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Really lean around 3500 is like 18:1 - which I think is the limit of the A/F sensor as it flat lines around there. But, its 12:1 otherwise.

Question - look at the photo of the WUR. Is that the right one for a 1981 911 SC Euro? According to this:
Welcome to Adobe GoLive 5

that may be the WUR from a '78-'79.

Old 04-02-2012, 10:42 AM
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If the AFR goes back to rich, like 12-13:1 above 4000 rpm, I would say you are getting bad data. No small variation in WUR spec can cause that. It is easy to get bad data with a wide band sensor for many reasons.

I think the warm control pressure spec for ROW is 2.7-3.1 bar, your 3.4-3.8 bar is for a USA model with lambda. If you really have a repeatable serious leaning out at 3500 rpm, you want to be monitoring system and control pressure at that point under load.
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Old 04-02-2012, 12:19 PM
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Wow psalt, never thought that my euro WUR would be different than a US WUR. Do you know where I can find information on euro CIS? All the info I have does not differentiate between the US and ROW so if there are any differences, I am blind to them. That makes this testing pretty useless.

My original problem was felt by the driver (me) on track and at high rpm, not at 3.5k rpm. The undesirable A/F readings on the dyno seem to be measurement errors (like you suggest) more than anything related to the problem I'm having.

If the specs for the euro WUR are like you say, then it is working correctly and I don't have any ideas as to what is causing this as all other measurements are in spec.

Do you know the part number for the 1981 911 SC euro WUR? (I'll be taking mine off tonight.) I only ask because the on-line parts places show one that looks different than what I have - and they don't differentiate between US and euro models. Theoretically, I could have a different fuel distributor, WUR, fuel pump, etc, with all different specifications.
Old 04-02-2012, 12:38 PM
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The CIS on a 81 US 911SC is completely different than the ROW. The K Basic part of the US lambda CIS is too lean everywhere and the ECU pulsing of the FV brings it back into range. The ROW WUR is Bosch 089, USA 090. All the specs are in the factory manual or the Technical Specifications book.

If your engine really was going to 18:1 under WOT load at high rpm you would have melted the pistons.
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Old 04-02-2012, 03:57 PM
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I can confirm I have a Bosch 089 WUR. Unfortunately, neither the Bosch service manual nor the Bentley service manual have any information on the 089.

I'll look for more sources of information unless someone can post the cold and warm pressures for this WUR.
Old 04-02-2012, 04:56 PM
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Cold control pressure 1.0-1.4 bar (10C), warm 2.7-3.1 bar, warm, full vacuum (420 mmHG) 3.4-3.8 bar. System pressure 4.5-5.2 bar
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Old 04-02-2012, 05:29 PM
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Thank you psalt for those specs. My WUR, the 089 seems to be in spec.

So the car runs on the dyno ok, tests good to CIS specs, yet sometimes runs lean on the track and there are obvious signs of lean condition on just the left side of the engine.

Are fuel pumps the same between US and euro cars?
Old 04-03-2012, 07:52 AM
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Brian,

Before you go farther, repeat the definitive test: swap back the fuel lines at the Fuel Distributor.
The lean/rich condition should swap sides again.
This is such an easy test, you can repeat it regularly.


Some basics:
The CIS sensor plate measures the total air flow to both sides of the engine.
The Fuel Distributor is not supposed to differentiate L-R, it is simply plumbed most conveniently.
Swapping the 1-2-3 hoses at the Fuel Distributor with the 4-5-6 tells you the issue is in the Fuel Distributor.

I think your fuel flow test at the nozzles is not precise or controlled enough to detect the difference.

There are several other things about the engine that can cause a L-R difference but none change with swapping the fuel hoses.
For reference those things include:
Different cam or cam timing L-R.
You have separate exhaust L-R, possible flow difference?
Prior 1-side rebuild with different components or machine work.
Different L-R cranking compression or cylinder leak.
Again, none of these change with your swapping fuel lines.

It is good procedure to confirm (or make) every system in & around the engine perform exactly as intended.
It is also proper to have a ‘baseline’ for all the measurements and settings for future diagnosis.

A ‘simple solution’ is to try another Fuel Distributor.
A bit more expensive is to have your Fuel Distributor rebuilt by a real ‘pro’. I suspect there are many who will charge for ‘tinkering & cleaning’ but are not capable of the precision you need.

