CIS WUR Parts Number Question

[RarlyL8]

Nick, the fuel pressure is about right for the temperature. You mentioned previously that the mixture screw was turned 4 times to get the engine started. Does this mean 4 complete 360° revolutions? Typical adjustment is maybe 20° or less. You also mentioned a lot of gas came out the tailpipe when the engine started which is not typical.
To properly diagnose this an AFR gage is needed along with the fuel pressure gage. You can have proper fuel pressure and the AFR's be way off due to vac leaks or fuel leaking into the cylinders. What do the plugs look like?

[Nicks911]

4 turns of the mixture screw. Just kept making 1/4 turns until it fired. Then adjusted the air screw and the mixture until idle was and smooth. Drive the car for an hour no problems and put it away. Now it won't start. Just looking to get to a point where I should expect the car to start. It was 4 turns towards lean to get the car to fire the first time. Not sure if a gas analyzer will help at this point as the car will not run. I only manged to get it go for a few seconds where it was backfiring through the intake and billowing tons of white smoke. I did pull the plugs and one was black the rest looked clean. I apologize for typos doing this on my phone

[Vereeken]

4 turns to the lean? So counterclockwise on the mixture screw?

Again that is a lot but in the lean direction.

So assuming that timing is well and that Idle screw is about 4 turns out, I would disconnect the cold start valve at the ThermoTimeSwitch -just to make sure it is out of the equation- then I would give the mixture screw 1/4 turn clockwise and try to start it.

I would give 1/4 turn clockwise until it starts.

What you could also do is push up on the air sensor plate with the key to on. You will hear the injectors squeal. Do that for a second. Then start. If it catches but dies you can start to move 1/4 clockwise at a time.

Michel

[Nicks911]

Update:

Decided to go with the all is lost method. Pulled an injector and put it in a jar. set the idle screw 4 turns from fully closed and fired up the fuel pump. It took 4 turns towards lean to get fuel to stop flowing from the injector in the jar. 1/4 turn towards rich tried to start the car. Nothing. Pulled the injector again. placed it in the jar again and there was no fuel flowing from the injector even with the quarter turn. It took almost a full turn plus the quarter already done to make small stream of fuel from the injector in a jar more drip than a stream. put the injector back in a tried again. Engine coughed. kept doing small turns towards rich until car started and ran. Let the car idle for 10 minutes like that. Tapped the gas pedal. Car died and now won't start.

Thoughts on how to proceed from here? Just trying to get it to run well enough to get to the shop with an exhaust gas analyzer. Unless someone in the DC area has one I can borrow.

Nick

[boyt911sc]

Originally Posted by Nicks911

Update:

Decided to go with the all is lost method. Pulled an injector and put it in a jar. set the idle screw 4 turns from fully closed and fired up the fuel pump. It took 4 turns towards lean to get fuel to stop flowing from the injector in the jar. 1/4 turn towards rich tried to start the car. Nothing. Pulled the injector again. placed it in the jar again and there was no fuel flowing from the injector even with the quarter turn. It took almost a full turn plus the quarter already done to make small stream of fuel from the injector in a jar more drip than a stream. put the injector back in a tried again. Engine coughed. kept doing small turns towards rich until car started and ran. Let the car idle for 10 minutes like that. Tapped the gas pedal. Car died and now won't start.

Thoughts on how to proceed from here? Just trying to get it to run well enough to get to the shop with an exhaust gas analyzer. Unless someone in the DC area has one I can borrow.

Nick

Nick,

You don't need a gas analyzer to make your engine start or come to life. A gas analyzer is used for tune-up and setting the CO level. Now that you had tinkered the mixture screw setting without verifying the absence of significant air/vacuum leaks, troubleshooting would be more difficult at this point.

After all the hundreds of posts about CIS troubleshooting, people still tinker the mixture screw setting in order to make the engine start or run. This is a NO NO!!! Adjusting the mixture screw is for fine tuning and setting the desired CO level in the exhaust (engine completely warmed up). The two (2) major factors for a change in AFR (air fuel ratio) are: fuel pressures and air supply. Both these could be checked and tested.

If I were in your shoes, I'll check for air/vacuum leaks. This simple test has been discussed in numerous posts and very effective in CIS troubleshooting. Then check your control fuel pressures (cold and warm). The tests suggested could be accomplished without running the engine. If you could verify the absence of a significant source of air/vacuum leak and having the correct cold control fuel pressure and proper ignition timing, I don't see why you can not make your engine start on the first turn of the ignition switch.

