too much boost

[gvig]

Lately I am getting too much boost. At full throttle at the top end of second I am seeing 16 pounds of boost and then I get a SES light. When I scan for codes I get a code that says "fault in wastegate circuit" Sorry but I don't remember the exact number.

I like the boost as it makes it run really nice but I am getting tired of the SES light. Before I shell out the $50 or so for a new wastegate solenoid, is that what triggers this code??? I have checked the coil of the wastegate solenoid and it shows continuity. I also shot some penetrating oil in the wastegate solenoid but no joy.

I would rather rig a boost controller.

One other thing, I had been told the stock GM-4 turbo would only put out about 9 pounds. Is this true??? Somehow I seem to be developing a lot more.

[gwaidman]

George, the GM-4 turbo is efficent to around 14lbs boost, so 9 is an understatment. An overboost condition would be caused by the wastegate failing to operate (open). Any parts that fail in that circut could cause the wastegate to remain closed. Check your linkage as well to make sure it is not binding. For what its worth, I would shell out the cash for a TurboMaster. This eliminates the entire vacuum system, and is adjustable as well. I think you would be pleased with its performace vs. the factory system. I know I am. Happy motoring!

[whatnot]

Have you done anything with it before it started doing it?
Reversing the 2 vacuum lines at the solenoid can cause that.

[gvig]

I understand the failure mode, my problem is what is causing it. The error code seems to indicate an electrical fault, but I am not sure. The problem just popped up, the lines are still in the original position. The wastegate is getting full vacuum, or so it seems. I will try the wastegate in the morning with the engine off. Perhaps that will yield a clue. If I go to the non vacuum controller, what protects the system from DTC codes being set??? Does the ECM limit fuel when in a perceived overboost mode???

Thanks for the help.

[gmctd]

If the wastegate is not stuck closed, the wastegate solenoid is stuck open, or vent is plugged, passing vacuum continuously.
Check for no vacuum at wastegate with wg solenoid connector unplugged, engine running.

DTC-78 and 61 will go away as PCM resumes control.

[DickWells]

George: I don't think you're wastegate solenoid is your problem. I've been running with mine by-passed with a piece of hose now for most of two years. I just un-hooked the two vacuum hoses from the solenoid and piped them together. I do have a Kennedy boost control (variable resistor) up on the plenum. I also have perfect boost all the time. Something that I didn't have with the solenoid hooked up. After the first one went bad, I ran with the lines connected for quite a while and then put in a new solenoid. I lost my boost within a month and so I just re-connected my hoses again and they're still that way.
I know you don't like the SES light, so you'll not like the code 78 that I've always had with no solenoid, but I like the boost.
No one was ever able to explain why I don't have runaway boost, but that's OK too. I run with about 3-5 lbs at 60 mph while towing on a flat, and see up to about 15 when pulling hard up a grade at 2200-2500 rpm. I rarely see 800 deg F on the gage. (post turbo in the down pipe)
The big SpeerCo IC keeps everything cool. Whenever I lost boost, my EGTs shot up, and I had to back off to keep it from going past 900.
FWIW.
Dick

[patrick m.]

Dick, you dont have "run-away" boost because, at 15psi boost, the exhaust pressure is great enough to overcome the vac applied to the wastegate actuator and as a result, it opens anyway.
i ran my original turbo like that too for a while, and found no more power than running at 12psi.
a Kennedy chip will get rid of the code 78, or you can get an electronic boost controler from Kennedy. (maybe others sell them too)This will "hide" the extra pressure from the computer, leaving it to believe that everything is in range.
Thats how i can run a non-wastegated Garrett.

[patrick m.]

