1.9 JTDm missing top end power - Alfa Romeo Forum
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1.9 JTDm missing top end power

Hi guys,

after my 147 1.9 JTDm 16V had some vibration problems because of a broken cambelt spanner and slipped cam belt, I've replaced the broken parts and checked the engine.

Drives when driving, in the low end the power delivery is a lot better than before, but above 3000 rpm, the car almost drives like my 2nd stock 1.9 JTDm.

While repairing the cambelt spanner, i've also fitted a new exhaust camshaft, tappets and rockers because one cam was severely damaged, probably because of a faulty tappet.

Compression seems to be ok between 27.5 and 29 bar when cold turning without oil added to the cylinders.
Intake seems to be leak-less when testing from turbo outlet until intake manifold up to 2.0 bar over ambient pressure.

The car has FMIC, EGR deleted, Swirl Flaps deleted, Throttle Body deleted, DPF is empty, PreCat is empty and a remap with adjusted VNT+Closed Loop control, IQ and Timing.

When logging today, i've noticed that airmass and boost decline after 3000 rpm. I've also noticed this when diagnosing the initial vibration problem, but attributet that to the jumped timing belt (2 teeth).

Right now, i'm not sure what to check next. I've been running the same map on the car for the last
4 years and not had any power loss issues.

So where should I start looking for the culprit?

Attachted below are the logs in 3rd and 5th gear. It seems to overshoot boost (up to 2.8bar) when letting off the throttle and shortly afterwards going full throttle again, see 5th gear log.

Thanks in advance for your input.
Attached Files
File Type: txt 20190120-log-3rd.txt (775 Bytes, 3 views)
File Type: pdf 20190120-log-5th.pdf (55.2 KB, 4 views)
File Type: txt 20190120-log-5th.txt (1.1 KB, 2 views)
File Type: pdf 20190120-log-3rd.pdf (55.8 KB, 4 views)
gandolff is offline  
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In 3th gear boost control is good. Slightly fluctuation between 2.000-3.100 rpm, try to fix with VNT-injection quantity.

In 5th gear boost control is good. 2.800 mb overboost on transition is normal due to your free flow exhaust, try to fix with VNT transition map mod. MAF is slighty low but it could be better after VNT mod (1.200-1.250 mg/i).

I don't know if your exhaust camshaft will work better or worse.
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