Trying to tune cold control pressure

1986911 · 1986911's Garage

I am slowly learning how this works, this forum has really been a phenomenal source of information. I set my cold control pressure on my Leask wur. I am now tweaking it to perfection (at least trying). I agree with the philosophy of setting initial pressures with guages and then fine tuning with AFM.

Am I too lean? I set it to the Leask CCP baseline but it seemed too rich. Strong smell and weak idle. I raised the pressure one turn. My car starts with one twist of the key and idles at 800 rpm temp inside garage 60 degrees. This is after being off for 24 hours. My AFR guage delivers its first reading 30 seconds after start. Its at 13.6. Idle then starts to richen as wur warms up down to 12.8 then up back up to 13.6 at a warm idle. (next is adjusting rich cruise and rich full throttle)

Should I lower my cold control pressure to richen her out a little on cold start, avoiding the afr roller coaster? Or is this how is should be?

All these cars are different the CCP that works for you may not work for me. I don't know anyone else with a Turbo so not sure what a normal warm up is like for one of these.

Thanks!

patkeefe · 12-27-2012, 06:29 PM

Cold pressure is the least of the problems. I also have a BL WUR, on a turbo SC. I set the cold pressure to whatever BL said on the spec sheet. I think it's around 2 bar or so. Cold doesn't have much effect after it warms up anyway. I have also found that the WUR is very fussy regarding ambient temperature when you start up. So, I just get it to run OK at idle, and in two minutes or so, it's out of the picture.

I suggest you leave the CIS gauges on for a bit, and watch your pressures. I do know that some of the WUR's have different heaters in them, which sort of stages the heat up for faster warmup. I have a permanant gauge mounted, to observe the pressures, much easier than having the test gauges in the engine compartment.

911nut · 911nut's Garage

My car seems to start/run best at the high end of the spec for ccp.
You have to experiment to find the best value and treat the spec more as a guideline rather than the gospel.

1986911 · 1986911's Garage

Thanks guys, I just don't want it so rich that it sets of my natural gas alarm in my garage. I am looking for the leanest cold start I can run. If I idled for more than a few seconds in the garage it was so bad my home alarm would trip. I think I leaned it out too much on cold start so gave it a little bump to the rich side and so far so good.

T77911S · 12-31-2012, 11:39 AM

rich is better. set rich for good cold start but no surging. its not that critical. too laen can cause back firing and hard start, then too too rich can foul plugs.

mark houghton · 12-31-2012, 02:17 PM

Quote:

Originally Posted by 1986911

My AFR guage delivers its first reading 30 seconds after start. Its at 13.6. Idle then starts to richen as wur warms up down to 12.8 then up back up to 13.6 at a warm idle.

That doesn't sound right (could just be how you've stated it). A stone cold car should start with an enriched mixture, and slowly go leaner as the WUR heats up. Thus, you should be seeing low AFR's at first (anywhere from 10 to 12, depending on a lot of things), and within a minute or so you'll see the AFR's beginning to lean out. If your fully warmed up idle is settled in at 13.6, that's fine though maybe a tad on the rich side - though it seems most 930's like it there. Mine idles at 13.8-14.0, depending on it's mood for the day.

1986911 · 1986911's Garage

Yep, it looks like it was a little too lean on the cold control pressue side. I get about 12.0 when it starts now. No stink in the garage and starts like a champ.

I did read some of your pasts posts on disconnecting O2 sensors. I did it to mine and it solved that fluctuating AFR that I thought was related to timing. Keep the good posts coming!

Thanks

JFairman · 12-31-2012, 03:05 PM

Mine works like Mark described.
I have a leask adjustable WUR/CPR and a CIS Flowtech modified fuel head and 964 cams.

My warm steady cruise has never been far off, I've just adjusted it a little one way or the other 1/4 or 1/8 turn at a time over the years.
Also have an innovate digital AFR gauge.

I set the cold start control pressure entirely by ear and how the motor runs when starting stone cold. Just like I've tuned many carburators including multiple Weber 45DCOE's on BMW engines in the past.

