Engine runs unevenly and pinking on accelaration

[TorEnholm]

My TC1 323i 1979 has a slight "judder" in cruise. Acceleration is mostly fine. Any idea where to start troubleshooting?

[Jeroen]

Pfffffff in my opinion you can make a list like a telephone directory! Some more details please:
-from front or rear?
-depending on speed as well?
-has the car stood on these tires for a long time?
-how old are the tires?
-how fresh are suspension bushings?
-always apparent?

My first guess would be the propshaft bearing though, meaning the judder may feel like coming from underneath the middle of the car. If not pre tensioned a few mms or worn, this may be the cause.

[TorEnholm]

My apologies, It is the engine that "judder" (if you can call it that). It is almost like one cylinder misfires but sound in engine, does not sound like it is running on 5 cyl. Also if i add power on high gear is sounds like a crackling sound (the sound of detonation) I do not know if these two items are related?

[Jeroen]

Ahhhh ok. Well could be that 1 cilinder is not failing completely, but missing a beat here and there due to a bad spark plug wire, injector or compression. In these cases, you often see a different color on one of the spark plugs, ever checked?

Combined with the detonation that cilinder could be running lean (injector not having enough output perhaps?). Also, check igintion timing.

[TorEnholm]

Started by looking over the ignition system today. Engine has new rotor and distribution cap. All cables properly connected. Then i tried something as simple to remove the sparkplugs: Found my deep 21mm socket and tried to unscrew plugs. After trying and failing i realized that the plugs were smaller, must be around 16mm?? Anyone know the size of those small plugs? I have to borrow a socket to unscrew, and replace with proper plugs?

[Reck]

Have you tried the one in the toolbox (underneath the bootlid)?

[TorEnholm]

Have you tried the one in the toolbox (underneath the bootlid)?

Very embarrassing

Didn´t think of onboard tools. It sure did fit. It was 16mm. Bought new plugs for the car those are " normal" 21mm, taken out of the catalogue? Will look at it tomorrow.

[Jeroen]

Yeah imho these cars run fine on Bosch Super or Super 4 plugs

[TorEnholm]

No progress on this problem. Has been holiday so car has been left untouched. Changed sparkplugs, (rotor and distributor cap already done). Still runs unevenly in cruise, and pinking on acceleration. Took it to the shop today and they checked timing and mixture. Timing was spot on (22degrees at 1500rpm) with vacuum hoses off. Mixture on idle was also where it should be. As a test we put the vacuum hoses back on and tried again, with same result. Should vacuum on and off give same result? Any of you had any problems with advance mechanism? Can it be checked or fixed? Guess i will buy new spark-plug harness to eliminate another possible problem.

[silver-stue21]

One of the cylinders may be running on low compression as i found out on my car recently.

[TorEnholm]

Yes i´m afraid i have to do so, I´ve been stikking my head in the sand trying to avoid the subject, hoping to find a more hassle free solution than dealing with low compression.

[TorEnholm]

It is spring and time to crank up the classics. Last thing i discovered last fall before i put it up for winter storage, was that that the "vacum timing" on distributor does not seem to work. Talked to an "old" BMW mechanic and he could confirm that symptoms like mine could be caused by a failed distributor. His advise was to BUY NEW, Don´t try to fix. Anyone tinkered with these distributors?

Part number 12 11 1 266 723 seems to be the one that goes on my car (januar 1979 323i Baur). Does it make any difference in price buying them from Bosch or from BMW when it comes to price? What is the Bosch part number for this unit?

Thanks

Tor

[Jeroen]

From BMW will be the most expensive option I guess. Bosch service point or local parts specialist may be a lot cheaper but the Bosch service point may be able to do an overhaul as well perhaps?

But it will be an expensive part anyway but I believe there are a couple of people on here that had them rebuilt or worked on them themselves, at least I'd want to know the cause before spending several hundreds on a new part. Then still, used may be affordable and worth the try, will literally save you hundreds. Since there are a few different versions, try to locate the correct (Bosch) part no as indicated on the units housing to make sure, but the BMW part no you are indicating seems correct.

[trash-berd]

I have the same problem when I try to cruise at the same speed. It's more noticable in lower gears for me, seldem ever notice it in 5th but it does happen from time to time. New plugs, wires, dist.cap and rotor. I noticed it more often after I replaced the spark plugs and cleaned my injectors.

[Peter V.]

If the vacuumbox at the ignitionunit is leaking you will not have the right timing.
This is a part that can be renewed apart so a new distributor complete is not neccesary.

Try to suck at the vacuumbox and look if the inside of the ignition is moving. You will have the problem around the 2000-2500 rpm i pressume?