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Discussion Starter · #1 · (Edited)
Alright, so I bought the truck back in April 2020. It's a '99 K2500 but the previous owner put a '97 VIN S as he said the original engine crapped out. He said the '97 had around 170K miles on it when it was put in, but didn't say how many miles he's put on it after it was put in. The odometer reads 225K miles, so I assume the engine that's in the truck now has around 190 to 200K miles on it.

I've done a lot of work on the truck since I got it, and done some work on the engine as well.

The Knocks
There is a intermittent, rhythmic knock or "rattling" coming from the passenger side of the engine. Using an electronic stethoscope, I've located the strongest sound of the knocks to be coming from the vacuum pump. The pulley has some resistance, but I don't have the tools to measure vacuum at hand right now. I'm considering doing the "CDR test", but I need to do some more searching to see if I can find some documentation on the method.

Here is a link to a video I took of the knocks - it can be heard around the 0:05 marker of the video.

Has anyone had any experience with knocks from the vacuum pump before?

EGR
The engine that was swapped in is a VIN S - from what I can tell the previous owner has had some attempt at an EGR delete, as the EGR solenoids were disconnected. I found the vacuum line from the turbo actuator disconnected in the engine valley, and it's been that way at least the whole period I've owned the truck. I connected it yesterday, and now I have a CEL and a P0238 code for high voltage boost sensor.

644329

This is the only code I have at this time.

The Problem
The knocks are making me extremely anxious, because I'll have to depend on the truck. I'll be driving around the edge of civilisation, and if the truck craps out at the worst possible time (Murphy's Law), I'll potentially be several days walking distance away from help.

So, I figure I can do two things right now (call me out if there's other possibilities!)

1.
I can try to undo the EGR delete and buy a new vacuum pump ($250 shipped to Norway)
2. I can try to clean up and verify the EGR delete, do a vacuum pump delete and buy a Turbo Master from Heath.

So I'm looking for something to make the truck more dependable - HP is not important to me.

I would really appreciate some input on the matter! Reading and posting on this forum has helped me immensely, and the truck would probably not be in my hands any longer if it weren't for all of you.

Also - what the heck is the difference between a vacuum pump and an oil pump (RockAuto link)?

PS. I'm planning a good write-up on the forum about my trials and tribulations on the 6.5!
 

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The vacuum pump can be low on oil. The knock is the telltale sign the pump is worn out and ready to seize..
You can remove the pump oil things up and see if it improves but I would recommend that you just replace it.

The CDR testing can be found in the 6.5L FAQ page: CDR\PCV - what's it all about, Alfalfa?
It is recommend that you replace the cdr approx. 30,000-50,000 miles ( Do not clean it)

"CDR testing can be accomplished with 4' section of clear plastic tubing, sized to fit the dipstick tube, ~3/8".


Form a 3" U-bend , with 12" vertical columns. This could be attached to a piece of 1 x 6 with large u-staples, parallel-spaced at one inch intervals for indication of measurement.


Important - do not crush or deform the plastic tubing.

Place the free end over the dipstick tube, ensuring tight fit, with no leak-by. Position the manometer vertically, where the upper end of the U is lower than the end over the dipstick tube.

Note: this is to prevent water siphoning into the oil pan thru the dipstick tube.

Pour colored water into the U section such that about 6 " of water is in each leg, about 4 - 6" below the top of the open end.
Have someone start the engine, bring the rpm up to about 2000, keeping close watch on the water level in the U-tube. If the water in the dipstick leg rises an inch, the water in the open leg will drop an equal amount. Adding the drop level to the rise level, this would indicate vacuum at two inches on the Water Column.

Vacuum at idle should be around 1", depending on air filter restriction; at 2000 rpm, the CDR should limit vacuum to 4 - 6" WC on a calibrated Manometer. The shade-tree version should indicate close to those figures, depending on accuracy of staple intervals.

If the level in the dipstick leg drops, and the open leg level rises, this indicates the crankcase is slightly pressurized.

27" WC is equal to 1 PSI (Pound per Square Inch) 1psi is equal to 2" mercury
Atmospheric pressure is 14.7 psi, or 29" mercury, or 396" WC, rounding off"
 
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Also - what the heck is the difference between a vacuum pump and an oil pump (RockAuto link)?
The oil pump is just that... It pumps engine oil from the oil pan and circulates the oil throughout the engine.
The vacuum pump provides a vacuum ( negative pressure) to operate things like the EGR , Turbo wastegate control and ( in vans ) controls the AC functions
 

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First thing. Look at the 8th digit of your trucks VIN number. It should be either a S or F. If it is F you dont have to worry about EGR. F vin did not come with EGR. It is not programed into the computer. You can delete it all.
Re your code. It most likely is related to the Vacuum pump not working or cracked and broken vacuum lines.
Vaccum pump should pull around 22HG (745 MB). If under 20HG and making noise you should replace the pump.
 

