CIS guru's needed!! 83' SC cold start issue
 

Need some help. I have a 83' SC with a fresh rebuilt engine with new injectors new vacuum lines etc. The car has run perfect for the past 2 months since rebuild. Now that the temps have dropped to below 70 I have an annoying cold start issue. On the initial cold start the car will rev to 14-1500 and then drop rpms and either stall or slowly surge back up then down. Throttle has no effect during this time. When I restart car it runs up to 15-1600 and then gradually drops down to 950 and acts normal. The problem is only on the first attempt. The car has a new WUR and I checked the fuel pressures.
System 4.7 bar
control 1.8 @ 20c
warm control 2.4 @ 1min
3.4 @2min
3.5 @3min
3.5 @4min
Residual 1.8 after 10 min
The numbers don't seem bad to me. Control pressure may be a little low, but it is close to spec. Mixture issue? (seems lean during issue) I do not have a CO meter.

Is the car a US or Euro? What is the bosch number on the wur?

Going through a similar issue as you.

http://forums.pelicanparts.com/porsche-911-technical-forum/974868-running-lean-warm-up.html

How long should it take for the WUR to get to warm control pressure? I notice yours took about 5-6 minutes and mine took under 3 minutes.

Have you checked mixture? Check the cold start injector system. The thermo time switch etc... Check for power while cranking at the thermo time switch using a test light. Then you can try to get the connector off the csv (not easy) and test for ground and power there.
Do a search for testing the Thermo time switch and csv. During the rebuild the tech may have inadvertently swapped the sensor plate plug with the csv plug they're both blue and near each other.

CIS is temperature sensitive. It’s pretty common to have starting differences between cold and warm seasons. It tends to be a fine line in setting the pressure to a setting that works well in both. Also depends on how much variation in ambient temps in your location. I would like to hear what Tony says but 1.8 bar at 68°F might be a little lean. Would you say 68° is a fairly typical temp when the problem happens or is it usually colder?

Edit: I just looked at the chart. 1.8 is too low for cold control pressure at 20°C.

Check to make sure you have 12V at the WUR connection. Also take a resistance reading across the WUR terminals. My guess is that on your 2nd attempt your getting to warm start behavior.

Are you sure that warm control pressure maxed at 1 minute? That seems fast and the pressure seems a little low. Not looking at the chart though.

Edit: Your residual pressures are higher than warm control pressure. Suspect you did not wait long to report the correct warm control pressure value. Also residual should be same or nearly the same at shutoff. It should not increase. RP should slowly drop off over time. An engine that has rapid drop in residual pressure will have a hard time with warm starts. Doesn’t sound like your problem. It’s doubtful your RP was increasing over time. That would be unusual and suspect if it is realky the case.

Someone else already asked but is it US or Euro. Need to know that too.

Tony will no doubt ask you to verify that you have the correct WUR for your car. Please check the part number. It is amazing how many people have had a shop work on their car and the wrong (incompatible) parts were used. Not saying that happened in your case but it would be a good idea to rule it out.

Thanks for the help guys! The car is US spec the WUR is correct "090". It takes 4 minutes for the warm control to max out at 3.5 bar. The residual pressure dropped to 1.8 BAR after 10 minutes with the valve open.(I may not have been clear about that) The problem happens when temp drops below 70f. 1.8bar is on the low side @20c. Does the low 1.8 pressure @20c indicate a rich or lean condition? I thought low pressure indicated a rich condition. The car behaves like it is lean during this time. (after 2nd start or 2 minutes all is well) I want to make sure my fuel pressures are not causing the issue before I start looking at other components. I am thinking about trying to richen the mixture just a bit before my next cold start. In fact I am going to try that now, and report back. My engine rebuilder does not have a CO meter and adjusted the mixture by "feel".

I just did a cold start after turning the 3mm allen screw just a small amount clockwise. The start seemed better. I had a drop in rpm but it recovered more quickly and did not stall then went to 1500rpms and slowly dropped back. I will richen it up just a little more and then try another cold start tonight.
My deccel valve is not connected. Could this be the issue. The small vacuum line is capped and the deccel valve is capped off as well. (no vacuum leak created)
Arbita, I am not sure how long it takes for the WUR to reach max pressure. Mine is FlowTech rebuilt and it takes 4 minutes to reach max pressure.

I think the decel valve would only be a problem if the diaphragm is stuck in the open position causing false air to get into the intake. Maybe you can check it with a vacuum tester to see if it holds. I replaced mine when I rebuilt my engine.