Tony

[Nicks911]

Tony

Thanks for your reply. I don't think you read through the whole thread. The car initially was not running well so I check the Fuel pressures and they were way off. I got a new WUR and the the fuel pressures are good. Before I check the fuel pressures I confirmed good spark and correct timing. All vac hoses are less than 2 years old and I tested their connections with some ether and no change in idle. Air box is in good shape and flapper is correctly seated.

The car stopped running after the new WUR was installed. I theorized that in order to get the car to run on a bad WUR adjustments had been made to the idle mixture to make the car run with incorrect fuel pressures. Now with correct fuel pressure the mixture is way off. I think it was way too rich as when I pulled the injector it was spraying like a garden hose.

In order to get the car running I need a point of reference rather than just slowly cranking the mixture and hoping for the best. Unless Iget some other suggestions I think I will pull the injector again adjust the mixture so there is no spray and then slow richen it up from there until the car fires up.

[Vereeken]

I have been following your thread, and as it might be plausible you are missing an obvious air leak I agree with your approach given the pickle you are in at this moment.

The German bosch manual states that when all is lost you need to pull an injector an turn the mixture screw until the injector just starts to spray. Then back off 1/2 turn.

What you also would like to check is that your Air throttle plate is riding high enough in the throat. The earlier models had a spring loaded stop that would sag (the recent SC had a stopper with a screw). As a result the throttle plate can sink deeper into the throat effectively closing off fuel delivery because the vacuum created by the engine is not strong enough to lift the throttle plate high enough.
This also causes hard starts.

Michel

[Nicks911]

Michel

thanks for all your help! I will check the throttle and see if the flapper looks like it is in its normal position. For the all is lost method When you said turn the screw back I read that was toward rich as that was back in the direction I had turned from. Does back mean toward rich or lean from after the spray has stopped?

[timmy2]

Have you pulled all 6 injectors and measured for equal flow into seperate jars?
Maybe one or two need repair.
This thread helped me get my car running:

CIS Idle Speed and Mixture Setting Without an Analyzer

Ideally make it run rich, tune it lean until it won't run, richen it back up to the midpoint and then get an analyzer to fine tune it.
Running rich is not a horrible thing. (Our cars like it)
I basically tuned mine from rich where it was surging down to a point where it was driveable and had lots of power. Lots of short road tests, small adjustments.
I later bought an analyzer and when I checked the CO it was about 4%, tuned it down to about 3.5% (ROW car) and have been enjoying the ride ever since.

[boyt911sc]

Originally Posted by Nicks911

Tony

Thanks for your reply. I don't think you read through the whole thread. The car initially was not running well so I check the Fuel pressures and they were way off. I got a new WUR and the the fuel pressures are good. Before I check the fuel pressures I confirmed good spark and correct timing. All vac hoses are less than 2 years old and I tested their connections with some ether and no change in idle. Air box is in good shape and flapper is correctly seated.

The car stopped running after the new WUR was installed. I theorized that in order to get the car to run on a bad WUR adjustments had been made to the idle mixture to make the car run with incorrect fuel pressures. Now with correct fuel pressure the mixture is way off. I think it was way too rich as when I pulled the injector it was spraying like a garden hose.

In order to get the car running I need a point of reference rather than just slowly cranking the mixture and hoping for the best. Unless Iget some other suggestions I think I will pull the injector again adjust the mixture so there is no spray and then slow richen it up from there until the car fires up.

Nick,

You need to give us numbers to be able to understand what parameters you have now. For example: Incorrect fuel pressures, way-off setting, correct fuel pressures, too rich, turn 4 turns.......these are adjectives and descriptions when used in a technical forum like this means nothing!!!!!! Fuel pressures are measurable in psi or bar. etc. Not being able to find air/vacuum leaks does not mean you don't have any. You need to test and confirm. Don't guess and you'll find the culprit.

Why would you make a '4-turn' adjustment on the mixture screw to make an engine start? You could drop your engine from a ten-storey building and the mixture screw would not change from its setting!!!!

Do you still have the old WUR? I don't think there's something wrong with your old WUR. The engine was running before maybe not optimal as you wanted but it was running. Now it won't even start.

Test your WUR (old and new) with the FP running and record the control fuel pressures versus different time intervals (0-5 min. max.). And confirm absence of a significant source of air/vacuum leak/s by doing a pressure test. Keep us posted.

