warf90 Posted October 18, 2009 Share Posted October 18, 2009 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. Link to comment Share on other sites More sharing options...
HOrnbrod Posted October 18, 2009 Share Posted October 18, 2009 Did you change the fuel filter? Link to comment Share on other sites More sharing options...
warf90 Posted October 18, 2009 Author Share Posted October 18, 2009 Sorry, yeah I also changed the fuel filter. Link to comment Share on other sites More sharing options...
mvusse Posted October 19, 2009 Share Posted October 19, 2009 You did put a new sock on the new pump, right? Link to comment Share on other sites More sharing options...
warf90 Posted October 19, 2009 Author Share Posted October 19, 2009 Yes also installed a new sock on the pump. What does not make sense is that it ran great for a week and then started doing this. I wish I had a fuel pressure gauge. Link to comment Share on other sites More sharing options...
mvusse Posted October 19, 2009 Share Posted October 19, 2009 Pull the pump and check the sock. Also replace the fuel filter again. Wouldn't hurt to drain the tank and wipe it clean inside. I'm betting you have crud in the tank. Link to comment Share on other sites More sharing options...
warf90 Posted October 19, 2009 Author Share Posted October 19, 2009 The other thing that I forgot to mention is the check engine light is on and it does smell like it is running rich when it is running. You are probaly right though, I should change the filter again and clean the tank better. Link to comment Share on other sites More sharing options...
Eagle Posted October 19, 2009 Share Posted October 19, 2009 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. Link to comment Share on other sites More sharing options...
warf90 Posted October 19, 2009 Author Share Posted October 19, 2009 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. Link to comment Share on other sites More sharing options...
mvusse Posted October 19, 2009 Share Posted October 19, 2009 If the check engine light is on, first thing to do would be to read the codes. Link to comment Share on other sites More sharing options...
Eagle Posted October 19, 2009 Share Posted October 19, 2009 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. Link to comment Share on other sites More sharing options...
Automan2164 Posted October 19, 2009 Share Posted October 19, 2009 Just going on an off-shoot here, but is the fuel tank venting correctly? I mean, next time it starts to run like crap, pull the cap, and see if maybe the tank can't suck in fresh air... Just something simple to try... Rob L. Link to comment Share on other sites More sharing options...
warf90 Posted October 19, 2009 Author Share Posted October 19, 2009 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. Link to comment Share on other sites More sharing options...
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