Jeep Wont start
- Thread starter prescotte
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69jeepcj
New member
Check your ignition control module. You mentioned you have fuel and air, but didn't mention spark? pull a plug and connect it to the plug wire and lay, tape, or hold the plug tip to a metal ground and crank the engine, you should see a small spark at the plug if its firing, (use insulated pliers if you hold it to the ground). If no spark, I bet its the control module.
greg92jeepxj
Official Supporter
No question about having to check for spark . As long as the injectors are firing , fuel pumping , guess you got fuel . Are you finding fuel saturated spark plugs ? Incidently , the PCM fires the coil on your '91 , controls advance and retard ( ignition timing ) . If all went well with the PCM flashing , and PCM is said to be good , you will have to test crank and cam sensors .
Control modules are to blame many times , but were used on '90 and lower ( AMC Renix ) .
Did jeep install a dura spark ignition and distributor ? Did someone else ? But at least perform tests to the two sensors (cam & crank) as they are big ticket no start items next to PCM's as they provide important feedback to PCM . I had a no start on my '92 XJ about ten years ago and would up being an internally shorted PCM . It wasn't making a hot enough spark to start in freezing temperatures . That is not the case now , but there is a possible break in communications with the PCM and the two previously mentioned sensors are ripe to be checked . Best of luck to you and post any further questions as you like , we'll do our best to .
Welcome to Jeepz.com and thank you for your posts and joining the forum.
sorry , don't forget the MAP sensor too as advised , it feeds back important info to PCM on start that can contribute to hard/no start as well .
Control modules are to blame many times , but were used on '90 and lower ( AMC Renix ) .
Did jeep install a dura spark ignition and distributor ? Did someone else ? But at least perform tests to the two sensors (cam & crank) as they are big ticket no start items next to PCM's as they provide important feedback to PCM . I had a no start on my '92 XJ about ten years ago and would up being an internally shorted PCM . It wasn't making a hot enough spark to start in freezing temperatures . That is not the case now , but there is a possible break in communications with the PCM and the two previously mentioned sensors are ripe to be checked . Best of luck to you and post any further questions as you like , we'll do our best to .
Welcome to Jeepz.com and thank you for your posts and joining the forum.
sorry , don't forget the MAP sensor too as advised , it feeds back important info to PCM on start that can contribute to hard/no start as well .
greg92jeepxj
Official Supporter
Don't feel bad , I had to double check myself , but I remembered that my '92 was a close year to when Chrysler wrote the 2nd testament to jeep , who wrote the book on four wheel drive . My dad had an '89 XJ once and I forgot the dividing year when Chrysler took the helm . But you know jeep and AMC , Chrysler still picked from AMC parts bins. My brother once remedied an early '90's XJ with AMC PCM , ign. Module , distributor and engine harness . I thought it was factory he did so good .
Hesitations bug me and he tore out the Chrysler system for a shorted PCM and utilized salvage AMC parts to get his girls jeep going. I wonder if electrical grounding is playing tricks on these jeeps that are growing in numbers of the same complaint.
I think if they are to solve their hesitation problems , they must go back to basics . As you guys have always said , and I agree , check and clean grounds and all electrical paths . This may be the key , but at least there will be grounding and continuity.
Thanks for your post , I appreciate the hard work and effort brothers like put in to our forum. Thanks again, greg
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greg92jeepxj
Official Supporter
The cam sensor on your 4.0 ltr. is located inside the distributor. It replaces the ignition module we're used to because the PCM does all the work an ignition module did and fed back to the ecm or PCM . Now , the cam and crank sensors feed back and the PCM makes corrections from PCM's programmed fuel map that is calibrated for performance , emmissions and economy which controls injectors and ignition coil . Short answer , in the distributor.
greg92jeepxj
Official Supporter
I would like to suggest however , that the crank sensor be tested first as it is easier to test and easier to replace , although anyone who has removed one will beg to differ. The CPS is mounted on transmission bell housing on driver side position . You can just see it as you locate the wiring harness to it. Getting it off requires creativity ( some choice words are helpful ) and a LONG extension and swivel. You can try a gear wrench , but I think you will find it easier from under neath with a long extension. To test , unplug the harness and hold the CPS plug connector prong twelve o'clock so terminals are in a triangle . Top terminal is A , lower left is B , and by process of elimination , lower right is C . ( don't mind my humor, I figure by now you may need to laugh to stifle the no progress aggravation ) . Read terminals A & B with an ohm meter. Reading should be no resistance . Any other reading is said to be faulty. If uncertain of your results , record them and go on diagnosing . Resist parts changing until all testing is exhausted . It's happened before. You know , " yeah that's it ! Going to change it and its going to start ! " . Ever had your heart broken this way ? We would rather get all the testing done before you go to the parts store and waste time with unneeded wrenching . What if you find more wrong ? This kind of diagnostics requires not just finding what is not good , but WHY IT DOSEN'T START . Test everything on the list , research your results with specifications and then make decision , what to replace first as sometimes its process of elimination . People have swapped out ignition modules swearing that is always why a car won't start only to find later a bad pick up coil or Hall effect switch , for example. Don't rush , you'll find it. This is not the first jeep that did not start in the last thirty days . Keeping cool and staying in the game will get it running . Will post more on cam sensor.
