Is 26" of vacuum at Wastegate too much?

[Bruce_De_Mille]

I just got my vacuum tester and tried it on my wastegate actuator on my 1994 6.5TD "F". It reads 26" steady right at the turbo wastegate actuator. I can't get the vac tube off the fitting at the vac pump and don't want to break the little plastic line (again). As I recall Robyn had said it was supposed to be 26" at the vac pump and a lesser amount at the actuator. If it's 26" at the actuator is that too much?? I'm still fighting a pretty good sized black cloud under medium to hard acceleration. My 1994 has some JK mods.

Things I did recently: new GP's, new Bosch injectors (not rebuilds) & return lines, un-stuck the wastegate on the GM-4 Turbo, cleaned and checked the Turbo for play, new fuel filter, cleaned & oiled the air cleaner, and probably some other things. I didn't replace the plenum gasket so I think I'm down to a new gasket, possibly a new Boost sensor and then an IP timing check & reset.

Any ideas are greatly appreciated.

[Robyn]

Hey there

Try hooking up a T fitting in the wategate vacuum line and running it out and up by the wipers and tieing your gauge on so you can watch the vacuum as you drive.
This will allow the wastegate to work as it should and then you can observe the vacuum under operation.
26" is not too much during a no load situation.

As you approach maximum boost the vacuum should drop off and "Pulse"

Give it a go and let us know what happens.
The Puff of smoke can certainly happen if you have made mods.
Do you still have the CAT on the rig

Best

Robyn

[JohnC]

Make sure the vacuum lines are on the correct ports of the solenoid. The port with the restriction in it goes to the pump. Also, make sure the foam filter on the bottom of the solenoid is not clogged. AFAIK, there is no circumstance, especially not at idle, when the full force of the pump should be applied to the actuator. At idle is should vbe very close to 15 inches. If it is higher the solenoid may be stuck or the solenoid vent not able to vent.

Likely the pcm is seeing too much boost and so it shuts the solenoid down, which eventually does vent the actuator. Note the PCM does not monitor the boost if the fuel rate is low or if RPMs are less than 1800, so it can run haywire then and code once one of the conditions is met.

[Bruce_De_Mille]

JohnC and Robyn,
Thanks for the great information. While waiting for a response to my vacuum question, I started working on a fuel leak on my 1999 6.5TD. I moved the intake plenum out of the way and put a new s/s Ideal clamp on the line going into the IP. Problem fixed for now except that I'm totally p**sed off that the mechanic didn't replace the fuel lines when he changed out the IP !! From now on I plan to do all my own wrench work (while using your brains).

When testing the fuel leak repair, Dexcool began pouring out of the "Pesky quick connect" at the thermostat. So I'm waylayed on my original post while I remove the dual stat housing and perform "surgery" on the heater quick connect fitting!

I appreciate your help and will take your suggestions and get back to you on the results of your suggestions ASAP. Thanks again Robyn & JohnC !!

[More Power]

I've tested quite a few vacuum systems on these 6.2/6.5 diesels. I've not seen 26" on any of them - 20" plus/minus 3" was the norm. And, they would all produce a needle swing of 2-3" when the engine was idling - due to the vacuum pump's diaphragm being cycled.

GM indicates in their manuals that 15" is the minimum acceptable vaccum for the 6.5.

Jim

[wade-ve7trw]

At sea level under ideal conditions 26 inches of mercury (aka vacuum) is the maximum amount that can be obtained. As Elevation is increased the amount of inches of mercury (aka vacuum) will decrease. The density( the moisture content and temperature of the air) will also affect the amount of vacuum achieved. I work with vacuum all the time as i operate a vacuum truck with is capable of evacuating a three thousand gallon(us) tank to 22 inches of vacuum in under three minutes and load a liquid in four minutes{my pump moves 1200 cubic feet of air per minute under ideal conditions}. So what one person reads at sea level and another reads at a higher elevation are both correct results, and as long as the reading is above the minimum requirement for the wastegate to work-the turbo should function as intended .

[gmctd]

The 6.2 vacuum pump is driven at 1:1 ratio to the camshaft, which is 1:2 ratio to crank, so cam-driven vp runs 300rpm at crank 600rpm - idle rpm will vary

The 6.5 vacuum pump is belt-driven off the crank pulley, and can be seen that it is overdriven at some vp pulley/crank pulley ratio

Two methods of increasing pump output: # of events/unit of time = rpm, or intensity of event = displacement, or both.

Correct test of vacuum pump is comparing idle value to 2000rpm value - should be at least identical, without dropping significantly - this checks proper valve operation - I've never seen actual diaphragm failure, but then, I don't get out, much, any more.

