Spikeysash

Previous post information: (new timing belt problem towards the bottom)
“It's always up and down with this shark, up and down!


[ 928 85' euro, A/T ]

[past problem solved!)
I *JUST* fixed my prior overheating problem with the simple addition of a new thermostat. The car will climb to the white line in heavy traffic but now it triggers the electric fan at that point (it didnt before) and it will drop back down. I'd like it to be running cooler but, eh. Bang for the buck is what matters right now. Phew, ok, were good for a while right?

Eh.

(promising performance!)
Yesterday night decided to go for a drive with my friend (who owns a 2002 330ci) up to Long Island and back, as I had just gotten new tires. I decided to dump 2 cans of some generic Fuel injection cleaner/solvent as well (it was the only one available) Boy, did she handle like a champ! I was taking big curves at 90+ and I could have sworn the cleaner made a noticeable difference by the time we were coming back. Suffice to say he got burned ;] Off start he beats the shark on acceleration but mid-high range power is definitely on our side! I was very happy with the performance. She's still not running full power but we can beat the bimmer so .. getting there!


(yet another, new/old! problem!)
Today while driving the car after worked I noticed a strange, fairly loud buzzing noise when I spontaneously decided to get a visual of the exhaust smoke (nothing wrong with the exhaust) It was just coming from that area (back of the car).

I shrugged it off for a minute but then noticed that there was a strong fuel scent in the car. When I popped the hatch and removed the back panel and put my ear close to the .. uhm, not really sure what's exposed over there but I could hear a soft hissing, like vapors were escaping.

The buzzing is very noticeable in the car (its definitely coming from the back) , and the smell is as well. Neither of these things were evident last night. I can make the obvious connection, but lack the mechanical knowledge to pinpoint the problem.

The car was on and upon untightening the gas cap slightly, I could hear pressure being released. This went on for 30 seconds or so when I untightened it more .. still more pressure releasing .. more .. I finally took it off and let it all out. After this complete release of pressure my car started to surge in idle an sputter - sounded like it was gonna die & and I didnt have the heart so I just shut it off.

My friend and partner suggested it might be the fuel pump .. but as far as I know, we had a new one installed on our first round of maintenance a few months back.

I'm going to take a wild guess and say fuel pressure regulators .. but thats nothing more than a stab in the dark.

Any suggestions, my fellow Rennlisters?!
“

Sooo, in the morning after the fuel pump buzz incident the car fired right up as usual and the buzz was no longer present. Later that day, upon opening the hood we heard a noise which sounded like a belt doing something weird. I suspected the timing belt may be the culprit so I took a look under the intake hoses into the timing belt holes and may have noticed that the belt might have been oscillating about a mm back and forth. We dismissed the problem as we were unsure of the cause and figured it may have been the mechanical fan acting up. Minutes after while we were driving at moderate speeds the timing belt warning light came on and we immediately pulled the car over and turned of the engine. Terrified of having to spend thousands of dollars for an engine rebuild and most likely losing this wonderful shark for ever, we pushed it into a parking spot and have not started the car since. We are wondering what our next step should be. What are the chances we may have already bent some valves or skipped some teeth on the belt? We are not too mechanically inclined but have been learning a lot with this car (having about 1 lesson every few weeks in result of new problems) and as we understand it we should probably next check if the belt is properly tensioned and if we have not destroyed our engine yet, change the belt. If there is anyone in or around Brooklyn NY that can offer to lend us a hand with their belt tension checker tool we would be very greatfull for the help. The last maintenance and/or change of the timing belt are unknown to us. To be honest, we have been hoping for the best since we purchased this car in non-running condition and have quickly learned to expect the worst. So what do our chances sound like? I would hate to see this shark die :-( Thanks everyone, and happy thanksgiving!

