Dumb question of the day

[toyman]

Are vacuum leaks relevant with a MAP (speed density) setup since we are not dealing with metered air only manifold pressure.

Shortly before putting the car to bed for the winter last fall I removed the intake to deal with an oil leak between the intake and the block. I don't recall any cold start issues at that time. Now, when I first start the car the engine bogs/stumbles with the slightest throttle when cold. Since I haven't changed any of the operating parameters to the EMS, I was thinking a vacuum leak but with the MAP I'm not sure although there is now a whistle coming from somewhere that wasn't there or as loud last year. I was going to pull fuel (reduce fuel enrichment) for the cold engine start period but this doesn't make a lot of sense since it apparently ran fine before. If I just let it idle for a few minutes it's fine although the whistle is still there. I'll test for a vacuum leak but I still think the problem lies elsewhere. I'm thinking maybe the IAC valve.

 

[HISSIN50]

Vac leaks diminish the vacuum signal and this screws with SD badly. If you have a big enough leak, it's kinda like having the throttle kinda open. The EEC sees this vac signal but sees your TPS closed and isnt sure what to make of it. It generally leads to a rich condition at idle. This is why the old SD guys (like my fox) have to really watch cam specs if we cant get a tune.


Did you ever note your old manifold vacuum reading at idle vs the new one? Stock, we're right near 20" hg.
If you have emissions stuff still on the car, those craptastic plastic lines break real easy. Most of mine break right where the rubber boot begins, making it a real PITA to spot the source of the leak/whistle.

Bumpity for ya. Good luck Richard.

 

[toyman]

Vac leaks diminish the vacuum signal and this screws with SD badly. If you have a big enough leak, it's kinda like having the throttle kinda open. The EEC sees this vac signal but sees your TPS closed and isnt sure what to make of it. It generally leads to a rich condition at idle. This is why the old SD guys (like my fox) have to really watch cam specs if we cant get a tune.

I see where you are coming from. Note I do have a 270HR cam and am using an AEM-EMS.

If you have emissions stuff still on the car, those craptastic plastic lines break real easy. Most of mine break right where the rubber boot begins, making it a real PITA to spot the source of the leak/whiDid you ever note your old manifold vacuum reading at idle vs the new one? Stock, we're right near 20" hg. stle.

Bumpity for ya. Good luck Richard.

With the cam I was reading about 14"Hg. Closer to 12" Hg at the momement but moves to 14" Hg when warmed. (something expanding and sealing?)

The emissions stuff is still in. I'll have a smoke test done on Tuesday to see if there is a vacuum leak in some obscure location.

Thanks.

 

[toyman]

As it turns out that was a dumber question than I first thought. I am running a load based system so things that affect the MAP sensor reading are important. The vacuum leak test showed no leaks. I think the whistle/whine is coming from the TB or the S/C. It's just there and I can't nail it down even with the stethoscope.