My Discovery 1 3.9 v8i cuts out when warm, lacks power ! HELP PLEASE

Hi again every one, hope you are all keeping well? So where do I begin?
I replaced my cylinder heads after a over heating issue. Since replacement it's been laid up due to me having major stomach surgery and bloody covid!!!! Shuting all the pay and play sites near me. Anyway I digress, so I replaced the heads this time last year, I've kept on top of keeping battery charged every 4 months ,and I would start the old girl once a week and let it run till up to running temp.
So yesterday I was well enough to climb in her (like sitting in a favourite chair ) and instantly felt back at home as I've missed driving her. Wife came to, she started first click and off we went.
There was a slight hesitation on acceleration but seemed really good as she got warmer the hesitation got worse.
It's hard trying to put into words, it's as if the motor stops then comes back, if I try to accelerate it dies. So bloody frustrating.
I'm going to check,
Ignition amp as I replaced when doing heads
Rotor arm
Wiring rOundle coil
Can anyone give me some of there v8 know how
Many thanks

Well if it starts and runs the basic bits are there so it will be something silly.
If you have cats idling the engine to warm it over time may have affected the O2 sensors; when cold this is not too much of an issue but when the engine gets to about 70Deg. C lambda control takes over and if the O2 sensors are lazy the fuel mixture will be wrong and could explain the symptoms you describe.

Another candidate has to be the vacuum advance unit on the dizzy. Simple suck test should confirm. The other thing you could try is advancing your ignition timing by a couple of degrees. The V8 will run happily with more advance than standard, 8-10Deg.BTDC is realistic especially if you have fitted a different cam. HTH

Sounds like an ignition fault so check all the usual suspects, ht leads, coil, condensor if its not electronic. All of this can seem to get worse as engine gets warmer.

Col

Common issue is the ignition amp, which show as they get hot. If there was nothing wrong with the original amp then refit it & see if it makes any difference.

Is the rotor arm a good quality item with the strip moulded into the plastic or a cheapie crappie with the strip rivetted to the plastic?

I recon, as it gets warm the seal between the plenum chamber and the intake manifold becomes a little flexible and sucks more air in than the maf sensor is aware of, which in turn throws the whole thing off.
This starts to show as hesitating while under strain.

Ignition amplifier.

classic kev said:

Well if it starts and runs the basic bits are there so it will be something silly.
If you have cats idling the engine to warm it over time may have affected the O2 sensors; when cold this is not too much of an issue but when the engine gets to about 70Deg. C lambda control takes over and if the O2 sensors are lazy the fuel mixture will be wrong and could explain the symptoms you describe.

Another candidate has to be the vacuum advance unit on the dizzy. Simple suck test should confirm. The other thing you could try is advancing your ignition timing by a couple of degrees. The V8 will run happily with more advance than standard, 8-10Deg.BTDC is realistic especially if you have fitted a different cam. HTH

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I have an early V8 (no cats, no sensors) and no problem starting with the choke from cold but running was not right, this will sound daft but it felt as if the engine was trying to clear it's throat. I then found one of the carburettor vent tubes was blocked (the other was mucky), after I replaced both pipes the engine runs much better. Not sure if that is the case with yours but worth checking.

Globalforester said:

I have an early V8 (no cats, no sensors) and no problem starting with the choke from cold but running was not right, this will sound daft but it felt as if the engine was trying to clear it's throat. I then found one of the carburettor vent tubes was blocked (the other was mucky), after I replaced both pipes the engine runs much better. Not sure if that is the case with yours but worth checking.

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The OPs thread title is “My Discovery 1 3.9i” so definitely no carburettors or vent tubes.

discool said:

The OPs thread title is “My Discovery 1 3.9i” so definitely no carburettors or vent tubes.

Click to expand...

Need to go to specsavers!

Globalforester said:

Need to go to specsavers!

Click to expand...

Possibly on the right track, as its not unknown for a restricted crankcase breather to stall the early EFI engine in the RR & D1.