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Discussion Starter · #1 ·
I've had the issue of high consumption in a while and nothing really seems to help it. The board computer says 10.1l/100 km (28 MPG), but by filling the tank full, driving for 410 km and topping up again, 39 liters fit, which calculates to 9.5l/100 or almost 30 MPG, which is better than the board computer says but not too much. Here's what I did so far:

Overboost/Pierburg valve replaced
MAP sensor replaced
MAF not replaced, tested a new one and the measurements were the same (more on that at the bottom) #1
Bottom hose replaced (had a metal one before that ended up with a pretty big hole, like someone stabbed it, which is weird since it was metal) with a genuine rubber hose
Intercooler - manifold hose snapped, replaced with genuine rubber
Turbo vanes were sticking, cleaned them a bit, car behaves better now but consumption isn't much better - (more on that at the bottom) #2
EGR blanked for 2 years, never cleaned after that, however
Used injector cleaner + high quality premium diesel
New filters

- The "more on that at the bottom part" -


#1 Measurements suggest the engine is starved of air dramatically (all of these were done in neutral, sadly no driving measurements)

ACTUAL AIR MASS DESIRED AIR MASS
idle 50 g/cycle 150 g/cycle
high revs 400-500 g/cycle 950-1050 g/cycle

We tested a new MAF out the box (however, not genuine bosch - will try that soon and meaSure during driving) and the readings were marginally better - idle mass was 65-70 and high revs was about 600.

Haven't tried disconnecting it yet. Afriad to do it myself.

#2 A bit of turbo lag was present. It wouldn't pull until 2500 RPM, even on WOT, but then it pulls like a mule. Also on first start in the morning, when the car is cold, during WOT or a bit more throttle than usual, there was a LOT of hesitation and a LOT of black smoke out the back. It didn't feel like the problem above where it doesn't pull until 2500, it will exceed 2500 RPM but wouldn't start pulling until a lot of black smoke is expelled, after which it starts pulling "normally" after 2500 RPM, but getting there is laggy.

The problem seemed to be sticky turbo vanes, which have been cleaned as much as possible and it behaves a lot better in low revs. The hesitation that happened when the car has been started after a day is gone - possibly by cleaning the vanes, or by replacing the top hose. However a lot of black smoke is still present if WOT.

The mechanic suggested reconditioning the turbocharger, since it has started using a bit of oil, and he suggested cleaning the injectors or replacing them.

Can a turbo be bad even if turbo pressures seem very good? IIRC desired boost at high revs is about 1200 mbar, and actual is right up there at 1150-1180. And even actual fuel pressure is right up there with the desired values.
 

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How many miles? - the ebay MAF's are a piece of crap so I wouldn't judge anything against them.
 

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ACTUAL AIR MASS DESIRED AIR MASS
idle 50 g/cycle 150 g/cycle
high revs 400-500 g/cycle 950-1050 g/cycle

Can a turbo be bad even if turbo pressures seem very good? IIRC desired boost at high revs is about 1200 mbar, and actual is right up there at 1150-1180. And even actual fuel pressure is right up there with the desired values.
Firstly, you appear to have 2 sets of figures. I don't know exactly what the difference is. Was that a before and after parts replacement? Can you be more specific, please?

From what I've seen (and remember), I think the maximum airflow value should be around 30-40 times that of the recorded idle figure, depending on engine version. Also, you are using g/cycle or more accurately, mg/cycle. This is calculated data which is affected by data from other sensors. It is not really accurate. Ideally, use EOBD data or raw MAF voltage or airflow data for an accurate indicator.

I have a friend with a workshop and I'll ask to get some stationary figures from the 1.9 CDTI 16v engine to see if that helps. It is a shame no one with a healthy engine hasn't posted diagnostic data for reference in a sticky.

Yes, it still could be a turbo issue. Even cleaning vanes has resulted in some unexpected results but I don't think there has been a definite answer for this.
 

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Discussion Starter · #5 ·
Firstly, you appear to have 2 sets of figures. I don't know exactly what the difference is. Was that a before and after parts replacement? Can you be more specific, please?

From what I've seen (and remember), I think the maximum airflow value should be around 30-40 times that of the recorded idle figure, depending on engine version. Also, you are using g/cycle or more accurately, mg/cycle. This is calculated data which is affected by data from other sensors. It is not really accurate. Ideally, use EOBD data or raw MAF voltage or airflow data for an accurate indicator.

I have a friend with a workshop and I'll ask to get some stationary figures from the 1.9 CDTI 16v engine to see if that helps. It is a shame no one with a healthy engine hasn't posted diagnostic data for reference in a sticky.

Yes, it still could be a turbo issue. Even cleaning vanes has resulted in some unexpected results but I don't think there has been a definite answer for this.
This was with the current MAF sensor, the one I've had since I bought the car. The new MAF shows pretty much exactly the same actual values, except it's marginally closer to the desired - about 5-10% closer. This suggests (to me, atleast) that the old MAF is still working properly, and that there is a loss of air somewhere.

