Disco 1 misfire,1995 3.9 V8

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So, went ahead and removed the charcoal canister, fuel tank breather is free to breath ad plenum vacuum is blocked off. Also replaced the fuel filler cap, still has a fair bit of pressure within the tank.

Still cuts out briefly and then refuses to idle after that.

My next thinking is, fuel pump relay or fuel pump? I’ve ordered a relay and already have a pump. Also thinking it could be the ignition amplifier mounted next to the coil?

Any ideas folks? There’s not a lot else to change now, this issue must be coming to an end shortly!!
 
Am I right in saying the fuel pump relay is under the passenger kick panel and it’s the one with the green base/plug?

I’m told there is also an efi relay, is that so?

Still go issues so working my way through everything now.
 
V8demon said:
Am I right in saying the fuel pump relay is under the passenger kick panel and it’s the one with the green base/plug?

I’m told there is also an efi relay, is that so?

Still go issues so working my way through everything now.
Click to expand...
Look behind the drivers kick panel (RHD 300 series), there’s two rows of relays the one for the pump is on the top row, third relay in from the door edge it has an aluminium case, the fuel injection is the fourth one in again an aluminium case the fifth one at the end is fan timer relay and is green.
200 series is different, pump is on the passenger side with a yellow wiring connector.
 
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discool said:
Look behind the drivers kick panel (RHD 300 series), there’s two rows of relays the one for the pump is on the top row, third relay in from the door edge it has an aluminium case, the fuel injection is the fourth one in again an aluminium case the fifth one at the end is fan timer relay and is green.
200 series is different, pump is on the passenger side with a yellow wiring connector.
Click to expand...

Ah, perfect, Thanks buddy :)

I was looking the wrong side!
 
Exactly where you said they were, however...!

Top row I only have two relays, bottom row has three.
Top row are both ‘Bosch’ 30 amp 5 pin relays so those must be Efi and fuel pump.

Only have one new relay so have changed one for now, if issue persists I’ll swap it over and see if that eliminates any issue.
 
After changing the fuel pump relay it seems to have cured the cutting out issue. I’m still in doubt though as it used to cut out at running temperature on a warm day, today being cooler the temp gauge didn’t read the temp that it would normally cut out at.

Time will tell, but for now it appears to be cured.
 
Well it didn’t last for long, cut out on me today whilst driving along and as usual immediately fires right back up and carries on going until you come to a halt and the idle just drops as though there isn’t one.

This time I kept it running until I could pull over, I let the revs drop on their own and it cut out. I turned the ignition off and left it a few seconds (i have been trying to start it immediately after) and started it up, to my amazement it started and idled fine.

Something I also noticed this time, after it cuts out it runs rich, can smell fuel and when I let off the throttle it backfires ever so slightly.

Any suggestions folks?
 
Two things maybe to look at 1: vac advance - is it working, or is there a vacumm leak on the inlet side somewhere. 2: get the dvm out and check your throttle pot for base voltage setting then also check scaling.

As I think may have been suggested, might be worth checking your ignition timing and base idle settings. If you have read some of my posts, you might have seen I am a strong advocate of cleaning the plenum and ram housing, does wonders trust me.

I have seen with my Range Rover if the throttle pot voltage is too low it can stall but normally only after touching the throttle.It will then restart and idle fine until you move the accelerator pedal so worth a check.

For various misfires and idle issues check out the V8 section, loads in there and some unexpected fixes/symptoms.
 
classic kev said:
Two things maybe to look at 1: vac advance - is it working, or is there a vacumm leak on the inlet side somewhere. 2: get the dvm out and check your throttle pot for base voltage setting then also check scaling.

As I think may have been suggested, might be worth checking your ignition timing and base idle settings. If you have read some of my posts, you might have seen I am a strong advocate of cleaning the plenum and ram housing, does wonders trust me.

I have seen with my Range Rover if the throttle pot voltage is too low it can stall but normally only after touching the throttle.It will then restart and idle fine until you move the accelerator pedal so worth a check.

For various misfires and idle issues check out the V8 section, loads in there and some unexpected fixes/symptoms.
Click to expand...

