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Huh, first I've heard that - thought it was for all 928s.
Always learnin' something.
I've read about this here on RL a long time ago but it was not repeated often enough to make it well known. If I'm not mistaken GB mentioned that the tension requirements are different between the 16V and the 32V engine.
I cannot specifically remember when it was other than it was a long time ago but I distinctly remember something Jay wrote about the 9201 tool when he was developing his tool and that was about how in lab tests he found the 9201 to be somewhat inconsistent in lab tests and that his tool was very consistent.
Please correct me if I am wrong but his tool is based on an original Porsche design that was used for the 16v engines [the main dealers here had one] and as I understand his variant was specifically intended for the 32V variants because of the expense of the 9201 tool and thus an attractively priced option for DIY mechanics like myself.
I have used this tool for the last 5 years or so, I set it at the mid point of the range and have never seen an alarm. If the position of this tool makes a difference to within 1 tooth either way then that is rather alarming. As I understand one has to position this to test at the centre of the lower run on the 1/4 bank but do not remember ever reading it is sensitive within a hair's breadth of positioning and never thought to test for such.
Similarly I set my belt tension when the engine is cool on the presumption that it will in fact tighten up as the motor gets to full operating temperature but I am now wondering if I have misunderstood that concept at all. All I can say is that I have never had a belt alarm since I started DIY of this system and given the fail safe nature of the design presume my alarm system is working- having read this thread I think I will disconnect mine to see if I get the alarm after a few minutes of operation.
Similarly, I wonder how the 9201 tool is calibrated or how often it should be checked for calibration accuracy.
We [keen amateurs] sure do learn a lot due to this list and threads like this- hopefully this is why our 928's keep running well year after year instead of self destructing like many seem to. I have commented previously about why the cam wheels seem to wear on the flats and not on the teeth that are supposed to take the shear load of the drive - I have long harboured a suspicion that this is due to too much belt tension but nothing I can prove of course.
. All I can say is that I have never had a belt alarm since I started DIY of this system and given the fail safe nature of the design presume my alarm system is working- having read this thread I think I will disconnect mine to see if I get the alarm after a few minutes of operation.
I disconnected the through case plug, and grounded to the block. I just got done driving the car for about 15 minutes, and the warning light never came on.
Since I'm certain that the tension is at the tight end of the window per the Kemph tool, I can only deduce two things:
*The tool is out of adjustment, or
*There is an erratic connection behind the center cover that only comes about when the engine is running at high revs (the pin appeared to be grounded when I tested it, engine off).
The belt appears to be tracking fine.
Am I leaving out another possibility?
I disconnected the through case plug, and grounded to the block. I just got done driving the car for about 15 minutes, and the warning light never came on.
Since I'm certain that the tension is at the tight end of the window per the Kemph tool, I can only deduce two things:
*The tool is out of adjustment, or
*There is an erratic connection behind the center cover that only comes about when the engine is running at high revs.
The belt appears to be tracking fine.
Am I leaving out another possibility?
JP,
Did you tighten the belt and try that with nothing else changed or did you tighten and modify the earth simultaneously thus not sure which one of the two "variables" worked?
Put another way if you back off the belt to where it was previously and the light stays out you would know tension was no the problem [yes?].
What I did to diagnose this condition was to loosen the center cover and then check for ground at the plug while moving the cover in and out. At rest I got continuity to ground, as soon as i manipulated the cover slightly ground was lost. In my case the spade connector to the center cover plug had worked loose over time from being oriented incorrectly and making contact with the center cover.
Fred, I've been doing each step independently so that I can rule things out one by one. Step 1 and 2 occurred with the plug connected: Step 1: After getting the first warning, I added oil to the tensioner and checked the belt but didn't tighten it. It was 1/4 away from the tight side of the window. I suspected a loose plug connector. Crimped the brass socket to where the plug snapped onto the pin and fit snugly in the cover hole.
