Hkp7

Hi, I have an 84 928 16v which I have been trying to figure out what seemed to be a misfire which is more noticeable at around 80mph or when in neutral around 2200rpm. I just got the car a few months ago and have been replacing parts as believed needed. I recently noticed a scraping sound at idle in which I removed my timing belt top covers and found rubber built up on the inside of the covers. Also the timing belt itself has metal showing on the outside edge as if it has been rubbing. My guess is I may be a tooth off somewhere causing the rough running and low power. I know I need to change the timing belt and possible water pump/idlers etc. I am asking for any tips, what to look for on that tensioner to change, if power loss or stumbling could be from tooth off or even just being out of adjustment. Also It would be nice if anyone here was from the Cleveland Ohio area that could help me. Thanks, Bill.

Landseer

You should dive into this asap.

The tensioner devices on these pivot on plastic bushings through-which a shoulder bolt passes. The end of the bolt is necked-down to a smaller diam than expected. It mounts in the waterpump casting. The plastic bushings wear and cause belt to track wrongly, and, the torsion can bend the bolt and further-affect tracking.

Tensioner rebuild parts consist of 2 new bushings, pivot bolt, tensioner roller with bearings, spring clip that locates the roller (sometimes this is missing due to mechanic mistake, causing the tracking problems), O-rings for inside the oil filled tensioner (I think a big and a little one), boot, boot clamp, and a gasket that gets sandwiched between the tensioner body and the block. It holds heat transfer oil inside the tensioner.

It is possible to fit an alternative spring tensioning device, based on an Audi design, that is superior in function to the rather funky original. 928's RUS has these parts.

Also, a water pump bearing can fail and create tracking problems. One could conceivably drive the other to fail.

It will become evident on disassembly what needs to be replaced. There are many cautions on how to select the waterpump. Best bet sounds like new Lasso with a plastic impeller.

j.kenzie@sbcglobal.net

Agree. Your engine probably not interference, but still would not drive it. There are a number of timing belt/water pump articles searchable on this website. I recommend the tensioner device called Porkensior or something like that spelling. It is sold now by 928srus.com. I would change accesory drive belts and inspect water and fuel hoses carefully while you are in there. Preventative water pump replacement is controversial during timing belt replacement.
Good luck and welcome
Dave

docmirror

Welcome to the forums. Please list your location near your name or somewhere.

First, you need to resolve the timing belt/water pump/tensioner issues. As mentioned, 918sRUS can get you what you need to fix that.

Next, your belt issue aside, I doubt that is the source of a misfire. More likely is something in the ignition and/or fuel injection. There are a lot of threads on each of these areas if you use the search function. Although the search function isn't that good anymore.

As a quick test, find a very dark location at night and start the engine. With all lights off, look for little sparks along the ignition wires as you rev the engine. Sometimes called 'dancing spiders' it would indicate that your wires are breaking down.

Another fairly quick job is to simply remove all the injectors and have them cleaned or replaced. It's not very costly, and it could be the source of the problem.

Hi speed misfire is difficult to diagnose without fancy equipment. Sometimes it comes down to swap and test.