khalloudy

Hi all,

I think we tried to follow on this earlier, but still no progress. 1987 S4 Automatic. Have a vibration at 1600-1800 where it is very prononced. You can feel it when the car is in P, N. When driving and i have to accelerate of shift throttle position to moderate acceleration where i stay in that band, the car vibrates profoundly. I think it started happening 15k miles ago after i have replaced my motor mounts. I have new MM, Torque Tube, Bearings and all. The vibration is RPM related. What could it be? Any help would be greatly appreciated.

Sincerely,
Khaled

sweanders

I would guess torque tube related, I had a similar problem on my 944S2 at those rpm's. Have also noticed on another auto S4.

khalloudy

Anders,

We thought it was TT related, and i just got a new TT and Bearings installed... same behavior. It is something else.

Sincerely,

littleball_s4

I think one of my cylinders slightly misfire in that band, at little thorttle openings (usual at 1600rpm, isn't it). I know it's not purely rpm related, because it's fine when I'm hard on the throttle or completely out of it.

Could it be your case?

khalloudy

Umm... this is interesting. My mechanic did mention that he felt that a cylinder feels to be running soft, and he did point a potential misfire. We added some fuel system cleaner hoping to clean up any gumming in the system (maybe messing with an injector or so). As you mentioned, if i press the throttle hard, i do not feel the vibration, it is only at part open throttle that it is most pronounced, and yes starts at around 1600rpm. This might as well be the case. So what is leading to this misfire? bad injectors? LH, EZK? i know my leads, coils, plugs, rotors and all are pretty new.

Sincerely,

Garth S

I've had a fouled injector cause a 'stumble' or miss at low rpms - but smooth out as engine speed increased ( non Porsche): at its worst, it was a hammering type vibration in the driveline.
The plug from such a cylinder may well have a deposit built up due to the poor injector spray pattern - if that is the problem. If an injector is that dirty, it will need more than a can of additive in the fuel.

John Speake

Hello Khaled,
I had a similar problem with my 928 and after going through the ignition system, found it was a bad injector.

As Garth says, injector cleaner is unlikely to help - I also tried it, with no success. In the end I had to have all the injectors ultrasonically cleaned and flow tested.

Regards

Nicole

As strong as you describe this vibration, I don't think it's a bearing or something in the drive train. If it's that violent, it is likely coming from the engine.

I wonder, if you can replicate the vibration by pulling the wires to the injectors one by one. I had my injectors cleaned by Cruzin Performance (http://www.cruzinperformance.com) a few years ago. Just make sure you put everything together as it was (don't forget the clips that hold the injectors on to the fuel rail!!!) and don't drop anything into the open injector holes (i happens easier than you think - ask Bill and I how we know...)

A few more random thoughs from a clueless person:

A friend had a rough running problem shortly after she got her S4, and it turned out to be aftermarket caps and rotors that caused it.

How are your ignition wires - any chance one is bad? They say you should open the hood at night and spray a light mist of windex over the engine - if you see a light show, you need new wires...

I found that fixing the vacuum leaks made my engine idle smoother and appears to respond better to low rpm throttle inputs.

Also consider a Rislone treatment, coupled with an Italian tune-up.

littleball_s4

Sorry, Khaled; I can't help you any longer because my vibration is very slight and I don't even tried to sort it out.

Generally speaking, my car (87 s4 5spd) is strong (300kph), lambda is ok at idle, tempII and throttle sensors ok. However, it's hard to start when warm (extremly rich condition, even a short black-smoke blast) and idles at 900rpm. I would say old MAF is making the car rich at little flows (little rpm and little throttle) and the weakest plug (perhaps plugs in your car?) misfires.

NickT

OK, whats an Italian Tune up?

ErnestSw

Drive the #@$^$# out of it.

NickT

Kinda figured, the old first gear red line for 10 miles....

khalloudy

Thanks for the response everyone. I guess it seems like it is a plug/injector issue. I have removed the plugs before and yes, one of my banks was dirty (i think it was the right one). But that was like 6k ago and hope they did not get messy that fast (i know i have work valve guides). I do have a puff of smoke at start and idle at 900-1000rpm I do have a new MAF and my coils and caps are Bosch. I had the injectors cleaned a couple of years ago - I wonder if i just need a new set (can anyone say ouch?). I will run diagnostics this week on the car and see if everything is in order. I think my vacuum is ok, but you never know (specially with the high idle). I will go ahead as follows:

- run diagnostics on the LH/EZK
- check glugs/replace if dirty
- check wires
- clean injectors/maybe replace?
- engine vacuum

P.S. does a worn valve guide/oil use foul up the injectors or is it some dirt in the fuel system?

Sincerely,

Garth S

With the correct 928 O-rings on the manifold end, these Bosch Design II rated at 19#/hr will work perfectly. There are numerous suppliers on ebay, and $200 for 8 is about the max. The design III apparently work also .... that is ~ the price for one Porsche injector!
Worn guides will not normally foul an injector - or if they do, then the problem is major.

JimBob951

I have a similar vibration at around 3500 RPM. Thought it may have been the TT, but it also seems to disapate when hard on the throttle. Someone else had the same problem, and they cured it with fuel injector cleaner. I used a bottle of Techron, but didn't notice any diffence. How can the injector problem be confirmed, short of replacing the injectors? What about that Bosch tester they have at NAPA? Would that help?

Jim
87 928 S4
87 951