Please help, I’m at my wits-end!

[OZCarrera3]

I recently completed an engine drop in my ’76 Carrera 3.0 to undertake some gearbox work and ever since, the car has been running appallingly.

The confusing thing is that car was running fine before the engine drop (albeit with some minor snatchiness and some barely perceptible bucking and surging), with the only additional work undertaken at the time being the replacement of the fuel lines.

The problem is that the car is now running very, very rich and any adjustments to the mixture (using the allen key adjustment screw) result in the engine running too lean. The car is experiencing bucking and surging, particularly through the 2,300 – 2,600 rpm rev range, but also pretty much anytime you are using anything less than about 80% throttle. It also pops and crackles quite a bit under trailing throttle and misses badly at about 5,500 rpm.

Now I’ve had the car to both a local specialist Porsche tuner and the local Porsche Center (both at great expense – over 8 hrs labour each), both of whom have been unable to diagnose or improve the performance of the car, but they have confirmed the following:

1. The CIS has no air leaks (pressure/smoke test).
2. All CIS ancillaries have been tested and are apparently ok (WUR, accumulator, etc)
3. Fuel pressure and delivery is spot-on for all cylinders.
4. The ignition system is in good condition, with the points, condenser, rotor button and cap are ok and new plugs have been fitted.
5. Ignition leads ok (only 3 yrs and 20,000 kms on them).
6. Timing is OK (but strangely the timing marker fluctuates a couple of degrees at idle when checked with a timing light).
7. Compression on all cylinders is within acceptable margins (10%)
8. A valve adjustment has been completed.

Another item of interest is that the car has two different camshafts fitted; one a Carrera 3 (930 105 148 10) and the other a late model SC (930 105 147 08). I have been told that these cams, although from different eras, are essentially the same and both have been correctly set with “1 ML lift on inlet valve @ TDC overlap” to quote the receipt from the specialist.

For my part, the only aspect I can think of is that possibly the air-metering valve in the CIS may be sticking, but everyone reckons they have checked the CIS and its all operating ok.

So some $1,600 later, I am reaching the limits of my patience (and budget) given that the issue is no closer to resolution. It is in complete desperation and much anticipation that I seek your assistance with this problem.

[69911e]

"2. All CIS ancillaries have been tested and are apparently ok (WUR, accumulator, etc)"

Have they checked to see if there is power to the WUR?

[schamp]

Is there any way two lines are crossed? Line to wur going somewhere else. You might want to check each line carefully. schamp

[IROC]

CIS can be a very frustrating system to troubleshoot and it can be very expensive to just start replacing parts. Since it ran OK before the engine drop and bad afterwards, I would concentrate on something that could have been re-connected wrong when putting the engine back in rather that a failed component.

You mention that fuel pressure and delivery is spot on, but have you checked control and system pressures and operation of the WUR?

Good luck.

Mike

[T77911S]

on my 77, the vacuum to the WUR comes from the thermo time valve, check that 12v is applied to yours if u have one. after about 30sec of power, it should open allowing vacuum to lean out the mixture via the WUR. put a vacuum gauge on it and check for vacuum.
check all the elecrical connections to the cis.

[AZ1977911]

Just a thought... You say timing varies at idle, you might take a look at your distributor and see that the shaft is not loose and that the flyweights are free.

[chrisf]

I was thinking just what AZ1977911 has stated. My 76 2.7 was running exactly as you have described, and was running pretty well before I took it down for a month for an extensive tune up.

So, this past friday, I pulled the distributor, took it apart & cleaned, then re-assembled and replaced & regapped the points. The difference in performance was like night & day. No troubles throughout the RPM range.

If you pull the dist., check for vertical play in the gear shaft. I have read that there are bushings or shims that can be used to rebuild these. And be sure that you thoroughly clean the weights and they are free to move. Also clean & lube the advance plate.

this all worked for me! goodluck.

[Walter_Middie]

69911e and Schamp both mentioned this - the electrical plugs for the WUR and the Cold Start Valve are the same and can be easily mixed up. The result is that the Cold Start Valve has power all the time (runs very rich), and the WUR only has power when the key is in the start position. The Cold Start Valve is only supposed to get power during starting, and the WUR is supposed to get power all the time. Pull the WUR electrical plug (it's the easiest to get to) and see if it has power only when the key is in the start position - then you'll know that they are reversed.

[OZCarrera3]

Excellent feedback guys!

I'll start checking these items tonight, but it will probably be the weekend before I get a chance get to have a decent shot at them again. Both are very plausible solutions.

Once again thanks for your feedback.

[rdrr]

Hi Sheldon,
just saw this thread. I guess that means you won't be running her at QR this weekend - bummer! Hope you get her running again soon.

[gavinlit]

I recently had a similar problem. At appropriate fuel mix the car was hesitating and surging although mine was in the 200 - 3000 range. The timing and all other components seemed to be spot on. When running the mix super rich the car was smooth but obviously something was amiss. The entire injection system was removed & tested. Six new injectors required along with various sleeves & seals. Still the problem persisted.

The fuel distributor was tested & seemed to be ok but when a distributor off another car was swapped on the problem vanished. The distributor was sent back to the tester ( a company in melbourne I believe) they still couldn't find a fault with it. It turned out that the 'flow rate' or whatever setting they tested it at didn't show any problems but once the unit was tested at a variety of rates it was found to be all over the place. So it was basically tossed & a new one slotted in.

