So I'm pulling a 6k lb trailer up some pretty steep grades (8%+) and as my tranny drops into 2nd my boost shoots up to 12 lbs and then bam! no boost.
So after creeping up the mountain with no boost pressure I'm thinking maybe I just blew the hose to my guage, easy fix right? No

When I finally arrived at our destination I popped the hood to check the damage. All hoses intact, no fluid leaks, wastegate moves fine, everything looks normal. It didn't even throw a code. So I turned down my homemade boost controller(potentiometer wired into MAP) and opened up the needle valve to my wastegate, basically bringing everything back to stock Intake Pressure. Now the boost looks normal without a load, But Im really dreading going back up the mountain, I really don't think I'll make it.

Any input would be greatly appreciated!

A bad WG solenoid can cause this. Mine will provide boost then decide to drop off when I need it the most(I also have a bad solenoid) However mine threw a code for it. The truck may not throw a code until the next time you start it as that seems to be how mine operates.

It could have been that the PCM cut boost on purpose, because IATs, or ECTs or something was getting too hot. Even though you fooled the PCM you didnt fool the IAT sensor and regardless of what boost it thinks you have it will cut it when IATs get too high.

It's just busy being a stock GM PCM... what do you want?

You need a chip and a TM.

I have seen the same, and I have a bad solenoid, leak vac.
And I don't get any code.
Works good with a new boost solenoid.

If you had a leak in the vac system that isnt the same.

If you arent concerned about IATs, and you are watching ECTs and EGTs then you can put vacuum line straight to the wastegate actuator then PCM cant cut boost, and with the boost fooler it shouldnt code. Youll get a bit more boost though, so watch temps.

OBD-II, buddy... it reads IAT.

If you had a leak in the vac system that isnt the same.

If you arent concerned about IATs, and you are watching ECTs and EGTs then you can put vacuum line straight to the wastegate actuator then PCM cant cut boost, and with the boost fooler it shouldnt code. Youll get a bit more boost though, so watch temps.

or you could just weld the actuator shut? bad idea IMO

It will read IAT, but then it cant cut boost, so it might try to defuel some, but still have more power than cutting boost. And you can ulitmately defeat the IATs by unplugging that too and put in a resistor on the harness instead, like 500 ohms.

Theres nothing wrong with having the wastegate closed as long as you monitor EGTs and ECTs. Welding it shut wouldnt be immediately reversible as moving a vacuum hose connection.

yes that all may be good and proper to do on your own vehicle, but don't recommend bypassing things that are designed to to prevent the motor from damage to others.

You may know what your doing when you do these things, but not everyone that attempts to do these things does.

Don't weld the actuator shut, and don't bypass the IAT sensor. It's just not smart.

In your opinion you can choose not to recommend something, but in each case I caveat that you have to watch both ECTs and EGTs. No one recommended welding the wastegate shut, that would be stupid, and was used as a stupid example.

Putting on boost foolers and getting chips is all cool, that do the exact same things by allowing higher limits, but if you dont understand what the effects are then yeah, I dont recommend you do anything to your truck.

In your opinion you can choose not to recommend something, but in each case I caveat that you have to watch both ECTs and EGTs. No one recommended welding the wastegate shut, that would be stupid, and was used as a stupid example.

Putting on boost foolers and getting chips is all cool, that do the exact same things by allowing higher limits, but if you dont understand what the effects are then yeah, I dont recommend you do anything to your truck.

Applying 28 inches of vacuum to the actuator is as good as welding it closed. you can overboost before you notice an EGT/ECT issue.

I choose not to reccomend things that can do serious damage to people who may not understand the caveats.

Don't go around calling members stupid anymore, it won't get you anywhere fast.

-Peter

So I turned down my homemade boost controller(potentiometer wired into MAP) and opened up the needle valve to my wastegate, basically bringing everything back to stock Intake Pressure. Now the boost looks normal without a load, But Im really dreading going back up the mountain, I really don't think I'll make it.

Well we made it home without any major problems. I did notice though that as I came back into town and the grades flattened out and I shifted into overdrive, I lost boost again. I carried a consistent 7 lbs up until overdrive. ECM?

boost is relative to engine load.

if the engine has less load on it in overdrive your boost will drop off. my boost drops from 3rd to overdrive and drops more when the TCC lock engages.