Tony

[Vereeken]

Originally Posted by Nicks911

Michel

thanks for all your help! I will check the throttle and see if the flapper looks like it is in its normal position. For the all is lost method When you said turn the screw back I read that was toward rich as that was back in the direction I had turned from. Does back mean toward rich or lean from after the spray has stopped?

You pull the injector and run the FP. The idea seems to be that you turn clockwise (rich) until the injector just starts to spray (spray/dribble)
When it does that you turn the mixture screw 1/2 turn counterclockwise (lean). At that point the injector should no longer spray/dribble.

This is supposed to be the setting where the car would start receiving enough fuel (but not the setting for the correct co, that you need to do when fully warmed up.

Ofcourse all this means everything else is in fine fettle.

It seems that this is the method used when the engine and fuel system has been overhauled.

[Nicks911]

Tony,

Again thank you for your reply but I think you should be more measured in your response. As I said before I don't think you have read the whole thread. Information From my first post:

Original WUR 90 degree outside system pressure 4.8 bar control pressure 1.5 bar. car ran like this but had a light throttle stumble that I had been chasing. After confirming timing and spark and finding no air leaks I moved on to checking the system pressures

Were I am now:


I did not bother checking warm control pressures as the cold was down ~1 bar. Pulled the part number off my WUR and got a rebuilt unit from Rarelyl8. System pressure with the new WUR appears to be correct. 78 degree ambient temps 2.5 bar initially and after about 10 min with the fuel pump running rises to about 2.9 bar. However with the new WUR the car does not run. I'm theorizing that the previous owner of this motor and CIS system was working around the bad WUR by adjusting the idle mixture. Motor is new to me so I have no idea really what happened before I put it in the 914.

[prebordao]

Nick, just my 2c here:

- Are you sure there are no air leaks ? What about the underside of the airbox (where the runners connect), have you checked it ?
- When you say 4 turns of the mixture screw, you mean 4 complete revolutions ( 4 x 360º) or 4 clicks ? My mix screw has a notch everey few degrees, so 4 turns would be a lot of clicking... Just to really be sure we understand you.

[Nicks911]

4X360

I will have a poke around the airbox and runners and see if I can discover any leaks

[Vereeken]

Nick,

Do you have access to an innovate LM1 or 2?

Nice little tool.

I have trouble shot my CIS with this LM 1 and a pressure gauge.

On the basis of the AFM readings on the LM 1 I can make a lot of educated guesses.

Given that AF and co are interrelated it does away with the need for a gas analyzer (ok not really but its the closes thing we will get as amateurs).

Michel

[boyt911sc]

Originally Posted by Vereeken

Nick,

Do you have access to an innovate LM1 or 2?

Nice little tool.

I have trouble shot my CIS with this LM 1 and a pressure gauge.

On the basis of the AFM readings on the LM 1 I can make a lot of educated guesses.

Given that AF and co are interrelated it does away with the need for a gas analyzer (ok not really but its the closes thing we will get as amateurs).

Michel

Michel,

The engine has to run first before you could measure the AFR!!!!! I'm no CIS expert but I'm still looking for a CIS engine that I could not make to run. The parameters for running CIS engines is very simple and yet people make these requirements too complicated. Check your ignition (sparks & timing), fuel pressures, absence of air/vacuum leak/s, a fully charged battery and it would run.

I was away for 5 weeks on vacation and arrived home the other day. This morning, I went to the garage and started the the two (2) 911. One car started after the 2nd turn of the ignition, the other took 3 turns. Early this evening, both cars started on the first turn of the ignition switch. And same thing with the engine on my test stand. It started and idle as expected. There is really nothing difficult or magical in making these engines RUN!!!!! Keep or maintain the parameters within close range of the specs and they would run on demand. But how I do it? Test and confirm in case of doubt. Stay away from guess-work. Air/vacuum leak is the Achilles heel of Ketronic system.

Tony

[Nicks911]

Finally had a chance to work on the car. I pulled an injector and followed the method list earlier in this thread to etablish a baseline setting. car fire right up with a very fats idle ~5k. Gntle worked it back down to by riching up the mixture a 1.4 turn and turning the idle screw in 3.25 turns. Car now idles at 1K dead smooth. I have some rough running issues right at throttle tip in but other than that all seems well. I will get it on an exhaust analyser in the coming weeks.

Thanks to all who offered their advice.

Nick