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New issue. I’m going insane

C

Club31XJ

NAXJA Forum User
Location
Canyon Lake
Ok previously on my 1991 jeep xj 4.0 with auto trans I had a no spark issue. I changed the pcm because I found that to be my problem. Now I’m getting good spark and I’m getting fuel but the damn thing still won’t start. I’m driving myself nuts


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The pump will prime as soon as the key is turned to run, but won't really make sufficient pressure for a start until the pump starts back up during cranking. Worth a look, but unlikely to be your issue as the ASD relay fires up the pump, spark, injector power, and alternator power during cranking, as long as your sensors are all behaving. Or in other words if you are getting spark during cranking you are also likely getting pump power.

Make sure you are getting fuel pressure during cranking. If you are we can work from there.

One quick check is to spray a little Ether (quick start) down the TB and see what happens. Look down the number two spark plug hole and see if the piston top is covered in fuel, you may be flooded. Note be careful with Quick Start, too much can cause flame back issues or worse. Whatever you do don't look down the TB while cranking.
 
When we were cranking we had 39-42 psi. I’m thinking I might just be flooded. Poured fuel in the TB thinking that maybe I wasn’t getting fuel but looked into the TB and see a puddle sitting in there. So I have a feeling there is too much fuel in there.


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Holding the Gas pedal at WOT, to the floor, while cranking will let the engine breath and dry our fast, while telling the PCM to not open the injectors (stop adding fuel). When it fires, keep cranking if it dies, for a few more seconds. Then try a normal start process.

Also make sure the Cap and rotor are not bad, make sure spark is getting to the plugs, not just to the cap. Make sure the rotor is turning while cranking.

And ask why the PCM went bad????
 
I know a few folks who use WD-40 instead of starting fluid.

If there is air, spark and fuel pressure, then injectors firing signal and timing would be the next variable. Timing shouldn’t be an issue unless something else was changed or distributor broke, or the cam position sensor in the distributor is bad. Both Can happen but are less likely.

If the cylinder pressure are under 100psi then it’ll never creat enough pressure to start. Another possible but less likely problem.

Were you able to replace the original PCM with a same number unit or at least out of a 91-92 4.0 auto? I think you said you had found one a few days ago after testing with a 1995 pcm.


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I am using a pcm specifically for my my 91. Got it from rock auto. The distributor is new, spark plugs new, wires new. I’m getting a good strong spark from the coil and the distributor to the plugs.


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are you feathering the gas pedal while you try to start it, i am not too familiar with the older pcm, but on the newer ones i have worked on, when ever i started with a cleared pcm the jeeps will not run without manipulating the throttle, once i take it around the block it will idle finally, and will smoothen out over the next several restarts,

also hate to ask but are you 100% sure you installed the distributor correctly?
 
Haha it’s ok to ask. Yes I installed the distributor correctly. Cylinder 1 was top read center and rotor is pointing at cylinder 1 spark plug wire


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Ecomike said:
Holding the Gas pedal at WOT, to the floor, while cranking will let the engine breath and dry our fast, while telling the PCM to not open the injectors (stop adding fuel). When it fires, keep cranking if it dies, for a few more seconds. Then try a normal start process.

Also make sure the Cap and rotor are not bad, make sure spark is getting to the plugs, not just to the cap. Make sure the rotor is turning while cranking.

And ask why the PCM went bad????
Click to expand...



I think what fried it was a couple things. The other day my battery died while camping and I used the rangers battery charger and started the jeep while the charger was still hooked up to it. Also I found bare wire on a few different places (yes I properly repaired them before installing new pcm) and also water damage.


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TDC on compression or on Exhaust?

Water damage???? Water is know to kill the TPS...

Have you tried holding the Gas pedal to the floor and cranking until the entire system is UNflooded? Then do a normal start??? I had a bad IAT/MAT Intake temp sensor cause no starts like your having.

Are the injectors clicking???? Firing??? If not the Dizzy Cam sensor (1991 ?) may be bad??? I think starting in 91 the Cam sensor in the Dizzy, had to be good to fire the injectors???

Is it trying to start are all?????

Club31XJ said:
Haha it’s ok to ask. Yes I installed the distributor correctly. Cylinder 1 was top read center and rotor is pointing at cylinder 1 spark plug wire


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Click to expand...
 
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