Outline · [ Standard ] · Linear+ F-350 Turbodiesel, need help.

[95IntegraR]

since SRL is offline, i figured i would post this here, which is probably a big mistake, but here goes.

ok, while hauling with my uncles F-350 today, i noticed something strange happening. its a 6 spd manual(L,1,2,3,4,5), and i had just topped a hill and backed off the throttle in 4th, the rpms at about 3k (high strung for a diesel, the redline comes in at like 5k) i coasted down the hill, letting it hold itself back, then started back on the throttle, letting it climb so i could shift. well as it climbed and hit somewhere between 2k and 2.5k, when the rpms jump a few hundred then drop back down. so im like "wtf?". i top the next hill and downshift to 3rd so i dont overheat the brakes and the rpms jump to 4k, and start falling back down. well i start on a straight so i put my foot down while its at about 1.5k. the turbo spools nicely(soundes awesome too, you can hear it above the motor as it reaches full boost) and i shift into 4th at about 4.5k with no problems. i described it to my uncle and he said its done the "spiking" a few times but he described it as the engine cuts for a split second, then runs smooth as silk and never does it again. it seemed to me like a sudden spike in boost pressure. anyone have an idea what might be causing it? he said this is only the second time its done it.

please dont post unless you have some knowledge about the type of truck, turbo diesels, or turbos in general.

[jesus]

yes this spiking does occur when you switch gears because of a sudden raise in boost pressure. when your towing and you switch gears the turbo stalls causing the boost to decrease. when the turbo spulls up once again the boost increases and gives you an instant kick and raise in rpms. this happens more in the manuals than in the automatics. yoiu dont feel this as much when not towing because the engines shifts easier, which should be common knowledge. ive noticed this with my 350 and was wondering the same question. this is the only logical conclusion i can come to.

[97SilverGS-T]

dunno how it works in turbo diesels, but in a DSM (turbo eclipse, talon, laser) when you get that we call it boost creep and it happens alot with the evo 16g turbo and running a 2.5 exhaust...

as to what jesus said, of course you lose boost between shifts, you are letting off the throttle. If in an automatic, you wont feel that because its constant boost. In my buddy's DSM whenever we go up a hill in 2nd, his EGT's sky rocket...we are still trying to figure out why because mine dont....then again, he's running extremely rich and I'm tuned so maybe excessive fuel?

Usually boost creep/spike is due to a leak in the turbo, or a vacuum leak.

[95IntegraR]

yes this spiking does occur when you switch gears because of a sudden raise in boost pressure. when your towing and you switch gears the turbo stalls causing the boost to decrease. when the turbo spulls up once again the boost increases and gives you an instant kick and raise in rpms. this happens more in the manuals than in the automatics. yoiu dont feel this as much when not towing because the engines shifts easier, which should be common knowledge. ive noticed this with my 350 and was wondering the same question. this is the only logical conclusion i can come to.

this isnt when i shift, this is when its climbing back towards full boost. i know the usual shift "boost drop", but when i would shift, the RPMs would climb, the turbo would spool nicely, and it would shift perfect. this mainly happened after i had downshifted and the RPMs jump back up. i was thinking that maybe when i downshifted and it jumped to about 3.5k, that the boost had jumped back up so suddenly that it didnt suck enough air into the intake and just stalled it for a second, because after i dunno, 2 seconds maybe, it would smooth out and run great. it hasnt done it since.

[Brodie]

dunno how it works in turbo diesels, but in a DSM (turbo eclipse, talon, laser) when you get that we call it boost creep and it happens alot with the evo 16g turbo and running a 2.5 exhaust...

as to what jesus said, of course you lose boost between shifts, you are letting off the throttle. If in an automatic, you wont feel that because its constant boost. In my buddy's DSM whenever we go up a hill in 2nd, his EGT's sky rocket...we are still trying to figure out why because mine dont....then again, he's running extremely rich and I'm tuned so maybe excessive  fuel?

Usually boost creep/spike is due to a leak in the turbo, or a vacuum leak.

lol theres has to be a DSM term for every possible problem dealing with a turbo...

[97SilverGS-T]

lmao probably...

boost creep/spike/leak/whine/death whine etc etc

[GranTurismo4]

The turbo forces air into the engine thus creating Hi-end horsepower but when you shift the engine isnt connected to the rear wheels so there is less preesure on the turbo soit has a burst of extra power creating the spike u saw.

[9ten]

#1: Turbos work slower when the engine is moving under less load, ie. when the clutch is down, so no.

#2: CHECK THE F UCKING DATE ON THE THREAD BEFORE YOU POST.