offroader461 Posted April 30, 2008 Share Posted April 30, 2008 Ok...have a huge problem and ill explain it the best i can... Sunday night i was driving and the tachometer started bouncing up and down erratically but i didnt notice a loss of power so i thought nothing of it...Well as i got closer to the bowling alley it started bucking and acting like it was going to stall...now at this time if i held the gas steady it ran fine but as soon as i let up it would start acting weird. It finally just stalled and i coasted in the lot. I let it sit and went and had fun then when i went to leave it immediatly started up again and after 1/2 mile i just pulled over and towed it home. I already checked the TPS and its working just fine...i went to start it today and it fired up then almost immediatly started stumbling then just quit and i had a small amount of gas-smellin smoke come out of my K&N....any suggestions???? Link to comment Share on other sites More sharing options...
Eagle Posted April 30, 2008 Share Posted April 30, 2008 CPS That's exactly what happened the second time I had to replace it on my '88 XJ. (The first time it ran perfectly right up to the day it wouldn't start.) Link to comment Share on other sites More sharing options...
BLHTAZ Posted April 30, 2008 Share Posted April 30, 2008 X2 Not the most common way for one to go out, but I have heard that exact same story a couple times now and it has been the CPS. Link to comment Share on other sites More sharing options...
offroader461 Posted April 30, 2008 Author Share Posted April 30, 2008 see thats what i thought...i already bought a replacement one and unfortunatly for me my old CPS is hardwired in so i have to solder in a new connector so i can just plug it in Link to comment Share on other sites More sharing options...
Eagle Posted May 1, 2008 Share Posted May 1, 2008 Is this for the '87 MJ? Go to the dealer and get the replacement CPS with the bypass harness. That'll give you both connectors, and the new wire that goes direct from the CPS into the ECU without going through the main harness and the C101 connector. If that upgrade hasn't been done on your truck, it's a "must have" upgrade. Link to comment Share on other sites More sharing options...
jwilson25 Posted May 1, 2008 Share Posted May 1, 2008 Do you have a part number for this upgrade? I just got my 88 Comanche this weekend and it's exhibiting similar systems. Seems to stumble, but once I give it a little gas its fine until I let it idle for a few seoncds, then gets rougher and rougher until it cuts out. Link to comment Share on other sites More sharing options...
offroader461 Posted May 1, 2008 Author Share Posted May 1, 2008 Is this for the '87 MJ? Go to the dealer and get the replacement CPS with the bypass harness. That'll give you both connectors, and the new wire that goes direct from the CPS into the ECU without going through the main harness and the C101 connector. If that upgrade hasn't been done on your truck, it's a "must have" upgrade. do tell me more about this...i havent touched this yet and would like to know about it Link to comment Share on other sites More sharing options...
james750 Posted May 1, 2008 Share Posted May 1, 2008 what years were the cps' hardwired? Link to comment Share on other sites More sharing options...
offroader461 Posted May 1, 2008 Author Share Posted May 1, 2008 I went and looked at my CPS wiring and i noticed that it goes from the sensor through the firewall directly into the computer?? Link to comment Share on other sites More sharing options...
Eagle Posted May 1, 2008 Share Posted May 1, 2008 what years were the cps' hardwired? They were never hard wired. The CPS has a pigtail about 10" long that terminates in a 3-connector weatherpack connector. Link to comment Share on other sites More sharing options...
Eagle Posted May 1, 2008 Share Posted May 1, 2008 I went and looked at my CPS wiring and i noticed that it goes from the sensor through the firewall directly into the computer?? That suggests that your truck already has the bypass harness installed. Link to comment Share on other sites More sharing options...
offroader461 Posted May 1, 2008 Author Share Posted May 1, 2008 I went and looked at my CPS wiring and i noticed that it goes from the sensor through the firewall directly into the computer?? That suggests that your truck already has the bypass harness installed. so i can just splice my new cps into those wires and solder them or should i put the connector back in but leave it running directly to the computer and call it good? Link to comment Share on other sites More sharing options...
Eagle Posted May 1, 2008 Share Posted May 1, 2008 I went and looked at my CPS wiring and i noticed that it goes from the sensor through the firewall directly into the computer?? That suggests that your truck already has the bypass harness installed. so i can just splice my new cps into those wires and solder them or should i put the connector back in but leave it running directly to the computer and call it good? The CPS has to be replaced periodically. It should be good for about 100,000 miles, but the original on my '88 Cherokee (which I bought new, if you haven't been here long enough to know that) lasted 175,000 miles and the second one lasted ... a LOT less. If you hard-wire it, every time you replace you'll be cutting the harness apart. Plus, the test for it requires unplugging it and using an a/c voltmeter, so if you solder it you can't test it. I would get the correct connector and solder that to the harness, and keep the connector on the new CPS intact. Link to comment Share on other sites More sharing options...
offroader461 Posted May 1, 2008 Author Share Posted May 1, 2008 Ok i soldered in a new pigtail and replaced the CPS and it starts up quick but immediatly begins to stumble and wants to stall...give it some gas and it just putts throughout the process and then when it quits running it blows out some smoke through my open element K&N....ANY NEW SUGGESTIONS??? Link to comment Share on other sites More sharing options...
fiatslug87 Posted May 2, 2008 Share Posted May 2, 2008 Check your EGR system? Just a thought. http://comancheclub.com/forums/viewtopi ... highlight= Link to comment Share on other sites More sharing options...
offroader461 Posted May 2, 2008 Author Share Posted May 2, 2008 i thought of that but its got all new stuff within the past year....I actually talked with a fellow jeeper here and we are thinking its the Cam Sensor in the distributor...gunna try that :roll: Link to comment Share on other sites More sharing options...
