MS2 cruise stuttering/jerking issues

[MattPro]

Since my e30tech account is taking forever to get approved I thought I take a shot at posting this here and see if anyone had any insight.

I'm having an issue with my MS2 setup, sometimes at low throttle cruise situations the AFRs will jump rapidly up and down and the engine will begin jerking/bucking/stuttering. Here's a screenshot from a datalog of the issue happening (the issue starts right after the line in the middle):



Some notes:
- My CLT signal appears to fluctuate a lot, but the range it is fluctuating in is small so it isn't changing the pulsewidth based on CLT temperature
- The engine runs great at all other times
- It really doesn't feel like the engine is misfiring at all when this is occurring
- I've tested the following ignition components: plugs, coil packs, ignition drivers, spark plug wires
- My ignition setup is: wasted/COP hybrid with M50 coils and BIP373 drivers
- AE is not being triggered when this happens
- The lower the dwell and the leaner the mix the worse the issue seems to become

I can attach the full datalog/my MSQ if that would help at all. Thanks for looking!

[blasphemy101]

Does your timing map look okay at that point? I had my timing too retarded in a spot and it would make the car go lean and sputter.

[Jaxx_]

post up your maps... I bet you have some significant "hole" either in timing or fuel in those cruise areas. If you fade them properly (or add another row to the bottom) you shouldn't have the jerkiness as you get on and off the throttle, or at light throttle.

So, post up your map (either 2d or 3d) or your msq. I bet something is lumpy.

[ColdAsLife]

Also check your overrun fuel cut as well if its enabled.

[MaxBell]

On an unrelated note, WTF E30TECH?! It's been like years for me...

[nightbear]

I have just the same issue, still unresolved.. but I run EDIS.. I have the same spikes in voltage and CLT and the symptoms described are the same

[MattPro]

Sorry for never responding to anyone, I never received any notifications that anyone actually ever responded to this post. Thanks for the responses. Here's the latest info on my struggle with this:

Well I found out the stuttering and jerkiness is definitely misfiring, and I pulled my plugs and found that 1,3,5 looked extremely terrible and 2,4,6 looked great. So it seems like a problem with one of the injector batches.

I'll post my MSQ when I get my laptop from the car inside at some point. I do not believe it is timing or fuel map related though, I've used some safe stock maps that work well for other cars with no crazy mods and for fuel I've made from an extremely smooth curve to just running it super rich everywhere and the problem happens in the same way. I've also "turned off" EA and EAE. If I turn off overrun fuel cut the engine backfires extremely horribly so I have to keep it on for now, I don't think overrun is directly limited either.

Some more testing:
- The problem still persists with a different set of injectors, the lower flow injectors I go the better the problem gets
- The richer I make the mix on low loads the less the misfires happen.
- I rewired both injector groups using the factory wiring as opposed to how the P/O of my MS setup had it
- I replaced both Q1/Q5 Q14/Q15 on the MS board

The problem is still there. It has gotten better at this point though. Am I going completely insane thinking it's fueling related? Since I have wasted spark I'm having a hard time believing that three cylinders could be having ignition issues.
All of these things just really lead me to believe one injector circuit is not opening the injectors fully and leaning out those cylinders on the low loads. That's why I get the horrible backfires on extremely low loads and the random misfires on just low loads.

Sorry for the huge reply this is just driving me insane at this point.

And nightbear let me know if you make any progress with your diagnostics, I'm willing to try anything at this point to find out the root of this problem.

[Q5Quint]

Dude- your sensor signals are jerking all over the place- map, clt, even rpm. Maybe add a ground somewhere and see if that helps? If your pw are jumping up and down 10% every 2 seconds I can assure you it will feel jerky.

Is your afr table trying to adjust your fuel map by too much? You comment about the lower flow injectors make me thing you have a injector setting and a grounding issue that may be off.

[MattPro]

Dude- your sensor signals are jerking all over the place- map, clt, even rpm. Maybe add a ground somewhere and see if that helps? If your pw are jumping up and down 10% every 2 seconds I can assure you it will feel jerky.

Is your afr table trying to adjust your fuel map by too much? You comment about the lower flow injectors make me thing you have a injector setting and a grounding issue that may be off.

It definitely could be a grounding issue at this point, I know the sensor readings definitely are not right. But from what I've seen they do not affect the PW when the car is misfiring. The example I posted was an extreme one, and the drops in the RPM/MAP were causing the PW to get all lumpy. I have other datalogs that show the PW as a straight line when the car starts to misfire on the low loads.

Before I start trying to figure out anything else I'll try to take care of any hardware/ground issues I have first...I'm going to go through the harness because I have no clue how the P/O has it wired up. Hopefully I'll find something obvious in there because I feel like I may have taken a few steps too far in the wrong direction in diagnosing this at this point.

Thanks for the response, everything is helping at this point.

[Q5Quint]

The PW is an output from the megasquirt based on the sensor inputs. If your inputs are jerky like that then the pw will output jerky trying to match its inputs.

I would see if you can find a tune from another member with a similar setup/ same injectors etc that we know works properly, and see if that tune has the same problems. That will rule out tune/software issues.

If the PO soldered this baby together you might simply have a loose connection somewhere. Testing the ms unit itself with a jimstim to make sure the sensors are not jerky will rule if there is a wiring issue on the board itself, or in the wiring harness of the vehicle.

The misfire at low loads could be several things. Software fueling or coil timing, fouled up spark plugs, some kind of deceleration fueling issue. Try to rule out one system at a time before doing a general system grounding. If your spark plug gap is off there is no point in rewiring your megasquirt. If your crank sensor signal is backwards and gets too much interference at low rpm causing the ms to be unsure about rpm and misfire... you may just need a new sensor cable, or sensor, or just adjust/clean the sensor. Compare the signal to the jimstim signal.

Fun stuff ;-)

[nightbear]

Ha! I think I got the problem of the cruise stutter fixed!
Was reading everything I could on the issue and at some point found a guy with a 2002 with just the same issue, which was finally fixed by upping the timing advance at that point!
So I tried setting the timing to 40-50 degrees at that area and voila, sputter-free cruise!
Hope that helps!

Now I'm on to the next trouble.. sometimes if the car goes to low rpm, like 500-ish, it kinda "switches" into a mode where only half of the cylinders work. So it stutters badly and needs a restart.. Haven't found the problemmaker yet..

[scoobydo]

Regarding your new problem, are you getting a lean misfire perhaps?

[MattPro]

I've moved on from this car, but saw this got bumped a couple weeks ago and wanted to share my findings in case anyone has the same problem and is searching. It turned out to be low compression in one cylinder...No matter what configuration of spark/fuel I changed and however I rearranged the cylinders the same cylinder always misfired... so I spent months rebuilding/wiring/re-tuning all for nothing.

[BMWManiac]

Thanks for closing out the thread with your solution. I kind of am having a similar problem, which isn't too bad, but when I am cruising in a high gear, and just perhaps slight throttle, the car will start jerking because it is too lean....I wonder if I up the timing a bit in this area, it might get better.