I'm back, registered, and have a question about the intake

[Robert D]

So on my '91 TBI 350, the truck has been having issues with cold cold starts (below 40-50 degrees). It seems to miss, stall, and surge when the air outside is cold. I've checked the vacuum lines, t-connects, 2-way valve, etc. I also have replaced in the past year the temp. sensors, PCV, TPS, and plugs/wires/cap/rotor.

Now, I've been searching through the forum and have decided my O2 sensor I've never replaced would not cause the truck to run this poorly, correct? Also, upon inspecting my intake I found the hose running to the headers for the temperature riser to control the flap on the intake is missing. The riser is there and the flap is somewhat open, but the hose and all traces of there once being one are gone. Would missing this hose cause such poor running of the truck in cold weather (voice in my head says yes, but it isn't always right)? Can I pick up this hose at AutoZone/O'Reilly and what do I ask for?

Thanks guys.

 

[HarryH3]

First thing to check is that the engine temp sensor that feeds that info to the ECM is working properly. If it's sending a "warm" temp to the ECM when it's actually cold then the ECM won't go into cold enrichment mode. A decent scanner is what you need to read realtime data and is a great thing to have with an EFI vehicle.

The intake heat hose is available at any parts store for 4 or 5 bucks. The parts folks can help you find the correct one for your rig.

 

[Robert D]

I've actually replaced the engine temp sensor and water temp sensor in the past 12 months; I can't imagine it already failing...I'll test it though.

For the hose, I'll stop by the store this afternoon and pick one up. Would there be any need to replace the riser controlling the flap position?

 

[HarryH3]

I don't think that the thermac (the part that controls the flap) can be purchased seperately. Do check to see that the little spring that returns it to "open" is still there. You can see it through the bottom of the hole where the hose attaches. When the spring breaks, it causes some bizarre driveability problems as the flap swings closed at random times.

 

[Robert D]

Ahhh, yes the spring is still there as I was moving the flap open and it would close up a bit after I let go. I guess I'll just hook up the thermac hose and see what happens . Thanks Harry. \

 

[Robert D]

SOLVED!

The hose is a 1.5inch thermo hose found at autozone/oreilly/pepboys. It cost me about 3 bucks and my cold start issues are gone. The truck warms up quicker than ever and doesn't miss like it did before on cold starts.

Thanks for the input everyone.

 

[Can Can]

Nice to see you got it fixed. Up in my neck of the woods, all of the factory "warm up" equipment is a must- you've just learned why....

For future reference, you can use a hair dryer to test your Thermac valve.