Need some diagnostic help. Excessive exhaust back pressure

[nitronick]

Hey guys,

I'm about at my wits end here. I'm working on an International VT365.

Last week I was at the end of my route driving at highway speeds. Truck had run great to this point. Got stuck behind a slow car. I let the surrounding traffic clear and went to pass. Truck had no power. Since I have had problems in the past, I keep my laptop and interface in the truck (running Navistar's Master Diagnostics software). I was limping the truck to the shop and fired up the laptop. Showed a DTC 343 Excessive Exhaust Back Pressure. Listed possible causes are stuck turbo vanes, turbo actuator bad and wiring harness issues.
Since the truck has a tick over 300K, I started with the turbo vanes. Ordered the cleaning kit since I would need the o-rings and gasket to go back together with it. The vanes and other associated parts were surprisingly clean for having that many miles. Very little soot or rust. Since sticking vanes was obviously not the issue, I ordered the actuator.
Assembled everything and no help. After starting, I almost immediately got a DTC 361 Unable to reach VGT commanded set point. Once up to operating temps and driving, that goes inactive, but get the DTC 343 again. I could hear hissing as if the vanes were closed.

I have inspected all of the intake piping and cooler and dropped the exhaust pipe ahead of the muffler and have found no problems. I have also replaced the exhaust back pressure sensor. Nothing has helped.

Since I overlooked this the other day, I pulled the snap ring and cover on the turbo and the piston moves in and out freely. After installing everything, it did idle normally while warming the truck up. The VGT % seemed to be working properly, and it was showing signs of proper boost and back pressure. This, however, changed once the truck got to temperature and I went to drive it. Almost immediately got the DTC 361 again and the back pressure shot up to over 40psi, giving me the DTC 343 once again.

Any ideas?

I'm almost sure it has to be something in the turbo, but what? I need to get this truck back working again. Rentals are killing all of my profits!

Thanks.

[dannyboy950]

Did you run the truck with the exhaust disconnected and did you still get ebp too high?

What were your maff; map and Iat at dureing all of this?

While the turbo was apart did you check the unison ring that the hole for the actuator was not oblonged wallowed out?

[ford_doctor]

Originally Posted by dannyboy950

Did you run the truck with the exhaust disconnected and did you still get ebp too high?

Excellent question. You have not mentioned whether this is a Ford or Navistar chassis and the exhaust coniguration... some med trucks do run a cat/muffler combination which could have broken up.

[nitronick]

Sorry guys. I was typing so fast trying to keep up with all of the thoughts in my head I've lost a lot of sleep over this trying to figure out what the heck is going on.

This is an '04 4200 International. Build date is mid '03. Around June if I remember correctly.

No cat. I did unhook from muffler and EBP is still high.

Unison ring looks great. No ob-longed holes. As I said, it showed relatively little wear and gunk for an engine with a tick over 300K. I do believe there has been some things changed out before I bought it. The serial numbers on the head do not match the VIN, so at the very least, the head has been changed.

When driving, I'm using the Master Diagnostics DTC Monitor Session. IAT is normal with what I have monitored before. Don't recall MAF. I will have to check that and MAP readings tomorrow, but I know boost pressure is low when I drive it. Not sure what it is at idle warming up (where things seemed to be OK today) and idle after driving it.

Just can't figure out what would have happened immediately like it did.

Thanks for the replies.

[dannyboy950]

I can't remember off hand if that engine used the egr throttle plate or not. If it does check it to see if it is trying to close off on ya. I have seen that happen a few times but really rare.

EBP tube is clear? No restrictions to airflow thru filter ( didn't suck up a rag by any chance)?

[nitronick]

Nope. No throttle plate

[dannyboy950]

Have to think on this some more. You have allready checked and confirmed most causes I can think of off hand.

Thought of somethin else check your air cooler look for a blown seam or tube. Also rare but since you have eliminated all the common causes we gotta think outside the box. Even if way out in left field LOL

[nitronick]

I'm going to try to get to it tomorrow morning and get some updated test numbers.

Here are some numbers from Friday morning.

Doing the Master Diagnostics Continuous Monitor Session, Key On Engine Off test

EBP voltage is .86v
MAP voltage is .88v
BARO is 14.8psia
EGRP is 0% and .68v

Run Output State Low Test shows EGRP 74.5%

Cancel Output State Low Test shows EGRP 0%

Key On Engine Running VGT

Low, Medium and High duty Cycle tests all are 6.4 - 7
(Service Manual test sheet says there are supposed to be distinct changes in EBP during each duty cycle.)

All of these numbers are from Friday morning after I installed the various parts but before I messed with the piston.

[bismic]

What was the EBP reading in psi at KOEO? Same w/ MAP.

Sure sounds like the turbo is the root cause though.

[nitronick]

OK. I think I may have found a problem.

I had planned to pull the snap ring and cover and pull the piston to about the mid bore, re-install and run the truck getting some numbers. I decided to check something. When using a magnet to pull the piston, I was shining a light to watch the vanes. There was no vane movement at all when going back and forth with the piston. I pulled the hex plug to watch the cam, and it is moving.

Are the vanes supposed to move as a direct action of moving the piston?

[nitronick]

My question is should this cam/gear rotate freely on that shaft with the piston pulled out.



Cudos to mil-specrestro. I hope he doesn't mind that I'm linking to his pic!

[Paul H]

I would have to say the the VGT vain position is do the the shaft turning and the excentric pin moving the unison ring. if the gear spins on the shaft then I would say it is not moving anything.

Now is the shaft stuck in the housing making the gear shear itself from the shaft? A stuck shaft would hold the vains in one position not letting them blow open or closed with exhaust pressure.

[nitronick]

The eccentric pin was rotating when I had that apart for cleaning. It was not stuck.

Is it and the shaft cast as one piece or is it secured to the shaft with a pin or some other such fastening mechanism?

Kind of difficult for me to post now. I'm driving!

[Paul H]

I have not had one appart but I thought from looking at videos and diagrams that the eccentric and shaft are one cast part and the pin is pressed into it and the gear is a seporate part attatched on the other end. The grear has to turn the eccentric to open and close the vains so must be affixed to the shaft by some means.

Found this but no clear photos of the eccentric and gear.
http://www.fordtechservice.dealercon...6lvgtguide.pdf

[nitronick]

Pin is broke into three pieces. Got them extracted and will try to find a replacement tomorrow morning.

Sure wouldn't think there would be enough pressure from any of these components to shear it like that....