Hi,

during my trip to Sweden, I've got some error codes set when towing my camping trailer; the SES light came on. It stayed on for about 3 days, and then, after driving around in the area for a day or so without the trailer, the light went off. My idea was that it could be the glow plug relais again, as the symptoms were similar to a broken glow plug relais.

About a week later on my way back home, the SES light came on again while I was towing on some highway at 80kph, and stayed on the rest of the way.

Today, I had the codes being read, and they were as follows:


P0404: AGR system function
P0406: AGR sensor circuit --- high voltage
P1656: wastegate solenoid control circuit (?)


I'm not sure about the translation, as I've only got the descriptions in German:


P0404: AGR-System Funktion
P0406: AGR-Sensor Stromkreis --- Spannung hoch
P1656: Bypass Klappenventil --- Magnetventil-Steuerung Stromkreis


Is this a wastegate solenoid beginning to fail? What can I check to find out what's going wrong?

The codes were cleared, and the SES light didn't come on again yet. The truck's running fine, and it develops a tremedous amount of towing power, even when the SES light is glowing at me :)
Edited by: 0lee

Olee,


Assuming 96 & 98 are same codes judging from my 98 manual they look to be indicating some vacuum problem as that is common link for them all. Check vac plumbing, also main vac should be 20+"Hg, another possibility is venting firewall baro/EGR feedback sensor used in L56 engines, or EGR solenoid itself, could be WG sol but I'd check others 1st.


P0404= EGR system performance


P0406=EGR sensor hi voltage


P1656=WG solenoid control circuit

TD,

thank you very much! I'll get into it this weekend --- think I'll start with putting hose clips on the connections of the vac tubes to make sure they're set tight and draw no air. The vac pump should be ok, otherwise the SES light would be coming on again very soon, I think.

It could very well be the EGR feedback sensor. How does it work, i. e. can it actually tell whether EGR's working or not? Can it detect a leaking EGR vent?

Can I check the EGR solenoid? I've just made a search on that term, but the results are not very helpful, as there are too many. Where is it located?

On L56 of my vintage, they are in a row drivers side, the 4th the baro/EGR FB is on firewall one side it teed to EGR dump sol and other side is open to atmosphere, as for FB IIRC it does a comparison between the 2, there you go again asking questions that make me have to hit the books http://www.dieselplace.com/forum/smileys/Big Smile.gif.


Might be a while before I get back to you I'm heading out for a week, hopefully some one else can chime in to help out. In one of QMs posts is the schematic of how it's laid out schematically, basically solenoids modulate per PCM request and vent as required the supplied vac. from main pump.


Even though you don't have an active SES code; still check main as what you are seeing may be early indication of vac pump fail.

from what mine has taught me it could be:


vac pump going bad


vac hoses leaking


waste gate solenoid or wire harness

Update:

Now I've applied hose clips to the vac tubing at the wastegate actuator, the EGR valve, the baro sensor on the firewall and another one to the tubing of the EGR valve where the tube to the baro sensor T's in.

It seemed to me the seal of the EGR tube had loosend a bit so that it could draw partially air and partially drive the EGR valve. I guess that at special conditions, the codes were being set. I've strenghtened the seal with some adhesive tape.

The engine seems to run a bit smoother now and to start lighter, and I can hear the turbo whining somewhat more. So that's the state things should be, and the problem is probably solved, unless it appears again.


BTW, TDoc, what kind of sheet metal do you use to plug the EGR valve? It has to be very thin, but must seal tight and withstand the heat.


Thank you all for input! :) I'll let you know if the problem comes back.


PS: I'll see that I'll check the vac pump. If it starts to fail, I'll want to get hold of a replecement in time.


PPS: The wastegate actuator moves very sluggishly when moving the lever by hand. When idling the engine, it's pulled up, and when you move it down, it slowly goes up again. Is it normal that it moves so slowly?
Edited by: 0lee

18 gauge sealed with Hi temp RTV silicone sealant(red) of course law abiding citizen that I am I only bypass EGR when off roading. I traced the EGR valve base and then used tin snips to cut it out.

Update:


PS: I'll see that I'll check the vac pump. If it starts to fail, I'll want to get hold of a replecement in time.


PPS: The wastegate actuator moves very sluggishly when moving the lever by hand. When idling the engine, it's pulled up, and when you move it down, it slowly goes up again. Is it normal that it moves so slowly?



If you can move it at all with the engine running then something is wrong. With the engine off, it should move a little hard and if you take the hose off the actuator then it should move real easy.


If you don't have a gauge to check the vacuum, just take the hose off and see how hard it sucks.

