Vibration from 2.5tdi Engine under high power from 1800-2600rpm.

Engine: 2.5tdi 5cyl (1996 Volvo 850) 11mm pump Race520 Nozzles (Upgrade from standard 502’s) KKK14 waste gate turbo, mild porting to head and turbo waste gate. (Dual mass flywheel). 155k miles and was well maintained until the water pump failed taking out the cam belt. I have rebuilt with new exhaust valves and followers and everything else seems fine.

Vibration sounds like going over rumble strips at side of motorway, but not quite as harsh.

Vibration occurs with standard ecu and modified ecu.
Vibration starts at about 1800 rpm, with more than 70% throttle by which time there is only about 11psi of boost and no smoke. Less throttle and the engine is perfectly smooth. The vibration completely disappears after 2600rpm.
I have tried running the modified ecu with losts of extra fuelling in my good lady’s identical standard car and power is smooth at all rpms.

Vibration cannot be felt during WOT accel in 1st or 2nd and only just be detected in third. In fourth and fifth it is very obvious.

As the only real change from standard is the Nozzles from 502’s to race520’s, any ideas of what needs to be modified to iron this out? I have searched the forum and seen only couple of similar problems, but no resolution.

My thoughts were that for vibration we need somewhere to store energy, which would probably we the dual mass flywheel, and the excitation force being the higher cylinder pressure being produced before TDC by the larger nozzles. If this is so can the ecu be reprogrammed to retard the start of injection angle for this range, and if so what would a good value to try be, say 3 degrees? What sort of advance would be standard under these conditions?

Many thanks in anticipation.
Chapelhill.

Either put in a single mass flywheel or take out the race nozzles or take fueling off between 1800-2600 rpm. Timing changes might help, I don't know if anyone ever tested. On a VAG tdi, stock timing curve bottoms at 2000 rpm and it is about 5...7 BTDC I think and starts to climb from there on.
Do you smoke at wot with the race nozzles? What is the boost at WOT?

Thanks for the reply.
No there is hardly any smoke at WOT (a liitle bit of grey smoke, but can only be seen very close to the exhaust exit if you follow the car, no smoke visible from drivers view mirror) and max boost is just under 18psi (1.2bar), but it does not reach that by 1800rpm only by 2000rpm. At 1800rpm boost is about 11psi.
It is not producing that much torque in this range and it would seem a backward step to fit back smaller injectors, but I will do if all other solutions fail. The clutch on the Volvo is quite strong, so i am reluctant to change that especially as options might be more limited with this engine.
The Volvo standard spec for 140hp from 2.5l is quite aggressive, presumably for economy as the turbo is small, standard 502 nozzles, 11mm pump and from what I have read the cam plate in the pump is also aggressive.
Chapelhill.

What comes to clutch change for that volvo I remember that shadowmaker had a volvo once or was it wifeys car but there was also problems with clutch slip before it was updated.

The spores on the main axle to gearbox might be the same as some vw's so propably there is a cure with reasonable price(if there is ever any when building a car) to that problem..

Are your engine/trans mounts in good shape?

Many thanks for the suggestion, I changed the top mount to polyurethane, but it did not make any difference except make everything louder. I thought engine mount issues would be worse in lower gears, but I changed it anyway as it was tired.

Anybody got any further test ideas?
Is there a way of making the injection timing retarded like fooling the fuel temp sensor, and if so any idea of the amount of retard?
Chapelhill