MGW-Fla

Help froim the Rennlist experts needed!
Yesterday I was on the way home, on the interstate in rush hour traffic. Was going about 65-70 & traffic started to clear, I decided to punch it so the car would downshift(not stand on it though) so I could go around someone & clear the pack. At the instant I did & the car downshifted, I heard a slight knock, pop, or thump noise from the engine area & at the same time the Central Warning light came on along with the Belt Ten light. I was afraid at first that the belt had broken, but it had not. The belts & hoses were replaced by the local Porsche dealer Brumos last Oct. so I knew it would not be due to the age.

I reset the Central Warning light & slowed down to about 60 & drove a bit to see what happened..... nothing... the car seemed fine, other than the Belt Ten light staying on the rest of the way home(5-10 mins.). Once home I popped the hood, the belt seemed tight & ok, no other problems noticed. I considered myself a true 928 novice however, so that just means there was nothing staring me in the face as an obvious problem. I started it back up & no light, no problems of any kind.

I have yet to have this happen in the 9 months I've owned it. It used to shake badly & basically not accelerate when I punched it at speed on the highway until a few months ago. The engine was trying to go, but the tach would just wiggle as the car shook, my shark would barely accererate any. It would shake so bad that you had no choice but to back off & slow down 10-15 mph to stop the problem. I took it to a local Porsche mechanic who is highly regarded in the local Porsche crowd,(he used to work for Brumos & he says he is well versed in the 928). He said it was two things in his opinion, the intakes were sucking too much air causing the vibration upon heavy acceleration & the engine & tranny mounts needed replaced which added to the problem. I could only afford so much at the time so I opted for the resealing of the intakes since he said that would also help with the get up & go on an overall basis. Once he resealed the intakes, the shaking when I punched it went away & I definately noticed a bit more giddy up, especially from a start.

My WAG.... Is it possible that due to my car still needing engine & tranny mounts that the torque of the engine when I punched it somehow caused the belt to slip or something?? That was all I could think of since I know the engine does need the mounts replaced. Has anyone else experienced this or know what exactly happened when I punched it? I don't want to assume all is ok if this is a possible indication of a more serious problem about to rear its ugly head $$!! Especially need to know what this problem might be since we are making the trek up to SITM in a few weeks. I appreciate all of the insight & help, THANKS!

sharkmeister85

If the Belt Tension Warning came on you must look into that to find out why. How do you know the tension was okay? Did you actually measure it with a tensioning tool. You can't eyeball everything in the system and know its okay without some disassembly. Did you do that?
Glenn

Mongo

I've had a couple false tension warning lights. It's not that hard to set the little tensioner light off. If you look at the sensor, it seems sort of cheesy. Mine came on when I was in traffic on monday. I pulled over, turned the car off (BTW when I signaled to turn to the shoulder I got a tweaker blinker, definitely a short). When I restarted, no tensioner light and still a tweaker blinker indicating a gremlin.

BUT if you have no record of last timing belt, you may want to get that checked. hey is it 4 years/ 30,000 miles to change the timing belt? I have about 10,000 on mine but it's 4 years old.

Big Dave

First of all, you ought to check the tnesion on the belt as well as the basic timing of the engine. I know you said that you popped the hood and looked at the belt, but the proper way to check tension is with either the factory tool or the aftermarket tool (sold by 928 International). The engine should be COLD when you check the tension. Tension must be checked at the right location: where the belt passes from the passenger side cam gear down to the large tensioner roller, one tooth to the left of the right edge of the rear cover plate.



To check the timing, put the crank at 0 degress top-dead-center (TDC) which looks like this "O|T"

Next, check the markings on the cam gears to be sure they line up with the markings on the rear timing belt cover plates (you may need to rotate the crank around 360 degrees since the cam gears rotate 1/2 a turn for each full turn of the crank):



If the marks don't line up, let us know....you've got some work to do.

MGW-Fla

Well I didnt mean to imply that the belt tension was completely ok, I only looked to see if it was broken & felt to see if it had an obvious looseness to it(since I thought when I heard the noise that it might have broken). I did not check it with a tool or disassemble anything as of yet. After the basic look I gave it & restarting it, I closed the hood & left it in the garage, & drove my BMW 325 today. Had other things last night I had to deal with so that was the extent of the time allowed to look into it & wasn't sure exactly what I would be looking for either!

deliriousga

YOU REALLY NEED TO CHECK THE TENSION PROPERLY! Not yelling at you, just want to make sure it's prominent. Don't drive the car until it's checked properly or you may be posting a "Need an engine" thread.

