99 5.7 4x4 Yukon Intermittent Run Issue

[OR VietVet]

Compression test should be done with all plugs removed when you do it. Did you do that? IMO, the results shown have a very high variance and indicate that the cranking time intervals and battery power may be suspect. I would do it again with all plugs out, battery charger on the battery and crank for approximately 4-5 seconds on each cylinder and then post results.

 

[Cousin_J]

Thanks for the input. I did remove all the plugs before testing, but the battery was/is on the weak side. I had to jump it after the test to get it running so your probably on to to something. Ill retest.

 

[OR VietVet]

Your test results always count on all things being equal.

 

[easymoney]

Thanks for the responses guys. 5.3 was a typo it is indeed a 5.7.

So I hooked up a pressure gauge this evening, and was getting around 52psi while at idle. At the point of cut out, the pressure dropped to 15psi and stayed there for the first 10 minutes regardless of if I was cranking or not. I turned on the ignition a few times over the next 30 mins and the pump was gradually building pressure, 15psi, 20psi, then 30 psi. I checked voltage at the fuel relay and have the same voltage as at the battery, I also jumped my fuel relay(pin 87 to 30) just to be sure it was not an issue with the new relay, but same psi. After about an hour I checked again and sure enough pressure was back up to 52psi and it started back up.

I have tried listening for the pump with key on engine off, but cant really hear it running. I just see the pressure gauge instantly jump from 0-50psi when key is turned on. Once primed, the PSI seems to hold well - it only dropped a few psi over the 10 mins I watched it with everything off.

I couldn't really see anything regarding the fuel pump, so I tired to reach up and feel around but nothing was obvious.
I believe the pump I installed 4yrs ago was plug and play, I don't recall splicing. The pump is a GMB aftermarket pump I got of amazon - great reviews but it was cheap. Maybe I get what I paid for.

As for coolant loss, yes it does go through some coolant. I have had the truck 8yrs and the lower intake gaskets have not been changed in that time, I am not sure about the history prior to that.

If PSI is supposed to be at 60-66psi then the fuel pump is probably the issue right? Just seems strange how it runs strong for a short period and then just cuts out.
Assuming I change the pump, any thoughts on the ACDelco MU1777, Delphi FG0089, or?

Sounds like fuel pump to me it needs quite a bit of pressure to stay going. Do you keep your gas tank full? I have read that the gas actually helps keep the pump cool. I wouldnt think a leaking injector would stop an engine like this. It would sputter around for a bit. Maybe the fuel pump heats up and not able to maintain pressure but from what you observed on the fuel pressure seems like it has to be the fuel pump. You didnt install the fuel filter backwards? They only flow good in one direction

 

[east302]

Thanks for the input. I did remove all the plugs before testing, but the battery was/is on the weak side. I had to jump it after the test to get it running so your probably on to to something. Ill retest.

Here is the compression test info from the GM manual.