Technical Fiat coupe 20v turbo inlet manifold sensor leaking oil-HELP!

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Technical Fiat coupe 20v turbo inlet manifold sensor leaking oil-HELP!

Aug 22, 2022
Hi Gentlemen,

Long time no post.

So I changed all intercooler pipes on my fiat coupe 20v turbo for nice silicone ones with new heavy duty clamps and when I left my pals garage the car was boosting between 23-25psi boost and was going like a good un!

Few days later I noticed the car would only boost upto 10psi no higher.

Had a look under the bonnet and can't find anything obvious but there's this sensor on the inlet manifold near the oil filler cap that has a electrical plug on it.

Sensor looked abit wet so I removed it and it seems to be leaking oil from this sensor. Cleaned it up and sealed it as best as I could with some gasket sealer.

Car still won't boost over 10psi.

Does anyone know the purpose of this sensor?

I thought it might be some sort of variable valve timing type sensor but could be wrong.

Any ideas as to why my boost has more than halved I'm all ears. Please let me know if anyone has any suggestions or has had similar problems.

Thanks in advance

Guessing it is a MAP sensor(manifold Absolute Pressure)
Any chance the increased boost pressure with new good hoses etc. finished off the seal/bearing in the turbo where it is oil fed, if so there may be oil building up in the intercooler etc.
A guide would be if you take the turbo pipe off where it enters the inlet and hold your hand in the air flow for a few seconds whilst it is revved you may find oil on your hand.
I did this on a 2010 Doblo 1.6 multijet prior to replacing the turbo cartridge which had worn seals/bearings on impeller.
Apart from that my daughter had a VW Golf GTD 130 that the variable van turbo vanes would stick from town use and go into limp mode until freed off with turbo cleaner etc. Then OK as long as she kept adding turbo cleaner additive to her fuel.
Hi Bugsymike,

Thanks for reply.

Previous owner fitted a new hybrid turbo so turbo should be fine fingers crossed but will have a check in the hoses on the weekend.

Anyone else know what the sensor is on the inlet manifold in previous picture?

I went online and some people were calling it a cold start valve but it didn't smell of petrol when I took it out. It had oil in there and inside the cavity where it sits.

Any suggestions/advice greatly appreciated.

Quick question what should boost gauge read on idle on fiat coupe 20v turbo anyone?

P.s ive got a psi gauge stack one.

Thats the solenoid valve that controls the variable cam timing, you would expect it to be oily as it allows the flow (or not) of oil to change the cam timing.

There is no MAP on the 20vt only a MAF. The boost you are running is very high for a standard engine, you should be looking at 18.5 psi max continuous. You have most likely got a boost leak somewhere, go through all the piping again
Hi major clanger

Thanks for the reply.

I did suspect that sensor was a variable cam timing sensor/solenoid so thanks for confirming.

I have replaced it today with another solenoid out of a donor inlet manifold I managed to get my hands on. The solenoid I removed had a small o ring in the middle of the length of the solenoid but the replacement solenoid I put in had a much bigger oil seal almost the whole length of the body of the solenoid so my guess is someone fitted a cheapo solenoid at some point and the oil o ring seal was failing allowing oil past it and probably air could of been getting in.

I'll be able to test drive the car tomorrow on my way to work so should be able to update later. I'm hoping the oil seal leaking on the solenoid was the problem.

My car is running a gtec 2 chip, hybrid turbo, 3.8 bar fuel reg,ram air filter,uprated fuel pump,stainless steel exhaust system with decat,stainless steel exhaust manifold,silicone water,boost and ancillary hoses.

It still has standard electronic boost controller which after doing some research online seems like standard ebc can only handle standard power so I was thinking in the future to uprate for an aftermarket ebc. I've seen the greedy profec one and like the look of it so that may be on the horizon.

Anyone know what the boost gauge should read on a fiat coupe 20v turbo when on idle let me know.

Thanks in advance
Idle vacuum on mine reads between -12 to -15 psi cold engine to hot.

I believe the standard boost solenoid can be a weak point, I run a manual boost valve which is a bit raw but I prefer that to the complication of an electronic boost controller.

A good diagnostic tool for fueling is MES, it allows you to read the STFT and LTFT and to log and graph your closed loop fueling. That 3.8 bar regulator might be spoiling your fueling on closed loop. Another really good addition is a wideband O2 to see what is happening under boost. Just be careful with 23-25 psi on boost with a non forged engine.
le problème est que la pression du turbo est trop élevée. avec un turbo hybride un gtec (1 ou 2) peut convenir pour le carburant, mais certainement pas pour la pression du turbo. Le calculateur enregistre donc trop de charge et réduit progressivement cette charge pour revenir à des valeurs acceptables ; voir ça passe en sécurité avec une pression équivalente à 1b au final. dans votre configuration vous devez installer un contrôleur de suralimentation externe pour gérer la pression du turbo ou refaire une eprom adaptée à votre turbo.
So in simple terms; the boost went too high, the ecu did not like what it saw via the MAF calculated load figure and so restricted the boost via the ecu controlled boost valve?

I thought the gtek controlled the boost via the boost tables, Graeme L talks about the boost being set to 1.3 bar, is this not the case?
the airflow of a hybrid is not at all the same as that of an original turbo; At 1.3b, the flow of a hybrid will not be at all the same as the flow of a stock turbo ;the airflow enters into the calculation of the load. the ECU can reduce the ignition advances and act on the N75 to return to the load values indicated in the map.
Ok I think I understand; it all comes back to the MAF and the calculated load based on airflow. The load maps are the governing factor and regardless of the fuel, ignition or boost pressure maps, the ecu follows the load map.

Thanks pasto.