Poor running and distributor end float

[Hil911]

My car (1976 911S) is still running really poorly in transition. Idle is pretty good and above 4000 rpm is good but driving in traffic is horrible with staggering, misfires and backfires.

I have worked through as far as the ignition distributor. With the timing gun the marks seem to jump around irregularly as much as 5 mm at 2000 rpm. It may be completely missing beats as well but that is rather hard to see.

Dwell and points clearance are reported by the garage as being good.

So I pulled the distributor. I can get 1.27 mm of feeler gauges between the shims at the bottom of the distributor housing and the gear, as in the photo. I reckon this will not help to get precise timing. There is not a lot of radial play.

Any thoughts on whether this could cause my problems and should be fixed, and where to source shims would be appreciated.

[timmy2]

PartsKlassic dot com sells shim kits.
https://www.************.com/p-1196-911-distributor-shim-kit.aspx

Don't forget the drive shaft pin you will need to replace if you don't already have one from our host

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[DRACO A5OG]

+1 add shims, they needs to play but no more than .5MM+/-. Make certain when you spin it, it does not wobble radially. The inner snap in bearings are not replaceable. When you spin it there should be some resistance.

[Hil911]

Thanks Guys!

I'll recheck the radial wobble when I get the shims.

Has anybody fixed radial wobble? I'm thinking ball bearing and a friendly machinist ...

We just did German Car Day, so here is a pic just for fun. Mine is the orange one in the second row.

[timmy2]

The link I gave you also sells bushing kits for radial wobble.
They need to be pressed on. No ball bearings In these units.
There are a few threads on replacing the bushings, do a title search.


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[timmy2]

83 SC Ignition Distributor Bushing Replacement


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[Targalid]

I do not think your poor running is related to the axial play in your distributor. Rather your symptoms sound like ignition crossfire and/or a lean mixture. Some potential causes: carbon tracks in distributor cap, old ignition wires, dust/dirt at coil connections. Clean everything with alcohol, Q-tips and clean towels. Then check your timing again. I bet you see more stable advance. Try 1/8 turn richer (clockwise) on your fuel distributor and see if it runs smoother. If that helps, go another 1/8 turn. When the engine starts to surge at idle, you have gone too far, then back off 1/8 turn. Cleared up similar hesitation on my car by doing this.

[fanaudical]

I went through this with my 2.7 last fall and distributor shaft end play did seem to contribute significantly to those issues. It didn't fix all of it - some minor CIS tuning was needed.

[stormcrow]

Hil911

I would disassemble the distributor. There is a washer that the top end of the distributor rotor sits on and when that wears the distributor contact posts just barely touch the distributor cap.

I had the very same problem - as a matter of fact when I would be driving the engine would shut off and I would have to push in the clutch, turn the ignition off and on a gain - loud boom coming from the muffler.

Anyway look at your rotor cap and see where the burn marks are - if they are at the very end of the terminals then that's what your problem is. There are several posts out there on how to take apart the distributor - not that difficult - also gives you a chance to visually inspect the spring and advance mechanism to clean it up.

[Hil911]

Thanks Folks

I think that I have done EVERYTHING that it is possible to do with the CIS. I have played with the mixture until the cows come home. All systems have been checked (pressures etc) and all seem good.

It has been smoke-tested for leaks.

Why would the engine run lean at mid-RPM and then go fine, but perhaps not very gutsy, at high RPM?

I'm not saying that there isn't still a problem but honestly I can't think of anything else profitable to do. And the problem is not all regular - sometimes the engine starts fine and other times it makes a major fuss of bangs and pops. It starts well when hot.

The garage says that the idle is a bit rich but that the mixture leans as the revs go up. BUT although lean it blows out unburnt hydrocarbons. They agree that the good idle etc suggest that there is not a problem with the valves etc.

So, I am going to attack the distributor next. The engine does make a strange squeal on startup and I've read here that can be a distributor problem.

Sorry, I am not trying to squash or ignore people's advice, it's just that I have run out of things to work on with the CIS. Unless somebody fitted the wrong plunger or something completely weird.

One other thing - the car was pretty much like this when I bought it. I have improved it by completely rebuilding the CIS (checked WUR, checked all other functions, rebuilt distributor, new lines, new injectors, checked plumbing {it was wrong} and heaven knows what) but the basic problem is still there.

[Hil911]

Oh - I should have said: new distributor cap, new leads, new plugs, new points.

Yup - I'm spending the money!

[fanaudical]

I have always found that most perceived CIS issues are generally ignition. Are you still running points or have you switched to another trigger method? Have you verified the advance curve? Is their vacuum retard on your distributor? Is it working?

Do you have EGR on that car? Is it still active?