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Discussion Starter · #5 · (Edited)
OkDually: Right, I replaced the CDR in the winter and haven't put many miles on it since. I am 100% confident that my pump is ready to seize at any moment. The reason I asked about the oil pump and vacuum pump is that I thought they looked similar, and I don't seem to have a pulley for my oil pump (?), only vacuum pump, water pump, alternator, P/S and HVAC.

Tommygunner: I just checked and my truck is a VIN F, so I'll go ahead and verify that the EGR delete has been done correctly. It's still the right move to replace the pump?

If I'm not mistaken, the vacuum pump's only task now is to operate the WG. If I replace my VP, I'll go for an OE GM one. Is it in your guys opinion that the truck is more reliable with this VP versus a Turbo Master with no VP? Also read that the TM affects mileage negatively.

Edit: Vacuum pump might also be running cruise control? I tried the cruise control out last winter, but it was really sloppy and "lagging".

I'm also considering a GM8 turbo down the line, if that affects this decision in any way.
 

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OkDually: Right, I replaced the CDR in the winter and haven't put many miles on it since. I am 100% confident that my pump is ready to seize at any moment. The reason I asked about the oil pump and vacuum pump is that I thought they looked similar, and I don't seem to have a pulley for my oil pump (?), only vacuum pump, water pump, alternator, P/S and HVAC.
The vacuum pump and the oil pump do not look anything alike..
The oil pump is inside of the oil pan, attached to the bottom of the motor, and is driven by a gear. To see it you would need to drop the oil pan.
 
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If I'm not mistaken, the vacuum pump's only task now is to operate the WG. If I replace my VP, I'll go for an OE GM one. Is it in your guys opinion that the truck is more reliable with this VP versus a Turbo Master with no VP? Also read that the TM affects mileage negatively.

Edit: Vacuum pump might also be running cruise control? I tried the cruise control out last winter, but it was really sloppy and "lagging".

I'm also considering a GM8 turbo down the line, if that affects this decision in any way.
The vacuum pump in your 6.5 only operates the Wg control. The ECM controls the amount of vacuum needed to operate the WG and helps maintain the best mpg in your truck.
You can install a manual wastegate controller, set it and forget it but the downside is you lose a little mpg because the ECM no longer controls the amount of vacuum.

It is best to leave the vacuum system as stock with a vacuum pump for optimal performance.
Your 1999 should already have the GM 8 Turbo installed
The vacuum does not control the cruise control function.
 
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Any idea which computer you have? Is it the 99 or 97's? If he kept the 99 computer it won't be trying to run the EGR so its kinda already deleted. If its the 97 then its going to be looking for the egr.

I think the 238 often comes from oil getting into the MAP sensor and slowing down the response time of the sensor. I have had that on 2 different trucks and if I either clean or replace the MAP sensor it stays away for a while but once oil works itself back into the sensor the code randomly comes back.
 

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Discussion Starter · #9 ·
OkDually: It's the '97 engine with what I presume to be the '97 turbo that's sitting in the truck now - is this also a GM8? You're absolutely right about the oil pump looking nothing like the vacuum pump, I've been reading myself green on RockAuto and have definitely gotten confused.

57: I assume the '99 ECM is still in the truck - I think I would get all sorts of codes if it was the '97 because of the deleted EGR. I'll be looking into the MAP sensor next. Any tips for cleaning/preventing the oil from getting into the sensor? Also, any difference in the MAP sensors over the years (EGR / no EGR)? If I'm buying a replacement, should I get a '97 VIN S or a '99?
 

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With a high miles engine I don't think there is any way to keep the oil out of the sensor. To clean it I was using the electrical motor/contact cleaner which appears to basically be alcohol. I pull the sensor off the intake and stick the straw on the can and squirt it in there to flush the oil out. I thought about brake or carb clean but not sure how tough those sensors are. They seem to be able to take the oil ok but didn't want to also add some harsh solvents to the mix.
 
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Discussion Starter · #11 ·
I ordered a new ACDELCO MAP sensor from RockAuto, so I can do some experimenting on how much/what the old MAP sensor can withstand.

Are you concerned about getting electrical/contact cleaner into your oil?
 

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OkDually: It's the '97 engine with what I presume to be the '97 turbo that's sitting in the truck now - is this also a GM8? You're absolutely right about the oil pump looking nothing like the vacuum pump, I've been reading myself green on RockAuto and have definitely gotten confused.
Yes, the 97+ model years came with the GM 8 installed. You can verify by looking for the GM-8 stamped into the turbo housing
 
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Undoing EGR delete is not going to solve your issue.
EGR actually clogged the intake and cause issues.

The challenge is did they do the proper EGR delete?
 

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Your truck most likely has the 99 F vin PCM. If it had a S code PCM you would get a bunch of EGR related codes and the CEL light would be on, as you suspected.
You can pull all the EGR stuff. Also, if you can find a F vin intake manifold. You can switch your S vin intake manifold out for the F vin manifold. It is a fairly easy job. It will restore your engine to the way your truck came from the factory. F vin manifold will totally cut out the egr restriction and you will make a little more power. There are usually some for sale on ebay all the time.
 
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