My 90 C4 had 4 broken head studs at 83k miles and I have seen several others as well. All earlier engines. Not sure if the later engines are less prone to this. The engines with the broken head studs made a similar noise.

 

My MY 91 early engine no head gaskets also had 4 broke head studs

 

Wow. Call me Sally and beat me with a switch. You learn something new every day. I have 3 964 motors I beat daily. One is a Feb 90' motor, had top end, gasket grind done at 77k I believe. Never one stud. Other 91's no idea. I guess now I am doing a rebuild soon. Cursed myself. My own fault. Moms calling from upstairs, wants her tapioca pudding and a foot rub. Must go. Carry on boys.

 

^^ well you won't know unless you go through a full diagnosis. I had a 91 C2 yesterday that had a slight mis. Was especially annoying to try to figure out. Figured it was a bad spark plug but pulling wires didn't change anything. Pulling the main lead to the cap showed it would arch so we had no coil issues. Finally broke down and dusted off the old Hammer. Who says 90's technology is useless? Came up with a ground fault issue injector #2. Low and behold it was the injector not working. Pulled it and tested it for resistance and nothing. At $300+ for a new injector only available through Porsche I decided to play with it. Ended up being corrosion on the contacts. Cleaned them up tested it showed 16 ohms reinstalled it and she runs like a top. You never know with these older cars it could be anything.

If the removing of each plug wire individually doesn't do it then it is on to removing the valve covers and see if anything is an issue there. GL hope it isn't a broken head stud.

 

I am knee deep in helping my daughter with her college applications and I also started painting the inside of our home just before this happened, so I have to finish that first. It may be a month or so before I can get to it, but I thank everyone for the tips. I’ll also make sure to check the AFM cable to see if the TSB has been performed, I read it can cause similar issues.

 

I finally had some time to dedicate this past week and while it is still early for a full vote of confidence, early indication points to the winning online diagnosis! So simple, yet so frustrating.

I took the distributor caps off and I could not turn the rotors by hand, so I assumed everything was in good order on that front. I then checked my battery and I was not getting anything, so I went back to Napa, they confirmed it was dead and they gave me a new one under warranty. I stuck the new battery in the 964 and crossed my fingers. I was really nervous because it would start but ran really rough and then it would die, but after the third try it stayed running and after a minute or two it started idling smoothly. I went for a spin around the block and all was good.

So now, I started to think about what may have caused my battery to go bad and the first suspect is the blower delete. I never had a battery issue before and the battery drain coincides with the blower removal in favor of the bypass. There are many variations on how to do it properly depending on the year and I was (and still am) really never clear about it. So, I simply took the relay out and put the dummy one in (964-610-184-00). So, for now I put the blower and relay back in and I will have to figure out how to properly do the blower delete on my ‘91. In the meantime, I will drive it some more in hopes that is is the end of my woes.

 

So your diagnosis is that the blower delete and the dummy relay caused a battery drain? Have heard of this before and was going to try the dummy relay but maybe it’s not the right solution? Mine is a MY 90 built Dec 89

did you have the battery on a tender?

 

I am not 100% sure but it seems to be the case unless the issue comes back. I never had battery issues before and I did the blower delete earlier this year. I usually have the 964 on a tender, but I forgot to put it back on and left it a couple months off of it. As far as the solution for the blower delete, there are various ways that worked for members and I am still trying to figure out which way is right for mine.

 

I hope it is resolved... and I hope mine is fixed after a new battery too (which it is getting anyway).

Let us know after some more miles please.

 

A follow-up question: Is that Porsche relay part you posted what is used on RS cars that come with the heater blower duct bypass from the factory? And is there a fuse that needs to be removed as well (30A #11 as shown on the 993) but not sure if it applies to our 964s?

 

Yes, this is a Porsche part (see pics below). As for fuse vs. no fuse... With the relay and the fuse out, my fans cut out past 10 degrees and did not come on at the warmest setting. With the relay and the fuse in place, my fans worked at both the coldest and warmest setting only (they cut out in between). Not sure either scenarios were right.

 

Can i just be cocky for one moment...




I'm glad it wasn't anything terribly expensive....

 

Reviving this for an update and more....

All was good and my issues were behind me, or so I thought. I took the 964 for a drive a few weeks back and it ran beautifully.... until it did not! I was getting on a freeway onramp when of a sudden there was a total loss of power, and it was hard to keep it running and all the symptoms from before resurfaced. I was running out of ideas on the cause, so I decided to let the pros handle it and had it towed to Mayo Performance. Chris started the car and sent me a video, you guessed it, running beautifully but by a stoke of luck, the car started acting up again and Chris found that it was the ISV. He unplugged the ISV and the car ran well, plugged the ISV back in and the 964 would stumble and die. We tried to clean it up but we had poor results so in went a new ISV, expensive little bugger! While the battery was in need of replacing due to a drain from the blower delete, the ISV was ultimately the main contributor to this whole mess. Weird because it was so intermittent that I was convinced it was an electrical gremlin. As a bonus, we also found the source of the rattle which was a loose exhaust tip, and I asked Chris to recharge the A/C system to see if it would hold up.

A few $$ short and a lighter wallet later, I was back in business but since we are driving old cars, a project is always around the corner and sure enough a new one popped up. Everything was fine and dandy and I was happy to have A/C back but when I came to a light and downshifted from 3rd to 2nd with the A/C on, the rpms dropped like a rock and the car stalled. I popped the clutch to get it going again and then turned to A/C off and the problem went away. Yesterday morning I tried it again, and experienced the same stalling when engaging the clutch to shift from 3rd to 2nd. When stopped at a light, no issues with rpms with the A/C on or off, barely a tick when the compressor kicks in. When driving with the A/C off, no issues whatsoever. With the A/C on, everything is fine until I engage the clutch to downshift and then the rpms drop and the car stalls. Chris thinks I have a LWF because my 964 revs really fast and pulls super strong. To be honest I have no idea since I never bothered with the A/C all these years, so I went through the maintenance records from the PO and I can only find records for new pressure plate, throwout bearings, clutch disc, etc... but no flywheel. Is there a way to tell without taking everything apart?

 

You'd be able to tell immediately when driving the car. But- if you can't tell, find another guy w a 964 and swap keys. It'll be very obvious in a back to back comparison.

I'm about to pass through Dallas btw...i will wave from the highway...

 

Maybe upload a quick phone video to Utoob with you blipping the throttle at idle?
I know my car doesn't have a lightweight flywheel as the engine rev counter definitely doesn't fly around the tach when I blip the throttle. Revs drop smoothly, but not fast at all as I would imagine would be the experience with LWF.