At idle it should fight you to go back where it wants to or your boost will be weak.

That's interesting ... I just went out and made some pictures of it. Here's one with what I think must be called the wastegate actuator:


http://www.dieselplace.com/forum/uploads/646_pict0750-crop.jpg


What I think the wastegate actuator is, is that brass-looking thing right to the airbox ontop of the turbo charger, having the black tube on it with the hose clamp.

There's a pin --- hard to see --- coming out at the bottom of the wastegate actuator that moves a lever at the turbo charger housing up and down. I think the lever moves the wastegate, which is inside of the turbo charger housing.

Did I get it right?


When the engine is off, the lever is down. When the engine idles, the lever is pulled up by the wastegate actuator.

Whith the engine off, moving the lever gives some resistance, feels like coming from vacuum. When I take off the tube, there's less resistance, feeling like there's a spring somewhere in it that pulls the lever down. That seems ok to me.

I'll have to check again with the engine idling (didn't want to start it just for that), but from what I remember after I put the hose clamps on, it is as follows:

The lever is pulled up, but I can move it down without much more resistance than there is when the engine is off. Moving it down is easy enough, the only thing about it is not to get burned when it's hot :) When I let it go, it _slowly_ moves up again.

My thought was that the lever should move much quicker, like popping/snapping up immediately, but it doesn't. I think it doesn't go up all the way it could, too.

There was a bit of vacuum on the tube, but not very much. It seems that the vacuum is just enough to pull the lever up. I'll try to get a gauge tomorrow to see what it says.


I've no idea of how things should be, but if I should guess, I'd say that the actuator is ok, but either the wastegate solenoid or the vacuum pump is bad.


PS: Can I drive without the tube on the wastegate actuator? I'd guess that pulling the lever up lowers the boost pressure, moving it down increases boost pressure. Thus, if I would drive without the hose on the wastegate actuator, I could be running with too much bost.

I'd like to try, as I don't feel the turbo charger kick in at any time, never did so. Maybe it's not working correctly ever since I bought the truck.
Edited by: 0lee

Vacuum leak some where in the line or clogged/sticky solenoid.
If you're not firmly closing the wg, you're loosing your compresion through the wg.

> Vacuum leak some where in the line or clogged/sticky
> solenoid.

Hm, solenoid is that peculiar thingy made of plastic on the drivers side, among several of them, vac tube going in on left side, wires on right side? Can I somehow check it?

> If you're not firmly closing the wg, you're loosing your
> compresion through the wg.

I thought the wg works by leading exhaust gas more or less off of the the turbine in the charger?

So, if I'd try to drive without the tube on wg actuator, I'd get more boost pressure but less compression?

less boost and less compression in the turbine.
There's a place in kansas that says you can make the same hp and torque with their headers as with your turbine.
This shows that a better turbo/exhaust is a real issue as a better intake.
Edited by: quantum mechanic

Sorry, I've to correct myselfe:

When the engine idles, the lever is _not_ pulled up as I said, except for a litte.

It would be a logical way to build it that way: The spring pulling the lever down is much more unlikely to fail then the wg actuator, wg solenoid, the tubing or the vacuum pump. Thus, in case something fails, the spring would still hold down the 'wastgate lever' and thereby keep boost pressure as low as possible.

Building it the other way round, a failing part would set the TC to make maximum pressure and result in engine damage.

Does anybody know for sure which way it works? Where is the wastegate lever supposed to be at idle, up or down?

Unfortunately, I coudn't get a gauge to check the vac.

It should be up and too tight to move at all.


You loose all boost pressure as soon as it opens at all. The computer pulses it at different speeds to control boost pressure.


Since you have very little vacuum at the hose there, try back before the solenoid. (black plastic thing on the other side of engine that you mentioned above)


If it is strong there, then it is probably either a bad solenoid or computer/wiring problem.

whatnot, it somehow seems to work now! I've been reading your reply while eating my lunch @ work and became very tempted to tie the wastgate lever up :)

Before going home later, I pulled the tubing from the wg solenoid and then started the engine. There was so little vacuum on the tubes that I could hardly feel it.

So I put the tubing back on, engine still idling, and wanted to tie the wg lever up with a cable fixer to carefully drive a mile or two, to find out if it would make a difference.

But the lever was already pulled up all the way by the wg actuator. I could still move it down, but not easily, and it went up quickly enough, almost snapping.

What can I say, the engine makes an almost dangerous amount of power and torque now! If it continues, I'll have to get used to it :)

After driving 3 miles or so, I stopped to check the lever, and it was still up.


