Hi,

when going to work today and back, I was very surprised, almost scared, about how much power the engine makes now. I don't know what it comes from, can be the cat burned free from the towing I did the last two weeks, or just being myself confused, but it was really impressive. Even the tranny does the shifts much faster and a bit harder than usual --- maybe that's something to worry about?

The only thing I changed was putting hose clamps on the vacuum tubing, especially on the tube where it goes into the wastegate actuator, so that the tubing seals tight on it.

Now, I wonder if anyone has some hose clamps at hand and is willing to try it out. I don't really believe yet that it can make for a difference, but if it does, it's very worthwhile.

Could be first indication of rubber\plastic deterioration from heat, ozone, and the dep cold encountered in your locale.


Might be a good time to inspect the vacuum harness for heat cracking, ozone powdering, and crumbling plastic from cold exposure.


If rubber comes off hose onto your fingers, it's time for replacement.

Have you cheched the wg arm again to see if it's pulling hard now?

gmctd, it seems to be the wastegate actuator getting not enough vacuum, eventually due to something plugging the tubing at the wg solenoid or plugging the solenoid itselfe.

It hasn't been working as it should ever since I got the truck a year ago, I think. Now that it does, the engine shows up with unusual amounts of power ... :) You can see how it turned out in the 'error codes' thread.

I'll leave the hose clamps where they are, it's good to have them. The tighter the seals on the vac tubing are, the less likely something can be pulled in that can make up for a plug, and the lesser air is sucked in at the connections, the better the parts connected are supposed to work.

Maybe some places where small amounts of air can be drawn must be left for the pump having something to work on, but with my three clamps, it's far from being sealed up too much.


Hm, a wastegate actuator hanging too low can very well be something that's hard to find. There are no symptoms other than reduced power and eventually less turbo whine, and one may not notice them if the problem develops slowly over time. There's been no smoke, no hard starting or the like, and the error codes/SES light don't show up unless very special conditions are met. If my camping trailer had been a bit lighter or heavier, the problem might have remained undiscovered until I get gauges ...


PS:

QM, yes, it's pulling strong now. I won't exactly say 'hard', though.

BTW, how much vacuum is 15hg? 15 inches hg? Pulling 15 inches hg would be quite a lot, I think, if not impossible (at ambient pressure). Can it be expressed in PSI or so? I've noticed on the turbo gauges that pressure is always given in PSI, but vacuum is always in <something> hg. There must be some reason for that?

(We use metric measurements in Germany also on pressure/vacuum. Pressure is commonly given in bar, but oficially should be 'Hektopascal', afaik. I don't know what's used for vacuum, but considering it the other way round, from the inside of a vaccum, there's ambient pressure pressing on the vacuum. Thus, vacuum could be expressed in any terms of pressure. Hm, philosophically, can there be a vacuum --- like in space --- without pressure pressing on it? And can there be pressure without vac?)

So, how much pressure (in PSI or bar) presses on a vacuum of 15hg? If it is about 0.150 bar, I'd need a gauge to check it. If I should guess, the force pulling the wg lever up, considering the possible size of the membrane that must be inside the wg actuator and the spring pulling it down, may correspond to 0.150, maybe 0.200 bar (2.14--2.86 PSI). Hm, 15 PSI is 1.05 bar, I think I could feel that very well if that much were on the tubes.
Edited by: 0lee

Inches of mercury because mercury is dense and was used in graduated colums for vacuum measurment untill plastic and diaphrams.

If you like having boost, open your ehaust so you can use more.

Hmmm, thx, but really _inches_ HG!? ... Ok, 1 in HG makes 0,03386 bar, so 15"HG is about 0.5 bar. I don't think that there's 0.5 bar vacuum on the tubes, but without a gauge, it's hard to tell.


PS: I'm thinking about the exhaust since I've been reading here how clogged it is. I'm thinking of it even more since I was towing.

It is illegal here to modify it, and I cannot simply order a nice downpipe to begin with. Nobody makes them here, and shipping could become costly. I have the option to order parts in the US and even get them shipped over with no additional cost, but a downpipe is rather large. I'll probably have shipped a pair of new door handles, some gauges and eventually a Holley fuel pump over, as there's almost no chance to get these things here, at least not at a reasonable price.

But I keep thinking about the exhaust :)
Edited by: 0lee

Vacuum is measurement for pressure less than Barometric Pressure.


.Barometric Pressure is measured in "hg, Inches of Mercury.


30"hg Barometric Pressure is 0"hg vacuum


0"hg BP is 30"hg Vacuum.


2"hg is equal to 1psi, so BP of 30"hg is equal to15psi.


Baro Pressure at 29" and rising means fair weather.


28" and falling means bad weather.