Eagle Posted May 2, 2008 Share Posted May 2, 2008 Ok i soldered in a new pigtail and replaced the CPS and it starts up quick but immediatly begins to stumble and wants to stall...give it some gas and it just putts throughout the process and then when it quits running it blows out some smoke through my open element K&N....ANY NEW SUGGESTIONS??? Does your truck have a fuel pump ballast resistor? If so, jumper the contacts and try it. The starting circuit bypasses the ballast resistor so when the key is turned to START the fuel pump gets a full 12 volts. When you release the key, the circuit feeds through the ballast resistor. That means if the resistor is broken, you can start because the fuel pump works, but as soon as you release the key you have an open circuit to the fuel pump ==> no power. The engine runs until it uses up the fuel already in the lines ... then it dies. Link to comment Share on other sites More sharing options...
offroader461 Posted May 2, 2008 Author Share Posted May 2, 2008 Ok i soldered in a new pigtail and replaced the CPS and it starts up quick but immediatly begins to stumble and wants to stall...give it some gas and it just putts throughout the process and then when it quits running it blows out some smoke through my open element K&N....ANY NEW SUGGESTIONS??? Does your truck have a fuel pump ballast resistor? If so, jumper the contacts and try it. The starting circuit bypasses the ballast resistor so when the key is turned to START the fuel pump gets a full 12 volts. When you release the key, the circuit feeds through the ballast resistor. That means if the resistor is broken, you can start because the fuel pump works, but as soon as you release the key you have an open circuit to the fuel pump ==> no power. The engine runs until it uses up the fuel already in the lines ... then it dies. No the MJ doesnt have one Link to comment Share on other sites More sharing options...
Eagle Posted May 2, 2008 Share Posted May 2, 2008 Are you sure? I know you have an '87, but some 87's were retrofitted with the ballast resistor under a TSB, and it may not be in the usual place. Does it start consistently and then die consistently after you release the key? If it does, you might try running a hot wire directly to the fuel pump just as a test, to see if it'll keep running when it's hot wired. Link to comment Share on other sites More sharing options...
offroader461 Posted May 2, 2008 Author Share Posted May 2, 2008 yea I'm almost positive it doesnt have one....I'm getting the cam sensor tomorrow and when i do that ill poke around and see if i can find it hidden somewhere Link to comment Share on other sites More sharing options...
maddzz1 Posted May 2, 2008 Share Posted May 2, 2008 If it starts consistently and dies as soon as you release the key back to run then i had the same problem. Will it stay running if you hold the key forward to start? If so then it is a bad wire behind the battery next to the fusible link. After rereading the whole post your symptoms sound different than mine. Link to comment Share on other sites More sharing options...
offroader461 Posted May 4, 2008 Author Share Posted May 4, 2008 OK...i changed the whole distributor w/ new cam sensor and it still won't run...now it just cranks :headpop: Link to comment Share on other sites More sharing options...
offroader461 Posted June 4, 2008 Author Share Posted June 4, 2008 Update: here's what ive done to try and get the MJ running... -New CPS -checked computer (good) -Changed distributor (for cam sensor) -Cleaned ALL the grounds -checked fuel pressure (38 PSI) -changed plugs -checked coil/moduale(getting spark) when you turn the key it wants to start but just won't...I am getting spark and fuel but just can't seem to get my poor truck to start..HELP!?!?!? :cry: :cry: Link to comment Share on other sites More sharing options...
87ComancheLB Posted June 4, 2008 Share Posted June 4, 2008 If it used to at least run before you did the distributor swap, but now just cranks over sounds like maybe your timing is off, since your getting fuel and spark. Did you check for cracks in your exhaust manifold also been known to cause stalling problems. Link to comment Share on other sites More sharing options...
ejndssn Posted June 4, 2008 Share Posted June 4, 2008 would like to know if this is the original eng non over haul with many miles if so could the possibly that the timing chain has got some slack in it and jump a tooth or two. This similar symptom had occurred with a v6 eng I had a long time ago and I did every thing under the sun to correct :brows: when someone mention the chain may have gone slack and jumped. :hmm: Just a thought one way to check is to loosen the distributor retainer bolt so that you can move the dist left or right and see what kinda results get Link to comment Share on other sites More sharing options...
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