Timing mark on 3.2 distributor, how close do I need to be?

[Chris T]

Morning all, an ever on-going story that I won't bore you with.... 3.4 twin spark now back on Std ECU and distributor in an attempt to get the bl**dy thing going at last. Lining up the rotor arm with the notch on the rim of the distributor at TDC I cannot get it spot on, it's either 15 or 20deg before the mark (but centrifugal weights allow advance to the mark) or 15-20deg ahead of the mark. Same story if I turn engine through 360deg and re-align. Manual says it should be on the mark but it never is, anybody know why/how this happens? How close to the mark does it need to be to fire? I know the ECU corrects it assuming timing sensors work (3rd new set).

Thanks, Chris.

 

[PeterK]

The ECU will control when the spark occurs, but the dissie timing controls which plug fires & so the rotor arm needs to be ‘in the right place’ relative to the terminals in the dissie cap to give the strongest spark.

[PorscheApostle]

20 hours ago, Chris T said:

Morning all, an ever on-going story that I won't bore you with.... 3.4 twin spark now back on Std ECU and distributor in an attempt to get the bl**dy thing going at last. Lining up the rotor arm with the notch on the rim of the distributor at TDC I cannot get it spot on, it's either 15 or 20deg before the mark (but centrifugal weights allow advance to the mark) or 15-20deg ahead of the mark. Same story if I turn engine through 360deg and re-align. Manual says it should be on the mark but it never is, anybody know why/how this happens? How close to the mark does it need to be to fire? I know the ECU corrects it assuming timing sensors work (3rd new set).

Thanks, Chris.

 

This is normal , the ignition is controlled by the ECU. The distributer just positions itself over the correct firing terminal in the cap. The offset is as you say to the advance of the centrifuge. You can still check the timing and the advance just like an SC but you can't adjust it as the distributer is fixed in a 3.2 and even if it wasn't the ECU does the ignition.  

 I suppose you could slot the the m8 hole in the distributer housing to adjust the position of the rotar relative to the cap to achieve the shortest arc length but this would not really achieve anything as the ECU does the spark and you'd need to see where the advantage would be. Under load I dare say the factory advance would achieve this. 

 

DBS 

 

 

 

 

[Chris T]

Thanks for your replies. Obviously the ECU sets the timing, but with the rotor arm much further away from the mark than expected, and therefore further from No.1 HT output, there must be a limit as to how much the ECU can compensate for. Bently manual shows rotor arm leading edge just about on the mark, mine is some degrees before that. Next tooth on the distributor's shaft brings it way past the mark. Sprocket is fixed on distributor and on crankshaft right? So how can it have moved perhaps should have been my question, I'm wondering if I'm now on the edge of what the ECU can compensate for....

Chris.

 

[PeterK]

The ECU cannot compensate for the rotor arm positioning.  If the timing was altered to ensure that the rotor arm was in the 'right' place, the spark would occur at the wrong point of the suck, squeeze, bang & blow cycle.

My only other thought is 'how accurate is your timing mark' ?.  

 

I would go with just before rather than after.

[Chris T]

Timing mark is scribed into distributor casing at the factory..... The ECU MUST compensate as with only 12 teeth on the distributor drive the only positions you can place the distributor are 30deg apart. (there is no slotted hole to allow swinging of the distributor on a 3.2) If one of those positions fails to line the rotor arm up accurately with the mark, then the ECU makes the compensation and times the ignition in line with it's maps. So, I re-fitted the 964 distributor. This time the rotor arm lines up accurately with the mark where No.1 HT lead exits the cap.....

And..... Still doesn't fire at all, although it did cough a bit briefly. Still no further forward. I gave all the injectors some exercise in situ with a cleaning machine and confirmed fuel pressure is present. Still nowt. 

Next up is a 2 person job to confirm sparks are happening, a friend is popping over on Saturday. Will report back.

Chris.

 

[PeterK]

Sorry Chris - I meant the TDC timing mark in the pulley & casing

[Chris T]

Pulley and casing marks gotta be accurate right? Besides with distributor turning only 180deg for every 360 of the crank, any tiny errors would be halved, and it's only a necessity to get rotor close to No.1 when refitting so I'm confident that is correct. 

TBC in a couple of days..... Chris

[PorscheApostle]

6 hours ago, Chris T said:

Timing mark is scribed into distributor casing at the factory..... The ECU MUST compensate as with only 12 teeth on the distributor drive the only positions you can place the distributor are 30deg apart. (there is no slotted hole to allow swinging of the distributor on a 3.2) If one of those positions fails to line the rotor arm up accurately with the mark, then the ECU makes the compensation and times the ignition in line with it's maps. So, I re-fitted the 964 distributor. This time the rotor arm lines up accurately with the mark where No.1 HT lead exits the cap.....

And..... Still doesn't fire at all, although it did cough a bit briefly. Still no further forward. I gave all the injectors some exercise in situ with a cleaning machine and confirmed fuel pressure is present. Still nowt. 

Next up is a 2 person job to confirm sparks are happening, a friend is popping over on Saturday. Will report back.

Chris.

 

I haven't been following your build thread but I've used a 964 dizzy on a 3.5  twinplug application on a 3.2 motronic ecu before. If I  new more of your setup I'd be able to advise how to get around the issues you're having.

DBS 

[PorscheApostle]

https://www.instagram.com/p/B8PLwSCluJK/?utm_medium=copy_link

[Chris T]

Nice, and s'funny. I'm seeing Russel Lewis formerly RSR engineering on Saturday..... Glad to see he (or his team, he's retired) has experience with modified engines like mine.

[PorscheApostle]

2 minutes ago, Chris T said:

Nice, and s'funny. I'm seeing Russel Lewis formerly RSR engineering on Saturday..... Glad to see he (or his team, he's retired) has experience with modified engines like mine.

Russell is semi retired, he was my mentor for years but we haven't worked together in over 3 years now. I saw him today incidentally . Geoff(formerly of cridfords and ronnoco) works a couple days a week in my place. He and Russell used to be apprentice at Porsche AFN back in the 70s. 

 

Russell should be able throw some light on your issues the system that runs on that  twinplug is 1 by andial, it has a signal amplifier for the ignition modules to run both trigger switches and has separate standalone switches to test each circuit. It also runs a maf conversion . You need at least a 3.5 volt trigger feed from your crank sensors to switch it and it has to amplified for the 2 triggers.

 

Bit of an antiquated system but still going after so many years

 

D

[sopor]

A well-timed (sorry - bad pun!) article in the Feb 2022 issue of Excellence reads:

Interestingly, the Carrera 3.2 distributor and that of the later 964 and 993 retained centrifugal advance weights; these did not affect timing advance, but Porsche stated that the weights were used to keep the distributor rotor tip(s) close to the individual cap terminals at higher rpm. This was important because there was insufficient space within the 911's small six-cylinder distributor cap for a broad-tipped distributor rotor as used in the 944/968 and 32 valve 928s of the period.

[Jonny Hart]

^ True that the weights are to align the rotor arm with the post across the Rev range - AKA rotor phasing. 
 

My CDI+ box works fine with a locked distributor and no dynamic phase correction.   I have a cap that I made with a hole around post 1 which allows direct viewing of the rotor arm with a strobe light.   The higher the RPM, the more the rotor arm moves towards the centre of the post so there are no problems at all.   At low RPM (idle),  the rotor arm is offset to one side but still enough on the post.  There is very little cylinder pressure ar idle so the chances of a misfire are further negated.     Never had a problem.  

Edited January 15, 2022 by Jonny Hart