Therefore, measuring 15" Vacuum on the wastegate actuator indicates Barometric Pressure has been reduced by 15", or 7.5psi, on the control side of the diaphragm.


With only 7.5psi on the control side and Barometric Pressure, 15psi, on the opposite side, we have the difference, 7.5psi, pushing on the diaphragm.


Diaphragm 'piston' is 2" dia, so (pi r squared) gives 3.14 square inches area.


7.5psi pushing on a 'piston' of 3.14 square inches gives a force of about 24 pounds on the control rod - the control arm is equal in length to the wastegate arm, so pressure on the wastegate is directly equivalent.


Wastegate port is 1.25" diameter, so using the same routines, figure the amount of Exhaust Pressure required to open the1.5" diameter wastegate against the 24pounds holding it closed.


Now, who said math and science is no fun? Edited by: gmctd

lol :)

I've been thinking that non-metric units can make things quite complicated, but in this case, they make it quite easy. And if you get used to it, a 3" downpipe is somehow much more evident than a 7.62cm one, same is with an 889mm one, which happens to be just 3.5" :)

Did you know that some years ago they wanted to specify sizes of computer monitors in cm rather than in inches, just because inches are not an official unit? Ppl didn't accept it since nobody could figure the size of a XX cm monitor, but everybody knows the size of a 19" one. But they give sizes of televisions in cm rather than in inches --- a thing that somewhat confuses me because I cannot figure the actual size of, for example, an 41cm television. 41cm is a standard size, but I've no idea how much it is. If they only gave the size in inches, I would.

Hmm, I'm not good at mathematics ... Wastegate port at 1.25" has 1.9625, at 1.5 it has 2.355 square inches --- which diamter has it, 1.25 or 1.5?

I'm not sure how pressure on a surface translates into the force on it. If 7.5psi and 3.14 sq inches make 24 pounds, 1psi would make 3.2 pounds. But on 2.355 sq inches, 1psi makes 2.4 pounds, thus 10psi get you 24 pounds. With a wg diameter of 1.25, you'd neet 20psi.

Hm, I thought EG-pressure is higher?

> Now, who said math and science is no fun?

It sometimes does :) And I always like asking questions when I get the chance to ;)


Well, you again make me curious about how the wastegate exactly works. If've seen a disassembled turbo charger on some picture here, but I couldn't see much of the wastegate.

It looked as if the wastegate lever would move a small plate inside the TC housing. I imagined the plate would route more or less EG onto the turbine, depending on its position.

But the wg plate, having a diameter, it must be round, eventually holding shut a hole (or opening it). The hole's there to let EG get out of the TC housing so that it cannot drive the turbine.

If that is so, where does the EG that goes through the wastegate get out of the TC housing? There seems to be only one inlet and one outlet on each side of the TC?

And I wondered if there better were some blow off vent. If the wastegate does not open before there's too much boost pressure --- due to a faulty PCM or such --- serious damage could be done to the engine.

The pressure of the EG that could push open the wg plate doesn't seem to get high enough before the damage can occur; otherwise it would take the function of a blow off vent.


At least I come to understand that I'll still may be loosing boost pressure in case that the vacuum on the wg actuator is lower than it should be, as the wg plate could be pushed open. Hmmm ...

I must admit that I'm not exactly fond of the way GM designed the control elements of the turbo charger. Controlling it electronically is suspect to me, and utilizing vacuum is a flinching design. If they had to insist so much on using air, they at least should have thrown in a decent compressor rahter than the vacuum pump. One could use the compressor not only for controlling the wastegate and the EGR vent, but also for inflating the tires, blowing air horns and driving tools with it ...
Edited by: 0lee

It would take ~13psi of EGP to open the wastegate against 7.5" Baro on the diaphragm.


As EP increases, PCM compensates to maintain ~7.5psi Boost, with 25"hg out of the vac pump to compensate with - 12.5psi on the diaphragm and 40 lbs needs only ~20psi EP to open the 'gate.


The 'gate is just a bypass around the turbine wheel - 'gated exhaust gas re-combines with turbine exhaust in the exhaust elbow, thence out the pipe.


Years ago, rising Boost pressure was used to open the wg against a spring - some oem mfr's seem to be headed back in the direction.


And, as in the early 6.5 GM turbo's, exhaust gas pressure has been used to 'blow' open the wg against a spring.


Good job on the inch\metric conversions, Lee.

The wg port is ~1.25" dia, and the 'gate itself is ~1.5".


Closed, EP pushes on 1.25" dia, but as 'gate opens, it's larger dia is also effected by EP, to a lesser degree.


So - how do we arrive at effective diameter?


Gives me a headache - I'm off to the sack.......

> So - how do we arrive at effective diameter?

