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Discussion Starter · #1 ·
Hi, I have a 1995 mustang with a Dart 331, AFR heads, and 70mm master power turbo. It has an AEM EMS 1400 in it, but I am having some misfire problem and hoping someone can help.

What is happening is the car will run and drive great at anything over 1800rpm, once the car goes below 1800 it will miss and start chugging really bad. I had a oscilloscope hooked up to it and the voltage for the pickup coil drops from 10v to 8v at anything below 1800. The car also has a factory distributor with a new Motorcraft pickup and tfi module.

Any idea's or suggestions would be greatly appreciated, I have been trying to figure this out for 2 weeks now.

Also I just received the computer back from AEM for the newest updates.

Thanks,

Jake
 

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Have you scoped the PIP signal coming from the distributor into the AEM? What do the Sync Errors and Timing Errors doing when this is happening? Can you post an internal log of channels Crank Tooth Period, T2Per and T3Per?

The stock distributors are notorious for causing timing problems with the AEM. If you can narrow down the problem to not be voltage based (make sure you don't have a problem that's causing voltage to drop from 10V down to 8V), then you need to make sure your timing signal from the distributor is good. A new TFI module and pickup won't fix anything if there is slop in the mechanics inside the distributor.

I recently had a car that was having a similar issue with a totally stock distributor. I fixed it by modifying the distributor to only input a cam signal and added a crank trigger for better resolution. We now have ZERO timing errors and the car starts up faster than any other EFI vehicle I've seen: AEM or not. It's an inexpensive modification if you're not looking to go distributorless like the LS style coils with an EPM or crank trigger/cam sensor style setup.

- Trever
 

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Discussion Starter · #3 ·
I actually had the volatge backwards it goes to 10v below 1800 rpm but 8v after 1800 rpm. the crank signal varies equally at the distributor and at the input to the pcm. when this is changing from 8 volts to 10 volts the pcm intermittently drops the pulses to the coil
 

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Can you post or PM me your cal? Or just a screenshot of your Cam/Crank sensor template screen?

Did you get a chance to datalog the Crank period, T2per and T3per parameters?

Are you looking for a short term fix or long-term? And if long-term, what's your budget and how much are you willing to change? Would you consider adding a crank trigger?

I don't have a ton of faith in the stock distributor providing accurate crank angle values to the AEM. If you can get it to work, that's great and you should consider yourself lucky. For about $100 in parts you can make some minor mods and get a completely reliable & stable setup.
 
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