wranglercory Posted May 20, 2010 Share Posted May 20, 2010 1987 MJ 2.5L 5 speed tranny with four wheel drive. I have a problem that I can better explain. This truck I just bought has a problem that when it gets up to opperating temp.(not exactly sure temp. without a gauge)after about 10 min. the vehicle can not be ran any faster than idle. If you give it gas it spits spudders and as soon as you let off the gas it idles fine. I have disconnected the O2 sensor. The problem continued after that . I also the time I drove it tried to dis-connect different sensors but no change. One thing the last time I drove it I noticed that if I while moving would shut the key off and restart it it would run ok untill I slowed down to a stop then back to idling again. I think I tested the sensor on the driverside of the throttle body but not completely sure it tested right. The truck is a pretty good truck once I get the bugs worked out. The other things I do know is that the fuel filter has been replaced. :headpop: Link to comment Share on other sites More sharing options...
Wildman Posted May 20, 2010 Share Posted May 20, 2010 2 things come to mind......... The EGR valve........you can unplug the vacuum line to it (and plug the rubber line) and "test" it that way. And.......you still running a catalytic converter???? Link to comment Share on other sites More sharing options...
Pete M Posted May 23, 2010 Share Posted May 23, 2010 x2 Link to comment Share on other sites More sharing options...
wranglercory Posted May 24, 2010 Author Share Posted May 24, 2010 I will try the EGR valve and yes it does still have the cat on it I havent gotten to opening up the passage for the air to move through better :brows: . So Do I just bypass the EGR valve and run it that way till it gets to the temp that it has problems at? Link to comment Share on other sites More sharing options...
Wildman Posted May 25, 2010 Share Posted May 25, 2010 Yes, disconnect the vacuum line to the EGR when the engine is cold, and just plug the end of the vacuum hose, you should notice a difference right away, and more so after the engine hits operating temperature. If no change, well, it cost you nothing but 5 minutes of your time just to check the EGR valve. Then we move on to the next thing. If the cat was clogged, you would notice it more on acceleration than anything else, like going up hill and giving it a little extra gas. The engine will bog down really bad and act like no power at all.......that's a sure sign that the Cat is plugged. A plugged cat can also cause rough idle, where there is to much back pressure from the exhaust. Just remember, the 4.0 and 2.5 are designed to run with some back pressure, so a full open exhaust is not the ideal running conditions for the engine. I'll still put my coins on the EGR valve :D Link to comment Share on other sites More sharing options...
wranglercory Posted May 25, 2010 Author Share Posted May 25, 2010 its weird the truck will idle all day long like a new truck even when it gets warm. but with it warm it will not go past idle at all??? :headpop: havent gotten to try the EGR weve got it in the garage stripping the bad fender and doing a few odds and ends I know I'm loosing clutch fluid havent been able to track it down yet so soon as I get that back together Ill check the EGR. Link to comment Share on other sites More sharing options...
sinkrun Posted May 27, 2010 Share Posted May 27, 2010 Not sure if this is a high jack sorry if it is. I was watching this thread as my 4.0 was doing the same thing. I unhooked the EGR plugged the line and it runs and idles great now! My question is will it hurt to let it plugged also if I get a new one should I get the one that comes with the round black plastic disk thing? Link to comment Share on other sites More sharing options...
Wildman Posted May 29, 2010 Share Posted May 29, 2010 sinkrun - your in par with the original poster :D No problem with leaving the vacuum line plugged, and running it with out the EGR valve, I've been running my '89 4.0 for at least 4 years that way. As long as your inspection don't have the sniffer test :roll: Link to comment Share on other sites More sharing options...
sinkrun Posted May 29, 2010 Share Posted May 29, 2010 Great that saves me $80.00 as the only sniffers round here are my two beagles and hound. Link to comment Share on other sites More sharing options...
wranglercory Posted June 17, 2010 Author Share Posted June 17, 2010 I may have found the problem . The Manifold Air Temperature MAT . I noticed that the wire was exposed on both wires. I havent been able to drive it yet but hope to soon. Link to comment Share on other sites More sharing options...
wranglercory Posted June 25, 2010 Author Share Posted June 25, 2010 I got the truck out yesterday. same problem . I have came to one conclusion that it still could be the sensor or maybe the fuel pump. if the wires had there insulation melted back it could have damaged the sensor or the fuel pump is weak. I tested the fuel presure and got nothing with the ign on but got 16 psi. with it on then real quick bleed off like 5 psi. before I could look at the gauge. then bleeds off to nothing in seconds not min. what do you think. Link to comment Share on other sites More sharing options...
Wildman Posted June 27, 2010 Share Posted June 27, 2010 The Book says.........At idle, the pressure should be 14-15psi. If the pressure is not correct, adjust the pressure regulator to obtain the correct fuel pressure. Turn the screw at the bottom of the regulator inward to increase pressure or outward to decrease pressure. Note the above is for the 2.5 engine, and while the engine is running and idling. From what you write, your with-in spec's if the engine was running. Link to comment Share on other sites More sharing options...
wranglercory Posted June 29, 2010 Author Share Posted June 29, 2010 I will test the MAT sensor and see if that could be it. We'll see :oops: Link to comment Share on other sites More sharing options...
wranglercory Posted July 16, 2010 Author Share Posted July 16, 2010 The MAT sensor tested good any other hints ??? Link to comment Share on other sites More sharing options...
wannabeMJ Posted July 16, 2010 Share Posted July 16, 2010 my bet on this is a plugged fuel pump(meaning you got sh*t in your tank) runs fine at idle but as soon as you step on the gaz all that junk wants to up the fuel line bloking the pick-up in the gaz tank..... Link to comment Share on other sites More sharing options...
wranglercory Posted July 25, 2010 Author Share Posted July 25, 2010 That might be my next thing to work on . I have just tested the ECU, MAP, and MAT sensor in my other 2.5 comanche and they all worked fine. I think it would be a good idea to drop the tank and check it all out. Link to comment Share on other sites More sharing options...
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