3400 Vacuum Connection

[geoffinbc]

Ok doing the 3400 swap in place of a 1990 3.1L in a J-Body.

Now the vacuum hose for the charcol canister on the old 3.1L was connected to a ported vacuum source on the throttle body. But on the new engone there is no ported source. Is it ok to connect the canister to manifold vacuum?

[korbendallas68]

I would assume yes. Just use the spare one on the rear left of the manifold.

[bszopi]

IIRC, the 3x00's tap off of the MAP vacuum line for the purge tank. Or you can just use the spare one...

[korbendallas68]

I think you're right. It comes off of the EVAP solenoid, then into the canister.

[Guest]

I noticed the same the other night. I have mine connected to the "spare" vacuum port in my truck, seems to be fine, although I have not had my truck e-tested yet, working on getting the EGR working now, I left my intake with a great welder I know, who has a TIG, I no longer have a spool gun for doing this.
Anyway, I felt with the purge solinoid directly on the canister it will only purge when the ECM tells it to, though it may actually be a cutoff, so I may have to add a second ported vaccum source the modified TB that I have. we'll see.

[geoffinbc]

Yea Raven I think you are right. On the new motors the solonoid valve actually regulates the release of the vapours so it does not need a ported signal. But on the old systems I think it is just an On-Off solonoid.

But so long as it does not trip any lights or affect drivability it will be ok. I would not loose any sleep if the fumes vented to atmosphere while going through air care. Then only check exhaust and never pop the hood.

[Guest]

Well I did some checking into this tonight, since after thinking about it some more from this thread, it may be the cause of a few issues on my truck, it appears I was correct.

Here's what was happening:
After warm cruise, coming to a stop, at anything between 20 KPh, and almost stopped with the clutch pressed, the idle would wander, as low as 500 RPM, and in a lot of cases stall, I'd have to feather the throttle to keep it from doing this, and sometimes as soon as I came to a complete stop, the idle would stabilize at 875 RPM, with may a 10 RPM wander either way. Even just rolling forward, you know less than .2 KPh, the idle would then again surge. It would also be reading quite rich on my A/F gauge and stay that way for longer than I felt comfortable with.

So, I thought maybe the solinoid was not to control when the EVAP canister would purge at both ends of the RPM, maybe only the top end, or somewhere above idle.

So I decided to temporaoly disconnect and plug that fitting.

I then checked with another EVAP canister I had, and I could blow into it, with no power being applied to the solenoid.

What's that mean? Vacuum leak! even though it is quite small and restricted, could cause the idle to wander.

So far (just the drive home from the shop), I have seen an improvment in drivability, there is still a low speed wander, but no where near as bad as it was, I'll also be able to tell how this effects cold start idle vaccum, since it was always a little low, but after warm up, would start to rise. I noticed with warm start idle vacuum to be a stronger and more stable signal. Only time will tell.

Looks like I'll have to drill another hole in my TB for the EVAP canister.

[Cliff8928]

Re: 3400 Vacuum Connection

Ok doing the 3400 swap in place of a 1990 3.1L in a J-Body.

Now the vacuum hose for the charcol canister on the old 3.1L was connected to a ported vacuum source on the throttle body. But on the new engone there is no ported source. Is it ok to connect the canister to manifold vacuum?

If you get the vacuum hose from the canister to the purge valve for a 94-96 L/N body (it goes from the purge canister around the strut tower to the back of the engine)... you can connect it to the same place as the stock 3400's purge solenoid would hook up to, which would be located just below the ignition module (over the rear valve cover) on the pre-2000 models, or right next to the plenum on the 00+ models.. Although on the newer ones, it would be better to get the other vacuum line that leads to by the valve cover where it was on the older models...

Cliff Scott
89 BerettaGT
89 Volvo740

[geoffinbc]

Well I did some checking into this tonight, since after thinking about it some more from this thread, it may be the cause of a few issues on my truck, it appears I was correct.

Here's what was happening:
After warm cruise, coming to a stop, at anything between 20 KPh, and almost stopped with the clutch pressed, the idle would wander, as low as 500 RPM, and in a lot of cases stall, I'd have to feather the throttle to keep it from doing this, and sometimes as soon as I came to a complete stop, the idle would stabilize at 875 RPM, with may a 10 RPM wander either way. Even just rolling forward, you know less than .2 KPh, the idle would then again surge. It would also be reading quite rich on my A/F gauge and stay that way for longer than I felt comfortable with.

So, I thought maybe the solinoid was not to control when the EVAP canister would purge at both ends of the RPM, maybe only the top end, or somewhere above idle.

So I decided to temporaoly disconnect and plug that fitting.

I then checked with another EVAP canister I had, and I could blow into it, with no power being applied to the solenoid.

What's that mean? Vacuum leak! even though it is quite small and restricted, could cause the idle to wander.

So far (just the drive home from the shop), I have seen an improvment in drivability, there is still a low speed wander, but no where near as bad as it was, I'll also be able to tell how this effects cold start idle vaccum, since it was always a little low, but after warm up, would start to rise. I noticed with warm start idle vacuum to be a stronger and more stable signal. Only time will tell.

Looks like I'll have to drill another hole in my TB for the EVAP canister.

Shit I knew it. Hmm well how precise does this hole have to be? I noticed on the 3.1L TB I took apart the ported signal is VERY exact. It is exposed to vacuum as soon as the TB is cracked open.

[Guest]

I drilled a hole in my 3400 TB to run a vacuum EGR valve, I haven't installed it yet, just getting things ready, it did take me a few minutes but I was able to measure where it needed to be, you know the spot, just in front of the throttle plate when closed, but just behind when the throttle is just opened, now I need to add another larger one, damn you betterthanyou, damn you. hehe, J/K.
So I would say it needs to be pretty exact, to function absolutly right.

[geoffinbc]

Ok sounds good. For now we are going to leave the purge canister out. We went to crank the engine over last night but the battery has taken a turn for the worst. I guess not being on the charger and the cold wether took its toll.

Ohwell cost overruns.