LukeG

I'm having a stuttering issue under full boost that almost feels like something in the drivetrain slipping. Car has a 1.8, FMII and Hydra, and I am thinking it might be the factory coils after doing some reading.

What does it feel like in the car when the coils are having issues keeping up with boost?
How much boost can the factory coils reliably deal with?

If it is the coils, the easiest swap seems to be get a new oem set and see if it fixes it.

Thanks for any help!

slowcarfast

If you buy used coils and diy a bracket you can switch to LS coils for about the cost of a parts store replacement coil and you will no longer have to worry about crappy 99 coil pack I don't know if that's your issue, I switched to the LS coils before I even had boost after i had the second coil pack fail in a span of about 18 months or so.

LukeG

Thanks! Was looking the FM kit that is a little pricey. How was the integration with the MS2? Any recommended write ups that you used to do the coil swap?

slowcarfast

This is the thread I referenced most: https://www.miataturbo.net/diy-turbo...-thread-82744/ although there are others if you search. Genuine D585 coils are around $40-50 on ebay, You'll need to splice the wiring, I paid something like $10-15 on Ebay for a pigtail that would connect to the oem LS connector and spliced wires to my oem harness. I bought LS plug wires for around $40 for 8 plug wires (I still have 4 if somebody wants to buy em!). It would be better to make, or have made, custom plug wires with real miata ends, but that costs more. I made a bracket out of aluminum flat bar from the home depot. With MS2 and correct wiring it's just a matter of adjusting the dwell settings. to get it running.

codrus

The FM kit is pricy because it includes 4 genuine GM coils from GM. There are lot of fake GM coils out there, so be careful on ebay -- If you find "new" GM coils for a price that's way less than what GM charges, they're probably not genuine.

The truck coils are less expensive, but bigger and harder to mount. They also supposedly have an annoying tendency to self-discharge if you dwell them past the saturation point, which will amount to a massive amount of timing advance if it happens while you're driving. So setting dwell properly with these coils is critical.

You're better off buying used genuine coils than new fake ones.

--Ian

LukeG

Awesome, thanks for the help guys!

I want to confirm that the coils are indeed my issue before I go dumping a bunch of money and time on them.

Can anyone tell me what it feels like when the coils cut out?

Current symptoms on my car:
It almost feels like a traction control system kicking in or an open diff sometimes at high boost. Kinda of hard to describe. Maybe I need to get some video of the tach as it happens as it looks pretty apparent on some of the youtube videos I saw showing the tach with random spikes and drops.

Does that sound like it is the coils?

ByteVenom

I have the same issue in my car. I played a little bit with injector dead time, and advanced the timing at those points and it seemed to help a little bit.
I'd also like to hear people's thoughts on this.

concealer404

iTrader: (3)

Do you know what your AFRs are like? Or what your timing is like at high boost?

My MSM with Hydra felt like that pretty often. Worse in certain weather conditions. Hydra was just pulling timing like crazy, like for "safety."

DNMakinson

iTrader: (3)

The absolutely best way to control fueling at high loads is to randomly adjust dead time.

ByteVenom

I also had an iffy idle, I should've mentioned that.
I'm using mustang injectors with a DIYPNP. I had to calculate the slope needed that the ECU uses to calculate dead time. My calculated slope based off of the given graph didn't really work because the graph was exponential, so I had to play around with it to get the most accurate value within the battery voltage range that the ECU would see.

DNMakinson

iTrader: (3)

But I couldn't resist.

ByteVenom

Do you have any datalogs to post? In mine whenever it stutters, it doesn't show up in the datalog at all. No wild AFRs or anything.

LukeG

Found out it was my ignition system and probably the coils. I also replaced the battery, plugs, wires and alternator at the same time. Car runs perfectly now.

Details in the thread below.

https://www.miataturbo.net/diy-turbo...0/#post1426429