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ATT Performance Loss

Big T

Big T

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Location
Fullerton, CA
I purchased my '99 Suburban in January 2010 and it came with the ATT. It also had the Heath GL4 programmed ECM which was later updated for the ATT. Also had Bosch HO Marine injectors as well as all the requisite cooling goodies (see signature data below).

When I first had the truck, it would push 14 psi of sustained boost at sea level without towing. I could sometimes see 17 psi momentarily while pounding it up the local mountains. Now I'm lucky to see 10 or 11 at sea level and 12 psi going up the local mountains. Whereas previously it felt like the engine wanted to keep pulling, now it feels like there's a governor on it.

I can't pinpoint a specific event or time when this happened. I've had other issues that have grabbed my attention such as a broken downpipe that continually separated at the v-band clamp, loosened crossover pipe and leaking silicon intake boots. When the latter intake leak occurred, I knew exactly what the problem was as I could see that the silicon boot had slipped off. Once replaced, the boost would go back to normal until the silicon slipped off again.

In my current situation, I'm not seeing the detached boot. I've got a new downpipe installed, so engine compartment noise is back to normal. I'm not hearing any increased turbo whistle which typically occurred when the downpipe separated or the silicon boot came off. I've checked the crossover pipe and it's solid. Curious as to where/what I should be looking for to cure this
 
Smoking when wound up? Air filter condition? Fuel filter and lift pump PSI? Possible collapsed crossover or other bent up exhaust parts including muffler coming apart internally.

The loss of boost for me usually is a fuel problem like plugged tank sock, plugged fuel pump screen, plugged fuel filter, kinked fuel line... Usually from something growing in the fuel.
 
WarWagon said:
Smoking when wound up? Air filter condition? Fuel filter and lift pump PSI? Possible collapsed crossover or other bent up exhaust parts including muffler coming apart internally.

The loss of boost for me usually is a fuel problem like plugged tank sock, plugged fuel pump screen, plugged fuel filter, kinked fuel line... Usually from something growing in the fuel.
Click to expand...

Not smoking when wound up.

Air filter has 2K miles on it.

Fuel filter has 5K miles on it.

Lift pump PSI? I don't have this monitored. I intend to install a FRC-10 to replace the Heath Lift Pump.

Crossover is not collapsed and no other exhaust is bent up. Muffler is a Diamond Eye and really has nothing to come apart. Soot trap is deleted.

Not sure I even have a fuel pump screen.
 
Quick and dirty is to drain some fuel into a glass jar from the water drain. If opening the valve doesn't kill the engine the lift pump is doing something. Check fuel condition and how much dirt came out. If you see any water... Miles is not the factor on a fuel filter here as bad/dirty fuel can ruin it quick.

No smoke and boost is down has less fuel written all over it.

I would check the hose behind the FFM to make sure it didn't kink. Blow air back to the tank from the lift pump connection to see if the tank sock is plugging up. If you drop the tank loose the sock and use the screen in the Walbro. Tank lining coming off, bad fuel, or bugs can plug screens in a week/quick.

Further fuel issues will be a fishbite and vapor lock with a near complete blockage.
 
First thing I thought of too was lack of fuel. Got have a fuel pressure gauge on these rigs. Its the most important gauge IMO.
 
Burning oil said:
First thing I thought of too was lack of fuel. Got have a fuel pressure gauge on these rigs. Its the most important gauge IMO.
Click to expand...

And if you do drop the tank get the indestructible fuel level sensor from this outfit.
 
If you are in need of a fuel pressure guage. I have a isspro model r8709 mechanical guage that I didn't use as it was to big for the blank area behind the turn signal on dash. It is size for pillar which is 2 inch I think. 20 bucks plus the ride. You can look it up on thier website. I ended up using a tiny mallory unit.
 
Burning oil said:
First thing I thought of too was lack of fuel. Got have a fuel pressure gauge on these rigs. Its the most important gauge IMO.
Click to expand...
Hands down it is.
Case in point,..Wife's 98 lost power off and on the other day fuel press fluctuated between 0 and 5 psi then lost it all together.
Culprit was the OPS gave out,....full fuel press in glow mode,..none with engine running.
So much for having two power paths to the LP on 98 and up as is claimed :nonod:
 
bison said:
Hands down it is.
Case in point,..Wife's 98 lost power off and on the other day fuel press fluctuated between 0 and 5 psi then lost it all together.
Culprit was the OPS gave out,....full fuel press in glow mode,..none with engine running.
So much for having two power paths to the LP on 98 and up as is claimed :nonod:
Click to expand...

The OPS is still a safety cutout in all years to stop fuel flow if the engine quits after a wreck.
 
OK, finally got a look at it in daylight and the silicon boot to the intake had blown off in the middle (underside). I got it cleaned up and put back together so that she could drive it to Big Bear while I attend the Utah St vs USC game. It should hold.
 
Seems like they last a little more than a year, then they're stretched I'm dealing with this. So It looks like I need new boots.
 
Are these the same as Dennis has for the updated boots?
 
Yes. The sleeve between the two silicon pieces needs to be 1/2" to an 1" longer.
I had to reposition it several time to get the clamps to hold between the lip on either side. If the clamp was anywhere near or on top of a lip, the whole thing would just slide off. The clamps have to be right next to each other, or there is not enough space. It's not a good set-up.
 
I use the cloth wound over silicon boots and with all the junctures my set up had, it never blew off a boot until I went over 20 psi with the new turbo/motor. Great White observed the issue was a short section of hose was slipping under the clamps because there wasn't enough material under and outside the clamp. I concur. That and there's no bracing to keep the joints together like the GM to OEM set up had. One of the trade offs to going aftermarket.
 
That's why I believe the sleeve connecting the two needs to be longer. As it stands now, the clamps have to be perfectly side-by-side in order to fit between the humps of the sleeve and to provide enough silicon meat under the clamps. When I I initially installed the silicon boots everything was clean and dry. Once on the boot on the intake side was impossible to move/rotate and still is tough to move. This made it hard to get the right angle for the boots to seat properly on the sleeve. Imperfect seating and the silicon stretches to fit it. Add oil from the CDR and they start blowing off.
 
I started on my ATT swap this weekend. Have another thread going on it. Anyway Im the type that I dont want to cut the stock wire harness if possible, I'll make adaptors or get creative to avoid it.
So as this is my first ATT swap when I saw you had to cut the manifold I did not like the idea. Sometimes you just have to modify though when going aftermarket.
So I started making a sandwinch adaptor lastnight, it go's between upper and lower intakes. It will put the upper intake right where it needs to be. Same relationship as factory but raised and forward. This makes it possible to use one short hose between turbo and intake.
I'll need to get with a "real" welder and see if a boss can be welded to the ATT to allow the factory metal brace to be retained.

This is all just prototyping right now so no gaurranties, but so far it looks do'able.
 
Leroy, sometimes necessity, errr bitching is the mother of invention.

I just got back from running drywall and trash to the local waste station. Short run of like 2 miles one way with a flat level section at 6,750' elevation. With it floored I saw 14 psi sustained through the first 2 gears and 15 psi sustained in 3rd before I had to back her off (40 mph zone and I was going 60). So it's back and the clamps are holding.

Typical Steve, showed up 15 minutes late to the Associates Lunch ahead of the USC vs Utah St game with grease under my nails.
 
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