Outer Limits 4x4 Board

Has anyone come accross detonation problems with TD42? A mate has just pulled his head off due to some other problems and has found that the engine has been detonating. ie 3 pistons are almost holed where the flame has been coming from the pre-combustion chamber. The motor as been running reasonable boost ie it does go over 20psi at times. It has a TD42T pump and TD42T pre-combustion chambers, a ported head, cam, Safari Turbo. The intercooler arrived yesterday ie the day we fund the problem!!!!!! The pyro temos have never been above 1100*F ie about 550*C and the pyro is in the manifold so is very acurate. It is not over fueling and didn't appear to be running out of fuel.

We are going to build a new motor and want to make sure it doesn't happen again.
Any ideas ie Timing, ruch/lean etc etc?

I rebuilt a non turbo late GQ TD42 which had flogged the big end bearings, after the rebuild I test drove the car and heard audible knock at high rpm similar to what petrol knock sounds like. I sent the pump away for repair as I suspected the internal advance was over advancing, the problem was solved with the reco pump. The knock was what killed the big ends bearings no doubt.

Cheers

Joel

You mean to tell me, you were running 20PSI into the motor without an IC? thats where the problem is. the temp inside the pre-comubstion chamber thanks to the extreme heat in the compressed air from the turbo is igniting the fuel prematurely, its too hot in there, and i can only imagine the EGT's of this,

MyGQ wrote:You mean to tell me, you were running 20PSI into the motor without an IC? thats where the problem is. the temp inside the pre-comubstion chamber thanks to the extreme heat in the compressed air from the turbo is igniting the fuel prematurely, its too hot in there, and i can only imagine the EGT's of this,

He said EGT's pre turbo never went over 550.......but that seems very low for that much boost - thats about 350 post turbo - mine will touch 550 post turbo easily if I push it. Maybe a problem with the pyro gauge?????

yeh what did it idle at?

anything over 130ish deg c and im thinking the sensor or the gauge isnt playing cricket?

Initial static timing may be wrong, poor fuel quality, poor injector atomisation. Has guage accuracy been verified?

It might not be detonation, it may be too much heat. What injectors, nozzles, opening pressures?? Pump calibration.

That should keep you going for a bit.

Andy

1100F is actually 593C but since it's in the manifold I wouldn't be concerned about those temps in fact I would think they should be higher so a calibration of the EGT gauge may well be in order.
At 20 psi boost pressures it would be interesting to know what your air intake temps were without an intercooler. Through the roof would be my guess, which should also be sending your EGT's higher so again we question your EGT gauge.
Regards Andrew.

what breather setup does it have ?
any oil leaking from turbo?
could be burning a little bit of oil before fuel is injected causeing increase in compresion temp.

the other thing is what compression are you running ? with that much boost mayby drop it a bit.

You've touched on few things I was thinking about.
One is whether the pyro is acurate but it is a new VDO unit, but it will still get a check.
The other is timing. It has a rebuilt pump on it and the timing was set when it was refitted, but we'll check it before it comes apart and see what it is now. I think timing was set at factory specs.
The injectors have new tips etc and have had break pressure increased about 115 atmos. I think.

We'll check a few things and see what the results are.

Sorry I didn't read the post carefully, I thought you had audible detonation, not a rooted motor. I'd agree with whats said. There are pumps and there are pumps, use a shop with a pump room to check it, i've seen some shockers. Make sure the pyro is inserted a sufficient depth or it will read cool.

Joel

Also you dont want the pyro sensor to be anymore than 6 inches from the turbo or the gauge wont read accuratly
Before you put that pump on another motor get it checked out

A little more info.
The pistons in 3 and 4 and to a smaller extent 2 have significant damage where the flame has been coming from the pre-combustion chamber. 1,5 and 6 have no damage. The injectors, that were reconditioned with new tips etc less than 6 months ago should significant heat damage. ie colouring and the tips eaten. They are getting tested by a different shop.
Having 3 cylinders damaged an 3 fine would indicate timing is OK, I would think???
Also th pre-combustion chambers are loose in 4 of the cylinders and this is a fresh head that has had new ones fitted about 3 months ago.
Our current thought is that the injectors have been dripping so that will be checked and then we'll go from there.

Something isn't right as it was a very good motor with a good head and everything that had been put on was either new or reconditioned. Thankfully we have plenty of spares lying around that I don't obviously need anymore.

There was no external reason to expect this. ie no noise, no over fueling, egt were very safe. The boost and turbo setup are the same as what I ran for 3 years without any issues. We only found this due to another problem.

Thanks for the help guys as we don't want to put it back together and have the same problem!

You may have picked up some bad fuel. Having 3 cylinders still good may mean they were on there way out except the other 3 beat them to it. Check them all. It sounds like heat has caused most of your problems, maybe the precomps werent fitted with the right clearance.

Now that the injectors have been damaged, this makes for testing of dribbling hard, as they probably will.


What was your other problem to warrant pulling this apart?



Andy

rough rule of thumb is rear pistons generally run a bit hotter. its sounds like it was running on the ragged edge and flame temp was to high. (crude way to put it but its late here)
either to much timing, to much effective compression, or poor quailty fuel.

I have to be careful due to who else may be watching, but uncontrolable revs had something to do with it! So rolling right on we have a idea that it is a combination of a few things. Injectors obviously are hard to nail down now but must be contributing, pump tining is going to be checked by a different shop and by someone I trust personally. We are also now questioning the acuracy of the pyro so will test that.
I'll let you know anything we find.

Thanks.

If your rev problem was caused by blowby, then you have found your problem.

It will do all that you have listed.



Andy

The cylinders with piston damage have also had the ends of the glow plugs eaten as well. Is it possible for a faulty glow plug to cause pre ignition?

Blow by wasn't a factor in the over revving and as far as can be told now there wasn't accessive blow by but the breather was in to the inlet so this is something that will be changed.

There is a better pyro going in and it will be calibrated to ensure acuracy. The pump timing is getting checked and the boost gauge is also getting replaced just to be safe. Obviously the injectors are getting done again. We are using a different motor but it will have the same pump, turbo etc etc on it. Then with some dyno time to make sure it is all good.

still sounds like to hot.

check your intake temps.

imho for 20psi drop the compression down a bit.

Darin,
Those 3 or 4 motors we toasted in Aarons truck expired in largely the same way you're describing. Always the cylinders closest to cross-over pipe from turbo (we used twin cross-over remember), pyro never got high even with the fuel we were running....dropped boost to below 20psi and it lasted a bit longer, so look at your intake temps first.

Drop the rocker-cover breather pipe into a catch-can or down into slot in RH chassis rail just in case.

We are going to copy the twin entry inlet like your (old) truck. I also thinking that an inlet temp gauge is going to be fitted.
The biggest suprise is how quick this has happened! I sure we will never know for certain what has caused it unless we want to kill several more and change one thing at a time!!!!!! Not in the budget that is for certain!

one thing comes to mind........

asuming the egt temps are correct....... going by egt's your not pouring in a lot of fuel, so why run such high boost when you don't need to ??