Originally posted by Patrick m.:
Dick, you dont have "run-away" boost because, at 15psi boost, the exhaust pressure is great enough to overcome the vac applied to the wastegate actuator and as a result, it opens anyway.
i ran my original turbo like that too for a while, and found no more power than running at 12psi.
a Kennedy chip will get rid of the code 78, or you can get an electronic boost controler from Kennedy. (maybe others sell them too)This will "hide" the extra pressure from the computer, leaving it to believe that everything is in range.
Thats how i can run a non-wastegated Garrett. on edit, some of this stuff is for George ;)

[charliepeterson]

I too know about this over boost. I actually lost boost altogether for a short while. After following the circut I found out the power side is good and the ground circut is at fault. The ECM modulates the ground to the waste gate solenoid like a duty cycle. The weather has been so poor here that I couldn't get to the 24 pin connector under the A/C accumulator so I just grounded the Yellow wire from the solenoid.
When you do this you get "crazy boost". I saw 16lbs on a hard pull with no problem. With no IC this is a big issue for me. I too got the Turbo Master adjustable waste gate system. It's nice but when the weather get's a little better here I will look into why the ground signal was lost to the waste gate solenoid. (Ground goes to pin A3, pink connector @ ECM, yellow wire IIRC)

[gvig]

Thanks guys, but I found the problem..... the wastegate was stuck totally closed. It wouldn't budge till I got a wrench and got ahold of the arm on the turbo. I worked it a bit, sprayed it with LocTite penetrating oil and now it works a bit. When the boost goes up near 9 pounds then it will allow the exhaust pressure to push it open and then it drops back to about 4.5 or so. Then next time it does it all over again.

How common is this sticking of the wastgate??? What is the accepted procedure for fixing it, short of disassembling the turbo and honing the hole and polishing the shaft???

I am thinking about the long term solution and right now I am thinking about a pot on the MAP sensor lead, I believe the term is "homemade boost controller" But that only will work if the turbo keeps working as it should.

[gmctd]

Sticking is not the usual problem seen. Disconnect the rod at the arm, then excercise the arm till you get full travel, about an inch.

Reconnect, start the engine, listen for exhaust leak around the shaft, resulting from hi-mileage wear.

[JohnC]

Originally posted by Dick Wells:
I know you don't like the SES light, so you'll not like the code 78 that I've always had with no solenoid, but I like the boost.Ah, but you're fooling yourself. When the SES light comes on the PCM reduces the fuel rate to a level that prevents overboost even when the wastegate is totally fubar. Less fuel, less power...

[gvig]

The SES light is what I have been trying to avoid, becuase of the fuel cut back issue. I am exercising the arm and will till I get it free as it should be again. Right now I am putting back my pennies, nickels, and dimes for a new 4 inch exhaust system and EGT gauge with pillar pod and I figure that I can work the wastegate arm regularly and keep it operating and fix it later this year.

Just today I resealed the power steering pump shaft, several days ago I added the new ss braided oil cooler lines. No more leaks there either. As of today it doesn't mark it's territory anymore. Yippee!!

Thanks guys, you have been most helpful. Once again the diesel pages saves the day.

[DickWells]

Hi Guys: Well I may start an argument, but I DON'T have an ECM fuel reduction, or any other problem with boost control. I do have the Kennedy boost controller, and it works just fine. How do I know I'm not getting an electronic fuel reduction. I'm towing with an all-up weight of well over 15,000 lbs., and I can gain speed on a 5-6 % grade in 3rd gear, going from around 2100 rpm to about 2500. I'm seeing 7-800 degrees F EGT and about 12-14 lbs of boost. This is at 75-80 degrees outside temp. I see up to close to 200 degrees coolent and (sometimes) I see as high as 210 degrees trans temp, depending on the lenth of the pull. When I'm in hilly country, my towing mileage can go as low as 10 mpg, compared to 13-15 in flat going.
This indicates to me that I'm getting a whole lot more out of my 6.5 than I was getting back before I had an IC, a number nine resistor, cooling up-grades, bigger exhaust, and boost control. If I wasn't getting fuel, I wouldn't be getting power.
Back when I hadn't done anything to the engine, I used to get cut way back on power when it was hot and I was towing up hill. The change was very noticeable, and frustrating. Now, If I want to, I can maintain 65-70 mph on most interstates, regardless of the hills. The difference in fuel mileage is worth it if I'm in a hurry to get someplace, otherwise, I stick to the blue highways and putt along at 50-60 in Torque-Lock (I work the button in and out for hills) and enjoy the ride.
I'm still running without a wastegate solenoid, and I've got pretty good power. I don't understand why, but I can't complain.
Dick

