95 D1 running like a shocker

[ozscott]

Hi all.

My 95 V8 auto 3.9 has developed a bad misfire when hot - cold its pretty good. Excellent compression and no vac leaks.
To summarise within the last 12-18 months its had:

1. New genuine LR pick up coil in the Dizzy;
2. New genuine Amplifier HEI module;
3. New Plugs;
4. New HT leads;
5. New LPG Converter (3 months ago) and vapor pipe;
6. Rotor Button;
7. Dizzy Cap;
8. New genuine Lucas coil.

I have read that the Discos tend to miss within a very short time with aftermarket rotor buttons. I just put on a new one a month or so ago, branded Lucas, but I picked it up from Repco and its not genuine LR. The cap looks good but its about 12 months and 20,000 old (aftermarket). I have not tested each lead. If it’s the module I will be surprised because it should last more than 18 months (certainly the Bosch ones in Commodores etc have a much longer life).

The misfire is much worse on LPG, but thats to be expected because of the better flame front that it needs.

Any ideas?

Cheers

[PhilipA]

I think you have covered the electrical stuff very well.
I would be looking for a sticking exhaust valve now seeing it does it on petrol and gas.
Regards Philip A.

[ozscott]

Thanks matey - I was worried that it might be a sticky valve - its done 240,000k so its probably up for one....

Cheers

[DEFENDERZOOK]

have you tried putting the old rotor button back in.......?

[ozscott]

No - I threw it! I fitted a new Marneli alternator and the mis started around that time - I have read that alternators can interfere with the pulse - pick up/hei amp module....I am looking at that also before pulling the rocker covers.

Cheers

[PhilipA]

Usually it's a characteristic of Bosch alternators that they create noise which interferes with the ign pulse to the computer. AFAIK the miss is at a single rev band eg 2500
But seeing that yours misses on both injection and gas it is less likely to be the case.
The Marelli alternator was the OEM type I assume.
Regards Philip A

[ozscott]

Thanks Phillip - yep its on gas also so that should rule that out largely. It an OEM one Magneto Marnelli for a range rover 3.9 of the same year - same specs only difference is size of pully which I changed for the old one.

Cheers