Since the forum didn't seem to busy today, I figured I'd post this. This is not a major issue but i'm getting a bit tired of it. The issue started a couple of months ago and seems to be getting worse (hard to tell because the change is probably quite slow).
The problem is most obvious when the engine is below operating temp but it still persists even when engine is hot. It occurs at speeds between 20 and 50 mph when travelling at a constant speed (zero boost situation) and then you try to accelerate. The truck violently shudders and blows a whole pile of blue smoke (like a really smoky camp fire color) until the turbo spools and provides boost > 0 psi. The whitish-blue smoke is very apparent when the engine is cold and it changes to black when hot. What makes this annoying is when you accelerate slowly (actually, its starting to do this just trying to keep constant speed) it will keep shuddering and smoking like crazy (I can hold it there for 1/4 of a mile) until you either:

A) Mash the accelerator pedal down further to spool the turbo

or

B) let off the pedal and let the truck coast

Problem with option 'A' is you start to pick up speed to much and have to let off and slow down (then you start all over again to speed it back up) and with option 'B' you have to speed up again right. I can be driving a long for quite some time, even at constant speed now, and look in my mirror and realize that I have been hazing two lanes of traffic for who knows how long.

Of course the issue seems to point at the turbo not spooling properly. I believe that the shuddering is caused by the call for more fuel as you try to lightly speed up. So, the pump starts delivering more fuel, but then the computer realizes that there is not enough air being supplied for that amount of fuel so it gets cut back. But then the computer again observes the throttle is pushed in and wants to deliver more fuel---the vicious cycle continues.

I know that a turbo should not take 5+ seconds to start spooling (once it does it goes great). It seems to have a very hard time getting the boost off of zero. What doesn't make sense is that the snorkel in fender is gone, upper intake around EGR has been cleaned, whole 3" straight through exhaust has been installed so there is no reason that airflow is restricted. I will replace the air-filter shortly (maybe to a K&N) but the smoking/shuddering issue seems way more severe than a bit of restriction from a 10 month-old air filter. Any thoughts? Thanks. Sorry for the lengthy read.

Turn the boost up!
The stock vac system is probably faulty somewhere.

That's the problem, it goes to zero because there's no load but then trying to get it off of zero is the problem. Once it spools up to 7-8 psi it goes nice but to get it there is another story.

I was thinking something along the lines of a fault in the vac system. Thanks qm for the suggestion. Just out of curiousity, what boost do you see normally at 40 mph constant speed w/ no load? Is there a difference when comparing electronic vs. mechanical boost control?

Whitish blue smoke? Black I can see for boost issues, but that other color? Couple questiono's fer ya: does your radiator hose get hard while the engine is still cold?

Other thing too maybe the engine coolant temperature sensor is out of whack? Any takers on that one? Just a thought.

knkreb, did you mean does the hose get hard while the engine is still hot? I believe the coolant temp sensor is working okay. Nothing goes funny with the gauge on the dash if that means anything.

Do you see oilspray off the intake or other signs the intake is leaking (or the exhaust crossover) other than that it's going to be the vac pump/ lines or solenoid.

ECT sensor sets a DTC same as MAP when disconnected but I've seen fuel starvation give a cloud of white smoke.

Answer: engine cold. Coolant system won't build pressure until warm. If pressure is built before it's warm, then you have pressure coming in from another area: e.i. head problems. IIRC, there are two coolant sensors. One for you and one for 'puter. Of course WE don't get to see the one for the computer.

I still would start with the WG Control System, and really look at the solenoid to start. I'm told that a shot of wd-40 in the ports of the WG solenoid helps them work better. If that makes it better than replace it for bout 25.00 bucks. Also check to insure vacuum is present at the solenoid and actuator.

I see what you mean knkreb, I hope it isn't a head problem. I will try what you have suggested bowtie, it makes good sense. If I find that it is a WG/solenoid issue, it just may be time for a turbomaster.

Edit:
I just did some searching and found that most people who had a WG/solenoid problem had syptoms of belching clouds of black smoke and no power. My problem is a bit different. Could this be a computer related issue?? Another fellow claimed he went for a pcm upgrade and it solved some issues originally thought to be wastegate/solenoid related. Thinking back, ever since the truck was new it has always sputtered like this at the lower end of overdrive but without the smoke. But then again (man i keep double guessing:confused: ) after i did the exhaust upgrade in december, the original shuddering in overdrive dissapeared and I was thrilled. She ran smooth as silk. But now, that has started again and also happens in all gears, not just bottom end of OD and now it belches blue when cold and black when hot. It honestly must be that wastegate/sol.

Just came in from outside. Popped the hood with the engine off and the first thing I did is wiggle the WG arm right next to the turbo. When I pushed the arm back and forth, I could hear a swooshing sound on each push (air blowing through or out of something) over on the driver side. I could not pinpoint the exact location because i'm a small guy and can't wiggle the WG arm on pass side and stick ear on driver side at the same time. Odd I thought. Can anyone confirm that?

