Starter breaker

[MURF]

1990 944 cabrio..3.0 1990 block and crank,je pistons with 8 valve cutouts,
2.7 cyld head..turbo wiring harness ,lindsey computers.we've had car running..problem is it will lock up on cranking sometime and break the nose cone off of starter [4 starters bosch]with dme relay out it will crank fine..turbo lindsey flywheel..set up with new harness from 1988 turbo...please advise ...lost in ny

[MURF]

Seems like my timing is too advanced..could the flywheel be the problem?
3.0 crankshaft in 3.0 block..with 944 turbo lindsey flywheel and all turbo harnesses and timing components...breaks starter nose cones?

[kdjones2000]

That would seem a possible cause. Hard to debug with all of the modifications going on...

What are you using for engine management?

[MURF]

Wiring harness is 1988 turbo stock components with lindsey chips

[Techno Duck]

Could be starter kickback, which speed and reference sensor bracket are you using? The later ones had a EMF shield for one of the sensors (forget which one). When the smaller starters on the turbo started being used they produced a higher EMF which causes the computer to fire at the wrong time giving you kickback. Something worth checking.

I had this issue when i did the clutch on my car, broke the bracket and replaced using the older style. Would get a kickback probably 1 in 4 starts until i replaced it with the proper later style bracket.

[MURF]

Techno thanks i already have the updated stuff replaced cables and insulated them..i had both computers checked first by linsey,second by ecu doctors..was advised there fine...already broke nose cones off 4 bosch starters

[Techno Duck]

Some other things i was thinking of...

What starter ring gear is on the car? The turbo ring gear is 132 teeth while the one from the 8v n/a is 130 teeth. 2 teeth wouldnt throw the timing off a little but not by much.

Another thing i was thinking of is the 951 bell housing is different than the 944; the starters are interchangeable but not the bell housing. The spacing of the starter relative to the ring gear is different to accommodate for the larger ring gear diameter. Its possible the combination of parts on the car might be off; for instance a 951 pressure plate / ring gear / clutch assembly in a 944 bell housing. The part number on the bell housing should start with 951, but in typical Porsche fashion its possible a 944 prefix bell housing could be either or. So if you have a 951 prefix bell housing its probably right, but if its a 944 prefix you will need to check in PET to make sure its the right one.

Strange that it cranks fine with the DME relay out though, leads me to think its the engine firing at the wrong time. Do you guys have an oscilloscope handy to check the signal from the speed / reference sensors? I am pretty sure the factory 944 shop manual has a good section on troubleshooting the sensors and shows what the wave form should look like if you scope the sensors.

[MURF]

I have 3.0 crank with 951 flywheel..are the dowel pin for sensors the same?..seems like my timing is too advanced i was told it was the same but salesmen lie .it appeared to be correct when installed?