Strick

Background: I'm putting a 95 LT1 into an 83 Camaro. the LT1 came from a 95 Chevy Caprice. I'm using the PCM and engine wiring harness from the Caprice. One more thing, I'm installing a 2001 Firebird fuel tank that has the EVAP system on the tank. On the Firebird EVAP system there are two solenoids, a purge and a vent. The Caprice only had a purge solenoid. Looking at a wiring diagram of the PCM from the Caprice, there is only a lead going to the "evap purge solenoid valve" and nothing going to the "evap vent solenoid valve." I would like to utilize the evap system. I'm looking for my options here. Do I need to get a PCM from a 2001 Firebird and would this run my 95 LT1? Or can the 95 PCM be tuned or modified to run the "vent solenoid valve?" If I had a 2001 Firebird FSM, I might be able to figure this out. Any suggestions? Thanks

Injuneer

95 didn't have the same EVAP setup as the 2001. Completely different. By keeping the later EVAP system, you will have monitoring of fuel tank pressure, and at other points in the system, to detect a loose gas cap, or other leaks in the system, plugged purge line, vacuum in purge line when purge solenoid is not supposed to be open, etc. Just adds a bunch of emissions codes that have no real effect on the way the engine runs..

You can't run an LT1 with an LS1 (98-02) PCM, unless you do a 24X conversion from EFIConnection. LT1 has a distributor and one coil, LS1 has a direct fire 8 coil ignition system. Not compatible without the changes incorporated in the 24X conversion:

EFI Connection, LLC - EFI Connection 24x System

FSM downloads.... 2000 appears to be similar to what you are describing:

http://www.firebirdnation.com/forums...2-wiring-diag/

Strick

Thank you for the link.

Very helpful.

GaryDoug

The vent valve solenoid and fuel tank pressure sensor takes the function of the evap purge vacuum switch from earlier years. In the earlier cars, the pcm just checks the vacuum switch to verify adequate vacuum to the canister. The later years take the test process farther by eliminating the vacuum switch, closing off the vent from the canister (vent valve), and measuring the vacuum in the tank over a short period of time (fuel tank pressure sensor). All you should need to do with the newer tank is to leave the vent valve connector unplugged and bypass the tank's purge valve; and it will operate just like the 95 car.

Strick

You have my attention. When you say "leave the vent valve connector unplugged" do you mean the electrical plug and/ or the tubing?

Next is how do I bypass the tank's purge valve?

Injuneer

Still think it would be easier to get a sending unit from a 93-97 LT1 car, along with that year's the pressure control valve (mechanical, not electronic), and the charcoal canister. As long as the sending unit fits into the opening in the later years plastic tank (should, people replace their rusted metal tanks with plastic tanks), you have simplified all the issues. The only electronic component in the system will be the EVAP purge solenoid, and that is controlled by the 95 PCM.

http://shbox.com/1/evap_system.jpg

I suspect it would be easy to incorporate the 2001 canister in the 95 system.

GaryDoug

My mistake; there is no purge valve on the tank. It is on the engine as usual. I was looking at a diagram (in the factory service manual, of all places) that mislabeled the vent valve as a purge valve. As for the vent valve, just leave it alone. You don't have an electrical cable for it anyway.

FYI, the vent valve I am describing is for the canister, not the fuel tank. The mechanical tank vent valve is still used.

How this EVAP self-test works on the 98+ cars: The pcm energizes the normally-open canister vent valve (mounted next to the canister on the tank), which closes it. At the same time, it energizes the purge valve and looks for an increase in vacuum from the tank pressure sensor. If it doesn't reach the expected vacuum level soon, a "large leak" is reported. It then waits a minute or two and rechecks the vacuum. If it has dropped too much, a "small leak" is reported. The vent valve has no other function but to test the system for leaks. But your car won't do all that. It will just operate the EVAP system as usual for a 95.

Fred has a good point about the sending unit compatibility. I think the LS1 pump creates more pressure than the LT1 pump. However, I suppose the regulator on the LT1 engine and the return line would take care of that if the return line was connected to the new tank somehow (?)

Strick

Thanks Gary. This is the route I will try first. I'll just leave the vent portion of the 2001 tank alone. I'll use the 95 PCM to control the purge valve. As far as the fuel lines, I'll run a 3/8 line to the fuel rail and 5/16 return from the fuel rail's FPR back to the tank. The FPR in the 2001 tank will be removed as it will not be used.

