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AcesProxy · Posted: Tue Dec 03, 2024 9:13 pm Post subject: Diagnosing Fuel Distributor issue

Hi All,

This is my first time posting here. I have very limited knowledge and this has been my first ever project car. So an all round noob

I have a 1982 931 that I am working on. It was running and driving when I purchased it.

I took it in to get the timing belt changed as I didn't want to attempt that myself with limited knowledge.
When the car was having the timing belt changed the guy who was working on it noted that there was a bit of a flat spot when pulling from 2nd gear. I was aware of this, but it was on the "later problem" list.
He took it on himself to ultrasonic clean the injectors and the fuel distributor (no disassembly was done). This was when the problems started. He eventually gave up on trying to fix it and gave me the car back not running.

I have now replaced injectors and assume that something is blocked up in the FD after the ultrasonic clean. However I wanted to get your opinions on it here also, since I am guessing at this point.

The behaviour currently is that I can get the car to run if I push down on the pressure plate in the mixture control unit and simultaneously open throttle. The thing that is strange is that I have to push the pressure plate down quite far before any fuel comes through to the injectors at all.

So my question is whether anything other than the FD could cause that sort of issue, or if it is worth me just getting a new FD. I have access to a new old stock unit nearby.

Any insight would be greatly appreciated.
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1982 931 - Restoring

peterld · Posted: Tue Dec 03, 2024 11:06 pm Post subject:

Well, that's one mechanic you won't be going back to! Hope he didn't charge you for his blunders.
Unless he messed with other things as well, the FD is your problem.
Here in OZ a gasket/o-ring kit will cost @ $100. It's not difficult to rebuild if you are methodical, however often the unit needs to be recalibrated which simply means the four little nipples inside need to be either pushed in or pulled out to get correct fuel flow. Without a CIS flow bench it can be very difficult to get the flow rates spot on
The few CIS repairers left charge @ $400 to rebuild a four cylinder FD, which involves the above steps (including new gaskets, etc)
If you have access to a new (unused) FD at a reasonable price, then that's the ticket. Just make sure it exactly matches the part number plated on the side of your existing FD. There are many differences between S1 and S2, and ROW and USA or even other markets.
Do not get rid of your old FD. There is nothing in them that wears out except for the F/A ratio plunger. They just need careful rebuilding and calibrating.
NB. Prices mentioned above were some 4-5 years ago, so probably have risen somewhat now.
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80/81 932/8 ROW

AcesProxy · Posted: Thu Dec 05, 2024 2:34 am Post subject:

Thank you for the info.

I did grab a refurb kit, but I chickened out last minute due to the horror stories I saw online describing the all but guaranteed failure of all those who have tried in the past. Maybe Its worth giving it a go anyhow, since I dont have much to loose at this point.

But yea, I have found an unused one locally for around R20000 ($2000)... Its a costly grudge purchase but better than the paper weight I have currently.
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1982 931 - Restoring

peterld · Posted: Fri Dec 06, 2024 12:53 am Post subject:

Check out k-jet.biz on the old interweb. Or ring him Colin 61 0422 424 415
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80/81 932/8 ROW

Beartooth · Joined: 05 Apr 2022 Posts: 255 Location: Roberts, MT

It's very possible whatever he did knocked some crud loose, or maybe pushed some hardened o-rings over the edge. FDs aren't that bad to work on, in my experience. I've rebuilt three and not ruined or got stuck on one. As mentioned, if you could get a working one, then you could fix up or experiment on what you've got, but it sounds pretty expensive. I wouldn't pay more than $250 for one in known working condition, and definitely not more than $100 for one in unknown condition. Obviously, that's in the US; I'm not sure what your options for a replacement FD are.
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1980 931 diamond in the rough

AcesProxy · Posted: Thu Dec 19, 2024 6:57 am Post subject:

After going through my options move decided to give the refurb a go again.which type of sealant, if any, would you use on the membrane? If anyone has done this before or has a link to a guide of sorts it would be amazing. I know there are quite a few walkthroughs on YouTube, but it’s always nice to be able to refer back to a guide if possible.
As always I really appreciate all the help and any advice you may have.
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1982 931 - Restoring