Do you have a duty cycle meter that can help you get your mixture set correctly?

A have an old analog type dwell meter. Can I use that to help set mixture.

As Tim (tirwin) says you are too lean at cold start.

You can set your CO pretty close with an old dwell meter. This is secondary to pressures.

You are in Deleware. You could almost walk your WUR to Tony's house. Pay him a few bucks to re-calibrate your 090 for Cold Control Pressure. He can dial in WCP as well, if necessary. Get this done first.

The dwell meter business is pretty easy once you get the WUR baseline set.

For 83 US model @ 20°C, the range for CCP should be 2.0 - 2.4 bar. That means you are overly rich on cold start for that temp. Lower pressure, richer mixture. Pressure starts low at cold start for AFR to be richer than normal and leans out to stoich AFR for normal operation. At 1.8 you are slightly rich at cold start.

3.4 - 3.8 is fine for WCP.

As Bob said, don’t muck with the mixture if CCP is off. When you change the mixture you are affecting the IDLE mixture. So if you make it richer or leaner for a cold start you can be affecting AFR at cruise and WOT.

If you are certain with your WUR tests, then get in touch with Tony and have him re-calibrate your WUR. If not, double check.

Once WUR checks out, then adjust idle mixture, timing and idle rpm following factory procedure.

Just want to confirm...is the temperature referenced in those ccp charts ambient air temperature?


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I just want to emphasize something. What you are experiencing is not totally abnormal. If you set your WUR in the winter months it will be fine in the winter and a little off in the summer and vice versa. It’s just the nature of the WUR. It is not a super-sophisticated piece of equipment.

In my opinion, you have a few choices:

1) Live with it.

2) You can fiddle around with the calibration. Basically you want to move the pin just enough to find the sweet spot for cold starts. It may take a few tries.

3) You can make the WUR adjustable. Some have done this mod and have different summer/winter settings.

4) You can look into something like the FrankenCIS.

My car behaves better for cold starts in summer than in winter. I have to be patient with cold start in the winter. I’ve chosen to live with it for now.

Basically the assumption is the engine and ambient air temp have equalized. If the WUR temp was significantly higher or lower than the actual ambient air temp for some reason then that would affect the result.

There is also a note in the Bentley that says “engine temperature should be below 20°C (68° F) for the most accurate check of the control pressure regulator.”

Thank for correcting my screw up.

Just talking, 1.8 bar is rich but is that enough to stall the car? Surge up and down, I'll buy that.

Good question. The desired range from the Bentley for all temps is only .4 bar (2.4 minus 2.0). .2 (difference between the low end of 2.0 and the measured 1.8) doesn’t sound like a lot but then again that is also 50% of the entire range. Just thinking out loud. Is it enough to stall on a cold start? I don’t know.

Thanks guys, all comments made have merit. I think I will do another pressure test tomorrow afternoon. I did see the Bentley recommendation to check at temps below 68 and we are supposed to be in the 50's tomorrow. I will use my IR temperature gun to read the temp at the WUR. (I based my 1st temp info on the thermometer in my garage and I am not sure of the accuracy) I just attempted another cold start with the mixture richened a little more and the symptoms remained the same. I will return the 3mm screw back to the original spot as that simple test did not improve the symptoms. My WUR is a remanufactured unit from Flowtech and has a 1 year warranty. If my cold control # is out of spec when I do my test tomorrow I can send it back to them for calibration. I am sure I can live with issue as it acts perfect on the second start, but I am finally getting this car dialed in and I know it did not behave that way off the showroom floor. I will post the new cold control results tomorrow evening.

Wur-090.........
 

Bob,

The WUR-090 was sent to me in August 2014 for FREE test and evaluation. The test results showed the WUR to be out of spec and would not work well without re-calibrating it. The owner wanted it back as is and so I sent it back to him.

Tony

For the record, it was my screw up. I was thinking it should’ve been ~1.5 bar at that temp so I said it was probably lean. Then I looked at the Bentley and it was 2.0-2.4 bar at that temp. So that’s what I get for thinking instead of knowing. You were just going off my mistake.

Tony, The WUR I sent to you in 2015 is not the same one that is on this car. The WUR I have is a new reman from Flowtech. When I had the engine rebuilt I put on this new one. I did not need the old one calibrated because I had sent in a "089" core to flowtech in partial exchange for the correct 090.