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Hello, and oh dear -- boost pressure.

35K views 94 replies 27 participants last post by  zverx 
#1 ·
I have been reading the 'threads' (or whatever) about the possible causes of the power going 'flat' with my 156 2.4 jtd when overtaking or when asking the engine to work hard and at mid range (2800 - 3000 rpm) just when changing up a gear. This coincides with the 'motor control system failure', 'go to dealer' icon appearing on the display screen. When connected to a snap-on computer it showed up two codes; EGR valve, and Boost Pressure. Initially I removed and cleaned the EGR valve but that made no difference. I then bit the bullet and bought and replaced the EGR valve but still the 'motor control system failure' showed on screen. Reconnection to the computer still showed two codes until we zeroed the codes, blasted the car up the road until it again showed the dreaded warning and then reconnected to the computer. Only one code showed up -- boost pressure. So now that the EGR fault has been eliminated, I have to turn my attention to the possible causes of high or low boost pressure.:confused: Having read some of the posted comments on this forum, I am realising that the variable vanes within the turbo might be stuck. But before I (or the garage) go wading into the turbo my questions are these - would the boost pressure have damaged the EGR valve or vice versa, would these two faults have in anyway damaged the ECU and does anyone out there have any further points of view on this problem? I apologise if this problem is one that has been discussed at length previously, but any Alfa owner who is suffering with this fault knows how frustrating and dangerous it can be, so all help will be appreciated. Thanks in advance.
 
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#3 ·
Hi, Nick

First, EGR or other components do not get damaged by the over boost problem.

Secondly, ECU’s rarely go on any car.

The variable vanes work by directing more exhaust gasses on to the turbo wheel.

In simple terms;

Little wind condition (tick over, low rpm) = You turn your windmill into the wind to make it turn faster.

Loads of wind (higher rpm) = Once your Windmill reached full speed, you turn it away from the wind to protect it from over spinning.

On your car, this is done via vacuum.

At low RPM (tick over to around 2200 rpm), the vanes are set that the Turbo spins faster.

After 2200 to 2500 rpm, the Help of the vanes is tapered off, as the max speed of the Turbo is reached without extra exhaust flow.

Over boost comes if you still have vacuum after the 2200 rpm limit OR the vanes are stuck in the max boost position.

A boost pressure sensor in your inlet manifold measures the Turbo boost.

If the boost is to high the ECU cuts the injection of fuel to protect the engine.(Engine light comes on).

The vacuum is controlled by the VNT solenoid.

(Bolted to the slam panel, next to your bonnet catch).

The VNT is a 3 way valve,
1.vacuum-in
2.vacuum-out
3. vent to the surrounding air.

Once the cut-off point is reached the vacuum-in is blocked and the vacuum-out is flooded with air from the air vent.

Neutralising the existing vacuum in the pipes to the Turbo advance mechanism.

How to test;

Pull the rubber pipe from the VNT to the Turbo actuator and block it off.(Small screw or similar).

Go for a spin,

If the car pulls like normal up to around 2000 – 2500 rpm, that would point to stuck vanes on the Turbo.

Why?

No vacuum = fail save setting of the Turbo is vanes in park position = no extra boost.

IF the car pulls slowly up to around 2500 rpm, but comes on boost AFTER the 2500 rpm.

The car should rev now right up to the red line if pushed without the Engine light coming on. :)

Then this would point to the VNT as the fault.

This simple test can point you in the right direction.

best regards

Mike
 
#66 ·
Many thanks to you Mike (Got one two) - my turbo was all gunked up, stripped and cleaned but still suffering some problems due to engine light popping up and cutting me to 3500rpm / half power
Checked everthing out after reading your thread and found small split in hose from solanoid valve to turbo - now engine running the best it has in ages
Cheers
 
#4 ·
Thanks to Mike of Got one two. I'll try the simple test, but being the eternal pesimist I want to ask if you have experience of reconditioning the stuck vanes within the turbo? What might I use to ease and clean the pivots of the vanes? I have (from my eLearn CD) located the VGT solenoid should it be as simple repair as that.
 
#6 ·
There might be a relatively simple way of cleaning the turbo.

I am investigating that in the moment.

A company in Salisbury has a Turbo cleaning kit on offer.

This kit is sold to workshops only at the moment it appears.

It’s a gel, you fill into the Turbo after taking the short exhaust pipe off and blank the turbo with a bit of card board.

(The card board is used to be able to fill the Turbo up to the rim).

After one hour you replace the Gel with a neutralising solution to remove the gel (and gunk) from the turbo.

The kit is called Turbo clean and is made specifically for variable vain Turbo’s.

Innotec Supplies Ltd. - Turbo Clean Set

If that works, that could be just the ticket. :p

Even if you have to pay your trusted indie to do the job, perhaps 2 hours labour?

