My rpm signal seems to be breaking down at high rpm's, my datalog showed a drop in rpm for a split second exactly where the miss fire is occuring. I have changed distributor as taught it would be that but problem still persists. Could it be a ecu problem? I haven't noticed my rpm needle on dash acting strange but it does happen so quick that the needle probably doesn't have time to drop.

Here is screen shot of datalog


You can see around 7400 rpm there is drop in rpm signal for a split second.

Any ideas what could be causing this?

 

It appears you're boosted from the duty cycle item in logging, so when was the last time you checked/changed your plugs? Are they the right heat range and are they gapped properly for what you're running? And lastly, how aggressive is your ignition timing/fueling in that area? You may want to post details on your setup.

 

It's not boosted, it's NA. It's only on a run in map at the moment. Plugs are new and I have tried a second set so it's not that. I have also tried plug leads. Judging from the drop in the rpm that the ecu is seeing I taught sure it would be the distributor at fault but the problem persists even with replacement distributor. Wiring or ecu problem?

 

If you're running around on a basemap that's probably part of the issue. I'm not sure why you're jumping to wiring or the ecu as the fault for a misfire. Tune it or get it tuned.

 

The map is good that's not the issue, I don't even know why your suggesting that when it's clear to see from datalog there is a drop in rpm signal! It's not distributor as I've changed that already so should my next port of call be to check wiring?

 

ive tuned several cars like that. very rare and difficult to diagnose. its def electrical related.
ecu, plug wires, is what i would check next since youve tried swapping dizzy and plugs already

 

If the map is tuned then I retract my previous statement. You said it was a basemap, and it appeared to be for a boosted car even though you're NA since PWM is clearly setup and running. Sorry for getting confused. Good luck tracking your issue. Definitely check plug wires and associated wiring.

 

I think this is going to be a hardware or wiring issue related to the primary ignition... Not tune related or secondary ignition, IMO.

You can clearly see the RPM signal dropping out. This seems to point to one of the sensors/ignitor in the distributor, or the associated wiring. Check for corrosion or loose pins at the the distributor and ECU connector as well as the shock tower connectors.

 

I said run in map not basemap! PWM is not setup either, I have my wideband wired to EGR input, duty cycle is injectors(there 750's hence low DC)
Question for you actually, upon restart when car is hot and left for a bit it runs really lean, IAT's do rise but I have zero'd out any fuel correction past 40 degree's. Normally IAT's would be around 40 and when it get's heat soaked from been parked up after a run it could read 60 degree's. Any ideas?

 

I'm going to try a different ecu as i've changed most parts of the ignition system bar the wiring from distributor to ecu so don't know what else it could be