vacuum @ actuator @ 2000 rpm??

[Hubert]

Sorry guys one more time humor me...
I have read lots of threads on wastegate vacuum double check me here please.

Teeing in a vaccum guage at the wastegate actuator: At idle I can get about 20"Hg vacuum. It dips and wiggles the needle a little as low as 18 and as high as 21"Hg. If I rev it parked to 2000 rpm it immediately drops to dancing around from 9-5"Hg on the guage. Is that normal? I see lots of posts saying it should read a min of 15 or 20 ish inch Hg at idle @ actuator (depending on which post you read) but doesn't say if it should hold a steady minimum at any other rpm. I understand the ecm solenoid cycles on off according to command but should it drop vaccum that much so quickly and stay that low??? Coming back to idle vaccum climbs back to around 20"Hg.

1. What should it do as I come off idle parked reving it up?

I went to try to Tee into solenoid and see the mounting bracket broke on the electronic solenoid. 2. Does that matter?

I couldn't test vaccum at the solenoid yet as I don't have the correct size tubing and T's to plug it up.

3. Whats the best way to get to the actual vaccum pump connection from under the truck or from above dang I don't see where the line attaches.

4. At the vacuum pump that should read what and I assume peg the guage if reved up correct?

[Robyn]

1- check the vacuum at the pump. should be steady at 25+ inches
2- If you get the same readings as you had at the waste gate toss the vacuum pump and get a new one.
3- If vacuum good and steady at pump replace the waste gate solenoid.
4- when all is good the vacuum at the wategate at idle should be 25+ inches and hold even when reved up.
These pumps will do what you are seeing and the performance goes out the window and the black smoke rolls out the tail pipe.

Hope this helps.

Robyn

[Hubert]

Thanks Robyn,

I get medium to heavy smoke on interstate sometimes climbing rolling hills trying to keep up with traffic ~70-75 mph unloaded and truck seems weak. So I am diagnosising wastegate operation. Have clean air filter and fuel spiked with FPPF cetane booster and Stanadyne Perf. Form...

I think its a periodically failing sticky wastegate solenoid.

I Tee'ed the vacuum guage in at pump side of solenoid (easier to reach and tests for leaks too at the same time?) and read 25-26 " Hg for several seconds steady. It did not really climb much when I revved it up.

I was curious and Tee'ed into vacuum line from solenoid to waste gate actuator near the solenoid and drove the truck.

Idle I get 20"Hg then accelerating it starts to drop at the top of a gear its down to under 10" Hg. Playing around on a 2 lane country road with little rolling hills. Uphill downhill varying throttle vacuum goes up and down from 20 to about 10"Hg. If I coasted no throttle it would climb to 20"Hg if I matched throttle to just cruise hold steady speed and hold 1700- 2000 rpm no real load on engine no compression braking either the vacuum drops like a rock to just under 5"Hg. If I add throttle it climbs slowly. If I let off throttle it climbs steady too.

Which all sounds pretty normal??. I'll have to repeat on vacuum side to see if the pump holds the 25"Hg steady same conditions tomorrow.

The vacuum pump should hold pretty close to 25 "Hg all the time right.?

[Warren96]

The vacum pump on my truck used to work good when cold but as it warmed up on hot days with air on it wouldn't hold 25''.Now that cooler weather is here it will be a non issue.May switch back to my 180* thermostat next spring.

[Hubert]

That is a real possibility too. It usually acts up worse when its hotter and made towing my boat (3000lb +/-) a gear changer with rolling hills. It did not like 5th gear at 1800-2000 rpm but felt ok with 2300-2500 rpm 4th gear. Makes sense If rpm helps the vac pump work which intuitively to me it would.

This would be a little easier to diagnose with boost guage too I know. I am saving up for Boost/pyro/? Fuel pressure or oil temp? guage triple mount. Very tough decision on the 3rd guage.

[Robyn]

The vacuum pump should not deviate much at all if any hot or cold.
The reading at idle at the waste gate should be the same as at the pump.
As the boost approaches max allowable the vacuum should fall off and if you drop the throttle back a little it should go right back to full vacuum again.
I would replace the solenoid.
Takes only a few minutes to do
One issue is if you are seeing black smoke and the HP is down you are getting high EGT's
The hight temps over time will toast the little beast.
Be sure you have a good steady vacuum at the wastegate and not any wiggling of the needle

Robyn

[gmctd]

Slight correction needed - PCM is pulse-width modulating the wg solenoid, even at idle.

Output is 66%, meaning 66% on-time, 34% off-time.

The result is 66% of vacuum pump output at the wastegate.

Even in an aged system, with 25" fluctuating at the pump, the wg will usually have about 15" at idle

If you're getting 20" at the wg at idle, the solenoid may be leaking, and\or the connector\wiring may be faulty

At 650rpm idle, the vac pump is cranking 325rpm, or about 5 pumps\second, so the idle readings will fluctuate.

At 2k rpm, pump output should be steady as a rock.

[moondoggie]

Good Day!

I'm not sure anyone's diagnosed one of these problems from the vacuum side B4 - seems like a good way to do it. Usually we just look at boost. BTW, JK told me eons ago that at idle & low elevations, Wastegate Actuator Solenoid duty cyle was more like 75% (stock program), but my memory sure isn't something anyone would want to count on; in any case, 66% or 75% are pretty close, close enough to troubleshoot.

In addition to the above info from others, keep in mind that the PCM keeps this 66/75% duty cycle at any rpm below 1800 or 2000 (I've heard both). So, it won't reduce vacuum, reducing boost, below one of those rpms. The PCM begins taking action when rpm is above one of those rpms, & if other conditions warrant.

Too bad you don't have an old vacuum/pressure gauge laying around. I've been temporarily monitoring my boost with one for three years or so now. It just lays on the dash - gives me something to look at. I'm sure it's horribly inaccurate, but probably consistently inaccurate.

I had a Wastegate Actuator Solenoid go intermittent on the Sub once. I caught it because I saw black smoke, so I moved my temporary boost gauge from the pickup to the Sub. Sometimes it worked perfectly, other times the boost clearly wasn't there when it should have been. Since every time I checked vacuum at the Actuator while idling it was nominal, I surmised the Solenoid was intermittent - I guess right.

Blessings!