I realize boost is relative to load, but I've always pushed at least 4lbs just cruising in overdrive. Now there is absolutely nothing, but when I'm in the lower gears it's normal

I didnt call anyone stupid, didnt mean it that way at all, I meant the example was used as a deliberate stupid idea to make a point. The vac system can easily be changed on the side of the road if ECTs and EGTs become as issue, welded shut is much different. Ive done this myself and several others have wired their wastegate closed without issue. If you dont know yourself then you dont know. There is nothing wrong with high IATs or boost, Ive run 20psi no problems and 16-17psi sustained. Its just the heat that kills the engine, thats why you have to keep EGTs below 1200 and ECTs below 210. Do that and all is well. High sustained IATs will usually lead to high EGTs and ECTs, which is why if you keep them down then IATs dont matter too much.

If you are having boost while accelerating but losing at cruise, then you probably just have a cracked plastic vacuum line.

okay, finally got a SES light to come on. P0236 something about the turbo

Will it do any good to put a turbo master on without the ecm upgrade?

Thats a generic boost system fault saying the boost sensor is not seeing what the PCM meant there to be. Most likely from a vacuum leak. If you inspect the tubing you might find it cracked and can just repair it with vac hose. If you check vacuum at idle and there isnt any at the wastegate, but there is vacuum across the solenoid then you have a crack between solenoind and the turbo.

I dont really understand why you have a valve on the vacuum system can you explain that?

I'm not really sure either, my buddy did it one weekend while he had my truck. Said it would allow boost to spool up before the wastegate let it go

Thats a generic boost system fault saying the boost sensor is not seeing what the PCM meant there to be. Most likely from a vacuum leak. If you inspect the tubing you might find it cracked and can just repair it with vac hose. If you check vacuum at idle and there isnt any at the wastegate, but there is vacuum across the solenoid then you have a crack between solenoind and the turbo.

I dont really understand why you have a valve on the vacuum system can you explain that?


a valve on the vac system? interesting. i know you don't mean the electric solenoid, so i wonder what it could be for. :confused: if the valve is limiting the vac to the wastegate, there's your problem. Bypass said valve and remove it from the "circuit" as it's not needed to begin with.

It could have been that the PCM cut boost on purpose, because IATs, or ECTs or something was getting too hot. Even though you fooled the PCM you didnt fool the IAT sensor and regardless of what boost it thinks you have it will cut it when IATs get too high.

Sigh....:rolleyes: If I could steal the thread for a second......What is am IAT and an ECT?

That was one of the first things I did to alleviate the problem. I opened the valve completely and turned the potentiometer down on my MAP sensor. I've pretty much narrowed it down to a bad boost solenoid which I hope to remedy by adding a vaccum pump elimination belt instead of replacing it because I believe the diaphram in the actuator is sticking and causing the problem anyways.

Could someone explain to me the actual mechanical workings of the elimination belt and how a turbomaster would benefit me without a reflashed pcm?

Intake air temperature and Engine coolant temperature

Could someone explain to me the actual mechanical workings of the elimination belt and how a turbomaster would benefit me without a reflashed pcm?

The TM will provide a *Constant* boost without the electronics = no drop off untill the pressure (NOT the ECM/PCM) opens/closes the wastegate = again **Constant**

The PCM/ECM has been known to drop boost when you need it most......It's a bolt on deal, if you don't like it pull it off.

2Cents

Having that valve on the vacuum line is completely backwards. That would cut your boost, while you have a potentiometer to increase it (by making the PCM think there is less there). Vacuum on the wastegate means closed wastegate equals max boost possible. So at idle you have full boost and as you speed up the PCM cuts some vacuum to open the wastegate. It works just fine on mine, aside for some cracked plastic lines I repaired, but if it were to fail I'd make a manual controller.

If you actually checked the vacuum at the wastegate at idle and it was in spec then I might be suspect of a solenoid, but if you havent then Id suspect leaks.

Uh oh, if you put a manual wastegate controller on you could damage the engine, since the PCM cant control the boost. Just playing. Its a good idea, and you can build it youself with an L bracket, a metal rod, some washers and pins, a spring and a drill. So for a project and some of your time its not too hard, but heath sells a nice one and a vac pump elimination belt, which is just a shorter belt that you could find at a parts store.