Vacuum leak, can't figure out where

[carrollcw]

So, did my first engine run today. I have 2 manifold pressure sensors, one for the g3x and one for the EFII. Both would indicate ambient pressure before and after engine start. So, I disconnected the 2 vacuum lines from the throttle body, applied vacuum to each side of the system, and the sensors indicated normally (would drop manifold pressure when vacuum applied). They also did not leak when tested with a vacuum pump.

Thus it would appear I have a massive vacuum leak somewhere in the throttle body/engine. Any ideas before I take off the throttle body of additional trouble shooting tests? By the way, with the EFII, I could get the engine to run smoothly, but only when I went maximum lean. I am guessing this is because the EFII is thinking there is high manifold pressure (ambient air).

Thanks

[Mike S]

Originally Posted by carrollcw

I disconnected the 2 vacuum lines from the throttle body,

You could try taking manifold vacuum off the head------look for a 1/8" pipe plug below the valve cover, intake side.

One port can be "T"ed off to supply both sensors. It is best to use a restrictor fitting.

[hydroguy2]

you sure it's hooked to a proper port? or that the port isn't blocked with a gasket or something.

disconnect them at the throttle body again, start the engine and spray a spurt of carb cleaner on that connection.

[carrollcw]

Definitely hooked to the right port. The EFII has an adapter plate above the throttle body that connects it to the bottom of the sump. On the adapter plate are 2 vacuum ports. I have one going to the garmin map sensor and fuel pressure regulator, the other to the EFII map sensors. I've disconnected each of them fro the adapter and checked that they hold vacuum, which they do. I also have verified that when I apply vacuum to the lines going to the two pressure sensors they read a manifold pressure drop.

Additionally, I have taken out the fittings from the throttle body plate and made sure the orifices were not blocked, which they weren't. So, it must be a leak either in the throttle body or in the engine.

Guess I have to try the carb spray method.

[tim2542]

Sure sounds like your pressure tap is upstream of the throttle plate, or the tap has another port that's not sealed or connected. A leak bad enough to put ambient pressure inside the manifold would be huge, like a an entire part missing, not just a gasket. And it probably would not run at all.
Tim

[DanH]

Originally Posted by carrollcw

Thus it would appear I have a massive vacuum leak somewhere in the throttle body/engine. Any ideas before I take off the throttle body of additional trouble shooting tests? By the way, with the EFII, I could get the engine to run smoothly, but only when I went maximum lean. I am guessing this is because the EFII is thinking there is high manifold pressure (ambient air).
Thanks

Ok, if you actually do have ambient atmospheric pressure in the manifold when running, you could not throttle the engine. Since I assume you could throttle it (it didn't light off and immediately run at max RPM), it probably doesn't have a massive vacuum leak.

You didn't mention the pressure regulator vacuum connection. The two taps on the adapter plate are typically connected to the MAP sensor and the pressure regulator, not MAP and G3X. You have a tee fitting in there somewhere? Open vacuum port on the PR would drive fuel rail pressure quite high (mixture rich) if the manifold was actually under vacuum. It maintains rail pressure 35 psi above what it sees as MAP.

[vic syracuse]

Dan is correct. You do not have an engine issue, so don't start tearing anything apart. You either have the sensor installed in the wrong port or the sensor is not working.

Vic

[carrollcw]

Here is how it is run from the adapter plate:

Port 1 - through firewall - to tee fitting - to the two EFII map sensors
Port 2 - to pressure transducer for garmin - to fuel pressure regulator

If I disconnect a port and apply a vacuum tester directly to either vacuum line, the sensor operates normally and the line holds pressure.

The engine runs and responds to throttle movements, but I have to have the EFII mixture control knob full lean.

[DanH]

Originally Posted by carrollcw

Here is how it is run from the adapter plate:

Port 1 - through firewall - to tee fitting - to the two EFII map sensors
Port 2 - to pressure transducer for garmin - to fuel pressure regulator

If I disconnect a port and apply a vacuum tester directly to either vacuum line, the sensor operates normally and the line holds pressure.

The engine runs and responds to throttle movements, but I have to have the EFII mixture control knob full lean.

No vacuum leaks in the sensor lines, and the PR is connected.

The engine responds to throttle, so the manifold is not actually open to atmosphere.

That suggests an issue with the adapter plate, i.e. no signal. You ran on the dyno at Titan, so you had a vacuum signal then. Not much you could have changed, except perhaps to rotate it in relation to the throttle plate?

[carrollcw]

Had to swap out the sump, so the adapter plate was taken off the old sump and put on the new one. I have the fittings pointed to the right side, usually they point aft. But the instructions say you can orient it any direction. Probably gonna have to take it off today. Don't see any way to avoid it.