90 vs 91+ evap emissions system

[zr1don]

I am installing a 1991 plenum, air horn & throttle body on a 1990 engine. There appears to be a difference in the evap emmissions systems on the two models. The 1990 has the cannister purge solenoid next to the cannister & the 91 has it under the plenum & I can't locate the ported vacuum fitting under the throttle body. I think I can remove the 91's vac plumbing from under the plenum & hook up the 90's purge line to the plenum fitting. The question I have is the ported vac line. There appears to be a boss on the bottom of the air horn that coould have been for a ported vac source? Can I drill & thread a vac fitting to provide the ported vac?

[8upZR1]

I have a 90 and my vac line for the can is located on the bottom of the air horn. I would imagine that you could drill and tap this.

[zr1don]

Thanks for the reply 8upZR1, confirming on the 1990 the ported vac source for the canister goes to a vac fitting on the bottom of the airhorn?

Just change the fitting on the plenum.

[zr1don]

Thanks Jeffvette, are you talking about the plenum fitting on the bottom driver's side of the plenum, the one that curves back to the rear on the 91 plenum? The one that the cannister vapors are supposed to be returned to the plenum through?

Is that friction fit & can be pulled out and replaced with a straight fitting?

That's half my problem, the other half is the ported vac line that on the 90's goes to the bottom rear of the airhorn on the 90. The 91 does not have this fitting, but there appears to be a boss where the 90's fitting would have been.

Thanks for the info!!!

The straight pipe for the plenum can be replaced. It's a friction fit or a really a crush fitting.

What happened to the original air horn?

[zr1don]

Thanks again Jeffvette, I bought a complete engine, block manufactured in 1990 & originally installed in a 1991 production car, for installation in a 1990
zr1. My engine harness & computer are 1990. That's the long answer.

Can I drill a hole & install a fitting in the airhorn where the boss is for a ported vac fitting?

Don, sending you a email.