How easy is it to inspect an airbox, to see if it is broken? And could a broken airbox be a cause of such a dramatic loss of air? The car gets 2-3 times less air mass than it thinks it should.
 

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Airbox is not pressurised. Anything after the turbo should be tested.

How old is the car (is it a Euro 4 engine with swirl flaps)? That seems too much to lose through manifold swirl flap spindles though.

Perhaps get a solution of soapy water solution (anything which foams) and cover the boost components with it. Then run engine and apply full throttle for 1-1.5 seconds (don't let it rev too high- certainly not above 4k) before releasing throttle and letting it return to idle). Repeat a few times and look for bubbles or foam which has formed. That will be the leak, if any.

Holding a constant engine speed will not show up anything. I stress this as I have explained to people before and even shown then, and they still tickle the throttle to a constant 2500rpm which is no use.

What is needed is full boost but obviously the engine will quickly accelerate and reach the limiter by which point boost is reduced to a minimal value.

Short stabs of full throttle will allow the boost to increase without over-speeding the engine or doing any damage.
 

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I wouldn't go any further until I had replaced the MAF with a new genuine Bosch item. Your symptoms are all pointing at the MAF, and only a Bosch will suit it.
 

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Have you got any error codes, a failing MAF will throw up codes
 

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Discussion Starter · #9 ·
The engine is a Cf3, Euro 3 without swirl flaps. Where else to look for leaks? Doesn't the turbo go directly to the MAF?

Is there a diagram of the components? Both hoses are new - Turbo-IC and IC-manifold and show no leaks. Will test a new MAF tomorrow probably. Is it possible that the MAF housing is broken?

My current understanding is that turbo blows air towards MAF, and then to IC and then into the engine. Is this not correct?
Only one error code - EGR (but it is blocked) and no MCSF.
 

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Discussion Starter · #10 ·
Variable geometry doesn't work anymore at all. Vanes stuck again (what can cause them to get stuck again in 3 days?) Or the actuator isn't working? Or some other vacuum issue? Will check again today with mechanic who cleaned them and report back.
 

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Have you got any error codes, a failing MAF will throw up codes
In many cases only a dead MAF will .. often a failing one doesn't tell you anything .. unplugging it and seeing how the performance is affected is usually the only way ..

It also depends on the diagnostic kit as some earlier diesels had a "custom" version of the ODB code that only Fiat/Alfa specific kit will read correctly .. or MES.

I've had the same with a Pug and Renault (both pre 2005 diesels) and different kit would give different codes ... even the AA one failed to spot the duff glow plugs on our Clio!! I found them the old fashioned way with a multimeter!! They said it was the high pressure fuel pump!! :disappointed:
 

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I'm a bit worried by the question about the airbox. Has the airfilter ever been changed? It's an awkward job, so they tend to be 'left until the next service' for many years, and awkward again getting it back together and sealed properly. It sounds like it may be struggling to breathe.

I can't quite remember now, but (on a 16v 150bhp) I couldn't get mine out or replace it until I loosened and somewhat displaced the airbox end of the crossmember that supports the radiator and aircon condenser.
 

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Test the VGT with a vacuum pump, eg the cheap Mityvac clones on eBay cost about £12. You should get the full range of deflection of the actuator rod, about 15-17mm (eLearn claims 10mm, and that's wrong), in the range 0-17ins.Hg. If not, either the vanes are sticking due to carbon or rust, or the actuator is cattled. If you do see the full range, the problem is upstream - the vacuum solenoid, piping, or even the vacuum pump itself (but your brakes will be horrendously heavy, if that).

If the vanes are sticky, Mr Muscle will help get rid of carbon, but not rust which is jamming the VGT blades (which is the problem I had). I removed the turbo, split the case, used emery paper to remove the rust, and it's been fine since. I think it happened because the car had stood, run occasionally for a few minutes by the previous owner, for almost a year.
 

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Discussion Starter · #14 ·
Air filter has been replaced 500 km ago, and I have replaced it every time I did a service. The problem now seems to be the actuator rod. When the car switches off it goes too far up and is unable to go down when the car starts by itself, I have to push it down with a long screwdriver and then the turbo works properly. Seems like I have to do this every time I start the car.

Not enough vacuum in system?
 

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Well, that does sound like sticky vanes or possibly wear in the VGT mechanism allowing the lever that the actuator rod operates on to jam or go over-centre. Can you feel any slop there? There should be none to speak of. Unfortunately it's really hidden and probably impossible to actually see while the turbo is on the car. A mirror might help.

The vacuum actuator can play up, but I suspect not, if it works as normal once you've given the VGT a nudge.

Rust in the turbo was what was causing my vanes to jam toward the vanes open/rod forward position. Mine opened OK but were jamming on the rust so they were reluctant to close, so I had overboosting rather than underboosting and black smoke. See the photo. Your rust may vary, of course.

If you can, try the vacuum pump check I suggested so you can be sure whether it's a sticky turbo or fault on the vacuum side.
 

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