Fuel delivery?

[Cartier16]

Hello all I have a 2003 Yukon Denali 6.0 with 170k miles. Purchased about 6 months ago I’ve currently replaced cv axels, radiator, and trans cooler lines. Truck has been running perfectly fine and the night of New Years it died on me. While driving my engine died I pulled over and kept turning the engine but no start. I put about a gallon and half of gas in the tank it started right back up for about 10 seconds then died again. Wouldn’t start after had the vehicle towed sat over night. Turned it over about 20 minutes ago and it idled fine for about 60 seconds then began to shutter like it was going to die again. I’ve ran sea foam through the system before and have done all the maintenance myself replaced the fuel filter a few months back but have no check engine light. Any similar experiences? I plan on tested the pressure in the system but what else could cause this can it be evap related the sending unit in the fuel pump bounces around sometimes I originally thought my pump died when it first stalled out but obviously not. Any advice or help would be appreciated thanks

 

[OR VietVet]

Sounds like a fuel pump to me. Make double sure the inside of tank is clean and IMO, I always replace the fuel filter and relay when I do a pump. Get a tester on the line and watch as it dies.

 

[Fless]

Probably not evap related, but if it's flooding the purge valve on the engine could be staying open with the key off. Flooding is less likely than fuel starvation with the symptoms but we'd need some more info to be pointed in that direction.

Is the fuel gauge accurate? When it dies, have you filled it up and how much fuel does it take? (Caution, you'll want to have the tank low on fuel when/if you get to dropping the tank for the fuel pump change, otherwise the fuel will need to be siphoned. But you're a ways from that.)

First action should be to test the fuel pressure KOEO (key on, engine off) to see how high it gets and if it bleeds off quickly after the pump stops running. Next is to monitor the fuel pressure when the issue happens, as @OR VietVet suggested.

And, next time it won't start, bang on the underside of that fuel tank to shock the pump, maybe while someone cranks it over.

When it won't start, have you tried clear flood mode by flooring the accelerator to turn off the injectors?

The fuel pressure regulator is also suspect. Lots of possibilities to consider, especially without any test results.

 

[Cartier16]

Sounds like a fuel pump to me. Make double sure the inside of tank is clean and IMO, I always replace the fuel filter and relay when I do a pump. Get a tester on the line and watch as it dies.

To my knowledge a fuel pump isn’t intermittent. It’s either going to work or not and when it stops it’s going to cut the engine as soon as the gas stops flowing not stop then start working again 12 hours later but I could be wrong. Just don’t reallly have the time drop my tank and don’t have the money to pay someone else to tow it and do it thanks for the reply though

 

[Cartier16]

Probably not evap related, but if it's flooding the purge valve on the engine could be staying open with the key off. Flooding is less likely than fuel starvation with the symptoms but we'd need some more info to be pointed in that direction.

Is the fuel gauge accurate? When it dies, have you filled it up and how much fuel does it take? (Caution, you'll want to have the tank low on fuel when/if you get to dropping the tank for the fuel pump change, otherwise the fuel will need to be siphoned. But you're a ways from that.)

First action should be to test the fuel pressure KOEO (key on, engine off) to see how high it gets and if it bleeds off quickly after the pump stops running. Next is to monitor the fuel pressure when the issue happens, as @OR VietVet suggested.

And, next time it won't start, bang on the underside of that fuel tank to shock the pump, maybe while someone cranks it over.

When it won't start, have you tried clear flood mode by flooring the accelerator to turn off the injectors?

The fuel pressure regulator is also suspect. Lots of possibilities to consider, especially without any test results.

I was questing the regulator or the pressure sensor. How can you test those though. I’m going to pick up the tools to test my line pressure here soon. Thanks for the reply

 

[Cartier16]

I was questing the regulator or the pressure sensor. How can you test those though. I’m going to pick up the tools to test my line pressure here soon. Thanks for the reply

And the gauge is accurate most of the times it’s usually just upon initial start and or after I fill up the tank it’ll register empty then go to full tank and then read accurate. I’ve ran it down to where it said about 1/8th tank and then proceeded to put about 22 gallons in it so I’d say it’s someone accurate

 

[Fless]

Well, mine was intermittent. Got stuck in Laramie, WY a few years back pulling a camper and it wouldn't start. No fuel pressure. After considering a few things, I banged on the tank and it fired right up. I didn't turn it off until I got home later that day and changed the pump a week later. So an electrical connection can be intermittent, or the motor gets in a funky spot and might need a little attitude adjustment.

There is no fuel pressure sensor; everything that has to do with that is in the pump module (the fuel pump). (There is a fuel *tank* pressure sensor in the pump module but that's only for onboard evap tests.)

For the pressure regulator (FPR) the most important test is the fuel pressure at the rail. If that checks out it's probably okay. But with the engine off, pull the vacuum line from the FPR and watch the FPR connection there to see if any fuel is getting out into the vacuum line -- give it two or three minutes. Also check the vacuum line there for fuel contamination.