PCM modulates WG solenoid to ~66% at idle, depending on altitude - thus WG value should be ~66% of vacuum pump value, give\take for mechanical solenoid losses - if 26"HG at pump should be min ~15"HG at WG solenoid if all is copasetic

If it's 15"H2O, you got big problems..............

[ak46champ]

Sorry to borrow the thread, I have hooked up a vacuum gauge to the vacuum line after the waste gate solenoid valve and checked the vacuum in various conditions. I have not seen any different reaction in the waste gate. it seem to operate all the time allowing boost at idle and during a load. I'm sure there is something faulty here. My question is, would it hurt to just bypass the solenoid valve and hook the vacuum pump directly to the wast gate to keep it open. I do run a boost gage. What purpose does the valve serve?
thanks!

[DmaxMaverick]

Constant vacuum to the WG actuator will keep it closed. As in, no relief. Heavy acceleration or load will see an overboost. Taking away the vacuum will prevent it from closing, and it won't develop boost. The WG should be held tightly closed when the engine is running and boost is below the relief value (or another sensor hasn't screamed). JD is correct, the vacuum at the actuator should be modulated to around 15"Hg. It doesn't take much to keep the gate closed against the exhaust pressure. At idle, you shouldn't be able to move the WG by hand.

[gmctd]

Several general misconceptions on wastegate operation:

Wg function is inherent in it's assigned tagname: waste gate - close the gate to prevent waste, open the gate to allow waste
Fluids - gasses and liquids - always seek the path of least resistance - the wg provides a path of least resistance around the turbine blade wheel

"Wg is closed - I must be making Boost at idle": maybe if you live and work and drive on top of Mt Everest - a simple Boost guage will prove correct operation
Remember: if the Boost guage is showing 1psi Boost when you take it out of the box, it will show 1psi Boost after you install it, engine off or engine idling

"Wg must be fully open to reduce Boost": wg will prevent Boost if fully open, but not practical in real-life scenarios, as 6.5 Boost will be fully dumped and not recoverable at 10% open
PCM modulates applied vacuum according to demand, beginning at 66% apply - less than 66% to reduce Boost, more than 66% to increase Boost, depending on engine rpm and loading
- 100% applied vacuum at idle is still 0psi Boost near sea level
- 100% vacuum at 3500rpm - revving the engine no load - can reach ~1-2psi
- 100% vacuum at 2500rpm at full-load is upward of 20psi - full load being on the higway pulling a trailer going up a steep hill - or even going up a long steep hill without the trailer

Thus the necessity of PCM management.

"I never see the wg move - it must be broke": wg arm movement while managing Boost is imperceptible - movement cannot be seen in a van with the engine cover off - movement cannot be seen in a truck with a remote camera mounted to monitor wg operation - no arm movement is discernable - in those scenarios, Boost guage is the only visible indicator of managed Boost due to engine reaction to torque variations imposed by on-road loading during testing.

A Boost guage is a fair indicator of engine loading -an EGT guage is an indicator of engine loading -
when Boost guage is combined with an EGT guage, you will have an accurate view of your engine's heartbeat.

[Bruce_De_Mille]

I took Robyn's suggestion and hooked up a Tee to the vac line going into the waste gate actuator and ran the tubing into my cab. I read the boost at idle and then under load. I'm basically at sea level (maybe 30 feet above) and both my 1994 and the 1999 6.5TD's read 25" to 26" at idle. Thanks to wade-ve7trw for the altitude expanation, I hadn't thought of that. I don't have any real hills close by, so I read the vac at hard acceleration and it went down to about 15". I don't know if it was pulsing since I was trying to keep and eye on the road as I was under full acceleration :eek: but it seems the wastegate actuator is working as designed. I don't have a CAT anymore, I dropped that when I went to the JK exhaust system (so no clogged exhaust). I also verified that the vac line from the vac pump goes into the restricted side of the vac solenoid as JohnC suggested.

When under hard acceleration I noticed I do not have the black cloud anymore!?! I'm thinking the black cloud may have been caused by the brand new injectors that I had just installed and the vac system was working fine all the time. Now my 1994 with mod's and my 1999 w/o mod's do not seem to have any discernable black cloud, even under hard acceleration :):)

Thanks to all who responded. I learned a lot about how the whole vac / boost system works on these 6.5TD's. Now I have a good vac tester, tee's, extra clear plastic hose, etc, so I can test the vac system anytime. I might just do it once in awhile just for the fun of it ! :D