You can pull on the belt and it feels fine, but once the engine is hot and the belt stretches it's a whole different ball game. Make sure you check the tension with the Porsche or Kempf tool (Kempf unless you want to shell out $600) and do it according to the directions.

heinrich

Nope. If the light came on it came on because the belt became slack. Have you hav tension rechecked after the tbelt job? It may be as simple as that. Or it may be that the belt and pump are in terrible shape following a hack job, and you need to fix it asap. Less likely ... but I've been through that one.

MGW-Fla

I have all of the service records back the past few yrs(15-20k miles) from the PO. He spent over $10k with Brumos doing any & everything they knew it needed. I know I asked about the timing belts & checked when that was done. Dont remember the exact date/milage, but I know that should be ok, I have the receipts at the house. The car has just under 124k miles & think the timing belt was done when it was in the low 100s maybe. Perhaps that is getting close to being needed again. I also talked to the head of service at Brumos before I bought the car last Aug, since he knew it well. Then I took it to them in Oct. to have them go through it for me to advise of anything they thought it either needed now or preventative might need done. They did the CV boots, steering gear boot, etc. things like that. Said with the records of what they have done & what they saw all else looked ok. I also had it with the other Porsche mechanic in Dec/Jan. & asked him to check the car out throughouly in case he saw anything needing done. Other than the intakes seals leaking & sucking too much air and the motor/tranny mounts, he said the car looked in great shape. Maybe I was just having false comfort in thinking the car should be in good shape after having it looked at recently by two different reliable sources.

I will have to get the tensioner measuring tool as suggested. I know I had a 1990 911 cab for five years and I had once or twice the Belt Ten light come on & it was nothing. My bigger concern here is the noise I heard when it happened I think. THANKS AGAIN!

Jim_H

This is the point where I need a shower and clean boxers.

Big Dave

Ditto. That's why I suggest you confirm that the timing marks still line up. Hopefully your belt didn't jump one or more teeth.

Big Dave

Actually at that point I needed a box of tissues.

SteveG

I would certainly do a visual on the belt. Measure the tension, verify if the cams are still lined up with their notches. If it slipped for any reason, that needs to be corrected before driving it. Some are adamant about tensioner being full of oil. I have not gotten lights w/ tenisoner 1/2 full. Your tensioner piston might be binding not allowing the piston to take up slackc for some reason. I suppose the wire from the cam cover to ground could lose contact if the engine is moving excessively due to MMs.

Jim_H

I am interested in this. I would think the cam timing would have to be way off for the belt to skip a tooth??

MGW-Fla

Oh wow.... yeah, I got that sick feeling in my stomach when it happened, mainly cause of the noise. It all happened so fast, the noise was there, but along with all the other noise of the interstate, it was raining, the car trying to accelerate, & my hearing sucks, its hard now to say more definately what the sound was. Once I saw the Belt Ten light, I thought it might have broken, cause it kinda sounded like a pop. I knew I wouldnt drive it again till I checked everything out. I truly appreciate the insight & help greatly. I want to learn how to do as much as I can myself on the car, for cost obviously, & cause I want to know all about it that I can & if I can do a repair myself I know I will take more care in doing it than someone else too. I will order the Tension tool & also attempt to check the cam notches as suggested too. I have noticed that things under my hood never seem to have nearly the amount of room that appears in any of the pics I see anywhere showing how to repair something!

sharkmeister85

The sensor system may seem sort of "cheesy", but it will do the job it was designed for, if maintained. In the 9 plus years I've had my '85s and 3 TB/WP jobs done on it in that time, that warning light had always started coming on when the tension was low. Typically, the first indication came under a hard acceleration scenario. I don't like seeing that light come on (who does!), but I found there was no need to panic. After it came on a second time, I would know it was time to plan an inspection and possible re-tension. In the meantime, since my car is my daily commuter, I drive it, but limit the rpm's to 3000. I've gone months like this. No doubt I will be severely chastised for doing this, but I'm confident about the quality of the TB/WP job that was previously done. Obviously, if the Tension Warning light was coming on more frequently, even when not under hard acceleration, more attention would be required and sooner, not later. I guess the moral of the story is, make sure your warning system is working as designed and it will give you adequate notice of potential problems. Don't ignore it.
Glenn