How do I use a vacuum pump to diagnose rough idle?
 

So, I rented this thing and have no clue ho to use it. Anyone have a link to a test procedure to follow. I want to rule out vacuum completely. My ccv fittings are cracked and shot, but, I don't think they'd cause a rough idle. Want to check everything else.

Any ideas?

You use a gauge, not a pump, although that pump seems to have a gauge on it

A pump is used to test if a specific line has a leak somewhere

Here's a couple vacuum gage diagnostics charts you can use.


I do vacuum checks using my Harbor Freight vacuum brake bleeder.


Pic an empty vacuum nipple on you intake manifold - 1/4" nipple if you can find one. Hook up that vacuum pump, start the engine, watch the gauge while it's warming up, then go through a few of the drills listed on these charts.


Generally a 4.0 should have around 17 in/hg at hot idle.


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On my (pre91) the line that provides vacuum to the cruse and heat/AC is a large one rear of the TB. That goes to the vacuum Rez, (ball) behind the left front bumper. Your's has one also, but I don't know where. It's the line that goes back, across, then forward inside the left fender. If mine worked I'd use it to see that that line holds vacuum. The balls break, the lines can leak...I suppose checking that one line wouldn't tell you if check valves were bad.

The rearward line to the CCV valve, indeed could leak and cause idle trouble, since it too needs to hold intake manifold vacuum.

Like said, just using the gauge can tell you things also.

Thanks everyone for the input. I found a gauge on Amazon I'll order. OTC tools sells some decent stuff and it comes with a case. I'll check it out and go to work if I don't resolve this rough idle this weekend.

This board seriously needs a "Thanks" button. Just this past Sunday I picked up the plastic Mityvac set that Harbor Freight sells now and was pondering this very issue. That's exactly the info I needed.

So thank you for that informative post!

Gotcha' there Shakey...but that opens up another box. I actually prefer leaving that out....direct communication with direct answers, without someone piping in with the hope of a ""thanks" for whatever. We learn to respect people like Cruser54 or Ken, other searchers will see that. Don't mean to omit .....Actually Blue, any help on that long crank would be welcome. Not to discredit the idea Shakey, but here nub's pop up with stuff that skunks others posting, (like me) , with oceans of info. Both works I suppose!

:bow::bow::bow::bow::bow::bow::bow::balloon: