davek9

That's exactly what I used along w/ a rebuilt MAF,

ihoe

Injectors, distributor caps and rotors replaced.
Leak down test performed, no issues found.

The engine starts easily and idles perfect, but the "vibration" starting at 1200rpm is still there. It's not running as a V8 should.
I will check how it runs without the MAF and also check the fuel pressure.
Afterwards I am planning to replace the motormounts to make sure they don't amplificate something minor.

BRB-83-911SC

I had similar issues, and in the end it was the Motor Mounts.

Here is my thread documenting all of the rat holes I went down.

https://rennlist.com/forums/showthre...ferrerid=34007

ihoe

Very interesting. Thanks for your reply. Any reason why you didn't use new Volvo mounts again? I have new Volvo mounts ready for installation.

BRB-83-911SC

After all the time and frustration chasing this down, i didn't want to risk the possibility that it was a fit issue with the Volvo mounts. They did work fine between the time I installed them and the time I pulled the TT and transmission, but I just felt more comfortable using the Porsche mounts after all I had been through.

In the end, I would say I ruined the Volvo mounts by letting them support the engine without the drive train in place to share the load.

ihoe

A little update on my engine problem. Yesterday I did a test with my Innovate LM-2 wideband 02-sensor. First I removed the lambda sensor and replaced it with the lm-2. I have a x-pipe with mounting holes on each cylinder bank so afterwards a second test was done for the other side. My theory is that a repeated misfire on one or more cylinders will show up as lean mixture. The test started at idle and the engine rpm was increased slowly up to the speed where vibration can be noticed. I observe that one of the cylinder banks runs a little bit richer than the other(14.2 vs 13.8 at idle). I plan to do a test where I disconnect one spark plug to see the effect. At the moment I dont know exactly what type of difference it will make on the AFR. I think this additional test will help me in the intepretation of the measurements. Take a look at the figures and give your comments. Anyone done something similar?

Mike Frye

Nevermind- deleted

Misread your post.

ihoe

Today I checked the AFR when one spark plug wire was removed. The AFR jumps directly from 14 to 16. This test show me the effect misfire has on the AFR.
Based on this result, combined with the figure in my previous post, I am pretty sure it fires on all also in the rpm region where I feel the vibration.
So after all, the problem might be the motor mounts!

TRA

Anyone use the solid rubber mounts from 928 Motorsports? They look like a pretty solid budget option.

Bilal928S4

If you are on a budget I would get Roger's option with the volvo mounts. Much better and feel like the original Porsche ones, in my opinion.

TRA

Not trying to thread-jack, but are they easy to swap?

(I am doing the same updates as the OP)

Bilal928S4

Dwayne has an excellent writeup for MM replacement.
https://rennlist.com/forums/928-foru...-tomorrow.html

ihoe

Think I have found the problem. The motor mounts were very bad and it is metal to metal contact. Looking forward to feel the difference.

BRB-83-911SC

I think that will solve you problem. If you have spare time, here is my saga chasing a vibration, that in the end turned out to be motor mounts as well.

https://rennlist.com/forums/showthre...ferrerid=34007

EDIT - I'm a dummy - I had already linked this earlier in the thread! Sorry to hog the bandwidth.

I hope the new MM's fix your vibes.

SMTCapeCod

Good man, you're taking good care of a very nice example, great to see!