The least expensive confirmation of the performance of your Fuel Distributor is to develop a more precise measurement of the flow differences among the Fuel Distributor outlets, lines & nozzles.
Once you have mastered this, you can repeat after swapping fuel lines again.
The measurements should move L-R.

Measuring mass can be far more precise than measuring volume.
Measuring volume requires six calibrated containers.
If you rely on a single calibrated container you introduce errors from transferring the fuel.
Measuring volume also require careful attention to parallax and interpreting the meniscus position.

You should be able to borrow a balance capable of resolving less than 0.1 g . Even a student ‘Triple-Beam Balance’ can do this with a full container total mass up to about 2.6 Kg.

The more precise your measurements, the greater care is necessary preventing the gasoline evaporating between your first and last measurement.



All this effort is very worthwhile for your track application.
You want to get every bit of performance without the risk of damaging a cylinder from a ‘too-lean’ condition.

Best,
Grady
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Old 04-03-2012, 08:41 AM
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We did more testing, this time on the dyno. The left side runs 1 to 2 points more lean than the right side. If the right is 12:1, the left may be 13 to 14:1. This is both at idle and at mid-range rpm.

Normally, we thought this would be too much air or too little fuel to that side. But, as reported before, CIS is supplying fuel correctly, based on pressure measurements and the injected quantity test.

We then sprayed brake cleaner on the left side and got some engine hesitation. We thought it was intake runners 1 and 2 so we removed them and used some high temp silicon to re-seal the boots. That didn't help, although the engine now doesn't hesitate when brake cleaner is sprayed near the boots.

While analyzing, we tried removing a spark plug wire to see what affect that has. With a removed spark plug wire, the A/F ratio went way up and showed a lean condition.

We then considered if spark was not correct, but this makes no sense as we have other signs of actual lean conditions, such as white residue on the exhaust and spark plugs. The plugs are pretty new. We also measured the resistance of all 6 spark wires. They seem to increase in length from 2500 ohms to 6100 ohms.

One other point. We removed all 3 spark plugs on the left side and #3 showed it was running lean (white dust) while the other two cylinders did not.

We noticed that cylinders 3, 4, 5 and 6 were very hot (the wire part that clips to the plug) while 1 and 2 were less hot.

In my mind, it can't be fuel, due to the injected quantity test.
It can't be bad spark, because we have evidence of lean running with the white residue.
So, it has to be air. I guess I need to remove the CIS and airbox stuff to check for leaks in places we can't spray.

If you have a link to any good "how to" for removing CIS with engine in the car, that would be great. I've haven't had a reason to lower my engine yet either, so that will be new.
Old 04-09-2012, 10:00 AM
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Brian,

Before you go taking things apart, perform a cylinder leak test.
You may want to go around the firing order several times to confirm consistent measurements.


I still think you need to make fuel-flow measurements more precisely.
If one side is 12:1 and the other is 13-14:1, it switches side swapping hoses at the fuel distributor then something is wrong with fuel delivery.

Rule #1 – diagnose first, fix when you know what to fix.

Best,
Grady
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Old 04-09-2012, 10:12 AM
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Again, I would say you are getting bad data. Has your original problem, 18:1 AFR disappeared? Your goal should be 13.2 AFR under load at WOT. Idle and part throttle readings should be considered separately. 12, and 13 or 14 is not accurate enough to make any decisions, you need more granular, repeatable data. A slight vacuum leak from injector seals or boots will have little effect on WOT data. The O2 sensor only knows O2, it does not know anything about fuel. The reason it reads lean when you disconnect a plug, is that you are increasing the amount of O2 in the exhaust from the lack of combustion. This is normal. My advice is to get the engine hot by driving 10 miles, pinch off the brake booster hose and make additional runs until you can get repeatable AFR data down to at least a 0.1 level before making any assumptions.
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Old 04-16-2012, 04:24 AM
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I would like to thank all of you for your help and suggestions on this thread. Since the last round of posts, we found an air leak - not on the intake, but in the exhaust header. I have Euro Racing Headers and the metal has rusted near the exit flange on one side. Its a small hole, about 1/2 the side of a pinky nail, and obscured from view by the nut on the bolt that holds on the tail pipe. This may account for air getting in the exhaust system and giving a reading that differs left to right. Until I fix this, I can't use O2 readings in the exhaust as a reliable measure.

Old 10-15-2012, 08:36 AM
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