Looks like I need to spend some more time and money getting to the bottom of my smokey TD4. To cut a long story short, it sat unused for most of 2020 due to lockdown. It was working fine last February, but a year on it's a different story. Smoking like hell once revved or driven, and now a strange reading on the original MAF and its brand new replacement.

I've managed to get an old Hawkeye on 2003 TD4, and airflow at tick over of 780RPM reports 457 mg/stroke. If I give it some throttle, the MAF reading starts decreasing straight away. While stationary, taking it to 2500RPM the MAF reading drops to 343 mg/stroke. Kicking out a nice lot of white/possibly blueish smoke in there process. The tick over MAF reading is below what it should be. 515 seems to be the default, and what I've seen others read on YouTube etc. But the decreased reading definitely seems wrong with increased throttle.

It does this on both the old and the brand new Bosch MAF. Disconnecting the MAF to run with the defaults shows how the MAF should increase, where it should be over 800 mg/stroke at 2500RPM. It makes no difference to the running of the engine disconnected. It still chucks out plumes of smoke.

Two MAFs, and no MAF, all doing the same thing, make more think it's not the MAF, and something else (possibly obstructing airflow, or a leak into the system?) causing the problem.

I wondered if anyone had had experience of this before I go trying to get at the turbo, which seems to be the only major thing in the airflow to the engine that could be a problem. I guess there could be a hole in the intercooler, so maybe air is getting sucked in there. The induction hoses are all good condition silicon hoses., and connections tight. EGR is stuck shut, so acting as a bypass.

No increase in boost pressure noticed on the MAP. But the high pressure rail starts off at 28,000 kPA and rises with throttle.

I've tried the tissue paper test on the hose that goes into the intercooler from the turbo. Revved for 20-30s and no marks appear. But I would say the EGR and inlet manifold that were cleaned perfectly before I started her up again, now have an oily film over them again, with the engine hardly being run since replacement. So I wonder if failing turbo seals are still a probably possibility.

Other things that have been done.
- New fuel.
- New fuel filter
- New air filter
- New oil and oil filter
- New breather filter, and since checked again and it's still perfectly clean after running a few smokey tests
- Inlet filter and EGR degunked, and nice and clean - horrendous job
- 4 refurbished injectors - two of the originals were kaput, causing misfiring and proper white smoke at idle, so changed all 4, as the engine has 120,000 miles on the clock, so were probably not their best.
- Vacuum hoses checked and chaffed ones replaced.

A lot of time and money now spent on this now, so hoping I can soon having it running again. Any suggestions as to if I'm on the right or wrong track much appreciated. In the meantime, as time allows, I'll get to the bottom of this and report back as to what it eventually turns out to be.

Does it still smoke, if the elbow boost pipe is removed?

Thanks Nodge.

When I was concentrating on sorting the injector issue, I had the inlet manifold off, and run the engine. No smoke with the new injectors, apart from around 2500RPM when it would start to misfire a bit, and some white smoke would appear. Ease of the throttle and no smoke at all. I could hold it at 2000RPM, and no smoke at all.

I've just checked it again with the inlet manifold etc. in place, and disconnected the elbow hose as suggested. I had the plastic airpipe moulding resting on top of the elbow hose, revved it to 2000 and 2500 RPM. No smoke all the way up to 2500RPM, then the misfire and smoke as per the inlet manifold off configuration. I noticed however that there was some oil splattered on the nearby hoses, and on the cooling fan assembly that the hose was directed too. After 30 seconds or so of holding the revs high, does this look too much oil to be splattered from that open pipe? (on the photos, the outlet from the plastic moulding is just off the top of the photo, resting on the elbow hose)

On an earlier test. I didn't notice any oil being expelled from the inlet hose to the intercooler, when I disconnected that one to run a similar test. So I'm wondering if the excess oil is just coming from a build up in the intercooler? But then again, that doesn't explain the MAF readings decreasing with increased throttle.

Quick update on this...

I've had a chance to clean the intercooler and hoses, and now back on, no more smoking. Great!

Still got the problem with the fueling though. But I've ruled out the MAF being the source of the problem. - Two MAFs I thought were unlikely to give the same fault, especially when one was brand new. I was able to check their operation by removing by the air filter, which makes the airflow on the less concentrated on the MAF sensor probe, resulting in an expected drop in value at idle. Moving my hand across the MAF intake, also caused an instantaneous change in MAF value as expected. Why is this significant? Well..

What I've noticed on the live readings is that at idle the MAF reading is 515ish mg/stroke. But as soon as there is even the tiniest increase in throttle, to 800rpm for example, the MAF reading drops to 320mg/stroke, and stays there. If I take my foot off the throttle, the MAF reading stays at 320mg/stroke for about 30s, then the engine changes note, as the reading changes back to 515mg/stroke. This behaviour is consistent.

To me it seemed like something in the fuel delivery setup is taking a while to settle, whenever there is change in fuel demand. So the first thing I changed was the fuel pressure regulator, with a new Bosch one. No joy though. If anything it's made the delay in returning to normal behaviour a bit longer. (Maybe as the old one did have a slightly worn hard washer.

So, my thinking is still that something is causing over-fuelling, when there is demand to take it out of idle. HP fuel pump or the fuel pressure rail sensor perhaps has gone out of calibration/performance.

I think I will try the pressure sensor first, as that will be the easiest to replace.

In terms of the of the HP pump, it's not leaking, so does anyone have any thoughts as to if it's worth having ago at trying to change the internal washers etc myself? Or are there rusty things best left to being refurbed professionally because of the potential for rust on the internal surfaces.

The only other thought is could it be a faulty cam or crankshaft sensor that is messing with the timing of firing the injectors.

I'll get there... and report the results. But any suggestions that will save effort and money are most appreciated.

New HP fuel rail pressure in and the overlay harness, and it’s solved the dodgy decreasing MAF readings. Yippee!

Getting closer I think/hope to having it on the road again…. I’ve still got a smoking issue after having driven it briefly up and down the drive a few times. I’d previously cleaned all the intercooler pipes and the metal pipe that feeds around the engine from the turbo. But when I took the hose off that connects that pipe to the intercooler, oil dripped out again, and there was a trail of oil sitting at the bottom of the metal pipe ready to drip more if it was left.

I suspect this is more oil than should be deposited so shortly after the clean, so it looks the the next step is getting my knuckles sore getting at the turbo to either replace it or it’s cartridge.

Still, at least one of the problems appears to be solved. That pesky pressure sensor seems to be the root of many people’s woes.