Td5 misfire rough running at low revs

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biggmw

New Member
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4
Good evening to everyone.

First time poster

Have a disco td5 on a 1999.

While sitting ticking over the other day a slight miss developed....

As the day progressed it got worse.

Now we have the following.

Missing slightly at no load low revs... 'revs through it' and is fine at 2000 plus and beyond

With a load on, ie pulling away with light throttle seems worse

Injector loom changed 6 months ago and very little residual oil left in ecu plug, cleaned to make no change

Plug at head end clean and dry

Pump in tank can be heard which seems like a new thing?

Starts easily and quickly

Cylinder balance out by teens at tick over, very little at revs

Thinking pump on way out?

Opinions please??
 
plug it in a tester first of all...to make sure there's no injector fault present... if it's the pump there will be no trace in the ECU memory cos this one is not covered...nor the FPR
 
Thankyou for your reply.

So far have had nanocom on it and have no injector faults shown.

Have a maf sensor needed so far as reading air flow as 0 all the time, that would equate to maf disconnect though and therefor should go to default maping etc and not cause misfire?

Will change that anyways as it is needed.

Pump in tank is audible, where I don't remember it being so before.

Even after standing 10 hours it starts in 2 secs on tuirn of key, without heat so that should point to injector seals being ok?? Also no gurgling noises from pump just a whine.

Have cylinder inbalance into teens on 1 and 3 at tick over, cold but all five in single figures at 2000rpm (no load)

After a run it gets worse with the misfire, and now we are looking at cylinder inbalance on most at tick over, ruling out injector issues me thinks?

Have checked egr is ok, still fitted....ha

Have tried without maf fitted and same issues.

Have cleaned map but readings seem to be sensible on that anyways??

Me is thinking still tank pump is my culprit......

This, in my mind, would follow....but why does it rev clear at 2000 (no load). Under load mis does creap further up the revs.... Will free rev or under load well past 4k easily.

I await you replies with interest and thankyou in advance.
 
see the last two ways of failure:

The MAF sensor can fail the following ways or supply incorrect signal:
l Sensor open circuit.
l Short circuit to vehicle supply.
l Short circuit to vehicle earth.
l Contaminated sensor element.
l Damaged sensor element.
l Damaged in wiring harness.
l MAF supplies incorrect signal (due to air leak or air inlet restriction).

unplug it take a multimeter and check for voltage on pin 3 of the plug...there must be 12V there, but before that check fuse F2 in engine bay fusebox and swap R9(main relay) with R8(heated screen) ...just to rule out an electrical issue
 
biggmw said:
Thank you for your reply.

So far have had Nanocom on it and have no injector faults shown.

Have a maf sensor needed so far as reading air flow as 0 all the time, that would equate to maf disconnect though and therefore should go to default mapping etc and not cause misfire?

Will change that any way as it is needed.

Pump in tank is audible, where I don't remember it being so before.

Even after standing 10 hours it starts in 2 secs on turn of key, without heat so that should point to injector seals being OK?? Also no gurgling noises from pump just a whine.

Have cylinder imbalance into teens on 1 and 3 at tick over, cold but all five in single figures at 2000rpm (no load)

After a run it gets worse with the misfire, and now we are looking at cylinder imbalance on most at tick over, ruling out injector issues me thinks?

Have checked egr is ok, still fitted....ha

Have tried without maf fitted and same issues.

Have cleaned map but readings seem to be sensible on that any way??

Me is thinking still tank pump is my culprit......

This, in my mind, would follow....but why does it rev clear at 2000 (no load). Under load mis does creap further up the revs.... Will free rev or under load well past 4k easily.

I await you replies with interest and thank you in advance.
Click to expand...



Re your MAF, you may well have to replace it, but I would suggest you consider buying one of the cheapies (about £30) of Ebay.

Contrary to what others might have you believe, I have found these to work perfectly well.

PS You should be able to hear your in-tank fuel pump. But it's a really good idea to take it out once a year and clean the internal filter which can get blocked with black crap!
 
Last edited:
Ok

Thankyou very much for replying

I have now got the air flow issues sorted out, new maf is sitting in and flow reading

Have swaped the pump and fpr for known good ones and still have issue

Am I now looking at injector seals?

No injector faults showing on nanocom

No rise in oil level, so o rings would appear to be ok

No issues starting however which doesn't sound like seals to me, but maybe??

Cylinder inbalance is quite bad, into 20s, but not consistently on any one cyl??

MMMMM.....
 
Forgot to say fuel filter was first on list to be done.....

The misfire is getting worse and under load quite bad, with no power at all

The slight oddity is that it started quite suddenly....
 
redhotmax said:
Hi bggmw,
Did you ever solve your disco problem on this thread as i have what sounds to be the very same probem for the last 9 months now. Spend a lot of money on replacement parts without success.

Best regards
Red
Click to expand...
Hi red
Check you inter cooler hose mine had delaminates and under load it was collapsing caused it to run rough as hell ,also have you checked the injector loom theses get oil in them it then makes it's way into the ecu there is an upgraded loom available too you will have to remove ecu (next to jack ) open it up and clean out reseal
 
Hi I'm new to this forum game I was wondering if any one can help I'm unsure if I'm posting this in the wright place but il try any way
I own a 2003 discovery td5 you start it up and it's sounds fine but after about ten minutes at a stand still it starts to tick over funny like I've put a set of race cams in it it starts juddering and when going to pull of it's judders like mad up to 3000 rpm I've changed ecu fuel pump injectors harness fuel filter cleaned egr and still juddering it's sending me crazy as and I know there's nothing major wrong as u get in the car 1st thing in the morning it runs great for so long no faults at all then randomly runs crap
Please help
 
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