GM wastegate operation

**Superbee** · 03-26-2017

Hello guys, I have issues with my boost control. Here is a quick rundown of what i have and what my issue is,

I have 2.0 turbo sunbird. It has an external wastegate on it now with rock solid boost at whatever wastegate spring i choose.

Right now I put a 5 psi spring in it.

Hook the boost solenoid up with METAL port to a vac Y that goes to turbo compressor housing and wastegate BOTTOM port..

Vent port of solenoid has the factory foam on it. Other port goes to TOP wastegate port.

Electrical connector has 12V going to side of wastegate solenoid that has the ( + ) inscribed in it. Other a ground. (factory connector)

ISSUE: 99% duty cycle allows spring pressure boost.

0% duty cycle allows for ALL the boost until I let off.. This is exact opposite as it should be. which is why Ive got crazy boost issues when trying to use a factory electronic setup.

WHY WOULD IT BE DOING THIS???? I cant explain it. Obviously if i set it to say 50% DC, the car will hit my desired boost and then it may drop off a little so the ecm will add more DC, which causes the boost to drop off more, which causes the ecm to go to 99 soon, and im riding on spring pressure 5 psi....

Car off, i can blow through solenoid through the turbo side vac hose....start the car and its blocked..

I dont get this.

Dont think it matters but Im running $59 code59.

**1project2many** · 03-27-2017

The boost solenoid plus ecm control is a sophisticated way to trick the wastegate into operating differently than built. When the solenoid is "on," boost signal from the engine or compressor is vented through the solenoid at the metal port to atmosphere through the foam keeping the pressure at the wastegate low and allowing boost to build. The wastegate is isolated from the signal and atmosphere. When the solenoid is "off" the wastegate is exposed to signal pressure. This allows wastegate opening to be delayed until desired pressure is built. It also allows for boost to be controlled if the ecm is unable to control the solenoid. Boost is always directed to the wastegate with no venting.

In your system the compresor signal is connected to the wastegate pressure signal sense port. The signal is also Teed to the boost solenoid which can either vent it to atmosphere or connect it to the spring side of the wastegate to delay opening. When the solenoid is not connecting boost signal to spring side, any pressure in the spring side of the wastegate is sealed off from atmosphere and from wastegate signal. The effect of this is you have spring pressure plus any boost pressure trapped in the spring side and no way to vent it.

You have a couple of options. The first is to use your wastegate like the single port version and leave the top port vented to atmosphere. The system will work like an OE Sunbird system with the ecm venting boost signal to trick the wastegate. The other is to try turning the solenoid around. This will permanently connect the boost signal to the pressure sense port on the wastegate and will allow the top port to switch between atmosphere when the solenoid is off and the pressure signal when the wastegate is on. This will limit max pressure to spring pressure if the solenoid isn't working and will allow you to use ecm control to increase boost as needed. You will probably need to experiment to determine the best control settings for this method. One advantage is that if you get it worked out, this approach may result in no boost flare or creep, a problem common with the stock Sunbird and with the SyTy.

**Superbee** · 03-27-2017

In the car now... Just switched the two lines going to the solenoid.. I.e. the steel port and port that doesnt have the filter.... Now the car has no boost control wither the dc is set to 0 or 100... Just goes higher and higher.

**1project2many** · 03-27-2017

What is controlling solenoid? Ecm? Is steel port connected to wastegate top port?

**Superbee** · 03-27-2017

Tried steel port to top of wastegate. Plastic port to source "T"

Just now i tried source T to steel port only of solenoid and left top WG port open. That didnt work.

Then i went turbine housing to steel port of solenoid. Plastic port on solenoid to bottom of wastegate... With that setup, 0 duty cycle makes boost hang around 10 or a little more with target set at 7.. 99%dc makes it climb to whatever

**Superbee** · 03-27-2017

Yes. Factory ecm controlling solenoid. I may have a bad ecm too.

**Six_Shooter** · 03-27-2017

I had issues at first getting the boost control to work, it's been a while so the details are foggy, but once I got it working it worked very well.

Let me see if I can recall how I did it...

