1993 6V92 Turbo Wont Boost

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1993 6V92 Turbo Wont Boost

September 25, 2016, 05:53:26 pm

I've been noticing a loss of power since I had the top end redone last April. Turbo boost seemed to be getting lower and lower but today while climbing a big hill on I-70 in Missouri things really got bad. Now the best I can get is 5 psi. I pulled off into an RV park to work on the old girl. I am afraid to taker her back on the Interstate with the power so low. Does anyone have an idea of what can cause so much loss of boost.

As a little background, the boost measurement is via VMSPC. The turbo has normally had a maximum boost of 20 to 22 psi at 2200 rpm on long hills. Until today it had been running about 14 to 15 psi maximum but I had been doing OK and was going to be back to the mechanic that worked on it in November. Its too hot to take anything apart right now but all of the plumbing connection seem to be tight. The turbo isn't making any unusual noises. I can't hear any air or exhaust leaks. The engine is running very smoothly as normal. The engine temp was in the 170's and oil pressure normal. My guess is the DDEC, electronic engine control, may be the culprit but I would like it to be something mechanical that I can fix myself.

Has anyone had a similar experience or have any ideas of what could be wrong.

Re: 1993 6V92 Turbo Wont Boost

Reply #1 – September 25, 2016, 05:55:58 pm

Are you burning any oil? Turbos( in my experience) either smoke or blow up, both have happened to us.

Re: 1993 6V92 Turbo Wont Boost

Reply #2 – September 25, 2016, 06:42:17 pm

Quote from: mike leary – September 25, 2016, 05:55:58 pm

Are you burning any oil? Turbos( in my experience) either smoke or blow up, both have happened to us.

Mike, no smoke at all. Not gray or black. That is something I have been looking for after talking with Ken Hatfield.

Re: 1993 6V92 Turbo Wont Boost

Reply #3 – September 25, 2016, 06:49:05 pm

Check all the rubber connections between the intercooler and the turbo one of the bands may have come loose.

Re: 1993 6V92 Turbo Wont Boost

Reply #4 – September 25, 2016, 06:53:07 pm

Quote from: Bill Willett – September 25, 2016, 06:49:05 pm

Check all the rubber connections between the intercooler and the turbo one of the bands may have come loose.

Thanks for the thought. 6V92 doesn't have an intercooler. It has a roots blower (super charger).

Re: 1993 6V92 Turbo Wont Boost

Reply #5 – September 25, 2016, 07:20:02 pm

Check air filter gauge if it has one if not open up and check for rats nests, its happened before also possible plugged fuel filter. There is no blow off on the blower. I only am familiar with the old 71 series but believe that if it has a belt and fuel pressure and air it works.

Re: 1993 6V92 Turbo Wont Boost

Reply #6 – September 25, 2016, 07:35:58 pm

Sorry Kent, I should have looked at your signature.

Re: 1993 6V92 Turbo Wont Boost

Reply #7 – September 25, 2016, 08:11:32 pm

PM Dave Metzger

Re: 1993 6V92 Turbo Wont Boost

Reply #8 – September 25, 2016, 08:22:40 pm

Quote from: craneman – September 25, 2016, 07:20:02 pm

Check air filter gauge if it has one if not open up and check for rats nests, its happened before also possible plugged fuel filter. There is no blow off on the blower. I only am familiar with the old 71 series but believe that if it has a belt and fuel pressure and air it works.

Been years since I been around a roots but I thought they had a pair of spring loaded waste gates on the front or rear. My 30 year old recollection has to be taken with a 10 lb grain of salt.

Is there a belt tensioner or an idler on the belt if it has one?

Re: 1993 6V92 Turbo Wont Boost

Reply #9 – September 25, 2016, 08:30:15 pm

Quote from: Old phart phred – September 25, 2016, 08:22:40 pm

Been years since I been around a roots but I thought they had a pair of spring loaded waste gates on the front or rear. My 30 year old recollection has to be taken with a 10 lb grain of salt.

Is there a belt tensioner or an idler on the belt if it has one?

My memory of 0ver 30 years ago is dim also. I think they were there if the engine started to run away. Those engines could start sucking crankcase oil and take off.

Re: 1993 6V92 Turbo Wont Boost

Reply #10 – September 25, 2016, 08:33:58 pm

Are your fuel filters good and clean? Dirty fuel filters will cause loss of power. The 6V92 turbo feeds air into the blower underneath,The blower is gear driven. Under the blower is a cooler,they can get clogged with oil buildup and restrict the air from passing through to the cylinder openings.

