Kenosha Warrior Posted September 1, 2009 Share Posted September 1, 2009 1987 MJ 4.0 AW4 - NP231 If I'm in gear idling at say a stoplight, it will settle into a 250-400 RPM idle, will die when at operating temps. In Park/Neut will sit around 500-700rpm If by chance it doesn't die, as I accel from the stoplight, it bogs. Rich fuel smell from exhaust. Unknown age of O2 sensor. Where should I start looking? The IAC was my first complaint but I'd like a 2nd opinion. Link to comment Share on other sites More sharing options...
SkipshotMJ Posted September 1, 2009 Share Posted September 1, 2009 I might be wrong, but it could possibly be the CPS sensor (located on the top of the transmission). They're known for going out in our jeeps. Does it ever just die randomly while you're driving down the road? Link to comment Share on other sites More sharing options...
SkipshotMJ Posted September 1, 2009 Share Posted September 1, 2009 also you could check out the MAP sensor. Link to comment Share on other sites More sharing options...
Pete M Posted September 1, 2009 Share Posted September 1, 2009 I would start with a good cleaning of the throttle body and IAC hole with Q-tips, a tooth brush and an O2 save throttle body cleaner. :thumbsup: Link to comment Share on other sites More sharing options...
Kenosha Warrior Posted September 1, 2009 Author Share Posted September 1, 2009 I might be wrong, but it could possibly be the CPS sensor (located on the top of the transmission). They're known for going out in our jeeps. Does it ever just die randomly while you're driving down the road? No random deaths nor will it die if I keep working the gas pedal Pete, all of them are nice and clean save for the O2. THats my next step Link to comment Share on other sites More sharing options...
thedave360 Posted September 1, 2009 Share Posted September 1, 2009 Try un plugging the MAP sensor then starting the truck. It should idle better, but it'll start running like crap around 1500rpm. My frontier had an idling problem that turned out to be a very dirty MAP. I cleaned the hell out of it, and now it purrs like pissed off kitten!! Definitely try cleaning it first before you just buy a new one. Link to comment Share on other sites More sharing options...
Eagle Posted September 1, 2009 Share Posted September 1, 2009 The oxygen sensor could account for the rich smell. If it isn't reading accurately, the ECU may be "overclocking" the injectors because it thinks the mix is too lean. The last time I replaced the O2 sensor on my '88 XJ, I could hear it. It's a 4.0L 5-speed, and I began to notice muffled backfiring either in the downpipe or in the catalytic converter when I'd upshift or when transitioning from acceleration to coast. I don't know if an over-rich mix could cause dying at idle, but I suppose if it's VERY rich it might essentially flood out. Link to comment Share on other sites More sharing options...
Kenosha Warrior Posted September 1, 2009 Author Share Posted September 1, 2009 How would one clean out a MAP? Just for future reference as.... Unplugging the MAP at Idle makes it idle even worse, if there even is a step down from bag of sh it Link to comment Share on other sites More sharing options...
Oizarod115 Posted September 2, 2009 Share Posted September 2, 2009 unplug the idle air control and see if it changes anything, try using http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm to help check all your sensors how recent is the tune up? Link to comment Share on other sites More sharing options...
cracker Posted September 2, 2009 Share Posted September 2, 2009 I am in the same boat. :hijack: Tried IAC (2 of them), MAP, Both CPSs (Cam/distributor and crank), spark plugs, EGR, TPS, compression tested the engine, wires, O2 sensor (2 of them), checked all the intake and TB bolts for leaks and changed the air filter :rotf: Next on the list is the checking power to the injectors and then maybe swapping them out with some spares. Funny thing about this is it went bad and went bad QUICK. Link to comment Share on other sites More sharing options...
Kenosha Warrior Posted September 2, 2009 Author Share Posted September 2, 2009 I am in the same boat. :hijack: Tried IAC (2 of them), MAP, Both CPSs (Cam/distributor and crank), spark plugs, EGR, TPS, compression tested the engine, wires, O2 sensor (2 of them), checked all the intake and TB bolts for leaks and changed the air filter :rotf: Next on the list is the checking power to the injectors and then maybe swapping them out with some spares. Funny thing about this is it went bad and went bad QUICK. I know eh, this dropped itself on me when it went from driving 15 feet TOPS to carting my @$$ to work each day. Its still running super rich as fawk. I swapped out a known good O2 sensor lastnight. I'm wondering if my coil is weak, as its began to putt-putt while at speed (unless I'm accelerating) Link to comment Share on other sites More sharing options...
Pete M Posted September 2, 2009 Share Posted September 2, 2009 Checked the engine block ground? Just a thought. I also had a super rich condition in my 86 (carbed, so I don't know if it really correlates) due to a weak connection at the coil (the wire that feeds 12volts to the coil). The weak spark wasn't burnign all the fuel in every cylinder. Eventually I blew up my muffler while trying to diagnose it. :D Link to comment Share on other sites More sharing options...
Kenosha Warrior Posted September 2, 2009 Author Share Posted September 2, 2009 Nice, Pete. The block ground looks good, but I'll check it anyway. Link to comment Share on other sites More sharing options...
cracker Posted September 3, 2009 Share Posted September 3, 2009 Checked the engine block ground? Just a thought. I have a brand new ground but my battery ground is not very nice. :doh: I should make a new one tonight out of some welding cable I have. Link to comment Share on other sites More sharing options...
cracker Posted September 4, 2009 Share Posted September 4, 2009 I ran an additional ground so that wasn't it. I checked the power to the fuel injectors and they all checked out. We pulled spark plugs while running and it is cylinder 6 that makes no difference. I changed the fuel injector on cylinder 6 and that didn't work. Did a pressure test on it and it lost some (50%). Cylinder 6 also was the lowest on the compression test too (125 when the others were 130-150). Some buddies think it might be the head gasket. I find it hard to beleive that I potentially damaged a head gasket in the driveway moving it 40 feet once a day. :doh: Link to comment Share on other sites More sharing options...
maddzz1 Posted September 6, 2009 Share Posted September 6, 2009 Maybe a clogged cat? Link to comment Share on other sites More sharing options...
cracker Posted September 6, 2009 Share Posted September 6, 2009 Maybe a clogged cat? Maybe for the OP but not for me. I have a brand new cat and exhaust. Link to comment Share on other sites More sharing options...
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