Hi

Sorry about this but still have problems

When I had a bad WUR giving control pressure of 15lbs, car started perfectly but had no power above 2500 rpm

Changed the WUR, car it very very hard to start, when it does it idles fine, you can drive around no problem so long as you dont exceed 2500rpm. If you do the car misses and then cuts out, starts again very easily will pull once noly then the control pressure goes banananas fluctuates from 40-70+ all on its own and screwed again.

Been working on this for months now, received lots of useful advise and help.

Any ideas on the current problem?

Can incorrect mixture cause this , I have changed leads and coil (just for fun)what other factors can alter these pressures

Help needed and appreciated

Thanks
Paul <img src="graemlins/c.gif" border="0" alt="[ouch]" />

 

jackin,

The hard cold start now sounds like the air fuel adjustment may be too rich. Might try backing off the adjustment a little at a time to see if any improvement.

Dennis

 

Jack,

I presume that you have access to a pressure gauge with connections and shutoff valve suitable for diagnosing K-Jetronic fuel injection systems?

A control pressure of 15psi (1.0 bar) is full rich for the "warm-up" regulator (I prefer "control pressure" regulator, as it provides full-throttle enrichment (and, on some K-Jet systems, altitude compensation) as well as cold-running enrichment). My limited experience, supplemented by the vast experience of a great 928 mechanic, is that the WUR/CPR tends to lean progressively as it fails, not enrich. Mine was on the way out for a while (increasingly lean), and failed to full lean last year (the car wouldn't start at all).

Possibly, your problem above 2500rpm is a weak fuel pump or blocked fuel filter, or perhaps a partial blockage in your fuel distributor. You really should diagnose this systematically with the gauges.

If the car was starting well when the control pressure was 15psi and now is hard to start, it almost certainly is too lean when cold. Does it backfire through the air cleaner and/or suffer a massive flat spot if you plant it at low rpm when it is cold?

BTW, at what temperature did you measure the control pressure as 15psi? The CPR/WUR should be at full rich at 10 degrees C (50 F) and below when the engine is stone cold. 15psi (approx 1.0 bar) is the lower limit for the control pressure at 10 deg C for the Euro 928 and 928S and US/Japan MY78 and 79 928 with automatic transmission. The manual US/Japan 78/79 has a minimum control pressure at 10 deg C of 1.2 bar (17.5psi). Control pressure, when the engine is stone cold, will increase with ambient temperature.

Is your fuel pump delivering to spec? (at least 1360cc per 30 seconds) This should be measured at the RETURN line to the tank. If the fuel delivery is significantly lower than this, measure the fuel delivery from the SUPPLY line ie not through the fuel distributor. If the delivery is higher, you probably have a partial blockage in the fuel distributor. If there is no change, your fuel pump is suspect ... or your fuel filter is blocked!!! If I recall the numbers from my mechanic correctly, the car should run with fuel delivery of 1000cc/30sec or even lower, but will not run at higher rpm.

If the fuel delivery is to spec:

Is your control pressure when the engine is fully warm to spec? (3.0 +/- 0.2 bar (43.6 +/- 2.9 psi) with engine stopped, without vacuum and fuel pump running, and

3.6 +/- 0.2 bar (52.2 +/- 2.9 psi) with engine at idle and vacuum connected)

You should check all these specs for your particular model in the workshop manual or the Porsche "Models, Dimensions and Tolerances" book.