P0299 Turbo Underboost That Won't Go Away

mchan68 · April 5, 2011

2004 Late-build Excursion in for the usual trifecta with head studs to boot. Original complaint of coolant venting from degas bottle and lack of power. BEFORE the repair, VGT duty remains steady at 84.99% at idle, and won't get out of its own way until about 2800 to 3000 RPMs. After head studs, EGR & oil cooler replacement, along with turbo service and unison ring replacement, SAME FUCKING THING!!! The unison ring was pretty stiff to remove from the housing, but cleaned up and went back together with no issues at all. BARO at KOEO is indicating 13.93 psi (a little low?), MAP 14.2 psi at KOEO and EBP 14.1 psi at KOEO. At KOER, MAP fluctuates between 13.96 to 14.02 while EBP increases to about 15. This truck just got new hot side rubber boots (as per customer request). When driving on the highway, just above 2800 RPMs MGP peaks out at about 26 psi (which I consider normal), but on the low end it struggles to accelerate. When active commanded to 1200 RPMs, VGT duty cycle stays steady at 84.99% with ZERO change in MGP. I tried unplugging EBP and driving it. Somewhat improved with EBP unplugged but not 100%. Drove home. Swapped a VGT from a turbo I had laying around. No change. Getting back to the basics. A P0299 lists possible causes as VGT and EBP. Where else do I go next? MAP sensor? Posted Image

mchan68 · April 5, 2011

Furthermore, I even removed the EBP and verified the tube not blocked up as well as the MAP sensor hose. I should also point out that this truck has the CAT and EGR throttle plate removed.

blown99 · April 5, 2011

Be sure the fitting in the exhaust manifold is not plugged.

EGR valve hanging open - any black smoke conditions

BLittle500 · April 5, 2011

Had a state truck in from another shop one time, wouldnt get out of it's own way but once you got it wound up it seemed fine. Hotline thought it was a trans concern, but after going down that road they sent out an FSE. We monitored LOAD at hot idle, he reccomended that anything over 30% to check fuel pressure and then put 'er down for all 8 injectors due to being weak. I was cautious about dumping 8 injectors into the truck, but it did fix it. A few months later, had an excursion in from the same shop (imagine that), wound up having a junk fuel pump that in turn wiped out the injectors (Diagnosed the injectors the same way).

Something worth checking into maybe

Brad Clayton · April 5, 2011

We also just replaced a fuel pump in an Excursion that ended up needing 8 injectors also. Thing runs like a champ now.

mchan68 · April 5, 2011

Well, I just ran it outside with the EBP tube disconnected at the EBP end, and I feel pressure exiting the tube when the engine is revved up. It seems as though EBP is not increasing to the expected value is what I surmise to be why VGT duty cycle remains locked solid at 85% at idle (650 RPMs). What is EBP supposed to increase to when the engine starts? I'm getting old. It should increase to at least high 15s or low 16s correct? This thing remains at about 14.2 psi, so I'm comfortable to say that the PCM is seeing as good as NO INCREASE in EBP is why it's doing what it's doing. The question I have is, have any of you guys seen an EBP cause this issue before, even though it reads where it should at KOEO? The last time I had an '04 do this, was one that the owner replaced the T-Stat on himself, and spilled coolant all over the EBP sensor. But on that particular truck, the EBP reading was WAY OFF. Replace the sensor and that fixed it. Again, this thing only sets a HARD P0299 by itself when I attempt a KOER self-test. No P0470, no P2262 or P2263 or other DTCs for that matter.

joshbuys · April 5, 2011

I've always been of the opinion that if the unison ring is hard to get off the center housing, then it needs a center housing and unison ring, I've tried cleaning them in the past when they were stuck together and this fixed it for a short time, but they always come back with the same issue, maybe your unison ring/center housing are sticking together again?

mchan68 · April 5, 2011

I've always been of the opinion that if the unison ring is hard to get off the center housing, then it needs a center housing and unison ring, I've tried cleaning them in the past when they were stuck together and this fixed it for a short time, but they always come back with the same issue, maybe your unison ring/center housing are sticking together again?

