Help finding trigger of huge stumble at higher RPM

[ohecht]

Saturday I started having a very bad stumble (that's an understatement...it felt like hitting a rev limiter) at around 5800 rpm. It happened 3 times and I got two logs of it...the 30-minute drive just before the one where this started was perfectly smooth up to 7000 rpm, and no physical changes were made to the setup. The car is an '82 911, running twin-plug EDIS with a 36-1 wheel on the crank pulley, and sequential fueling.

I've been staring at the events in the log files, but can't figure out what's starting the bad series of events. I'm hoping someone with more expertise reading logs can spot at least what's happening first in the logs if not the root cause of the issue. I did notice much higher Timing Error % values in the bad logs vs the logs without issues driving, but I'm not exactly sure what that value indicates.

The first log section shows the issue starting while accelerating in 3rd gear.

The second log section shows the issue starting while accelerating in 2nd gear a few minutes later (after filling the fuel tank).

MSQ is also attached...thanks in advance!

Olivier

2015-11-14_15.26.16_modified.msl

2015-11-14_15.37.26_modified.msl

2015-11-14_14.24.42.msq

[kjones6039]

running twin-plug EDIS

Probably has nothing to do with your issue, but FWIW......... This is exactly the reason that I (and lots of others) ditched our EDIS systems on engines that turn 6000+ rpm!

Now, before I get flamed, I fully agree that EDIS is a robust/reliable ignition system, but I am always suspicious (of EDIS) when users say that they have high rpm issues while using this system.

Just my 2 cents of course......

Ken

[dontz125]

Has anyone ever established if there IS a rev limiter in the EDIS module?

[kjones6039]

Has anyone ever established if there IS a rev limiter in the EDIS module?

Not to my knowledge, Don. I am just offering my opinion, based on my own experience.

Ken

[billr]

I thought EDIS is a "wasted spark" system; you have the MSQ set for EDIS and single-coil... and you note you have "twin-plug". Is this a somewhat non-standard EDIS?

[kjones6039]

I thought EDIS is a "wasted spark" system; you have the MSQ set for EDIS and single-coil... and you note you have "twin-plug". Is this a somewhat non-standard EDIS?

Excellent point! (never looked at the MSQ) EDIS, is in fact a "wasted spark" system!

ohect, are you using an EDIS module or just the coils?

Ken

EDIT: you have me curious now........ I am not familiar with "twin-plug EDIS"...... What's up with that?

[jsmcortina]

EDIS uses a single control signal from the ECU to the module, so DOES require "Single coil" as the output setting.

James

[ohecht]

Thanks all. I have two EDIS modules and two coils, but they are still triggered by the MS3 together as a single unit. I didn't change anything with the EDIS setup as this started happening, and I had no problems spinning the engine to 7000 rpm in the few months I've been driving the car like this.

Can anyone see in the log what is actually starting the sequence that causes the massive stumble? While driving, I noticed that the engine went super-rich as it was happening, in case that helps...

[billr]

Have you tried running it on each EDIS separately? I'm thinking disconnect between MS and an EDIS, not just disconnect power to one EDIS. I'm kind of "grasping at straws" here, but there have been other threads about problems trying to drive two ignition systems from one MS ignition driver... with "twin-plug" Porsche engine.

[ohecht]

The plot thickens? Here's the entire timeline so far in one place and with the new information from yesterday and this morning added. I apologize for the length of the post, but I wanted to get the entire history of this issue in one place.

Friday night: I rewired the TPS with a shielded cable to try to solve some noise issues in that signal. I used DIYautotune's shielded wire, running the TPS 5v ref and signal wires though the new shielded cable. I didn't change the sensor ground and I grounded the shield to chassis ground where my other shielded cables (Cam sensor and VR crank sensor to EDIS modules) are grounded. I also added a fuel pressure sensor at this time and shared the TPS 5v ref signal from the TPS with this sensor. I added the fuel pressure sensor to replace a liquid-filled gauge that was giving me different readings based on the temperature of the fluid in the gauge. Sure enough, the more stable reading from the new sending unit was different than what I had used in my required fuel calculations, so I adjusted those in the ECU and shifted my VE table slightly to account for that. I think the required fuel moved from 5.2 to 5.

Saturday morning: 30 minute highway drive trying to log good data to tweak my tune after the required fuel and VE table changes. I ran the car though the rev range in almost all gears and it ran perfectly...no issues and very smooth.

