Re: Throttle body backfires

From: Bob Tom (tigers@bserv.com)
Date: Fri Apr 07 2000 - 10:13:50 EDT


At 04:04 AM 4/7/00 -0400, you wrote:
>Does anyone know what causes a backfire through the TB? I've got the
>4bbl bolted onto my Dak and the sensors sort've hooked up. (Nothing
>permanent, just to get the engine fired up.) Anyway, after checking the
>readouts on the sensors I fired it up. It ran exremely rich for maybe
>20-30 seconds or so, then started to level out. The temp came up a little
>bit and it went into closed loop; the computer seemed to be able to switch
>rich/lean to maintain stoich without any difficulty. I don't have the
>throttle cable hooked up yet, so I just moved the throttle linkage by
>hand. I never let the rpms get really high, but I noticed if I opened it
>slowly, it seemed ok, but if I snapped the throttle open relatively quickly
>like what might happen if you blipped the throttle, I would sometimes hear
>a pop inside the intake, which sounded like a backfire to me. Is it
>possible that the engine needed to warm up some more? (I think the coolant
>temp got up to about 150-160 or so.) Or could it be something else? I
>didn't push it; I had visions of this expensive work of art blowing off my
>engine and taking my hand with it. ;-) Speaking of which, how much power
>can a naturally aspirated intake backfire create? Enough to damage the TB?

I had something similar happen just after installing the 24# injectors
and firing up for the first time. It did not happen again while the
24# were in.

My guess is that an extremely rich mixture was dumped in initially,
resulting in some pudding down in the combustion chamber, ignited in the
high temp. heat when the exhaust valves were closed or almost closed.
Subsequent running probably gave the computer enough time to adjust the
mixture.

Also, initial fire-up with the 24# shot enormous black smoke out of
the exhaust tips (ask Bill about his experience). Mine resulted in
two huge black spots on my daughter-in-laws '94 white Spirit around
her two fog lights (00ps) ... looked like her fogs had started a fire.
A couple of subsequent start-ups let loose less and less black smoke
until there was none at all.

Bob. Southern Ontario, Canada.
'97 Dakota CC Sport, FR, 5.2L, 3.55 SG, auto.



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