454 TBI truck backfires on cold start for about 30 seconds

[rich weyand]

Check the MAP sensor and the connections to it.  Without the O2 sensor on-line, that will determine your mixture.

[Irish_Alley]

i want to get on this post also. soooo, do you have your heat riser pipe still installed?
did you check timing?

[Chevy3+3]

Heat riser pipe is still installed. Everything is bone stock under the hood. I need to fix exhaust leaks first and go from there I guess. I just set the initial timing to around 5 degrees BTDC.

The dizzy cap is an MSD and the plug wires are 8.5mm and appear to be new and high quality. I think the previous owner put them on trying to resolve the same backfiring problem. I just bought this truck and this morning backfiring is the only thing left to fix.

I greatpy appreciate all the help and wealth of knowledge some of you bring and share here. I am a very mechanical guy but sensors and electronics are a little out of my element.

[Irish_Alley]

you "just" set the timing? when? not doubting your skills but you did connect the tan/black wire before setting timing at ot?
i know you siad you replaced the cts but if you have a used one in another truck i would swap them out or just replace yous again. heck i just bought a ckps from a dealer for $100 when i could buy autozones for $40. sometimes they are bad right out of the box
could try to test it also
212°f 177 ohms

194°f 241

176°f 332

158°f 467

140°f 667

122°f 973

113°f 1188

104°f 1459

  95°f 1802

  86°f 2238

  77°f 2796

  68°f 3520

  59°f 4450

  50°f 5670

  41°f 7280

  32°f 9420

  23°f 12300

  14°f 16180

    5°f 21450

[Chevy3+3]

Okay well a little update. I got the passenger side exhaust manifold replaced and the gasket was blown. Both flange gaskets were leaking also. The spark plugs were crap. Someone installed Bosch platinums and that was a bad choice. I replace the plugs with AC Delcos and replaced cap, rotor and wires also. After changing everything listed ablve I still have an exhaust leak. I hoped the drivers side manifold gasket wasn't blown but it apparently is.

Since I have a fuel mixfure issue and run a little rich at all timez I bet the drivers side gasket being blown is allowing aire to be drawn in before the O2 sensor causing a lean reading and therfore causing the TBI to dump excessige fuel.

As for the timing. I got thr truck to operating temp and then unplugged the brown wire with black stripe. After doing so the timing light showed the timing to be set at 0 degrees. A big block is to be set at 4 degrees BTDC. I set it on about 5 degrees BTDC. I then shut the truck off. Unhooked battery cable and plugged bypass wire back together. Then hooked up the battery and proceeded to start the truck. Let me say what a difference it made having the timing set properly. Itruns so much better now. The motor feels more responsive and smoother.

[454Man]

Glad to hear all is going well. After that next gasket you'll be even more happy...

What's under the hood??? If you have to ask maybe we shouldn't race...

[Chevy3+3]

Well I just finished replacing my drivers side exhaust manifold gasket. There wasn't a lot left of it. The truck is runningso much better. Who would have thought exhaust leaks could cause so many issues.

Now I need a cooler morning and see if she backfires on a cold start up.

[454Man]

I believe the term its reversion. Cold air being drawn back into the cylinder causes it. I'm searching for some good header gaskets now. Mine keep telling me to shhh lol

What's under the hood??? If you have to ask maybe we shouldn't race...

[bd]

...Now I need a cooler morning and see if she backfires on a cold start up.

They'll be upon us soon enough....

[Chevy3+3]

I believe the term its reversion. Cold air being drawn back into the cylinder causes it. I'm searching for some good header gaskets now. Mine keep telling me to shhh lol

What's under the hood??? If you have to ask maybe we shouldn't race...

I bought some years ago that were Mr. Gasket. They were around $18 for a set i think. They were black with some blue print on them. I used those with some good header bolts and never had another problem for many miles and several years.

[454Man]

I'm gong to look into those thanks. Glad to hear its running better

What's under the hood??? If you have to ask maybe we shouldn't race...

[Chevy3+3]

Well it was officially cold enough early this morning I got to try a cold start up. I was pretty nervous and hoped I had solved the backfiring issue. I cranked the key over and she fired up and ran smooth and no backfiring. No I can concentrate on other things. My 2.5" lift will be here today but probably won't have time to intall it until next week sometime. I also think I am gonna throw a Flowmaster Super 44 muffler on it. I don't drive it everyday and I am still young enough I don't mind hearing a little noise out the back.

[454Man]

That's what I'm takin bout :-)

What's under the hood??? If you have to ask maybe we shouldn't race...

[bd]

>Chevy3+3
     Rave congratulations on your success!!!

>454Man
     You may want to look into the Felpro 1404 for your exhaust, as well.

[454Man]

Thanks bd.

What's under the hood??? If you have to ask maybe we shouldn't race...