Things I'm doing to improve boost (pics)

Scott & Heather · May 17, 2017, 10:06:03 AM

Cliff, as far as I know, this 8v92 DDEC II came with the coach from the factory...along with the Allison 748 ATEC trans. Ken and I just were noticing she is sluggish and smokey and runs a tad warm all the time and boost (even under load up a hill towing my 7000lb land cruiser) maxed out at 12psi. I am just trying to work through some of the simple stuff first...again, we uploaded a 500HP program to the coach that was a factory setting for an 8v92 DDEC II. So everything should be ok on that end...I'll keep this thread updated. Exhaust, filter/intake tubing, and new boost sensor should arrive by Monday. I'll have my work cut out for me.

luvrbus · May 17, 2017, 01:52:22 PM

There was 2 versions of the DDEC ll one version would support up to 475 the other one would support up to 450 hp , I never knew MCI ever went above 400 hp with a 8v92.Arnold is smart guy he will figure it out

Scott & Heather · May 17, 2017, 08:06:25 PM

I am
Wondering if this was a program someone made adjusting fuel tables pulse width modulation etc. I don't know exactly but it gave me more powah and I'm happy. But, still having some issues.

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Prevost45 · May 18, 2017, 12:42:22 AM

It looks like the v-band clamp is missing on the hot side. At this point in it's life it's
Become one piece.. Probably going to need a fresh turbo from the rest of the symptoms.

Scott & Heather · May 18, 2017, 07:04:47 AM

Hi Prevost45, you have to read through the whole thread and catch up a little lol. I removed that clamp to replace it with a new one. Also, my turbo is fine. Spins freely, no lateral play, no fin damage. I can hear it sing pretty when I'm on the throttle. I never had much black smoke on the coach until we turned up the fuel. But boost isn't matching what we've done. So I'm trying to chase down some other possible issues.

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Scott & Heather · May 18, 2017, 11:04:07 AM

So I removed the turbo boost valve, and it was moving freely. The problem is the small hose that is attached to it was completely clogged with soot. Literally it was completely clogged. Even the brass nipple that that hose is connected to on the engine side was completely clogged with soot. I'm purchasing a new hose today and a new nipple.

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B_K · May 18, 2017, 11:35:20 AM

That $0.50 hose could be your whole problem!

BK

Who was it that said to check that bypass valve again?

Iceni John · May 18, 2017, 12:07:24 PM

But why is there soot in it at all? I'm wondering what else is causing that problem.

John

eagle19952 · May 18, 2017, 12:12:57 PM

uhm...that is more than soot....

Scott & Heather · May 18, 2017, 02:07:31 PM

Lol. It was cliff. And yes, you're seeing old grease and oil on the outside of the bypass valve but that's not what was inside the hose. The hose had dry carbony soot inside it. I am wondering why too???

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Scott & Heather · May 18, 2017, 02:08:40 PM

Can someone explain to me exactly how the bypass works? Does it have vacuum and pull the valve into the retracted position? If that hose is clogged would it send the valve into "always bypass" mode?

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Scott & Heather · May 19, 2017, 09:44:41 AM

Bypass valve is cleaned, moves freely (it did when I pulled it out) and is going back in right now. Turbo boost MAP sensor hose is replaced and waiting on new sensor.

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Geoff · May 19, 2017, 10:36:24 AM

Quote from: Scott & Heather on May 18, 2017, 02:08:40 PM
Can someone explain to me exactly how the bypass works? Does it have vacuum and pull the valve into the retracted position? If that hose is clogged would it send the valve into "always bypass" mode?

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The blower by-pass works like this: when the turbo boost gets to a pre-set pressure, the by-pass pushes a release so the blower spins free allowing more air into the engine. Without the by-pass, the intake air is limited to what the blower drive allows. So, the by-pass allows more air into the engine because the turbo can produce more air than the blower. The freed up blower lobes turn faster with turbo boost.

The only way you could have soot in the by-pass is from the little nipple on the turbo mount. Your turbo must be leaking exhaust smoke into the fresh air side of the turbo; or more likely, your engine exhaust is getting sucked into air intake somehow. Take the inlet hose off the turbo and wipe it with a clean rag and see if there is soot. If there is no soot, then it is the first maybe-- the turbo exhaust is leaking into the inlet air side of the turbo.

--Geoff

Scott & Heather · May 19, 2017, 11:28:32 AM

Thanks so much for
That explanation. Makes much more sense to me now. I think you're right about the exhaust getting sucked into the turbo. The exhaust had a leaked at the down pipe right next to the original air filter housing. Somehow I think the drain hole was sucking soot into the air filter because the filter was completely black with soot after just a few thousand miles of driving. I'm moving the air filter to the other side of the coach as we speak so that won't be an issue anymore anyway. I'm also replacing the wide band clamps that hold the two pieces of downpipe together.

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Iceni John · May 19, 2017, 12:19:26 PM

Is that new Push-Lock hose going to withstand the high temperature there? I originally had an Alkon AQ-DOT push-in fitting there for some 1/4" plastic air tubing to my turbo boost gauge, and it completely melted the fitting's O-ring and the tubing. The air there is very hot! I replaced it with an all-metal compression fitting and a few feet of copper 1/4" refrigeration tube before the plastic tube.

John