The Dreaded Misfire

Hi everyone,
Im new here to both this forum and landrovers. Bought a disco td5 about 4 months ago and its been great until last week. Drives well and smooth up to about 2500 revs then starts backing off. im guessing its the limp mode kicking in. Anyway, after reading countless posts on here about misfire faults, ive gone ahead and replaced the injector wiring harness and the wastgate modulator as they seemed most popular choices. Checked all visible witing for chafing, and all visible hoses for splits.Checked wastegate to see if it was seized, it wasnt. result? No different!
i was starting to wonder if it might be a fuel issue.
Also, i dont know if this is normal, but when reving up in neutral, the engine wont wind past 3500rpm either.

Thought it best to join this already busy discussion rather than to just start a new one. Hope this is ok.
Has anyone got any other ideas as to what else i could try?
One thing, i am not hearing any noise what so ever from my fuel pump. surely the car wouldnt start if that was faulty......would it?
Any ideas would be greatly appreciated

feul pump should make a noise try disconecting maf and see if it revs past 3500
somtimes better to start new tread and introduce yourself with good info on model year etc

Hi Mikes lr,

Ive disconnected the maf and it still tops out at 3500/3700 revs. What does that mean?

I thought it better to join an existing thread cos it seems this topic has been quite well done, and as such, i thought that starting a new thread would not attract many viewers! Ive searched this forum for this misfiring topic and its been very informative. I have carried out what seemed the most popular solutions to the problem but to no avail.
If i dony get much response ill try a new thread and see where that gets me.
Its a 1999 by the way.
As for the fuel pump, i really cant hear any noise from it at all. but i didnt think that the car would even start if that was knackered. am i wrong?

to read the fault codes would be a good start....and you're right, if the pump is out it wont start...but there is a not very common but real issue with the output pressure of it if it's tired.... u have to test the pressure with a gauge inserted instead of the fuel temp. sensor in the FPR ... it must be a constant 4 bar there.... the FPR could missbehave as well

thanks for that sierrafery.
Im going to try to get fault codes read tomorrow. If there is a problem with the pump, will that throw up a code?
ive been trawling the internet again tonight and am leaning towards a fuel pump problem as ive addressed all the other common reasons for these symptoms.
Is changing the pump a difficult job? im not a mechanic but im happy to do a bit of part switching!

no fault code on pump failure... replacement procedure here TD5 Disco Fuel pump/sender unit - LR4x4 - The Land Rover Forum

ZXpower - check thread on fuel pressure, before I try cranking the engine I have to wait for air to be purged from system otherwise I have same issue as you.

For the others - I had misfire at around 2200 revs, eventually found small split in vacumn pipe from intercooler inlet pipe to wastgate. Only discovered this by blowing through the pipes and not finding any resistance. Visual inspection is not enough.

Good luck

Thanks chrimcne, ill have another look at those pipes. I read somewhere about one of them de-laminating and collapsing when under pressure so was going to have another look at it for that reason.
Took it into local garage to have codes read, loads came up but he said a lot of them were probably due to me changing parts ang generally fiddling, so he has cleared everything and in going back today for another read.
He told me that the misfire is actually the limp mode kicking in.
Also told me it may be egr valve and recommended removing it. I had read about this and was going to do it anyway. Maybe it will be sooner than planned!

Sorry to hijack, but the symptoms are very similar.

No power at all in my 2001 auto TD5. Ive done several nanocom live data readings, but they mean little to me. Ive noticed the clyinder inputs vary wildy, at one point it goes to -255, -1278, -1020, #####, 867. There are other similar readings over numerous data read outs on different days.

The acc supply reads 5.026 mostly except at one point it rockets to 38.571 and later on it drops to 1.036. There are other small deviations too.

The higest the turbo reads is 217.
The run I do involves a 60mph dual carrigway up a long steep hill. The turbo should be working overtime, but the car struggles to hit 40MPH.

Its really getting me down, as the car is just so limp. I borrowed an ancient T reg TD5 disco that was battered beyond belief and really not looked after, but it was like a rocket. It was fully standard. I want mine to be like that!

Any help would be most welcome, I can supply some nano readings if it helps.
For info, the car has had a new harness, new MAF, egr removed and shows no other fault codes

Don't know if this helps, but in the light of my recent problems of misfiring, engine dying etc, I eventually re-newed the injector "O" rings and seals after advice from this forum. What a difference! Engine a lot livelier, starts OK and keeps going.

TRadford said:

Sorry to hijack, but the symptoms are very similar.

No power at all in my 2001 auto TD5. Ive done several nanocom live data readings, but they mean little to me. Ive noticed the clyinder inputs vary wildy, at one point it goes to -255, -1278, -1020, #####, 867. There are other similar readings over numerous data read outs on different days.

The acc supply reads 5.026 mostly except at one point it rockets to 38.571 and later on it drops to 1.036. There are other small deviations too.

The higest the turbo reads is 217.
The run I do involves a 60mph dual carrigway up a long steep hill. The turbo should be working overtime, but the car struggles to hit 40MPH.

Its really getting me down, as the car is just so limp. I borrowed an ancient T reg TD5 disco that was battered beyond belief and really not looked after, but it was like a rocket. It was fully standard. I want mine to be like that!

Any help would be most welcome, I can supply some nano readings if it helps.
For info, the car has had a new harness, new MAF, egr removed and shows no other fault codes

Click to expand...

Tried a known working CKP (crankshaft position sensor)?

UPDATE.......

After changing virtually every part on the engine in an attempt to solve this, I can finally put this to bed. Hopefully it will help someone else and save them some money.

If your Td5 auto starts with hanging gearchange, rough/missing at 2250 and vibration, change your coolant temp sensor for a genuine part. I did all of the usual oil in loom, injector harness, maf reading ok and so on. I had replaced the temp sensor with an aftermarket one at a cost of £4, so disregarded this. However some months later, the temp gauge started to drop to cold and the coolant warning light came on. This was only every now and again and I thought I had a short. Checked all wiring, found no faults. Checked the sensor and got a reading with a meter. When the temp gauge dropped the ecu changes to default settings and I found that the engine was smooth revved cleanly and the vibration had gone.

I purchased a genuine sensor £20 and put it in. Also put heat wrap around the wires to the sensor, that pass around the head. Problem sorted....The engine warms up quickly and drives smooth no vibration. The aftermarket sensor must have been giving incorrect signals etc affecting engine fuelling.

So the moral is, buy genuine sensors.

Hope this helps someone.