Diesel Place banner

1 - 17 of 17 Posts

·
Registered
Joined
·
39 Posts
Discussion Starter #1 (Edited)
Almost had my first experience getting a GM towed. Randomly about a mile from my house, the truck started sputtering, the more throttle I applied, the more it stumbled and gave me a bit of a popping sound almost like a back-fire from the intake. I immediately plugged in my cheap scanner. No codes thrown, tried to pay attention to the live data. Only thing I could really pick up on was that it behaved the best under 20% tps which was about 1300-1500 rpm trying to climb the hill to my house. Never stalled on me, just no power and bad popping with too much throttle, ran very rough all around. After finally making it home safe.... unplugged the MAF, made a short term difference but I was able to recreate the problem again shortly afterwards. Also noticed it smelled rich when I was sitting there trying to build power to make it up the hill. Definitely smelled fuel.

Definitely baffled. No codes, clearly must be some type of sensor or perhaps fuel pump just gave up...... I'll check fuel pressure tomorrow AM. Only thing that's suspect to me is that I just replaced the battery. Put a Yellow-top Optima in back in Nov..... was fine until a few days ago and then I've had to jump it frequently. Just put a new one in and things seemed fine. Wondering if the dramatic voltage drops during trying to start with little to no juice could have taken it's toll.

Truck is 2001 3/4 ton 8.1L Suburban with 170k mi. Other than the crank position sensor which we replaced a while back I've never had any issues with this truck. Any help would be greatly appreciated. Just moved to OR and any good local shop suggestions around Portland would also be greatly appreciated.

THANKS!
 

·
Registered
Joined
·
1,016 Posts
Engines just act like that when a convertor is clogged up tight. Try removing the O2 sensors and taking a test drive to see if that makes a big difference. If so have the convertor(s) replaced.

Vernon
 

·
Registered
Joined
·
39 Posts
Discussion Starter #3
Thanks for the suggestion. I have had a lot of exhaust noises recently coming from up under the hood, whistles and such so this could make sense. Been trying to find time to go through and replace a bunch of gaskets.

Assuming you mean pre-cat sensors correct?
 

·
Registered
Joined
·
39 Posts
Discussion Starter #4
Well, did a quick fuel pressure check and looks like that may be where my issue is. Main thing that's suspect is the needle is jumping around a lot. I'm also only seeing about 43-48psi. WHen I pull the vacuum line off the regulator it does not seem to jump all that much more and when it does it's not consistent..... sometimes a little over 50, sometimes no jump at all.

Just recently did a regulator and filter, dialed it in to I think around 68psi? or maybe 71psi? Can't remember the suggested pressure, going to do a quick search. I guess I'll try the filter but I'm suspect that the pump may have started to crap out as the filter only has about 4-5k mi on it. That being said, they were hard towing miles so lots of fuel through there.

Vernon I also read one of your posts on the impact of exhaust leaks on the tune. My guess is that while that's not the primary source of my current issue.... it's likely a major factor in why I seem to be down on power. Going to chase that as soon as I get this fuel issue chased down.
 

·
Registered
Joined
·
1,016 Posts
It's probably the pump. I almost said to check that also but pumps usually fail all or nothing, rarely do they go weak like that first. And the popping through the intake is usually clogged exhaust. But from what you're saying about the pressure it's the pump. Clean and tighten the pump grounds down on the frame/cab mounting ear under the drivers foot well while your doing the job.

Vernon
 

·
Registered
Joined
·
39 Posts
Discussion Starter #6
Yeah, I agree, I always thought the pump would work one day and then die the next. I have heard though up the the NE of the power to the pump degrading as the wiring corrodes, you get voltage drop, and then loss of pressure and power. This is a CA truck so not likely that could be the issue.

What am I aiming for for pressure again? Could not find with my search. I think it's 68/69 target with the vaccum line off correct?

Thx!

Eric
 

·
Registered
Joined
·
113 Posts
These are also bad about burning up the fuel wiring harness connector at the pump. when you buy a new gm fuel pump it should come with a new connector
 

·
Registered
Joined
·
39 Posts
Discussion Starter #8
These are also bad about burning up the fuel wiring harness connector at the pump. when you buy a new gm fuel pump it should come with a new connector
Yeah, that's what I've heard. That could certainly also be a factor. My buddy has an old beater shop truck (old TBI set-up that needs less pressure) that he just uses for junk-yard runs. His pump started to go and he did not want to invest the time or money to replace it so he put in an extra in-line pump he had laying around and that seemed to work just fine. Would be nice if that was an option on this truck as you'd have a better quality pump that's more easily serviced, etc. but I think plumbing it and wiring it would be more of a pain than just sucking it up and dropping the tank..... not sure if it would be a great idea to suck fuel through a dead pump.
 

