6.0L e-series loss of boost

Matt Saunoras · September 20, 2016

I've had a real head scratcher here for a couple weeks. I spent quite a bit of time on this thing for a relatively easy fix I wish I would have heard about before. This school bus came in for a loss of power while accelerating up a hill and wouldn't upshift. When they told me about it over the phone I was thinking I'd nail injectors on it and be done. No one wants to do E-series injectors so I got them on nearly every one that came in sooner or later. This was a fresh bus I'd never worked on with about 120k miles.

I get the bus, check all the obvious stuff like power balance, DTCs, FICM voltage etc. Nothing. Go for a ride and it runs okay. Hit the throttle pretty hard up my diag hill and as soon as the 3-5 shift completes it falls on it's face and I have to turn around and head back. It didn't smoke, didn't miss, didn't stumble basically ran fine except boost dropped to zero. Actually boost dropped below zero which I found weird (MGP said zero but MAP went lower than KOEO). EBP didn't skyrocket like a plugged CAT and fuel pressure didn't drop even a little. I could accelerate for a bit and it would be fine until it hit a certain point, usually after a shift, and it would just bog and I'd have to stop to regain power.

I drove this thing up the hill no less than a dozen times trying to wrap my head around what was happening. I figured it had to be VGT related so I dug in a little bit, found the VGT solenoid wiring hacked all to shit and thought for sure I found it.

The only thing I really found out was that someone tried to fix this thing before me, infact it came directly from another dealer that gave up on it. That didn't make me feel too great.

So I fixed the VGT solenoid wiring and much to my surprise that didn't do anything. Put a known good VGT solenoid in it, that didn't do anything either. Re-ran turbo boost and EGR KOER self tests with no avail. Checked the air filter which was new and finally I pulled the EGR valve out and found it to be exactly like the known good one I have. I'm nervous at this point.

I didn't really think it was EGR because my EBP was consistently higher than my MAP..... BUT my MAF did start to dive before the boost started to drop. I knew it was something air intake related but I just couldn't put my finger on it. When I had the intake duct out of the way I found about a 4" long piece of hard plastic floating around near the compressor wheel, I thought maybe that it was jamming in the wheel but that wasn't the case. I couldn't imagine where it came from or what it was. I then borescoped the hot side of the intercooler which wasn't one of my better ideas but I was desperate. Didn't find anything.

Today I was ready to pull the turbo and I was feeling pretty sick about it because I knew deep down I wasn't going to find anything. I grabbed the long intake duct to pull it over the cold side cac tube and it felt squishy for a lack of better terms. I knew right away why as soon as I looked down the duct.

I've never once thought about that duct or even looked down one. There's a hard plastic shell inside to keep the thin middle part from collapsing. Well guess what this bus had missing, about half of that shell. Whoever broke it and removed the inside pieces really needs an ass kicking. That's where that piece of black plastic came from that was near the compressor wheel.

So after all this I'm still not convinced this simple ass find is going to fix it, a new duct is 2 days out and I really didn't feel comfortable waiting (aka wasting more time). I had a seat for a minute with the brain hat on and it hit me, the towing company down the street has junk 6.0 ambulances in their yard (ones that I basically put there 0:) ). Made a call, grabbed some tools, climbed over quite a few cars and found one out of sight that still had a usable duct. I sweated my ass off getting that duct out while laying on the hood of another car jammed right up against it.

I couldn't have been happier walking into the shop with a perfectly good duct ready to proceed with my findings. Slammed it into my short bus and away it went. The damn cat was so loaded up with soot I thought I still had something wrong but eventually it cleared itself up and ran great. It felt so good to make that shift at the exact point it would act up every time and not have to turn around.

So all in all it was the rubber intake duct collapsing once I hit a certain load due to someone breaking the hell out of the inside. Very simple fix that couldn't possibly happen on an F-series.

jimmy57 · September 20, 2016

You should have told us you fixed it with duct tape in the very last sentence of your post. But alas, we still don't know of anything that duct tape really fixed.

Great find.