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Discussion Starter #1
Hey guys,

My '79 280zx has developed a stumbling/hesitation issue from 3k RPM and higher. When it does this, the tach needle ticks up/down in sync with the stumbling. I researched a good bit on this and other Z forums to find common causes for this issue, and I believe I have ruled a few things out. I have 1) replaced the fuel filter, 2) checked fuel pressure at idle (32 psi) 3) checked the plugs/gap (all look good and gaps are to spec), 4) tried two sets of plug wires, and 5) swapped the ignition coil. None of these had any effect.

I have also suspected the ignition timing, and have tried various settings. On my 79, the stock setting is 10 degrees BTDC, and I have always run the car at the stock setting without issue. Unfortunately, at 10 degrees, the hesitation/stumbling is pretty bad. However, I recently discovered that if I advance the timing to the maximum possible setting (20 degrees BTDC) the issue seems to be resolved. The issue gets progressively better the more I advance the timing, eventually going away at the 20 degree maximum.

My question is, does this set of facts point you to a faulty mechanical advance in my stock distributor? I've read up a lot on the vacuum and mechanical advance mechanisms, and my symptoms seem like it could be possible that the spring weights are not swinging out properly, and thus, not advancing the timing with RPM properly, thus causing my stumbling. I'm merely hypothesizing here though, so please correct me if my thinking is off here. I would really appreciate any thoughts you guys might have.

-Alex
 

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1983 280ZX Turbo
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940 Posts
Does this happen all the time, or only when the engine is hot? If hot, there are some aspects which sound like an ignition module...but it usually cuts the ignition completely.
 

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Discussion Starter #3
@pilgrim

Interestingly enough, yes, I would say that it most commonly occurs when the engine is hot. It seems that on average, it will rev/drive smoothly for the first 5-6 minutes and then the hesitation/stumbling begins. I wouldn't say this happens 100% of the time (there are rare occasions where it stumbles almost immediately), but most commonly it happens once warmed up.

So given this, you'd be leaning towards the ignition module? Thanks for responding.
 

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Super Moderator
1983 280ZX Turbo
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940 Posts
Here's what I did when I suspected the module in my '82 when the car was dying after it got hot. the tach would drop as the engine dies.

I carried a thermos of ice water in the car. When the car shut down, I pulled over, popped the hood and poured ice water on the module (side of the distributor). Then got back in and it started right up. Easy diagnosis.

Those modules on non-turbo cars have been known to fail in strange ways when they get hot, and they're right in the airflow from the radiator. Might be worth a look.
 

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Pilgrim is right on the money. Because you see a reaction in the tach needle that coincides with the stumbling it has to be ignition. In this case it's almost always the dizzy module. They're not expensive anymore like they use to be. The quality control of the aftermarket modules has improved enormously at least on most of them it has. I'd have to order you one but my zcar.com price is 79.95 for one of them. Always be sure to let me know you use this forum when ordering parts. I usually carry them in stock but I've replaced a few of them this year already. Z man of Washington 360-668-2979
 
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