[JohnC]

The Kennedy Boost Controller fools the PCM into thinking the boost is less than it really is. Fuel rate reduction happens when the SES light comes on and DTC 78 sets.

[DickWells]

Well, the SES light has been on solid for over a year. I'd be scared to think of how much power I might be putting through my transmission if I didn't have that (supposed reduction) in fuel!
I also have a code that's always there because it sets whenever I use the Tork-Lock. Say's the converter is stuck in lock-up. Quit worrying about that a year ago, too.

[JohnC]

Originally posted by Dick Wells:
Well, the SES light has been on solid for over a year. I'm betting that has nothing to do with DTC 78, so there probably isn't a fuel rate reduction. DTC 78 only sets when the RPM is over 1800 and scheduled fuel rate greater than (fill in correct value here) and boost greater than (fill in programmed limit here)for 20 - 30 seconds continuously. When all those planets are aligned, DTC 78 sets, the SES light comes on, boost solenoid duty cycle goes to zero, and max fuel rate is reduced to (fill in one more value here). When the conditions are no longer present, operation reverts to normal. DTC 78 is stored in history.

[DickWells]

JohnC: Ah! If you keep at me long enough, I can (maybe) understand. I'm just an old (really, really old) Vermont farm boy, who doesn't understand things that he can't see. Sixty-five this fall. What keeps me going is finding out what works, and sticking with it, even when I don't know why it works. Well, that, and all the good stuff I get from the experts on the DP.
Maybe you've already read elsewhere in here that I have a mechanical pump with oversized rollers and head that I'm going to install this summer. I (might) start to trust the old Sub. (sob? S.O.B?)
after that.
Thanks for your patience, guys.
Dick

[gmctd]

It's simple to prove or disprove, Dick.

Clear the codes before you make another trip, leaving your adjustments set, no changes.

Make the trip, and pull the codes when you arrive, to see if DTC78 occured, or only the other codes that keep your indicator lit.

It's likely the settings in use do not cause the wastegate fault.

[DickWells]

Whoops. My last note should have read; oversize head and rotor, not rollers.
GMCTD: Actually, I have done that. The only thing is, without the solenoid in there, I get a code 78 immediately. I think everyone is right. I wish I could afford to put my Sub. on a dino. According to Jim B., with my equipement, I should be getting close to 250 HP. By the "seat of the pants", compared to how it used to be, I have to believe that I'm getting close to that. I never felt that the Banks chip was much of an improvement. From what I've read in here about some of the more agressive chips from J.K. and others, I could probably do better if I changed it out. ? Anyway, I going to try my rebuilt mechanical pump. I don't like getting a thump in the engine at intermittent times. Always have for six years now. Can't always blame it on the FSD, either. Last time, it was a broken wire to the pump. The purple one.
BTW, what's the purpose of that rubber block where those six or eight wires are molded together
just at the front of the manifold? Short harness. I looked it up, and knew where they led while I was fixing it. But, that was a month or so ago, in Florida. Is the block just to cancel out stress to the wires at that location? I bugged them all out, and couldn't get any resistance readings there. Just curious.
Thanks, Dick.

[gmctd]

Believe those are emi\rfi chokes - no resistance, just impedance. DC vs AC

[JohnC]

Originally posted by Dick Wells:
I (might) start to trust the old Sub. (sob? S.O.B?)
Dick SAAB?

I didn't realize you have a Banks chip. (dnt rd shthnd 2 gd) They may be ignoring the DTC 78.