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6k ignition break up and tach goes wild simultaneously no matter the engine load
1994 FD RX7. Just replaced my engine, old one was running fine. Now i have a misfire at 6k Rpms and at the same time my tach goes wild. The issue correlates with each other. Wideband also goes RICH when this happens further confirming what i believe is an ignition break up. It does it free reving or under any load. Doesn't matter if its light acceleration of WOT.
Running Power FC master (by FC tweak)
New ignition coil (L1 and L2 pack)
new spark plugs
new wiring harness
new extra grounding kit
gauge cluster already rebuilt
take a look at these videos to see clips. in 2nd video i get some good clips on the end.
https://www.youtube.com/shorts/fwR-Crtv4AM
https://www.youtube.com/shorts/UVMWPXi1LJM
Desperate for help or suggestions! Car runs great besides this issue.
Finally figured it out. I pulled my trigger wheel and it had 2 very slight bends in it! I swapped it out with a spare one i had in my shop that was perfectly straight and everything is good to go now. Hope this helps someone else in the future!
Finally figured it out. I pulled my trigger wheel and it had 2 very slight bends in it! I swapped it out with a spare one i had in my shop that was perfectly straight and everything is good to go now. Hope this helps someone else in the future!
Nice find, and kind of an usual one, you could have been running around in circles forever finding that issue.
Finally figured it out. I pulled my trigger wheel and it had 2 very slight bends in it! I swapped it out with a spare one i had in my shop that was perfectly straight and everything is good to go now. Hope this helps someone else in the future!
Wow, explains why it was localized to the tach too.
I was getting break-up on the dyno at 6000 as well. Shop felt it was the lower engine harness aging out. I replaced the coil harness a year ago and that got rid of some stalling issues.
Just replaced the lower engine harness with brand new from Nengun (C$1000).
There was some delay in delivery, which makes me think they were waiting for a new batch to be made.
Will likely get back on the dyno soon to check things out.
New and 27 year old harness side by side. It was a straight plug in replacement. Seems there is liittle change in the harness across the years and JDM and USDM. My car is a 1999 RHD.
Went for a 1000 km cruise immediately after changing in the harness and the engine was purring like a kitten when cooling down after long runs at high loads.
While we are on this, and since the OP has figured it out. I'm actually suffering a similar issue. Above 6500 on load, I get a breakup. I'm using an aftermarket wheel, aftermarket pickup (hall effect), and I've checked grounds, have the 1A coils, replaced plugs, and new plug wires. I haven't been able to really dig into it since im going through a divorce and have my car at an old folks community where I cannot work on my car. UGHF.
93 LHD, the OP had me thinking I needed to look at my trigger wheel setup, its too close, so FFE was kind enough to send me some different length stand offs. Hope it works.
Non-spec spacing of the trigger wheel vs the CAS sensor can point to a bigger problem - the dropping of the needle bearing in the e-shaft "stack" behind the front buss the trigger wheel is mounted to.
Keep that in mind. Particularly if loosening off the front e-shaft bolt.
Non-spec spacing of the trigger wheel vs the CAS sensor can point to a bigger problem - the dropping of the needle bearing in the e-shaft "stack" behind the front buss the trigger wheel is mounted to.
Keep that in mind. Particularly if loosening off the front e-shaft bolt.
Should be all good, I installed it before my rebuild and now the sensor is sitting close after my rebuild, but the stack is currently fine, I don't know if its because I used a different gasket for the cover, since the mount is on the cover if i remember right. I'll only be adjusting the sensor mount. Mind you this is an aftermarket CAS setup.
While we are on this, and since the OP has figured it out. I'm actually suffering a similar issue. Above 6500 on load, I get a breakup. I'm using an aftermarket wheel, aftermarket pickup (hall effect), and I've checked grounds, have the 1A coils, replaced plugs, and new plug wires. I haven't been able to really dig into it since im going through a divorce and have my car at an old folks community where I cannot work on my car. UGHF.
I'd check your ignition grounds and consider adding more and thicker grounds to your setup. Talking all the grounds-- edit: star chain between battery and chassis and block and ignition. I had serious issues with my original IGN1A coil install many years ago and this resolved it.
Last edited by GoodfellaFD3S; May 25, 2026 at 03:34 PM.
I'd check your ignition grounds and consider adding more and thicker grounds to your setup. Talking all the grounds-- daisy chain between battery and chassis and block and ignition. I had serious issues with my original IGN1A coil install many years ago and this resolved it.
Did you mean to say, "star" instead of daisy chain. Daisy chains set up ground potentials/ground loops, stars don't. Never daisy chain grounds.
I haven't had a stock ground in the car for a long while. It was all re done. The block is central to everything including the ecu, the battery as well as it is not in the bay.
I haven't had a stock ground in the car for a long while. It was all re done. The block is central to everything including the ecu, the battery as well as it is not in the bay.
I didn't say anything about stock grounding, and please define 'redone,' what quality wire and how thick? How many grounds? Best to be specific
Those coils are powerful and need (very) overly robust grounding, otherwise you'll have weak spark as it'll go everywhere but where you want it to.
You're getting break up at peak torque on load/boost.... you may have an issue with your ignition
I didn't say anything about stock grounding, and please define 'redone,' what quality wire and how thick? How many grounds? Best to be specific
Those coils are powerful and need (very) overly robust grounding, otherwise you'll have weak spark as it'll go everywhere but where you want it to.
You're getting break up at peak torque on load/boost.... you may have an issue with your ignition
Can't remember the size, its what i used to use when building engine harnesses for off road racing, so beefy. I'm no longer in the industry. Going off of memory, Block to chassis, block to battery, Emtron ecu ground pins go to the block, i think they are 18 or 16 awg, tefzel. All sensors go to their respected returns to the ECU. The coils have 18 or 16 tefzel going to the block, i think there are two grounds, don't remember the layout, which may be something I should look at again. The 0v coil signal returns go to the ECU.
