Thread: Another interesting find...

Today while chasing an excessive EGT and fuel consumption problem with a D2a Td5 auto, I came across something unusual. Rocker cover off inspecting injector harness etc I noticed that there seemed to be way more thread visible above the injector rocker adjusters than there should be. During checking the bump clearance I was able to turn each one 4 to 5 whole turns to bottom them out. This would explain this vehicles performance issues as after they were set properly almost 100degrees was wiped off the EGT gauge on the same uphill run The temps also dropped off quickly when lifting off the throttle, previously this engine would climb rapidly to 850 degrees, and would if held flat posibly break the 950 degree mark Hence the reason for investigations. Even flashing a standard map back on it would still climb rediculously.

So, the function of the cam profile on the injector lobe, and the length of travel of the injector plunger are critical as these 2 processes are concerned with actual injection pressure and volume. timing is I guess ultimately controlled electronically, but would be affected by a 'late' plunger action. My hypothesis is that less plunger travel equates to poor pressures and thereby low volume, causing less than satisfactory atomisation and excessive afterburning, hence high EGT's and poor performance.

The other interesting result was that the engine sounded like a diesel again. A nice amount of detonation noise had appeared

The head had been off this vehicle prior to current owner purchasing it, i'd say whoever fitted it back adjusted the injector rockers as you would valve clearances. When I checked them they were actually loose when at the base of the cam lobe.

Anyone add to this? Agree or disagree?

JC

Originally Posted by CraigE

Really interesting, may explain my higher fuel consumption and slight smell of diesel from the exhaust. Mine appears it has had a cam change early in life (previous owner).
Is this a specialist job to check or should I be able to check it at home? No one up here I trust to take it to. Nearest is Whyatts, but that is a long way away.
May have to get Andrew to check it if I get to Perth in it, may be driving down at easter.
Cheers
Craig

Craig,

The bump clearances are easy to adjust, rocker cover off, rotate engine until injector rocker is at max 'lift' (Fully compressed plunger) and ulock locknut, screw adjuster all the way in until it bottoms, then undo 1.5 turns. Lock up locknut and move onto the next. I would check the valve timing while you are there, underneath bellhousing offset threaded hole (IIRC it is at 7 oclock when viewed lying underneath) look up into there and a slot in the flywheel should appear when the cam is at TDC. The little hole in the top of the cam retaining housing just behind the timing chain allows a pin to be inserted into the cam slot. If the cam is pinned and the flywheel slot isn't visible from underneath, loosen the 3 cam gear bolts and rotate the engine slightly to align the slot centrally. Tighten bolts and remove pin, rotate engine 2 revolutions and recheck.
WARNING: There is a hole also in the edge of the flywheel, DO NOT align to this, the slot is the timing mark and is close to the hole...definately a trap for young players.

JC