Engine/Transmission (1998.5 - 2002) IAT sensor and exhaust brake

[jlccc]

My apologies for posting this twice. I wanted to make it a new thread so more people would be likely to see it and COMMENT.

jlccc



Several people have postulated that exhaust brakes increase the "fouling" rate of the IAT. I disagree for the simple reason that when the exhaust brake is in use, no fueling/combustion is taking place.



In my opinion, what CAN cause increased fouling is high turbine drive pressures. You guys who like to run 30+ psi of boost with the stock HX-35 and 12cm housings with blocked wastegates have turbine drive pressures in excess of 60 psi. During the period of valve overlap that 60+ psi of drive pressure overcomes the 30+ psi of boost pressure and forces combustion products through the cylinder and into the intake plenum. I believe this is a more likely explanation of how the IAT fouling happens. On a stock turbine housing--wastegated at 20 psi--drive pressure is much lower and combustion products are not forced back through the cylinder and into the intake.



Doesn't this sound a bit more likely than use of an exhaust brake?

 

[Steve Campbell]

John....

I agree/disagree, but it is only my opinion. The heavier fueled a truck is with the stock turbo, the more likely a person is to "foul" the IAT. Reason being is two fold, not enough air for complete combustion and the drive pressure differential under under heavy boost, as you stated. The combination of the two gives the high EGT readings so many are trying to cure.



It would be interesting to see if the people running twins that have reduced their EGT's so much are now having less IAT "fouling" due to complete burning of the fuel.



I still feel that the exhaust brake does lead to "some" of the fouling for a couple of reasons. I watched this topic when first postulated by ME about a year ago. A lot of the people (not all) who did post that they found their IAT "fouled" were exhaust brake users. That in and of itself is circumstantial. The reason I "think" they are a player is that there is still an "Idle" amount of fuel still being injected into the cylinder with no boost to go along with it. I postulate that this results in a "fat" mixture leading to some of the "fouling" a lot of us are experiencing.



With all of that said, maybe they are both culprits!



A poll with a few choices like.....



IAT never gets dirty/stock fuel/stock wastegate

IAT gets dirty with stock fuel/boost fooler

IAT gets dirty with heavy fuel/stock turbo/boost fooler

IAT does not get dirty with heavy fuel/stock turbo/boost fooler

IATgets dirty with heavy fuel/aftermarket turbo(s)

IAT does not get dirty with heavy fuel/aftermarket turbo(s)

IAT gets dirty with exhaust brake

IAT does not get dirty with exhaust brake





This list of questions needs to be refined to actually get the true reason for "fouling".



Hey, maybe it has something to do with elevation (or some such reason), and all of this speculation is for naught!!!

 

[Steve Campbell]

Did some more thinking....

Perhaps the "fueling/timing" boxes change the amount of "fouling" because of when the fuel goes into the process. Do the larger injectors add"fouling" due to more fuel and boost/or/decrease "fouling" due to shorter injection time with larger holes?



Thanks for the topic John. It will keep me busy all day.

 

[JR2]

I have to disagree... from my experience. If you look at the pic of the dirty IAT in the other thread, it is my Dads. It came out of a bone stock truck with a exhaust brake. My truck is far from bone stock and has never foulded the IAT. Its has had too small of a turbo and too much fuel for much of its life and never fouled the IAT.



Just my 02... .