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So where did your getty-up-and-go, go anyway?

The most famous part of the 6.5TD engine is the “TD.” That stands for Turbo Diesel. We all love the singing of that turbo under the hood. Some sing, some are of key, and some don’t sing at all. So, let’s dive into the common turbo issues.
One of the most common problems that comes around on these turbos are:

“I'm blowing black smoke”
“I don’t have much power anymore”
“My service engine light comes on”

So how does this macho piece of hardware work? Pretty simple actually. It is an exhaust-driven turbine motor driving a centrifugal air compressor. There are two “wheels” connected by a shaft. One wheel or turbine-fan is in the exhaust stream, the other wheel or compressor-fan is in the intake path. As the engine runs it pushes the exhaust gas out through the exhaust system. The turbine-fan wheel is driven by that exhaust gas. It in turn spins the compressor wheel. The compressor wheel pushes more air into the intake of the engine. More air, more fuel, more exhaust. More, more, more, which means more power “available” to be made. This increase of air is called boost.

What is a wastegate? The wastegate is a flapper-type valve that opens up on the exhaust turbine side of the turbo. This flapper will allow exhast gas to bypass and not spin the turbo as much. This will reduce boost pressure. This flapper remains closed under most conditions (idle, cruising, etc). It is designed to usually open up during high-load conditions, which causes high cylinder and exhaust heat.

So does more boost mean more power? Not really. It means that more power can be made. Boost is air. Air is cheap. If you want power, you have to pay for that at the pump. Power is fuel. More boost means you can burn more fuel. You can always dump in more fuel (to a point) but it won’t burn effectively until you have enough air to complete combustion.

So how much boost can I build? There seems to be ongoing discussion as to how much boost you can make. Some people like the idea of engine-splitting boost pressures, others like longevity. Which ever you prefer will be the answer to your question. The fine folks at GM have said the 12 is plenty. You can run higher levels, but you better do some reading, and have some cash ready too. That will be spent on modifications to the engine, or modifications to the engine after it’s failure. You can run more than 12 psig of boost without blowing it up. How long will you get away with this? That’s a variable not yet established, but the event is usually marked with exciting noises and other fanfare.

So why doesn’t my turbo work? There is are some common failing parts on these systems that will put your turbo on holiday. They would be:
°Wastegate solenoid
°Vacuum leaks
°Vacuum pump

Let’s go over some vocabulary here real quick: (For pictures go here)

Wastegate solenoid - This little piece of s. . . Plastic, yeah, that's it.....plastic....is a small solenoid-valve that PCM pulses in order to regulate the vacuum supply to the wastegate actuator.
Wastegate actuator - this is the small gold canister on the side of your turbo that pulls the rod to the wastegate. It opens and closes the wg by vacuum on a diaphragm which creates thrust on the rod.
Wastegate - This is a flapper-valve on the exhaust turbine side of the turbo that allows exhaust gas to bypass the turbine fan, reducing boost pressure.
Compressor - That is the intake air side of the turbo. It pushes the air into the intake.
Spool-up - That is the spinning-up of your turbo.

More in depth coverage lies below in this post. More great information can be found in the Wastegate Thread, courtsey of gmctd.

So, with that covered, now we talk about what is going wrong with all this pieces and parts. When the turbo stops working, it is usually because the wastegate is open, or opening. The wastegate is used to regulate the amount of boost coming into the engine. Why, you ask? Well for some very simple reasons.

How do I check to see if I have wastegate problems? A quick test would be, at idle, see if the wastegate rod is pulled up into the actuator housing. If it is, that is a good start. Now, pull on the rod, and see if you are able to move it. Pulled in means there is vacuum. Suction is good, but how much? If you are able to move it, then you may not have sufficient vacuum to maintain boost.

To really test the system you should get a vacuum gauge to verify readings - with engine idling you should have 26"hg at the vacuum pump and 15"hg at the wastegate, but the above 'pull-test' will show if you're in the ball park.

The wastegate solenoid is the most common failing part in the whole system. Chances are if you have problems, this is it. Now, don’t just condemn it because it’s everyone else’s problem. Verify first that it is bad. How?

