Disco 1 misfire,1995 3.9 V8

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Update...

Cleaned connections to fuel cut off switch, and cleaned the fire trap breather and hoses. Also cleaned and inspected connection to charcoal filter.
As matter of course I removed the stepper motor (it’s only a week or so old) and cleaned. I did notice when removing it that it wasn’t as tight as it should have been, assuming it’s worked loose with expansion and contraction from temps. I also spotted a vacuum hose below the stepper motor, the end nearest the throttle body was badly perished, I’ve replaced with new and refitted the stepper motor.

Still a cold engine, I fired it up, it idled slightly low (just below 750rpm) until I have a slight blip of the throttle (blip no more than 1200 rpm) and it then settled quickly to 800 rpm.

I shall pop out later on today and see how this goes, I’ll update later.

Thanks to all so far, I know these issues are common, your probably sick to death of hearing the same questions!
 
Things seem to be getting worse!

Driving along and it cut out, fired it back up after several attempts, it now has the battery light showing on the dash, no rev counter working and a whine which resembles a supercharger from under the bonnet!
I’m thinking alternator??

Thing is it’s still cutting out, only this time it didn’t show the ‘check engine’ light. Once it cuts out it continues to idle badly, usually just having no idle at all.

This seems to be happening as the engine is reaching its optimum temperature after 20-30 mins of driving.
Fuel temp sensor maybe??
 
The two items battery lamp plus rev counter are supplied from the alternator so that could be a prime suspect especially if making that sound.
As for the temp sensor I’d go for the engine coolant temp senso that provides info to the EFI ECU, it’s the black topped one just to the rear of the distributor.
With cutting out the ‘spider’immobiliser may be playing up, if your vehicle has one... they were introduced with the 1996MY D1.
 
discool said:
The two items battery lamp plus rev counter are supplied from the alternator so that could be a prime suspect especially if making that sound.
As for the temp sensor I’d go for the engine coolant temp senso that provides info to the EFI ECU, it’s the black topped one just to the rear of the distributor.
With cutting out the ‘spider’immobiliser may be playing up, if your vehicle has one... they were introduced with the 1996MY D1.
Click to expand...

Thanks for the reply.
The battery light has gone out now but still now rev counter. I’ve cleaned all connections on alternator and battery along with Earths, still no improvement.
The alternator is getting red hot, can’t touch it! This is even when engine is cool, so a short time running and it’s scorchio!

I’ll order a temp sensor and see if that helps, I know the location of the one in question.
As for the spider, I haven’t looked for it, I’ll take a look tomorrow, really hoping it doesn’t have one as there a royal pain in the rear to get at aren’t they!!

Am I right I’m saying that the alternator sends a pulse signal to the rev counter? Or is that the coil? I read somewhere that one or the other does or are linked.
I’m thinking (I don’t know for sure) if the alternator is toast then it wouldn’t be sending a Signal to the rev counter or is it possible it could cut a feed to the coil?

My above thinking is on the basis that the alternator bearings are toast and at times have gotten that hot they’ve momentarily seized and broken free again.

Does that make any sense at all?!
 
1, rev counter
2, iffy bearings would be one symptom of a hot alternator, touching an alternator to find if it’s hot is something I’ve never need to do :)
Don’t bother looking for the spider, if u have a two button fob then u have one hidden in the depths of the dashboard.
A simple test is with the vehicle stationary with the engine is misfiring place a wire link from the battery + to the coil + if the misfire ceases then that circuit within the spider is faulty much the same if having difficulty in starting ie. cranking but doesn’t fire up.:(
 
Ahh ok, I’m that case I don’t have a spider, thankfully!

So would a dodgy alternator cause the cutting out issue I keep getting?

Edit: It just randomly cuts out, engine checkmlight shows and then it comes back to life and drives like nothing has happened!

I’m obviously chasing more than one issue here I think.
 
Last edited:
Alternator ordered, just awaiting delivery. Definitely no spider in my vehicle, pulled the radio and had a look earlier on today.

However....!!

The misfire appeared again this morning on start up but cleared with a blip of the throttle.

Going to order temp sensors (both) this evening, something else to eliminate from the equation isn’t it.

Tomorrow my plan is to check fuel pump connections and fuel pump relay.
The alternator packing up and loosing the rev counter is comincidental I think so I shall continue to chase the cause of misfire and cutting out until I take delivery of the alternator.

