Technical overboost problem on JTD110?

[jankoh]

Hi,

I'm new here and hope to get some help on my problem. I own a 2001 Marea JTD110. The car is not running very well and I suspect that the VNT is clogged but before i remove and disassemble the turbo i would like to hear what you guys mean.

I also have a problem with the EGR so its disabled now. To check the boost I've installed a boost gauge and when I step on the throttle it boost over 1,5bar (if I'm right 1bar is nominal). The boost stays high for 2-3 seconds and then it drops to ~0,5bar and starts to raise slowly again. When the boost drop happens the power has a heavy neck down. So if my reading and understanding of it was OK the car is over-boosting and then it cuts down the power (some kind of safe mode). Today I also disconnected the MAF. The difference is that the car does not go into safe mode and boost stays above 1bar even with 1/4 throttle.
So what do you mean is this happening because i have disabled the EGR or is the VNT clogged? When the car is running I can see the VNT shaft move.
Sorry for the long post.

 

[EI4GGB]

probably best to get examiner or some other diagnostics on this one and see what is actually happening. most likely there is a code stored. check the readings from the MAP sensor (and actual and requested MAP or manifold pressures). do an actuation test on the wastegate control solenoid valve to check the wastegate is fully stroking (I think the turbo is a normal wastegate turbo, not VNT). without the MAF the engine may be in limp mode anyway, so this by itself won't tell you anything..

 

[jankoh]

Done some additional tests today with MAF disconnected. Looks like it behaves the same as with MAF. And there is no noticable difference on how the car runs.

I was accelerating the car up a hill in 5th. When I hold the throttle so that boost does not go over 1bar the boost is stable. When I press the throttle more in the boost goes up to like 1,4bar then drops down to 0,6 bar and goes again up to 1,4bar and then gain down. So it fluctuates around 1bar.

When I was checking the turbo part number it should be a VNT but I'm not sure.

There are no codes stored regarding this. I only have the code for EGR and I had the code for clutch pedal switch but this one should be OK now because i fixed it (i hope i have)

 

[jug]

disabling the EGR valve leads to problems, power loss and erratic performance when open, and when closed the turbo will overheat and eventually fail.

replace the EGR valve, or try cleaning it first as most EGR valve problems are simply due to dirt.

 

[jankoh]

The EGR was already disabled when I bought the car. The pipe was blocked with sheet metal. And the EGR was completley clogged with carbon. I've removed it and cleaned it. But doing this i have broken the shaft of the EGR while removing the nut so I'm waiting for the EGR. Now I have both pipes blocked so I can drive with the car.

@jug: Why will the turbo fail if EGR is blocked (closed)? Is it controlling the boost by releasing it into the exhaust sistem? That sounds strange to me because if you do so the MAF will measure this air and the car will overfuel. Or am I wrong

Sorry guys I'm new to diesel and would like to know what is happenenig...

 

[jug]

@jug: Why will the turbo fail if EGR is blocked (closed)?

same reason it fails if EGR is stuck shut, the exhaust gas heats up. the EGR system is only there to drop cylinder temperatures to prevent NOx gas formation. it heats up the turbo because the turbo is driven by exhaust gas, causing the turbo to overheat and eventually fail. you usually have a long period of poor performance before total failure. your erratic boost pressure could easily be caused by turbo damage from overheating.

 

[jankoh]

OK thats right but I never tought that you can burn a turbo on a diesel engine because the exhaust temperatures are way lower than on petrol engines. But OK goot to know i'll fix the EGR first and see what happens. I will also report here.

Thanx for the help

 

[EI4GGB]

lets not blame turbo's first... turbo failures are not that common (on FIATs anyway). diesel exhaust really only heats up enough to cause damage if the engine is being ragged the whole time, or there is a timing or fueling problem causing incomplete combustion etc.. e.g. a damaged injector.. in this case the problem (as observed) is most likely due to a boost control problem, which really needs to be examined with diagnostics to find out what is going on..

 

[Mr Marea]

i 'm not technical (dont really understand half of what was said) but i had an overboost problem with my JTD110.

It would be fine until i hit a certain hill on the way to work when the red ignition light would come on and the car would go into limp home mode for 20 miles or so (3000 rev max). Switching off the engine after work would not get it out of limp home mode.

After several garages (thankyou JCS) it was found to be the vacuum chamber on the turbo was leaking. This was sealed up and has been fine for about 2yrs. I replaced EGR, MAF manifold valve etc obviously with no luck.

The only way this was found was someone at the garage had a JTD and they compared results and parts until the offending part was identified - as at idle it was fine.

Hopes this helps

cheers