Pete L

I’ve described the poor running characteristics of my 1986 (early) 5 speed in another post.

No power, poor running. Symptoms, 11” of vacuum at idle (no vacuum leaks verified with smoke test). Engine is solid for a 170K motor, under 15% leak down in every cylinder and 160# of compression +/- in each cylinder (cold). Timing belt, camshafts, crank damper are all in proper alignment and good condition (I’ve replaced the TBelt 5 times in the 26 years I’ve owned the car, it’s all in alignment and correct). The MAF, computers are known to be good.

Diagnose Rational - At idle the timing light when on #1 cylinder is at 18 degrees after TDC vs 10 degrees BEFORE TDC per specification. Thus, the initial and virtually all timing appears to be 28 degrees retarded. At 3000 RPM timing advances to about 5 degrees BTDC at no load – should be around 35 degrees BTDC

So my question is this - is my diagnoses of a slipped or moved timing ring gear that is press fitted to the flywheel correct or plausible? Anybody else have this problem in the past? I was told of an 85 in Virginia that had exactly this problem by Rich at Electronik repair. Mark Anderson at Sharktoberfest told me he had seen these timing ring gears crack in the past.

Is there a way to check the timing ring gear teeth alignment short of dropping the clutch and removing the flywheel; for example, at TDC where would / should the alignment of the double tooth gap be located – could I verify by removing the crank position sensor ?

Thanks all

Pete
86 early 5 speed (US)

Mrmerlin

with the engine at TDC you should be able to see where the double tooth is without clutch removal and then all you need is a picture of the flywheel installed at TDC to match what you have.
IIRC Carl at 928 Motorsports had an issue of a moved timing ring you might give him a call and see if he will share what he knows.

I think he wound up moving the timing ring then pinning it

GregBBRD

You're still suffering from this?

I've never seen the trigger wheel slip, but anything is possible....

Here's a bit of free "food for thought"....since you've been dealing with this, for so long.

Years ago, for the early cars, Porsche was sending out the "green" ignition wire from the distributor to the C/D unit with the two wires switched. This retarded the igniton timing a country mile....much like you are describing.

I'm wondering if the wires got switched at the crank trigger on an injected car, if the same thing would occur?

No one repaired the connector to the crank trigger just before this occurred, right?

Pete L

Mrmerlin-Thanks I did leave a message for Carl earlier this week and yes, if someone out there has a photo of the two missing ring gear teeth with the engine at TDC, that would be really helpful

Greg - Still struggling to figure this out but working too many hours on a mega project in downtown LA. The problem manifested on the third pull of a dyno test at circa 5000 RPM. First two pulls were good with 310 +/- RWHP (had Kens chips at that point + X Pipe). On third pull, motor went completely flat - kept running, but absolutely no power. I flat beded the car to my garage, where it sits today up on the scissors lift and determined that the Tbelt /cam chains and motor internals are all checking OK. Good thought, but no changes or revision to the the crank trigger or its wiring since the dyno pull

Anybody have photos of the orientation of the ring gear teeth I can use to compare where my car sits? How is the ring gear aligned / oriented to the flywheel by Porsche, are their punch marks for exampel?

V2Rocket

How old is your crank position sensor?


http://jenniskens.livedsl.nl/Technic...7/MyTip704.htm

GregBBRD

Looking for the obscure and bizzare is rarely the place to start.

I'm not saying that a slipped trigger ring isn't the problem....I just wouldn't start there.

I'd confirm that I was testing cylinder #1 spark....and didn't make a mistake and be looking at the timing from the wrong cylinder.

Then I'd try a different set of computers from another car....ones that had the original chips in them and were verified to run correctly.

Then I'd replace the crank trigger.

Pete L

Greg thanks

I've tried two different computers. I have a factory original as well as the ones with Ken's chips. nnumber one cylinder is confirmed

realize this may be an obscure problem I've tried all the normal things

Any advice on how to check the position of the ring gear with the clutch and flywheel still on the car is appreciated

V2rocket. The car still runs in the crank sensor is virtually new

Mrmerlin

did you ever get a hold of Carl?

GregBBRD

I can certainly take a picture of an '85 flywheel still on an engine....I've got one, sitting here, on a dolly.

And I can bring the trigger up to the sensor hole and tell you where TDC on the front damper is, when this occurs.

Is this what you are trying to do?

Pete L

Greg this is exactly what I'm trying to do

Mrmerlin

why not put the trigger gap on the bottom dead center so its easier to see in the OPs car and then note the location of the damper and where TDC marks line up

GregBBRD

Because I want him to have to pull the crank trigger and stare down that little hole, looking for the gap, while he turns the engine over?

That's a good idea! I'll see what lines up. If we had a BTDC mark on the damper, this would be simple....but I think the gap is going to be near TDC and at the top.

Pete L

Greg so appreciate your ideas which ever works I don't care if I have to pull the crank trigger sensor . How does Porsche guarantee the alignment of the crank ring gear trigger with the flywheel? that still befuddles me

GregBBRD

Friction only. Heat up the trigger wheel and drop it onto a cold flywheel.

In the days before Sharktuning, I removed a few and shifted them, a bit....

When we make new flywheels and use the original trigger, we pin them, nor trusting the whole friction thing.

John Speake

IIRC the two tooth gap on the ring the CPS uses is 68.4 degrees before TDC.....

We had to get this info while developing the Sharktuner. It would be good if Greg can verify this ...