Hey All;

New poster here. I have a 1997 K3500 6.5TD/auto dually crewcab with 162k miles on it that I've had for about 3 years. It has been blowing lots of black smoke when under power ever since I bought it, but it gets 15-15.5mpg on the freeway doing 55 to 60 mph. Recently it has developed a slight miss at highway speeds but not when I'm just driving around town. I changed the fuel filter for the first time since I have owned the truck, but that didn't change anything. I had heard that there was a procedure that I could do that would check out the vacuum system. Any truth to this? Any ideas on anything else that could be causing the miss? Thanks.

GaryB in Prosser, WA.

 

an injector going bad can cause a miss

 

Vacuum system
Why Does the 6.5 have a Vacuum Pump?
Diesels do not create vacuum inside of the intake like gasoline engines. Gasoline engines rely on vacuum for numerous things, such as: brake boost and HVAC controls. The Diesels rely on hydroboost systems for brake boost and electrical motors for HVAC operations. GM put the vacuum pump to control a couple of devices on the truck, read on for more info.

So, where's the vacuum pump?
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Please note, you may not have the piece of tubing in the way unless you have an intercooler.

What components does the vacuum pump provide for? The list includes: EGR (if equipped) and the turbo waste gate system.

On vans the vacuum system also controls the HVAC system.
EGR's are normally found on "S" Vin engines. Another way to tell is if the truck is a 6 or 5 lug, it will have an EGR (unless its been removed).

Where are these EGR and Wastegate solenoids?

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So how do I know if my vacuum pump is working correctly?
You will need a vacuum gauge to properly test the pump itself. You will want to hook the gauge up as close to the pump as possible. You want to see at least 20”+ Hg of vacuum at Idle.

Do I have to hook directly up to the vacuum pump?
It is best if you do, however, you can test farther out on the on the vacuum system. You can check the vacuum at the soleniods, EGR, wastegate. This will help you determine if it is a bad device or a bad vacuum line if the vacuum pump tests good.
*Note: Testing after the solenoids may give a skewed reading as they regulate the amount of vacuum given to the devices.

My vacuum level is not very good?
If you are directly attached the gauge to the pump, and you have low or no vacuum, then your pump is bad. If testing further out on the system, you will need to connect directly to the pump to insure that you have no leaks in the lines between the gauge and the pump.

Are leaks common?
Very common. Leaks come from chaffing, hardened plastic lines cracking, etc... Sometimes the vacuum level may be okay, but if the engine rocks one side to another, it may open up a crack in the line and you will lose vacuum.

I don’t have a gauge, but I suspect I don’t have good vacuum. What do I do?
A real quick check of your vacuum system, which can be done at any time, is checking your waste gate actuator.

With the engine at idle, locate the turbo, and the can on the side that has the arm in it, should be drawn up inside. Pull on it, to see if you can pull it out. If you can, you don’t have sufficient vacuum. That is not to say that the pump is bad, but just an indicator that you vacuum level to the turbo portion is not enough. You will need to do further troubleshooting to determine what’s wrong. If it doesn't move then you most likely have enough vacuum at the wastegate.

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My waste gate actuator failed the test, now what?
You will need to determine if the waste gate solenoid is bad, have a leak, or bad vacuum pump.

How do I determine if my waste gate solenoid is bad?
Check to see if you have vacuum BEFORE the solenoid. These solenoids will go bad after some time. The little ball inside of them will rust that actually opens and closes the vacuum to the actuator. It will get stuck not properly regulate the vacuum. It may get stuck “off” which means no vacuum gets to the actuator, it may get stuck “on” where it has full vacuum all the time. The last condition would create a DTC (computer code for over-boost).

How do I check to see if I have computer codes?
Depends upon if you have an OBD-I or OBD-II computer. 1996 and after are OBD-II and require a code reader, pre 96 you can check with a paperclip. Check the FAQ’s.

I have a code for my turbo, and EGR.
Coupled together these two codes indicate a vacuum problem. Both systems rely upon the vacuum system to work properly.

I have a heavy duty vehicle that does not have an EGR. My vacuum system is not working, what are my options?
If you have a 2500HD or 3500 truck, not equipped with an EGR system, you may opt to abandon your vacuum system, and use strictly a spring tension waste gate operator. Instead of using a vacuum system to hold the waste gate closed, you use spring tension. Once boost is built to it’s maximum allowable level, the waste gate blows open. The spring tension provides the proper pressure to maintain a safe boost level.