Oh - And buy multiple shaft pins (just in case you have to take the thing apart again - they're cheap).

[Hil911]

I am running the original ignition system with points.

I crudely verified the advance curve but I am wondering if that might be a problem. I ordered a new pair of the primary springs.

There is a vacuum retard and it is working. I tried disconnecting it (plugged the pipe) and it MIGHT have been a bit better but it was hard to tell.

No EGR.

[Chuck.H]

Just as a suggestion, I've seen ignition misfires due to excessive spark gaps as the energy finds easier paths to ground...

Chuck.H
'89 TurboLookTarga, 382k miles

[T77911S]

side to side play is more important on the dist.

plug the hose, not the pipe on the dist if that is what you are talking about.

check the fuel pressures warm. you have a vacuum controlled WUR. check pressures with vacuum on WUR and no vacuum. should be about .8bar different.
the other option is to bypass the thermo time valve that the vac line goes to before it goes to the throttle and just run it dirrectly to the TB. it needs to be connected below the throttleplate.
if you do not have gauges, with it idling, remove the vacuum line from the WUR. the idle should get worse due to it being richer. make sure there is vacuum at the hose at idle.

here is what i did to my 77.
the points just provide a ground for the CD unit. that ground is thru the body of the points, to the plate inside the dist to the sdist body/outer shaft then the engine block.
i took my dist aparts and cleaned all the contact places so there was a good connection for all those points, including the dist shaft where it contacts the block.
it seemed to help with the idle but it really helped when setting the timing. when iwould set the timing, the engine would cut off and back on when adjusting timing.

[john walker's workshop]

try removing and plugging the vacuum hose on the END of the warmup regulator.

[Hil911]

Hi Folks

Thanks for your suggestions.

It's taken me a while to get the parts and try things.

The WUR - I tried plugging both sides when the engine was warm and it didn't make a lot of difference - at idle the engine still goes Brrrr-bmp-brrrrr-brrrr-bmp-brrrr. In other words a misfire. The misfire gets worse at a slightly higher throttle and then appears to disappear under a heavier load when you are driving.

I got the parts to rebuild the distributor. I finally got the pin out that holds the gear on - aaarhh what a beast! I then pulled the shaft and examined the bearings. There's very little radial play so I made the decision not to redo the bearings. However the centrifugal advance springs looked badly stretched, and the top fibre shim on the shaft had self-destructed and was floating around in bits. I rebuilt the distributor to leave only minimal end-float, using a new top washer. I fitted a new primary and secondary advance spring. My felt lubricant wick under the rotor arm was falling apart so I cut a long strip of Jay cloth, rolled it up Swiss Roll style, shoved it in and soaked it in oil.

The engine timing now advances MUCH later than it did. So I guess that it did need new springs.

However the poor running and misfire are still there.

One thing that I decided to test was the running pressure on the fuel system - I've already tested full flow and it was over spec, so no probs there. I plugged the fuel distributor to WUR line and put a gauge onto it - I've discovered in the past that if the WUR is blocked, that line rises to system pressure. SO I took out the air filter, turned on the ignition and lifted the flow sensor. The pump started but then stopped immediately. I lifted the sensor a bit more and the pump ran a bit more. Basically, at low flows the pump runs discontinuously and doesn't run all the time except at high flows. At an intermediate flow the pump runs brr---brr---brr---brrr and I can feel the sensor kick down when the pump runs. Is that normal? My fuel pressure must be surging up and down? The accumulator is clearly not able to smooth it - and it's a new accumulator.

Does the pump normally cut out when the pressure rises?

[Hil911]

Sorry, I didn't give very good replies on the WUR connection suggestions.

In other posts I have talked more about the CIS itself. I have checked and rebuilt pretty much everything that I can, including testing the pressures in the WUR, which are within spec. The WUR was rebuilt here (Australia) in the last couple of years and I rebuilt the distributor. I've been over the usual questions of how to connect the WUR etc.

By the way, I don't think that mine has a thermo valve before the WUR - the line comes through the deceleration valve on this version.

I didn't notice the pump issue before because it does not show up much in the WUR line, where I have a T piece that I use for testing.

[fanaudical]

The fuel pump should run at constant speed all the time (you should never hear your fuel pump stall).

It's not clear to me from your description above, but it sounds like you may be dead-heading your fuel pump during your test (which is a bad thing to do). In normal practice, the fuel pump is constantly moving fuel from the tank, through your CIS, and back to the tank.

[Hil911]

No - I have the pump running in the normal setup - through the fuel distributor with its pressure regulator and back to the tank.

The pump had been replaced with a used one before I bought the 911, and the car has never run even vaguely properly. I wonder whether they put the wrong pump in? Hmmm