I know initially I had to set the "Closed Loop Boost Mode Threshold High PSI (KCLBSTEH) to 0 PSIG. The ECM will not try to control boost until this threshold is passed, but I found that even if the threshold was within a few PSIG of the target boost, this was an issue.

I thought there was more to it than that, but I can't find any other settings so far that differ between a starter bin and one where I got boost working. I try to find some even newer bins and compare them.

I remember the wastegate duty cycle tables being really important to get boost control to work well as well.

Also do you have a solid vehicle speed read into the ECM? If you're using the MPH based tables and the vehicle speed is not correct or solid that will also cause boost control issues.

**Superbee** · 03-27-2017

Thanks for the reply but thats doesnt appear to be it.. I already set that seting very low.. When you first start the car and take off the desired boost is 0..... first time you hit that target boost number the DESIRED boost pid then changes to your desired boost vs mph setting...

Once I hit my desired boost, just like I have set in my settings, it will throw the initial duty cycle to the solenoid... And just like its supposed to, if the boost KEEPS raising, the duty cycle goes down, clear to 0 in a short time and boost keeps rising... if the car goes into boost slow and doesnt quite hit the boost target, the ecm commands more and more DC untill its at 99.6 and boost keeps dropping untill its a spring pressure.

I want to say the OE solenoid acted like this... Took it off... Lost solenoid, bought another solenoid year or so later (for a gm diesel truck) and still wouldnt work right, eventually gave up.. converted the car over to external wastegate several years later, figured id give the electronic controller a shot now (internal wastegate fluxuated boost with a MANUAL boost controller) now still does not work properly.

Let me back up a little further.

So I converted my NA sunbird over to a turbo engine YEARS ago, I had accidentally put a ground wire onto the starter terminal (due to the harness sitting in a box for about 5 years and had no "shape" to it anymore.

First fire up. hooked up battery, engine ran..

Many months or year later, i was battling some ecm issues, like the whole car freaking out. MPH gauge go to 0, CEL comes on, just a complete power down and on of the car engine and electrical while driving.

Tracked down a 7749 ECM at a salvage yard... Drove to yard, bought ecm, brought it out to car, plugged it into the car, turned key on, smoked rolled out from under the glove box area (the ecm)

Thought it was bad ecm, so i saw 2 wire terminal ends at the ecm were burned. so i luckilly got the car back home, replaced the two terminal ends and got me origional ecm back on... I think i either tried another ecm and same thing or i couldnt imagine why the ecm would cause that but anyways i checked ALL my powers and grounds on the car and found the switched wire! OKay, thought I found the problem all along, so fixed the wire, got it on the block instead of starter terminal and away i went. Phantom freaking out still occurring!

Okay, so the ecm had to be damaged but somehow miraculously still worked after having 12v sent through one of its ground! So searched for another ecm. Found one on EBAY.

Plugged ebay ecm in, NO SMOKE! yay. Put my OSTRICH on the ecm in place of the chip. (i have 72 lb injectors so there is no firing car up with stock memcal) Also the ecm was for a quad 4 im guessing but still a 7749 ecm.

Turned engine over. No start... tried a few more times, no start, smelled fuel. Plugs were DOUSED with fuel!..... cleaned plugs, threw OEM ecm back in, got the engine fired up and fuel burnt out of cylinders and exhaust before it washed them anymore.

Put ebay ecm back in, double checked everything, tune was still on, cables plugged in good, go to start. SAME THING. So i contacted ebay seller and told him ecm was bad (there was also residue on the case)

Drove with OEM ecm in car again.. Few months ago, got ANOTHER ebay 7749 ecm. Swapped over the onstrich chip adapter and ostrich, plugged ecm in. Tried to start it ONE time and didnt start so i ripped the damn thing out and didnt touch it again because i was so pissed.

That was months ago now here i am AGAIN facing potential faulty ECM issues due to the ground mess up.

So question is, did i get TWO bad ecm's?????? Both were from quad 4 engines but SHOULD work, right???? a 7749 is a 7749 right??? This has almost been an ongoing nightmare but the car STILL has been a lot of fun.... But its ALWAYS one obsticle after another from this ancient bastard gm drivetrain that i cant find parts or info for.