Perhaps even once all two years as preventive maintenance???

Hope that makes sense.

Mike
 
#7 ·
theres some really good advice above, the vnt/overboost module-the solonoid in it can stick, its a pieburg unit and is about 40quid to replace.

It could be a small split in a boost pipe or hole in the intercooler, a small hole need not cause noticable black smoke (as diesels run lean anyway) but could still be enough for the ecu to keep trying to compensate for loss of pressure, the ecu then gets to a point where its out of parameters and puts on the mcsf light,

I have experienced this myself, even cruising when you get close to 3,000rpm.

So a no-cost option is to remove and check the boost pipes by tugging and pulling them as small holes can be really hard to see.
Also, check the IC for leaks too.
 
#8 ·
I've been living with this problem for months now and just haven't got around to properly getting a garge to investigate, but after this thread I will follow Got One Two's advice and perform these checks. I like the sound of the Turbo cleaning kit too. As suggested a good clean every couple of years can only be a good thing.


Thanks :thumbs:
 
#9 ·
Have you tried cleaning the MAP sensor ... could be that that is just provided the wrong readings to the ECU ...
 
#10 ·
Chris is absolutely right, regarding the MAP (inlet manifold pressure sensor).

The little Test with vacuum pipe off can test the MAP (up to a point) as well.

How?

If the MAP is duff, you would still get the Over boost signal with the Engine management light coming on, but at a later stage at @ 4500 -4900 RPM.

The engine management light will stay on, even after the revs drop back down.

With a solenoid fault the engine light comes on at @ 2500 – 3000 RPM, AND goes off again once the RPM go down below that limit.

Another give away of a problem with the VTN is a frightening noise from the Turbo on over run. :eek:

Depending on the severity of the over boost pressure.

This noise comes from the Turbo blades “chopping” true the “Surplus” air not getting (out of the Turbo housing) into your engine.

I have been told that this “chopping” does not harm the Turbo.

Still, I am not convinced that the Turbo bearings will take that rumble indefinitely. :rolleyes:

best ragards

Mike
 
#11 ·
Hello again Mike at Got one two, bit of a delay due to internet provider playing silly sods, but I tried out the test that you suggested. Well ,I removed and blanked the pipe and began to drive off. EEEEh gods, it was like driving my first Morris MInor all over again; very lethargic up to about 2500rpm then it started to pick up speed as I might have expected at those rpm. At about 2800-3000 the dreaded warning appeared and stayed despite me dropping the engine revs and bringing the car to a halt. Reconnected the vacuum pipe and drove off with the warning still displayed on the screen. I raced the engine up to the revs at which the warning would normally have come up, then the engine was being restricted again, and as the revs dropped the warning display disappeared. Now, I'm thinking that the turbo vanes might be OK but please correct me if I'm wrong. I did notice that when I pulled the vacuum pipe from the VNT there was a momentary delay before it emitted a 5 second long hiss. This weekend, weather permitting, I'm going to check the MAP sensor and check that the air filter was changed at the last service. Regards from bewildered Nick
 
#12 ·
Hi, Nick

I doubt that your vanes are stuck, as you would notice power right from tick over with the vacuum disconnected.

Your Turbo is fine. :thumbs:

As you say, everything points to the MAP, but do not discount the possibility of the MAF giving wrong readings too.

The VNT is controlled by the ECU, using input from the MAF and the MAP.

Both signals have to “make sense” (to the ECU) to operate the VNT correctly.

Hope you get to the bottom of it soon.

Best regards

Mike
 
#13 ·
#14 ·
Back again, hello Mike of Got one two. I took out the MAP sensor and cleaned off all the black carbon goo using a q-tip to gently remove the goo from down inside the orifice. Replaced the sensor and renewed a rather filthy air filter which was supposed to have been changed 5000 miles ago -- I don't think so! I road tested the car to find only a slight difference --- it would rev up to about 2800-3000 before the warning would come up on the screen. But, it would allow me to continue accelerating albeit sluggishly. The engine also seems to be a bit freer(?) possibly because it is breathing easier.
I hooked it up to a computer to zero the codes before running it again to see if that would make a difference. It did; initially the warning came on at its much earlier rev band but that gradually went up as I accelerated time and time again. Strange! I connected to the computer to see what this test run had thrown up and it came up with two codes. PO235 boost pressure, and PO236 over boost valve cicuit (or something like that). The explanation for both of these included a referrence to the MAP sensor. So, now I'm thinking I will replace the MAP sensor unless anyone can recognise these codes and the cause of them being thrown up, or can suggest an alternative remedy.:confused: Auld Nick
 
#15 ·
Hi, Nick

The “strange” getting better and better as you drive could be caused by the ECU re-learning the new running settings (after you cleaned the sensor, it has to re-learn the readings).

