85 cj will not start - JeepForum.com

 
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post #1 of 6 Old 09-20-2005, 09:19 PM Thread Starter
otrain
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85 cj will not start

I have a 85 cj7, died after about 25 mile ride. replaced coil, cap, rotor, and wires. ran for about 2 miles after this, then sputtered a couple of times and died again. this time replaced distributor and ignition module. ran fine until it warmed up, now it is blowing the fuse for ign/lps. could ignition module be bad from store?

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post #2 of 6 Old 09-20-2005, 09:47 PM
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Hmmm.... possible but not likely at this very second. So how long does it take to pop the fuse? Get some spares and start disconnecting stuff to protect the circuit. Keep doing it until you can no longer reproduce the short.

Usually this happens after people tinker with their dash wiring, so usually I'd just say disconnect the fuel gauge and oil pressure gauge RED I terminal Wire, but in this instance, if it has to be warm before it pops, that's probably not going to be it. In fact it sounds like it could be a sensor or an EECU circuit kicking in after the engine warms up.

I started putting a page together on the things that the IGN LPS sees, so it would be easier to troubleshoot. I never finished, but it might help. Clicky...

By chance *fingers crossed* have you nuttered the ignition or upgraded at all from the OEM duraspark EECU ignition setup? I'm hoping the EECU has been bypassed already, because the IGN LPS also runs to the EECU and other Emissions crap that can get to be a PITA to troubleshoot. If it has been bypassed you can rip all that crap out (barring any Etesting) and not deal with it ever again.

I've already ripped my EECU wiring harness bank out of the engine compartment so a compare may be difficult looking at my own harness, but I'll look at it and see what I can find.

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post #3 of 6 Old 09-20-2005, 10:13 PM Thread Starter
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no I have not done the nutter bypass to my jeep. although this will proably happen in a couple of days now, since all these problems. if the starter resistor was not hooked on to coil when last time ran could it have shorted out the ignition module? never blew fuses before this.
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post #4 of 6 Old 09-21-2005, 06:17 AM
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Well if the nutter is an option for you, and it's something you want to do anyway, it may open up a few doors for you here. Problem is, doing more than one thing at once to get the idle back can confound the troubleshooting process, so it's easier to get in over your head if you're not careful. At some point though, the computer may have to be unplugged, at which time, you'll have to atleast temporarily bypass it to see if you can get the engine to idle so it can warm up and duplicate your short. What a pita... a short that only shows itself at NOT...

What do you mean when you say: if the "starter resistor" was not hooked on to coil? Do you mean the ignition resistive wire that runs to the ignition coil positive terminal? And if so, what do you mean it was not hooked up? You bypassed it with standard wire or you left it off altogether or what?

If you bypass the resistive wire the ignition module (and coil after a while) will likely cook. I lost 3 reman duraspark ignition modules experimenting without the resistive wire before I went with the TFI/HEI hybrid. One went the same day it was installed. But clarify that's what you mean to say before I waste too much of your time harping on that.

Again, how long does it take to pop the fuse? Kind of helps to determine the nature of the short. Immediately after the key is cycled to ON? Does the engine actually have to START for it pop? START and warm up? Things like that. Get yourself some spare fuses, you're likely gonna go through a few of them.

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post #5 of 6 Old 09-21-2005, 11:19 AM Thread Starter
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the fuse blows as soon as you turn the key. also had the resistor wire disconnected from coil. only power hooked up to positive side of coil.
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post #6 of 6 Old 09-21-2005, 12:27 PM
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Ok.

First, don't bypass the ignition resistive wire if you're still running the duraspark ignition module, which it sounds like you are. You'll kill it. Sounds like the ignition coil probably got upgraded to a hopefully tougher unit with the juicebox you did, but that still stresses your ignition module if the coil gets to chew on 12v unregulated. You'd have to upgrade the ignition module or go with a different setup to do that.

Second, if it pops as soon as the key is cycled to on, you have two choices. One, start disconnecting crap tied in to the IGN LPS circuit until the fuse stops blowing. Or remove the fuse and take a DVM to the downstream side of the IGN LPS port on the fuse panel, you should see 0 resistance (or very low resistance) to ground. Start disconnecting things one at a time until the resistance spikes. Both options are a process of elimination, but you're essentially shooting in the dark here. I would disconnect the gauge RED leads (I terminal feed, illustrated below) , the 4wd indicator bulb, and also the EECU 60 pin connector, and then try it to see if it pops again. That's a quick way to see if the short is likely to be inside the passenger compartment.



See what happens after disconnecting those items.

If you're concerned about the ignition module and the passenger compartment items don't resolve the short, disconnect the ignition module wiring plugs. Keep doing things like that and retrying the fuse one component at a time until the fuse doesn't pop. Give a few of those ideas a try and see what happens...

85 CJ7 / 258 / T176 / Dana 30/ AMC 20
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