what causes backfire through inlet manifold?

richard165

Hi all

Just searched this topic and cant find any answers.

what are the possible causes of backfire through inlet on startup?

i don't have any air leaks, its done it for ages and im at a loss as to why. the timing chain is lined up correctly using the setting tool so i doubt ures a timing issue.

on a side note, i have white smoke kicking out when it red lines, is this normal? ive just had valves rebuilt so i can rule that out.

vocky

I did see this happen once, but cannot remember what it was.

white smoke is usually coolant.

richard165

thanks for your help as always mate.

it only does it at top of red line and hasn't lost any coolant that i can measure, so based on this is it a cause for worry?

richard165

has anyone experienced backfire through inlet and found a fix? it doesn't happen often but still hoping for a reason why it happens

thanks guys

dewismotorsport

is it a bit of a lazy starter? could just be the excess fuel igniting going back through the inlet. Normally though its from ignition timing being out or cam timing

KevinH

richard165 said:
what are the possible causes of backfire through inlet on startup?

Have you got a genuine GM coil pack installed? They have the proper CSI sensor made by Delphi whereas aftermarket coil packs don't have the correct sensor and can cause all sorts of running problems.

Berto

It could be due to a leaky fuel injector filling the intake manifold with gasoline vapours after engine has been shut down for a while. On next start up the flammable vapours can "see" a spark thru the open intake valves of any cylinder sparking on exhaust overlap, and BANG.

Shit can happen with DIS ignition systems, like in Z22SE. Notice our intake manifold comes OEM with a blow off valve to relief intake backfires:

Does the intake backfire just by turning the key to the contact position, or only after you turn the key a bit more and cranking up begins?

richard165

hi there

thanks for the replies!

it does have a genuine coil pack installed. and it only does it after a night's rest on first start, after that its fine.

might explain a few other electrical gremlins I was going to ask about. EML cones on every so often for either injector 4 or MAP sensor failure. I can reset it and it won't happen for another 150 miles or so. car runs sweet through it all.

thanks again!