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Unread 11-01-2008, 07:22 PM   #1
ScottN3N
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1994  
 
Join Date: Nov 2008
Location: OK
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Bloody Forhead ('94 ZJ 5.2L running rough)

My forhead is bloody from banging it against the wall. Any help is appreciated. I have a 94 Grand Cherokee, 5.2L all time 4wd. Starts & idles fine. Runs VERY rough above idle. Won't go over 20-30 mph & did I mention ROUGH. After it warms up for 15 min or so it will run just fine - plenty of power, smooth. Like something comes up to temp & decides to work properly. I've done the following with no luck. New plugs, wires, coil, cap & rotor. New MAP sensor. Removed & cleaned all injectors (soaked in B-12) new O rings. New fuel pump & filter. Fuel pres. in spec. Compression good. Run several cans of B-12 through it. Plugged Idle AIr Control valve - (all that did was make it idle poorly). I thought maybe it was stuck open. Can't find a vacuum leak. Codes are 14 - Map sensor voltage (has a new MAP sensor) 27 - injector control output drivers. All injectors seem to work. 54 - no camshaft position sensor signal from distributor. (can that be affected by operating temp?) What has me realy puzzled is that it will run fine after it warms up for 15 minutes or so (thoroughly warmed up). I've not changed the O2 sensor - yet - but I don't think that would have this much affect. Thanks for your time & help.

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Unread 11-01-2008, 11:30 PM   #2
bjf498
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1983 CJ7 
 
Join Date: Jun 2004
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Have you checked the temp sensor?
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Unread 11-02-2008, 12:37 AM   #3
willness33
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1999 TJ Wrangler 
 
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Quote:
Originally Posted by bjf498 View Post
Have you checked the temp sensor?
Good thought, however I think it's working properly since it runs poor in open loop "cold operation mode" and runs fine when warmed up. I think it is seeing the temp differential. The TPS would be another thought, and only because it's one of the few sensors that the ECU pays attention to in open loop. Honestly, this is where I'd spend the next dollars.
Quote:
Originally Posted by ScottN3N View Post
What has me realy puzzled is that it will run fine after it warms up for 15 minutes or so (thoroughly warmed up). I've not changed the O2 sensor - yet - but I don't think that would have this much affect. Thanks for your time & help.
See above explanation. The o2 sensors don't come into the mix regarding the ECU and engine management until the engine is up to temp. Since you say it runs fine when warmed up tells me the o2 sensors are ok.

Now the one thing that has me a bit cornfused is why would a bad TPS cause these problems in open loop and not closed? Input from the TPS is still used in closed loop "warm mode", but it's integrated with the feedback from the o2sensors at the same time. Headscratcher for sure. Since you've thrown every part at the whole thing but the temp sensor, TPS and o2 sensors and are likely to throw more parts at it, I'd still suggest a new TPS. At least, that's what I'd do. Take it for what it's worth.
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Unread 11-02-2008, 08:28 AM   #4
ScottN3N
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I'll give the TPS a shot. Thanks.
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Unread 05-19-2012, 07:36 AM   #5
vol96
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1997 ZJ 
 
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So was it the tps? Is only been 3 1/2 years. I'm sure you still have the jeep and can report the solution :-)
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