I got to thinking about my old blown Avalanche. I had power right off idle, not the 2500 that you speak of. Are you sure you're getting the right boost reference point to the blow off valve? Or that the vale is good? I vaguely remember something similiar my first test drive but that was years ago.

There are any number of things to look at, timing too. If you did not use a good tune, even the one from Magnuson, its going to be wayyyy to retarded to give you any down low power.

Tim

 

I added an EGT probe on the right side exhaust manifold in the front b/c it was the easiest to get a to tap. With the readings I'm seeing around town and the test pull I did, I don't see above 1000F. But I will be doing a longer trip in the spring and we will see what the reading is when it's hot out and towing hills. But if I never see above 1000F then there's a good chance I'll remove it b/c I don't like the clutter under the hood or inside.

I think the reason why EGT doesn't spike like in a turbo is b/c there's not the impediment of the gasses. When I had this same probe on our turbo diesel excursion it was not hard to hit and sustain 1200F. I'm just not seeing that from the H2 but let's wait till it's 105F outside towing a hill.

 

What MPG do you get when you are not towing?

 

Above I mention it drops to 5.6mpg. But I do need to update this thread with the latest information. I have done my towing test during the summer 100 degree heat and the results are not good.

Summary: The heat in AZ is preventing the supercharger from being utilized when towing. On the plus side the mpg increases.

Details: After a couple towing tests in the heat I noticed the performance was not the same as towing in the winter. To control the engine heat, the computer retards the timing and essentially runs the truck like stock i.e. no supercharger. So I brought the H2 to a local 'reputable' tuning shop to get a custom tune. I asked them to have the fans come on sooner and I put in a lower temp thermostat. I'm pretty sure they ignored my requests and gave me their generic escalade/cts-v tune and took my money (snake oil). The results of their tune were marginally noticeable when not towing and everything ran hotter when towing. So I took it off and went back to the magnuson tune.

Conclusion: With or without the supercharger our 5000lb travel trailer is too much for the H2 during the summer months towing these hills. Don't get me wrong, it will tow the trailer but you have to be prepared to down shift into 3rd go 45mph up the hills while keeping an eye on temps. When it's cool out, the supercharger turns it into a different animal altogether and pulls like a horse. I would think in a cooler/flatter climate it would do better.

Next steps: Not sure, might sell it but no one in the family wants to. On the other hand, I sort of like the challenge of figuring out how to keep it cool in the summer.

 

So you get 5.6 mpg when you are NOT towing? And you have a supercharger with 4.56 gears correct?

 

read #50 https://www.hummerforums.com/forum/h...e5/#post368271

Not towing it's the same as stock 10mpg.

 

That's great!

 

I just read your entire post here. The problem is your 4000ft and higher elevations. You're running thinner air so you need to compensate your injector duty cycles accordingly and I would put a smaller pulley size to get more boost. If you're running the stock pulley, I think they are 8lbs of boost, which is calculated at sea level. Rough numbers you loose about 10% per 1000 ft.

You didn't mention replacing the MAP sensor, that could be faulty which could account for some of this too.

Also look at your cat's or replace or gut them if you can, remember you're moving more air than before.

Tim

 

Just Curious. Have you had any issues with pinging/spark knock? I have the same year h2, same engine, same magnuson kit and the tune they gave me back in 2016. It has very apparent spark knock when towing up grades at 3200-3400rpm with 4000 lbs.
I’ve never towed with it before and the first time was yesterday. I’m not even going to tow it home today for fear of blowing a head gasket. I’ve contacted Magnuson and I’m hoping they can get back to me with a new tune or something. I wonder if the tune has been changed since 2016. And yes I’m running 93 pump gas.

 

maybe a few cans of octane booster can get you back till magnuson contacts you.maybe they need to tune timing on heavy loads