You know, with MAP/MGP and EBP not increasing to the expected value, I'm beginning to point to the center housing itself as the culprit (what are the chances that BOTH EBP and MAP sensors are bad?). I'm just reluctant to tell the guy he needs to spend another $1200 after he's already into me for the trifecta repair. I KNOW that I've had hundreds of these center housings apart and re-assembled without further issue. Just by virtue of the fact that it DOES build boost at the upper RPM range to the peak 26 psi tells me that I can safely rule out improper re-assembly, or any leaks on the intake side or the exhaust side. Have anyone of you ever seen a faulty center housing that you couldn't condemn by looking at it visually?

lmorris · April 5, 2011

At hot idle, the PCM will try to hit around 16 PSI, 70% VGT usually does this. Can you ramp up RPM and actuate VGT, you should be able to hear it going though the sweeps and see EPB change also. Also try VVT test, even on the older models without the cam in the turbo it can help.

Keith Browning · April 5, 2011

Since this is a late build 2004 engine could you not just use the VVT tool and remove all doubt?

Once upon a time not so long ago I was working on a 6.0L that was running just fine. Guy came in for an oil change and a cooling system service. I noticed one of the turbo to pedestal bolts missing which is not too uncommon. I keep some spare bolts around so I did the guy a favor and installed one. Well, turns out that I must have distorted the turbo in the process and damaged the VGT actuator. Silly things happen.

joshbuys · April 7, 2011

I've seen a few where everything looked fine, cleaned it and re-assembled only to find the turbo still sticking.

Had one a while back where I replaced the center housing, test drove and released only to have it come back 2 days later with a P0299 and lacking power. Performed all my tests, contacted hotline and was told to put another center housing in it....cool, put in new center housing and test drove - immediately set a P0234 - overboost condition - now it's sticking wide open!!

Called hotline and the guy says "they should have never had you put a second center housing in it, you need to replace the whole turbo, and prior to installing the new turbo I would recommend cleaning it".

Apparently enough center housings are fixing these things, that the turbos are hanging out on the shelves too long and rusting....even with all that oil they dump in them?!?! Posted Image

joshbuys · April 7, 2011

Had another one the same week as above where I installed a complete turbo, only to have it come back a week later dumping oil out the exhaust....that one got another center housing!! Posted Image

Brad Clayton · April 7, 2011

Damn son, I bet you can change a turbo in 0.3 hrs, key to key!

mchan68 · April 7, 2011

Well, this guy customer has opted to order a complete aftermarket turbo from the States. I'll be going to his house to help him install it this weekend. Keeping my fingers crossed.

joshbuys · April 7, 2011

Damn son, I bet you can change a turbo in 0.3 hrs, key to key!

Nope, it takes 2.0 hrs....haven't you seen the SLTS? Posted Image

mchan68 · April 8, 2011

Originally Posted By: Brad Clayton

Damn son, I bet you can change a turbo in 0.3 hrs, key to key!

Nope, it takes 2.0 hrs....haven't you seen the SLTS?

Hmmmm. I wonder how long it takes this guy?

Posted Image

Keith Browning · April 8, 2011

That guy talks funny. Did you ever notice that when people swear they lose their accent? LOL! I was waiting for him to put that air chisel through his hand. And lookie! Another EGR hose with a hose clamp around it!!! Posted Image

Brad Clayton · April 8, 2011

I don't know if any of you know this or not, but that's none other that our own big angry hillbilly. Mr Aaron "captain obvious" Robertson. Seriously he sounds and talks just like him. Posted Image

mchan68 · April 14, 2011

A new turbo it is, for the win (just as I thought it would)!!!!

Disassembling the old turbo (again) revealed nothing wrong with my work (also just as I thought it would). Sooooooo, the million dollar question becomes, what could/should I have done differently so as to avoid this from happening again? Posted Image

iceman · April 21, 2011

be careful of the new chras i have put some on only to pull them back apart for leaking oil at a stake plug near the vgt solenoid or making a loud ass whistle noise on the chra near were the shaft goes to the back of the turbo that controls the unison ring just some things too look at sometime u get a good one but most of the time u dont hell don't matter to me turbos are grave off and on and fixed lol