Technical JTD power loss symptoms

[Argonought]

Very interesting post

A blocked shut EGR valve should have minimal effect on an engine except it would seem when it blows fuse F11

Glad to hear it's sorted

 

[multihull]

Yes, fuse F11 has the Turbo Boost, Accelerator Position 1 and mass air all in is circuit. So theres nothing to operate the circuits for the ecm to give voltage to the turbo boost. There are some others but they did not seem to effect the loss of performance.

I would have thought that it deserved a better description than secondary injection functions.

 

[thetoilet]

Hi there,

I have a similar problem, but my car smokes like crazy when i rev it,but it will not rev over 3000 rpm. it is a turbo diesel punto JTD.

i have a couple of threads running for diferent reasons, and i am making progressbut just wondered, did you get white smoke when yours reved up?

 

[thetoilet]

my problem was a blown turbo... nasty.... sorted now

 

[Hydrocw49]

Hi there, I appear to be suffering some of the same symptoms, appreciate any advice/steers:

During last weeks snow I started to suffer power losses when cold from startup, which once engine revs were upto 3000, power would kick back in (interesting drive in snow and ice)after approx 25 miles all seemed to settle down with power available all through rev range. The only fault codes present were P0101 (Mass meter) and P0235 (boost pressure).

Following advice within the forum the boost pressure solenoid (in nearside wheel well) has been checked as dry (i've had this wet from driving through puddles in the past). Both fault codes were reset and have not re-occurred. The EGR valve has also been removed and cleaned - its done 100k and was almost totally choked - not easy to remove from back of engine, but easy to clean with Wynns EGR valve cleaner.

Car still suffers identical power losses/lag and no fault codes present! Loss of power makes driving pretty scary, especially pulling out of junctions - so not prepared to drive for longer distance to see if things improve. Power comes in randomly anywhere between 2800 and 3500 rpm and once in stays in.

I'm using the Fiatecuscan diagnostic software and checked all the monitorable parameters and have noted that the desired air flow and actual flows do not match - typically tickover required 280, actual 28/30, at higher revs the gap closes but is still along way out, ie required 500, actual 120. Thought it could be the mass air flow meter - disconnecting loom had no affect, fitting an old one replaced 18mths ago, made things worse - a diesel that pinks!! So I'm pretty confident that its ok.

Further diagnostic checks reveal that the boost solenoid activates anywhere between 2800 and 3500 rpm and coincides with power coming in. .....boost solenoid removed from car and left in airing cupboard overnite to dry out - its been replaced in 18mths ago after driving through a large puddle!.....refitted with no improvement - now suspect it is the solenoid that is defective, although still no fault codes present.

Any other possibilities? Is it worth bypassing the boost solenoid by connecting the vacuum pipe direct to the turbo actuator - assume this will provide maximum turboboost - is this likely to cause any damage?

Hydrocw49

 

[Argonought]

Any other possibilities? Is it worth bypassing the boost solenoid by connecting the vacuum pipe direct to the turbo actuator - assume this will provide maximum turboboost - is this likely to cause any damage?

I wouldn't do that although well worth looking for leaks in tubing (vacuum gauge makes it easy to check).

Have you checked the MAP sensor (on manifold) ?

 

[Hydrocw49]

Argonought thanks for the advice - Plan to check the vacuum pipework tonight, a kindly neighbour works for a Toyota main dealer so has access to some decent gauges. Will also check the MAP sensor - apart from obvious connection issues, is there anything else to look for, presumably if i remove it from the manifold i can clean it.

.....No vacuum gauges available tonite. MAP electrical connection checked ok. Have also checked the diagnostic results taken a couple of days ago. They all indicate that the actual boost pressure is always within a few millibar of the desired boost pressure - I'm assuming that the actual pressure is recorded via the MAP, therefore believe MAP is working ok. Is my assumption on MAP function correct?
Hydrocw49

 

[Argonought]

Have also checked the diagnostic results taken a couple of days ago. They all indicate that the actual boost pressure is always within a few millibar of the desired boost pressure - I'm assuming that the actual pressure is recorded via the MAP, therefore believe MAP is working ok. Is my assumption on MAP function correct?

I think that might be a dodgy assumption (although could easily be wrong) :chin:

If MAP if faulty and is returning high pressure readings to ECU then the ECU will back off the VGT valve to compensate and may not be aware of any issues with the engine.

I know Examiner can predict MAF readings but not sure about MAP predictions.

 

[Hydrocw49]

If MAP if faulty and is returning high pressure readings to ECU then the ECU will back off the VGT valve to compensate and may not be aware of any issues with the engine.

All of the actual readings are less than the desired figures - and seem to accurately lag just behind the desired figures. Looking at all the captured data over the last couple of weeks, the MAP figures have been very consistent, although engine performance is gradually getting worse, therefore still believe that MAP is OK. This brings me back to the VGT/Boost solenoid. This was replaced 18mths ago, but remained under the headlight! I know I've been thorough several large puddles over christmas/New year - so suspect that this is the problem - the actuator test on FIATECUSCAN confirms that the solenoid operates, but not whether vacuum is applied to the turbo (still dont have access to the vacuum gauges!).

When the VGT is resited to the battery box, is it rubber mounted? The original mount under the headlight incorporates a double mount that isolates the solenoid.

 

[Argonought]

Quite a good image in this thread:

https://www.fiatforum.com/stilo/77193-engine-fault-sensor-fault-jtd.html

 

[Hydrocw49]

Probelm solved.....it was the boost solenoid valve. Proved it last night by checking the vacuum, eventually connecting a hand held vacuum pump to the turbo actuator, applying full vacumm and then taking it for a spin - result, full power restored. Running like this does however trigger P0235 boost fault to occur (detects that boost solenoid is at fault). New solenoid installed this morning and normal engine performance restored.

Thanks for all posted advice

PS solenoid now fitted on side of battery box - will post some pics later