Saturday afternoon: after using MLV to tweak my VE table based on the morning's log data, I drove home about 3 hours after the first drive. Everything was fine until a 3rd gear pull on the highway where I ran into the "massive stumble" issue...this happened again after a quick stop to check things and these are the two logs in my original post. The only thing I noticed and changed was to increase the values in the last column of the VE table since I never hit that RPM during the morning drive and was worried that the mixture going lean near that part of the VE table was the cause of the issue.

Sunday: performed the second valve adjustment, 1000 miles after the rebuild...all the valves were close and nothing unusual happened during the process

Monday morning: drove ~10 min to work and nothing unusual happened, but I didn't really get a chance to hit high RPMs due to traffic and since the engine never really warmed all the way up.

Monday afternoon: drove to run an errand and pushed the car a little harder once it warmed up...still nothing major or sustained and no issues. On the way home from the errand, though, I noticed that the AFR reading in TS was pegged at 19.9. I have a 14point7 Spartan 2 on the right bank and an Innovate MTX on the left bank. I'm in the process of switching to dual Spartan 2s, but 14point7 is out of stock until January so I've been using the Spartan 2 to feed the ECU and the MTX just to display the AFR on the MTX gauge. The MTX gauge was displaying normal AFRs, so I drove home about 2 miles at low rpms. I checked for wiring issues, ignition misses (since I did have to disconnect all 12 spark plugs during the valve adjustment and they're a pain to reconnect), but the engine sounded normal and I could not detect any misses or misfires on the right bank. I emailed 14point7 about the issue and also ordered a new WBO2 sensor in case that was the problem, even though the sensor is barely a month old.

Tuesday morning: I switched over to the Innovate MTX to feed the ECU to see if the AFR issue would go away while I waited for a new sensor to try. As soon as I started the car, I noticed that both AFR readings were now pegged lean. You can see them in the attached log, even though only the MTX was feeding the closed loop in the ECU. I disabled the WBO2 authority (set to 0) so I could get to work. The drive was normal until another 3rd gear pull on the highway, where the same thing happened...you can see that in the attached log file...this is just a snippet of the log from just before the issue starts in the log as it's all I could upload here. I was able to limp the car to work keeping the RPMs very low, but the engine didn't run smoothly even when idling after parked. A quick restart did result in a smooth idle, so something is triggering the issue at higher loads/RPMs and then the car is getting stuck in some type of cycle until a restart. I did also manage to capture a Composite Log while the issue was happening just before getting to work...that log is also attached. It looks normal to me, but I'm not an expert at reading those logs. The logs also show no Lost Sync issues at all...there are Timing Errors when the issue starts, but I don't know if those are the cause or the effect and even exactly what a Timing Error indicates.

So, I was hopeful that it was something with the AFR issue I found yesterday, but that seems unrelated unless it's somehow through the wiring changes I made on Friday night (even though those didn't seem to cause any issues at all during aggressive driving Saturday morning all across the rev range). Since I had the closed loop system locked out on the way to work this morning and the issue happened again, I don't think the AFR correction is causing the issue.

I've never had issues with the EDIS setup before, but I'm starting to suspect something in either the VR signal, modules or coils...I will have to figure out how to isolate and identify any issues there without running single-plug under load, since I need both plugs to avoid detonation under load. Here's a link to how my EDIS system is wired, and I'm not sure how to check everything without just replacing things and seeing if the problem goes away...http://forums.pelicanparts.com/uploads1 ... 541009.jpg

2015-11-17_08.49.37.msq

2015-11-17_08.44.48.csv

2015-11-17_08_modified.msl

[ohecht]

On the drive home today:

- The MTX WBO2 was now reporting normal values...not sure what changed there as all I did is park the car for ~12 hours

- I went past 6k RPM in second gear but did not encounter the same issue

Here's a Composite log of me revving the engine to about 7k rpm sitting still. Can anyone see if this looks normal? Again, I'm running dual EDIS with a cam sensor for the sequential fueling.

I've poured over the log from this morning to try to find the first thing to go wrong, but can't see it...it looks like the RPMs just drop off and then the cycle starts. I'm going to go through all the new wiring from Friday night again to see what could be going on...

Thanks again,

Olivier

2015-11-17_19.58.41.csv

[thedrew]

unrelated, but I noticed during the stumbling your knock sensor being triggered and its pulling timing back.

also your fuel pressure is all over the place....where is the sensor?

[ohecht]

I did notice the knock spiking and then the timing pulling back, but I thought that was a reaction to whatever was starting the event. The knock seems to spike just as the RPMs fall off, and then the timing isn't pulled back for a few more cycles because I think I have the knock sensor settings set to pull timing after 3 knock events. Let me know if you're seeing something different in terms of the order in which things are happening, though.