I’m glad parts for these Disco ones aren’t as expensive as my previous L322 RR! Haha!
 
i'm very interested in this thread as i only picked up my first disco 1 two days ago and it is suffering similar issues but not cutting out. Please keep us updated and I hope you get it sorted out soon
 
Daz36uk said:
i'm very interested in this thread as i only picked up my first disco 1 two days ago and it is suffering similar issues but not cutting out. Please keep us updated and I hope you get it sorted out soon
Click to expand...

First bit of advice would be to change all ignition components, plugs, leads, dizzy cap, rotor arm and coil. Also clean every electrical plug under the bonnet, I cleaned mine then sprayed with contact cleaner followed by a spray of WD40. Then see how things go from there.

I’ve just ordered an ignition module, both temp sensors, a crank sensor and a fuel pump.

I’ll keep you posted, fingers crossed the above will sort my issue out.
 
V8demon said:
First bit of advice would be to change all ignition components, plugs, leads, dizzy cap, rotor arm and coil. Also clean every electrical plug under the bonnet, I cleaned mine then sprayed with contact cleaner followed by a spray of WD40. Then see how things go from there.

I’ve just ordered an ignition module, both temp sensors, a crank sensor and a fuel pump.

I’ll keep you posted, fingers crossed the above will sort my issue out.
Click to expand...
Send the crank sensor back, the UK spec D1 V8s don’t have one. :)
 
V8demon said:
First bit of advice would be to change all ignition components, plugs, leads, dizzy cap, rotor arm and coil. Also clean every electrical plug under the bonnet, I cleaned mine then sprayed with contact cleaner followed by a spray of WD40. Then see how things go from there.

I’ve just ordered an ignition module, both temp sensors, a crank sensor and a fuel pump.

I’ll keep you posted, fingers crossed the above will sort my issue out.
Click to expand...
Thank you for advise. To compound the problem I have just moved to Turkey 3 weeks ago and have no idea where to go for bits out here but have been told its very expensive to get car bits sent from the uk due to import tax.
 
Daz36uk said:
Thank you for advise. To compound the problem I have just moved to Turkey 3 weeks ago and have no idea where to go for bits out here but have been told its very expensive to get car bits sent from the uk due to import tax.
Click to expand...

Daz, I’d use eBay and look for the parts with free shipping :)
 
It appears I have fixed the cutting out issue, AT LONG LAST! Haha

I got a recon exchange alternator fitted that, I also picked up a coolant temp sensor, replaced that at the same time, been fine all day on two journeys and being used around the yard.

I’d like to thank all of you for your help and guidance, it’s very much appreciated.
 
So then, it’s been nearly two days and no issues, no misfire, no cutting out.

One thing that still doesn’t seem spot on is the idle from start up (cold engine/morning start up) for the first five seconds.

It will start pretty much straight away, no misfiring or spluttering but the idle hovers between 250 and 850 rpm for a few seconds or so. It’s been a while since I owned a 3.9 V8 but don’t remember this on any of the others.

I’ve already replaced the stepper motor, would a dirty plenum (near the stepper) possibly cause this to happen?
 
So then, it’s been nearly two days and no issues, no misfire, no cutting out.

One thing that still doesn’t seem spot on is the idle from start up (cold engine/morning start up) for the first five seconds.

It will start pretty much straight away, no misfiring or spluttering but the idle hovers between 250 and 850 rpm for a few seconds or so. It’s been a while since I owned a 3.9 V8 but don’t remember this on any of the others.

I’ve already replaced the stepper motor, would a dirty plenum (near the stepper) possibly cause this to happen?
 
So then, it’s been nearly two days and no issues, no misfire, no cutting out.

One thing that still doesn’t seem spot on is the idle from start up (cold engine/morning start up) for the first five seconds.

It will start pretty much straight away, no misfiring or spluttering but the idle hovers between 250 and 850 rpm for a few seconds or so. It’s been a while since I owned a 3.9 V8 but don’t remember this on any of the others.

I’ve already replaced the stepper motor, would a dirty plenum (near the stepper) possibly cause this to happen?
 
Something I noticed this evening that is a worthy mention for future reference is fuel tank pressure.
When I had the issues stated above the tank when opened to fill would suck in or release air, that no longer happens. Not entirely sure why!
 
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