Engine cuts out at 1000rpm

[billjam]

Engine runs fine, but regardless of engine temperature, if I let the revs drop below 1000, it stalls.
In the attached log, at 1005s, 1230s, 1412s and 1635s, you can see what happens when I let the revs drop to 1000.
The engine dies immediately and a sync loss event is registered. I am presuming the sync loss is because the engine has stopped ... correct?
I also have a sync loss issue while cranking (separate thread), but this doesn't seem related to the 1000rpm cutout.

The engine is a 3.6 Porsche with ITBs. There are no vacuum leaks and ITBs are balanced.
Idle is currently set at around 1100 to get around the problem.
I can replicate the stall by slowly adjusting idle speed down and as soon as it hits 1000, it stops.

Got any hints?

[slow_hemi6]

Ok so from what I can see your cranking sync loss and this problem are one and the same. It definitely starts loosing sync under 1000rpm. It is registering several sync losses before it registers you going into cranking. Most likely the sensors gap or the pots setting but it is loosing the signal sub 1000rpm.

[grom_e30]

can you post a tooth log? i had a problem just like this when i first started on my and it turned out to be the vr was wired backwards a tooth log will either confirm or rule this out.

[billjam]

Ok so from what I can see your cranking sync loss and this problem are one and the same. It definitely starts loosing sync under 1000rpm. It is registering several sync losses before it registers you going into cranking. Most likely the sensors gap or the pots setting but it is loosing the signal sub 1000rpm.

Luke,
I have double-checked sensor gap. For standard Porsche (= Bosch) sensor, the gap should be (and is) 1mm. It might be worth closing this up to see if it has any effect.
Pots setting seems to be a bit of a mystery. I have played with R52 and R56 in the past to solve initial starting problems, but there doesn't seem to be any science to this.
The starter is kaput at present. It's sprag clutch recently died due to the brutal kick-back I am getting, so I have to wait for parts from the US before I do any more testing.

[billjam]

can you post a tooth log? i had a problem just like this when i first started on my and it turned out to be the vr was wired backwards a tooth log will either confirm or rule this out.

Grom,
I have already been down this path. I had this polarity wrong when I tried first start, but got it sorted early on. I don't have a tooth log handy right now, but the last time I ran one, the log was perfect for 60-2 flywheel.
The log is something I need to recheck once I get the starter working again.

[cmonref]

Bill,

In looking at your MSQ, you have IDLE VE turn ON and CLOSED LOOP IDLE turned OFF. It does not appear to make any difference, but it does seem odd.

In looking thru the MSL, it appears that something in the ignition is quitting as the RPM goes thru 1000. The fuel variables (PW, MAP) stay where they should. So I hoped to wander thru the variables, looking for something that changes at the right time. But I am surprised at the lack of variables available for selection. Did you delete a host of the variables in the MSL in order to reduce its size so that you could post it? I think so, since there lotsa variables not present, but you have 18000 records. Normally, the file size is reduced for this purpose by deleting a number of records, leaving enough records to show the picture you describe in your post.

If you have the complete MSL, send it to me without deleting anything. Send it to my email -- I believe you have it from previous correspondence. I will continue my searching and "wandering" thru the variables.

Brian

[billjam]

Brian,
I don't recall deleting anything from the log but I'll have a look at it tonight and get back to you. Maybe it was one I ran without all parameters selected. I may have other logs that have more detail as well.
I have been through every screen in TS trying to identify anything that is related to "1000 rpm" in tables or settings, but obviously I haven't found it yet either.
What would be nice to determine is whether the sync loss is the cause or result of both the difficult starting and <1000rpm cutout. It seems to me that there is an issue in the crank sensing department. Whether that is something as simple as closing up the sensor gap or adjusting pots I don't know.
I am a bit stuck at present because the starter died due to the kick-backs it has been dealing with. A new pinion drive clutch is on its way from HiTorque, so I can't test out any suggestions received here until the part arrives.

[cmonref]

Bill,

Will be interested in seeing a log with all of the variables, with perhaps fewer records, in order to go thru it in detail looking for the variable that is cutting out the ignition. If you routinely log only the small set of variables, you should consider logging all of the data. I certainly don't use all of them, but as experience is gained, more and more get used. And I cannot forecast which variables will be useful tomorrow. But I am beginning to understand why the experienced heads want the whole log, not just a screen shot.

In the meantime, I mentioned in your other thread that your cranking speed of 500 RPM is too high. Mine is 350, and it looks like that will also work for you. Looks like 500 gives you a very long crank period. I doubt that this is causing the sync loss.

Someone mentioned that the sync loss is definitely occurring AFTER the engine cuts out as it passes downward thru 1000. I tend to agree, but leave open the possibility that it occurs AT 1000 and kills the engine.

It may be that the advanced timing results in kick-backs, especially combined with your high cranking speed setting. 5 degrees (certainly less than 10) and 350 RPM will help.

Log to my log name at Verizon dot net when you find one with all the variables.

Brian

[BigLou240sx]

Sorry in advance... No insight on your 1000rpm sync loss, but just wanted to give a clarification to the cranking speed setting:
Cranking speed setting should be set to 100rpm higher than your nominal cranking, and does not influence the actual cranking speed your car experiences. It only changes the point in which megasquirt considers the engine running (and turns to using the ve/ign tables and after start settings).

[billjam]

Sorry in advance... No insight on your 1000rpm sync loss, but just wanted to give a clarification to the cranking speed setting:
Cranking speed setting should be set to 100rpm higher than your nominal cranking, and does not influence the actual cranking speed your car experiences. It only changes the point in which megasquirt considers the engine running (and turns to using the ve/ign tables and after start settings).

Thanks Lou, I have been wondering what was the significance of the cranking speed setting.
I have had a few suggestions on this setting, but none explained its purpose ... seems obvious now! Last time I looked, I don't think the manuals explained its purpose either.

[billjam]

After a few weeks on the sideline waiting for starter motor parts, I made a few adjustments based on feedback on Pelican Parts Porsche forum.
I reset pot R56 fully CCW and set R52 at one turn CW and problem is fixed. I can now idle as low as 400rpm if I back off the idle screws.