Just remove the heater plug on the WUR first so it doesn't start changing the CP right away after starting it while you're setting it.

Then tap the pin down until it's running a little too rich and then turn the 10mm nut clockwise that draws the pin back out until it idles good and doesn't miss or hesitate at all when blipping the throttle.

At that point the motor isn't cold enough anymore to continue so I wait a day for it to cool off completely and then start it again and blip the throttle, etc.
If it missfires or hesitates it's a little too lean. If the exhaust stinks really bad and is full of black smoke it's too rich and I turn the 10mm nut clockwise a little more to raise cold start CP a little and lean out the cold start a little more.

Then see how it starts the next day whne it's cold again and repeat if needed. If it's all good I'm done and then I'll hook up the CIS gauge and write down what the cold start CP is and the outside ambient temperature so I have a reference point.

1986911 · 1986911's Garage

Thanks J. it seems we have the same idea. Over the last few days I would tweak it little by little with the wur plug off. Seems good right now at 12.0 afr on cold start up. If only all the adjustments were that simple.

turbo ride · 12-31-2012, 04:27 PM

Great info guys. I plan to do a BL WUR soon so this is great. Thanks.

Question - how do your cars start (and behave for the first few minutes) when it's close to freezing - say between 25- 40F?

1986911 · 1986911's Garage

Quote:

Originally Posted by turbo ride

Great info guys. I plan to do a BL WUR soon so this is great. Thanks.

Question - how do your cars start (and behave for the first few minutes) when it's close to freezing - say between 25- 40F?

Can't go wrong with a Leask Wur I don't know how they did it before someone started modding these things.

You are out of luck with us down here when it comes to freezing temps.

911nut · 911nut's Garage

Quote:

Originally Posted by turbo ride

Question - how do your cars start (and behave for the first few minutes) when it's close to freezing - say between 25- 40F?

Stumbles for the first 10 seconds if I press on the gas pedal, then it's ok.

mark houghton · 12-31-2012, 07:11 PM

Quote:

Originally Posted by turbo ride

Great info guys. I plan to do a BL WUR soon so this is great. Thanks.

Question - how do your cars start (and behave for the first few minutes) when it's close to freezing - say between 25- 40F?

I haven't had mine out in freezing conditions...the lowest if I recall was around 38F. No problems at all, not the slightest hint of a bog or a stumble. Of course that's with starting from her 60 degree garage, and letting her warm up for a minute or two before hitting the road.

JFairman · 12-31-2012, 10:43 PM

It rarely gets below 40 in south Florida but I've started it around 45 sometimes and it fires right up with a nice smooth vroom and idles perfectly smooth around 1200 rpms and it's ready to drive immediately.
I don't let it sit and warm up at all, I just drive off and it runs perfect. I have it dialed in really good.
Bosch does a really fantastic job designing and tuning their fuel injection systems.

My static ignition timing at idle is around 8 degrees before TDC and that helps cold starts in a big way.
If I enable the origonal peirburg vacuum solenoid that blocks vacuum retard to the distributor during a cold start the ignition timing is advanced quite a bit more below 1500rpms and that helps improve real cold starts even more.

turbo ride · 01-02-2013, 03:56 PM

NOT trying to hijack the thread - but as a datapoint for cold control - hoping this helps me and others - my car - stock WUR still - starts fine, idles very smooth at about 1000 for several seconds then drops - to about 500 maybe a smidge less. Lumpy, smells VERY rich. Need to feed it a little throttle (oddly - as I'm asuming its way rich). But drives fine. Takes several minutes for it to idle properly. This is at about freezing - no heated garage unfortunately....

mooney265 · mooney265's Garage

MG,

One thing you want to be aware of is that all of these settings "stack" on top of another. What I mean is when you adjust the Warm CP to say 3.5BAR and the enrichment to 2.75BAR the difference is 0.75BAR.

Now, you go back and adjust the Warm CP to 3.25BAR, then your enrichment will move to 2.5BAR. Please keep this in mind as you begin fooling around with all of these settings.

This is what I've found with my BL-WUR. Maybe someone else could second that or better explain.

Good Luck!!