 

[OR VietVet]

So many things, mechanical or electrical, can be good one minute and bad the next and then surprise us and work again. If you feel the fuel pump can't be intermittent, all good with me. That is why the testing process is needed. @Fless suggested the tap the fuel tank method because it can happen. Same thing with a starter. But, it is your truck and you can approach the diagnostics any way you want to. Good luck.

 

[Cartier16]

I was tapping the tank yesterday when I was stranded and there wasn’t any luck which is why I was surprised it started today

 

[OR VietVet]

I was tapping the tank yesterday when I was stranded and there wasn’t any luck which is why I was surprised it started today

Any other methodology you want to share? When does not start, have you burped the shrader valve?

 

[Cartier16]

I’ve heard that the harness is notorious for faulting on these pumps is this true. I can replace the relay but I feel like that’s another thing that’s just spending more money. Mechanically you typical don’t get intermittent issues that’s usually electrical faults is there specific grounds that tie in with the pump assembly that I can check. I will defiantly be testing the fuel system pressure within the next few days and update my findings but I’m not in a position to buy parts that may not resolve my issue. Thanks

 

[Cartier16]

Any other methodology you want to share? When does not start, have you burped the shrader valve?

Shrader valve?

 

[Fless]

Shrader valve?

Yes, Schrader. It's on the passenger side fuel rail and it's where you'll be checking the fuel pressure. It's a larger-sized valve than a tire air valve, but similar construction.

IIRC the ground for the fuel pump is on the body mount (on the frame), underneath the driver's door hinge, behind the left front wheel. There should be two ground wire bolts there, probably 3 if 4x4. It would be a good idea to remove and clean those contacts. But I'm not sure if that's the one without some research.

If you can hear the fuel pump run when the issue is happening, you likely don't have an electrical problem. Of course, you could swap the fuel pump relay with another one in the underhood electrical center (fusebox).

 

[justchecking]

My experience: The next time you have the problem touch the fuel pump relay and see if it is HOT. If it is your fuel pump is stalled on a bad spot.

 

[Fless]

Here's a pic of the ground points; the attached file is the full page and can be zoomed in. The red rectangles are to the point I described previously. The green rectangles are where the fuel pump relay grounds.

 

[nonickatall]

I was tapping the tank yesterday when I was stranded and there wasn’t any luck which is why I was surprised it started today

I had shortly a problem with another car that starts always perfect and runs for 200 miles, but when you turn off the car, it won`t start again until you wait 1h. After that it starts again and runs another 200miles without any problem. No rough run, no weak acceleration, no excessive fuel consumption.

I have my own Garage and checked everything, i have a lot of spareparts for that specific car and exchanged spareplugs, distributor, even ECM, where i had one from another car. Nothing helped. I searched with test equipment, and parts to quick change and test, short before getting nuts.

At the end, it was a strange combination of fuel regulator, which was slighly out of tolerance, oxygen sensor and fuel filter, which was new, but why ever, not having enough fuel flow.

I don't say that is your Problem!!

What I want to say is, that are some common suspects like fuel pump, fuel Regulator, fuel filter for your problem. And like @flees correcly said, a fuel pump can work and when warm quit function and when the get cold, work again, that is possible. Or much other parts can cause this problem.

So how can you find your problem?
You can't find the problem in two ways.

One is trial and error. You can change the fuel pump, the fuel regulator and so on and hope that you find the problem. This can lead into drop of a lot of money in your car.

Second is logically check your system, but this needs test equipment, like a fuel pressure gauge to measure the fuel pressure. This gauges are cheap. And you see on a scale if the result of, your fuel pump, pumping enough fuel, which go through a fuel filter and fuel lines, which should not be damaged at any place and a fuel regulator which at the end regulates the fuel pressure for the injection valves, to make sure that that the calculated time for injection of the ECM is correct, like it should.

If the pressure expecially at the moment when you engine won't run is not correct, you know that the problem comes from the fuel system and you can start to look for the causer.

If the pressure is correct than you have another problem like a weak air mass sensor or whatever...

That way of search for your problem, is the correct way to get close to the solution.

Good luck

 

[Cartier16]

So I did some fuel pressure tests. Truck is still turning over and running. Initial pressure test was 50 psi then it fell down to about 35-40 psi. Primed it a few times initial was 50 fell to about 40. Started truck stayed steadily at 50 psi. I drove the truck a very short distance and have been starting it everyday no problems but haven’t taken it a long distance

 

[Cartier16]

A fuel pump? Or could there be something else vacuum leak or something causing pressure to fall

 

[Fless]

The initial test is to install the fuel pressure gauge on the Schrader valve, and turn the key on without starting the engine. Write down the initial reading, and cycle the key off and on a few times to get the highest pressure reading. All this without starting the engine. Test (from Haynes) is detailed below, along with further tests.

Typical engine running pressures tend to be in the low 40psi range, say 42-45 psi.

Specs for this test on a non-Flex Fuel V8 is a pressure reading of 55 to 62 psi. Flex Fuel spec is 48-54 psi.