SO, what should i do.... waste money on a THIRD ecm??? its just odd i have ALL these "weird" issues and its that original ecm that had 12v zapped to it and the others didnt work.... I wish I had a KNOWN good ecm to try. I know one friend with a syclone but that kind of like asking to borrow someones newborn when asking to borrow a working electronic part from a vehicle like that lol.

Oddly enough I saw a Turbo 90 sunbird with a 5 speed pop up on a fairly local craigslist, want it for parts so bad but its almost 3K. and for a white turbo bird without even the gt front end, thats a bit much for parts hoarding.... but GOSH i would love to have a FACTORY piece of equipment to reference from....One can imagine how much trouble ive been through building a turbo 5 speed car with absolutely no reference other than a couple google images....every nut, bolt, bracket, and wire i had to GUESS!

**Xnke** · 03-27-2017

If you built the car from guesses and you already found one swapped up wire, suspect your wiring. Go through your wiring harness one pin at a time and make sure it's correct.

Get out one of your ebay 7749's and build a bench flash harness for it, and fire it up on the bench. Make sure it responds appropriately to a datalog first-then the ostrich, then datalog the ostrich, then into the car AFTER you check your wiring harness.

As far as boost control, you've already found your problem if you can't even get it to hold boost with a manual controller. If a manual controller won't hold steady boost, the ECM will not have a chance! Get that wastegate under control first, then try the boost controller again.

**1project2many** · 03-27-2017

SO, what should i do.... waste money on a THIRD ecm???

Use tools and diagnose this properly. Connect the wastegate manually, set desired boost higher than what the wastegate allows, and use an LED or a voltmeter to see if the ecm is actually commanding the wastegate solenoid on.

OEM wastegate solenoids are designed to work with an OEM system. Too much boost too fast and the solenoid may not be able to reduce the signal enough to get the control you need. Folks have tried using different solenoids, removing the restricted orifice in the solenoid, and running multiple solenoids to get a handle on this.

**Superbee** · 03-27-2017

That comment was in reference to the internal wastegate setup. With the eternal it hold exactly at whatever spring i install.

**Superbee** · 03-27-2017

Originally Posted by 1project2many

Use tools and diagnose this properly. Connect the wastegate manually, set desired boost higher than what the wastegate allows, and use an LED or a voltmeter to see if the ecm is actually commanding the wastegate solenoid on.

OEM wastegate solenoids are designed to work with an OEM system. Too much boost too fast and the solenoid may not be able to reduce the signal enough to get the control you need. Folks have tried using different solenoids, removing the restricted orifice in the solenoid, and running multiple solenoids to get a handle on this.

I'll check with a volt meter or light soon

**Superbee** · 03-27-2017

Originally Posted by Xnke

If you built the car from guesses and you already found one swapped up wire, suspect your wiring. Go through your wiring harness one pin at a time and make sure it's correct.

Get out one of your ebay 7749's and build a bench flash harness for it, and fire it up on the bench. Make sure it responds appropriately to a datalog first-then the ostrich, then datalog the ostrich, then into the car AFTER you check your wiring harness.

As far as boost control, you've already found your problem if you can't even get it to hold boost with a manual controller. If a manual controller won't hold steady boost, the ECM will not have a chance! Get that wastegate under control first, then try the boost controller again.

Test bench is probably out of the question. I dont have the parts or really even the time to build one of those. I could probably buy an aftermarket electronic boost controller and be done with it for similar price and way less hassle

**Superbee** · 03-29-2017

so dumb question, is there something I can EDIT to make duty cycle in the strategy go down to increase boost vs up and vice versa? or is that impossible making it do something it wasnt designed to. I have no idea why or what would make it do that but that seems to be what it is doing.

If i cant change that or cant get another ecm to work and rule that out.... then i will probably invest in a fancy aftermarket boost controller. Creating enough boost to actually make a little power on the road 3rd gear and higher just destroys the tires in first gear and feels like its going to break something as violently as it does it, and pedalling this car doesnt really seem to work very well like an NA engine does. Need to be able to dial it back to 5 psi in 1st and end up at 20psi in 3rd and higher.