Disco 1 v8 misfiring

[Willyboyau]

Hey guys, I’m a long term Land Rover lover and new to this forum. Just managed to get my first ever Land Rover the old disco 1 v8 3.9l, love my car but I have been recently having issues with it wondering I could get some advice.

So the issue is that currently at 4,000 rpm and at full throttle to 50% throttle the car seems to misfire on all cylinders and losses power also sometimes hard to start escpecially when warm but give it a crack of throttle and she fires right up. I know there has been forums on this issue before and here’s what I have done. Firstly changed the ignition coil, leads and spark plugs inspected the cap and rotor all seems to be ok. This issue seemed to go away but on a trip to the country for my first longhual it came back and came back even worse, misfiring badly and backfiring at any sort of throttle load ie flat or half throttle and in low revs now say around 1,500-4000. Since then I have replaced the fuel filter, checked pump pressure running 35psi constant and whilst under load running 40 psi constant all normal, removed and tested this injectors all good, tested tps, maf sensor and every other sensor all reads really healthy, fitted a new rotor button, new ignition amp and carried out the Bosch conversion with the BIM 024 amp and it is still doing it!!! Mind you it’s only having issues now at 4,000-4,500 rpm and only at full throttle.


The vehicle does have a 3”exhaust, could have flow issues? Although seems ok

Loose valve springs?

Faulty ecu?

I am running out of ideas 😡

[LRJim]

Hey mate I'd be checking your advance weights to see if they have seized up. See what timing it's running at and reset if necessary (solved alot of problems for me). But it really sounds like your dissy isn't advancing far enough after 3500 you get a lot of noise but no go.
3inch exhaust is crap, stick with the stock size. If you want noise get rid of the resonator at the back and if you want more noise free flow the centre. The exhaust is too big it will cause you problems especially off road and it will effect what economy the disco has.
Have fun with the old girl.
Cheers Jim

Or you have pulled you button off too hard look up Lucas distributor shaft screw fix. Sounds like your gonna have to pull the dizzy out anyway, may as well do that screw fix also.

[PhilipA]

but I have been recently having issues with it wondering I could get some advice

Has the car been playing up since you bought it or have the issues started only recently?

Did you do anything before the issues started eg change the alternator to a Bosch?

One very simple reason that they play up is using an aftermarket rotor. The Lucas ones are damned expensive but one of the few that work.

You should check that you haven't dislodged the bob weights in the dizzy by pulling on the rotor.When I fitted a new rotor , I just crushed the old one with pipe grips. Check that the timing moves from say 10BTDC up to 35 or whatever as the car is revved with the vacuum advance plugged using a timing light.

You have done all the right things that should have fixed it.
You should run through the 14CUX diagnostic to check the ECU .
Regards Philip A

[Willyboyau]

I’ve managed to fix it today!!! Thought about it over night and bit the bullet this morning and bought a new amp and coil to put them in together. I originally replaced the coil with the old amp and still in, seemed to fix the issue but it came back a week later and I read somewhere yesterday that you should replace both at the same time due to one of these two products being faulty and causing the other to fail. So she is driving exceptionally well, running Bosch dizzy cap, xf rotor, Bosch bim 024 amp and Bosch coil, revs out to 5,500 with no miss at all, drove it for 4hours this afternoon never missed a beat! That’s being said I also checked the mechanical advance operation that’s all good however vacuum advance plunger is seized so I’ll be taking that to performance ignitions tomorrow. But thanks for the advice and really quick replies!

Still having trouble starting and idle issues some times not all the time but noticeably at a warm start up, give it a 1/4 of throttle while cranking and fires right up. I’m thinking idle control valve is blocked up with carbon going to take it off tomorrow and clean it out any thoughts? Vacuum hoses are fine no vac leaks what so ever.