ImBrandon

I have a 1991 305 Tpi Firebird. When I bought the car the heater core was bypassed. I recently replaced the heater core and have no idea of how to run the heater core hose. I need a picture or a diagram to run the hose correctly. The previous owner said he had the hose and said it was in the trunk of my car but I don't think he got the correct hose. I tried searching the forums for a diagram/picture but all I find are paths to run coolant hoses for carb swapped cars. It's just too damn cold lately to be outside for over an hour to try and figure this out.

paulo57509

I've attached a couple of old diagrams. They're from an '86 assembly manual so the routing may have changed.

Using both diagrams, you might be able to figure it out.

What doesn't show is the heater control valve (usually used with an A/C equipped car) which should be in line with the hose that runs from the throttle body to the heater core.

Edit: I took a quick look at my '87 IROC and the hose routings are quite different from the attached diagrams. Sorry about that.

ImBrandon

Thanks. It's snowing out right now so maybe later this week I'll give it a go.

paulo57509

Maybe this will help.

I can't get back to see the heater core connections but I believe Hose C goes to the left heater core nipple; the pipe that Hose B and E are connected to attach to the other core nipple (with another hose).

antares57

iTrader: (8)

This is out of an '88 Firebird service manual for TPI. Have a '91 Firebird service manual and info is the same. Good luck.

ImBrandon

Thanks again. Antares your diagram is perfect. Hopefully the 2 ft of snow around my car will melt soon so I can hook this up and drive my car in the winter.

ImBrandon

Gonna go and try to hook the heat up while it's 45* outside.

Ed1LE

iTrader: (39)

Hose #2 in this diagram (from heater core to hard line) is available at your local auto parts store. It has correct bends with both ends several inches longer so you can cut to fit. I'm pretty sure it's the same for all years as I replaced it on my '87 Iroc (TPI) and just replaced it on my '91 Firebird (TBI). The original routing on both of these cars was different do to location of heater hose to engine (TPI connects at TB, TBI connects at back of intake manifold). If you are deleting the diverter valve, the above diagram will work and you can just cap off the extra outlet on the hardline.

ImBrandon

So I bypassed the heater control valve because I couldn't remove the old hose for the right heater core nipple(the connector behind the ignition coil because the wire harness was in the way and I couldn't reach in to open the hose clamp. So I ran the hoses to run coolant through the core all the time. It works but I was wondering what the heater control valve does. I only bypassed because I wanted to get it closed off after trying to open the clamp for nearly 3 hours I gave up.
I also knocked off a vacuum line and didn't take the time to figure out where it went because my back began to cramp after three hours hunching over the engine trying to un-clamp the other hose. Is it ok to run the hoses like this just for a little while or no? My SEL light came on so I wasn't sure if it was from the heater control valve being bypassed or the disconnected vacuum line or both. Tomorrow is another day

antares57

iTrader: (8)

The heater control valve allows you to adjust via vacuum the amount of heat you want from the core. If you by-passed it and the core is running all the time, you should have heat, once the engine is warm, all the time. If you knocked off a vacuum line and the SEL is on, you may have knocked off the EGR valve line off. That's the only one I can think of that would give you a light.

Ed1LE

iTrader: (39)

This valve diverts coolant from heater core when AC is turned on-hence it's name "diverter valve"-to help compensate for the lesser efficient AC systems in our cars. My 91 1LE with factory AC delete didn't come with the diverter valve. Also, when I deleted it on my other third gens, I uses the hard lines from factory non-AC cars that didn't have the outlet sticking up that hooks the hose to the valve on AC cars. The flaps inside the heater box are what regulate the heat. True, coolant will run through the core at all times but will be unnoticeable inside the car. All other cars I've owned, as far as I know, were without this valve as well.
As for the CEL, I doubt that vacuum line would cause it but plug it, reset the ECM and see if it comes back on. If it does, start looking elsewhere, starting with EGR as previously mentioned, since that was the area you weren't working in.