Thread: 3.9 power surge at startup

Clean your Stepper motor.
When you shut down the stepper motor goes fully open so that when you start you have a bit of air entering the engine, like putting your foot on the accelerator.
When the engine is cold on a cold morning it will stay up at around 1500 until a certain temp is reached then down to 1100 then down to idle.

This is normal depending on temperature.

If it is doing it hot, the stepper is worn out or dirty and should be cleaned or replaced.

The stepper is the thing at the right hand rear of the plenum chamber with 4 wires coming out of it. Try cleaning it first with carby cleaner and clean the hole /mount with a cotton bud.
Make sure screws holding the mount to the plenum chamber are tight.
Regards Philip A

Thank you Phillip, will give it a go and report outcome

Rgds / Barry

93 / 3.9 / Auto

Phil,

I did as suggested:-
- Unscrewed the stepper, cleaned (filthy) with Carby cleaner and then cleaned interior again filthy....all cleaned

- Replaced all and no start, cranks ok but will not fire up.

- I noticed in cleaning the stepper, that the "bullet head" tip could be rotated...
on first removing it, i noted it was approx 1/4" from its base and during cleaning could rotate outwards by about 1"..I wound in back to 1/4" before replacing it back in.

Question
- does this "bullet head, rotatable part" have a fixed setting, i.e. at 1/4" from it's base or should it be all the way out ????

- any ideas what I may have done wrong...


Many thanks / Barry

does this "bullet head, rotatable part" have a fixed setting, i.e. at 1/4" from it's base or should it be all the way out ????

- any ideas what I may have done wrong...

Hmmm.
The rotatable part has a screw thread which is turned in and out by the stepper reacting to signals from the ECU.
There is no fixed position as the stepper should retract fully on engine shutdown , then wind out as the starter is turned , and the position is determined by engine revs.
The problem with yours is that this process was too slow .

If you have screwed it out too far, it will disengage from the "motor" and not work at all.In this case you have probably broken it and need to buy a new one.
This should not really stop the car from starting unless you have reinserted the stepper and it the "bullet" is hard up against the hole and no air is coming in. In this case the car should start if you place your foot on the accelerator a small bit.
You may have flooded it when trying to start.
If this is the case , first try to start it with your foot flat to the floor. Do not pump the accelerator.
If it still does not start, remove the fuel pump relay which is the one with the blue base under the driver's seat at the back. Turn the starter until it fires , then turn off reinsert the relay and it should then start.

As an interim measure you can raise the "base idle" by turning the allen key you will see on the top of the throttle body outwards until you get a stable idle.
Regards Philip A.

Thanks Phil, will try all that in the morning and will revert outcome

Barry / RR / 93 / 3.9auto

Phil, update.....

Tried all and finally called NRMA...after much testing declared stumps..."reckon your fuel pump has had it"...will be towed to mechanic next week.

Will update again next week.....meantime many thanks for you input and telecon offer...

Barry / RR 93 / 3.9auto

Phil,

The update...
Towed to local fixit person, pulled out fuel pump and tested ok, fault traced back to "fuel pump relays" and now replaced....runs like dream.

Back to the over revving...did the step motor cleaning as advised, but obviously could not test the result until received back from the fixit guy.

Still over revving at start up but only to about 1200 rpm, not as previous around 1600/1800rpm....

Anyways there is the update

Originally Posted by alltrans

Phil,


Still over revving at start up but only to about 1200 rpm, not as previous around 1600/1800rpm....

It is doing what it is supposed to do so all is well.