Its a bit more technical .
Its a bit more technical .
greg92jeepxj
Official Supporter
To check the cam sensor : this is from my 1992 Chrysler factory shop manual , 1991 should be similar . Be prepared to back probe distributor wiring harness with a voltmeter (computer safe , ten mega ohm impedance) . Positive test lead to grey/black wire & negative test lead to brown/red wire set to 15 volt scale. Remove cap and rotate until PULSE RING ( what rotor attaches to ) enters SYNC SIGNAL GENERATOR (cam sensor) . Ignition on , should read 5 volts. You may have to manipulate engine to be sure of pulse ring and sync entry , continuously looking for voltage if not found first . Make certain of voltmeter lead contact connections . If voltage not found , check for voltage at a white/black wire (supply wire). If voltage still not found (put down that sledge ! I was a small block guy too ) , check pin 7 and ground on PCM with PCM harness connected. Harness connector supposed to be numbered with microscopic numerals (lol) , they are , I've seen them. Hopefully voltage found now, but this would mean cam sensor is bad . FUN ! Now you get to disassemble the distributor ! Well , at this point it's between the distributor and PCM so we want to be certain of our measurements. Hoping for your sake the PCM good and cam sensor good . Injectors firing and fuel pump working is a good thing but I went through once and my jeep started above freezing but not below. How convenient. PCM was bad . If I had to choose what to wish on you ( only because I like you because your a small block guy ) , it would be the joy of changing the crank sensor . Their not too bad , just hard to reach on xj's , not sure of the six banger in wranglers though . I'm keeping my fingers crossed for you , members got other members jeeps started , yours should be fine. Crank sensors are more typical than cam sensors , did not hear of many cam sensors bad myself. Really wishing best of luck as I have a personal problem with no starts , I HATE THEM ! I WISH THEY'D DIE ! Just kidding , I went through one too many no starts and while good for your own edification , not good to the neighbors ears , Sundays included . On a serious note , don't give up , I know you got experience . You will kick much butt . Post when you can , I take personal interest in these posts of no starts , I'm sadist like that . Hoping for good news soonest . Greg
P.S. - ever think of putting a small block in a YJ ?
P.S. - ever think of putting a small block in a YJ ?
greg92jeepxj
Official Supporter
Hey , forgot to mention , a month ago you had that PCM and harness plug issue , how did that work out ? Sounds like you got somewhere but wiring from PCM harness plug checks out ?
you said you got fuel I'm thinking that went ok . Just that I'm trying to get a history going on this. I'm sure you took an ohm meter to the wiring .
you said you got fuel I'm thinking that went ok . Just that I'm trying to get a history going on this. I'm sure you took an ohm meter to the wiring .
I've thought long and hard about a small block swap. The motor mounts are cheap and easy, and finding a transmission to pair to a Chevy block is easier than blinking. But that's all a matter or building some cash to do it. I can't stand working on these early EFI jeeps compared to my last 355sbc. It was so simplistic and so stupidly easy to modify, that this just ended up ****ing me off and throwing me in a state of disgust for the jeep. But, I must carry on. Th stock wiring harness didn't get eaten up as bad as a thought when I found the ECM melted. It had one spot, and it scraped off and all the terminals are clean. I'm having a huge issue with the sensor testing. I was told by a jeep specialist in the area to check voltage coming off the ECM to the sensors, but all of them are coming up as zero volts. No clue if that's bad, or if im even doing the right thing. I'm gonna check the cam sensor in the morning. But if I can't get this thing to work right, I'm gonna set in a blaze where it sits.
Not really. I'm taking it to a mechanic. Im so irritated with the wiring that I'm just gonna shove it offthe to the pro. I'm friends with the guy, so hopefully he won't screw me and just do what needs to be done. Really appreciate all the tips and advice. If I had more patience, I'm sure I could have put it to use a little better.