Kaz

Concerning the buzzing noise from the rear it could be a fuel pump about to let go. Sometimes it makes noise, sometimes it doesn't. My experience has been that the car rarely just breaks. Usually there's plenty of warning. Of course plenty of warning means knowing the normal sounds and habits of your particular 928. As for your t belt if it had skipped a few teeth you would definately know about it. Since you don't know when the T belt/Waterpump was changed last you might as well do it now for peace of mind.

Garth S

You were correct to shutdown the engine: since you have little history on the car, I would do the following.
Remove the air breather tubes to allow a look at the timing belt (TB) , visible through the air vents in the top cam belt covers. If the belt is still 25mm wide ( new spec) and shows no sign of shredding on its edges, turn the engine over with a 27mm socket on the crank bolt to examine the rest of the belt. If it looks OK, loosen the locknut on the tensioner adjuster, and screw the adjuster in MAX 1/2 turn ..... if you need a quick repair to get you home. Then, plan on replacing the TB, tensioner roller, etc ASAP.
If the TB edges are shredding, get towed home ....

heinrich

Buzzing is very normal and I would ignore it. Especially on low-fuel conditions. Tbelt ... CAR IS NOT DYING. NORMAL. Just do the timing belt work. You SHOULD have the belt inspected by a knowledgeable 928 owner (post your location here) .... and especially the water pump.

heinrich

Btw post year also.

WallyP

First the bad - IF the timing belt fails, the engine will be severely damaged.

Now the good - Most timing belt tension warnings are due to the warning system, not the belt - but it is not a good idea to count on that! (See the first paragraph!)

First, a couple of comments about the "tensioner"...
It would more properly be called an "un-tensioner", as one of the primary purposes of the tensioner is to REDUCE belt tension as the engine gets hot. The aluminum block and cylinder heads grow much more than the belt as the engine gets hot, and this would increase tension to an unacceptable level. The conical, bimetallic Belleville washers in the tensioner relax as they get hot, keeping approximately the same tension hot or cold.
It is also critical that you realize that the tensioner does NOT automatically adjust belt tension to account for wear or belt stretch. Repeat: There is no automatic adjustment of belt tension on any 928, other than that for engine temperature.

The warning system operation is:
- There is a wire that runs from the warning computer (under the "dead pedal" under your left foot on left-had drive cars) to the pivoting tensioner arm. The tensioner arm is electrically isolated from the engine block. On the tensioner end of the arm, the wire attaches to a nylon insulator at a spring.
This short, stout spring attempts to push the arm away from the tensioner push rod. If there is adequate tension on the belt, the tension holds the spring compressed. This makes electrical contact from the arm to the grounded tensioner body, and the tension warning is not set.
- If the belt tension falls below a safe level, the spring pushes the tension arm out slightly, and this breaks electrical contact between the wire and ground. This loss of ground causes the belt tension warning to be set. There is a built-in delay for the first activation of the warning system.
- Note that the warning is set by loss of electrical ground. There are several places where a bad connection will cause the warning to be set, even if belt tension is adequate. The most common are the flat spade connector from the arm to the wire, and the round connector at the timing belt cover (immediately behind the oil dip stick).
- Another possible cause for a tension warning is a loss of oil in the tensioner. The tensioner should be filled with engine oil on your car. This oil helps with heat transfer, lubricates the tensioner, and damps belt flutter. If the tensioner has not been rebuilt when the belt is replaced, it is very common for the rubber boot to harden, crack, and let the oil out.

All of that being said - If you have no positive knowledge of when the belt was last replaced, it might be a very good idea to replace the belt, check all of the rollers and guides, and rebuild the tensioner. If you are paying someone else to do the work (not recommended in most cases), you should seriously consider having the water pump replaced at the same time, as the labor involved is much the same.

Go to http://members.rennlist.com/pirtle/svc.html and http://members.rennlist.com/v1uhoh/timing.htm for more info, including step-by-step instructions on replacing the belt.

If you call Jeannie at (828) 766-9280, she can put together a complete kit of all of the parts that you need.

Feel free to ask questions - someone will always be happy to do a "Cliff Clayburn"!