Technical JTD - Extreme Turbo Lag!!

[Argonought]

Well it had to happen didn't In nearly 3 years all I've had wrong with my Stilo has been split overboost tubing and a single brake light bulb :spin:

Now I seem to have a real fault and I have to admit it's got me foxed :chin:

Basically, all that wonderful torque JTDs are renowned for is completely missing on mine until I'm well past 2.5k Hit 3k and it pretty much takes off like a goddamn rocket. The car's no fun to drive though. Change a bit too early (before the red-line) and you fall back into turbo lag land In other words you either feel like you're driving like a snail or like a bat out of hell :devil: By extreme lag I mean if you floor it at 60mph in top then any passengers in the car will mostly likely think you've just engaged cruise control

Whatever the cause, it's been gradual and certainly not sudden. I first noticed it when the engine didn't quite offer the surge I was expecting but since it still flies if you drop a gear then initially at least I've tended to put it down to driver error.

I've changed the overboost valve and blocked off the EGR so both of those can be discounted.

No engine faults at all but I'll check for stored codes tomorrow. I'm also going to disconnect the MAF and if that fails carry out an ECU reset.

It feels to me like the vanes in the VGT are maybe caked in soot and stuck half open but I'm hoping not as that sounds expensive :bang:

 

[john55]

Could be your MAF. Try with it disconnected. A lot of other makes behave like this with a failed MAF.

There is nothing in the turbo to get caked up. They run too fast for that. When I took my turbo apart after it died, it was very clean, even after 100K miles. The vanes are also not variable in the turbo. i.e. they do not move. I think it is something cleaver that directs the airflow over different parts of the vanes at different speeds. The vane is called variable because it has a varying pitch over its length, not because it moves in the way a variable pitch propeller on an aircraft does.

If it is the turbo, it is probably the waste gate stuck open, or could be a split pipe somewhere else in the system.

It could also be the ECU limiting fuel for some reason which would give the same effect.

Does the turbo sound normal?

 

[ABZSTILO]

Interesting, did it start off as a bit of a 'flat spot' around 2.5k revs by any chance

 

[Rackham115]

Interesting, did it start off as a bit of a 'flat spot' around 2.5k revs by any chance

i have to say iv got a 'flat spot' at around 2.5k as well. could this be the start of something more serious???

 

[Argonought]

Bit more info but it's not looking that good.

No error codes stored.

Disconnected the MAF and it's produced quite a change but not for the better. The 'turbo lag' seems to have disappeared until you realize there isn't much torque available to have any lag over anyway. It climbs through the rev range pretty smoothly (no flat spots) but just rather leisurely The peak power that was available now seems to have gone (it may have been down a bit on its peak mapped performance anyway)

To put it into perspective these are the performance figures which are strangely far worse than it feels:

• Now: 40 to 80 in 4th = 25 secs
• As standard (pre remap): 40 to 80 in 4th = 15 secs
• After remap: too damn scary to use a stop-watch

I'm currently reseting the ECU (I'll give it an hour or so).

There is nothing in the turbo to get caked up. They run too fast for that. When I took my turbo apart after it died, it was very clean, even after 100K miles. The vanes are also not variable in the turbo. i.e. they do not move. I think it is something cleaver that directs the airflow over different parts of the vanes at different speeds. The vane is called variable because it has a varying pitch over its length, not because it moves in the way a variable pitch propeller on an aircraft does.

If it is the turbo, it is probably the waste gate stuck open, or could be a split pipe somewhere else in the system.

Many thanks for the insight on that (and a little bit of reassurance) I'm still confused when you use the term "waste gate" though as I thought the VGT ran fully open (exhaust gases flowing without restriction) to produce the same effect. As I understand it, that would be when the overboost valve connects the actuator fully to the vacuum reservoir.

If you mean you think the actuator is stuck then that would make a lot of sense to me (not that anyone has ever reported that problem). I've tried pulling it but it can't easily be shifted and didn't want to use too much force :chin: Any ideas how to test it?

It could also be the ECU limiting fuel for some reason which would give the same effect.

Certainly feels like that although mpg figures aren't brilliant

Does the turbo sound normal?

No much to hear really but if you mean a whoosh from a split intercooler pipe then I certainly can't hear anything - but I'm tempted to have a look anyway :chin:

 

[john55]

Bit more info but it's not looking that good.

No error codes stored.