Can I get more boost out of my turbo with a spring type waste gate actuator?
Yes, but remember, there is a limitation here for the engine. You don’t want to be driving more than 12 psi of boost pressure into the engine with stock tuning, or more then 15 psi with an aftermarket tune.

Where can I get one of these spring type waste gate operators?
There are over the counter ones available from vendors, or you can opt to build you own (Check the FAQ’s). Other members have done so, and you can search to see what they have built. Search the term "Turbo Master."

*NOTE: If you install a Turbo Master, your computer will no longer be able to control boost levels.
I have an EGR system, can I fully abandon my vacuum system?
No, you will still need vacuum for your EGR to work properly.

You must still leave all your solenoids hooked up to the electrical system, because the computer is looking for feedback and a circuit to them. Without them connected, the computer will generate a DTC code. You can only remove the solenoids and EGR if you have an F code computer or an aftermarket tune that has EGR Delete on it.

What would keep me from abandoning the vacuum system?
If you have an EGR or your HVAC controls are vacuum operated.

If I abandon the vacuum system, can I remove my vacuum pump?
Yes, you can, this means that you will require a shorter serpentine belt. Members have reported that it needs to be 1 inch shorter than your original, you may want to do some further investigating to make sure on your own.

Normal Vacuum Pump Delete sizes are:

* 94-95 :: 101.5"
* 96+ :: 99.5"

 

You may want to do the wastegate modification. Sounds like your turbo is not opening up like it should causing black smoke on hard acceleration. Do a search on wastegate modification on the search engine and there are instructions on how to modify it to be a manual instead of a vacuum wastegate. Best improvement I've done so far.

 

Hey;

Thanks for the info. I tried searching the forum for wastegate modification but it only came back with this thread. Is there somewhere else I could check? This sounds like something I would like to do. Thanks.

 

here a pic's of mine

it only cost less then $5.oo

i got spring from ace hardware

spring # was 68

the brass cap is water cap for washer and dry hose did that keep the Jhook center in the spring

the rod is J hook for battery tie down

 

Hey Crazy;

Thanks for the reply. That looks like a real easy mod. It also appears to be adjustable. As I was searching around the site, I found this;

"look at the arm on the wast gate with engine off then start it and look at the arm if pull up then screwdrive try pushing down on wast gate arm if you can't most likey there no vacuum leak and if that arm don't move when starting the truck try tapping on the Wastegate solenoid they get stuck"

So I went out and found that before and after I start the engine the wastegate lever doesn't move from the down position. While it was running, I used the screwdriver to move the wastegate lever up and down with no resistance. I then put a vacuum gauge on the vac line going to the wastegate and found 0 inches of vacuum (this was at idle). I guess that I'm suppose to be getting some vacuum at idle? I'll see if I can follow the vacuum line back to the pump, but is there an easy way to check the output of the pump? It looks pretty crowded down there.

 

You will need a vacuum gauge to properly test the pump itself. You will want to hook the gauge up as close to the pump as possible. You want to see at least 20”+ Hg of vacuum at Idle.

Do I have to hook directly up to the vacuum pump?
It is best if you do, however, you can test farther out on the on the vacuum system. You can check the vacuum at the soleniods, EGR, wastegate. This will help you determine if it is a bad device or a bad vacuum line if the vacuum pump tests good.
*Note: Testing after the solenoids may give a skewed reading as they regulate the amount of vacuum given to the devices.



read post 3 again it tells you how check

 

Hey Guys;

Thanks for the great information. I went ahead and did the manual wastegate modification. I then took it out for a drive and it is quicker to 60mph than before. It still seems to be blowing out some smoke when I while I have the pedal floored, but not like before as far as I can tell. After going to two Ace stores and two True Value stores I still couldn't find the right spring as none of these stores had springs that went by numbers, so I got one that looked like the one in the pictures and used it. I have it set at the minimum pressure to keep the wastegate closed but don't know when it is opening. will have to wait until I get the boost gauge installed to check it out and get the right spring and setting. Thanks again for the help with this. Now I have to see if it is still missing at highway speeds.

 

get that gauge ASP you don't want to over boost and blow head gasket or motor