Help, another that won't start

[jeeepxj]

94' YJ 4 banger. No spark, but I've got good voltage to the coil. Tried new coil, and same thing. Tried known good coil from another Jeep, and same thing. What tells the coil to send a spark, if it's already got supply voltage?

Thanks for any input.

Craig

[jeeepxj]

Nobody out there with any input? The check engine light apparently doesn't work either, so I can't pull codes with out a scan tool.

[Rock WoRM]

when it comes to electrical, I know zip. :bangtard:


but... this "IS" my pat. answer to this kind of Q., cause it happened to me.

double check the little 15 amp ignition fuse on the main fuse block under the dash... if its blown, the dumb thing will turn over but not fire :D

I was told by a shop who fixed it for me that it controls the fire, AND the fuel pump and reverse lights... all on the same circuit :werd:

note: this is what I was "told", so no flameing if someones knows different! :hah:




WoRM :bsod:

[jeeepxj]

Yeah, fuses are definately a great place to start. I've already checked all fuses in the dist. box under the hood and the dist. block under the dash, several times. All is good there. I've even went as far to check the "load" side wire of the ignition and comp. circuits.
Any other thoughts out there?

Craig

[jeepincj78]

I only have experience with the 4.0ho, but I beleive your problem may lie with your crank position sensor. This is what tells your computer to actuate the spark.

[eljeepo89]

I'm having the same problem with my '89 2.5 4 squirrel...i tried a new ignition coil, no luck. i tried replacing tons of vaccum lines, thinking it wasnt getting fuel, no luck. i cleaned my little crank postion sensor, but didnt get a new one. it started after the cleaning, but then died. Next ill try pushing it into the grand canyon, and buying a different jeep.

[jeepincj78]

You can try cleaning the sensor all you want. If it has an open circuit or has a lot of resistance it will not operate correctly.

[crapshot]

if you know you have spark that tells you the crank sensor is ok. without the crank sensor while cranking you wont have spark or a rpm signal. If you have both the only other thing is fuel. Thats providing you have a good spark and not a weak coil or low compression. Also a map sensor thats out of range can also not add enough fuel to do a cold start. try pouring a little fuel down the tbi throat to see if it tries to start. this all will give you a direction to go. If this all fails its possible you have a bad computer thats why you need to get the check engine light to work. It may be just a burned out bulb but the burned out buld is not the reason it wont start. Also a clogged exhaust system could cause a no start but it would at least try to start then die. This is the extreme for a clogged exhaust.
CA Smog Tech

[eljeepo89]

well i dont know what i did, or why it runs, but ill be damned if it doesnt start up like nothin ever was wrong. i replaced the coil, and it didn't work, so i put the old coil back. when i tried to take the "new" coil back to pep boys, they saw right through my story of "I never even installed it, those screw marks were there" and they would not take it back. So i put the "new" coil back on, let it sit overnight, and came back the next morning and drove it home! wierd!!I hope i didnt jinx it by writing this...

[eljeepo89]

well i jinxed it. today it doesnt run. No spark to the plugs, but it ran this morning when i drove it to my parking spot. and none of the crap parts stores around here carry the CPS, and if they order it, it doesnt come in. BAHH!!!!

[jeepincj78]

Did you try the dealer??

Frank

[eljeepo89]

I just ordered the CPS off Quadratec.

[crapshot]

You know its easy to tell if the crank sensor isnt working. What it does is tell the injectors and or coil to fire Its used as a reference point. It sees the notch in the flywheel to know where # 1 is. If you have spark on the negative side of the coil ( a pulse, on off ) then its working. Or just have a friend hold a sparkplug. If he gets pissed you know the coil and CPS are working. If not and your not getting a pulse off the coil but you see wetness on the plugs or you use a noid light on the injectors to see it thier pulsing , all this point to a bad coil. Or an ignition fuse. A test light can be used on all of this. Use a needle to pierce wires and then just check the needle for voltage. The bottom line is no voltage at the sources points to a open somewhere before that point. In most cases when you have voltage at the injectors and at the coil then its pointing to the computer. It may just be brain dead. If no voltage only at the injectors then its most likely a bad quad driver in the computer if all else checks out. The quad in the computer is what turns on the injector. What we do is check resistance on all wires to be sure you do not have an open, both ground side and power. You could go to autoshop101.com and learn about how everyhing works Its free and could save alot of headaches in the future.
ASE Smog Tech
Remembered you stated you have voltage at the coil. to be sure the ground side is working touch the test light to pos and neg of the connector unplugged. You need or do a quick. bridge the connecters as quick on off as possible. if you get a spark you know the ground side is ok too. this is where a test light comes in handy. If the light lights up you know the circuit is ok and you wont pop a fuse. Now if you have fuel and power to and ground return its most likely going to be a module problem. They can work intermittantly when going out. This will prevent spark at the plugs.

[jeeepxj]

Still no luck on getting my rig started.
Anyone know where I could get a computer besides the stealership?

Craig

[lessthanchris1]

did you throw in the new CPS? or did it not come in yet?

[jeeepxj]

did you throw in the new CPS? or did it not come in yet?


Yes it has a new Crank Position Sensor.

Is there any way to "check" the computer, before I drop over $200 on one?

Craig

[jeeepxj]

Well, a buddy let me borrow a computer from a 93' YJ and after cranking for a few seconds it finally started. I guess I'll be ordering a comp. from Rock Auto.
Thanks for the help

Craig

[lessthanchris1]

use the computer for a while to be sure (unless he needs it back) :) It sucks guessing and changing $200 parts!