Re: 1993 6V92 Turbo Wont Boost

Reply #11 – September 25, 2016, 08:55:17 pm

Finally someone who has one of these engines. I never worked on a 92 series quite different it seems.

Re: 1993 6V92 Turbo Wont Boost

Reply #12 – September 25, 2016, 09:58:27 pm

Quote from: craneman – September 25, 2016, 07:20:02 pm

Check air filter gauge if it has one if not open up and check for rats nests, its happened before also possible plugged fuel filter. There is no blow off on the blower. I only am familiar with the old 71 series but believe that if it has a belt and fuel pressure and air it works.

The filter gauge is green so I guess its not an air issue.

Quote from: Old phart phred – September 25, 2016, 08:22:40 pm

Been years since I been around a roots but I thought they had a pair of spring loaded waste gates on the front or rear. My 30 year old recollection has to be taken with a 10 lb grain of salt.

Is there a belt tensioner or an idler on the belt if it has one?

The waste gate has been a suspicion but I have no idea how it works on this engine. Is there any way a waste gate can get stuck open? Is the waste gate controlled by the DDEC?

Quote from: stump – September 25, 2016, 08:33:58 pm

Are your fuel filters good and clean? Dirty fuel filters will cause loss of power. The 6V92 turbo feeds air into the blower underneath,The blower is gear driven. Under the blower is a cooler,they can get clogged with oil buildup and restrict the air from passing through to the cylinder openings.

I'm thinking that the fuel filters may be suspect. I had just refueled before this happened so I'm also considering bad fuel but I called the Loves and they claim they have had no complaints. The engine had the top end done, heads etc. in April this year. Less than 1000 miles. Would that work affect the blower and the cooler. Could an error in reassembly have caused this?
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Re: 1993 6V92 Turbo Wont Boost

Reply #13 – September 25, 2016, 11:29:48 pm

It's the fuel filters. This has happened to me. I had semis passing me on hills! (laugh) The primary fuel filter is super easy to change, and that might fix it. The secondary fuel filter is way up high so the fuel runs down your arm and you smell like a real mechanic for a couple of days afterward. Open the small door at the far rear of the coach on the passenger side and you'll see filters in there. The one with the black knob beside it is the primary fuel filter. The black knob is the primer pump. If you can't get the primer pump to work anymore don't despair, your engine will still start right up if you fill the new filter with diesel before you install it. The other filter without the black knob beside it is the coolant filter. The secondary fuel filter is at the far rear of the engine on the driver's side way up high so you can barely reach it. Even if you fill the secondary fuel filter with diesel you'll still have to crank a long time to get the engine to start. I suggest changing the primary fuel filter to see if that fixes it, unless you really want a diesel bath? Order both filters and carry them with you at all times from now on.

Re: 1993 6V92 Turbo Wont Boost

Reply #14 – September 26, 2016, 12:06:42 am

Kent,
I think Stump might be on to something. Maybe the low boost is a symptom.
Maybe I'm wrong but I think if you had low boost pressure (due to bad turbo, etc.) you would see a lot of black smoke. Since you are not that would indicate full fuel flow is not happening.

You didn't mention if you saw any fault codes from the DDEC.
I doubt there's anything in the DDEC that could directly cause low boost. The DDEC has many inputs but really on one output: fuel control. Attached is a simplified diagram.
Looking at the diagram the throttle position sensor (i.e the gas pedal) could be bad. The VMS should read it with only the ignition on. Should go from 0 to 100% when pedal is floored.
I suppose it could also be the boost sensor itself. You should see a code though.

I had something similar happen after I worked on my engine but the symptoms sound a little different but I explain what happened anyway just in case. While crawling around on the engine my foot must have unclipped an electrical connector. It was the throttle position sensor to the transmission. The engine seemed sluggish as I was driving on surface streets around the neighborhood. When I got on the freeway on-ramp I knew something wasn't right since it was extremely slow to accelerate and I canceled my trip and turned back home. What I didn't realize what that it was not downshifting. It took me weeks to figure out it was just this little connector with a few wires that was disconnected by only about 1/4 inch. It's located on the passengers side, longitudinally about where the bell housing ends. It's one of those weather-tight connectors with a green accordion looking seal on it. I didn't have the VMS back then so i don't know what happened with the boost.

