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Discussion Starter · #1 ·
Hey Y'ALL,

Here's the story: About a month ago, I dropped a 91 N/A 2.3 with a T5 in a 92 2.3 auto mustang (look at my avatar, lol). Got it running (first try!) and it is doing great, but the tachometer is reading "exactly" half. The first time I started it with coolant, I let it run until it was up to operating temperature, and the tach jumped back to reading "correctly" after a few minutes of idling and revving. And at times it would jump back to reading half, and then back to reading correctly again.

Last night, I had to move the car, and noticed that the tach was reading half again, but I never let it run long enough to reach operating temperature.

This is really a minor driveability problem (some cars I drive don't even have tachs, lmao) and it's really low on my "list of thing to do", but it is really erking me. I have an extra instrument cluster, but don't want to waste my time installing it, if it's not the problem.

What would cause the tach to read half like this?

Thanks, Steve:bigthumbsup
 

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Are you running the dis system of the dual plug engine or distributor and tfi? Maurice
 

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Discussion Starter · #3 ·
Are you running the dis system of the dual plug engine or distributor and tfi? Maurice
All stock for 91-93. So DIS system. What are your thoughts?

Steve:bigthumbsup
 

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I don't know. Will do some thinking on it. Maurice
 

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Discussion Starter · #5 ·

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Wow! Strange stuff. Not like the older Fox body ones. They had a screw that you adjusted for 4/6/8 cylinder.

Would be interested why they do this.
 

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Discussion Starter · #7 ·
Okay... did a little digging, and found out what the modules are for a DIS ignition system: http://www.chiltonlibrary.com/content/images/8815/images/88152g15.pdf

The ICM (ignidtion control module) sends the tach signal. I am going to swap out another used one and see if that fixes the problem. Maybe it's only sending spark to one coil too?

I will check for spark on both coils just to make sure. Just to make sure I am going about this right, I take my multimeter (analog) and put the positive to the coil and the negative to a ground?

Steve:bigthumbsup
 

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Discussion Starter · #8 ·
Update: I took the extra ICM off of the 92 intake, cleaned it up. Took the ICM off the motor. TROUBLE: Whule taking the ICM off the engine, 2 bolts broke due to corrosion. They are currently stuck in the intake and there is really no way of getting them out. I replaced the ICM with my extra and bolted it down with one bolt after coating the mounting surface with dielectric grease (they didn't have any heat sink grease). The car will not start. It turns over, but I think there's no spark. So I replaced the ICM with the original, and again no start.

So is it that important that all 3 bolts hold the ignition control
module onto the intake? I think they are grounds, but wouldn't 1 be good enough?

So now I guess I get to replace the lower intake and clean up the other one. This stinks! I can't believe I tried to fix the tach and ended up with a no-start condition!

Steve:frustrated::cursing::madas::banghead::scream::mad:
 

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Discussion Starter · #9 ·

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Discussion Starter · #11 ·

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Then to add insult to injury, dielectric grease is non-conductive. So not only does it not transfer heat, but it inhibits the module's ability to ground against the manifold.
 

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That point sends the GROUND out. If memory serves me the two bolt holes are in COMMON. Did you break both of those bolts OFF. If you did that is definately a problem. The tach takes its pulses from the controller and clearly yourss is defective. That is the only thing i can come up with. I cant view the TF website at home so i have to wait till tomorow at work. Seems like the TF website is shrinking. May be some are fed up with the ADDITUDES. I see you post there Steven. Well thats COOL just do not answer to many Questions correctly. Thats when they get MAD and BAN YOU. I cant wait till SERICUSE. The first TF T shirt i see will probably be THAT ANDREW. Cant wait just have a FEELING i am going to see him their. Peace TOM

PS Big C is correct do not use dialectric grease.
 

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I guess it is only 2 bolts. Learn something all the time. But then again I am not real up on the dis system. Maurice
 

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It's either 2 or 3 Maurice. I know there's at least one hole that's not used. If I remember right, it's not even drilled and tapped on the manifold. The first time I ever took one off, I thought someone left out a bolt, then when I got the module off, I saw that there were only three holes in the manifold.

You can tell which one's ground the module. The bolt hole has what looks like a metal eyelet to make sure there's good metal to metal contact between the bolt, module, and manifold.
 

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Discussion Starter · #16 ·
It's either 2 or 3 Maurice. I know there's at least one hole that's not used. If I remember right, it's not even drilled and tapped on the manifold. The first time I ever took one off, I thought someone left out a bolt, then when I got the module off, I saw that there were only three holes in the manifold.

You can tell which one's ground the module. The bolt hole has what looks like a metal eyelet to make sure there's good metal to metal contact between the bolt, module, and manifold.
Yeah, there is one that is not drilled out at all. On mine, it's the top left one. Also, it looked as if all the holes had metal eyelets. I didn't think about it; Di-electric grease really should not conduct electricity... lmao.

I'll get some real heat-sink grease tomorrow, clean up the other lower intake (because the bolts actually did break off inside the intake!) and swap them out and try the other module. It's really too bad that they decided to use bolts so small.

I'll keep you guys informed.

Steve:bigthumbsup
 

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Yes aluminum and steel bolts not GOOD. Use some anti-seize in the threads. Also use some sort of washer to make a good ground. Also make shure the module and mounting is clean and polished for a good ground transfer. I use some of those brown DISCS in an angle grinder. Post some photos. If memory serves me those bolts are rather THIN. Can you drill out the broken ones and use a coil to repair it?? That may be the answer and use a bigger bolt. This is why i like studs in places like this. I keep an extensive assortment of TAP BOLTS on hand and make my own. Good luck Tom
 

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Discussion Starter · #18 ·
Yes aluminum and steel bolts not GOOD. Use some anti-seize in the threads. Also use some sort of washer to make a good ground. Also make shure the module and mounting is clean and polished for a good ground transfer. I use some of those brown DISCS in an angle grinder. Post some photos. If memory serves me those bolts are rather THIN. Can you drill out the broken ones and use a coil to repair it?? That may be the answer and use a bigger bolt. This is why i like studs in places like this. I keep an extensive assortment of TAP BOLTS on hand and make my own. Good luck Tom
I guess I could always take the alternator and PS pump off and drill out and tap new bolt holes, but it might be less work to just replace the whole intake. The chances of me finding another set of bolts that small is slim as they are so small, so I wouldn't even be able to make a set of studs unless I tapped a bigger hole.

Steve:bigthumbsup
 

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You know i really do not have extensive knowledge on DUELIES. But i have built a fiew. I have one in my sisters MUSTANG . But why cant those coil packs be remote mounted?? I know chandler gave a great reason with heat disipation?? But i feel it can be done rather easily. So the problem is where to mount them ??? Any idears about this or any heat sinks come to mind?? I say remote chevy Diesel module heat sinks ???? Anyone up for this discussion?? Thanks TOM:bigthumbsup:bigthumbsup
 

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A good friend of mine sent me a heatsink after having this same discussion late last year. I've sized it up and seen that it will fit with either a little milling or shortening to clear the harness plugs. I just haven't gone any further.

I see no reason why it can't be done.
 
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