Jeep Tricks Posted July 6, 2006 Share Posted July 6, 2006 I have an '87 Jeep Comanche 4.0L 4WD. Last weekend I went to start my truck and it wouldn't start. After a while of cranking it started but when it did it had a really high idle. It was idleing at 2900 rpm. I let it sit for a few days and now when I go to start it, it won't start at all. So I pushed it in reverse and had my cousin start it in gear. Thats the only way it started and again the idle rose to 2900 rpm. After about 10 minutes of idleing high it came back down to a normal 600 to 700 rpm. I shut it down, let it sit for a few seconds, turned the key and it started right up again with a normal idle. After it cools down it does the same thing again and won't start. I have spark and the fuel pump is running but the injectors aren't fireing. Does anyone know what might be the problem or guide me in the right direction. Any help would be appreciated. Thanks! Link to comment Share on other sites More sharing options...
DirtyComanche Posted July 6, 2006 Share Posted July 6, 2006 Clean the IAC. Then check the CPS. They like to bugger up. Link to comment Share on other sites More sharing options...
CWLONGSHOT Posted July 6, 2006 Share Posted July 6, 2006 I agree...a clean TB is a happy TB.....becareful with the TPS...they can be ornery.....and expensive!!!! CW Link to comment Share on other sites More sharing options...
Dadinator Posted July 6, 2006 Share Posted July 6, 2006 Let me know if you need a TPS. . . I have a new one that I bought for the son's and didn't need it. Turned out to be something else. It's new in the box. I'll sell it pretty cheap. . . Link to comment Share on other sites More sharing options...
Jeep Tricks Posted July 7, 2006 Author Share Posted July 7, 2006 Thanks ill check on that! Link to comment Share on other sites More sharing options...
Jeep Tricks Posted July 9, 2006 Author Share Posted July 9, 2006 No good! I replaced both the IAC Valve and the CPS, and I also cleaned the TB and still nothing. Doesn't even act like it wants to start. Any more ideas? Link to comment Share on other sites More sharing options...
Dadinator Posted July 10, 2006 Share Posted July 10, 2006 If it is cranking and not starting, I'd go up on the fuel rail and have someone turn the key on and off while you push the fuel valve. I don't know if that's what you call it, but; it is like a tire valve that you can use to bleed the fuel lines. It's on the main fuel rail and should have like a screw on cap on it. If you do that and no fuel is coming out of it, then your fuel pump is most likely bad or a clog in the line. Have you replaced the fuel filter? If you don't get fuel out by doing that then I'd pull the fuel filter and turn the key on and off again to see if fuel pumps out of the line. don't be smoking or around open flame. :eek: If no fuel from their either, then I'd say you have a fuel pump issue. You should also be able to hear the fuel pump when you turn the key on and off. Good Luck. Link to comment Share on other sites More sharing options...
Jeep Tricks Posted July 11, 2006 Author Share Posted July 11, 2006 I have fuel pressure. The pump runs every time I turn the key. I changed the fuel filter when I first got the truck back in January. When I press the schrader vlave gas flows out. I have spark and I have fuel pressure. I just don't know if the injectors are fireing. Does anyone know of a way to check if the injectors are fireing? And also what other inputs to the computer can cause this problem. If no others then I think its the comp..... :cry: Link to comment Share on other sites More sharing options...
Dadinator Posted July 11, 2006 Share Posted July 11, 2006 You got me. :cry: The CPS was the culprit when My Sons acted like that. I don't know of a way to tell if the injetors are firing. Could be the computer or another sensor. Sorry I can't be more help. . . Good luck with it. Link to comment Share on other sites More sharing options...
87manche Posted July 11, 2006 Share Posted July 11, 2006 crank it a few times then pull a spark plug. If you smell gas or the end of the plug is wet then the injectors are firing. You didn't mention is you checked the TPS or adjusted it. That's where I would go next. You may also want to make sure that the fuel pump is running while cranking, it's fed by a different circuit when the key is in the start position. Link to comment Share on other sites More sharing options...
