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Discussion Starter · #1 ·
Still fairly new to the forum and working on our first Jeep. We have a 1987 YJ with the 4.2 I6. Just finished taking care of the rear main, valve cover and oil pan gaskets and Jeep was running just fine. Decided to go ahead and do a Tune Up just because I have no idea how long it had been so I got a new cap, rotor, wires and plugs. I gapped the plugs as instructed to .35 changed out each plug and wire one at a time so I didn't mess anything up and replaced the cap and rotor. Now I can't get it to turn over. Cranks strong like it did before and I can tell its getting fuel, it was converted to fuel injection before I bought it, and I even put the old cap and rotor back on but still nothing so I am assuming I am not getting spark. My question is where is the smartest place to start? I was extremely careful but is there something I could have inadvertently bumped that would cause this issue?
This forum has helped immensely so thank you in advance for some expert guidance.
 

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So you started it after you changed all of the seals? If not did your reinstall the knock sensor?

Also stupid question but I have done it. Are you sure the plugs are in the right order? Double check them and while your there make sure the rotor is in right, the cap is on and seated well, and then make sure it's also plugged in.
 

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So you started it after you changed all of the seals? If not did your reinstall the knock sensor? Also stupid question but I have done it. Are you sure the plugs are in the right order? Double check them and while your there make sure the rotor is in right, the cap is on and seated well, and then make sure it's also plugged in.
x2 on checking the plug wires. I swore I did mine in the exact correct order when I was doing a tune up on my 94 and I finally went back and checked and I had swapped two of the wires at the cap.
 

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Discussion Starter · #4 ·
I did start and drive it after the seal change and I swear I kept the wires the same did them one at a time but i am gonna check them again at the cap just in case.Keep the suggestions coming and I will update it with my results.
 

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After you've verified correct firing order and are sure you have the cap a rotor on right you need to verify that you have spark. Pull your longest spark plug wire off its plug and insert one of the old plugs you replaced. Get helper and while you hold the threads of the plug against a ground have your help try to start it (recommend caution and heavy gloves. It smarts to get bit). If you don't have spark start looking at the coil and it's connections.
 

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If you're not getting spark you could have either a bad coil or a bad Ignition Control Module.
 

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Discussion Starter · #7 ·
Okay went and reverified the firing order and triple checked the wires were in the right spot. Took a minute and reinstalled original cap,rotor and wires and still nothing but strong crank and fuel. Going to do the recommended checks for spark. And this is definitely a newb question but can a coil go bad that fast? It was only a day of sitting between the last time I drove it and decided to do the tune up?
 

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Discussion Starter · #8 ·
Okay checked for spark with an inline tester on all six plugs and I am getting spark so now I am extra confused because after spark and fuel I don't know what else it could be. Do I just go ahead and replace the coil to eliminate it? If that doesn't work what next? I also double checked the gap on the old plugs and it was the same as what I put in .35. Something tells me this is something really simple and I am missing it. :atomic:
 

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Okay went and reverified the firing order and triple checked the wires were in the right spot. Took a minute and reinstalled original cap,rotor and wires and still nothing but strong crank and fuel. Going to do the recommended checks for spark. And this is definitely a newb question but can a coil go bad that fast? It was only a day of sitting between the last time I drove it and decided to do the tune up?
Depends is it new or not. If it's not it could be something as simple as everything was already one its way out, add new plugs and wires, they pull a little juice and its dies? I donno. I have had wires out of the box bad (caused a miss) so it could just be bad.

You have power to the ignition right? It cranks over? I'm on my phone and don't remember what you said
 

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Discussion Starter · #10 ·
Yes it cranks strong might be starting to take its toll on my battery though.
 

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I know you have gas but humor me and dump a little down the throttle body and see what happens....
 

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Discussion Starter · #12 ·
Went ahead and replaced the coil no changes. Also dumped a little fuel down its throat and still no changes. I don't know if it matters but as I said originally this jeep was converted, or so I was told, to fuel injection and I can see it spitting fuel down the carbs. It also has a toggle switch cutoff inside that you must turn on to get it started. I believe it turns on the fuel pump but I am not sure as the fuel system is a little frankenjeep but this thing ran like a champ two days ago. Fired up instantly and ran good starting to wish I hadn't decided to tune it up! After all my checking now my battery is about dead so I am stuck until I can get a good charge on it.

Thanks for all of the input so far keep them coming! :)
 

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Have you looked at the possibility of the crank position sensor? My 98 grand Cherokee was running fine one day, parked it and went to sleep. Next morning it would not start. Crank sensor went kapoot just like that.

Of course, now that I'm thinking about it, it may not be that if you have spark. Couldn't hurt to ohm it out though and make sure it's good?
 

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He doesn't have a crank position sensor.
Make sure none of the fuel injection wiring is anywhere near you sparkplug wires. They will cause interference, flood your throttle body, and foul your plugs.
It's probably the ICM. You can take it in for a bench test. Have them run it multiple times, like 10. Return the coil while you're there.
 

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Discussion Starter · #15 ·
Okay double checked the wiring and I don't see anything that would cause interference. Took the ICM out and had it tested a total of eight times by two different places and it passed all eight times.

I'm at a loss.
 

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What do you have, tbi? If so unplug one of the injectors and see if it will fire.
What do the plugs look like after trying to start. Are they wet?
 

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Discussion Starter · #17 ·
Pulled one of the injectors still no start but it acted like it wanted to. Plugs are wet but not overly so rear three a little more than the front.

Yes it says Rochester TBI
 

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Discussion Starter · #19 ·
Yes that's it.
 

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So you have a junkyard tbi conversion. Can you post some pics of your engine bay and the plugs. Can you also set the #1 cyl to TDC and post a pic of the rotor location. Did the PO put Schrader valves in your fuel lines so that the pressure can be checked?

Pull all the plugs, and dry them off. Put them back in, then try to start it with one of the injectors unhooked. If it fires, snap the injector back on quick before it dies. It should stay running. If it doesn't fire try it with both hooked up, which won't work but it will get the fuel there, then unhook one and try again.
The injector wires and the wires coming off of the distributor need to be isolated, which is tricky because they are so close to the sparkplug wires. All of those wires can't be anywhere near the sparkplug wires. I mean like 8" to 12" away. Also check that the purple and orange wires coming off the distributor going to the ICM are twisted together. Any of these wires within range will pick up the voltage off the high tension spark plug wires and flood you out. I'm guessing this is the issue since it was running fine until you started moving wires around. If it will fire by doing the steps I said above, then you are definitely getting interference and flooding.

BTW make sure you put more thermal paste on the ICM or it will fry.
 
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