1999 GMC Sierra Engine Not Running Correctly

1999 GMC SIERRA

165,000 MILES • V8 • 4WD • AUTOMATIC

FRANKSTL

MEMBER
5 POSTS
FOLLOW

My truck is a half ton with the Z71 off road package, it has the 5.3L engine and 4L60E Transmission, I've put the last 83k miles on the truck with few problems and my transmission lost reverse, second, and fourth gears, no problem got the tranny rebuilt with a new sunshell and whatever else the guy thought it needed, or so I thought, he gave me another tranny off the shelf that supposedly had been rebuilt but 200 miles after I get it back it starts making noise in first and reverse and he says its a planetary bearing, a fluke he says and he will make it right.

That being said I'm nursing it out to him because it seems fine in every other gear but those two, so half way there my truck dies out like its running out of gas or something, I put two five gallon cans worth of premium fuel and still it will only run sporadically at best and to keep it running you have to keep the gas pedal at a certain spot maintaining around 2k rmp to keep it moving, otherwise it starts acting like its sucking only air and going to die out and I'm wondering if something being wrong with the trans would affect how the enging runs,and I am wondering first off did this guy do something to my truck or is this a coincidence because I'm sure he has the computer and software to mess with settings which I don't and this is the first time I've used him to do auto work for me? Secondly since I know its getting some gas I am assuming the fuel pump is trying to work, so I am next putting a new fuel filter on it and then going to check the fuel pressure to see if its good, and if it isn't ill assume it must be the pump, but if it is good then what next?

Thanks for any help, info, and/or advice with this problem.

Nov 7, 2010 at 1:31 PM

HMAC300

CERTIFIED EXPERT
48,601 POSTS

trans problems can make it think like it's running bad but the engine should runok. Those trucks of that year ahd a fuel pump wiring harness problem that made it run sometimes then people would replace the fuel pump and it would go bad or so they thought. Itturned out to be the harness. Delco or Delphi makes a fuel pump that is supplied with the harness that has to be put in. However ifyou say it sounds like it's sucking air then check the air duct going to the throttle body for holes. that can cause sucking sounds as well as effecting the way the truck runs.

Nov 7, 2010 at 6:09 PM

FRANKSTL

MEMBER
5 POSTS

Didn't mean it sounded like it was sucking air like that, just that it seemed like it was only getting the air and not fuel or if it was getting fuel it was sporadically getting it, or else its not getting consistant spark to the cylinders, and at this point the transmission mechanic said that the crank trigger sensor on my truck was located on the block near the starter in such location that the starter would have to be removed in order to replace that sensor, and this I'm not sure of as I was told by someone else its somewhere near the back of the block by the distributor?

Thanks for your reply and any more help and info.

Nov 7, 2010 at 8:07 PM

HMAC300

CERTIFIED EXPERT
48,601 POSTS

the crank sensor is in the engine block and you may have to remove the starter, and the cam sensor is in what you call the distributor. but check the fuel pressuree as well if it's under 55p.s.i. that may be your problem. it's suppposed to be 55-62

Nov 7, 2010 at 8:38 PM

FRANKSTL

MEMBER
5 POSTS

Ok, I will change the fuel filter right off once I get it back from the trans shop and then will check the fuel pressure, if its below 55 then I will assume its pump and change it out and go from there, and also you mentioned a problem with the harness to fuel pump, what kind of problem is it with harness? So that I may check that also before going to the trouble of changing the pump out for a possible harness issue.

Thanks much once again.

Nov 7, 2010 at 8:48 PM

HMAC300

CERTIFIED EXPERT
48,601 POSTS

it is onot all harnesses that have the problem. the harnesscorrodes and doesn't make good contacta nd makesthe fuel pump act like it's bad but itreally isn't. the newfuel pump may come with the newharness asthere may be a connection difference. that is one of the things that was corrected. Alot of the fuel pumps come with the harness already if it's the wrong connection. that's why i said i know Delphi comes with it and air something but i can't remember what the rest of name was lol......

Nov 8, 2010 at 12:05 PM

FRANKSTL

MEMBER
5 POSTS

Got it to my friends barn today and checked fuel pressure, was 19 lol, anyhow then changed the fuel filter and checked it again and it was around 45-47, it ran fine and dandy for about 10-15 minutes idling and I moved it around and it was smooth running as before this problem occurred.

Then after it was running about 10-15 minutes it died/stalled out, checked pressure again and it was back down to 19. I was told by someone else with a gm truck that his was doing the same thing and that his problem was a temp sensor near the front of engine which once his truck was warmed up the sensor was telling the computer it was still cold.

Just hate having to spend the 300 on the fuel pump and find I'm still having the same issue, but if that's what I need to get back to working then so be it because I've been without my work truck going on three weeks and spent 1000 on the trans rebuild which seems to be doing great when the darn engine is working right. Just haven't received any trouble codes for any sensor/s other than saying my truck was burning lean on the left and right banks which another guy with same truck who's a mechanic at the dealer who tells me a tune up with new plugs will likely fix this code as it was all it took on his truck.

Thanks

Nov 8, 2010 at 11:41 PM

HMAC300

CERTIFIED EXPERT
48,601 POSTS

MINIMUM fuel pressure is 55p.s.i. until you fix this it will act up. It is not your coolant sensor causing this it's the fuel pump. the brand name of the fuel pump with the harness besides Delphi is Airtex. if this has a pick boc, pull that off to get to teh pump. so much easier. 8 bolts hold it on and disconnect the harness at the back driver's side. 4 guys to lift it back and just put it back far enough to reach thepump and harness, everything is out in the open.....

Nov 9, 2010 at 11:22 AM

FRANKSTL

MEMBER
5 POSTS

Thanks everyone for the help, I dropped the tank yesterday, only thing easier would have been if off the ground on a lift, but anyhow took only 45 minutes down and same back up in place, lol took more time going to get the pump, I decided to go with the delco since my friend got me the employee discount at the dealer and it was only 30 more than an airtex. Figure the original factory pump lasted 11 years and 165k so wth cant be all bad, and also as last note my pump is putting out 50 psi steady at idle and most pumps I looked up were rated at 45-55, and will work fine down to about 42psi as my truck was running fine on that before the original pump failed.

Thanks again and good luck to all with your mechanical/electrical woes.

Nov 11, 2010 at 1:08 AM