For the fuel pressure sensor, it's an AEM 1-100 psi sensor that I mounted where the liquid-filled gauge was...I have a short section of hose from the metric test fitting on one of the fuel rails to transition to the 1/8" sensor fitting. I'd have to recheck the fuel flow schematic, but I believe this would put the gauge before the fuel pressure damper and FPR...the fuel rail setup is stock from a '84-'89 Porsche Carrera and the sensor is mounted on the rearmost section of the driver's side fuel rail.

Olivier

[thedrew]

yeah, the knock isn't causing the stumble -- just something i noticed.

yeah I'd just make sure you're not having a fuel delivery issue -- my fuel pressure readings fluctuate maybe +/- 1psi.

[ohecht]

Thanks...I'll take a look at that. I assumed that level of fluctuation was normal as the MAP reference changes, but maybe not...

[thedrew]

it might not be the root of it...but steady fuel pressure never hurts My fuel pressure tracks w/ my MAP, but its pretty smooth.

just stepping through the records during the stumble event I see the PSI oscillating between sometimes 20psi and then up to 45+psi in like .5 secs. If your injectors are truly seeing this kinda pressure changes they're not gonna be happy!

whats your target PSI at 100kpa?

[ohecht]

Thanks again. I agree more stable pressure could only help. I'm not sure how to answer your question about the target pressure. What should that be based on?

I just replaced the WBO2 sensor for the Spartan2 and its reading normally again...not sure what was going on there with one new sensor going bad and the. The other one read full lean for one day and then went back to normal. Weird and not sure if it's related to what's going on with the stumbling...I haven't been able to recreate it since Monday but will keep trying...carefully.

[ohecht]

I thought more about your fuel pressure question...if you're asking for the target fuel pressure at atmospheric pressure (with the fuel pump running and the engine off), that's set at 43 psi and only varies +/- .5 psi around that number.

[thedrew]

whats your fuel supply setup look like?

how big of lines and how big of a return?

[ohecht]

I don't know the exact sizes of the hoses and lines, but it's all brand new with the rebuild and stock 911 SC stuff on the chassis with stock 3.2 fuel rails and lines. All the soft lines are new as are the hard lines running between the engine in the rear and the tank in the front. The fuel pump was replaced about 5k miles ago, but before the rebuild so it's a few years old. The lines might be ~7.5mm in certain places, but I think the diameter varies with the supply and returns and I don't know all the dimensions.

The problem popped up again last night after 3 days commuting without issue (my commute is short and the rain and traffic have prevented me from really getting the car fully warm and up to high RPMs for any period of time). It also happened this morning, and it seems that once it happens once, I can trigger it intentionally just by exceeding ~5500 RPM. However, I've exceeded 5500 RPM several times commuting this week, albeit for short periods of time, and not triggered the issue.

Anyway, after recovering from it on the highway with a rolling restart, I was able to trigger it once parked by revving the motor in neutral. Watching the real-time display, there was a clear and massive oscillation of the timing advance, from about 5 degrees to 35 degrees. I tried disconnecting the TPS, and the magnitude of that timing oscillation immediately went down so it was from 12 degrees to 15 degrees. I tried connecting and disconnecting the TPS and each time it had this impact on the timing advance. Clearly there is some noise being introduced into the ignition circuit (probably into the VR crank signal going to the EDIS modules) from the TPS, and I did add that shielded wire to the TPS the night before this all started. When I get home I will change the TPS back to standard wiring (the shield didn't seem to reduce the noise in the TPS signal anyway). When I connected and disconnected the TPS, it seemed like only the ignition advance changed...the RPMs kept oscillating and the timing error kept oscillating between -100% and +50% whether the TPS was connected or not...the engine didn't really smooth out, but the variation in the ignition advance was clearly reduced.

Hopefully removing the shielded wire from the TPS will eliminate this issue from even starting...the ignition has been rock-solid up until I made that wiring change with the TPS, but I'm still not sure how adding a shielded wire would cause this level of issue. I have the following shielded wires on the car, all with the shields connected only at the chassis and not at the sensors:

- EDIS VR sensor to EDIS ignition modules...this wire is about 24" and all in the engine compartment and the shield is grounded to the chassis in the engine compartment
- Clewett cam sensor to MS3...this wire runs all the way to the ECU under the passenger seat, where I believe I grounded it to the chassis...I'll check on that when I get home.
- 2 Bosch knock sensors to the chassis ground in the engine compartment
- The TPS wire, grounded to the same chassis ground in the engine compartment...this is the one I added just before this issue started and will try removing today

Olivier