when I removed the vac line from intake to regulator.
Replaced fuel filter, regulator, no change in pressure.
swapped a delphi pump assembly and had 55psi initially, but still took a while to start after cranking. Noticed down on power under WOT, checked fuel pressure and a steady 35psi at idle but same dropoff at 30psi when I turn the key on but do not crank. hits 30, relay clicks, pressure falls off. I replaced the filter again, no change. weak pressure at the rail.
Swapped in an AC Delco (2 weeks later) and still only 35psi at the rail but it seems to run much better. is there anything I'm missing? no CEL, but pulling codes previously showed each bank is lean. no misfires.

Is my gauge broken? could be be fuel pump wiring?

*EDIT* I failed to point out/didn't invest enough time into thinking about the fact that the regulator I swapped was a used one from my silverado I had gone to aftermarket rails (apparently factory regulator couldn't handle 210lb injecors?), so it was used, but worked fine a few years back.. I think? Bought a new AC Delco from Rock auto, tossed it on and away went the issue. I appreciate the guidance/support/sanity checks y'all gave.

 

[PNWYukon]

Vehicle specs?

If one of the fuel injectors is damaged and stuck open, this can cause a low fuel pressure in the rail. You will often notice this by misfire codes on a specific cylinder at the same time.

It sounds like you need a new OEM fuel pump. You say you swapped a Delphi? Was it new? A known good one?

 

[OR VietVet]

Welcome to the forum.

Is the engine flex fuel or gas? What engine? Possibilities are 4.8, 5.3 and 6.0. For the sake of moving on I am going to assume a 5.3L. All 03 Denali's do not have the same parts.

Agree with @PNWTahoe about a possible injector problem. How old are the ignition components? Pull the plugs and inspect. Post pics of them here. That is just to react to fuel pressure but that 35 psi is not enough.

Flex fuel: https://www.rockauto.com/en/moreinfo.php?pk=7056044&cc=1415551&pt=10147&jsn=893

Gas: https://www.rockauto.com/en/moreinfo.php?pk=1300750&cc=1415551&pt=10147&jsn=892

Fuel pressure regulator-flex fuel: https://www.rockauto.com/en/moreinfo.php?pk=344238&cc=1415551&pt=6124&jsn=904

Fuel pressure regulator-gas: https://www.rockauto.com/en/moreinfo.php?pk=1029862&cc=1415551&pt=6124&jsn=905

 

[CBIII]

wow. ok.
Would a stuck injector throw bank lean code on both banks?
Both the Delphi and AC Delco pumps were brand new. The AC Delco had the holographic stickers and gm oem ****.
I'm almost certain there was only 1 engine and fuel option for a 2003 yukon (non XL) denali.
I replaced the plugs myself a few months back but if my fuel pressure is that low and im running lean on both banks but not bad enough to throw a CEL so I think we can all agree as to what they'd look like. TR6 gapped to. uh. whatever recommended spec was on ls1tech. .065? idk

 

[OR VietVet]

The line/hose attachments are totally different on the flex fuel and gas option fuel pumps. You could not have used one in the wrong application.

 

[Fless]

@CBIII the 8th digit of your VIN is what... Z? T? or ? That's the engine code. Gap on these spark plugs should be 0.040". (40 thousandths)

Flex pump will have two fuel (hose) connections and the non-flex will have three. Can't really mix 'em up unless it's F-U-BAR. (that word is banned!)

 

[CBIII]

@CBIII the 8th digit of your VIN is what... Z? T? or ? That's the engine code. Gap on these spark plugs should be 0.040". (40 thousandths)

Flex pump will have two fuel (hose) connections and the non-flex will have three. Can't really mix 'em up unless it's F-U-BAR. (that word is banned!)

It's a 2003 yukon denali. non XL so it's a u code. They ONLY came with 6.0s and I'm almost certain no non-XLs were flex fuel in that year.

 

[OR VietVet]

After I mentioned, in post #3, the choices of engines, this is the first time you have mentioned the engine size. That is why that is best to post all rig info in the beginning or in your signature like we do. Takes the guesswork out of it. That is why I had said I was using the 5.3L option in my links.

 

[CBIII]

After I mentioned, in post #3, the choices of engines, this is the first time you have mentioned the engine size. That is why that is best to post all rig info in the beginning or in your signature like we do. Takes the guesswork out of it. That is why I had said I was using the 5.3L option in my links.

