Hello, I have a 2000 7.3 with a AFE cold air intake and 4" exhaust. I also have a SCT programmer. Many times when shifting from 1st to 2nd I get a big hiss from the engine; it sounds to me like a compressor stall but, I am not sure. I thought about data logging it so I could see exactly what is going on but, it seams like the boost drops off quickly when this happens. I asked a friend of mine if these have pop-off valves and he said no (but that is kinda what it sounds like too). So here are my questions.

1. Has anyone had this problem and were you able to solve it and how?

2. What is the max psi of boost I should run? (I see like 22.5 at times).

3. While I am asking questions: what is the max EGT on a 7.3?

Let me know if you have any of the above answers; anything is helpful.
Thanks,
Cameron:

it is the wastegate venting boost when it shifts. normal in a overboost condition.

are you at wide open throttle when this happens? as truckshop said its the waste gate letting boost out so it dont over boost the motor and that is normal.

the max boost level will be in the low to mid 20s on a 7.3
and your egt shold be in the 400-500 range for normal driving if your towing or running it hard its going to go up but dont ever let it get above 1100. and these temps are after the turbo.

Yea, I kinda thought of that too but, I didn't think that was it. (I didn't have a valid reason for not supecting the waste gate; I just didn't). I don't think this happens at WOT, only when in a heavy throttle position and it shifts. I also notice the hiss starting gradually as I am pulling a hill with a load and increasing boost slowly.

My EGT is in th exhaust manifold before the turbo. It regulary sees 800 - 1000 degrees F. It will hit 1100 to 1150 when pulling a load. I suspect this will read higher than after the turbo; does anyone know the max EGT at this location?

those temps are ok, i am guessing you see 400-500 at idle. if the temps go above 1250 I would watch it.

hey crector, noob here. if possible, you should try to move your egt sensor to after the turbo.. that's where most people talk about when talkin temps. the reason for this is when you have been on a long haul (even just playin on the freeway) you need to let your turbo cool down before shutting off the engine. post turbo egt's of 350* or so means you have a cool, well oiled turbo and the enigne can be shutdown. as far as max egts, some people say 1200*, others say 1350* for a short time is ok. personally, i let off if i hit 1250* because that the temp that things can start to melt. maybe some this will help ya.

pre turbo and post turbo egt are two totally different animals.
pre turbo (exhaust manifold) = max 1250
post turbo (downpipe) = max 900
on my 99.5 i have it post turbo, and towing itll get up there, but 900 is my limit.

hey crector, noob here. if possible, you should try to move your egt sensor to after the turbo.. that's where most people talk about when talkin temps. the reason for this is when you have been on a long haul (even just playin on the freeway) you need to let your turbo cool down before shutting off the engine. post turbo egt's of 350* or so means you have a cool, well oiled turbo and the enigne can be shutdown. as far as max egts, some people say 1200*, others say 1350* for a short time is ok. personally, i let off if i hit 1250* because that the temp that things can start to melt. maybe some this will help ya.

Good point on the turbo cool down, but in ever other instance pre-turbo is better. You want to see temps straight out of the engine. I think having a pre and post turbo gauge would be good, but most diesel guys will tell ya go pre-turbo. Usually 1250 degrees preturbo is max for sustained temps. And about that hiss, its probably compressor surge. Its common on the 7.3s. Check out the diesel forums, some people use an ATS turbo compressor housing to eliminate this on the stock turbo.