Weird 1jz Vacuum pressure

[Supra-Man18]

When i first put my 1j together it idled at -20in vacuum.. It idled the same after i singled it.. Then i put some BC 264's in there and it idled with a hunt at -15in.. I had the car parked about 2weeks, and the battery was low so i changed the battery and when i started the car up it now idles at 10in.. Air fuels are still good and the car runs and pulls hard. Id just like to know whats going on there ?

 

[te72]

Do you have any leaks anywhere? At that altitude you should be seeing more vacuum than that.

 

[IBoughtASupra]

In NY I had about -21 vacuum. Also, you probably do have a leak. On a full speed density system like the 1J, it really wont show a leak like a AFM based system would, like the 7M. It is how I check for leaks, if my vacuum reading is off, then I know something is wrong. I always smoke test any 7M, 1JZ and 2JZ on the engine hoist after building it to make sure all the gaskets and crush washers are doing their job.

 

[Dylan JZ]

with cams, the motor is going to pull different vacuum.. that being said, you shouldn't be at +10in.

I recommend testing for leaks as well.

 

[IBoughtASupra]

It will pull different a different vacuum but not by that much.

 

[RacerXJ220]

My car has always idled at -6-8 in. vacuum with my large core 272's. I actually lost about 1-2PSI when I swapped out to a 1J block. If it's a hot idle (1500rpm), I might see -13.

Your vacuum sounds normal with 264, 9.3mm lift cams. If you get a leak, you should see a run away idle.

My idle was running up after getting into different timing areas on my map, and I lowered timing degree or two there and the issue went away.

Intake and exhaust are set at 0.

 

[Supra-Man18]

Im going to check for leaks asap then... I know something is wrong because the cams were in almost a year and it has always idled at -15in.. so i assume something must be leaking now...

---------- Post added at 02:04 PM ---------- Previous post was at 02:04 PM ----------

Would an exhaust leak cause any of this ?

 

[te72]

Would an exhaust leak cause any of this ?

Going on my limited concrete understanding of vacuum, I'd say no. Once the air is out of the system, it's out. Where it goes from the exhaust ports shouldn't effect your vacuum...

I believe my typical idle pressure is ~15in/hg at 900-1000rpm. But I'm at 6500' altitude, down south it's closer to ~18-20in/hg. Same cams, different turbos.

 

[mensrea]

If one of your coils is bad, your vacuum press is gonna be low, also it'll idle/sound weird, but still gonna pull, mixture would be rich.

 

[Dylan JZ]

-15Hg is pretty normal for 264s, and as RacerXJ220 said, for 272s the number is going to be even lower.

 

[mkiiichip]

[/COLOR]Would an exhaust leak cause any of this ?

It could, where is your exhaust leak? Pre O2S?
Stock ECU?
What are your VR readings?
Do you have an AF sensor?

 

[Supra-Man18]

Yes stock ecu.. Its right at the turbine housings V-Band.. air fuels are the same as usual.. vr ?

 

[Supra-Man18]

Problem solved.. And a leak it was !!! The Leak was on the little hose that ran behind the motor.. it had a hole the size of my fingernail in it. Now Pulling 16-18IN of vacuum !