ihoe

Hi to you all

I have a problem with my 86.5 S3 that I hope you can help me with. I have just recently finished an intake refresh and TB/WP job. I hoped this should cure a problem I noticed before this job, but the problem is unfortunately exactly the same:.
-The car starts easily both cold and warm
-Idles well at 680 rpm. To me it seems to run on all cylinders at idle and all spark plugs look ok.
-It picks up rpm when I use the throttle, no popping in exhaust or other sounds
-When I gently increase the rpm just above idle the engine start to vibrate at approximately 1200rpm. The vibration continues at higher rpm and from the coupe it is easy to feel that the engine is not running as it should. From the outside with the bonnet closed it is not easy to notice anything wrong. I suspect that one or more of the cylinders are misfiring, but no popping in exhaust or other sounds
This is what I have done so far:
-New spark plugs and wires. Distributors and rotors look ok.
-Full intake refresh with all new rubber parts, gaskets, vacuum hoses, ICV, throttle switch , temp sensors, crank sensor ++
-The fuel injectors are not professionally cleaned, but I used pressurized carburetor cleaner and a battery to check them.
-Checked all grounding connections on the engine
-Compression test, nothing unusual. But I will do leak down test shortly as I prefer that.
-I have used an inductive sensor connected to an Innovate LM-2. The rpm log file from all the spark plug wires looks the same (also above 1200 rpm)

It is a nice car so I would like to solve this problem, any suggestions?

Ivar

ammonman

Check the power connections on the ignition coils for corrosion. Also check that the ground cables from the coil mounts to the body are clean and tight.. You mention new plug wires. Did that include new king leads from the coils to the distributor caps? Did you clean the grounds at the back of the block under the fuel pressure dampers as part of the intake refresh? These are the main grounds for the fuel and ignition computers and will cause all kinds of problems if there is corrosion.

Mike

John Speake

Unplug the MAF and see if it behaves the same.....

JBGold07

How are your motor mounts?

Mrmerlin

recheck the spark plug wires for correct routing its easy to get two of them swapped

Mike Frye

I always go back to the basics when the symptoms don't make sense. I like to take a timing gun out and put it on each wire and make sure it's firing (and all seem to be equally bright). Could be that the cap and rotor LOOK good but you've got some bad connection somewhere.

Check all plug wires and injector wires for proper seating, connection and no bare/touching wires.

Lots of old brittle wiring in these cars and it can look fine on the surface but be broken and just rubbing together on the inside.

Pfc. Parts

I had a similar problem after my new wires went in; I had a couple of them wrong. Put them in the correct order and the problem went away.

If that doesn't work, I'd check the motor mounts next.

SeanR

Sounds like you are feeling the vibrations of collapsed motor mounts or torque tube bearings.

ihoe

The motor mounts are not in good shape. I have new ones ready for installation. But personally I don't think the vibrations are caused by the motor mounts, its not the way it feels. My brother had bad motormounts in his 84, and it was not like this. How much vibration can this smooth v8 generate at 1200rpm with bad motormounts?

SeanR

Depends on how far the mounts have collapsed. Had one car that the owner refused to drive because the car was mis-firing so bad he had it shipped from Arkansas to Dallas as no one up there could figure it out. I found one vacuum leak, and everything was running good but the vibration was horrible. Jacked the motor up and slit a piece of rubber between the oil pan and the cross member and no more vibration.

ihoe

Ok, I will take a close look under the car tomorrow.

Pfc. Parts

The thing that makes me suspect the MMs is the harmonic. You mention it happens at 1200 then goes away? That doesn't sound like a misfire to me, more like something mechanical. I agree with looking at the TT also.

I have the same problem with my 89 944S2 and the first thing I'm planning to do is replace the motor mounts, which are original 1989 and are in bad shape.

If you already have the parts and are putting them anyway, you may as well do it now, at least it eliminates one possibility?

Pfc. Parts

'Course that assumes you weren't going to do anything else while replacing the mounts I suppose. Also, I don't know if the 928 is as simple as the 944 is supposed to be. From what I've been told you can just put a transmission jack under the block, lift it a bit and replace the mounts, but that's what I've heard about the 944. I suppose it might be more complicated on a 928 (why not? Everything else is

davek9

"..-The fuel injectors are not professionally cleaned, but I used pressurized carburetor cleaner and a battery to check them. ..."

I too did this, however New Fuel injectors and a rebuilt MAF made a big difference in the way my 86.5 runs.

The static check you did doesn't really show how well they work under real operating conditions.

Dave

ihoe

Bosch Design II 4 hole (remanufactured) injectors are on its way from Mr.Tyson. Replacing the distributor caps and rotors as well.