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Old 04-07-2012, 10:21 AM
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HEI, Vacuum, and Tach issue

OK, this one is weird to me. I just bought my car and it has a 350 ZZ4 motor with HEI distributor. Now, the tach did not work when I bought the car and I discovered the wire on the side of the HEI unhooked. So I hooked it up and the tach started working. Now, here is what is interesting. The car driving down the road just started to die but when I put on the brake it would start running again. Vacuum! Iím going, okay, this has something to do with the tech connector and distributor. I unhooked the tach and she runs great now. Could this be a bad vacuum advance or distributor? I didnít think it would be electrical since it cleared up with a push of the brake, again, vacuum. I could use a little help on this one and thanks

Mike
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Old 04-07-2012, 05:53 PM
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Quote:
Originally Posted by mscaggs
OK, this one is weird to me. I just bought my car and it has a 350 ZZ4 motor with HEI distributor. Now, the tach did not work when I bought the car and I discovered the wire on the side of the HEI unhooked. So I hooked it up and the tach started working. Now, here is what is interesting. The car driving down the road just started to die but when I put on the brake it would start running again. Vacuum! Iím going, okay, this has something to do with the tech connector and distributor. I unhooked the tach and she runs great now. Could this be a bad vacuum advance or distributor? I didnít think it would be electrical since it cleared up with a push of the brake, again, vacuum. I could use a little help on this one and thanks

Mike
The tach has nothing to do with vacuum advance. Check to see if the tach feed wire is rubbing on the brake pedal under the dash. A short there WOULD cause the car to die out.
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Old 04-07-2012, 06:17 PM
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Originally Posted by joe_padavano
The tach has nothing to do with vacuum advance. Check to see if the tach feed wire is rubbing on the brake pedal under the dash. A short there WOULD cause the car to die out.
X2 on this. Probably a sub par tach install
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Old 04-08-2012, 05:46 AM
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Quote:
Originally Posted by joe_padavano
The tach has nothing to do with vacuum advance. Check to see if the tach feed wire is rubbing on the brake pedal under the dash. A short there WOULD cause the car to die out.

Agreed, however, there is no short and wiring issues as I have already went through that very carefully. When I disconnected the tach from the dizzy issues gone. Like I said before, when I would touch the brakes causing a change in vacuum it would clear for a moment. This is a weird one for sure...
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Old 04-08-2012, 09:13 AM
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Originally Posted by mscaggs
Agreed, however, there is no short and wiring issues as I have already went through that very carefully. When I disconnected the tach from the dizzy issues gone. Like I said before, when I would touch the brakes causing a change in vacuum it would clear for a moment. This is a weird one for sure...
If you disconnect the tach wire and the problem goes away it is not a vacuum issue, it is a tach wire issue. The fact that stepping on the brake fixes it would show that the movement of the pedal is doing something with the wire.
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Old 04-08-2012, 09:36 AM
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If you are completely certain that the problem is not the tach wire, then the only other connection between the brake pedal and the distributor would be the brake light switch. Applying the brakes causes a slight voltage drop, if the installation of the HEI is marginal from a wiring standpoint or if there's a grounding issue with the tach, then the voltage drop MIGHT be related.
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Old 04-09-2012, 06:45 AM
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Originally Posted by joe_padavano
If you are completely certain that the problem is not the tach wire, then the only other connection between the brake pedal and the distributor would be the brake light switch. Applying the brakes causes a slight voltage drop, if the installation of the HEI is marginal from a wiring standpoint or if there's a grounding issue with the tach, then the voltage drop MIGHT be related.

I know all that sounds likely but I really have checked all the wiring between the tach and the dizzy as well as anything thing that the brake pedal would interfere with. That is why this is so crazy. I WILL get to the bottom of this soon. With Easter last weekend I did not get a chance to disappear in the garage. I will take a look at the brake light circuit too which I had not done yet. Thanks guys for your input...


~m
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Old 04-09-2012, 07:45 AM
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I was thinking this morning that this could very well be a bad coil in the HEI. Maybe the hookup of the tach wire is enough to kill it. The symptom is that of a bad coil, but the brake pedal thing is still somewhat of a mystery to me. Thoughts anyone...

~Mike
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