Jeep Tricks Posted July 12, 2006 Author Share Posted July 12, 2006 I didn't know the TPS could be adjusted. I got home and checked the output voltage on it. Adjusted it to 0.8 V and my truck fired right up. It ran at a normal idle. I shut it down, and started it a few times then the voltage spiked to about 4.5 volts. My truck wouldn't start anymore. I tapped the TPS a few times then the voltage came back down to .75 V. So i readjusted it to 0.8 V and it fired right up again. This time the idle came back up to about 2500 rpm at .77 V. As the output voltage kept coming down to about .72 the idle rose even higher to 2900 rpm. So now I know my TPS is bad. Thank you all for your help I appreciate it!!! Link to comment Share on other sites More sharing options...
Dadinator Posted July 12, 2006 Share Posted July 12, 2006 Glad it's fixed. Like I said above, I've got one if you're interested let me know. it's new, I just didn't need it. I'll sell cheap. :D Link to comment Share on other sites More sharing options...
Jeep Tricks Posted July 13, 2006 Author Share Posted July 13, 2006 How much? Link to comment Share on other sites More sharing options...
Dadinator Posted July 13, 2006 Share Posted July 13, 2006 How's 25 sound? + Shipping. Let me know. Thanks, Mike. Link to comment Share on other sites More sharing options...
Jeep Tricks Posted July 14, 2006 Author Share Posted July 14, 2006 Are you sure the TPS you have will fit my truck?!? Link to comment Share on other sites More sharing options...
Dadinator Posted July 14, 2006 Share Posted July 14, 2006 Well, now that you mention it, no. It was for the son's '90. I assume they are the same, but; maybe not. Call your local parts store and see if they have the same part number. If so, I'll sell you this one. if not, oh well. . . :cheers: Link to comment Share on other sites More sharing options...
jpdriver1 Posted July 14, 2006 Share Posted July 14, 2006 not to beat this to death, but does anyone know what the voltages should be --- mine are currently 4.87 input and 1.14 output this is on a 90 pioneer, metric ton Link to comment Share on other sites More sharing options...
mjeff87 Posted July 14, 2006 Share Posted July 14, 2006 From the '88 FSM: (note the difference between auto and manual) THROTTLE POSITION SENSOR (TPS) NOTE: Adjustment of TPS only applies to the 4.0L models. It may be necessary to remove throttle body from intake manifold, to access sensor wiring harness. Checking & Adjusting - 4.0L (Automatic Transmission)1) Locate the square TPS connector. Note connector terminal identification stamped on the back of the connector. Turn ignition on. 2) Connect voltmeter through back of wiring harness connector. Connect negative voltmeter lead to terminal "D" and positive voltmeter lead to terminal "A" to check input voltage. DO NOT disconnect TPS connector. 3) Hold throttle plate closed against idle stop and note voltage. Input voltage should be approximately 5 volts. Disconnect voltmeter positive lead and connect to terminal "B" to measure output voltage. 4) With throttle plate closed, measure the output voltage. The output voltage should be approximately 4.2 volts. If output voltage is not within specification, loosen TPS retaining screws. 5) Partially tighten one retaining screw. Rotate TPS to obtain correct output voltage. Tighten retaining screws once correct voltage is obtained. Checking & Adjusting - 4.0L (Manual Transmission) 1) Turn ignition on. Connect voltmeter through back of wiring harness connector. Connect negative voltmeter lead to terminal "B" and positive voltmeter lead to terminal "A". DO NOT disconnect TPS connector. 2) Hold throttle plate in the closed throttle position against idle stop and note input voltage reading. Input voltage should be approximately 5.0 volts. 3) Disconnect positive lead from terminal "A" and connect to terminal "C" to check output voltage. Output voltage should be checked with throttle plates fully closed. 4) Output voltage should be approximately 0.8 volts. If output voltage is not within specification, loosen TPS bottom retaining screw and pivot sensor for a large adjustment or top retaining screw for a fine adjustment. 5) Adjust sensor to obtain correct output voltage. Tighten retaining screws. Remove voltmeter. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now