if you read my other post my sapphire is a wierd starter. some times it goes first time you turn it over then it can take ages for it to start. so i tried a p8 in it and it starts fine first go every time but boosts wierd so i put another l8 in that we had and it does the same thing as the other l8. runs fine when it runs but takes an age to start sometimes. is it just the l8 ecus that do this or is it a fuel pump prob or something??? help please

 

Its almost always a Crank or Phase sensor problem. Usually phase.

 

have changed them all before. the wierd thing is is that the p8 worked first turn every go? its a lambda sierra

 

have changed them all before. the wierd thing is is that the p8 worked first turn every go? its a lambda Sierra

 

Check the alignment and gaps. Its the fact that your P8 works that is directing me to those sensors, but I dont currenty have time available to explain why that is.

 

does the p8 work differently with the gaps

 

the p8 has a very clever function called error mask

 

huh really could you explain this because it would be very interesting to know about

 

at an uneducated guess the P8 isnt as fussy about the gaps being 100% right as the L8 is and compensates for it.....

 

Allow me Stu...

The P8 has better signal processing amplifiers on the sensor inputs and is more tollerant to noisy and/or low voltage inputs.

Low voltage output from the crank/phase sensors can happen as they age or the gaps are wrong.

I.E. The older ecu's require a clearer stronger signal over the P8.


Tony is probably busy so allow me...

This is a function where the ecu software tracks the normal sensor inputs.
If one or the other fails, the ecu can continue to run normally as it knows where it was (or should be) so assumes it can carry on the same sequence of events.
However, this normally triggers a limp home mode so the car can still be driven but at a reduced RPM or boost level to prevent possible engine damage from incorrect ignition timing positions.

 

So that would explain the weird boosting and idoiling in the p8

 

Its more likely the chip you have for the P8 is less suited for your engine that the other.

 

If The P8 goes into Limp home it will limit rpm to 4000 rpm

 

the sensors are all new all spaced correctley and still the same. runs fine just doesnt start good. and is extremely annoying

 

Ignoring the ecu types for one moment, the chips for both will be different even though they may be for the same engine setup and state of tune.

It does sound like to me the chip in the L8 may need extra fuel for starting in the map !!

 

i had a standard l8 in it that its always had never EVER opened and at the moment i have a different chipped one in it for more power but both the l8s start the same.

 

So are you saying one of the L8's is totally original, and the other has an uprated chip ?

What state of tune is your engine ? (map sensor type/ injectors/cams/turbo etc... )

 

Yep and both do the same. As for the engine all standard for a 4x4. Brand new engine done about 700 km

 

A quick experiment to try...

Disconnect the vacuum hose from the fuel pressure regulator....

Does the car start up quicker and idle better ?

(This should enrich the fuel slightly during starting)

Do not drive the car like this !

 

turns out it was the knock sensor. the wire must have been shorting out on the body somewhere because the wire was split

 

goes to show all the above fellas know there stuff, they all quickly said crank sensor issue of some kind or another

handy info to know

 

glad its sorted fella.