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-   -   91 YJ 4.0 6 cyl No spark won't start (http://www.jeepforum.com/forum/f12/91-yj-4-0-6-cyl-no-spark-wont-start-1526450/)

737Jeep 05-21-2013 03:47 PM

91 YJ 4.0 6 cyl No spark won't start
 
No start and no spark. A couple of months ago I had no spark and no fuel pressure/fuel pump. Mysteriously started running again till now.

After searching the forum I replaced ignition coil, crank position sensor and ECM with no change. Engine turns over and I can hear the fuel pump come on but no spark. Next I'm planning on a new distributor and cam sensor. Any ideas? I'm especially interested about testing the wiring if the distributor and cam sensor don't work.

Que89YJ 05-22-2013 06:36 AM

Check your fault codeas and dont throw parts at it. Troubleshoot it.
http://www.jeepforum.com/forum/f12/h...codes-1257145/

Post what you find. There are a couple pontential issues that are common.

737Jeep 05-22-2013 01:59 PM

Thx Que. I checked the fault codes as soon as it quit running. #'s 12 33 55. Pretty standard and didn't tell me much. I've been reading topics on the forum and the 3 replacements seemed most likely the cause.

As for trouble shooting. With the ignition on I get the CEL light, shift arrow and the fuel pump comes on. It cranks fine but no spark. There is pressure at the fuel rail is good (depressed the shrader valve and had fuel squirt out) but I haven't hooked up an actual pressure gauge. On a side note this same problem was intermittently occurring with no fuel pump coming on (no pressure at the fuel rail) with the ignition in the on position.

Last night I did get it started retrying the new ECM. And just for kicks I tried the old ECM and of course it started as well. Tried driving around the neighborhood twice and both times (different ECM's) it stalled like it ran out of gas. Pushed back home and it hasn't started since.

I'll take any suggestions for trouble shooting. I'm new at this and not sure where to start.

Que89YJ 05-22-2013 03:21 PM

Two possible things. Check and make sure you have power to the coil when it isnt diving you spark. You can try hooking up power direct from the battery to the coil next time it doesn't give you spark. The other is what you mentioned. The pickup cam sensor can be replaced by itself our get the entire distributor for 25.00 more. I recommend the whole unit.

737Jeep 05-22-2013 03:43 PM

Thx again Que. I'll check for power to the coil. How do you hook directly up to the battery?

I've checked all the fuses in the Power Distribution Center and the accessory fuse box in the cab. All check good. I'm also getting 12.6 volts (same as battery voltage) at the dome light fuse and 12.25 volts at the Ign-LPS fuse with ignition on.

I also checked the wire harness/plug to the ECM at pins 3, 9,11,12. Pin 3 (main power) was hot at 12.6 volts. Pin 9 (ignition sense) was 12.25 volts with the ignition on. Pins 11,12 (main grounds) had good continuity to ground.

Que89YJ 05-23-2013 06:13 AM

Just jumper power with a wire 16 ga. or bigger from the battery positive to the coil B+ feed. I think it's green/red. If it does start then we can back trace the power issue. If it doesn't then it is probably the distributor pickup. If you have a test light hook it up and check power then hook it to the ground side of the coil. Crank it over to see if it flashes as the coil is grounded to see if it is being controlled correctly.

737Jeep 05-23-2013 01:04 PM

Ok Que.

I have power to the wire harness into the coil. I also used a jumper and no start. Not sure I understand how to check the ground on the coil but I'll give it a shot.

Today I had the engine start and stall out immediately. I tired to start again but his time no CEL light, no upshift arrow, and no fuel pump. After letting it sit for a couple hours, it still won't start but I'm getting the CEL light, upshift arrow and fuel pump again.

Any ideas? Time for the cam sensor/distributor?

737Jeep 05-23-2013 02:20 PM

Update

Ordered cam position sensor/distributor and cap. I preparation for the swap I took the existing cap off and checked out how I was going to do the replacement. After putting the cap back on I used a spark tester hooked up between the coil wire and distributor. Turned the jeep over to look for spark and it started. Obviously had spark. Shut off jeep and reattached the coil wire and started again. Took it for a couple laps around the neighborhood and it stalled out at my house on the second lap.

The question is does the cam position sensor send a signal to the ECM for controlling the CEL, upshift light and fuel pump? As well as spark?

Que89YJ 05-23-2013 03:41 PM

no but out does sync to the cps. it should always allow the pump to cycle when you turn the key on. ate those things happening when it isn't starting.

50rck 05-23-2013 03:53 PM

Check the wiring from the that cam sensor (its actually a stator). It runs under the dist cap. I pinched one and it was grounding out on the side of the dist. Once it did that it would throw my relay and cause a no spark.

737Jeep 05-23-2013 05:23 PM

I've looked at the CPS wiring and it looks ok. New distributor, CPS, and cap tomorrow. BTW the connector to the CPS shows 5 volts on 1 of the three pins with the ignition ON.

Que89YJ 05-24-2013 10:54 AM

that is good then. replace the cps first.

737Jeep 05-27-2013 09:13 AM

After a weekend of soccer I replaced the Distributor, cap, rotor and cps. Fired right up first try so I let it idle for about five minutes and seemed to be ok. Decided to take it around the neighborhood and within 100yds it started running rough with a loss of power and eventually stalled. Pushed it back to my yard.

Help, any ideas?

Que89YJ 05-27-2013 01:49 PM

did you check to see if you had spark when it stalled? It sounds like fuel. early on you said you wanted to check fuel pressure but didn't. right now there are 5 jeeps in the last month dieing because of fuel pressure issues. check for spark.if you have spark get a guage on the fuel real and see what is going on there. if no spark post back.

737Jeep 05-28-2013 04:56 PM

The connector leading into the ignition coil seemed like the solution. I've been thinking it was an electrical problem and had been chasing from the opposite direction. It wasn't until I replaced the distributor that I chased all the wires around the distributor. Looking back it was probably obvious but that's with 20/20 hindsight. Off to the junk yard to find a replacement connector plug since you can't seem to get one from the auto parts stores. Keep reading .....


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