Control Pressures vs Time

[Paulporsche]

In another thread I am trying to track down a poor start/hesitation/backfiring situation w/ my car. One of the things I have been doing is checking control pressures w/ a CIS fuel gauge.

I know a lot of you have done this. Does anyone know/remember how long it took to go from your cold cp to your hot cp setting while Idling?

Mine seems to take only about 1 1/2 min to go from about 1.8 bar to about 3.7 bar when starting from cold @ 20C (68F).

[boyt911sc]

Paul,

I've been trying to locate an old notebook where I had jot down the control pressures readings over a period of time. But not getting any luck finding it. Anyway, I clearly remember that from the initial control pressure (COLD) of 20 psi, it goes up to 55 psi (WARM) more than eight (8) minutes. It took more than 10mins. to fully warm up the motor at idle speed (1700 rpm @start down to 950 rpm).

I took control pressure readings before start and immediately after the motor started. Then every minute for the first 5 minutes and at 2 mins. interval afterwards. I stopped after 15 mins. This will give you a profile of your control pressure from COLD to WARM.

The Bosch 0-438-140-XXX WUR will take more time to attain its WARM control pressures at idle speed. I strongly believe that your problem is not only about your WUR but with the fuel delivery and unmetered air. Not until you could confirm that your fuel delivery (injectors & FD) and air leak are not the problem, your trouble shooting would be ineffective.

Tony

[T77911S]

those pressures look good. my brother has the fuel gauge now. i need to get it and check my bleed down pressure and i will check the time to heat up.

if you have the 033 or 045 WUR, remove the vacuum line and plug it and start it cold and see how it does. when i got my car i was not sure if the vacuum line was connected to the correct port on the TB. if it is not it will cause a hesitation and popping when cold.

i bought my car from my brother, when he bought it, it would not rev past about 2500. he got it running better so it would rev to amost 4000 before it would ping but you could not floor it. we thought it was a fuel delivery problem, either fuel dist or fuel pump. i bought the car and playing with timing i got it to rev to 4500. thats when i started thinking someone set the cam timing wrong. sure enough, it was 15 degrees advanced. anyway, in all this troubleshooting i learned how important the vacuum ( and the TTV) are to the WUR and its effects if it is not right.
my cold pressure is .8 bar, then 15 seconds later it jumps to 1.8 bar then it continues up to 3.7 bar. i have NO popping or backfiring with it like this.
i hate to see you overlook this and cause work for yourself.

[Paulporsche]

Thanks again for your responses, guys.

Tony,

My times are quite a bit different from yours. As I mentioned, my cps started rising right away and hit their high point in about 90 sec. Yours are much more in line w/ the warming up of the engine itself. I'm wondering if the WUR is warming up too soon for the engine, causing the lean condition. I wonder if this is because it usually has a lambda control, which my car does not. I'll have to go back to the 045, which I have reassembled, and see if it operates the way you have described. I don't disagree re fuel delivery and vac leaks. We are checking all this out.

T77911S,

And yet your time vs cp figures are more like my recent ones w/ no ill effects. Both the 045 (911 78, 79) and the Audi one I was using have the vacuum port that should connect to the lower port on the throttle body. AFAIK the cam timing has been the same for many years.

[Paulporsche]

I have just confirmed w/ the Probst book that under shop conditions (say 20C) the CP from a cold engine should rise from cold cp to warm cp in "one or two minutes" so my time of about 90 sec seems fine.