Next i fired up the engine and went to push the WG arm....solid as a rock. I then pulled off the little black line that plugs onto the front of the WG arm apparatus and shot a good amount of WD-40 in toward the cannister. Put it back together and went for a drive. The issue is still there but I think it has lessened somewhat. Its hard to tell when the engine is warm so I will find out tommorow morning whether there is a greater difference.

You need to shoot it the other way. Into the actuator isn't going to lube the little rusty ball in the silinoid. Sorry didn't explain that too well before, you had a 50/50 shot.

That hushing leaking noise *may* have been out of the WG noid. That should be normal. The 'noid has three ports. One vacuum (to the vacuum pump), one to the well lubricated actuator :) and the other is a vent. To regulate vacuum, it will switch the actuator between vent and vacuum.

Black smoke I've got my bets on the WG noid, but the white/blue has, in my feeble mind, to be another problem.

You're hearing air leaving the waste gate solenoid on the driverside.

Silvy, according to your sig, you have an L56 or EGR engine right?
Is your EGR active? That is, have you done anything to bypass it from operating?

If so, then this might be your problem, L56 PCM is programmed to give less advance under light load because the PCM is assuming you have partial EGR gas flow into the intake. This warms the intake air and less timing advance is needed, without that, your timing will be late and give you white/blueish smoke.

If not, then I would still say your problem may be EGR related.

I know you've probably heard tons of guys, including myself say that disabling the EGR is the first mod to do on a LD engine, and it is entirely possible, and a lot of guys get away with it, but not everyone. My truck was similair to yours after I put in the HD intake, and never really was cured until I got a HD PROM.

Just drove it to work and back today with the WD-40 remedy and the problem seems to have lessened quite a bit but it is still there. At most it now only stumbles once or twice and then the turbo catches up (thanks knkreb for the correction:) )

TDG, nothing has been done to the EGR system. It has only been taken off the intake a couple of times when I had the screaming/whistling noise. I think that its still working....

What happens to the EGR and other L56 specific components when you chip it (Heath's for example)? Would this solve the problem IF we conclude that it is an EGR problem, not the WG/solenoid?

Swissed air-box? Is that something left over from the A380 air bus???

Yes, that's exactly what it is CR;) Sorry, I should get rid of that. I put that in when I followed JK's method of opening up the air intake.

I thought maybe you drilled it full of holes, like Swiss cheese....lol, sure used to make the ole filter box on the 360 hum nicely.

teh swissed air box does free up some air on the LT1 caprice and Impala SS cars. It's one of a few free mods you can do to get more power out of them. Why wouldn't it work here too?

teh swissed air box does free up some air on the LT1 caprice and Impala SS cars. It's one of a few free mods you can do to get more power out of them. Why wouldn't it work here too?

cause it will suck in hot underhood air

Silvy,

did you try wiggling the wires going to the wastegate solenoid? I've had to repair the wires on mine for the third time today after having symptoms like you describe --- it seems that the wires continue to crumble away once they started to do so.

Gauges are a must, it was very helpful to see what happened to the boost pressure.

Thanks Olee, I'll give it a try. I was away for a while, went for a 1600km roadtrip on the weekend. The truck runs good on the highway. Still studders in town though (i've gotten used to it already). I'm impressed with the mileage on this unit now that the exhaust has been opened up. If I keep it around 70 mph with no wind I can get 24 mpg (imperial gallons i believe--so in US gallons, not sure?). If i slow down to 60 mph, I have seen 25 mpg. Overall, this is about 2 mpg better over what it used to be so i'm happy.

i hope thats imperial gallons or i am doin somethin totally wrong

Yeah, I worked it out and 24 miles/imperial gallon is equivalent to 20 miles/US gallon. 25 imperial is about 20.8 US.

Back to those wires going to the WG solenoid, one of the wires on the middle connector is half-way chewed through thanks to the sharp edge on the wire protector wrapping. I guess that could have something to do with it.

Just had a neighbor quickly troubleshoot the issue (he is a diesel mechanic for the city of Edmonton) and he had some good points. He asked if the boost is where it should be under a load. I said it was which it is. He seemed to believe that since the boost is where it should be and the wastegate cuts it back when it climbs too high, that I should look at another culprit. The vac pump and solenoid must be doing their jobs since I do get adequate boost and there is no belching of black smoke when I get on the pedal.

He thinks that one or more of my injectors are on their way out. I guess this could explain the whitish-blue smoke when it studders and the now very-regular puking of black carbon spray all over my driveway out my exhaust pipe when I start the engine cold. Obviously, its belching out unburnt fuel ($$$) onto my driveway. But the main symtoms of injector failure are not yet apparent. I don't have a loss of fuel mileage, there is no lack of power, and it doesn't rattle like a tin can or anything. Plus the shuddering and smoking goes away when the turbo spools. Any advice on this?? Thanks.

P.S. It is on the original injectors at 219 000 km (136 000 miles)