TD4 miss on acceleration

Hi
I am racking my brains to resolve a problem I have had for nearly a year!

On acceleration I get a slight miss which clears at around 2500 rpm. I have posted about this before but thought that I had cured it with each thing I did.

Ok it's a 2003 model
All injectors now seem fine but a couple were leaking back - I have had recons etc and now there is a small leak-back equal from all. I have just had one bad one done so was hoping it would solve it - it's better but not cured.

I have a Synergy 2 and Piersburg MAF set to number 6 if it's higher the miss is worse.

I have changed things like VCU, Crankcase breather, a driveshaft, complete clutch and DM Flywheel, new intercooler hoses.

I took the pro off to eliminate rear drive train problems but it made no difference - prop back on now.

It seems ok when cold but not when hot!? I have checked as best I can for any pipe leaks splits etc

On runs and motorway it is great plenty of power and no missing - just on accelerating mostly in 1st a bit in 2nd can feel it after that.

Any ideas?

Hi angeloc ,i had a slight miss ,turned out to be a loose jubilee clip on one of the hoses ,failing that ,sounds like a fuel problem have you replaced your fuel filter ? hope you get sorted keep us informed i j

All hoses tight - so much has been taken off and replaced I am sure of that. All filters good with recent fuel filter done. Also once through it the car flies - top speed (on private track of course) is showing over 100mph - acceleration is excellent and pulling up hill is powerful.

This is one of those really odd ones that can cost stupid money in replacement parts to no avail. I had it checked by Hippo on his Hawkeye and nothing showed up as faulty which suggested to me it was injectors. These have been troublesome and I changed a couple - had one reconditioned yesterday locally (Electro diesel) and fitted this am. It was better and the leak back it had which was a lot is now consistent across all injectors but still there is this miss - well it's more of a shimmy - it doesn't sound like a miss. ARRRRGGGHHHH!

Hi, not sure I'm no expert but check crank case breather,mac snsr and egr - all prone to cause problems, also a known loom where water gets in to a section of the loom but this can be an expensive repair as the loom needs to be striped back to the ecu. Try changing breather filter and cleaning egr first, if you find they are badly contaminated would advise remove map sns and check too.

I forgot to say I have an EGR bypass, the crank case filter is the BMW one and is clean. What is the MAP sensor? I have thought it could be the injector loom - it feels very stiff and has been moved back and forth a number of times - its about £40 I think so may give that a go.

I wonder if it's an LP pump causing your problems. When my under-bonnet one went last year, my engine developed a slight misfire. At one point the MIL light came on too (ironically when I was on my way back from the parcel depot, having just picked up my new fuel pump!). Admittedly this was under extreme load, close to top speed (well, I waned to get home to change the pump...), but all symptoms went away after the pump was replaced.

Even before I had a replacement injector a couple of weeks ago the engine was still running silkily, albeit just very tricky to start.

Worth a thought. Apols if I missed that on your list of things already done/investigated.

At high speed even high rpm and pushing it all is fine - it runs beautifully - smooth quiet - a pleasure to drive. It only happens in first and s bit in second as I pull away and more so when the engine is hot after a run.

I am going to zip the synergy off and put the old MAF back in case there is a fault on the synergy.

Probably a good idea. Of all the mods you've made it's the most drastic. Go back to basics and take it from there, I guess. Do you know that your original MAF is working though?

Just re-read this thread and I agree - it's probably not the pump if you can get 100mph out of it and all is still smooth!

Not sure original MAF is ok but at one point I was chasing solutions to a few faults that I now understand - bit by bit are sorted so it may be the origin MAF was ok to start with.

Changing injectors has been a long story - I got ripped off by a guy in London who reconditioned one of mine badly and when I sent it back ( not registered or recorded Doh it was a bad day!) says he didn't get it do bought a second hand one which has failed now reconditioned locally and all seem ok now.

So yes back to basics may be the way to go. And perhaps the wiring harness after if it isn't the synergy.

I have no smoke even on hard acceleration so its all sweet except this. I had wondered about the Turbo accentuator but it definitely has turbo boost and smooth as well.

It definitely sounds like something electronic then. I've never really had the need to delve into Td4 electronics in any depth, but, being an engineer who works in embedded systems, my in-built alarms tell me that I think you've probably hit the nail on the head with the wiring harness or something in that chain, despite my earlier comments.

Normally with diesels of the age we own, problems come down to something mechanical. They usually are, thus my suggestions earlier. This is definitely sounding like a signalling problem (the wiring) or possibly even an ECU fault. What ECU, I have no idea (as I said, I'm no expert on Td4 electronic systems), but, thinking about the diagrams in the Haynes manual, the "Engine Management" ECU may be the culprit. It is the brains behind the whole fueling and firing business after all.

If removing the Synergy and reinstating the Bosch MAF makes a positive difference then you can definitely assume the Synergy "ECU modifier" (which is what it is) is the problem (no disrespect meant to this well proven modification unit - if I had the spare cash at the mo, I'd buy one ). If not, I would pursue the wiring route first as it's a) cheaper and b) more open to environmental abuse ("**** in your engine bay, sir." ... "How often do I have to do that...?"), and then look at the ECU for faults there. You've pretty much looked at everything else mechanical it could possibly be.

Once you've got it fixed, allow me to make you an offer on your well sorted Freelander...

It's on the head, they are prone to fail, type it in on google and pics u will see how to get to it, try disconnecting , ifvitvruns better chances are that's the place to start, don't leave it disconected though, burns a lot of fuel

Yep I remember it now. Ok with do this lot on Monday now - its too cold out there for me today and tomorrow is Playday!

Ok I know about unplugging a MAF to check it but not a MAP!? Can you unplug the MAP and drive ok?

Angeloc, I had the same problem but on my TD5. I know it is a different motor but the fault was identical. The fix turned out to be a cable from the fuel pump that had rubbed through and was shorting out on the chassis.Took me ages to find but now runs smooth as silk.Also have a TD4 and since that fix am now working my way round the freelander looking for same problems with tired wiring.

If it was a chaffed wire wouldnt it happen at all odd times - this only happens in 1st and 2nd when the engine is hot. I have even considered it to be a gearbox or drive pinion fault!?

This is really odd - more so as I have put up with it for nearly a year thinking each time I changed something it would go!

My TD5 is an auto and it happened in 1st and 2nd only. Really wierd

Could be something to do with the torque converter.

twister1264 said:

Could be something to do with the torque converter.

Click to expand...

No mines not an auto it's a geared 2003 TD4

sorry then mate i am as confused as you. I know you have done loads to your TD4 so at a bit of a loss.

I will keep at it - off with the synergy first and clean MAP then perhaps the injector harness. Hey ho thank goodness I can do it myself

Too right keep us informed will you as these nasty faults can stump the best of us. Any new info from yourself would be most welcome.