the engine would die out from idle, I finally found I had a vacuum leak, I think? I'm unsure what's been done to the vacuum lines coming from the two ports on the side of the middle plenum and the Fuel Pressure Regulator (FPR). The vacuum line from the FPR (Green) seems to come down and merge with the vacuum line from port (B). The weird vacuum line coming off port (A) comes underneath the plenum towards the break reservoir but was connected to nothing, which I'm assuming is my main leak. But after looking at some videos of people replacing the FPR (which is what I'm planning to do) it seems that there should be a short vacuum line that goes from port B to the FPR. What kind of mickey mouse BS is wrong with these vacuum lines, Is this how it is designed or did the previous owner butcher this job? How should I fix this to get my car running strong again?

P.S. pictures are included and color coated for your convenience.

Vacuum line B


clear picture

part of it seems to come together and then split apart again, I'm not sure if the tubes are actually connected together and then separate again or if that connection is just holding the two lines together.

I read that this goes out to the HVAC, where and what is the HVAC?

The two ports

 

On my '88 there is a very short line from your "A" port to the FPR.

"HVAC" means the vac line goes through the firewall to operate the heater/AC controls.

There should be no vac line just "open" Try plugging an "open" line to see if idle smooths and manifold vac comes up into the correct range on your gauge.

 

the line u say goes towards your break fluid reservoir, should hit a 3way splitter situated near the driverside of the distributor base with a one way valve built in.the two outgoing ports...1 to the cruise control above the battery and the second towards the firewall, near the oil pressure sensor, into the thick bundle of wires that behind thedizzy, between the firewall and the rear of the distributor, towards the ac evaporator box, and into the cab of the car.

inside that bundle there is a vac line.

it is very common (2 out 5 of my tpi cars) to have this vac line broken off by the distributor base. one car i had to find tge broken end of it inside the bundle, near where it emerges from thevwire harness bundle at the oil pressure switch.

reconnect/splice into the hard lines with rubber vacuum line from your local parts store. its an easy and almost free repair.

this was how my 86 was:




edit / ps, hvac will only blow on defrost if you do not restore the vacuum supply into the cab.

 

further note, a vac leak the size of 1 vac line will not cause the engine to stall out. it would probably have a high idle. by 86, the ecm is pretty good at adjusting idle. My guess is that you have multiple leaks and that your minimum idle setup is all messed up from well intentioned tinkering. i see you have your plenum out. get it all done while u are in there.

when done, thoroughly go through the minimum idle adjustment procedure and do it properly do not skip steps. google c4 corvette minimum idle adjustment.

 

[QUOTE=VikingTrad3r;1605858219]the line u say goes towards your break fluid reservoir, should hit a 3way splitter situated near the driverside of the distributor base with a one way valve built in.the two outgoing ports...1 to the cruise control above the battery and the second towards the firewall, near the oil pressure sensor, into the thick bundle of wires that behind thedizzy, between the firewall and the rear of the distributor, towards the ac evaporator box, and into the cab of the car.

inside that bundle there is a vac line.

it is very common (2 out 5 of my tpi cars) to have this vac line broken off by the distributor base. one car i had to find tge broken end of it inside the bundle, near where it emerges from thevwire harness bundle at the oil pressure switch.

[QUOTE]

Yup, your right I finally found that vacuum that ran underneath the distributor and it was broken, It also looks like that other vacuum line was broken as well, it seems that little three way valve wasn't connected at all and in fact had a broken tip at one end. Is this a sufficient enough leak to cause my engine to stall? or should i fix this leak and still go through that idle procedure to make sure?

I fixed up my other broken line with some vacuum tubing that had an inner diameter that same as the solid plastic lines outer diameter and gave me a tight fit and some heat shrink tubing to seal it up and seems to work just fine. Am I going to have to remove the distributor cap in order to find the vacuum line underneath?

 

well here was my revelation from an 86 i refurbed.

 

Ohhhhh, i see now. Thats where it broke off from. I cant quite see deep enough inside to find where it broke off and was thinking if I remove my distributor cap it would give me enough room to find where it broke off an repair it, but i'm worried about messing up my ignition timing. is this a good idea or should i try to find it using a different method?

