Engine/Transmission (1994 - 1998) Boost at altitude

[T-Bone]

Hi Forrest,



Thanks for the tip. Are you talking about the main injector line? I can't tell for sure, but the leak appears to be around the banjo bolt. Should I give both a try? Just don't want to break anything.



Hi Rhondasway,



I had a shop test for leaks and they said "no leaks". Although, I have no idea how or what they checked. I'm thinking about buying a boost checking set up and checking it myself. I have not checked the intercooler pressure specifically. Would this be separate from a normal boost pressure check? There is no play in the turbo shaft and it spins freely. I just had the coolant changed so I will watch that. I do burn a quart or so of oil every 5000 miles. Is that normal? Also, the pyro thermocouple was a bit loose. I tightened it up, but there was no evidence of an exhaust leak (I'm assuming I would have seen some soot near there) and no change in boost after tightening.



Thanks for the help folks,

T-Bone

 

[JGheen]

T-bone,



I would check it yourself for any leaks. Just find a piece of PVC pipe about 4" in diameter to fit around the compressor of the turbo and seal it all up and pressurize with an air line to about 15-20psi. Check the system with leak check soap or just some water and look for bubbles. The intercooler is part of your boost system and could very well have a crack in it that was undetected by the shop that checked for leaks. Check everything from boost boots, intake gaskets, head gaskets, exhaust gaskets, etc. If you have a leaking injector that will in turn loose some compression in whatever cylinder has the leak, as the injector washers are seals for the cylinders as the head gasket is. If you only have a 12cm turbine housing with the stock HX-35, I don't believe you will see any higher boost than what you are claiming.

Another thing you asked, how to check the Gov. lever..... well, with your AFC housing off, look down in the pump(obvioulsy, with your fuel plate installed ). Now take your left hand and lift the fuel shut-off solenoid in the up position and take your right hand and move the throttle linkage forward a bit. As you are doing this look down the in the pump and the lever will come from the back of the pump and should either be hitting on the very bottom edge of the plate you are running or going under the plate. If the lever is going under the plate then that would be why you are not getting full boost as well as full fueling throughout your RPM range. If it is hitting at the very bottom of the plate(about 1/16th" above the bottom of the plate profile) then you don't need an adjustment. The more you push the throttle linkage forward you can see how the lever rides the profile of the plate, but it will only go so far as it is RPM dependent too. With that #10 plate you have, you should be fine on the lever adjustment, but there are circumstances where one needs to have it adjusted even thought you are running the most versitle plate out there.

 

[T-Bone]

JGheen,



Thanks for the info. I will check the boost and thanks for the explanation on how to check the Gov. lever. It makes sense, now I'll see if I can do it! ;-) Are the folks that are seeing over 30 pounds of boost not running a 12cm housing? Even though I've had the truck a while, I'm still learning.



Thanks,

T-Bone

 

[pcorssmit]

FWIW, I live in Denver; with a #10 plate w/AFC spring kit, K&N (stock box), and 4" exhaust, I could hit 35 psi unloaded, and 36 psi loaded in town. Don't remember the max in the hills, but I don't think it was much different. Totally stock I ran 24 psi max.



Pete

 

[Forrest Nearing]

I was talking the main injector line. I've never had any leaks at the banjo bolts. obviously it could be at either place. get some brake cleaner and hose down the area and blow it dry so everything is nice and dry. then fire the truck up and run around and look at the offending area. you should be able to see exactly where it's coming from then.



Forrest

 

[T-Bone]

Thanks Forest, Will do.



pcorssmit, What's your secret? I plan on running a "test pipe" for the cat to see if that helps my boost. Could it be your 4 inch exhaust that allows higher boost?



Thanks,

T-Bone

 

[Forrest Nearing]

oh man, if you've still got a cat on there, get it off YESTERDAY!



especially being at altitude, you're going to tend to put out a little more soot than if you were at sea level... one of our members with a pretty stock truck recently had an engine melt down that was later attributed to a clogged cat!!!



Forrest

 

[T-Bone]

Forest,



The cat is on the operating table and should be fixed soon. Do I need to be concerned about the muffler and/or the rest of the stock exhaust? I'm not a big fan of loud (sorry guys). But I would like to free things up.



Thanks,

T-Bone

 

[Forrest Nearing]

the stock muffler is restrictive, but it isn't going to cause any catastrophic damage...



you could add a couple free flowing mufflers and still be nice and quiet inside the truck.



Forrest

 

[JGheen]

T-bone,

Run one or the other, as IMO, I would not run the cat with the muffler. Just run the cat if you need to have some kind of sound muffling device. Forrest had a good point about a cat clogging issue. I have definately heard stories of that kind of stuff happening before.

Oh, and just to answer your above question, going to a 4" exhaust will not increase your boost but depending on the application it can actually lower boost and kill spool up, depending on the application of course. I think if you went to a 4", you should be OK, but don't expect boost to come up. You should try running just a nice long straight pipe with no cat or muffler. It's loud, but not like Top Fuel dragster loud or anything. Mine only seems to really be loud in tunnels and such. I also don't get a drone at certain revs as some claim to have.

 

[T-Bone]

JGheen,



I was planning on running an empty (gutted) cat as I need to pass inspection. I've listened to a few straight piped rigs and I kinda think I have enough noise going on at the front of the truck. I'm pretty sure the wife would veto this anyway.



I've heard about the spoolup being slower with a 4 inch at altitude but am not sure I really understand why and would hate to go the wrong way here. My transmission is tight and spoolup is slower than stock now. Will just gutting the cat be the way to go? I’ve been told that the bad part of the stock exhaust is anything/everything from the bend over the back axel to the muffler to the cat to the fact that it’s just 3 inches and not 4.



Thanks,

T-Bone

 

[JGheen]

The reason you don't want to go too big on the exhaust diameter is due to maintaining the velocity inside the complete exhaust travel path. If it is too big right after the turbine, then that kills spool up as well as how fast the turbine spins, which in turn, if too big(like 5"+ on a stock engine), boost is decreased... . some. I am much better at explaining things in person, but i hope that was a good enough explaination.

 

[T-Bone]

JGheen, Thanks for the explanation. It actually makes sense now. I'm gonna try the cat fix and see what happens. I'm kinda hoping I don't have to go too far down the exhaust road. I'm concerned about drone and I already have enough strikes against me in the spool up arena - 4x4 club cab longbed with 3:54s running 295s in an auto with DDIIs at 7000 feet.



Thanks again, folks, for all the help.

T-Bone

 

[pcorssmit]

No secrets for me, I run a muffler but it is a straight thru type. Plate is in the stock location. My spoolup does suck, but I don't attribute it to the exhaust. Its never been great, but its worse now with 315s, 3. 54s, 5 speed, 90° temps (when its not raining), and my slide-in.



Pete

 

[LJHagen]

Cat Inspections

I'm up here in Northern Colorado too... While my truck might be gone soon (have it up for sale to buy a house), if it doesn't sell I've been concerned about the cat. plugging, but don't want to blow inspection either. Anyone with any experience gutting the cat? Any method more preferred than another to get in there?

 

[pcorssmit]

Colorado Diesel inspection consists of a visual test for required equiptment, and an opacity test. As far as I know, the cat does not reduce the opacity.



Pete