924Board.org

[B]

ok I am feeling somewhat dense about this but here goes

recently I had start up trouble and was trying a 931 wur resistance seemed ok but the control pressures were off - 4.7 bar running warm or cold - this was also the system pressure with this unit.

I had the original wur without boost referencing and my start up cold pressure was a little high at 3 bar but the running warm pressure was 3.6 bar well within spec according to the manual.

how bad is the 3 bar reading - I think that is rich at start up, but is it ok to drive with?

should I try to fix either? I would like to have the fuel enrichment of the 931 but if the original is workable, I would like to save the money - at least for now.

the manual also mentions cleaning out the fuel line - might that help as well?

thanks very much

Sean B
_________________
1979 924 n/a
BAE turbo
5-speed snailshell

[ptheskil]

The 3bar control pressure reading at cold will give you a weak mixture (the higher the control pressure the weaker the mixture). The engine will run rough until it is warm. If you/PO frig the idle mixture at the distributor to fix the cold running you will be running too rich when warm (watch out for bore washing).

Did the BAE turbo not have any other device to richen the mixture under boost? If not then would definitely recommend the 931 WUR. The one you have sounds like you could have the problem with blocked inlet filter or crud in the diaphragm. There are some good articles on here and links for how to service a WUR. Don't assume that the inlet filter is OK if you can blow it through with air - it can still be a restriction to the fuel flow.
_________________
1981 931 series2 Euro spec

[B]

thanks for the response -

I have not done anything to the distributor - I cannot be sure about the po

The BAE kit that is on the car does not have anything for fuel enrichment, that was my original reason for getting it. I was not sure how well it was going to work with the na pump and distributor - I was not sure if they were set up differently.

I had looked at some of the how-to's I think you are referring to - I had been a little nervous about trying a complete tear down - but at this point I suppose I have nothing to lose?

thanks again

SeanB
_________________
1979 924 n/a
BAE turbo
5-speed snailshell

[dpw928]

Did you take the control pressure reading with the engine running or static? Since the air sensor plate compresses the control piston when running, the static (non-running) reading will be more accurate. If the control and system pressures are within the margins on the chart, final adjustments can be made with the A/F mixture screw.

Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

[B]

for the tests cold pressure I jumpered the fuel pump connections and ran the pump with the engine off. For the warm - I let the motor run - usually 5-7 minutes. probably more than I needed to. should I try the warm tests with a jumpered connection as well? - wur and aav electrically connected. ?

thanks very much
_________________
1979 924 n/a
BAE turbo
5-speed snailshell

[dpw928]

I would do them both with the engine off and at the same temp. That way you don't need to worry about disconnecting the heater on the WUR. The system pressure should be the same running or static.

Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

[ptheskil]

Don't be nervous about a teardown. Make sure you have somewhere clean and tidy to work and take it slowly and you'll be fine. You will have to reset the cold control pressure once you get it back together again. It's a bit of a trial and error process so plan on setting it up with the WUR off the car as it's a PITA to keep taking it off all the time. With mine I found that electrical heating alone (ie. no heat direct from engine) of the bi-metal strip was enough to "disengage" the cold adjustment. I did all the adjustments and final checks with the WUR connected to the pressure tester but otherwise flapping in the breeze.
_________________
1981 931 series2 Euro spec

[B]

I started the tear down and cleaning process and had a probably oddly timed question

Is there anything connected to the top port of the 931 wur?

I was looking at several pictures of these and it seemed that some had a cap or plug of some sort and others had a vac hose connected. I realized that mine did not have anything and wondered if that was one of the problems.

Should something be connected there?

thanks very much
Sean B
_________________
1979 924 n/a
BAE turbo
5-speed snailshell

[ptheskil]

On the 931 wur the top port is open. The side port should be connected to the hose from the manifold. When the turbo is boosting and you get pressure in the side port this lowers the control pressure to about 3.0 bar from 3.65bar. This is how you get the boost enrichment. You can test this with a handpump once you have it reconnected.
_________________
1981 931 series2 Euro spec

[B]

thanks -

will the port with the distributor to the side of the throttle body work?

Sean
_________________
1979 924 n/a
BAE turbo
5-speed snailshell

[B]

ok - here are the numbers that I got this time around with the turbo wur-
system pressure was a little on the lower side - but I think still in spec for an na - 4.6 bar
at 80+degrees cold pressure test netted 2.9 bar - that is with the fuel pump jumpered (80+ degrees is probably not much of a "cold" test) and wur and aav disconnected

warm test - everything connected - it started at 3.0 bar then then rose slightly to 3.6bar where it seemed to rest at for the next 10 minutes until the temp gauge read 150 degrees
12-15 minutes after shut down the gauge read 1.8 bar

the ohms reading for the posts on the wur was 26.3

does any of this seem ok - I think warm pressure was in spec according to one of the posts I came across - but the others seem off
there seems to be quite a difference between the system pressures of the 931 and na - 4.5-5.2(na - 5.8-6.5 (931) ?

could that have anything to do with it?

any ideas are greatly appreciated

Sean B
_________________
1979 924 n/a
BAE turbo
5-speed snailshell