This is normally done by an ECU re-set after any sensors being changed.

Over boost valve is the VNT solenoid.

That caused my problems with over boost.

Check that the electrical connection is on properly and not corroded in any way.

The VNT can be actuated by some test button in the ECU test software on the laptop.

But I have no clue on how to be honest.

all the best

Mike
 
#16 ·
Hello once more to you Mike of Got one two, hopefully I'm nearing the end of this saga, but hey, there will be something else to sort -- it's an alfa. OK, so now I have the parts, the vgt sensor (as alfa call it) and a MAP. Before I fit these, do I have to zero or reset the car's ecu or computer first, or can I just fit them and reset things later?

Perhaps I should look on the 'menu' of threads for advice but I'll ask anyway (I did say there would be something else to sort). The LCD display on top of the dash starts out OK but gradually turns pink and then red so that you can make out very little of the warnings or advice, any thoughts, is it just needing replaced? Any reasonably priced units out there?
Thanks again Mike, regards Auld Nick.
 
#17 ·
did you try driving the car with the MAF disconnected?

i know the error light will come on BUT it might rev better across the massive 4800 rpm range:eek:
 
#20 ·
Hello to fishy-steve and hermann,
Well I have fitted the VGT sensor and the MAP but have not as yet zeroed the computer. There has been a definite improvement in that the engine will now rev up to about 4000rpm before the engine management warning appears. I'm hoping that this will disappear when the computer is zeroed. However, I it may throw up another code which I'm expecting to be the MAF (air flow meter), but they are cheap enough on ebay.
On hernann's point, I have already replaced the EGR valve but I am thinking that I will have to at least clean the turbo.
Unfortunately it is a busy time of year so finding the time to do the various diagnostics is difficult. The next computer plug-in will tell me a lot. I will let you know what I find.
For Steve, I would advise you to go and get plugged in to a computer (not a Bosch) to see what codes are thrown up and go from there. It's all very frustrating, but imagine what I would have had to pay if I had put it into an alfa dealer?
Regards, Auld Nick.
 
#21 ·
However, I it may throw up another code which I'm expecting to be the MAF (air flow meter), but they are cheap enough on ebay.
Just a word of warning ... the cheap ebay maf's general either don't work or will only last a couple of weeks ... best to get a genuine bosch one I'm afraid ..
 
#22 ·
Very interesting and useful thread :)

OK, so my 114k JTD was remapped at red dot at about 101k. A while back I noticed acceleration below 2200 - 2500 rpm was getting poorer. Once it got to 2500rpm it would take off like a scolded cat.

After much hastle I have cleaned and replaced the MAF. I then sat in the car on the drive for 5 min ticking over and then drove out. No power at all, throttle position made no difference. Ran like that for about 3 mile and suddenly there's a thump in the back and it starts going OK. Drove the 3 mile home, pushing it and leaving lots of smoke. That was yesterday.

Today, went out and no power again though a few bumps as it seemed to go/not go. Stopped and sat on a verge with engine ticking over for 15 min. Then drove off leaving a huge cloud of black/grey smoke. Went like a a bat out of h*ll but every time I slowed for a junction and moved away it would leave lots of smoke up to about 2200/2400 rpm then the rear view looked clear. Would rev up to 4500 without problem or any fault message. What would you say this fault is now? MAP or VNT solenoid?

My EGR valve is original and un-molested by me :rolleyes:

Some more questions: what does N/A mean? refering to cars

What is the fail condition of the VNT? No vacuum allowed to the turbo or the other way round. If allowing vacuum all the time (over 2200rpm), this would result in overboost fault?

How do you reset the ECU?

Thanks for answers. Jerry
 
#23 ·
N/A means normally aspirated ... i.e. non-turbo ... good luck getting it sorted ...
 
#25 ·
Hi, to all

Jeronimo, your problem seem to come from the EGR.

Why?

At idle, the EGR opens to let exhaust gasses back into the inlet.

IF the EGR stays open (stuck due to sod) your Turbo boost goes out via the EGR.

The Sod build up is worst on re-mapped cars!

Result; ECU chucks loads of fuel in expecting loads of boost.

Black smoke from the excess fuel and no go from the missing (escaped) Turbo pressure.

The On/off effect comes as the EGR closes some times and not at other times.

So nothing a can of carburettor cleaner can’t fix (£7.95 for the cleaner and some dirty hands.)

Auld Nick

After checking all the other options, I would try a new MAF.

The Alfa Part is expensive @£190 for a re-boxed Bosch unit.

If you order the Original Bosch part from Auto Factors it cost @£101 inclusive of VAT.

