Intake mod diesel power loss

[mikee55]

Hi, not been on here in ages, life's been a rollercoaster lately. Anyhow, I've got a Renault Scenic Alize 1.9D. Ive not done anything yet, majorwise, its not my chosen vehicle. I had to buy it after my VW Caddy gave up the ghost. I had a long winding airintake tube on it and thought this to be the vehicles main issue. Its meant to be a Sports model and yet it struggles to pull away! I took off the intake and ran a straight pipe to the front of the vehicle. It ran fine for ages, then I read that diesels like warm air to aid combustion and shortened the pipe to suck warm air off the engine. Seemed to warm up quicker and run smoother. Then after a few days running like this, I find a loss of power in the low rev range 15000 rpm to 30000! Feel like the engine has no air, so I re-lenghthened the pipe after reading that diesels like cold air!! The theorey of warm intake made sense of the fact it would be easier to combust than cold, especialy winter, but all talk was pointing to CAI cold air, so I reverted back to that! Problem remains, in that there is no get up and go! I figured maybe this vehicle has a computer and it has to re adjust to the air intake temperature change and the velocity its travelling in, but how long does it take to readjust the fuel/air mix? Also, is it true that a MAF sensor can give a wrong signal if the airflow is too great for it? Once the vehicle is rolloing I can keep pace, but pulling up a hill, might as well walk!
Can you tell me whats going on, so I can sort it please?

Thanks.

Mike

[DocDiesel]

Hey Mikee55,
It may be completely unrelated to the mods that you have made. Depending on age and miles of the vehicle and if you noticed low power before any modifications, a slowly clogging intake manifold could gradually choke airflow or an aging MAF sensor can gradually reduce power.

The power losses may also BE linked to the modifications. Filament type MAF sensors (if this is what the Renault are equipped with) are sometimes sensitive to modifications made to air flow depending on the vehicle and if you deleted the factory airbox and installed a oil type air filter (like a K&N cone filter) the filter oil will destroy the MAF sensor filament.

Not knowing the age or miles on the car, I would first unplug the MAF sensor and drive the car. If the car runs better with the MAF sensor unplugged than your MAF sensor is bad and has to be replaced.

[ksa8907]

Could be a lot of things. Im no diesel expert but the first thing i would look at are air filter and turbo. Sounds almost like the turbo isn't spooling fast enough.

[dirtydave]

Maybe a bigger turbo?

[DocDiesel]

Can you hear the turbo spool up?

[oil pan 4]

Do diesels like cold air or warm air?
Its all a matter of perspective. Diesels need cold air on warm and hot days to give the most power and fuel economy but on cold days you don't want the intake air to fall below -5'C to +10'C because then you don't get enough adiabatic compression heating to light off the fuel, this all depends on the engine and its compression ratio.
Cummins recommends that for their stationary industrial engines that if their engine will be operated in -5'C or below that the engine have an enclosure and draw its intake air from inside this enclosure. Once it gets much above freezing the air can be drawn from out side the enclosure.
Your intake air needs to be with in a certain temperature range.
With too much heat in the intake you waste energy by creating excess heat from compression, this excess heat is just absorbed by the cylinder head and piston and does nothing for engine operation.
Ideally you get 500'C to 700'C when you compress the air in the cylinder. If your air is too dense and too hot your compression heating could be as high as 2000'C, obviously it will not get this hot because some of the heat is absorbed as it builds. But you still do the work to heat it that much and get nothing in return.

[renault_megane_dci]

Hi,

As your Scenic is a 1.9D, it has no turbo.
It's a 65hp engine in a 1,2 ton vehicle so no wonder it is slow.

Tuning your intake is not the best of ideas as far as length is concerned since Renault people are almost anal about this.

If possible, I would revert to standard setup.

This vehicle is not fitted with a MAF sensor as far as I know.

I would check fuel filter and air filter.

Does it spin properly when not loaded ?

Whoever sold you the 1,9D as a sport model was being ironic, I dont even think you can get this engine with upper level of trim (RXT I believe)

Obviously, running air-con is that extra grunt taken out of the engine (if you have it ...)

What's your mileage ?

[mikee55]

It died!

[renault_megane_dci]

Rust in pieces then ...