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find the needle


markthehermit's Avatar
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02-10-04, 03:31 PM   #1  
find the needle

I have a 95 jeep cherokee, straight 6 cyl. engine, 4 speed auto trans, AC, 2 WD , with car alarm (viper 100, i bought it used this way) What it does is stall unexpectedly. It can stall
3 times a day or not at all for a 100 miles. Ignition power is totally gone. sometimes it also "twitches". ignition interrupts briefly (less than a second) and if you`re still rolling and the trans still in gear it will go on just fine. Other times you have to restart the engine.
sometimes it will restart right away, sometimes it will crank but not ignite for up to 20 min. , sometimes it wont even crank (turn over). I have visually checked all the wiring i can get to, I have tugged on wire harnesses, i have shaken the car while running, drove over bumpy roads to try to make it fail, I have checked all sensors one can check with ohmmeter.I sent the computer in to test, it tested fine. There is no difference in going uphill, hot day, cold day, cant find a character situation it breaks down in. what troubles my brain is the different fail symptoms in trying to restart it, sometimes it wont crank over for hours, then suddenly everything works fine. I`ve disconnected the car alarm, even though there is what looks like a factory anti theft installed also.
I`ve had it diagnosed at an automotive shop, it didnt fail for the day they had it, so no results.
I am currently clueless, any help will be greatly appreciated
has anyone had a problem with a jeep like this before, i wonder ?

 
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davo's Avatar
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02-10-04, 04:09 PM   #2  
Did you remove the alarm and all it's wiring and patched the damage it caused to insulation?That would be step one unless you have a loose battery cable at either end not just the battery.

 
Manic Mechanic's Avatar
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02-10-04, 04:47 PM   #3  
Manic Mechanic
I have had personal experience with the Crank Position Sensors on these Jeeps that will act just as you described without throwing codes or any kind of warning signals. It's a bit of a pain to replace, but not too difficult even for a DIY'er.

The other culprit is the ignition coil. On some of the older models, like yours, as the coil ages it will break down with heat and cause problems. I know your vehicle is a Cherokee but a TSB was issued for Grand Cherokees stating that the coil should be replaced with a "low resistance coil with an external resistor". Some guys go as far as relocating the coil on the inner fender to prevent any further problems.

My $0.02

 
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02-10-04, 05:17 PM   #4  
What manic says is entirely possible but if it is indeed the crank sensor dropping out then you likely would also be losing injector pulse along with spark. A noid light could determine that. If it is only spark that you are losing, then the ignition coil or ignition module are likely. The way to isolate between those 2 is to check for pulse at the negative side of the coil. No pulse indicates ignition module assuming you have injector pulse at that time.

 
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02-10-04, 06:33 PM   #5  
I had similair problem with a Jeep. My problem ended up being the crank position sensor was loose. I just tightened up. Only one difference my jeep would always turn over, just wouldn't fire all the time.

 
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02-10-04, 11:12 PM   #6  
mike from nj
i have seen a few crank sensors go bad too, usually with no codes either. these usually won't start at all though.

like stated, it helps to find out if you have injector pulse or coil pulsing too---or not. it will eliminate a few things.

 
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02-11-04, 11:56 AM   #7  
thanks for the quick response everyone. I`ll start replacing the coil and then checking pulse, (when i can get it to fail), I`ve already replaced the pickup coil on the distributor,didnt help, also this car doesnt have an ignition module (according to repair manual), I assume the comp. interrupts to create the spark.
what is a noid light ?
thanks for the hints, by the way it would still not explain why it sometimes wont crank at all (turn over).
does the comp. turn on a relais to power up electricity for the starter solenoid ?, what else could be interrupting power to the starter to prevent cranking ?

 
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02-11-04, 12:18 PM   #8  
Originally posted by markthehermit
by the way it would still not explain why it sometimes wont crank at all (turn over).
does the comp. turn on a relais to power up electricity for the starter solenoid ?, what else could be interrupting power to the starter to prevent cranking ?
That's another whole problem.

Are you sure there is no ignition module?

 
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02-13-04, 08:55 AM   #9  
module

the autopart store computer states there is no module for this year cherokee jeep installed, the haynes manual says it is in the distributor under the pickupcoil, but it includes all years from 90 to
97, I looked but none there, it also states that in some years it was sandwiched behind the ignition coil, but have`nt seen it there either. I`m gonna replace ign. coil & crank sensor this weekend and see what it does.

 
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02-14-04, 11:37 PM   #10  
mike from nj
no ignition module

asd relay powers the coil, pcm grounds it.


i'd be looking at the mickey mouse alarm you have for the intermittent no-cranking condition.


there's that word again----'haynes' manual

 
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02-15-04, 04:50 AM   #11  
A Haynes manual is a kind of generic give you enough help to get you in trouble book.A oe manual is best even though they are pricey so is replacing uneeded parts.I told you and now Mike has to suspect the alarm.Disconnecting the alarm means removing it not just unplugging something.I get aftermarket alarms with shorts to ground alot because it was not installed properly and face it they are junk anyhow.So as I said before remove the alarm and all of it's components(including wiring)before you continue.If it doesn't correct the problem you can reinstall it.

 
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02-20-04, 01:43 PM   #12  
success

after fiddling around some more with alarm wiring and still no good results, I replaced the crank sensor or flywheel sensor and it magically fixed all the problems. It runs good with no twitching or stalling for 3 days now. The comp never threw any codes towards this sensor problem, which made it kind of hard to find. I also so far havent had any "no crank" condition come up, is it possible the comp blocks power (via asd relay?) to the solenoid , if its `confused` about the engine speed/position ?.
Thanks a lot for the correct hint to all of you who helped me find this glitch. Its a bummer the car manufac. guys cant make it foolproof enough to really have the comp do a thourough job on error reporting.
Thanks again

 
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02-20-04, 03:16 PM   #13  
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Glad to hear it worked for you.

 
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02-22-04, 09:56 AM   #14  
mike from nj
Re: success

Originally posted by markthehermit
Its a bummer the car manufac. guys cant make it foolproof enough to really have the comp do a thourough job on error reporting.
Thanks again

they did, and it started with model year 96. (OBDII)

picture what your home computer was like back in 95, then you can picture the (lack of) technology under your hood. cars produced today are as every bit as fast as your home pc, and with communication networks as fast as a cable modem.

 
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02-22-04, 03:11 PM   #15  
Computers can only report facts that it's been programmed to monitor. That's why you still need us. Too many people thing the computer does all the diagnosing for you. It just gives you data and the tech has to analyze that. We don't go to a million schools for nothing.

 
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