Disconnected the MAF and it's produced quite a change but not for the better. The 'turbo lag' seems to have disappeared until you realize there isn't much torque available to have any lag over anyway. It climbs through the rev range pretty smoothly (no flat spots) but just rather leisurely The peak power that was available now seems to have gone (it may have been down a bit on its peak mapped performance anyway)

You have a dead MAF.
You described exactly how the JTD should run with an unplugged MAF. They seem a bit down on power with leisurely acceleration. That is normal for no MAF.

I wouldn't know how to test the turbo but as far as I know they are very reliable up until they self destruct due to the bearing collapsing (like mine did).

 

[Argonought]

You have a dead MAF.
You described exactly how the JTD should run with an unplugged MAF. They seem a bit down on power with leisurely acceleration. That is normal for no MAF.

I wouldn't know how to test the turbo but as far as I know they are very reliable up until they self destruct due to the bearing collapsing (like mine did).

Thanks for that

I'd always thought the JTD ran with full turbo with the MAF disconnected and hadn't realized it ran the engine with (substantially) reduced performance

....mostly likely because I never actually booted it :chin:

Certainly, the car feels more normal with the MAF disconnected then with it connected and you could most likely drive for a long time without noticing anything was wrong (unless you were in a hurry )

Hopefully a new MAF might improve mpg figures too

 

[john55]

Thanks for that

I'd always thought the JTD ran with full turbo with the MAF disconnected and hadn't realized it ran the engine with (substantially) reduced performance

It does run with the turbo, but just injects less fuel as it does not know how much air is actually going in. It underestimates it by quite a lot to keep emissions within spec even with a dud MAF.

Diesels are different to petrol engines. They do not require precise air / fuel ratio control like petrols, hence no butterfly valve or dump valve.
The diesels work on the principal of stuff as much air into the cylinder as possible with a turbo, then inject the quantity of fuel needed to give the power required.
The ratio of air / fuel is not particularly important, just the fuel quantity. If you are getting to the limit of fuel to air ratio you get black smoke, but you can never run a diesel too lean like you can a petrol engine.

 

[Argonought]

OK, so it's not the MAF either :bang: Fitted a new one and basically made no difference at all

Weird thing is the engine feels OK, aside from obvious turbo lag but clearly isn't.

This is how bad it is:
Pre remap figures
3rd 40-80 9.9 secs
4th 40-80 15.2 secs

Now (remember this is mapped)
3rd 40-80 11 secs (even in this range you can still feel the lag)
4th 40-80 20.5 secs (horrendous lag but starts to fly as it hits 80)

I suppose I could check out the MAP sensor but starting to run out of ideas on this one.

EDIT: Just been chatting with Angel Tuning and they reckon there's a fair chance the CAT has failed (or already failed and now starting to really fall apart) and that a remap can be the last straw if it's already on the way out.

This makes sense to me when you consider it's nearly 6 years old and the degradation in performance/economy has been gradual.

Anyone want to comment?

 

[bozzy]

Not a lot to say Argo apart from bad luck. What sort of cost you looking at?

 

[adamcot]

A cat failure can be detected quite easliy, although im not so familiar with the JTD unit compared with the 1.6 I had... (Although I should be, having the same engine in my GP ) Can you hear a rattling when you tap the exhaust? Or can you smell anything funny? This is what I was told to look for when I had cat problems with my Stilo

On the turbo side, it shouldnt get dirty on the vanes (or enough to stop them moving...) If it is, you would be very unlucky and you might need the turbo reconditioning, which will be cheaper than a new unit!

 

[custard]

wouldnt an emmisions test give an idea if the cat was failing?

 

[Argonought]

Sorry about that Bozzy - got more buttons to hit now

Not that bothered about cost to be honest but like you always used to say - it's no fun when you can't get a buzz from all that torque

Funny thing is, most folk would say it was OK if they'd just got in and driven it for the first time - doesn't even produce any smoke worth mentioning.

I'm taking in to my local Fiat garage for a hook up on Examiner tomorrow to get both the Lamda and the CAT checked.

 

[D4nny8oy]

Very strange- it's the classic symptoms of an EGR valve stuck open (which 'bleeds' air off the turbo until the gasflow at higher revs is enough to spool it up), yet you say you've blanked the valve off (which should've restored the performance)?

A blocked Cat would strangle the engine at the top-end, it shouldn't just have 'lag'- it would struggle to make boost at all. We had a 1.3 mJet with a collapsed cat that wouldn't rev past 3k with no boost whatsoever.