I'm pretty sure that the wg actuator has never been operating as it should ever since I got the truck a year ago. As far as I can remember, the lever has never been pulled up as it is now. With nothing to compare, I didn't notice that it was lacking boost. It somewhat felt like it could do more, but I thought that it just was as it was; the truck isn't meant to go fast, anyway. But now it feels that it has become as it should and still could do better, with some mods :)

I'll keep a close eye on the wastegate. Maybe something plugged the tubing or the solenoid and was removed with my attempt to check the vacuum, but it can still be something else.

And I should better get the gauges I'm planning on quickly. They would have told me of having low boost immediately.

Thank you all very much for you help so far! I'll let you know if something more shows up.

If the hose clamps helped that much then I would consider replacing all the vacuum lines. The might have small cracks in them.


You should be able to find similar tubing locally or maybe even use some rubber hose that won't collapse.


If you can find someone with a scanner, get them to plug it in and go for a drive. It should be able to hold at least 6 PSI of boost under heavy load. (like accelerating up a hill)

lee,
The solenoid is a steel ball and an EM that gets sticky. try WD-40 or the german equivilent.

Lee - the WG Solenoid is open to atmosphere thru one port, with a small felt filter.


Constantly venting to Baro, any moisture in the air also enters that port, resulting in eventual solenoid 'armature' rusting.


Armature binds up, valving function is reduced, as is vacuum on wastegate actuator.


With 25" at pump, PCM modulation of Solenoid should give 15" at wastegate actuator at idle.


It is easily dis-assembled - long-term wear between armature and tube result in leak-thru to vent port, so merely removing the rust does not restore full functionality.


Spraying with WD-40, a light oil, is only a patch - the Solenoid will require replacement.

Whow, thanks for all the hints! :)

Today, I went to the shop for an oil change, thereby, we checked vacuum with a gauge. There was almost no vacuum on the wastegate, so we unplugged the wg solenoid. There wasn't much vacuum there, either.

Which tube comes from the vacuum pump? There's a white one running along with the tube going to the wastegate; the white one seems to go down at the alternator to the pump.

Even on the white line, there wasn't really vacuum. Vacuum was about the same at any place we checked, about 0.1 bar/1.43 PSI. So I think the vac pump is gone.

Is there anything special about the pump, or can/should I just get a new one, and it will bolt on easily? Anything else I should do when I am it?


And there had been some oil leaking from somwhere, probably front of engine and/or rear side of oil pan. We washed it off so that I can see wheather it's still leaking. Maybe it leaked under the load when I was towing, maybe I was running too much oil at some time ... Known problem?
Edited by: 0lee

Check vacuum directly at the pump fitting - lines could be deteriorated - for 25" at idle.


Cadillac\Buick used similar pump, with fittings for pressure and vacuum, solenoid controlled for air suspension system use.

Well, I would have done so if I had seen a way to get at the pump fitting. The pump is hidden under the alternator, and with the engine running, some of my fingers could easily be teared off ...


BTW, I went to take in fuel and to town, and after driving maybe 40 miles, I couldn't see any more oil leaking. I hope it's ok, but I'll keep watching ...
Edited by: 0lee

the oil filter on your tahoe is probably where mine is on my blazer. it is right above the front driveshaft output from the transfer case. when they change your oil it spills all over that universal joint, coats it and continues to drip for about a day.

lupey6.5,

the filter is exactly there, but the oil probably didn't come from being spilled on the drive shaft or the U-joint. I took some pictures of the underside of the car (pics of the exhaust, actually) while the oil was changed last time; I'm usually standing besides when they do it. It doesn't take long, so I usually wait around and take the chance to examine the underside and watch.

If they spill any oil, they clean it off with some cloth and even some solvent that makes it easier to remove, if required. If they had oil dripping down from all the cars they change the oil on, they'd probably very soon get into some legal issue about polluting the environment. They do decent work not only on that, otherwise I won't take the car there.

There's a slight chance that last time it had gone unnoticed, I can't remember if it was cleaned. Most oil was at the back of the oil pan, but there was also some in front of the pan and on a rod of the steering setup that runs left to right in front on the pan. Above the rod, there's a large tube (engine coolant?), and the tube also seemed to have some oil on it.

It looked a bit as if the oil had come out of seal of the oil pan in the front and in the back of the pan. If it were oil that had been spilled on the driveshaft/U-joint, I've no idea how it should get to the front of the pan. The oil didn't run all over the bottom of the pan, too, just front and back.

The mechanic said it looked normal to him, could very well be that way on cars of that kind, and I shouldn't worry. Nevertheless I do, I know for sure that no oil was leaking since one of the lines to the oil cooler had been replaced about half a year ago.
Edited by: 0lee