Not really. I'm taking it to a mechanic. Im so irritated with the wiring that I'm just gonna shove it offthe to the pro. I'm friends with the guy, so hopefully he won't screw me and just do what needs to be done. Really appreciate all the tips and advice. If I had more patience, I'm sure I could have put it to use a little better.
greg92jeepxj
Official Supporter
I totally understand the cash situation . That is why I currently do not yet own a cj5. But I hope to change that soon . I will admit that dealing with the earlier generation obd 1 leaves much to be desired as I've been there and I share the pain . The only thing that kept me going was to take a step back and look at my jeep and decide why I went for it in the first place. Or else I would have parted with it. It's running ok now and has not been a problem for quite some time.
i even got the a/c working again. But I still dream of the cj5. I would hope you can still feel the same for your YJ , as long as the body , chassis , power train and drivetrain are good , I know you can beat this chop breaking(really want to say something else) problem . Your no amateur , you know how to wrench. As soon as you beat this down, it will be running and you can feel good about fixing it up to where you want it in the first place. I had to literally ohm out every wire coming from the PCM to check for continuity and shorts , I knew they should have been ok , but should have was not getting my truck started below freezing. I went as far as I could myself , but when the digital display on my meter froze , I cried uncle and took it to the dealer. I figured out all that was wrong , but I needed to be sure before I had to put more money into it. I can list the parts , but no use in that . I learned that we can do the same job they can for less money. Just takes us longer because we don't have the diagnostic tools they do. But we can get it done anyway. I feel if all your wiring is ok , it can carry signal from sensors to fuel system and ignition system and run . I know I am speaking out of terms as it is not me pulling my hair out , but I believe if wiring is good , the problem is what's plugged into it that is. It makes it that much easier to diagnose . If fuel system checks out right up to the injectors , it can very well be the cam or crank sensor since they are common . It's possible that since those two sensors which play a part in the synchronization of the injector firing order and ignition firing order , that communication with PCM is out of sync or not communicating at all resulting in a no start . It may be that simple. If its a pain to change one or the other sensor , at least we know what the cause is . I now you will take great comfort in that . Sorry for this major hassle. If you really feel it needs more diagnostic check than we are capable of , I will respect your decision. Just your statement of the wiring makes me feel there is more than I am aware. All I can say is that each sensor is supposed to receive 5 volts from PCM , if not , relays and fuses need checking. Hate to see you pay out if you can do it yourself , but when you are at wits end, all focus is gone, I concur. I got a 1992 Chrysler shop manual if you need procedure and specification , let me know should you decide to go that route. Wishing the best for you and hope all works to your favor.
best of luck brother ! Greg
i even got the a/c working again. But I still dream of the cj5. I would hope you can still feel the same for your YJ , as long as the body , chassis , power train and drivetrain are good , I know you can beat this chop breaking(really want to say something else) problem . Your no amateur , you know how to wrench. As soon as you beat this down, it will be running and you can feel good about fixing it up to where you want it in the first place. I had to literally ohm out every wire coming from the PCM to check for continuity and shorts , I knew they should have been ok , but should have was not getting my truck started below freezing. I went as far as I could myself , but when the digital display on my meter froze , I cried uncle and took it to the dealer. I figured out all that was wrong , but I needed to be sure before I had to put more money into it. I can list the parts , but no use in that . I learned that we can do the same job they can for less money. Just takes us longer because we don't have the diagnostic tools they do. But we can get it done anyway. I feel if all your wiring is ok , it can carry signal from sensors to fuel system and ignition system and run . I know I am speaking out of terms as it is not me pulling my hair out , but I believe if wiring is good , the problem is what's plugged into it that is. It makes it that much easier to diagnose . If fuel system checks out right up to the injectors , it can very well be the cam or crank sensor since they are common . It's possible that since those two sensors which play a part in the synchronization of the injector firing order and ignition firing order , that communication with PCM is out of sync or not communicating at all resulting in a no start . It may be that simple. If its a pain to change one or the other sensor , at least we know what the cause is . I now you will take great comfort in that . Sorry for this major hassle. If you really feel it needs more diagnostic check than we are capable of , I will respect your decision. Just your statement of the wiring makes me feel there is more than I am aware. All I can say is that each sensor is supposed to receive 5 volts from PCM , if not , relays and fuses need checking. Hate to see you pay out if you can do it yourself , but when you are at wits end, all focus is gone, I concur. I got a 1992 Chrysler shop manual if you need procedure and specification , let me know should you decide to go that route. Wishing the best for you and hope all works to your favor.
best of luck brother ! Greg
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