Re: More MB

[quk@isham-research.demon.co.uk (Phil Payne)]

In message <89f6e01c.360256da@aol.com> QSHIPQ@aol.com writes:

> The fact you are "topping out" the air flap at 4500rpm indicates to me that
> your control pressure is off, which could be a system pressure problem (since
> CP is a percentage of SP).  You may want to make sure that the "topping out"
> isn't giving you a rich, not lean condition at 4500rpm (since WOT FVDC +
> topping out usually happens at 5500-6000rpm).  If indeed the TO is happening
> with all other systems intact (and truly lean), then adjust control pressure
> up, and get the FV DC in the tables increased.  I find a slight increase in DC
> makes for a LOT of extra fuel.  And there is certainly enough to handle ANY
> mods with a stock boost level (even assuming 1.8bar for euro-spec cars)
>
> The topping out at 4500 sounds like you have a problem in the fuel system.  If
> your system and control pressure are OK,  I suggest a tire inner tube to the
> turbo oulet hose, and put 15 psi into the system.  Your leak will become
> obvious.

We have three cars - John's MB (the patient), mine, and Roger's.

a) All of the pressures test OK on all the cars at idle and when
   running the diagnostics from the ECU (I find that gives a much
   more readable system pressure).

b) My air mass sensor assembly (also carries the control pressure
   regulator and frequency valve) produces exactly the same symptoms
   in John's car.  All three control pressure regulators produce
   good results in my car and bad results in John's.

c) As I pointed out some time ago, the potentiometer in the air mass
   sensor is _MUCH_ more accurate than it needs to be for the job it
   does - less than 1% delta between the cars, measured using a 1348/1
   to hold the paddle.  Using this potentiometer, we can see that any
   of the air mass sensors, when fitted to John's car, tops out at
   4500.  On my car, there's still free movement at 6300.

d) All of the hoses have been bench-tested.

> Have you metered the DC while driving the car?  Could you have a bad FV?  Did
> you try swapping the fuel head and/or FV?   Did you try swapping the ECU (bad
> PT)?

Yup.  DC is slightly _lower_ on John's car all the time.  Max value seen
was 68% - my car occasionally goes to 78%.  See above for comments on
swapping fuel system bits.

> Yes to all?  Go after that coil.  Have you got a strong signal from
> your rpm sensor?

The coil is new, fitted by BR Motorsport during their attempts to fix
the problem.

--
 Phil Payne
 Phone: 0385 302803   Fax: 01536 723021
 (The contents of this post will _NOT_ appear in the UK Newsletter.)