How do I determine if my Wastegate Solenoid is bad? You must see if there is vacuum before and after it. Locate the solenoid by tracing the vacuum line back from the wastegate actuator. You will need to determine if you have vacuum after the solenoid. You’re looking for about 15” of vacuum. Many refer to this a pressure. It’s not really pressure, but suction. Notice I did not say 15 psig, but 15”.
This little valve has three ports. Only two of which you hook vacuum lines to. One is the vacuum source (to the vacuum pump), the wastegate actuator, and vent. Vent, is not something you hook anything to. Why a vent? That is how it regulates the amount of vacuum going to the actuator. There is a little steel ball inside the valve that switches back and forth between vacuum and vent. Here lies the problem. That ball will rust. When it rusts, it won’t roll anymore, so your engine power no longer rocks. Thus, you ain’t rock’n’rollin’ anymore. When the ball doesn’t move, it will get stuck and not allow vacuum (usually) to the wastegate actuator, leaving it open all the time. This means a no-boost situation.

The solenoid can fail in a vareity of different ways. It can fail to provide no vacuum to the actuator. (most common) It fail to provide vacuum always (not as common, but possible), the coil could fail, or no power to the coil from the ECM. Sometimes the ball will “stick” causing erratic boost, where it will spike up and down.

Can you fix this? Yes, replace it. No repairs ever found really. You can “limp it along” by spraying something like WD40 into the port. This may help to free it up, but it won’t live forever.

Where can I get one? Usually it’s a dealer item. Local parts stores don’t seem to have this item for some reason. Check around, there are some on-line parts sources.

I have no vacuum before the solenoid? You should check to see if your vacuum pump is working. If you have no vacuum present before the solenoid, then you either have a bad vacuum pump, or a leak somewhere. Chances are if you have an EGR equipped engine, you’ll have EGR codes if you have no vacuum, because they are all vacuum driven.
Weak vacuum too will also cause problems. You should have around 26"hg of vacuum available at the pump.

Where is my vacuum pump? It is driven by the serpentine belt. Look here.

Don’t rule out vacuum leaks. If you have a leak, you maybe changing parts that work just fine.

I am blowing black smoke, does this mean I have a turbo issue? Sometimes it does, if you have gone through all of the above diagnostics, and everything is okay, then may need to check some other things.
Does my computer (ECM) indicate problems with my turbo? Yes, depending upon your year, will depend upon what codes you will get. There are two generations of computer, OBD-I, OBD-II. The first one can be checked with a paperclip. The second needs a code reader. 96+ vehicles have the second generation that needs the reader. Check the FAQ section of this forum for specific codes.

What if my vacuum pump is bad? Well, economically speaking, you’ll have to make the determination if you want to replace it, or go with a simple spring on your wastegate to regulate vacuum. Yes, you can eliminate the problematic vacuum system on your turbo if you would like. So, why doesn’t everyone do this? Well, there are some things you need to watch in doing this. Your computer regulates everything with the stock system. You eliminate that, you will have to take over being the “brains” of the engine in the boost department. DO NOT replace with the spring system unless you have a mechanical boost gauge to monitor the boost pressure. Aftermarket products are available for a turn-key spring system, or you may fabricate your own.

How do I know if the actuator is bad? Well, this is not as common a problem, but does happen. You can check this by providing vacuum to the wastegate actuator, and see if it holds. If it leaks, then you may either replace the actuator, or go with the spring/mechanical system.
What happens if I build too much boost? Then, that’s called over boost. This is where the computer takes evasive action to prevent from blowing up. Depending upon what your computer is programmed to do, it will either dump the boost, or go into limp mode (may limit engine to 2000 rpm, and no power) This will also set the Service Engine Light.

So I can have either too much, or too little boost? Yes you can. Either is undesirable. Too little will not provide complete combustion, and cause higher EGT (Exhaust Gas Temperatures). Too much boost will cause unnecessary stress on the engine.

Are there any other things that will effect this system? Yes, the air filter. If it is dirty, it will reduce the amount of air that the engine can ingest. This can make noticable engine power losses. Don't trust that little pop-up thingy to tell you when it's dirty. Open the filter box up and check for yourself.

Does the turbo work all the time? Yes it does, mostly. At idle, under load, etc, it's spinning, or supposed to at least. The wastegate opens to bypass some of the exhaust gas to reduce boost under high-load situations. There is no occurance where the turbo "shuts off" under normal conditions or at idle. It will always be spinning.

