Subject: URQ freq valve trigger

[Michael, Dave]

I second what Huw mentioned. I spend Sunday first skewing up, and then
fixing, the mixture on my T44200QA because I fixed a huge  vacuum leak
(rotten crankcase hose). Part of the problem was that the Bentley
specified the WRONG connector to measure the duty cycle (Bentley says to
use the connector with the blue and white wire, ALLDATA and Scott
Mockery say to use the connector with the blue and black wire.) But of
course by then I had the mixture WAY off and it took me a while to get
things sorted out. In any case, things to look for regarding a vacuum
leak (from a posting Scott M made along time ago):


My original question:
	(snip)This morning, it was 25, and was in the teens overnight,
The car didn't even think of starting. Its a 1990 200 qw. I checked a
few things: diagnostic self check runs fuel pump, cold start valve and
all other valves. LED test lamp connected to cold start valve connecter
lights for ~4 seconds while cranking temp sensor ok at 3kohm Plugs look
pretty dry last week I checked: System pressure ok @ 87ps Control
pressure ok @ 15psi @ 32F air flow plate rest postion ok air flow plate
free play ok sensor plate to air cone clearance ok once all the gunk was
cleaned off - but maybe still not ok at cold temps idle speed and co
setting both needed adjustment - the freq valve was cycling down to 100%
duty cycle every 10 to 15 seconds. I reset every thing, and then it
idled fine. 

Scott M reply:
	>Dave wrote: >idle speed and co setting both needed adjustment -
the freq valve was cycling >down to 100% duty cycle every 10 to 15
seconds. I reset every thing, and then it >idled fine. 

	If you saw a very high duty cycle at the freq valve, this is
indicative of a vacuum leak in the system. You should never have to
adjust the mixture that much from the original adjustment with a
correctly sealed intake/breather system. This assumes the adjustment was
not fooled with by someone else and the fuel distributor plunger
movement is smooth and it is not sticking. Have you checked the
following:

	replaced the fuel injector inserts and o-rings? 
	checked the back side of the main breather hose? 
	check underneath the rubber Tee fitting at the valve cover? 
	checked the breather hose from intake boot to valve cover tee
fitting? 
	Replaced the valve cover gasket? 
	Accordion hose at intercooler? 
	Intake pipe rubber connection at Turbo? 
	Turbo exit hose? 
	Idle Stabilizer valve hoses blown off slightly? 
	Dipstick and oil cap gasket? 
	Sticking Decel valve behind r/fender (pretty rare) 
	Cam or Rear main seals? (less likely) 
	One other thing, did you pull the cold start valve and watch it
spray into a bottle during the output test? If you had the gauges
connected, you could also watch for a pressure drop when the cold start
valve is briefly actuated with jumper leads. My 89 200TQ would not start
the other day in 20F weather, I had to jumper the cold start valve to
get it to fire up. I was using a spare ECU that had a dead transistor
for the cold start valve circuit. The ECU output test confirmed it was
not getting grounded by the ECU. I am embarrassed to say I have been
driving it around this way for several months! It always started when
the temps were above 40F. HTH Scott Mockry