It's now running perfectly with no surging snatching or anything of that nature. Interestingly going back through the receipts of the previous owners it's been an ongoing issue for about 10 years. We've finally cracked it , although the bill wasn't pretty.

Given yours was ok before the rebuild it's probably not a worn part like mine but it highlighted to me the problems with 'testing' or fault finding. Most places seem to test only at certain reference points which might not reveal everything that's going on. I racked up 6hrs in labour before the problem was isolated, although those 6 hrs did reveal other things that were fixed while we were in there. Good luck with it.

[OZCarrera3]

Gavin,

I'm up to 16 hrs of paid labour and probably as many unpaid so far. This time around!

You comments about the distributor and the fact the it had been an on-going, long term issue for you ring true with my car also. The PO had spent many $'s at the FI specialist too. I have had to run my car very rich in the past to mask the bucking and surging issue (mainly because another specialist told me this was 'normal' for a C3 - what cr*p), and because no-one seemed to eb abel to get rid of the problem totally.

I will see if I can get my hands on another distributor and see if that works too. Thanks

[gavinlit]

Lets hope it's easily & quickly solved. If it is the distributor try & see if you can get one rebuilt. I was lucky with the mechanic having the necessary bits & only having to purchase some. An entire distributor is pretty pricey if bought new. My experience with the unpaid labour has been close to yours. While the maintenance on these things is not inexpensive it's nice to see mechanics not charging for every minute & giving you a reasonable go. This is the third time that Bob Whymms have saved me a fair whack of money by going down an alternative path rather than just replacing everything in sight with new parts. A big thumbs up again for their work.

[OZCarrera3]

Ok guys, I've found two more symptoms:

1) The spark plugs in cylinders 1-2-3 are very sooty compared to those in 4-5-6 (refer photo below); and
2) Following on from suggestions from T77911S and 69911e I checked to see if there is power going to the WUR. Surprise, surpise, there does not appear to be aby power going to the WUR (engine was warm, almost running temp).

Questions:

1) Why is this affecting one bank and not the other?
2) Why would the WUR not be getting any power?

Any ideas?

[OZCarrera3]

Forgot the pic in my haste...

[OZCarrera3]

Well look like a might have been a bit premature about the no current situation, just checked on a friends SC and got the same result.

I tried to see if there was current by disconnecting the cables to the WUR and the putting the multi-meter probe into the pin (on the cable connector) and the earth probe on the fan hosing, with both the ignition on and ignition off. Using both methods, there was no sign of power to the cablke on either car (both warm).

Is this the correct way to test the current on the WUR?

[Vereeken]

Weird that you have no power to WUR. I recall going over my CIS that there should be power when engine running, but I can not recall if I have measured it with the connector on an with the multimeter pins pushed in. I'll check tomorrow how I did it.

This said I would have also gone with the Distributor, giving the fact that he moves around, that is not normal, he should go to roughly 21 BTDC with vacum line attached but at Idle I have never seen it move.

Then I saw your next post and the spark plug on one side, that can not be induced by disitributor, he would affect all 6 randomly.

So I guess I would be going to the only item that can effect one row only and that is unfortunately the fuel distributor, which could correspond with your earlier comment on the allen key not accepting your inputs. Or by assembling you have accidently blocked the intake runners on one side.

Another thing that is weird is that emission testing comes back positive. I am using a LM-1 for datalogging and tuning of my CIS with RPM converter and in-equality of taht sort will definetely show up in the exhaust gasses and in the A/F ratio.

I too had an experience with P-mechanics charging me enough only to find that the car was still running as crap. I since then decided to invest my money in a LM-1 (250USD) and a fuel pressure measuring kit (75USD) a strobe light (80USD) and a multimeter (10USD). Thats all you need to troubleshoot CIS and ofcourse a lot of time...;o)

And should I forget this site http://members.rennlist.com/jimwms/CIS/CIShome.html

Good luck.

Michel

[kentSC]

He He. It's me. Yes I registered again. When I saw you on today, I thought I'd try and help out some others.

It doesn't sound like you're getting any confident responses that address the problem. Maybe it's just a process of elimination. Try borrowing parts from others like me before spending too much more.

Cheers

Kent

[Zeke]

Just joining in here. I don't know much (I guess I could consult the manuals I have), but should there be any power to the WUR when the car is.... warm? Seems to me I've seen here a couple of deals where one side was sooty. Have patience and a free bump.

[Vereeken]

Originally posted by milt
Just joining in here. I don't know much (I guess I could consult the manuals I have), but should there be any power to the WUR when the car is.... warm? Seems to me I've seen here a couple of deals where one side was sooty. Have patience and a free bump.

Indeed not Milt. The power to WUR should be (or can be ) zero when the engine is on temperature as the Bi-metal strip in the WUR will have leaned teh fuel out thanks to heat radiated from the engine. But when stone cold he should have volt reading.

I do not believe the WUR interacts with only one side of the injector, I believe it interacts on the fuel quantity delivered especially when cold prior to the fuel distributor on top. As the WUR acts continuously also after warm-up I think it can not act on one side alone. Warm-up regulator is a bad name I think.

Michel