Randomly Losing RPM Signal, Engine Stutter
 

Hey Guys, I finally got my car running again after 5+ years and I have been encountering an odd issue. The car runs and drives perfectly fine but randomly power will just cut out for a fraction of a second. It almost feels like you let completely off the throttle and back on. This will maybe happen 3 or so times out of an hour of driving.

I happened to catch this anomaly while datalogging for my tuner and dug into the problem a little more. According to the log, the ecu is losing rpm signal completely, which is followed by a lean spike in the AFRs, which would be normal if it thinks the engine isn't running. Thinking it may be the CAS at fault, I replaced it this weekend but I'm still having the same issue. The wiring harness is all new but I will be doing a continuity check between the CAS and the ECU when I have time.

I've searched endlessly and did not come across anyone having an issue like this. I'm curious if anyone has any possible ideas on possible causes. Here is what the log reads; green is RPM, red is AFR. Happy to provide the Eugene log file if needed.

S5 t2 streetport running on Adaptronic 440 select universal, stock cas, new engine wiring harness.

https://cimg9.ibsrv.net/gimg/www.rx7...83a21f1773.jpg

Does it correspond to any electrical switching like fans or going over bumps in the road?

I would assume it will likely be electrical noise, earth current issue or wiring problem.

Doesn't seem to be related to any large electrical loads like Efans or anything. The car is on really stiff springs with delrin bushings on everything so it pretty much vibrates 100% of the time. Could very well be related to that.

This could totally be in my head, too, but it seems to happen most when driving on a slight incline when the engines under more load. It does point back to vibration. I will do a continuity check on the connectors this weekend and try wiggling them around a bit. I'm thinking there might be a bad crimp on one of the terminals or one of the pins not inserted 100% into the connector somewhere.

Could probably also re-check your grounding points to make sure everything is tightly and properly grounded. And also the CAS plug(s) to make sure its not loose.
Could also have the car idling while parked and start shaking wires like CAS plug, etc and see if happens to see if there is a short or loose connection.

Does the voltage also drop to zero/very low during this period on the logs?

Hey thanks for the input. So quick update, I did try this, shaking the connector and moving it around as much as I could with the car running and could not replicate the issue. I ziptied the connector to something to make sure it didn't have any movement and took the car for a drive-still was happening. I also did a continuity check this weekend on the harness between the CAS connector and the ECU and everything checked out *as far as what I could tell* doing it by myself. It would have helped to have another person there to hold the lead for me since the two connectors are so far apart but oh well. I purchased a new connector for the harness side of the CAS and will be replacing it just to rule that out. Will report back once that's done.

Edit: the grounds for the CAS (2 of them by my findings) ground to the ECU's sensor ground terminal. That doesn't 100% rule out grounding issues, but does mean they aren't just going to some random chassis point that could be affected by ground offsets. I know there must be a splice internally in the aftermarket harness I have because multiple sensors need to ground to this terminal (ECU only has 2 sensor grounds IIRC) so that could be a potential fail point I suppose. Im not too thrilled about the idea of removing and cutting apart the harness to get to it.

I checked voltage on the log and it holds steady at 14.2-14.3v throughout the period the issue occurs. Heres a pic from the log. Voltage in tan, RPM in green.

https://cimg5.ibsrv.net/gimg/www.rx7...a67317ca3c.png

This past weekend I re-gapped the sensors in the cas just because and replaced the harness side of the cas connector-still having the same issue and starting to lose patience.

My tuner did have a good point in suggesting I test for any continuity between the sensor grounds and the chassis that would indicate a short, which I'm going to do next chance I have a minute to work on the car.

I'm running out of theories here as to what could be causing it. The only other thing I could do is run all new wires from the ecu to the cas.

Record using the onboard scope and see what part of the CAS signal is failing.

Thanks for the suggestion unfortunately I'm on the 440 universal which *I believe* does not have the scope feature. From some quick research it looks like it comes on the models above mine and the newer modular ECUs. I'm no expert though so please correct me if I'm wrong.

welcome back man. Haven't seen you post in these parts in a while. I welcome back your knowledge.

You are right. Didn't realise it was a select.

Tricky situation to be in. A second pair of hands to shake some wiring around while the car is idling and see if you can recreate the issue?

FYi i had a similar issue on a 440. I would lose signal from the cas (for a split sec) and my idle would shoot up. It was an issue in the ecu. I ended up buying a new ecu and no issues.

I actually did attempt shaking the cas connector and wiring around with the car idling but could not get it to happen. So far it has only happened while under load.

Well that is....not good news :tear: I wish I knew someone locally with the same ecu I could swap with to test but unfortunately I do not. Reaaally not trying to buy a new ecu right now. Not even sure I would do that at this point.

A few people I was bouncing ideas off of pointed out my spark plug wires were a little on the aggressive side and may be causing EMI, so I have some new ones on the way that I still plan to try out as a last ditch effort this weekend. If that doesn't work I suppose I have a big decision to make...

Installed some new MSD streetfire plug wires today that are supposed to have better emi suppression. Issue still remains....

Well unfortunate update here. I replaced all of the cas wiring this weekend (new connector, new shielded cable grounded at the eco sensor ground only) and the problem still persists, so at this point it has to be an issue with the ECU itself.

I bought it brand new when I started my build 4-5 years ago so Adaptronic won't do anything for me or even look at it because it's an outdated model. Pretty disappointing to hear and I'm now out $2k and countless hours. I will most likely pony up the money for a Haltech and will not be recommending Adaptronic to anyone in the future.

Ya that ecu they stopped supporting years ago. I was pissed also. But i didn't want to pony up the larger amount of $$ i had into the car already. I would have to change quite a bit of things to go haltech. I may still swap later knowing what i know now.

Did you sell your old ecu when you got the new one? I'm conflicted about what to do with mine now. There may be a chance it could potentially work for someone else with a different setup and it would be nice to recoup a couple hunny to soften the blow of the new Haltech I bought, but I absolutely do not want to screw the next person over and sell this to them if it has an issue.

No i didn't. I borrowed a friends ECU same model and ran it for 2 days With no issues. I chucked the old one. No sense in trying to sell it and it be faulty for someone else.