What are the drawbacks to this turbo system? Well, it performs well under the conditions it was designed for. If you begin to take it outside of those operating parameters, it becomes an expensive hairdryer. Turbo compressors produce heat.

What's wrong with heated air coming out of the turbo? Well, the heat makes the air less dense. You are wanting more density of air to burn more fuel. That's what a turbo is for. It's for jammin' more air into the intake. Once you heat the air, it becomes less dense, and starts to be counter-productive.

How can I overcome this? You must come up with some method of intercooling. That is a way of cooling the air charge before it enters the intake. Under high boost conditions, your intake air temperatures can rise to 200°+F. That's the INTAKE, not what's happening in the exhaust, or the clyinder, that's BEFORE it gets there.

How can I intercool my engine? There are intercoolers available on the market that uses air to cool the air charge. There is also water mist injection. There are posts out there on these topics, feel free to search them, with forum's search feature. You may also check out the FAQ's, or follow this link.

Do I need an intercooler if I don't do any towing or have any performance modifications? Well, it's up to you. The current stock setup will get pretty hot still. It's all in where you want to spend your money. Do some more reading on the subject and see if this is something that suits you and your budget. Of course we'd all like to have our engines as souped up as possible, but then again, we have other payments that are calling our names. . .

How can I put an intercooler in, and how does it fit? Check this link. Do a search, there are many others.
Hope this helps to you to better understand everybody’s favorite part of their engine: The turbo.
 

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Test gage critical to successful troubleshooting of any vac issue Harbor freight has them "on sale" all time if you can wait for specials, or local auto part store has diagnostic vac gauges
 

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Can the vacuum pump be bypassed and replaced with an electric vacuum pump
You can but I would avoid it due to the fact of the heat soak issues on the electric pump, would shorten its lifespan quite a bit..

These 6.5L engines can heat soak electronics to death.:HiHi:
 
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You can remove the Vacuum pump altogether and just install a Turbo Master ( manual wastegate controller) and a 1" shorter serpentine belt and installing a boost guage,
if you don't like the hassle of the vacuum pump.

One down side to using a Turbo Master is slightly lower MPG..
 

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Wasn't there some climate systems that used VAC to work....so eliminating the vac pump might not be possible....
 

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Wasn't there some climate systems that used VAC to work....so eliminating the vac pump might not be possible....
yes, IIRC some of the vans used vacuum for climate controls..
 

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Hello:

I own a 1995 suburban 6.5T. I have thought of cutting some holes in my air filter housing with a hole saw. This is to allow better air flow to the filte. Has anybody done this mod. Are they happy with it. Any bad thoughts opinions about this. I use this vehicle on pavement mostly and grave logging roads. Sometimes mud but nothing excessive.
Thanks
 

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Don't do it. Hot underhood air is bad for diesels. Look for a K47 option air box and replace the flat panel one you have. That's what a lot of us have done.
 

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Don't do it. Hot underhood air is bad for diesels. Look for a K47 option air box and replace the flat panel one you have. That's what a lot of us have done.
Isn't the flat panel air cleaner getting air from outside of engine compartment? Does the k47 allow for more air as it has more surface area?
 

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Isn't the flat panel air cleaner getting air from outside of engine compartment? Does the k47 allow for more air as it has more surface area?
The Flat Panel Airbox does draw air from outside of the engine compartment but the K47 draws a larger volume of outside air and is the most preferred.
 

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Don't do it. Hot underhood air is bad for diesels. Look for a K47 option air box and replace the flat panel one you have. That's what a lot of us have done.
Thank you for your reply. I would love this put a K47 in n place of my flat pane. Consequently, I don’t like the price tag. What was the year they started?
 

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Thank you for your reply. I would love this put a K47 in n place of my flat pane. Consequently, I don’t like the price tag. What was the year they started?
The K47 airbox are equipped on Diesel vehicles from 1997-2000 model years
 

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Isn't the flat panel air cleaner getting air from outside of engine compartment? Does the k47 allow for more air as it has more surface area?
Yes and Yes. IraqVet is talking about hole-sawing the air box and letting underhood air into the air intake :shake:
 
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