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Old March 8th, 2009, 04:49 PM   #1
camccardell
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Default 99 suburban stumble, acceleration problems

Ok, first of all, this problem is intermittent.

When the suburban gets warmed up and is going up a hill (usually this happens first to start the problems)
If I press the gas pedal down, the engine stumbles and the backfires. If I take my foot off the pedal the rear end bangs and then everything returns to normal.
I putted home and put it in park the other night and even in park it still stumbled and misfired.

I turned it off and started it back up and everythign was fine. Stomped the pedal and the rpms climbed just like they should have.

I put a fuel pressure gauge on it and it jumps to 60 psi when the pump is turned on, and drops to about 58 when the relay clicks off.

When I turn it over and start the motor the gauge reads about 50 psi give or take a few while driving it around.

I am really stumped.

I was thinking it was the fuel pump, but the dealership changed it 7 months ago when I bought it off the lot.

Running out of ideas.


Chris
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Old March 8th, 2009, 05:33 PM   #2
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Sounds to me like a mass air flow sensor. especially if its got a 7.4 (454)
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Old March 8th, 2009, 09:06 PM   #3
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it's got a 5.7

any way to check it, since it is intermittent and all?

Chris
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Old March 9th, 2009, 06:18 PM   #4
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try cleaning it with carb clean without the motor running, take it off if you have to, let it air dry, don't blow it off with air, may damage fine sensor wire! try that, if it helps, replace it! good luck! and also check the dist cap!
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Old March 9th, 2009, 09:07 PM   #5
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checked it all out and sprayed that special mass air cleaner on it.

Also cleaned up the throttle body, as well as replaced the plugs, wires, cap, and rotor.
Hurrah for the $250 tune up!

ok, I got regulat acdelco platinums, but I think it needs a plat +2 but not sure. anyway the zone didn't sell em in acdelco brand.

no probs as of yet, but haven't driven it very far either.

the old man thinks that the cat might be busted, since it only starts to fail when I go up a hill. he thinks something is loose inside it and drops when the engine shuts off, and that is why it works again if I shut it off and start it back up.

I'll post my findings, but I have asneaking suspicion that it isn't fixed.

Also I read that the cam sensor is a common problem with these things to do what I am describing.

I cheked for codes even though the check engine light wasn't on and found 2 old codes.
both front o2 sensors reported low voltage. I cleared them out and nothing has come back yet.

I'll keep you informed of the progress.
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Old March 13th, 2009, 07:12 PM   #6
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Had to put in a new distributor today. Took the cap off to change it and the rotor as well as the cam sensor and noticed that there was a lot of play in the shaft as well as oil.
Popped it out and sure enough over 1/4 of an inch up and down.
Wayyyy too much, so I put on another one for $200 this evening and it seemed fime on the test drive, but not a definite fix as of yet.

I'll keep ya posted.
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Old March 15th, 2009, 04:11 PM   #7
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Stop spending money on parts you dont need and get someone with a good scanner (NOT AUTOZONE) you need a scanner that can read the data stream, plug it in and drive it. When it acts up take a look at real time readings and see whats going on.
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Old March 15th, 2009, 09:32 PM   #8
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I own one, cost me about 1000 dollars. The scan tool isn't showing anything. That is the problem.
The stumble came back too btw. I personally am starting to think that there is a wiring problem. I know that the dealership power washed under the hood before they sold it too me, because it is too clean in some areas, and filthy as hell in others.

Gas pressure gauge isn't acting too wierd when it stumbles either. Just goes up 1 psi and kinda fluxuates back and forth that 1 psi.

Back to the drawing board.

Chris
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Old March 16th, 2009, 03:41 PM   #9
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If you got a scan tool that can read data did you check your o2 sensors when the misfire occurs. This could be the problem and the computer might not be setting the code again because it not in the right parameters for the test to run. Your 02sensors should be reading between 200mv and 800mv.
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Old March 16th, 2009, 09:38 PM   #10
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thanks, I'll check it again tommorrow. I remember the readings on them were between 185 and 836 but don't remember if they were front or back, but I assume front.

The misfire seems to have quit since I changd the plugs today. It still stumbles and the fuel pressure is staying around 50 when it happens.

If I keep the throttle down, I mean less than 40% on the tps I can accelerate from a stop all the way up to 70 though. The fuel pressure rises to about 60 psi when I do this, but if I stomp on it, or open it more than 40% it immedately drops to 50 psi and misses.

Just changed the fuel filter tonight, after the spark plugs and no dicernable diffirence.

I'll be driving it again tommorrow and seeing what happens.

Starting to wonder if it is in fact the cats...

Chris
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Old March 17th, 2009, 06:10 PM   #11
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new fuel filter and fuel pump again today...
Hurrah....
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Old March 17th, 2009, 09:47 PM   #12
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also my buddy has a tahoe with same problem and we went throuhg all that. but we ended up pulling the injectors and cleaning them real good. they were nasty and that helped it to run better.
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Old March 17th, 2009, 09:49 PM   #13
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copy

how many miles did it have?
this thing has about 90k on it.
was is a pain to remove that plastic intake?

Chris
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Old March 17th, 2009, 09:53 PM   #14
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What kind of fuel pump are you using? At the Chevy dealership I worked at, if we put in a Carquest pump, we likely had to replace it within a couple months because they were crap. We had an astro van I put 3 CQ pumps in. Finally on the 4th one, we talked the company into putting a GM pump in and we never had another problem with the pump again.
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Old March 17th, 2009, 10:13 PM   #15
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it had about 300thousand. but i had a machine at school and we could hook them up to it and it would clean them
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Old March 18th, 2009, 12:28 AM   #16
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Quote:
Originally Posted by Flexin' XJ View Post
What kind of fuel pump are you using? At the Chevy dealership I worked at, if we put in a Carquest pump, we likely had to replace it within a couple months because they were crap. We had an astro van I put 3 CQ pumps in. Finally on the 4th one, we talked the company into putting a GM pump in and we never had another problem with the pump again.
I would agree. I had a '99 Suburban and two years ago had to have the fuel pump replaces. Shop used the cheap version from Carquest and 90 days later it failed and left me stranded again. The shop had to have my truck towed 30miles back to them and install and better pump. I only had to pay the difference in prices between pumps. Which was like $100-150. Anyway the pump he finally used was the good GM part top of the line.

My buddy who does all the work on my vehicles(except this fuel pump issue) said they wont use the Carquest fuel pump because they have replace too many.
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Old March 24th, 2009, 02:04 PM   #17
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My s10 does the same thing, and its the knock sensors. I guess it retards the timing, but it is intermitten like you say
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Old March 24th, 2009, 07:38 PM   #18
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Mine Was Doing The Same Thing. Ended Up Being The Dist. Worn Shaft. Replaced It. Runs Great. Vortec 5.7
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Old May 30th, 2011, 02:30 PM   #19
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damn pump went out again today!

this is getting rediculous! Anyone have any luck with the bosch pumps? I mean they are $340 so they should be pretty good for that kind of money!
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Old June 1st, 2011, 03:56 PM   #20
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I would check your fuel pump wiring real well. Sounds like u might have a bad ground, iirc GM used a ground strap on these that simply clips on the frame.
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