3.9 weird starting problems

As it runs OK and restarts warm but not cold, how does it deal old fashioned choke?

You mention coolant temp senor in the singular, I had a car with two temp sensors one for the gauge and one for the engine management. Wiring to sensors? Is that rotation of the dizzy advance or retard? Not that I know if 30 degrees either way would enable starting sans choke.

Thanks mate,

This is the Rover V8 engine with hot wire fuel injection, so no longer has an old fashioned choke.

Turning the dizzy anti clockwise is probably giving about 40 degrees after top dead centre ATDC at which setting it starts.

Latest thought is maybe the injectors are leaking under pressure?

I didn't expect it to have a butterfly valve in the inlet but I don't think you can start a cold petrol engine without choke or the affect of a choke.

I *think* that is the way to make an engine run on a weak mixture. Which is effectively what a cold engine has without the affect of a choke.

Most engines don't need much choke. Might what happens if you start it let it run for a minute, so the cylinders etc are no longer cold but the engine is nowhere near normal temperature, switch off reset the dizzy (without risk to fingers!) and try to start it.

How the f*ck did you find out the 30 degrees thing?

Crikey

OK, tried that. Disco starts first time with dizzy in the 40 or more degrees ATDC setting. After running for about 1 minute, switched off & reset the dizzy to the correct setting of 6 degrees BTDC & disco refuses to start - WTF !

Has it an ECM? Could be stuck bob weights?

Well if you have sparks & you have fuel the engine should start, so played around with the dizzy thinking maybe timing chain has slipped a tooth or something.

Dual fuel - what is the fuel on the last run before the cold start? This may be a well-known dual fuel issue - Badger?

A richer cold start mixture is provided by the ECU increasing the injector open time in response to the signal from the engine coolant temperature sensor.

You weren't checking the fuel temperature sensor by mistake, were you? Same resistance values as the coolant temperature sensor

Resistance values (from my book) for sensors: Temp -10C 9100-9300 ohm Temp 0C 5700-5900 ohm Temp +20C 2400-2600 ohm. (Are these the same as you found?)

Just a thought, but providing a high resistance by disconnecting the coolant temp sensor may give you the rich mixture you seek and provide confirmation of a duff sensor. It also makes you think that a poor connection will give a rich setting in the event of poor connections (other than shorts) so you'd be wasting your time loooking for poor connections.

Makes no difference which fuel I use. My LPG system only cuts in above

Yes, I checked both fuel temp & coolant temp sensors - will recheck tomorrow as now almost dark.

Yes, ECM is standard Land Rover jobbie. As to bob weights, no idea but will have a look.

A possiblity but then the timeing would be off all the time. The OP says it runs and starts OK once warmed up and with the dizzy @ 6 BTDC.

Grasping at straws, maybe a minute isn't long enough. I've only experience of small engines rather than hulking great V8's and choke requirement.

Was there any difference in the coughing? Had it started to get rough when running at 40 ATDC?

Yes, it will drive at the very retarded dizzy position, but runs poorly. Runs best at the 6 BTDC setting, so agree that internal timing gear is unchanged.

I'd expect the ECU to detect an open circuit as a fault, what it does in response to that is another matter. Connecting the appropiate wires at the sensor end with a resistor of a few k value would better.

Assuming the ECU doesn't decide that such a thing is a fault and implies the engine temp from it's other inputs.

Wonder if there is a sticky switch over between gas and petrol?

Would not give these symptoms though.

Lee

Cheers guys,

Will get the multimeter out again tomorrow and recheck all the sensors and report back.

Don't know if it is possible to see the injectors opening/closing on a digital multimeter?

In other words is it stuck on gas? or are both switched off?

Definitely not stuck on gas as car starts with dizzy in 40 degree ATDC setting and when running pulling the fuel pump fuse stops engine - so definitely running petrol. Gas only cuts in at 1500 RPM, which it does with no problems.

Definitely not stuck on gas as car starts with dizzy in 40 degree ATDC setting and when running pulling the fuel pump fuse stops engine - so definitely running petrol. Gas only cuts in at 1500 RPM, which it does with no problems.