7mgte very low vacuum???

[1987mkiii]

Hey all,

I have recently installed my rebuilt 7mgte and am having to add a lot of fuel to make it idle at 14.7, I have good fuel pressure. What I am noticing is that my vacuum is at -9.6 at idle according to my maft-pro. It should be about -20.

I am thinking vacuum leak but have sprayed brake cleaner all over without getting it to raise idle.

Any thoughts on what to check now?

 

[Dan_Gyoba]

-20 what?

If that's inches Hg, then you should only have that when using the engine to decelerate the car.

 

[1987mkiii]

I assume it is inches HG

I found this link
http://www.cygnusx1.net/supra/TechTips/vacuum_gauge_readings.aspx

This shows that it should be between 17-21 at idle. It gives a lot of possibilities on what it could be. It really seems like a vacuum leak but I got no response from the brake cleaner.

 

[IndigoMKII]

how many miles are on the rebuild? maybe your rings havent fully seated yet.

 

[KTM530]

check to make sure vac line to the map sensor is not leaking.

 

[1987mkiii]

rebuild only has about 150 miles but -9.6 is really low vacuum and I am also running lean at idle if I dont add a lot of fuel on the maft-pro which again supports a vacuum leak but I cant figure out where else to check.

And the map sensor line is short and silicone and directly off the port in the intake (where cruise control used to connect)

 

[supraguy@aol]

I don't think the engine is supposed to idle at stoich, I would expect it to be leaner than that.
How is power output? I'm wondering if there's a possibility that one of your cams might be off a tooth on timing.

 

[NashMan]

rebuild only has about 150 miles but -9.6 is really low vacuum and I am also running lean at idle if I dont add a lot of fuel on the maft-pro which again supports a vacuum leak but I cant figure out where else to check.

And the map sensor line is short and silicone and directly off the port in the intake (where cruise control used to connect)

if you have cams this can lower vacume but not that low in less it has crazy over lap ps for your booster to work proplery you should have at lest 12 befor it's a majore issue

sounds like bent vavles to me

 

[1987mkiii]

Power output seems good to me, but Im taking it easy because of the rebuild. It was an NA car before and I have never driven a stock turbo supra but it feels stronger than it did NA.

 

[1987mkiii]

If it is not supposed to idle at stoich then what is it supposed to idle at? and what is a safe AFR range for idle?

 

[SC61 MK3]

It should be around 14.7 at idle give or take a few tenths. I had an issue with my bov leaking at idle it would idle low and go very lean. It was a greddy type s vented to atmosphere and i put my hand over the discbarge port the idle immediatly jumped up

 

[grimreaper]

whats the scale in the maftpro read out? should be in PSI or KPA, guess what -9.8psi is in inHg..

 

[Dan_Gyoba]

Warm idle should be closed loop, so that should be stoich. Cold idle should be rich.

 

[Another MkIII]

I have been told a lean idle is normal, as there is no risk to running lean at idle as the engine is under no load. Can someone clarify which it is?
-AM3

 

[IndigoMKII]

Not sure what 'normal' is but my car idles around 14.7 to 15 once it has warmed up, during cold start it's closer to 12.5-13

 

[1987mkiii]

whats the scale in the maftpro read out? should be in PSI or KPA, guess what -9.8psi is in inHg..

Wow I feel stupid, thank you for pointing this out. There is not a whole lot worse than sitting here trying to find a problem I dont have. It is in Psi which is just about perfect vacuum.


So now the issue is why am I running lean at idle?

 

[hvyman]

is your iac vented?

On my 1j i have lean idle afr after venting the iac. Not going to hurt anything being at 15-16:1.

 

[1987mkiii]

is your iac vented?

On my 1j i have lean idle afr after venting the iac. Not going to hurt anything being at 15-16:1.

Yes the IAC is just open to Atmosphere

 

[grimreaper]

Wow I feel stupid, thank you for pointing this out. There is not a whole lot worse than sitting here trying to find a problem I dont have. It is in Psi which is just about perfect vacuum.


So now the issue is why am I running lean at idle?

no need to feel dumb, the devil is in the details and beats us all at one time or another.