Series2 16V turbo hesitates/stutter

[Pierre]

Weird, when flooring the throttle in 2nd the engine hesitates/stutters at about 3800 rpm and then carries without any further problems. It does not happen in 1st and sometimes in 3rd. If I progressively step on the throttle it is smooth. Disconnected the overboost switch and knock sensors at different occassions to see if the source of the problem could be there, but no change. Plug change did not help at all. Problem definitely seem to be electrically based.

Any ideas or similar experiences???

[Angle Grinder]

It might be perished rubber hoses in the fuel tank between the fuel pump and the top of the fuel pump assembly.

See the Technical Tips on www.lancia-tdc.co.uk.

I had a similar problem on taking left hand bends with less than a 1/4 tank of fuel. This problem turned out to be a crack in the rubber hoses that was allowing fuel pressure to drop when the pipes flexed.

[Pierre]

It does not feel like a fuel problem. It is as if the engine shuts down momentarily as if there is no spark and then fires away straight after that. It only happens at 3800 rpm, nowhere else. And only with the pedal floored (wide open throttle). Maybe the fuel enrichment unit??? Anybody that has more info on it?

[Angle Grinder]

Have you checked the positioning of the throttle switch and the operation of the overboost 2 stage switch?

[Simon]

Pierre,

The garage I go to had a car in with a problem like yours, If you were moderately gently the car would accelerate fine, without any problems. But if you floored it, it would hesitate for a moment be for accelerating hard. They discovered that it was boosting at upto 1.4 bar. They did some investigation work and changed the acuator on the turbo for an integrale unit which cured the problem.

Regards

Simon
England

[Pierre]

Hi Simon,

I think you hit the nail on the head. If I disconnect the 2nd overboost switch the car accelerates without any problem. Reconnect and it hesitates when you floor it. Swopped the fuel enrichment unit around with one from another Thema which does not have this problem, no change. I started suspecting that the problem may be in the boost pressure. Will pipe in a boost gauge to see what is actually going on.

In the meantime I have fitted some 360cc/min injectors as the plan is to run 1.2 bar boost max and to aim for 200 kw. Noticed that the hesitation is dramatically reduced after this mod but it is still there. So it could be fuel related (too much boost) as disconnecting the overboost pressure switch did not make any change at all.

Will keep you guys posted......

[Pierre]

OK guys, found the problem. A bit embarrassing though. Firstly the connectors of the manifold pressure switch and the second stage overboost switch was swopped....OUCH!!!!

After that all was well until I reset the wastegate accumulator to activate at 0.9 bar (was 0.5 bar). 1st stage overboost took it up to 1.2 bar dropping down and settling at 1 - 1.1 bar. Second stage overboost took it up to 1.8 bar!!!!! Manifold pressure switch catches it at 1.6 bar causing you to nearly go through the windscreen........

I plan to put a restrictor in the line of the 2nd stage overboost solenoid so that max boost will not be more than 1.5 bar. Then off to the dyno...LOL

[Pierre]

Had a dyno run today with actuator set to 0.8 bar, 1st stage o/b to 1.2 bar and 2nd stage o/b to 1.4 bar.

Got 153 kw and 332 Nm. Going to reset actuator to 1 bar and have a go again. Depending on A/F ratio this will probably be the final settings using all the existing ECM and ignition units.

Couldn't get a nice pull on 2nd stage o/b though, kicks out after a second or so. Boost for most of the run between 0.8 - 1.0 bar.

Motor very smooth, clean burning and sounded schweeeet........

[Luke]

your engine is completly stock?

[Pierre]

Yes, turbo is stock as well. Only the injectors have been changed and the AFM recalibrated.