1999 Tahoe Misfire cylinder 5 with load on motor? Donation!

Tiny
HOUSEOFBRUGHS
  • MEMBER
  • 1999 CHEVROLET TAHOE
I have a 99 Tahoe LS 4d 4wd with about 86K miles 5.7 V8.

Since I purchased this truck with 52K miles on it I have been having this same problem repeatedly. The dealership where I purchsed it "tried" to fix it with the diagonoses of misfire on cylinder 5 several times with no luck and recently I took it to a GM dealership and they said it would just be a shot in the dark until we find the part causing it. Since the diagnotic machine does not give a definitive reason this is happening. I don't have 1000's of dollars to keep replacing parts until we hit the right one so I was hoping you may have some better insight than what I have been getting.

Here is what is happening. When I accelerate it does just fine when I reach between 1300 to 1500 RMP and 55-60 MPH the engine shakes like the motor mounts are broken. If you press the gas and change the RPMs or move past 60 MPH via passing gear not steady RPM gain it goes away gradually. This happens on the slightest of hills now if I am climbing a larger hill or towing. Basically any kind of load on the motor it is horrible. I have changed plugs, wires, fuel filter, DC and RB. I hope someone has some good information on what I can do to fix this. I want to keep the truck so come on guys help me out!

Michelle
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Sunday, October 28th, 2007 AT 8:30 PM

15 Replies

Tiny
BLACKOP555
  • EXPERT
One of the easiest things to check is to make sure the fuel injector is not plugged, also check the distributor cap and rotor for cracks melted point on cylinder 5 or excessive carbon build up.

Also test for compression at that cylinder to see if its less then the rest. Also check for spark at that cylinder.
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Sunday, October 28th, 2007 AT 8:44 PM
Tiny
HOUSEOFBRUGHS
  • MEMBER
The distributor Cap and Rotor button are new. I have not checked compression or spark to that cylinder yet. If either of those were bad would I only be having this problem with a load on the motor at those specific RPM's as mentioned in my orginial post?
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Sunday, October 28th, 2007 AT 8:50 PM
Tiny
BLACKOP555
  • EXPERT
That could be very likely.
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Sunday, October 28th, 2007 AT 9:47 PM
Tiny
JACK42
  • MEMBER
99 Tahoes had CPI engines. You need an injector. Gm kept kinda quiet on the fact that they were warrantying them to 100k. Big problem with that engine. Also had problems with the fuel pressure regulators.
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Monday, October 29th, 2007 AT 7:43 AM
Tiny
HOUSEOFBRUGHS
  • MEMBER
Thanks Jack! So I would still be under warranty then since I have not breached the 100K mark yet or did they have a certain amount of years that went along with that like 100k or 5 years which ever comes first. Etc? I guess the next thing will be finding a dealership that will do the warranty work. My local Chevy dealership didn't even want to look at it.

Probably wouldn't hurt to have the FPR checked out as well I would imagine.
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Monday, October 29th, 2007 AT 8:37 AM
Tiny
JACK42
  • MEMBER
If you are a squeeky enough wheel, you might get greased. This far along it is kind of at the dealers discretion
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Monday, October 29th, 2007 AT 9:36 AM
Tiny
HOUSEOFBRUGHS
  • MEMBER
Thank You again for your help. You have been wonderful! I spent 45 mins on the phone with Chevy. I have that squeaky wheel rolling now. They have contacted the dealership and guess what they are suddenly willing to look at it. At least that is a step forward with Chevy involved. I will let you know the outcome.
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Monday, October 29th, 2007 AT 10:04 AM
Tiny
JACK42
  • MEMBER
Go get'm
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Monday, October 29th, 2007 AT 10:20 AM
Tiny
999TAHOE
  • MEMBER
My '99 Tahoe does basically what you were describing. Did that remedy your problem?
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Sunday, December 16th, 2007 AT 3:58 PM
Tiny
999TAHOE
  • MEMBER
155,000 miles, random misfires accelerating through 68-72mph to pass, on hill, with trailor.
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Sunday, December 16th, 2007 AT 4:00 PM
Tiny
HOUSEOFBRUGHS
  • MEMBER
Here is the update.I took it to my local GM dealership. They kept it for 3 days and after they exhausted all of their "guesses" they contacted the GM engineers who continued to scratch their heads. I was given these options from GM you could start with replacing all of the injectors and a valve job (but we can't gurantee that will fix it) or you could replace the motor (we also can't gurantee that will fix it either) we can give you a 500.00 brand loyalty certificate and you can go buy a new one. That will fix it. (There lame attempt to make this a laughing matter) I told them that the brand loyalty offer of 500.00 was offensive to my sensibilties! I have dumped well more than that into this POS to try to find someone who knew what was going on. I guess when it boils down to it if the GM Techs & Engineers have no clue. No body else will either unless they just get lucky. I personally think GM knows this was an across the board problem that they just don't want to deal with.

Bottom line.I traded in the next day on a Chrysler!

My advice to anyone else. Good luck on finding the problem. Smartest thing to do is dump it and get something else if you can.
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Sunday, December 16th, 2007 AT 7:23 PM
Tiny
999TAHOE
  • MEMBER
My mechanic who I consider intelligent and trust said he has done some research and said it may be carbon built up on the valve guide that, when under a good load and therefore hot, may expand and touch or obstruct a valve and make the missfire occur. I'm not a gear head and may not have said all of that correct.

It may also have to do with the time I was at the usuall oil change place and got tired of the guys trying to sell me crap so I bought into a sludge flush out treatment hoping they would leave me alone in the future. I'm sure all it did was just stirr around all sorts of good stuff and subsequently damaged the engine.

I do know it's not the gas (current tank), fuel pump, fuel filter, mass airflow sensor, coil, wires or plugs. Haven't gotten around to the injector yet; maybe all that cheap wal-mart gas has caught up.
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Sunday, December 16th, 2007 AT 7:51 PM
Tiny
999TAHOE
  • MEMBER
Forgot one thing.I also had a head gasket recetly replaced. I've read on some forums that they thought it was water in the oil causing the problem. No dice
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Sunday, December 16th, 2007 AT 7:54 PM
Tiny
JACK42
  • MEMBER
You never mentioned the head gasket before. I have done so many of those I dont care to recall them! But when the top of those are taken apart the outer valve on the injectors sticks and causes misses almost every time. The updated injector only has one valve on it instead of two.
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Monday, December 17th, 2007 AT 7:17 AM
Tiny
PEAR69
  • MEMBER
999tahoe, My engine did exactly the same thing. It turned out to be a sticking exaust valve just as you described. I just replaced the heads with GM performance vortec heads. These heads come complete and assembled. You can just bolt them on. However I matched ported and smooth polished the ports myself and got significant performance gains. These heads cost about $570.00 for two and I got them from Jegs performance parts. On-line
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Monday, December 31st, 2007 AT 12:08 PM

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