82 FI Vacuum

bran100 · Post by **bran100** » Mon Apr 23, 2007 4:37 pm

I just received my mechanical vacuum gauge from Ebay today. I was looking for a place to T in and the only place I see is the vacuum hose at the very base of the throttle plate that leads to the vacuum advance on the electronic ignition.

I tried to T into that, but the gauge doesn't budge even when revving to about 4k RPM. I disconnected the hose and tried sucking on it and the gauge works fine.

What is that "body" that the vacuum advance hose connects to (at the base of the throttle body)? Is there an EGR valve in there or anything else that can be plugged?

Aside from fixing that issue, is there anywhere else I should be T'ing the gauge into?

pertyfly · Post by **pertyfly** » Mon Apr 23, 2007 6:12 pm

I would 'T' it into one of the vacuum lines that connect directly to the manifold. At the bottom of the manifold right by the driver's side fender there should be a line you can use depending on the size you need.

Chris

bran100 · Post by **bran100** » Mon Apr 23, 2007 10:50 pm

I T'd it into the vacuum line that went to some sort of fuel/vacuum diaphram on the driver's side of the block and the gauge works great. Now I just need to decipher what it means.

On another note, how about having no vacuum on the hose that leads from the base of the throttle plate to the distributor? I took the intake hose off of the throttle body and I see a bit of oil in there. It's not a lot, so I assume it's normal? Is there some type of EGR valve that could be plugged up?

So Cal Mark · Post by **So Cal Mark** » Tue Apr 24, 2007 12:47 am

no egr on FI cars. What you're seeing is oily residue from the crankcase vent. That could plug up the ported vacuum nipple to the dist. It can also build up on the edge of the throttle plate causing a stumble on acceleration or causing the throttle plate to hang open slightly. When you rev the engine can you see the vacuum advance arm on the dist move?

bran100 · Post by **bran100** » Tue Apr 24, 2007 6:16 pm

The vacuum arm doesn't budge a bit when accelerating or otherwise.

Brandon

So Cal Mark · Post by **So Cal Mark** » Tue Apr 24, 2007 6:47 pm

hmmm, time to do some diagnosis

bran100 · Post by **bran100** » Tue Apr 24, 2007 7:01 pm

Shall I assume that I need to remove the throttle body and clean everything? I'll be able to access that block where the vacuum hose attaches that way?

So Cal Mark · Post by **So Cal Mark** » Tue Apr 24, 2007 9:36 pm

if you're not getting vacuum, you could try to blow back through the nipple or remove the throttle body

bran100 · Post by **bran100** » Wed Apr 25, 2007 11:27 pm

Blowing through the hose didn't work, but taking the throttle body apart and cleaning it did. The orifice was a lot smaller than I expected. Easy to clog up. Now that the hose pulls a vacuum, I find that the vacuum lever still doesn't move though. I guess there were multiple problems. I'll order a new one tomorrow.

As an educational lesson, can someone 'school' me on the following.....?

I cleaned the housing and throttle plate with carb cleaner. There was a bit of a buildup on the edges of the plate. I also cleaned out any orifices that I could see. After cleaning, the car now idles at about 1200 RPM when it used to idle at about 900. What exactly happened that increased the idle RPM?

Thanks for the lesson.

So Cal Mark · Post by **So Cal Mark** » Thu Apr 26, 2007 12:52 am

there's an air bypass around the throttle plate, it may have been restricted.

bran100 · Post by **bran100** » Thu Apr 26, 2007 10:33 am

So with air bypassing around the throttle plate, there is more air volume entering the engine that results in a leaner mixture that in turn increases idle?

Forgive my ignorance, I'm just trying to understand the basics of the mechanics of it.

So Cal Mark · Post by **So Cal Mark** » Thu Apr 26, 2007 3:35 pm

it doesn't lean the mixture as much as increase volume. It would be the same as slightly opening the throttle, but with a position sensor on the throttle plate that isn't an option