In regards to previous work causing this: Hard to say. I have pulled my blower before to inspect the intercooler for debris - it was clean. The engine was pretty easy to work on and seemed hard to mess up. If it were me I would pull the boot off the turbo intake just to take a look at it and verify it spins OK and there is no blockage or anything else strange.

There is a bypass for the blower. The blower provides primary pressure at low RPMs and the turbo at high RPMs. When turbo pressure exceeds blower pressure the bypass kicks in. I believe it's a 1-1/4" diameter can thing with a small green hose attached to it. I really don't know much more about it.
Good luck

Re: 1993 6V92 Turbo Wont Boost

Reply #15 – September 26, 2016, 12:44:38 am

After some research I agree with craneman, there is most likely not a waste gate or pressure relief... I was mistaken by what I seen on a bogus show car, and it stuck in my mind as I am more turbo oriented. Air filter indicator may be stuck or faulty due to lack of sealing. Boils down to fuel supply, air supply restriction including the under blower charge cooler plugged somehow. Most of these pretty simple fixes. BTW does the crankcase ventilation go thru the roots and after cooler?

Re: 1993 6V92 Turbo Wont Boost

Reply #16 – September 26, 2016, 01:05:35 am

@Kent,

Do easy things first. Pull boot on turbo. Can be easily done from the back of the coach. 2 large hose clamps. Visually inspect turbo for impact damage, wiggle it around checking for play, and check that it spins easily. If nothing there change out the fuel filters. Use your judgement here. If they've been in for a year or more just change em' it's time anyway.

I'm inclined to agree that with no smoke it's could easily be a fuel problem.

Good luck. Let us know what you find.

see ya
ken

Re: 1993 6V92 Turbo Wont Boost

Reply #17 – September 26, 2016, 02:49:06 pm

Change the primary fuel filter and see if that fixes it. It'll take you a whole minute to do this. If that doesn't fix it change the secondary fuel filter. There's nothing wrong with your DDEC, your turbo, your supercharger, or anything else. You need to change your fuel filter because it's plugged. It happens at least every 30.,000 miles or more often. Thousands of dollars of expensive VMSPC toys won't diagnose this. It's just a plugged fuel filter. Carry both fuel filters with you from now on and change the primary fuel filter the first time you notice power loss climbing steep hills.

Re: 1993 6V92 Turbo Wont Boost

Reply #18 – September 26, 2016, 03:13:36 pm

Latest update. I am at a diesel shop in central MO. Seems like they really know what they are doing. We have changed fuel filters and air filter to no avail. There is no wast gate on this engine. The are checking for air box leaks now but still don't know what the problem is. Next is to start on the Turbo itself. Will let everyone know when I do.

Re: 1993 6V92 Turbo Wont Boost

Reply #19 – September 26, 2016, 03:42:07 pm

Could the muffler be completely stopped up

Re: 1993 6V92 Turbo Wont Boost

Reply #20 – September 26, 2016, 04:07:21 pm

On my big truck when I lost boost from the turbo it was a bad boost sensor. Don't know if these engines are set up the same.

Roland

Re: 1993 6V92 Turbo Wont Boost

Reply #21 – September 26, 2016, 04:48:41 pm

Quote from: Kent Speers – September 26, 2016, 03:13:36 pm

Latest update. I am at a diesel shop in central MO. Seems like they really know what they are doing. We have changed fuel filters and air filter to no avail. There is no wast gate on this engine. The are checking for air box leaks now but still don't know what the problem is. Next is to start on the Turbo itself. Will let everyone know when I do.

Ouch I smell coach bucks.

see ya
ken

Re: 1993 6V92 Turbo Wont Boost

Reply #22 – September 26, 2016, 04:57:00 pm

Can you look in the air box to see if it is plugged?

Re: 1993 6V92 Turbo Wont Boost

Reply #23 – September 26, 2016, 05:09:11 pm

Pardon me, but is that a turbo or a supercharger we're talking about? $:-\$

Re: 1993 6V92 Turbo Wont Boost

Reply #24 – September 26, 2016, 05:41:29 pm

Quote from: mike leary – September 26, 2016, 05:09:11 pm

Pardon me, but is that a turbo or a supercharger we're talking about? $:-\$

The DD 6V92 has BOTH. Supercharger for low speed, turbo higher speed.

Remember, it is a two stroke engine, so the supercharger is what scavenges the exhaust out of the cylinders.

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