PCV functionality & my Accel TB
Thread Starter
Le Mans Master
Joined: Nov 2009
Posts: 6,882
Likes: 234
From: Bangkok, Thailand
PCV functionality & my Accel TB
Since installing the Accel TB a few weeks ago I've noticed that I'm pushing oil out of the dipstick tube. I had some time to do some digging today and this is what I found:
I'm wondering if perhaps I could have an issue with a closed/plugged passage in the TB somewhere, or if there's some sort of difference in TB's for early and late cars, etc. There's no part number on the TB I bought, but it does appear to be correct for my year - everything lined up correctly.
- VERY strong suction on the PVC vavle if you pull it out of the valve cover while the engine is running
- no suction at all on the passenger side vent tube - if you pull it out of the valve cover there is no suction at the hole in the valve cover - and this is with the PCV valve back in place
- no suction on the open dipstick tube
I'm wondering if perhaps I could have an issue with a closed/plugged passage in the TB somewhere, or if there's some sort of difference in TB's for early and late cars, etc. There's no part number on the TB I bought, but it does appear to be correct for my year - everything lined up correctly.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The vacuum should connect to the opposite head through the oil drain holes into the valley. I'm sure some vacuum sneaks through the pushrod holes also. The crankcase connects to the valley through the oil drain holes.
I have a vague recollection that I checked this once upon a time and the vacuum wasn't very strong on the side opposite the PCV valve, but it was there. The way I remember it, I could feel it if I left my thumb on the hole for a few seconds and then pulled it away.
I have a vague recollection that I checked this once upon a time and the vacuum wasn't very strong on the side opposite the PCV valve, but it was there. The way I remember it, I could feel it if I left my thumb on the hole for a few seconds and then pulled it away.
Safety Car
Joined: Aug 2009
Posts: 3,752
Likes: 276
From: Melbourne, Victoria, Australia
It sounds like blowby past the rings 
That is really the only way to force oil out the dip stick or seals.
is usually a problem on high mile engines or supercharged/turbo charged engines. My old 170,000 mile 350 i removed a couple of months ago to fit my new 383, had glazed bores and worn rings and had the same problems.
That is really the only way to force oil out the dip stick or seals.
is usually a problem on high mile engines or supercharged/turbo charged engines. My old 170,000 mile 350 i removed a couple of months ago to fit my new 383, had glazed bores and worn rings and had the same problems.
Thread Starter
Le Mans Master
Joined: Nov 2009
Posts: 6,882
Likes: 234
From: Bangkok, Thailand
As a test today I disconnected the upper hose on the passenger side of the TB (the one that goes to the passenger side valve cover). That appears to have stopped the oil from being pushed out of the dipstick with no negative side effects.
I'm going to do some checking between the stock TB and the Accel unit, but I think I'm going to find that the Accel TB has a blocked passage.
I'm going to do some checking between the stock TB and the Accel unit, but I think I'm going to find that the Accel TB has a blocked passage.