 

[D4nny8oy]

And JTD turbo vanes do move, and there's no wastegate- there's no need for one as the vanes (2) control the airflow over the turbine and therefore it's speed-





Argonought- If you want to see if the actuator is operating, get someone to rev the engine while you watch the actuator rod- it should move about 10mm. If it's not, try pushing it downwards carefully with a large screwdriver- if it still won't move then you've got a problem here.

On cars that are driven gently, or have stood-up for a long time, I've known the vane mechanism to seize from corrosion. Though if yours is remapped- I'd be surprised if this has happened.

 

[Argonought]

Thanks Danny

I've managed to move the actuator a little (maybe 10mm) but it takes quite an effort (doesn't feel stuck though). I think I'm right in assuming that it produces max boost in its default position i.e it needs a vacuum to kill the boost as the ECU activates the VGT valve to kick in at higher revs.

The engine red lines real easy, and still puts on a good show at leaving other stuff behind, so you've got me thinking it can't be the cat after all - but the lag as the figures show is truly dire. As I've said before the car feels faster than the figures show. What's missing most is that lovely turbo kick you normally get around 2k rpm (which you get even on a standard JTD).

I'm absolutely adamant this has been a gradual process that maybe goes back as far a 18 mths - it just that the lag has now become distinctly more noticeable. I'm also convinced it's linked to a gradual degradation in fuel economy.

I'm forced to drive around town for extended periods and the engine can go for weeks on end without getting a good workout (plus I tend to use an economical style most of the time) so there might be a clue there too. Once out of town, usually give it a good blast once off the motorway though :devil:

Hopefully get some answers tomorrow (and how many have said that before )

 

[ABZSTILO]

I wonder if it could be fuelling related..... speculation on my part but on a boat with twin marine diesel engines I worked on last year, one engine was very lethargic to give even revs and was smoking badly.

Spent a bit of time with the boats mechanic (as I like that sort of thing) and we found it was two faulty injectors and a blocked fuel filter. Changed them all and it ran as sweet as you like.

Now I only mention this as I can't think of anything else off the top of my head that I've come across that's remotely similar to the symptoms Argo describes.... except for a turbo on the way out

 

[john55]

Common rail injectors are notorious for failing. They tend to wear and then drizzle fuel in rather than spray a fine mist. This causes poor running and more smoke. You could try an injector leak off test.

 

[2ippy]

I had turbo lag on my JTD punto once, turned out to be the sensor.

 

[Argonought]

Eureka!

Took the car down to Italian Car Spares this morning and lead mechanic Jamie got to work with Examiner.

Started off by giving him a demo of the problem and it seemed clear to me he wasn't convinced there was too much wrong with the engine. When we got back he checked everything (other than what I'd checked myself), checked the cat, the intercooler ducting, induction, removed stop valve (not that dirty). checked MAP sensor. Checked actuator.

He tried just about every test that Examiner could be set to do but everything came back good. About the only clue was that boost and air-flow were quite a bit different to what Examiner predicted (car producing less boost than predicted) but the general view was that the map might be having an affect on these figures.

After about 3 hours it was looking pretty dire with every idea having been exhausted and me thinking "there's only the turbo left"

All I'd discovered in that time was my JTD has 16 valves, 2 cats, doesn't have a lamda sensor (should have remembered that ) and has never been over-revved (little snippet of info from Examiner there)

Then, just as everyone had pretty much given up, he found the problem He was bending the tubing from the actuator, from underneath the car, and discovered.....

cut in half across the damaged area​

The tubing from the actuator had a crack in it that was only visible if you bent the tube. This tiny crack must have been getting very very slowly worse and worse over the years but never let enough air in to cause a boost fault (engine fault) or any error code.

With tube replaced, took it out for a spin and Wow!

4th 40-80 10 secs :devil:

Summary
OK, so it's cost me a good couple of rounds of drinks to get this fixed but at the end of the day it wasn't Fiat's fault but was down to the dealer that moved the overboost valve up by the battery. I'm now seriously thinking it might have been better if it was never moved in the first place since I've now had two issues and both have been due to defective tubing :bang:
As I matter of interest the newer VGT valves seem to be a lot more waterproof and I suspect they've most likely been modified for 'wet' use down under the headlamp .

Therefore, amazingly, in 3 years: Total faults = 3 glow-plugs + 1 brake light bulb :spin:

... and a final big thanks to Italian Car Spares (01202-660678) for a great piece of diagnosis