Also for that minimum idle adjustment you mentioned I believe that may contribute heavily to my problem seeing as how i replaced both the TPS and IAC valve without doing that and may be the reason for the engine stalling and the idle being all over the place. for the steps, were you taking about something like this? :

https://www.digitalcorvettes.com/thr...your-c4.58873/

 

the digitalcorvettes guide is fine but go for 550-500 min idle not the 450.

yes remove the dizzy cap. look up the firing order for the tpi, find #1 sparkplug wire by following the plug wire down to #1 cylinder. Then proceed clockwise around the dizzy cap. i write the cyl number on the wire and the cap and then its really easy to reinstall.

if you take the vac line and follow it back to the wire harness loom, you will find the stub of the broken vac line right there, by spreading the loom. it may crack.

 

alright, so shoot for 500-500 rpm idle and use a chart like this too mark my spark plugs, let me go do all this and I will report back.
When I'm putting the cap back on do I also want to mark the little stubs on the cap as to which cylinder they connect to or does it not matter as long as I marked the plugs in their correct order and place them in the correct clockwise order?

 

mark the wires, and the cap, in a way that u can put it back exactly as it was. take pictures.

you will not be removing the distributor base, not loosening the base lock nut/clamp.

You will be fine.

 

Note: The vacuum layout and connections for your specific car is shown on a sticker attached to the driver side of the radiator cover (at least on L98 years). Some options change this and that.

 

OP, do you have the C60 manual A/C controls ?? Viking if someone needed to just bypass this old hose and run new where would this connect in the cabin ?? The pic is of what I believe to be my C60 A/C plumbing.
.

 

Im not sure, how would I find out if I do?.

 

Makeout, if you have no digital display and buttons to PUSH then u have the manual as shown with the ***** and sliders. Here is a pic of the digital “c68l hvac head unit. The manual “c60” is pictured above. You can also look on your rpo sticker (under the center console armrest...look for rpo codes c68 or c60. rpo sticker can also be under the storage compartment lid behind the driver seat depend on year of Early cars.

I would *not* bypass. because it will be in that bundle u simply need ti remove the dizzy cap and carefully remove the tape and spread the plastic conduit. its there.

that plastic conduit runs towards the ac evaporator box and then turns in through the firewall. Once inside, it heads either to the c68’s vacuum solenoid controlled manifold, or, if c60, it appears from the picture above that the vacuum manifold is built into the c60 manual controller itself. So, on the c60, look for the line that comes through the firewall to the c60. This is vacuum supply. Technically you could run a new line. I wouldnt. ive never seen a set of vacuum lines damaged inside the can. even if they were, id use rubber bac line to sice back together.

if you have the c68, the vacuum supply runs to a stand alone solenoid controlled vacuum manifold. The solenoids in the little box are instructed by the digital c68 buttons you press with you fingers.

I can take some good pics because i have an 89 apart in my shop.

again, no, i wouldnt bypass or run a seperate line. id simply find the broken piece, i think my old video demonstrates it? use rubber vac hose to join the broken pieces of macaroni hard vac line.

 

like this.

 

Looks like i've got the c68 ac unit with that digital display. I simply removed the dizzy cap go into that bundle and found the broken line, then with some rubber hvac tubing from autozone that had a tight fit, stuck the two pieces together and sealed either end with heat shrink tubing. added a new rotor inside the dizzy cap. Put everything back together and now not only does my car start right up but it idles at 500 rpm, and the ac blows ice cold. I finally believe that i've solved all of my issues and managed to kill three birds with one stone. And thank all of you who responded from the bottom of my heart.

 

You are very welcome! Nice to hear you have had success.

 

If you haven't solved the problem, Your removed Vacuum line connects from port A to a Vacuum Check Valve. Part number 14056648. That hose routes from the plenum and crosses in front of the distributor and ends were the check valve is located on the drivers side right next to the distributor. When looking at the car from outside the drivers side, it is the left side of the check valve. The center of the check valve goes to the vacuum storage ball that is located in the front drivers side right behind the bumber. The right side of the check valve goes down below the Spark Plug wires and controls the HVAC system. If your AC and Heater doors don't work properly, this could be the reason. This will also affect the cruise control.