I would avoid the Chinese offerings for £29, as 156Chris mentioned.

They just not worth the aggravation, as they appear to go out of spec within days (Thermal problems I was told.)

If money is tight, you could get a Magnet Marelli unit @ £52-£55 form some out lets.

For the 10V CF3 engines the MAF Part numbers are:

Fiat/ Lancia/Alfa Romeo Part No : 46559804

Bosch Part No: 0281002309

Magnet Marelli Part No: WAM512

best regards

Mike
 
#26 ·
Lots of advice there, cant tell wothout looking, a few pointers to help, that you may or may not know.

The MAP sensor is Manifold Absolute Pressure sensor - incase you hear the term and think its something else, as the car has an air mass meter (MAF) the MAP is used to control boost not atmospheric volume measurement like ye olde motronic.

Personally, I think you have an EGR issue, or one of the smaller hoses is split to the actuator or a breather/EGR.

PLEASE dont touch the turbo vanes, if they appear to feather at all under control from the actuator, thats better than monkeying with them, honest.
 
#27 ·
ABSOLUTELY :cool:


Mike and CJ, brilliant. Thanks very much. :thumbs:

When the sun comes up and I can see outside, I will take a look and do some more cleaning. I will pull the MAP also and clean that too.

I know that I do have oil present in my inlet manifold. Quite how so much gets there when I do not need to add oil between services is a mystery :confused: A little goes a long way, I guess.

Ta, Jerry
 
#28 ·
Well my saga contiues so I apologise to Auld Nick if I am hyjacking your thread.

I did not have time this morning before going out to clean the EGR but I did fit a blind to blank off the flow. A gasket shaped piece of 1mm stainless steel in place of the gasket at the EGR outlet flange with the metal flexi pipe joining it to the inlet chamber.

That has stopped the smoke :thumbs:

But I have absolutely no power. Engine will not rev above 2300 or so and any slightly significant obstacle to get over at slow speed requires max revs available and a slipped clutch to get up it :tut:

Got home and tried bypassing the VNT solenoid but this made no difference.

Took out the MAP sensor. This was well gunged up so I cleaned this with the deposit free cleaner used on the MAF. Again, on starting the engine - no difference. I'm going wrong somewhere so I guess I need to get my car to a mechanic with a computer.

Do I need to reset my ECU somehow? How is this done?

Do I just need to get any fault codes cleared from the ECU? I have had no messages on the display - since the ABS / EDB messages encountered during the snow. Any further advice appreciated.

Thanks, Jerry
 
#29 ·
Have you tried disconnecting the MAF???
 
#30 ·
Jeronimo..

First try to disconnect the MAF.

Then

Try bypassing the VNT.

Connect the vacuum line coming from the Metal pipe just below the engine plastic cover straight to the turbo actuator.

Vacuum all the time = Turbo on full boost at low rpm.

IF you have vacuum in the first place that is.

Still no power?

Is your Turbo spinning? Are the Turbo pipes Ok (no splits or cuts).

Look again, what have you “disturbed” when doing the EGR (if it’s worst then before?) EGR plug back on?.. things like that..:rolleyes:

Diagnosis over the internet is a tricky business..

all the best

Mike
 
#31 ·
Thanks again for the help, fella's. It's been a frustrating time for me, what with being dumped out of my job by another company reneging on its promise of work for me, PC problems with my old PC (this one) now my new laptop won't boot up and the car :(

Ah well, possible result at last.

Cleaned the EGR. Got about an egg-cup full of carbon out from the space between the solenoid and the valve. Could not get the valve out of the body so cleaned as best I could and re-assembled and replaced on the car without the blank in the gas flow.

Engine starts and runs OK but will not pick up revs. No smoke but stuff me foot down on the peddle and the speed slowly builds to 3000rpm. Gets out of the car and switch the engine off through the window and dive under the bonnet. There's a click and a hiss as vacuum is filled and the turbo vane actuator strokes out. So that solenoid is OK.

I then pulled the plug on the MAF (why do they all have different locking methods :rant: )

Started and engine is a rough as can be but revs up OK but with lots of smoke. So it looks like a dead MAF after all :rolleyes:

Am I right?

do I need to do an ecu reset with a new one? If so how. (be appreciated if someone would answer this question - ta)

Thanks for the advices. Jerry
 
#34 ·
Don't know about the 15min idle, but when you take it for a drive you need to thrash the locks of it!

Why?...The sensors need to show the ecu there full voltage capacity, ie. 0-5volts, driving like your gran, or even some peoples version of a 'spirited drive' may not show the ecu the full 0-5volt (base to maximum) scale.

Rag it a few times through the gears and the ecu will not need the extra 40 miles or so to learn.
 
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