Help me!

SSchmi5519

LLY Cult Leader
Oct 18, 2008
3,387
1
36
Arizona
Hmm might be onto something there. Could be collapsing a hose or something in the evap/vent system that resets or force/test opens at key-on.

If it isn't venting properly over time you'll draw vac in there and the fuel pump just cant overcome.
 

Yngdmax92

Member
Sep 26, 2013
878
15
18
We have the 2.2 liter gm engines in the mail trucks. Granted they are 93-94 series engines. Fuel pressure is spot on, leak down is fine. Couple of things. There is a fuel pressure regulator that will fail and you'll see a vacuum hose on it. Pull the vacuum hose off and see if you see gas or anything on the belllow side of the valve.
Also, we've also had a damn similar problem like yours and we always point fingers towards the ignition module and coils. They got hot, truck will lose power and stall.
 

ZeroGravity58

Active member
Mar 23, 2008
1,259
24
38
35
Maryland
The flex fuel motors dont have a regulator on the rail it's built in the fuel filter. I put a fuel pressure guage on and at key on it primed to 52 psi, while running it holds 56 psi when cold. I left the guage on and drove to work and as the pump get hot it starts losing fuel pressure then the pressure starts to fluctuate more and more. When cruising it would start bouncing between 54psi and 40 psi. Then as you start accelerating it will start dropping into the 30's. I don't notice the surging until the fuel pressure drops below 30psi then the motor falls on its face. The pressure continues to fluctuate and drop until the pump stops and the motors bogs and dies. When you turn the key off for a couple seconds then back on it will build enough pressure to start back up but it immediately starts fluctuating again and the cycle repeats. I ordered a new AC Delco pump, filter, gasket, and lock ring off of rockauto last. Should be here Thursday, in the mean time I'm DDing the Dmax. Thanks guys!
 

dndj

Boost!
Apr 13, 2019
247
21
18
Oregon
Thanks for posting up the root cause. It's so incredibly helpful when people come across these threads years later with a similar problem that they know what the eventual fix ended up being.
 

ZeroGravity58

Active member
Mar 23, 2008
1,259
24
38
35
Maryland
I haven't fixed it yet :roflmao: hopefully this works. Every sensor on the motor is new and I swore up and down it wasn't the fuel pump :eek:
 

ZeroGravity58

Active member
Mar 23, 2008
1,259
24
38
35
Maryland
See! What I tell ya lol. Good to hear!
You did! I pulled the bed on it today. It was easier to pull the bed then it is to change wiper blades on some cars! Now I just need the pump to come in. While I have the bed off what do you all use to paint/coat the frame???
 

zakkb787

<that’s not me...
Sep 29, 2014
2,322
46
48
Granite Falls NC
Yes, yes! :hug: also when I pulled the bed I expected to find the original 200k ac delco pump. Instead I found a airtex junk pump. No wonder I've been having so many problems :mad:
When my dads 99 5.3 pump went he cheated out and bought an airtex. Was weak from the start. Has to cycle the keys to build enough pressure to start. I know an old man with a 98 k1500 that’s got almost 400k. He got tired of taking the bed off so he cut a hole in the bed and made a plate to screw over it haha says he can change a pump in 10 minutes now.
 

2004LB7

Well-known member
Dec 15, 2010
3,456
244
63
Norcal
^^ my uncle did the same except put it on a hinge so it opens like a trap door. I think he has gone through 4 or 5 of them so far. Oem and aftermarket
 

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