3800 SWAP / vacuum ??? (Page 1/1) TXGOOD AUG 03, 12:33 PM I`m running a series 3 fuel rail on a 3800 swap in my 88. I`m using a FPR with an inlet / outlet and return. My car doesn`t have the expansion tank and the lines are all messed up anyway so I just leave the cap loose. With my swap I just want to put an aftermarket charcoal canister connected to the vent tube of the pick-up assembly. My question is, will the vacuum port on the LIM be enough for the MAP, the FPR and the charcoal canister? Thanks phonedawgz AUG 05, 07:09 PM No. First off you didn't say SC or NA. I am going to cover both. The FPR and the MAP need to see actual LIM pressure. Neither of these flow air. They are sensors. Putting one of these on a vacuum line with something that flows vacuum (the charcoal canister) means the sensors will no longer be seeing accurate vacuum/pressure. So to conclude this the FPR and the MAP need to be on a nipple that is directly in the LIM and nothing else is connected to them. NEXT - If this is a SC application, there will be times that the pressure in the LIM is greater than atmospheric. Boost right? So yeah, that clearly isn't the right connection to send to the charcoal canister. So the charcoal canister - A vacuum tap near the throttle body will be vacuum always. It's before the SC. So that is where we are going to start with this. BUT the 3800 isn't going to run right with a constant vacuum leak. So the engineers came up with the purge solenoid. The purge solenoid will be controlled by the PCM, and will only purge the charcoal canister when the times are right. And what times are those? When driving down the road at part throttle. Not at idle. So wire up the purge solenoid. Locate it somewhere that it doesn't look ugly. Maybe the far away side of the SC. Maybe on the tranny. Maybe at the charcoal canister. And run a vacuum hose from the throttle body to the solenoid. Then start the engine and at idle make sure the vacuum isn't leaking through the solenoid. These valves are designed with an in and an out and if you install it backwards you can get a constant flow even without the 12v to the solenoid. And then once you have that connect it to the charcoal canister. If you use the Fiero one connect to both ports. One is a control port, the other is the purge port, but both need vacuum for the canister to be in purge mode TXGOOD AUG 05, 08:28 PM Thanks, that`s what I was looking for. But all of that trouble may be for another time. Looks like it`s time to get a vented gas cap.