CIS: Cold to Warm Control Pressure Transition Speed

[1982911SCTarga]

I'm replacing a warm-up regulator (control pressure regulator) on my '82 targa because the old unit was slightly out of bounds on the low side of the cold pressure/temp chart. This was giving me too-rich, low-idle cold starts, which would disappear within a few minutes or so of running. This may be a bit unusual because the traditional "knocking the pin" would make my situation worse. Once warmed up, the idle and driveability were fine, and the mixture checks out.

System pressure checks out fine, by the way. I've also checked out my auxiliary air valve (which is good) and pulled and checked my injectors and seals, so I'm not battling vacuum leaks. Ignition timing is good, too.

I swapped in a replacement WUR from my stock of spares and the cold pressure is right in the heart of the ambient temp/pressure chart for an '82. However, when I connect the electrical plug to the WUR, the cold pressure doesn't change at all. I tested the WUR's contacts and they ohm-out at 30 or so, which is good, and I've got proper voltage at the WUR plug when I jumper the fuel pump relay.

My question here is, shouldn't I be seeing a change in control pressure when I connect the electrical plug to the WUR? How quickly should the control pressure change?

Some other things: My J.C. Whitney CIS gauge leaks fuel (a drop or so every few seconds) around the bleed valve. I put a rag under it, and I don't think it measurably affects the readings. However, drive around with the gauge hooked up? I don't think so.

I like to look inside WURs, so I took the one that I'm replacing apart. It's got the proper numbers for an '82 911SC, but the last three digits are stamped on after the first set of numbers, so maybe it's remanufactured or something. Anyway, this WUR has this weird leaf-switch assembly and an adjustment screw. I've read somewhere that this was a Mercedes-Benz thing. Just something I haven't personally seen before.

Brian

[1982911SCTarga]

I found an interesting discussion of DIY warm-up regulator, or control pressure regulator, calibration here: http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1372083-warm-up-regulator-wur-calibration.html

Brian

[mca]

Originally Posted by 1982911SCTarga

I'm replacing a warm-up regulator (control pressure regulator) on my '82 targa because the old unit was slightly out of bounds on the low side of the cold pressure/temp chart.

My question here is, shouldn't I be seeing a change in control pressure when I connect the electrical plug to the WUR? How quickly should the control pressure change?

So did you do the pressure checks on your old WUR or did someone else?

The pressures will change almost immediately once you plug in the WUR. Might take 30 seconds or more before the pressure levels out after that.

[Paulporsche]

If you were knocking the plug down you were decreasing your cold control pressure, which was making your mixture richer.

Did any of your bimetal arms have a figure stamped on them? You say you measured 30 ohms. Not that I've seen them all by any means, but they seem to be usually around 22 or so. I had an Audi one that was 26. The resistance of the arm probably doesn't matter too much. I don't know exactly what it does, but I suspect it may either change the amount ot time the change in CPs occurs, or lilits how much it changes.

Check out Ricks911s. He has a video on testing the WUR. I also have (lengthy) thread on WUR issues.

When I did my tests, w/ the WUR connected, it only took a few seconds for the CP to start to rise, and the full change from cold to warm took about 3 1/2 minutes.

[1982911SCTarga]

The "new" WUR from my stock of spare parts worked great. Nice, smooth start-up and transition to warm running (just like my cabriolet). I'll keep the one I had been using (the one with the weird leaf switch) as a back-up, since I'm pretty sure it can be tweaked back into calibration.

I was worried about the new used one I put on because I couldn't detect it changing pressures once the heating element was connected. I'm paranoid about these things because I'm running my targa without the toilet bowl flapper in my original airbox. It's kind of a badge of honor now.

Brian

[Paulporsche]

Glad to hear it's working. Peter Zimmenmann has written here that a well tuned CIS car shouldn't need a popoff valve. He may be right, but for the one in a million time...?

[1982911SCTarga]

I'm with Pete on this one, and I'm a hard-core DIY person. I've also got an NOS spare airbox should the backfire gods smite me.

My cabriolet has a popoff valve (it was on there when I bought it, little good it did the previous owner). So, I'm not exactly Spartacus on the popoff-no popoff debate.

Brian

[VaSteve]

How long is the transition from cold pressure to warm pressure supposed to take? I tested mine this evening and it went from 2.5 to 3.5 bar very rapidly and thus I had a lousy idle.

[Paulporsche]

Brian,

That inner switch was also used on an Audi 5000 WUR I took apart. I'm not entirely sure, but I think I read somewhere it had to do w/ separating normal running from the extra enrichment reqd for WOT (in addition to either the lambda control or the vacuum control).

I certainly respect someone's desire to keep his car stock and not add a popoff valve, but I'm awfully glad when during testing to check my WUR this spring I had a potential airbox shattering explosion that was thwarted by the valve.

And later this summer, when a coil wire from the CDI suddenly broke underneath the sheathing and caused a backfire that echoed through the caverns of downtown Toronto on a Sunday morning, I was again glad all I had to do was fix the wire and not install a NOS airbox!

VASteve,

As I said, mine went from about 1.5 to 3.5 in about 3 1/2 minutes, which seems right for my engine.