We won't ;)

The exhaust gas will whirl around the gate into the port, at different speeds and pressures, arising a varying force that pushes the gate. You could eventually measure the forces and the pressures to calculate a corresponding diameter, but it would be more an approximation than anything else.

To drive the wastegate, you only need to have sufficient force to fully close and to fully open it. To get to the desired boost pressure, measure actual boost and open or close the wg solenoid to get more or less boost pressure, respectively. For not to overdrive the system, have a slight delay on the control signals that matches the delay between wastegate actions and actual pressure --- at best, build the ability to learn into the 'computer' that controls the solenoid. There's probably quite a delay from the mechanical parts ...

Does anyone know how they actually built it? The wg solenoid looks to me as if it is either fully open or fully closed.


> Good job on the inch\metric conversions, Lee.

THX, but I didn't do conversions --- the calculation is independent of the units :)

The GM-X series turbo Wastegate is a simple flat 'flapper' valve on a flat seat.


The amount of actual control travel is minimal, as the entire port diameter is uncovered as the 'gate moves off-seat.


Most folks think full travel is required, becoming concerned when 'gate arm contacts and binds against inner exhaust elbow wall. The 'problem' occurs when installing a mechanical controller, additional 'problem' being mech controller does not allow full travel when adjusted per instructions.


Full WG travel is not necessary to regulate or dump Boost.


Attempts have been made to mechanically control Boost fade under heavy load, as up long grades, steep grades, etc., by increasing control arm length, adding stiff springs, doubling stiffer springs, etc, to little avail.


As exhaust energy - heat, volume, pressure - overcomes spring pressure, the WG does not blow open, dumping Boost - it begins to chatter, long and loud, sounding like a lawnmower engine as the 'gate comes off-seat.. As Boost drops, and exhaust energy, the 'gate seals, Boost increases, exhaust energy increases, and the loud cycles repeat.


Altho 'gate is violently chattering at that point, noone has reported 'gate damage or breaking.


Due to a deficient WG shaft bearing, the mechanically controlled turbos did suffer from early failures due to excess clearances.


Enter the PCM digital vacuum regulated Wastegate.


PCM controls vacuum to the actuator by varying the duty cycle of a pulse train to a ported solenoid valve - wide pulses = more vacuum, narrow pulses = less vacuum.


It does this based on rpm, fuel, coolant and intake air temps, Baro pressure, and manifold pressure.


~63% at idle, to ensure rapid spool-up, ease off the line, run thru the gears normally, and PCM maintains ~63% WG Duty Cycle.


Head up freeway entrance ramp, kick it, and Boost spikes up to ~10psi, WGDC drops to level needed to control at ~7-8psi - low as 20% duty cycle - vehicle moves up to speed.


Back off the pedal, hit Cruise, WGDC settles between 50-60% WGDC, exhaust energy drops, Boost settles in at ~4-5psi at speed.


Even at hard pull, Boost hung at ~8psi, WGDC at 20%, no chattering is heard, ever.


With the PCM digital control, WG is always bypassing to regulate Boost pressure.


At 15psi Boost, no chattering.


At 20psi Boost, no chattering, just smooth control. And, at 20psi Boost, Exhaust Back Pressure is outta sight, but no chattering.


Indicating minimal travel, controlled bypassing.


In 'limp-home', or backup, mode, no-to-little Boost can be achieved, indicating 'gate travel is uncontrolled. Edited by: gmctd

Very nice description, gmctd, it helps me a lot by making things clearer :)

I think I know the sound of the wastegate, it tackeled continuosly on me. I wondered where the sound came from; it seemed to come from the charger, sounding like some vents opening and closing rapidly, but I couldn't think of something that could be on the charger that could make such a sound.

This evening, I found out more or less by chance, that tangling the wires at the solenoid bank had some effect on the wastegate actuator. I could even make the engine stall whith moving the wires. I fixed the wires to a position where they seemd to have contact and where the wg lever was pulled up, with a cable fixer, and it seemed to work on the ride home. The tackling I'm so much used to was almost gone, and I had good power.

Now, I've replaced some of the wire, and it seems that I don't make the engine stall with that any more. The tackling also didn't come back.

However, while testing, from pulling the wire going into the middle one of the solenoids on the solenoid bank off, the SES light has come on and still stays on. It should go away sooner or later, or I'll try to clear the codes by taking off the battery cables for some time to see if it comes back. Eventually, the PCM has gone to 'limp mode' and turned off boost pressure.

My feeling is that there's something more about it than only broken wires, but I will find out.
Edited by: 0lee

Sounds like EGR problems, also - would stall the engine if applying vacuum to EGR valve at idle.


And\or could be shorting power to ground, also causing stall.