The warning returned. Step 2: I then went in and tightened the belt to the tight end of the window.
The warning returned. Step 3: I disconnected the plug, grounded it and confirmed that it was solidly grounded. Step 4: I drove the car for 15-20 minutes with the plug disconnected but grounded. The warning didn't return. Step 5: I repeated the 15-20 drive an hour later, spirited driving. The warning didn't return.
It's cooling down now awaiting me to try Kevin's test which certainly can't hurt.
Mid 90's today, so cooling down may take most of the day
On the upside, SCCA let me move my track day to Sunday, and if I don't get this resolved, I can cancel and get a refund
When I did my timing belt and water pump a couple of years ago I looked at that connection that goes through the case and found some chaffing on the wire outside the case. Although I could find nothing functionally wrong with it I felt it was a bit of a strange way of doing things and a potential weak link. With that in mind I made a new wiring connection direct from the tensioner arm spade out through the case via the hole for the original connector and then back into the wiring harness. Figured that being a fail safe system nothing could go wrong given that if it did fail I would get a belt alarm that to date has not happened.
You seem to be getting there - a useful thread for all 32 valve engine owners.
Had this happen to me. My issue ended up being a corroded tensioner tip the plastic tip slides into. The plastic part jammed and never made contact for the tensioner thus breaking the circuit. If you don't have continuity with a cold engine I'd start there.
I do have continuity (ground) with a cold/non-running engine, but that's from outside the center cover at the pin.
I'm definitely not ruling out your symptom. I suspect that in your case before the corroded connection completely lost continuity there was some intermittent connectivity with it.
The wire connecting to the tensioner plunger rod (#2 in the illustration) is very loose at the plunger rod. Confirms the loose and intermittent connection behind the cover.
I only have the center cover pulled halfway to the side to see this and can barely jam my hand down in there enough to feel the wire.
Anyway, since it's been a few years since I rebuilt the tensioner in my GT and that was my one and only time to have it in my hand, I can't recall how the wire lug at the plunger end of the tensioner maintains its 'tightness' on the plunger end. Is it the spring, and if so, what would make the spring loose in this situation? I suspect a washer like what Kevin says in post #6...and I suspect that washer is missing.
So is this serviceable without essentially removing the belt?
It appears that the tensioner sans the arm and rollers can be easily removed from under the car and I'm assuming that the carriage/arm would stay in place. But I'm hesitant to remove the tensioner b/c aside from the oily mess, I'm assuming that main roller on the tensioner arm is putting considerable pressure on the belt from the presence of the tensioner. I'm concerned that I wouldn't be able to reinstall the tensioner given the tension. If I back off the tensioner adjustment bolt will that ease the tension on the belt to the extent that I could re-install the plunger assy from the underside of the car without too much trouble - or is the tension too much to get it bolted back from the underside once the repair is made?
Based upon your post, it is likely this wire that runs down the length of the roller carrier arm.
So is this serviceable without essentially removing the belt?
Yes. I've had to R&R tensioners on several occasions thanks to a poorly-completed recent belt service by the previous technician. I have done this job several ways. Any attempt to R&R the tensioner without getting easy access is likely to result in a poorly-installed tensioner gasket.
My recommendation - which will require about 1/2 of the time that is needed for a 32v belt service - is:
- remove the fan shroud, upper and lower radiator hoses.
- loosen the accessories and remove the belts
- unbolt the front lift loop from the water pump
- remove distal belt covers
- wiggle-out, from around the damper/pulley, the center belt cover (it can be deformed quite a bit without breaking.)
At this point you will have full access to the tensioner, roller carrier and the belt - should you decide that you need to re-string it.
Before you remove the tensioner, or loosen the tension, rotate to 45° BTDC and precisely mark the cam gears relative to the small notch on the back plate. At least one gear will jump on a GT once you have removed the tensioner.
09-08-2016, 09:35 PM
