Technical Multiecuscan readings, trobleshoot bad start

[aurick86]

Hi guys,
I'm having some difficulties with may car Bravo t-jet, basically it starts ..goes ok for 3-6 seconds then stalls/dies on cold starts a few times and no power for 2-4 minutes till the engine warms up... then it's great.
(no stored codes)
This is a problem that got worse and worse over time. Now i also feel a slight power lose at the top end. The car seems to come on boost not as smooth as it once did.

It feels like there is not enough fuel, but i checked the fuel pressure at the rail, and the pressure is right about where fiat specifies .. and does not drop or vary more than it should.
I have been monitoring the engine parameters with MES,,and to be honest i did not find anything out of place like the coolant temperature or air temperature, the MAP sensor seems to be ok also.

One thing that does not seem to be ok are the reading for "Desired boost pressure" and "Boost pressure".... in my understanding these two values should be relatively close to each other...but mine shows a "Boost pressure" value of ~1084mbar +/- a couple of hundred mbar .... this is totally different from "Desired boost pressure" value that is sometimes as low as 200 mbar and varies a lot. Could this cause a bat start?

Can anybody with a t-jet post their values for those two parameters? a graph might also be helpful.
Any other suggestions are welcomes.

 

[aurick86]

Forgot to mention, battery voltage is ok ( never drops below 10,80 volts even when cranking) and i have recently replaced the spark plugs.. but it did not improve the cold starting

 

[portland_bill]

My guesses:
a) Air leak in the induction system.
b) Idle control sticking.

a) Check all the pipes and hoses, from air cleaner to turbo, then all the way from there to the inlet manifold. Extra air leaking in will weaken the mixture and confuse the fuelling. Air leaking out would usually cause richer running. A flammable spray like WD40 at the joints, with engine running, should show signs of blowing out, or will cause the engine to change if sucking in. Don't get it in your eyes.

b) I don't know what controls the idle sped on your model, but hopefully someone will advise later. Most have some sort of valve controlled by the ECU. These can get a bit sticky and require freeing off, often carb cleaner will sort it.

 

[aurick86]

Thanks for the reply:
a) i would think a vacuum leak would be shown as a good increase in long term fuel trim, but it's situated at around 3% which is more than reasonable.

b) already cleaned the throttle body, it was a bit dirty, but cleaning it did not solve the problem.

As i said the major problem of stalling is only apparent when cold starting.. and only once or twice... then it goes back to normal.. except for bogging down/lack of torque for the first 2-3 minutes.. I was considering a fuel supply problem.. but as i said the pressure is good.

 

[portland_bill]

Further thoughts,
spark plug condition?
temp sensor issue? These can often give incorrect readings, but of course the ECU does not know they are incorrect.

Stalling might suggest that the ECU is reducing the fuel before the engine is ready, so a temp sensor may be the reason.

 

[aurick86]

As i already said, recently replaced the spark plugs, and i can see the same temps that the ECU is seeing with MES... and they seem to be ok.
It is really puzzling.

 

[maggers]

What does the boost pressure read with the engine off? It should be close to 1 bar, I have had sensors misread which causes havoc!

 

[fingers99]

And, hesitant start, poor cold running can be early sign of head gasket issue.

I'd expect most other running issues to trigger the EML.