Noob questions

I'm converting a 97 AHU to mechanical (got a 4bt pump all set to go by Westy).

My first question is - What is the thing held down like a distributor behind the injection pump and a bit lower? Looks like some vacuum lines are coming off it.

Thanks!

So I guess this is a vacuum pump? What will I need on this if I go mechanical?

Vacuum pump. It's driven off the intermediate shaft powered by the timing belt. Its keyway drives the oil pump inside the engine.

It will not change when you go mechanical.

Thanks for the response, Abacus!

So another silly question - What do I need a vacuum pump for if all my accessories are electric?

It runs the power brakes typically.
It cannot be removed either way, the oil pump is connected to it. If there's no vacuum pump there's nothing turning the oil pump.

For the brake booster - it works on vacuum, as well as the recirculation flap in the heater box. On later cars, VW ran the turbo control system on vacuum as well.

Thanks for taking the time to respond! This is very helpful. I'm doing an engine conversion so vacuum may not be critical for me.

Is it important to block off all the lines I'm not using to test the new injection pump? I'm going to try and test fire it soon. I know on gassers unconnected vacuum lines cause problems, but this is an entirely different kind of vacuum.

Well, you probably don't want to suck anything foreign into the pump. I can't quite recall (so don't take my word for it) but I think whatever makes it inside may end up in the oil pan.

But no, you're not going to have any high idle/lean condition because of it.

TDI-T said:

Thanks for taking the time to respond! This is very helpful. I'm doing an engine conversion so vacuum may not be critical for me.

Is it important to block off all the lines I'm not using to test the new injection pump? I'm going to try and test fire it soon. I know on gassers unconnected vacuum lines cause problems, but this is an entirely different kind of vacuum.

Click to expand...

Let me reiterate what vanbcguy said just in case you missed it. You cannot remove the vacuum pump because the intermediate shaft uses the vacuum pump to drive your oil pump. If you take it out completely you will have no oil pump.

I really cant envision a vehicle that doesn't need some sort of vacuum but perhaps not. In any event it would just be easier to add a small ccv filter atop the vac pump and leave it where it is rather than try and plug the holes. I suppose if you wanted to you could gut the pump so that it doesn't work anymore, then again I think they're like $400 new so I don't really recommend that.

Steve

Will definitely leave the vacuum pump in and will certainly try to make sure nothing gets sucked in it.

I appreciate all the responses.

I'm replacing my timing belt as I put on the new injection pump. Looks like I have the old style harmonic balancer so I will need to update that soon.

Stupid question number 3 - Is it a bad idea to test the engine/new pump with the harmonic balancer off? I'm guessing this is a resounding "yes", but thought I would check. Would save me from pulling the old one off again when I get a new one on the way.

Are most people doing the replacement "Bora" balancers?

TDI-T said:

Will definitely leave the vacuum pump in and will certainly try to make sure nothing gets sucked in it.

I appreciate all the responses.

I'm replacing my timing belt as I put on the new injection pump. Looks like I have the old style harmonic balancer so I will need to update that soon.

Stupid question number 3 - Is it a bad idea to test the engine/new pump with the harmonic balancer off? I'm guessing this is a resounding "yes", but thought I would check. Would save me from pulling the old one off again when I get a new one on the way.

Are most people doing the replacement "Bora" balancers?

Click to expand...

I've never done one and left it off. Once the new belt is on you can put the lower cover and HB back on. Any changes can be made above so it's not necessary to test it without those components installed.

Steve

I suppose technically you could run it without the HB in place. Given it's only 4 Allen bolts though I'd just put it on personally. Not a lot holding the timing belt in place otherwise...

If you're test running the engine then leave it off, no problem. But I would not want to run it long term that way because it does balance out the rotational irregularities of the crank.

I don't think I'd put a filter on the vacuum pump and let it run.

While that would give you true positive crankcase ventilation which is a good thing; I suspect it wouldn't last long since it was designed to be a vacuum pump not an air pump. Oiling might be insufficient.

KLXD said:

I don't think I'd put a filter on the vacuum pump and let it run.

Click to expand...

Just curious, what do you think I should do with the vacuum source if I don't use it for anything? I need to double-check, but my conversion vehicle may not even have a booster on the brakes.

Cap it off, don't let it suck air. That's what it does under normal circumstances, typically it's pulling on the brake booster which doesn't allow anything through unless you're just taking your foot off of the brake pedal.

Just pop the top cover and remove the vanes. Then it won't build any vacuum. The vanes slide right out.

I'd do either of the above.

You sure the HVAC system in the new car has no vacuum motors?

I took some time to try and get to know the AHU some more this weekend. My conversion vehicle actually DOES use a vacuum brake booster I think. I found a hose coming off from it that I think went to the intake of the gas engine.

So, I guess I will try to match the hoses together using some sort of concoction.

Thanks for all the help. I'm sure more questions will be forthcoming...