Dont take this the wrong way but if iI'm posting in a year/model-specific forum and you have to ask me what engine is in model that only has ONE engine option, I don't think you're going to be of any help to me anyhow.

I also didn't say if it was fuel-injected or carb'd. It's fuel injected.

 

[OR VietVet]

I said when I went to look up a part for you, that I supplied the link for, RA gave 3 engine options. That is why I said what I said. I know it is fuel injected but when I see 3 engine options, that is why I asked and I also explained that earlier. Just like the tv, if you don't want any of my help or thoughts, change the channel. All Good.

 

[hushko]

Welcome to the forum.

Is the engine flex fuel or gas? What engine? Possibilities are 4.8, 5.3 and 6.0. For the sake of moving on I am going to assume a 5.3L. All 03 Denali's do not have the same parts.

Agree with @PNWTahoe about a possible injector problem. How old are the ignition components? Pull the plugs and inspect. Post pics of them here. That is just to react to fuel pressure but that 35 psi is not enough.

Flex fuel: https://www.rockauto.com/en/moreinfo.php?pk=7056044&cc=1415551&pt=10147&jsn=893

Gas: https://www.rockauto.com/en/moreinfo.php?pk=1300750&cc=1415551&pt=10147&jsn=892

Fuel pressure regulator-flex fuel: https://www.rockauto.com/en/moreinfo.php?pk=344238&cc=1415551&pt=6124&jsn=904

Fuel pressure regulator-gas: https://www.rockauto.com/en/moreinfo.php?pk=1029862&cc=1415551&pt=6124&jsn=90

 

[Fless]

Thanks. This is a 5.3 gas, not flex. I removed all of the plugs and they were all clean, tan colored and the center electrodes not eroded. Gaps all at 0.040”. The plugs and wires have around 65-75k miles. I use Sea Foam in the gas occasionally, and in the crankcase frequently. The fuel pressure regulator is new BWD. It’s an ‘02 Silverado with a later revision ‘03 engine (no EGR valve). Fuel pressure ranges from 48-50 psi.

Is the above response in the right thread? Seems out of place.

 

[CBIII]

Is the above response in the right thread? Seems out of place.

I see him c/p vietvet's response with all the links on my end.

BTW. replaced with an ac delco regulator and all is well again.. As far as fuel issues are concerned. Now to figure out why it's only getting up to 185f

 

[Fless]

If the radiator's been replaced, the new radiator needs to have a restriction in the small hose that dumps into the surge tank. Having too much flow there can cause overheating or underheating. Obviously check thermostat and temp sensors first.

 

[CBIII]

If the radiator's been replaced, the new radiator needs to have a restriction in the small hose that dumps into the surge tank. Having too much flow there can cause overheating or underheating. Obviously check thermostat and temp sensors first.

Yeah, that's what I've been reading! Some folks put a valve in-line, others PLUG their WATERPUMP (tf?). I actually just replaced my radiator this week as the old one was cracked and finally blew out. The innards of the oil cooler portion came out when removing the fittings (my 03's lines/fittings were slightly diff than the ones on the 05 core support assembly I grabbed) so I wound up bypassing that also. I'd not been paying attention to temp previously, figured it was fine where it was until someone pointed out it was running too cool. It has a motorad thermostat (not sure why I didn't take a picture of it. ADD/brokenbrain) that I THOUGHT said 165, but got tunnel-vision and tossed it back in after deciding it was *probably* ok. The waterpump threads decided to give out when reinstalling said thermostat, but I found a longer bolt and it's tight.. enough. Not keen on yanking IT off at the moment. I'll prob be swapping to e-fans this weekend as well, so there's a lot going on around the cooling system now...

TL;DR: I absolutely agree with ya about the replaced radiator/restriction at this point, @Fless. I'm just not sure which method I'm going to use to resolve it, but I may just tweak fan settings in my HPT and see if I can force it to warm up more before replacing even more parts.

 

[OR VietVet]

You can use a small hose clamp and tighten to restrict flow on the hose and see if that takes care of the concern. If it does, you know you found the problem and can do a better fix, like a restriction in the hose itself instead of the clamp.

 

[CBIII]

You can use a small hose clamp and tighten to restrict flow on the hose and see if that takes care of the concern. If it does, you know you found the problem and can do a better fix, like a restriction in the hose itself instead of the clamp.

I didn't think about using a hose clamp.. Good idea! I was going to burp it again tonight after I got home as well. I did see a puddle under the truck when leaving this morning though, so not sure what that's about yet. I'm hoping it was just runoff from my sloppy radiator swap.