·
Registered
Joined
·
1,016 Posts
65 is spec, though a few pounds higher tends to help performance by reducing knock retard.

Vernon
 

·
Registered
Joined
·
39 Posts
Discussion Starter #10
Thanks Vernon. I think that's what I remembered but could not find the thread. When I replaced my filter and regulator just a few months ago it shot to 72+ right away and I dialed it back down to 68ish with the vacuum line off. Now it's jumping around +/- 55 with the vacuum line off. Just picked up a filter and will try that even though it's a long shot, otherwise it's time to have some fun dropping that tank. Just my luck I'm pretty sure it's almost totally full.

Does this truck have a hot lead you can tap into to run the pump and pump out the tank? I know my stock ECM on my Camaro had one and that made the process pretty easy. The fact that the tank was half the size helped too.....
 

·
Registered
Joined
·
1,016 Posts
I've never seen nor heard of one on this truck. I think if you take out the pump relay and run a jumper on the motor circut of the socket that would work.

Vernon
 

·
Registered
Joined
·
39 Posts
Discussion Starter #13
Good call, I should have thought of that when I was swapping the relay last night just to check to ensure it was not somehow the relay that was acting up. Figured that was an easy check.

Now I just need to find a good "pump-out" location to use to empty the tank. I'll have to check and see how much flex I have in the lines where they hook into the fuel rail to see if I could swing them out over the side of the engine bay. Otherwise I was thinking of pulling the fuel filter and plumbing a hose from the tank end of the supply line to a 5 ga jug and giving that a shot. If I'm lucky, I'll have enough hose to reach my wife's car's tank...

Sounds like everyone I've spoken with suggests sticking with the Delco on the fuel filter. My buddy who has a shop back east was telling me he stopped selling the aftermarket "lifetime warranty" units for GMs as it was killing him on labor. He had a high return rate and because of the warranty had to do the labor for free. Anyone have any other suggestions or just stick with the same one that lasted me 170k mi so far. I'd be happy with another 170k mi ;-)
 

·
Registered
Joined
·
631 Posts
when i replaced mine i used delphi. i've gotten 30,000 miles out of it with no problems yet.
 

·
Registered
Joined
·
39 Posts
Discussion Starter #15
Anybody know what jumpers to connect to activate the pump? Looks like 87 is constant 12v, 86 is switched 12v with the ignition. I'm assuming I'd use 87 to connect over and power either 30 or 85........ Not sure which one is ground and which one powers the pump. Any guidance would be greatly appreciated. Been a while since I messed with relays.
 

·
Registered
Joined
·
39 Posts
Discussion Starter #16
Figured it out. 87 to 30 powers the pump. Thing seemed like it was barely alive. Took forever to get 20 gallons out. Really nice having a completely empty tank to remove. The thing weighs practically nothing. Hardest part is dis-connecting those effing fuel lines. The necks of the plastic fittings have plastic bracing that interferes with both of my fuel line dis-connect tools. Finally ended up taking off a pretty decent amount of material off of my fuel line dis-connect tool so I could have the clearance to actually dis-connect the things. now if I can just get it all back together....
 

·
Registered
Joined
·
1 Posts
Thanks Vernon. I think that's what I remembered but could not find the thread. When I replaced my filter and regulator just a few months ago it shot to 72+ right away and I dialed it back down to 68ish with the vacuum line off. Now it's jumping around +/- 55 with the vacuum line off. Just picked up a filter and will try that even though it's a long shot, otherwise it's time to have some fun dropping that tank. Just my luck I'm pretty sure it's almost totally full.

Does this truck have a hot lead you can tap into to run the pump and pump out the tank? I know my stock ECM on my Camaro had one and that made the process pretty easy. The fact that the tank was half the size helped too.....
My regulator is different on this c5500 dumptruck the vacuum line is hard to reach with wires tapef and fastened tight right in front of it i cant get the vac line off im pulling hard kinda afraid of messing vac line or my hand coming back & jerking the wires out or a connector is vacumm line supposed to just pull off
 
1 - 17 of 17 Posts
Top