Oilystair

Actually scratch that. I did a did a second strip down of everything, cleaned it all AGAIN .... and waddya know... it’s all working. I’ve had a good day. Dashboard lights all on and courtesy lights now going too. Now I can concentrate on original problem of vibration. I have done the fuel treatment and I have also put intake cleaner in and run it through for about 50 Kms. The slight lumpiness seems to move depending on .... well nothing really, it just changes in level and moves around the lower rev range. 1000- 1700 rpm.. I think I can rule out an imbalance torque tube As it would be doing it consistently in the same place.Of course what I really need is a donor vehicle with everything working so I can try swapping leads distributor caps… And maybe even a computer that way I can rule stuff out without having to fork out for new ones....I’m getting the engine mounts checked next week as per the original suggestion and why is this my fix the vibration, I still need to know what’s causing it. I think I’m a cylinder down...

worf928

It's pretty easy to see if engine mounts are done:

- car idling. hood open.
- grab the throttle linkage and give it a quick rotation to 'blip' the throttle plate.

If the engine sits there in the bay like a stone, the mounts are done.
If the engine moves on the mounts then they are ok. With new mounts the engine will 'rotate' (from a context of standing in front of the car) by more-or-less two inches when you give it a firm blip.

chart928s4

+1 on Dave's diagnostic. If you want to be really decisive, have someone start it while you watch the engine. When it turns over it will oscillate visibly if the mounts are good. If not, the engine will not move.

Bill Ball

The RPM range of this vibrations is consistent with bad motor mounts. I know, others already have pointed you to the mounts, but they didn't say why.

Oilystair

I have to say you guys are awesome. I very much appreciate your wealth of experience. Whilst I was chucking the intake cleaner through it I was reviving it under the hood and, as you say, the motor didn’t move. Looks like that’s the problem. I’ve been advised that the Volvo mounts are good, the thread is a tiny bit long and needs to be cut down but apart from that they should be just as good as Porsche part. Can anyone tell me they’ve had good success with these. As I said, my 928 S4 and my 928 s have been in dry storage for over 12 years and I am so out of the loop with maintenance and what was meant to light up and what wasn’t !!! It’s like owning one for the first time all over again. Very cool :-) thank you guys for your assistance.

FredR

Just as Bill states, one of the first things I was "taught" about the 928 motor some 20 years ago was that a vibration at or around 1400 rpm was indicative of a failed motor mount and that vibration repeats at 2800 rpms.

I have been using the Volvo mounts for the last 5 years or so and no issues. Since I retired I have been doing my own maintenance and recently I "discovered" that the "fingers" on either side are "absent" on my installation. This has me a little concerned as under normal circumstances they do nothing but, they are there for a reason if the mounts fail. The mounts were installed by someone who knew what they were doing and I seem to remember they mentioned something about the fitment but it never registered that something was missing. Now I am wondering if they did this because the height of the mount was a bit higher than stock and with Roger's EIS inlet system being a bit taller than stock, they found difficulty closing the bonnet which also seems a tad higher than it should be.

Functionally, the Volvo mounts appear to work well and continue to do so.

Bill Ball

Welcome back. If this is your only problem, you are a lucky man.

Wisconsin Joe

The biggest advantage of the Volvo MMs is cost.

They are a fraction of the cost of the factory MMs.

There are a few guys who swear that the factory MMs are 'tuned' to the vibration range of the motor, and that the Volvo aren't.
They claim a substantial difference in vibration reduction between the two.

I never had good factory mounts in mine, so I can't confirm or deny this.

I do know that going from shot MMs to the Volvo ones was 'night and day' in terms of vibration.

