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Bogging Down- Losing Power while driving


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On my 89 with a 2.5 liter, I bought this after it sat for 3 years. I drained the gas and had to replace the fuel pump. It ran great for a about a week. Now after you drive it for about 10 minutes in starts to lose power. The more you drive it the worse it gets. I can drive it and then bring it back to my garage and it idles fine. Its just when you are driving it, it falls on its face likes it starving for gas. Sitting in nuetral you can rev it and watch the gas spray through the throttle body but it just bogs down. I am puzzled. Please help.

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Bad oxygen sensor will make it run rich, and a consistent rich mix will clog the catalytic converter. A clogged cat doesn't allow enough exhaust flow to make power at higher RPMs.

 

I'd say at a guess you need an O2 sensor and a catalytic converter.

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I would think a clogged converter would make it lose power all the time. This thng runs great for about the first 10 minutes of driving. Although I could see the O2 sensor causing problems. When you drive it, it seems like it is starving for gas or the spark goes away. You step on the pedal and it just bogs and some times it will back fire through the throttle body. But after all that it idles perfect.

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If the check engine light is on, first thing to do would be to read the codes.

His signature says he has a '90 and his post says it's an '89. Either way, that's a Renix -- there are no codes to read. It isn't a "Check Engine" light, it's a "Maintenance Required" light that's telling you to replace the oxygen sensor.

 

Why will it run for 10 minutes? Because the Renix system bypasses sensor input until it reaches operating temperature. During warm-up it runs in "open loop" mode, ignoring sensor inputs and using a pre-mapped fuel curve that's programmed into the ECU. Once the ECU temp sensor reads operating temperature (I think it's 165 degrees F.) it switches over to "closed loop" mode and starts adjusting things (such as fuel mix) according to sensor input.

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The 89 I am asking about is another MJ that I bought. It is a 4 cyl. The 90 I have is a 4 liter. Sorry for the confusion. The oxygen sensor makes sense, since it is running so rich. I do not want to put a ton of money into because I am junking the 90 and installing the drivetrain into the 89. The 90 I have is in pretty bad shape and the 89 I bought is in excellant shape. I just wanted to make sure the 4 cylinder was running good before I removed it and tried to sell it. The motor itself sounds and runs great. It only has 96,000 miles on it. Thanks for everyone's input.

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