Drifter

I bought the car @ 49.5K and was told it got a new TB & WP. At less than a thousand miles the "Toothed belt service warning " came on. I had the TB adjusted by a reputable local shop, that was about 500 miles ago. Just after starting it a few days ago I got the "Toothed belt service warning " again.

Is the warning light sensor (connector) to the tensioner have easy access or does it require major tear-down?

tia

ViribusUnits

Why would you want to have access to the warning light connector?

GregBBRD

If the light comes on....you probably should determine why it comes on. If there is a timing belt issue, a good inspection will tell you this. If there is a light problem, that can be traced. Ignoring the light or disconnecting it will probably not make you a very "happy camper". Just look through this Forum for the other happy people that have experienced timing belt failures.

greg brown

Drifter

I'M NOT IGNORING THE LIGHT, just checking for a loose connection first!

Bill Ball

You need to remove the passenger side belt cover. That way you can check the belt tension as well as look at the wire connector.

I did encounter an instance recently where the connector was worked off the spade on the tensioner arm in a buddy's 89 GT soon after the belt was repalced. Apparently it was intermittently losing contact and tripping the alarm. The alarm would cancel and not come on for several days. After two alarm instances, he brought it over. What we found was the spade had been installed on the arm such that it was on the cover side of the mounting screw and the cover made contact with the connector and worked it off the spade. We loosened the spade's screw and rotated the spade toward the rear, away from the cover, reinstalled the wire and made sure it was snug and not making contact with the belt cover. We checked the belt tension, and found it was on the high end of the window. We buttoned it back up, and he has had no alarms since.

You should be able to figure out how to remove the cover. Pull the smaller coolant return lines out of the way. Remove the distributor cap (3 slot screws with 8MM heads, a little awkwardly located). Remove the rotor (3 Allens). Remove the two bolts that hold the cover on (10MM heads). You may have to move a few other things out of the way, like the front bracket for the spark plug wires, the dipstick. The upper radiator hose is kind of in the way, but with small hands it can be left in place.

The wire passes through the center cover near the outer edge. Look behind and see if you see what I describe above. You should get the Kempf tool and check the tension too. This is done at TDC, so you will be rotating the motor.

When you go to put things back together, the distributor cap's 3 screws are slightly ecentric, so it can only go back on one way, but it may be trial and error finding the orientation where all three screws will align after you rotate the motor.

Bill Ball

If you are in Vegas, there are several locals who know the TB system well and should be able to help you.

Rich9928p

There are two reasons

a. The belt is loose. This could be for many reasons:
- improper tension (was a proper tension gauge used? Often, shops don't have the right gauge!)
- worn cam or crank sprockets
- bad bearings in idler and position rollers
- failing water pump (hope not if it was just replaced, but still a possibility)

b. There is a problem with the loose tension indicator. It is a pretty brain dead design.

It would be a good guess that the PO may not have replaced all the bits necessary if he/she knew the car would be up for sale - or the wrench only did what they were told to do. So even if a new water pump and belt was installed, other items that may cause the adjustment not to hold have been overlooked.

You need to remove the front cover to inspect either of these scenarios. It may be a good idea to even have a flat bed tow to the shop, you don't know how loose the belt could be! A slip of the belt can cause $5000 or more damage!

Does the shop know the 928 and have the proper tools? Many shops just "give the tensioner another crank" when the light goes on. This is NOT the proper thing to do, you MUST be sure that they don't do this. How to be sure, INSTUCT THEM that a full inspections needs to be done, components replaced if necessary (for example if there is any shine on the cam sprockets), and the Porsche recommended tension device used. Also, the tension must be checked with a cold engine (not warm, not after an hour ... it must sit for several hours), it needs to be checked, engine HAND CRANKED 360 degrees, checked again, HAND CRANKED 360 degrees ... at least three tension checks.

Drifter

Thanx Bill and thanx Rich for the excellent road map. Sound like I have everything I need for this weekend project. The Shark is in the garage and will not be going anywhere untill properly inspected and repaired.

Rich the shop that adjusted the TB mentioned that everthing looked very good regarding the tb & wp. The wrench that serviced my Shark is up to speed on 928s I was told from a reliable (?) source. And it makes alot of sense to have asked about the condition of all the components involved, not just the tb & wp.

Thanx again

gruffalo

I do not recomment tightening the belt without checking out what the tensioner arm is doing. If you have a bent sholder bolt, and tighten the belt... well... it could be disasterous. It will eventually derail the belt.

And there ARE bent tensioner arm sholder bolts out there.

Bill Ball

The 89 does not have the shoulder bolt. Certainly, if the belt is loose and this has been the second time in such a short period, the reason needs to be investigated.

Garth S

The very quick check on the alarm circuit is to swing the dipstick tube aside ( held to the cover by a short M6 bolt) to allow the single wire plug to be disconnected from the tensioner connector.
Measure continuity from the connector on the cover to ground: if you get a 'beep', or <1 ohm resistance .... the TB tension is above the minimum required .... and the problem is elsewhere.
If the circuit is open ( infinite ohms), the TB is truly loose or the electrical path to ground is broken by a loose wire, etc ..... open it up to check!

Some shops have never figured out that the tensioner bleed screws are there for a reason .... it is a 5-10 min job to bleed & fill - and it can also help with issues such as this .....

dr bob

This diagnostic is exactly backwards. Continuity of ground is the normal state when there is adequate tension on the belt. An open or infinite-ohms circuit to ground indicates that the belt is too loose.

Be aware also that the tension sensor is not an acceptable way to set the belt tension. It's a sensor that detects gross problems. The actual tension is set using either the complicated and expensive genuine Porsche tool, or the simple/easy/repeatable and less expensive Kempf tool. The Kempf tool sells for less than $100 at 928 Int'l, and is an essential tool in the 928 owners collection, IMHO.

As others mention, you can get a false reading if the tensioner is not charged with oil correctly. The oil dampens belt flutter, helps maintain a very constant tension as the engine runs and changes temperature. Think about how well a car rides with no shocks absorbers, ve one with shocks, and you'll be able to envision how the belt is treated by the empty tensioner. Worth a look and a refill, since the pass side cover is off for the tension check already. A little pump oiler can does the trick in a few minutes. 7mm Wrench on my late tensioner bleed screws.

HTH!

Garth S

Bob,
May I recommend a course in remedial reading and comprehension : what I have stated above is absolutely correct and factual - and you have restated the same to confirm that fact.
While being humanly susceptible to getting things bassackwards from time to time .... this was not the time ..
There is an anecdote of a father, who without warning, wops his eldest on the back of the head: "WTF was that for?" says the astonished sibling. " "That's for the next time!" says Dad ....
I will happily accept this admonishment for the next time ..... stay tuned

Stan.Shaw@Excell.Net

Reading through this thread, I am left wondering what could cause a "toothed belt service" light on my '90 GT that is not in the area of the timing belt covers, etc.

I just had the timing belt changed including:
1. timing belt
2. water pump
3. rebuilding tensioner with new bushings, boot and cap

The "toothed belt service" light has come on many times since, both during and after warm-up. I (don't ignore it) can reset it via the control stalk.

Since it is not constantly on, I don't see that I can perform the continuity check mentioned above. Is there a way I can confirm the problem is NOT related to the tensioner, spade connector or actual belt looseness? In other words how can I confirm the problem is not in the instrument panel, etc.?

Thanks for you thoughts in advance

Big Dave

+1 If your belt is loose again, there's something wrong.