Oilystair

Spoke to the legendary Roger at 928SRUS and I’ve got new motor mounts on their way.....the Volvo ones which he speaks very highly of. So hopefully that will fix the problem.

on a positive note, it’s been a week of discovery & problem solving . I got the rear hatch light switch done and the interior lights are now back in action. The dash lights are now on, dodgy rheostat. Fixed. The aircon which has suffered from being sat for 12 years got recharged and it’s holding it’s charge.... so now I’m cool again. Fixed. The fuel guage turned out to be a corroded sender which is now cleaned and working. So, it’s just motor mounts and then, now it’s running great, Roger suggested I gave it the ‘ Italian race tune’ ie, thrash the bung off it.... so I did that and it did a pop and backfire but it runs way better now The only problem identified is a cough under heavy load around 5000rpm where the exclamation light came on ... it lost power then it all came back to life again. Roger said the internal fuel pump, if it has one, will most likely have done it’s dash. He suggested I replace with just a strainer... should have done that whilst I was in there doing sender, in fact that’s probably what disturbed it in the first place.... so that’s a project for next week but... once this is done.... I’ll have a fully functional S4 again where everything works !!!!

I was cruising home with aircon on Friday and was tailgated 3 times ..... people wanting a race.... I just didn’t rise to it, I’m just enjoying the sun and the drive home. I’m so happy to be back in it again.

ROG100

Car should not have an in-tank pump but it was made for the South Africa market so who knows. Checking for wires into the tank at the boss will tell.
Glad she is running better.

Oilystair

yep Roger, haven’t checked that bit yet as you recommended, but it’s good to know I have options. Thanks for everyone’s help so far. 👍👍

Jason89s4

Great to hear! Drive, drive, drive that s4!
-Jason

Oilystair

Update for everyone that followed this thread.

The S4 is running sweet, an in tank gauze that had been put in the wrong way aroud cause the cough and splutter at high revs, geeeeez !!!!, al fixed now with a new one from Roger. New engine mounts also removed most of the vibrations, there is a slight vibration still around 1300 rpms then around 1800 rpm...but its not enough to worry about I dont think. Im running 100+ octane ( road legal ) fuel in it and im wondering if ive gone a bit over the top ????shoud i stick to 98 RON ?? Ive been tinkerng and getting things back to life...its been pretty cool and its working great, startng first time every time and ive finally got the confidence to overtake people again, very happy. Roger at 928srus helped me with lots of little bits and its running great now. We have some problem with windows now as they make a clunk when they go up and now have started to scratch the windows so ive started another thread for that. apart from that, it seem all Ok at the moment thanks to everyone.

Cheers. AL

FredR

Running 100 octane will only hurt your pocket not the motor that is generally tuned for 98 RON. I understand they did one or two strange things for some models delivered down under so whether yours needs 98 RON I cannot be 100% certain- I have it in my mind some examples down under ran with slightly lower compression pistons- doubtless the down under crowd will know more about that.

I always investigate any strange vibration however slight but then with 20 years ownership under my belt I tend to know what should and should not be there- difficult when new to the car of course. 1400 rpm was a sign of motor mounts but you have cleared that possibility- just do a visual check to ensure nothing is errantly close to touching- it takes very little to induce an annoying rattle especially around that 1400 rpm harmonic.

Oilystair

Interesting addition to this thread and somewhere I didnt look. The slight vibration mostly disappeared after the motor mounts were done, but there was a tiny vibration that i eventually just was put down to 'its what it is' The rev range where ist did it changed upwards by about 300rpm but it wasnt bothering me...until, its tarted to go into autumn and I got a hesitation whilst cold and a slight misfire. I checked the forums and suspected duff leads. I did the test of turning off the lights and checking for 'fireflies' on the leads. Nothing. It was quite dry and i was struggling to see so I leaned in for a closer look. As I got closer, sparks spread from closest to me and down the leads away from me... I realised it was the moisture in my breath as I breathed out was enough for it to go mad and it followed my outward breath away across the engine bay. Wow, I guess that says it all ( im not a dragon by the way ) . The tiniest amount of moisture was enough to send it mad and go all lumpy. Needless to say I have just asked Roger to add to my order of bits to send to NZ. I never even though of that but im sure its going to nail that last bit of lumpiness. Ill report back when ive got the bits fitted a to whether it ironed out the last wrinkle. Cheers with beers.