99 obs Tahoe - backfire through canister

For about the fifth time in three or four months, my 99 5.7 has backfired out the evap canister while cranking. Today, I went to start it hot, I it cranked for about a half-second then backfired. A ton of smoke came from
under the hood. (Almost as much smoke as in a message from Snoman.) I cranked it again and drove away.
No MIL and otherwise runs great. Where do I start?
skimmer
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Start with the ignition system. The distributor cap on this style ignition is notorious for cross-firing between cylinders when the cap gets some age on it. Use only a genuine Delco cap, no aftermarket cap will last more than 2 months. Make sure the vent screen in the bottom of the distributor bowl is clear. Insulation breaking down on plug wires will also allow cross-firing between cylinders, use quality Belden or Delco wires.
Now, how is the backfire getting to the canister?? Only way would be a leaking vapor purge solenoid AFAIKS.
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wrote:

Thanks Neal. I didn't think to start with the ignition. You're right that the unexpected spark is there somehow. Now on that cap, I put a cap and rotor and cleaned the distributor last winter when I changed the lower intake gaskets. (You might remember the problems I had with the P1345 code after stabbing the distributor.) I did put a new cap. I think I had to settle for a Borg-Warner...but I'll have to double check. I'll also check all the wires, etc.
Now let me tell you one ASSumption. The few times it has done this...especially yesterday. Smoke bellowed from under the front left corner of the hood. I'm ASSuming the smoke is coming out of that canister. The air intake is over on the other side. Could the smoke be coming from somewhere else? and let me tell you, that smoke stinks. First time I thought it was all the wires and the power distribution box that sits on the left front tire. Scared the crap out of me.
Alright, time for NASCAR with the kids.
skimmer
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The fan can move that smoke around, don't depend on where it winds up as the source, AAR is on the money here, BTW I've had a bunch of bad coil wires on those trucks.
wrote:

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Everytime this has happened, the engine did not start so the fan didn't turn much but certainly could influence.
Where do you think the smoke is coming out? Upstream of the filter? out one of the clamps / flex hoses to the TB?
Thanks...and I'll check those wires tomorrow night.
skimmer
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It could be coming from one of the hoses to the canister:
A good backfire can knock one off easily.
RK

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