Sudden loss of power under full load.

[Schultzy]

G'day all,

I have a 2005 3.0Zd . 104000kms
Mods: 2.75inch Beaudesert exhaust, Autron pyro and boost gauges, EGR blanking plate, Dawes valve and needle valve. Provent catch can.

Generally the car is performing really well. My problem is when I am under full throttle with a load, eg going up a hill, most times in 4th gear, it has happened in 3rd. As I reach around 3200revs or so there is a sudden drop in power, boost drops to about 10lb. Take my foot of the throttle and back on again hard it powers away again only to repeat the loss of power event again at around 3200 - 3400 revs. If I am not hard on the throttle it is less likely to occur.

Boost 16lb, EGt 450C. There are no dash warning lights.

Have just replace the headgasket (using water, leaking between 3 and 4). 2nd time in 22thou kms. Had major repair then, new head etc. I'm told block is true. There was an issue with a "muddy sand" in the radiator on both occasions. Block was ?? flushed on first occasion. Anyone else had mud/sand in their radiator. I have been particular with coolant and changes etc.

I did not have the problem prior to the headgasket change and the car was performing very well.
I think I have double checked everything twice.

Is this going into limp mode I read about, or is it something else?

Help please...

[threedogs]

Sounds like its over boosting , do you have dawes valve fitted

[Sir Roofy]

sounds like your going into limp mode back your boost of to 14or a tad less see how that goes
as for the gremlims in the coolant no idea sorry

[Schultzy]

Yes that what I thought threedogs but I have a dawes valves etc. and maximum boost is 17lb. Do you think this needs to be lowered?

[Schultzy]

Thanks roofy I'll give it a go

[threedogs]

EGTs seem high as well, do you have the EGR blocked off??

[Schultzy]

Thanks everyone,
It was a boost issue. I dropped the pressure down to 14 as you suggested roofy. Problem solved. I lifted it up to 15lb, still ok but crook at 16lb. Am leaving it at 15lb.
The max EGT I get is 520C after a long hard slog. I figure thats ok.

I still don't understand this overboosting stuff. I can understand if the pressure gets above 20 etc. and issues there, but before I put the dawes valve etc. on, my boost was often 18 - 20lb. Now trimming it to 15lb.
Don't figure...

My mechanic suggested the stuff in the radiator may be left over block casting sand, but that was just a vague possibility.

Anyway thanks to all.

[Sir Roofy]

whats the egt,s when your boost is at 14 or lower where you in 5th gear on the longhaul up the hill
if so drop back to 4th and see how ya go 520 is getting to high but then again all these trucks have there
own personalitys and perform different