Once and for all: ID of throttle vacuum ports

[surfdog4]

(also posted on Rennlist)

OK i have read many many posts on this topic so i am trying to put all this into one post and see if a) i finally have it figured out a b) answer some last questions

This is for an '81 US L-Jetronic car.

Below is a picture of the throttle, the shop manual labels 3 ports

Port 1: (front of throttle) distributor retard

Port 2: (rear of throttle, driver's side) decel valve, pressure damper, fuel pressure regulators

Port 3: (rear of throttle, passenger side) distributor advance, temp switch for carbon canister shut off valve



From studying the throttle, I think the following is true:

Port 1A provides manifold vacuum, with the butterfly passing over it with throttle just beyond idle

Port 1B provides manifold vacuum, with the butterfly passing over it with slightly more throttle than 1A

Port 2 provides manifold vacuum, larger diameter than 1A or 1B and way above the butterfly

Port 3 provides Ported vacuum, open to manifold just after idle.

Now the questions:
- Which Port 1 does the distributor retard attach to?
- What's the difference between the timing of port 1A and 1B?
- What (if anything) connects to the "unused" port 1?
- where does the diverter valve (or blowoff switching valve) connect to? I can't find a diagram anywhere relevant to '81 that indicates where it goes.

After reading up on it, I would tend to think it wants ported vacuum so you are not pumping extra air into the cat at idle. Does this make any sense?

If i get confirmation to these things and answers I'll edit the post so everyone will have the answers in one place.

Thanks!

[MarkRobinson]

Does this help??

[surfdog4]

well the red lines are tracing Port 2, which i think i have in hand, but this doesn't show the diverter valve..thanks for trying

[Danglerb]

AFAIK there are TWO types of distributor, vacuum advance and vacuum retard. I used a mityvac and tested mine to see which way it rotated with vacuum.

Vacuum is above the plate toward the manifold body, below it is at post filter pressure (very very slightly less than local atmospheric pressure). When the throttle plate opens it goes up in front and down in back.

To check the ports on my throttle body I put a drop of oil in each hose fitting and observed its exit point. The rest I would need to check my old thread for, but it is SO easy to get confused.

[surfdog4]

Thanks! From my investigation and the information from the manual the retard line goes to port 1a, looks like 1b is capped.

I'm going to put the diverter valve for the air pump on port 3 (ported vacuum) so on decel the air pump is dumped to the air filter box...from what i've gathered if the air pump keeps feeding the cat on decel you might get "popping".

This was either a boring post or nobody really knows the answers for sure because I got <0> responses on rennlist and only the couple here...

[surfdog4]

Scratch that previous post..just found some help from the '81 Service Information Manual..looks like port 1B is for the diverter valve since it's opening is just about 5mm above where the butterfly rests.

[Danglerb]

Wow, thats messed up always a parasitic load, increasing with rpm no doubt, and only used at idle.

Good info though.

[surfdog4]

well all for naught anyway..decided to test it and found out the diverter valve diaphragm is kaputt...so it failed in the "always blowing into the air cleaner" mode, so i just capped the vacuum line and let it be. Any idea how to get that think out of there? the bolt seems to to be underneath

Then got the rest of the intake together, only to find now i have the "oscillating idle" problem..it slowly drifts up in rpm, then dramatically cuts back, then slowly idles up again, over and over. I'm guessing it's the decel valve but i checked it before i put it back on. (and of course it's at the bottom of that whole pile of &^%&* you have to remove to get it out

[Danglerb]

Good news is that if you put on 8 fresh intake rubbers the body should come off fairly quick. I need to pull the body on my 85 Euro and recheck all the vacuum lines on it. I think I am going to use my Bosch PS40 and power all the clamps loose and later to tighten them, and save my screwdriver arm.

[surfdog4]

you're kidding, right? I did buy all new rubbers but they were a major pain in the %&^ to get on. Of course I realized i should have greased the tube after i had pushed them all the way on..still it was a pain...

I think i'm going to bring the hoses from the decel valve up to the top of the engine so i can experiment with capping them, or putting on a new one without haveing to disassemble the engine again. I saw a picture of a BMW or Alfa with L-jet in an L-Jet troubleshooters guide and the factory had mounted the same decel valve at the top..so you could get at it (imagine that!)

[Danglerb]

Silicone spray is your friend. Use plenty and the hoses slide easily onto the intake tubes. Use a fine hose pick to break the seal if you need to, and then spray some more.

*** Note I have 3 kinds that I use; Silicone spray a temporary lube that pretty much complete evaporates or whatever within a day or so, Silicone lubricant which is supposed to last, and WD40 which is slippery like first two when wet, but turns to something like super glue for hoses when it drys.

[Landseer]

Am in need of labeling of throttle body connections for an 84.

Distrib has what appears to be a vac advance only, one connection, not two.

[Danglerb]

Not saying I understand this, but I think there are two "kinds" of distributor.

I wouldn't bother labeling the ports. Easier to test them and once you know what goes where leave it that way.

[surfdog4]

well i pulled the vacuum line from the decel valve and capped it off...just left the valve in place for now..definitely fixed the "hunting" idle problem

LIke some others, i hooked up the mighty vac to the valve and when i pumped it up the hunting started back up..

now i have a fairly steady idle ~800..

..and of course i discovered i have a coolant leak somewhere in the front...cooling poolin on top of the air pump cover..

two steps forward, one step back

[Danglerb]

Fixing what breaks isn't practical on these cars. While your in there you need to replace everything that wears. Working through an area at a time is my plan.