3.9 efi cold start problem

[jeff]

Hi all have a probelm with my rr classic 3.9 efi ,

when I start it from cold it won't idle, when its warm is idles fine , just from cold ,

what could this be? Coolant temp sensor?

thanks

 

[3.5 efi]

i'd look at stepper motor, will be gunked up.

 

[joe1972]

Was this sorted?

 

[jeff]

No , havn't had a chance too look at it yet ,

going to change the CTS and clean stepper motor and go from there ,

thanks for replies

 

[classic kev]

You sorted this yet? Would suggest you get the multimeter out and check the base setting for the throttle potentiometer and then check that it is scaling properly. If the base setting is too low the ECU will not activate idle stabilisation and it will stall but otherwise run O.K. HTH

 

[jeff]

You sorted this yet? Would suggest you get the multimeter out and check the base setting for the throttle potentiometer and then check that it is scaling properly. If the base setting is too low the ECU will not activate idle stabilisation and it will stall but otherwise run O.K. HTH

no still have the problem ,

how do i go about checking the base setting on the throttle position sensor??

cheers

 

[classic kev]

how do i go about checking the base setting on the throttle position sensor??

It's easy enough. There are 3 wires off the throttle pot, one is 12v supply, one is ground and the other is the signal or output.

Where the wires go in to the plug you can insert the multimeter probes, I can't remember the wire colours but it is easy enough to identify which is which. You can check the resistance and base settings and scaling. You will need to look up what the base settings need to be but I think throttle closed needs to be something like 0.3v and WOT something like 4.5v+

The other way of checking the values is to measure the voltage at the ECU plug but I find it easier to measure at the plug in the engine bay. HTH

 

[classic kev]

BTW did you clean the stepper motor? and have you checked for an air/vacuum leak? Have you set your base idle and checked the ignition timing?

You might find it useful to remove the plenum and ram housing and give it all a good clean then check/set the throttle butterfly. Then you'll need to go back and check/set base idle and timing.

 

[jeff]

BTW did you clean the stepper motor? and have you checked for an air/vacuum leak? Have you set your base idle and checked the ignition timing?

You might find it useful to remove the plenum and ram housing and give it all a good clean then check/set the throttle butterfly. Then you'll need to go back and check/set base idle and timing.

Hi mate ,

thanks for reply , i have just bought a idle control valve and going to give this a go ,

also any ideas what could cause this, when cold if you go to rev it , it kind of bogs out/cuts out, but if you rev it slowly its fine??


cheers

 

[Mr Noisy]

It's lean on idle then.

Check for air leaks!

 

[classic kev]

Hi mate ,

thanks for reply , i have just bought a idle control valve and going to give this a go ,

also any ideas what could cause this, when cold if you go to rev it , it kind of bogs out/cuts out, but if you rev it slowly its fine??


cheers

Like Noisy said could be an air leak but I think I would also want to be looking at vacuum advance and ignition timing.

 

[jeff]

thanks for reply's

the engine is fitted in my series 1 , when i removed engine from range rover there was a long vacuum hose going to some air tank /ball thing , what does that thing do , could it be something to do with it ?

 

[jamesmartin]

vacuum reservoir ,vac was used for more than just the brakes on rrc,block up all vac openings apart from servo and dizzy ,and fuel reg , worth checking inlet manifold bolts they often loosen causing air leaks

 

[Mr Noisy]

The ball thing was to hold vacuum to operate the heater controls

 

[jeff]

The ball thing was to hold vacuum to operate the heater controls

Off topic slightly lol,

I put a 300tdi in the RR this engine come from , would the heaters not work with out the ball thing/ vacuume?

 

[Mr Noisy]

It was just the recirculate function on my 200 v8 disco.

And on that subject, 200tdi discos had the same heater so there must be a way, probably just take it off the vacuum pump...?

 

[discomark10]

It's lean on idle then.

Check for air leaks!

my disco had no gasket on the manifold - plenum, only started to run rough after a while.

 

[jeff]

had time to have a look at the engine today , found these faults , FPR vaccume hose was split/broken , had no gasket on the plenum , breather hoses were gunked up ,

so have cleaned hoses , replaced FPR pipe and sealed plenum ,
have fitted new idle control valve,


running a lot better now , have still got to set the base settings ,

also how do you set the adjustment on the air flow meter ?

cheers

 

[classic kev]

also how do you set the adjustment on the air flow meter ?

cheers

Search CO Trim, there are various posts on this.

TBH the only way to do it properly is with an exhaust gas analyser but if you do a search you will find the correct voltage settings for the air flow meter.

 

[Mr Noisy]

I found that the CO trim settings for the airflow meter did indeed give the correct output more or less when tested with the gas analyser.

Obviously it assumes your kit is working correctly but in theory settings the airflow meter to 1.0v should be around 0.9% CO