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Sherlock Ohms

What Caused the Hummer’s Rough Ride?

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Critic
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Platinum
Diagnosis
Critic   5/20/2015 11:54:34 AM
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Good thing you found the bad coil!

It is unfortunate that many repair facilities don't know how to diagnose problems.  Misfires are generally caused by fuel, spark, or compression issues.  If they suspected that you had valve sealing problems, which seem to occur frequently in H3s, they should have run a compression test.  If there was a serious problem with valve sealing, then the compression test would have shown this.

You didn't mention the presence of any fuel system codes, so the fuel system was vindicated.  You could have checked oxygen sensor voltages to be sure.  Oxygen sensor data would have implicated the ignition system.

This would have left the ignition system as suspect.  Swapping coils like you did was a quick way to find the problem, although it could have been the spark plug or something in the primary circuit.  Good job!

 

William K.
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Platinum
Re: Diagnosis
William K.   5/23/2015 9:11:10 PM
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I had an intermittant engine die-out problem on a Dodge Shadow, and the only fault code said that the engine control module had been reset, which did not tell me very much. I sold the car to a friend after waning him that I would not guarantee that the vehicle would get him home. So he new that there was a big problem. Eventually he discovered an intermittent short circuit in one of the injection solenoids, which would cause a reset of the ECM. The dealer had suggested a number of other things, mostly involving the replacement of non-returnable parts, none of which solved the problem. I believe that the fault was found by voltage monitoring, after reading a long list of all the things that could cause an ECM reset. Smart diagnostics and it was a great father-son project for my friend.

sputnik50
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Iron
Landy Transmission Experience
sputnik50   5/21/2015 9:25:59 AM
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A friend had a similar experience with a Land Rover, but this time he actually had the dealer do the work. 

Occasionally, the transmission would not shift out of first gear.  If he turned the ignition off and on, it was OK again.   It became frequent enough that it was a real nuisance.  The dealer said he needed to replace the transmission, which he did, at a cost of $4000, not under warranty.  Within a week or two after the work, he had the problem again.  Coincidentally, the dealer had actually gone bankrupt while he was finishing the work, so getting him to correct the situation was not going to happen. 

With some research, we began to suspect the fuel filter.  Even with the shocking price for a fuel filter ($400) and the need to drop the gas tank, we replaced it one Saturday.

The transmission has been fine for two years now.

Critic
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Platinum
Re: Landy Transmission Experience
Critic   5/21/2015 10:16:03 AM
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Did the fuel filter cause the problem because the engine was so lacking in power that the vehicle couldn't go fast enough to shift out of first gear?  Or is there some other mysterious connection between the fuel filter and transmission?

sputnik50
User Rank
Iron
Re: Landy Transmission Experience
sputnik50   5/21/2015 3:24:07 PM
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The engine had normal power.  I now recall that the transmission was 'stuck' in a high gear.  Apparently the vehicle's system includes programming that prohibits the transmission from going into low gears when the pressure in the fuel rail drops below a certain point.

Battar
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Platinum
Could not happen here
Battar   5/21/2015 10:13:06 AM
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Could not happen where I live. In my part of the world, where fuel is not cheaper than coca-cola, and the word "economy" commmands our attention, Hummers and Landrovers are sold exclusively with diesel engines.

RonSparky
User Rank
Iron
Lack of troubleshooting
RonSparky   5/21/2015 12:35:46 PM
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There are too many 'mechanics' today that don't try to do any real troubleshooting of the problems. They are just 'parts replacers' without concern for fixing the problem or the vehicle owner. This creates an incredible amount of frustration to us that have to take the car back multiple times at (as is shown here) considerable expence. We may have to pay for some of the mechanics time to do the real troubleshooting which would save us a great deal of time and money. 

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