Warm Up Regulator (WUR) question- how far out of spec before replacement?

[gsxrken]

Just the opposite of many threads I found via searching, my car idles too low at start up. There is no "high idle" for a minute or two.

I decided to check my 1986 turbo's fuel pressures. At 18*C, my specs and results are as follows:
Spec Actual Results
System 6.7- 7.4 6.8 Good
Cold Control 1.9- 2.3 1.8 Too low (but barely)
Warm control 3.75 +/- 0.20 3.4 Too low

I know there is a spec for a reason, but I don't know how critical it is. At one point, or how far out of spec, is a WUR replacement called for? I don't want to drop $300+ for almost no gain.

[T77911S]

sounds like yours is a prime candiate to make it adjustable. the reason i say that is when they start to fail, trying to get the DIFFERENCE between hot and cold is the problem, yours are just low.

this is srtictly my belief on the spec and it is only based on studying CIS, no testing to back it up:

the AFM portion is shaped like a funnel. how narrow or how wide that funnel gets determines how much the sensor plate will move for a given amount of air intake. more narrow makes the plate move more making the mixture richer vs a wide funnel which will result in the plate moving up less, thus leaner mixture for the same amount of air coming in.

now, if there are 2 transiton points in where the AFM gets wide and narrow, then the first one is from idle (rich mixture) to cruising (a leaner mixture) and the second one is from crusing to WOT ( the mixture needs to be richer). again, my opinion, but its these transition points that porsche want to happen at certain RPM's and in order for that to happen, the WCP needs to fall in a certain range.

i know on my car my mixture starts to get richer around 4k RPM. if i lower my WCP, and adjust my misture for the same AFR at idle, the mixture should transition cruising AFR's to WOT AFR's at a lower RPM. IE, the sensor plate would be higher in the AFM for a lower CP.

this should also change the transiton from idle to cruising, which i would think would be like having the wrong jets in a carb making it rough off idle, although i think CIS is more forgiving of this than carbs.

so if your CP's are low, and your AFR's are correct, it will not hurt anything. i think this would be better than too a CP which would keep the mixture lean in the higher RPMs.

for the 930, there is a guy that rebuilds them with a stronger diaphragm and makes them adjustable.
that is something else that needs to be checked. make sure the diaphragm will hold a vacuum. if it will not, that will lower your CP's.
also, make sure you have power to the WUR and that the heating element is working. an easy way to do that is to check the CP's as the engien warms up. if the pressure rises to WCP within a few minutes, it is working. if it needs the engine heat to raise the pressure, it is not.
or, you can ohm out the heating eleemnt. should be around 30 ohms.

[RarlyL8]

Before fiddling with the WUR I would take a look at your fuel delivery pressure and volume. Your system pressure is on the low side of spec which will drag down the controlled pressures as well. Goal is of course to get the presures in the sweet spot resulting in quick starts and proper warm-up rpm's. Your controlled pressures can be corrected with an adjustable WUR however attention should be paid to the top end on boost as it may lean out.

[gsxrken]

Thanks to all plus Todd for the PM and call. I can conduct a volume test tomorrow. My Charles Probst Bosch manual talks about shimming the plunger for more system pressure... Where can I obtain the Orings and shims to perform this operation?
I also possess an older LM-1 AFR that I can check AFRs with at initial start up, as well as across the board. Should have remembered this before I got the CIS gauges out.

[gsxrken]

WUR gets 12.8V, and control pressure does climb when I add connector and run pumps. Also, where does the WUR get vacuum or boost signal? The only things I see topside is

[Lorenfb]

"Is a WUR replacement called for? I don't want to drop $300+ for almost no gain."

A waste of money, as most have indicated that the WUR can be tweaked to the desired pressure.
Actually, it appears that the WUR may have been 'rebuilt', i.e. the red paint to prevent tampering.

"My Charles Probst Bosch manual talks about shimming the plunger for more system pressure..."

Probably not a good idea. The system pressure is O.K., so focus elsewhere or you'll have new
problems.

"There is no "high idle" for a minute or two. "

Then there may be a problem with the AAR. Try leaning it little (just for testing) at startup.
That way you can determine if it is really a mixture problem. If that doesn't make a difference,
then focus elsewhere.

[RarlyL8]

Vac/boost signal is at the one port located on the center plate.
Typical responce when ccp/AFR is low is a low idle until warm.
Shimming the fuel head is not necessary unless exceeding factory specs. Check/verify that your fuel pumps are receiving correct voltage and producing adaquate volume output. If one or both pumps are weak the system pressure will drop which can cause the symptoms you describe. Shimming the head or adjusting the WUR will only temporarily bandaid this type of problem.

[gsxrken]

Thanks again for posts.
Fuel volume was 1600cc at 30 seconds, manual said at least 1500cc. So pumps appear ok.
AFRs were on the low side looking at the handheld, but I can't download yet b/c my new laptop only has USB ports whereas Innovate LM-1 output is a female serial cable!

[gsxrken]

Oh and AAR was about half open after a night in the freezer, and closed to within about a 5/16ths drill bit size at 220 in the oven. However, although there is 12.5V to the plug, the valve did not close with key on. The oven closed it.

[boyt911sc]

Originally Posted by gsxrken

Oh and AAR was about half open after a night in the freezer, and closed to within about a 5/16ths drill bit size at 220 in the oven. However, although there is 12.5V to the plug, the valve did not close with key on. The oven closed it.

gsxrken,

You had 12.5 volt power to the AAR plug with the ignition switch @ ON position? Was the FP running? Were terminals 87a & 30 (FP relay socket) bridged? Keep us posted.

Tony

[gsxrken]

Originally Posted by boyt911sc

gsxrken,

You had 12.5 volt power to the AAR plug with the ignition switch @ ON position? Was the FP running? Were terminals 87a & 30 (FP relay socket) bridged? Keep us posted.

Tony

I had the plug on the fuel head disconnected, which allows the pumps to run with key in the on position. Didn't get into jumping relays. In addition to Brian's point about running rich gives low idle( on cold start up the LM-1 showed 11.9-12.3), I also think the bimetallic spring in the AAR is not up to the job anymore. Are they a DIY repair?