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A collection of helpful articles based on reader submissions
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Below is a collection of Jim Grant's Tech Tips sorted by Vehicle Make. These Tech Tips were answers to questions submitted to Jim by users over the course of many years.
If you have any questions, please feel free to email us.



Lincoln - Mercury
  Jim Grant's Tech Tips

96 Jeep Grand Cherokee, shuddering
Q: We own a ‘96 Jeep Grand Cherokee with 72K. We have had all routine maintenance performed. The vehicle is in great working order except for the following problem. Our check engine light keeps coming on when accelerating up hills at 55+mph. When we are about at the crest of a hill the light starts flashing then when the vehicle starts to down shift it starts shuddering real bad. This shuddering will last until you back off the gas and slow down. We have had the valve springs replaced, then had the mechanics do some work (because of the codes thrown) and this last week a new computer was installed. Two days after the computer was replaced the check engine light came back on under these same conditions. What could be the problem?

A: The ALLDATA Information System shows several Technical Service Bulletins (TSB’s) that are related to driveability problems with check engine lights coming on. The computer will report information to the technician that is not valid and send him/her down the wrong diagnostic path. With the recent replacement of the vehicle’s computer I would hope you got the latest and greatest software update. No, your Jeep isn’t running on Windows 98. If the computer is up to speed then the concerns move to the ignition and fuel system. If the problem is happening as the transmission down shifts and the engine RPM jumps higher than the norm, there may be a problem with the ignition wires. Strange as it may seem, we’ve found that under load and high engine RPM tired spark plug wires will introduce an immensely confusing engine skip that will not only turn the check engine light on, it also sends the computer into the high alert mode causing the check engine light to blink. The blinking check engine light on most ‘96 and up vehicles is the computer attempting to alert the driver to the pending doom of the catalytic converter. In closing, do not ignore the fuel system as a possible cause. A fuel pressure gauge should be installed and the vehicle driven in a manner that causes the engine to go into convulsions. Only then could you be sure of the abilities of the fuel pump. The fix will likely be simple. It’s finding the cause that will drive you nutz.

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