03 TD4 hesitancy at 60-70+

For the last month the TD4 has begun to 'hold back' a bit when trying to accelerate on the motorway, a bit of hesitancy accompanied by a flickering and on/off engine management light (though it doesn't stay on). Sporadic, and seems to largely disappear after about 15 miles...

The under-car fuel pump was replaced not so long ago, as have all filters, and one duff injector.

The car starts on the button and has no idle, smoking problems etc

Fitted a Roverron tuning box the other week (great performance) but the problem existed before this.

I guess the answer is to get a fault code read (will it store it if EM light is not permanently on?)

Does anyone have any rough pointers as to where to look first? Underfueling? electrical problem? in-tank fuel pump? MAF sensor?

Any ideas folks?

I might unplug the original Bosch maf to test....(90K miles on car), although I would have thought the Synergy2 would over-ride this. Would a maf problem show engine light?

It's ok at cold, just when heater guage sits on the middle (ie warmed up), and then it will drive lumpy (mainly at sustained 70mph or so)

Would normally suspect fuel delivery problem but it seems you've covered that.

Could be the boost control solenoid knackered or one of it's vac pipes leaking. Check (through right front arch) if it's moving the turbo rod when someone revs the engine.

The maf signal is less important once boost pressure is up but it's worth unplugging it as you said to eliminate that.
A dead maf won't put the mil on.

As you have seen the mil flash on intermittently there should be a fault code/s stored in the memory.


The synergy amplifies the maf signal so if the maf is completely dead the synergy can't amplify a signal that isn't there and the ecu uses a default setting.

Thanks.

Definitely not MAF - unplugged it and it's still behaving badly with MIL on and off quite a lot now - seems to be getting worse. I'll try and check the turbo connections etc. My friend has some diagnostic gear so hopefully get it plugged in on Monday. My worry is that it might be in the in-tank fuel pump.

Whatever next, this car has been a right money pit.......

bdd said:

Thanks.

Definitely not MAF - unplugged it and it's still behaving badly with MIL on and off quite a lot now - seems to be getting worse. I'll try and check the turbo connections etc. My friend has some diagnostic gear so hopefully get it plugged in on Monday. My worry is that it might be in the in-tank fuel pump.

Whatever next, this car has been a right money pit.......

Click to expand...

If you have a fuel pump under the right rear arch then there is no in-tank pump.

Chaser said:

If you have a fuel pump under the right rear arch then there is no in-tank pump.

Click to expand...

Thanks, that's good to know. I'm mentally narrowing it down to possibly the boost solenoid, but hopefully the diagnostic test should uncover it or even give a pointer....I replaced the wheelarch pump a few months ago, it's failure symptoms were no-start but when you gave it a bash it jumped into action. Having said that, I bought the pump 'new' off ebay, it did not look 'new' when I bought it.

I might also invest in a pierburg MAF in any case, the car has done over 90K and could probably benefit, plus it should work better with the Synergy2.

I'll report what the diagnostics show up.