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Discussion Starter #1
Hi everyone, I have a strange issue with my 2003 jtd m-jet 140ps.

The engine has been completely rebuilt, new turbo,decat and modified head.

EGR blanked off (This problem is not a stuck EGR..!")

Oil recirc blanked (now goes to catch tank)

The engine most of the time feels very sluggish under 2krpm, and the turbo seems to take ages to spool up, occassionally it seems a bit smokey under 2krpm as well.


I'm wondering if the MAF is a bit dodgy, maybe the connector pins need a clean (the sensor unit had been alcohol cleaned and looks very good)

Any ideas ? ~ I just dont see that it is a mechanical problem, more of a sensor issue i rekon.
 

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Connect your car to a laptop with FES and log an acceleration from 1500 to 4000+rpm in 4th gear.

Select parameters, Engine RPM, Measured Airflow, Measured Boost and Fuel injection.

Then post results here.

But it could be MAF, I seen a case just like yours on 156 m-jet. Everybody thought it was a EGR problem, but only replacement of MAF cured it.
 

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The is a small bore (5mm) vacumn pipe that goes to the vnt/vgt solenoid - if this is split or blocked the turbo will not spool up properly and can give this type of fault.
 

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Discussion Starter #4
Thanks guys. I will have an investigatory morning! I'll pull the MAF out and double check that, and pull some pips off and check. (could it be a split boost hose?)

when it is running perfect, its quite suprising how much torque the fresh engine is making..
 

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I have the same car as you.....it sounds like the maf and turbo hose (I had maf replaced a few months ago)
 

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Discussion Starter #6
I checked the vac/boost pipe to the solenoid and actuator - they were fine, and still under vacuum!

I've taken the MAF out and washed in alcohol, - suspect this is the prob. If its still bad or worse, I'll order a new MAF sensor element..
 

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Washing it does not necessarily fix it...

You should make a data log on you ECU to see what are the readings form the MAF.
 

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Discussion Starter #8
..aswell as the bad performance, Its had a strange tinkling rattle..which has now been tracked down to the AC pump pulley/clutch. as the car doesnt have ac anymore, the pump is out and being replaced with a dummy idler pulley instead.
 

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Discussion Starter #10
I couldnt visualise the path of the belt, around the idler>AC>PAS , if the idler was swapped for a toothed idler, would a shorter belt then work? what length would be needed..
 

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Discussion Starter #11
all done , thanks for the advice AlfaTuner = much simpler. Just getting a belt, aprx 6pk1070 - 6pk1080, getting some to trial.
 

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Discussion Starter #12
6pk1070 works a treat! no more squeaky metalic rattles..
 

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Discussion Starter #13
did some data logging in FiatECUscan plotted rpm/Desired Air quant/Intake air quant / MAF Signal v.



MAF signal is very spikey, almost sawtooth, even when on cruisecontrol the signal is still very jagged, but the desired and actual air quants were much closer.. on accell the difference between them is huge. Bad MAF.. need new MAF grrr
 

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OK, this is a useless log.
Next time you will try logging the ECU do it like this:

Put your car in 4th gear, start at 1500rpm or lower, push your loud pedal as hard as you can, accelerate till 4500rpm. Repeat this once or twice and then post your results.

You cat make any conclusions out of this log.
 

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Discussion Starter #15
how stable should the signal voltage be? when accel on full load the signal goes all over the place, even on tiny throttle idling +/- 0.5v is massive...
 

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MAF sensor is not linear... it is logarithmic.

At idle it will jump up and down a lot, but those voltage jumps ~2-3V mean relatively small change in airflow.

But if you are accelerating hard, you should see voltages well above 4V. At 4000rpm it should be something like 4.5-4.7V and relatively stable. (+-0,1V). At this voltages even the tiniest change in voltage translates to big change of airflow...

Anyway. Other thing, during hard acceleration intake air quantity measured in mg/inj should be above 1100mg/inj @ 2000-2500rpm, if your car is stock. If it has a remap or FMIC the numbers should be even higher, up to 1300mg/inj.
But at higher rpms it should fall back to ~950-1050mg/inj. If your MAF reports lower values then you have a MAF problem.

But if your MAF voltage jumps up and down a lot even at hard acceleration, then it is probably bust.
Make some more data logs during acceleration and post them here.
 

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Discussion Starter #17
i'll bought a cheap s/h bosch maf - which I'm going to clean in IPA and test out.
 
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