Thanks guys for the valuable information. I'll make this part of my thread that I'm currently running on the whole engine swap.

drptop70ss

Can anyone explain the sequence of the 95 EVAP system? Do the fuel vapors go from the tank to the charcoal canister, then stay there until the control valve mechanically opens allowing the vapors to move up to the EVAP solenoid? What parameter does the PCM use to open the EVAP solenoid, does it just do it every once in awhile or is it open whenever the engine is warmed up, etc?
Reason I ask is I am actually using a 24x controlled LT1 and the LS1 PCM is not going to be controlling the EVAP solenoid.

GaryDoug

That is the correct description of the vapor flow. I can't really tell you what the conditions for opening the purge valve are, but here you can download a scan file of one 94 F-car that logged all parameters, including the EVAP purge duty cycle:
http://www.mediafire.com/view/6wlx0p...P7R2xxxxxx.csv

I suggest downloading it instead of viewing it online. The viewer has some bugs.

Injuneer

As pressure builds in the tank, the pressure control valve opens and allows the HC vapor to flow out of the tank and into the charcoal canister. The purge strategy:

-not operated under cold engine conditions
-not operated at idle
-operates after engine is warm
-operates after engine has been running for a specific period of time
-operates only above a programmed road speed
-operates only above a programmed throttle opening

Can't state with certainty, but I would assume that as throttle opening increases, the pulse width duty cycle will be increased. You could verify that by looking at the sample data log.

All this comes out of the factory manual (I referenced the 94 version, but I'm sure it's the same in 95). Download the copy from Gary's link on Firebird Nation. EVAP system description is in Volume 2 of 2, page 6E3-C3-1.

The consequence of not operating the purge valve will be a buildup of vapor in the canister, until it vents our of the air tube, increasing vehicle emissions. You will have a fuel smell at the driver's rear fender, and it will enter the passenger compartment if stopped at a light with the window down.

If you feel it is necessary to maintain the EVAP system as functional, I would suggest you have the programmer delete the purge function, since you will have to have the LS1 PCM programmed for your LT1/24X application anyway. Incorporate a manual switch to open the purge valve, and only use it briefly when you start to notice fuel odor at the rear of the vehicle. The PCM should use the short range fuel corrections to compensate for the flow of air/HC vapor through the purge solenoid.

Strick

There are a number of inputs that go inside the PCM/ECM that are connected to the evap system. TPS, fuel level, VSS, tank pressure, and maybe more that effect the opening and closing of the fuel canister purge valve. From what I have dug up, there is a window where the purge valve will operate and it is dependent on vehicle speed, fuel level in the tank, and TPS. You don't want it open at idle or at WOT. It usually opens when the tank is not full and at the vehicle is at cruising speed. Now correct me if I'm wrong here, but the LS1 PCM also has a EVAP vent valve solenoid (at least in the 2001 PCMs). Do you want the EVAP system to operate? If so, I think you'll also need the vent valve solenoid and the purge valve solenoid to work which your LS1 PCM should be able to handle.

I've been researching this EVAP system for some time now as I'm doing a fuel tank swap out ie, putting a 2001 plastic tank into an 83 Camaro with a 95 LT1 engine and PCM. I'm still trying to figure it out so I can utilize the EVAP. Right now I'm not going to use the vent valve solenoid as my LT1 PCM has no vent valve tab. Good luck. Check out the post just above this one. Injuneer seems to know what he is talking about.

Strick

If I use the 95 PCM to control the purge valve solenoid, do you think I could manually control the vent valve solenoid which my 95 PCM doesn't have provisions for?

Injuneer

The description of the system in the factory manual is very lengthy, and would appear to take a bit of study to determine how the parts all function together. Most of the purpose for the vent valve appears to be to allow certain leak diagnostics to be run. It doesn't seem to be there to allow the system to function/purge. Since you will be using the 95 PCM, which doesn't run the leak diagnostics, I don't see why there would ever be any need to control it. Should just remain open. From the description, without power to the solenoid the vent valve is "normally open". They only close it to stop air flow into the canister, so the vacuum from the purge solenoid can draw a vacuum on the canister, and run the leak diagnostic.

But that's just from a cursory review of the system description ion the factory manual (only have 2000 for reference). Who knows what other purposes it serves. But since your 95 PCM isn't capable of operating it, I can't think of any reason to manually control it.

Strick

Thank you Fred. My first try will leave the vent valve alone. My 95 FSM doesn't have a good description of the EVAP system. Just a diagram showing where the purge valve solenoid is connected to the PCM and where the purge valve is located on the intake manifold. I'll use the solenoid on the tank instead of the one on the manifold. If that doesn't work I'll use the solenoid on the manifold.

Let me correct what I said about my FSM not having a good description of the EVAP system. I had a 3rd book that explained it all. Pretty much what Injuneer said earlier.