Thanks Kev, I’ll do the above and post back with the results.

If the the throttle potentiometer has low voltage to it how is that adjusted?

My issue is when driving it will randomly cut out for a second and then carry on driving as though everything is fine until you come to a halt, then the idle will just drop off and the engine will cut out.
After it has that blip, if I keep it running and turn it off myself and restart it will idle fine. If I come to a halt and let the idle drop off and cut out on its own and try to restart it won’t idle at all.

I’m awaiting delivery of efi relay, fuel pressure sensor and ignition module. I already have a fuel pump which I will also fit.
 
V8demon said:
Somit would be a case of replacing it then?
Click to expand...

IF, if you can find a new one. As said before they are obsolete & like rocking horse poo to find second hand and if you do they are ££££ I have a similar product on order and will have to modify it to fit. I've already tried one from a P38 which was a cheapy, but either it was a duff one or the voltage range is different and wouldn't work. Once I get the right one (which works) I'll share the joys!!!! :rolleyes::D
 
Fingers crossed it not the pot then! Looking forward to seeing what you come up with.
I have a friend in the USA who is a whizz with electronics, I may mention this to him see what thoughts he has.
 
So frustrating for me, totally rebuilt the top of the engine & the only thing stopping it running is a little tiny sensor similar to a bloody radio knob!:mad::mad::mad:
 
Jasonmichael said:
So frustrating for me, totally rebuilt the top of the engine & the only thing stopping it running is a little tiny sensor similar to a bloody radio knob!:mad::mad::mad:
Click to expand...

Yes I can imagine! I have searched for those pots and there’s literally none! Got my buddy in the states checking sites over there for one, hopefully he finds something.

If I can’t find the cause of the issue I shall just buy an inlet manifold and pair of carbs I think. I’ve never converted an engine from efi to carb but it can’t be that hard I’m sure.
 
Guys, you can adjust a throttle pot. You can slightly enlarge the mounting holes with a needle file so you can achieve the small amount of movement required to adjust it. As I have suggested before, get in to the V8 section and do a search, I have posted on efi and ignition checks and fixes.
 
V8demon said:
Yes I can imagine! I have searched for those pots and there’s literally none! Got my buddy in the states checking sites over there for one, hopefully he finds something.

If I can’t find the cause of the issue I shall just buy an inlet manifold and pair of carbs I think. I’ve never converted an engine from efi to carb but it can’t be that hard I’m sure.
Click to expand...
There seems a lot of concern with the TPS, as my quick search shows in the link below, also I understand that the 3.9 EFI ECU is a little more advanced than the 3.5 item in that it’s self learning hence no adjustments available, that’s something I found out once when my vehicles idle went up to 2000rpm straight after fitting a Janspeed cat back exhaust system, and after 30 seconds or so the revs dropped down to 725-750 rpm. And back to normal.
https://www.aulro.com/afvb/discovery-1-a/116624-tps-adjustment.html
 
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discool said:
There seems a lot of concern with the TPS, as my quick search shows in the link below, also I understand that the 3.9 EFI ECU is a little more advanced than the 3.5 item in that it’s self learning hence no adjustments available, that’s something I found out once when my vehicles idle went up to 2000rpm straight after fitting a Janspeed cat back exhaust system, and after 30 seconds or so the revs dropped down to 725-750 rpm. And back to normal.
https://www.aulro.com/afvb/discovery-1-a/116624-tps-adjustment.html
Click to expand...

I read that on an Australian LR forum actually, glad you’ve backed that up some.

I shall persevere for now, carbs are a last resort.
 
Some time ago some owners of the 3.5 RR found out that the TPS on their engine wasn’t immune from wearing out, and the 3.5 TPS was obsolete, so they purchased the 3.9 item which was available, of course they has to elongate the two screw holes to enable the item to be adjusted to suit there vehicle. That’s how the modification of the screw holes originally came about.

My 3.5 RR had 110,000 miles on the clock and the TPS was never touched, my disco has done a lot less and so far never been touched, so as the link gives you the voltages to expect so why no test and instead guessing that’s its faulty.
 
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