zum14

So this all started about a week ago. Was driving home and everything was fine. Started pulling a hill around 2200-2400 RPM and it basically acted like someone shut the key off for a split second. Then gone. Next day it was running fine, then found that it would buck, fart and cough at 2200-2700 RPM. Like someone was turning the key on and off cutting in and out. Running below these RPM's it pulled great, if you held on and forced it above the 2700RPM it would run great too. So got it to my work, pulled the distributor cap and found the terminals pretty crispy. Only a year old. Ok, none in stock so tried cleaning up the terminals. Started. Made it down the street, then had to turn around because it was cutting in and out and farting at all rpms. Got to the shop and stalled. Anytime started after that it would just fart and stumble. If you play with the throttle at all itll pop and stumble and really doesnt want to rev up at all. Got the new distributor cap and rotor on. Ran great for 15sec and then same problem. I tried a known working coil, wires. Spark tested coil. ok. Spark tested at plugs ok. Changed crank position sensor. (got a bad spec off the net) No change. Checked fuel pressures, within spec. Checked throttle body and IAC. Cleaned. No change. Checked wiring from cam position sensor, crank position sensor, ecm power and grounds ok, checked the supply voltage to the sensors as its a shared supply, found 9V with the sensors unplugged and key on, thought it was ok as the wiring diagram says its an 8V supply but the test for the cam position sensor says the meter pulse to around 5V and when you back probe the plug with the sensor plugged in there should be 5V supply on the same wire. The only test I hope to do tomorrow is the cam position sensor with the analog meter but if the engine is starting (doesnt really run after) but still starts tells me the sensor is sending out a valid signal to start. The only thing I can think of is either slipped a tooth on the timing chain or ECM. Anyone have ideas? \Also slightly concerned the Alldatadiy manual is only for non HO engines. The other thing that has me and a friend sratching our heads is that it was progressive. Would only do it within a certain rpm. Then after cleaning the cap terminals it got worse. Any help would be greatly appreciated.

BuckB91XJ

When you tried the known good coil, did you swap in the coil "AND" ignition module or just the coil? A bad ignition module can cause this problem.

freegdr

what about tps and map senor i have a 89 what kinda ignition ke do ypou have i now you just went what the hell does that have to do with it if you have a chrylser key you can check codes with out a scanner

zum14

Just the coil as its out of a different vehicle but same part number. Dont have an ecu to try and trying to determine if its the actual problem before i drop the 300$ it is for one here. Might check the wreckers if i dont find any other problems.

Sorry i should of mentioned there are no codes on the ecu related to the problem.

freegdr

what about the tps or map sensor did you read the codes

zum14

The reason we didnt think it was tps was that the jeep was driving around fine before as long as you stayed out of the 2200-2700RPM range. Not sure how tps could cause an rpm related problem but nevertheless i will check it out tomorrow with the map. The only codes on the ecu 12,33,35 which is 12 batt disconnect within last #? keyoffs. 33 and 35 are to do with a/c.

imehtoh

mine did the same thing.was the coil causing all the problems,got a new 1 relocated it away from the block, cooler location,no more problems.

freegdr

tps read position oh throttle plate sending signal to ecmif its not reading prop in that range could affect fuel supply or spark causing rpm drops gotta check it all you no

1992jeeper

Just for the record, I found out the hard way. You can have sufficient fuel pressure to your fuel rail, but that doesn't mean you have the correct quantity of fuel coming into the injectors. I found out that I had plenty of pressure in my fuel line but because the hose came off inside the tank I didn't have the correct supply of fuel. Just a suggestion but you may want to pull the pump, and check it! also, get a can of WD40 and spray your vacuum lines and see if you have any vaccuum leaks. don't forget the brake booster vacuum line! let me know if it helps.

zum14

Scoped the throttle position sensor. Works smooth all the way through from idle to WOT with no dips in voltage.


If that were the case you should see a drop in fuel pressure when trying to run, we have watched pressure while running and no drop. Also have tried pinching the return line to check pump output and pressure spikes over 80psi. If a line was off it would of leaked then. Thanks for the suggestions.

Ive also scoped the cam position sensor (CMP) and am seeing movement from 0V to 5V. Its about as inconsistant as the engine is running but its still putting a signal out and then engine is still running, telling me the sensor is good. Starting to run out of things to test.

Hommersimpson

sounds like a ignition problem... hit the junk yard get a used distributer... ecm...and anything eles you can get for a few bucks...
Have you shut the key off right when it happens... and pulled plugs to see if they are wet ? Like if its ignition and it just pops then dies..like you discribed as someone turning key off.... turn key off right then... pull plugs ... if they are wet then its prob a ignition problem..
might have a valve burning.. but im kinda doubting that... timing chain.. have you checked to see how much slop in chain ? you can rock the slop back and forth and use the timing marks to see how many deg of slop you acually have.. but usally they break or slip beyond running right at any rpm....

20 years ago.. we had a magneto that you could hook to battery... plug the mag wire into the dist and turn it on.. would run a constent spart... elementating everything in the ignition system except obviously the wires and cap... but it sure helped when it came to problems like yours... in 5 minuts you new if it was spark or fuel problem...

freegdr

what about module under dist cap is the connect corronedis under the rotor

zum14

That would of been sweet in this situation. The pattern on the cam sensor and crank sensor seem good. We even hooked the the scope to the signal wire on the coil and its firing. Its hard to tell as its not a consistant rpm but it is signaling it. We cycled all the injectors and were checking supply voltages when cycling the auto shut down relay. (have a reader to do all this) Ive got a compression tester to test it tomorrow to see if its slipped a cog. (should be low) Im not sure anymore.


Not sure what your asking here?? Cap and rotor are new.

Hommersimpson

in the distributer there is a modual..... it can go bad...is what hes talking about ^^^ up there

freegdr

thats it tke off the rotor see the electric plug thats either a pick up coil or module my 94 xj just stopped one day the connector had rotted went to napa put in new one away i went