Disco 3.9 V8 stalls

jaz · Aug 19, 2005

Hi all, here is my next challenge for you to resolve - as it looks like I'll be under the disco this weekend anyway... when I let the throttle off, the revs die back too far sometimes causing it to stall, it seems to be worse when I am 'dabbing' the throttle e.g. looking for a parking space etc. The idle speed is set to @800rpm and is normally quite steady. It is a 1995 V8 3.9ltr. Any thoughts??
Thanks
Jaz

Chris Jones · Aug 22, 2005

Ignition timing? When did you last check you plugs, leads, cap etc? Failing that it may be a vacuum leak somewhere in the intakes/plenum chamber area...

Chris

Charlotte · Aug 22, 2005

Hi I think the engine is roughly the same as the Range Rover's try checking the Fuel over run, especially a small black square plastic resistor which connects to the Coil.

If this resistor begins to loosen the car is going to do horrid things and give you plenty of faulse ideas.

Graham A · Aug 24, 2005

I had the same problem with my 3.9 Range Rover. I checked all sorts of things until somebody mentioned the Air Bypass Valve (Stepper Motor) on the back of the plenum chamber. It's on the left hand side as you look at the engine. It is a little plunger with a cone shaped valve on the end, and it usually increases the revs when put in drive on an auto, or you turn light etc on. It may just need a clean up with some WD 40, along with the seat inside the plenum chamber, a WD soaked rag over a finger usually does the job. If that does the trick, good. If not, see if you can borrow one from a fellow 3.9 owner. They just unscrew- after taking of the electrical connector of course. A new one is about £100, but if that's what's causing your problem, it's money well spent. Nothing worse than breaking down in rush hour traffic on the Catford One Way System!

jaz · Aug 25, 2005

Sorry, can't find the stepper!! Is it the thing attached to the air intake?? It is the injection engine.
Jaz

Graham A · Aug 26, 2005

Hi Jaz, The plenum chamber is the large alloy bit on top of your engine with 3.9 on it. The stepper motor/air bypass valve is at the rear of this, on the left hand side. It has a few wires going to it, with a black multi plug on the end. The unit looks like a large black nut, on the end of an inch long cylinder. I used a large adjustable spanner to get mine off. You'll have to move the two pipes that go through the bulkhead to the heater matrix out of the way to get it out. Good luck, Graham A.

Graham A · Aug 26, 2005

Hi Jaz, The plenum chamber is the large alloy bit on top of your engine with 3.9 on it. The stepper motor/air bypass valve is at the rear of this, on the left hand side. It has a few wires going to it, with a black multi plug on the end. The unit looks like a large black nut, on the end of an inch long cylinder. I used a large adjustable spanner to get mine off. You'll have to move the two pipes that go through the bulkhead to the heater matrix out of the way to get it out. Good luck, Graham A.

Graham A · Aug 26, 2005

Oops, looks like I double clicked!

jaz · Dec 12, 2005

Hi, sorry it has taken so long to get back, I've only just got round to fixing it. It was exactly as you said, the valve was all gummed up with black stuff, I gave it a good clean and all works well now. Thankyou.
Jaz

Disco 3.9 V8 stalls

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