Pulling codes will tell the tale, so not wise to clear memory at this time - something to check into very carefully.

Hm, EGR was supposed to be disabled, for testing; I won't do anything illegal ...

Shorting, hmmm, I don't think so. But is there something that controls the operation of the vac pump? Maybe the pump/vacuum can be turned off somewhere at or close to the pump. If that's possible, I might have a problem that leads to turning off the vac pump and not turning it back on unless special conditions are met. That would greatly confuse me with testing.

Reading the codes costs about EUR 20 each time and requires driving about 60 miles in total to get to a shop that can do it and back home. I come along there when going home from work, but they close so early that it's difficult to get there in time.

Codes won't help much for I know that there's something vacuum related, and I produced the current ones myselfe. The SES light will go off within three or for days if I let things alone --- it did so before. But it may come on again when I tow my camping trailer.

I've been reading somewhere that it can take several cycles of fully cooling down and warming up the engine before the codes will become historical and the SES light goes off. Is that true? When I tried to reset them by taking off the battery cables, the clock in the radio still showed correct time, so I probably didn't wait long enough for the codes to be cleared.

Sometimes there seems to be more vacuum on the system than at other times, for no particular reason. When I was checking with the gauge, there was almost no vac, but today I could actually feel it on the tube of the wg actuator. But shortly after, it seemed to have gone --- but then, why should the engine stall when a solenoid opens or closes unexpectedly on a tube with no vac on it?

My impression was that the stalling came from insufficient fuel, as if the PCM for some reason cut it off a bit too much. It could come from a short to ground, but it seems to have disappeard after I replaced solenoid wires.

Also, there's always been some shudder in the drivetrain when the TCC engaged in OD. The shudder seems to (almost?) go away when I seem to have boost pressure. I'm guessing that when the PCM is more in control of the engine, it can do something to avoid the shudder.

The shifts are now much quicker than they used to be, seems to be related to boost pressure --- or the ability of the PCM to control engine and trans.

At last, if the vacuum pump is broken, would it still have a minimal vacuum on it sometimes and more or less normal vacuum at other times? I don't think so, but I don't know how these pumps are designed.

Maybe I'll have chance to check it together with a friend of mine tomorrow. I'm sure he can find out what's going on, and all the things I could learn here will help :)
Edited by: 0lee

Vacuum pump runs constantly when engine is running. It is a pulley-driven crank, ball-bearing on the throw drives a pump rod connected to a spring-loaded diaphragm, two one-way plastic valves. Intake is vacuum, exhaust is pressure, ported to atmosphere.


Valve failure is usually what causes low\intermittent vacuum when all else checks ok.


Drive bearings fail, and pump craters, making loud noises, usually.


Initial failing vacuum is usually result of vacuum harness problems - deep cold really damages that plastic turbing and the rubber nipples.


Put the vacuum gage on the pump before cranking the engine and no worries on shredding fingers.


Wires you were 'messing' with are EGR Solenoid, EGR VENT Solenoid, and Wastegate Solenoid, connections from PCM, powered by +12v.


Short power to ground, and the computer fails, momentarily.


SES light is on while problem exists, off when trouble clears, but PCM will store DTC for most failures. If problem doesn't reoccur over series of STARTS, DTC will clear, but certain critical codes are archived as History, iirc.

Pulling the alternator yesterday and checking the tube coming from the vac pump, I´m pretty sure that the pump is gone. I don´t get any vacuum from it.

Can these pumps be repaird? I would have ordered a new one today, but they´re asking EUR 319 for the pump, plus shipping.

That would make about $400 just for the pump! It seems that the price in the US is about $166, so I´ll try to order there. As he´s on the forum, I´ll ask Jon Kennedy if he´s willing to help me making sure that I get the right part, buying it from him if I can ...

The crimped edge of the pump cover can be ground off, valves replaced, and the covers pop-riveted together, but finding the valves may be a problem.


Might give gmpartsdirect.com a try - dealer's cost + 20% shipping, gives equivalent of 30% discount at any US dealer.


DSG is in Canada, for Diesel parts.


Diesel Injection Service, DIS, is here in Texas, for new and rebuilt parts


Check the site policies for shipping and handling directives.

Ja, getting the vents won't be easy, and it's probably too much hassle. I need the truck to get to work each day, no chance having it sit around with the vac pump taken apart, waiting for new vents.

And as I know her, if I replaced the vents, the bearing of the pump would just fail shortly thereafter ...

John has the pump around, and I'll take the opportunity to get the gauges I'm planning on along with it. At last, it saves $$ on the pump and shipping costs on the gauges. --- I've been looking around for boost and EGT here, but there weren't boosts gauges I liked and no EGT gauges at all.