Knock retard with good O2#s

[dynoman]

The other day when racing my son's 09 Cobalt SS from a 15 mph roll my car backfired through the intake, I got out of the gas instantly. results were . 9* of retard O2's above 780 and a Cobalt way in front of me. MAF climbs to 255 and holds, TPS 4.48v wot, FP 42psi line on. This happens before making boost. I also sometimes get knock counts on the direct scan but no ignition retard. Can an exhaust leak fool the detonation sensor ?

 

[SCOOBY DOO]

Post your SM numbers...and let's see what's going on.

 

[berserker6]

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[DailyDrifter]

Can an exhaust leak fool the detonation sensor ?

It will fool the o2 sensor before anything else.

 

[dynoman]

What other number do you need ?

 

[dynoman]

The backfire seems to happen if I mash the gas fast, but not if I roll into it. It starts with a slight hesitation (rpm drop 100-200 rpm's) then accelerates for about 1 second then backfires and I let off.

 

[Tom R]

Subscribed

 

[SCOOBY DOO]

What other number do you need ?

BLM's

 

[SCOOBY DOO]

And is your fuel pressure rising with boost?

 

[Razor]

The other day when racing my son's 09 Cobalt SS from a 15 mph roll my car backfired through the intake, I got out of the gas instantly. results were . 9* of retard O2's above 780 and a Cobalt way in front of me. MAF climbs to 255 and holds, TPS 4.48v wot, FP 42psi line on. This happens before making boost. I also sometimes get knock counts on the direct scan but no ignition retard. Can an exhaust leak fool the detonation sensor ?

FP line ON is suppossed to be 37-38. Line off 43.

Could be a bad spot on the TPS. Could be too rich if line on your at 42

Retard was 9 or .9?

9 I would worry about if it where to be climbing.

Lastly how much boost is the car making?

 

[dynoman]

It was .9* but I got out of it instantly and I have seen it higher, up to 7*.
I'll double check FP and make any adjustments. It will make 22psi at WOT. laptop not hooked up to Direct scan when it backfired so no BLM's.FP rising with boost ? I don't know for sure I don't have a gage to watch when driving but I don't even get into boost when it backfires. TPS looks smooth with no spikes on Direct scan Redisplay in scope mode. Razor, it has your alky system in it but I don't know if it's hooked up right cause it came with extra parts from the kit and no instructions ( from it's last owner). Can I order some from you?

 

[SCOOBY DOO]

I'd be looking for a air/vacuum leak. Make sure the settings for Razors alky kit are on their defaults...just in case the previous owner adjusted them.

 

[Razor]

a weak ignition system will make it backfire, as will plugs with gaps too far open, as will electrical problems. Bring the boost down to 15-16 PSI and see if the problem clears out, if so.. start working back up on boost.

More than likely if it runs good at 15 and not 20.. then its bad coil pack/plugs/wires/etc.

 

[dynoman]

FP will not go lower than 41psi line on ( Bosch regulator), I also checked for vac leaks with carb cleaner , no luck, but the backfire is before I build boost !!! Any one!! thanks Sam

 

[iBoost]

It's ok to lose to your son. :biggrin: Now you've got about a year before I come back with my car. It should be running right by this time next year

just kidding...that car is crazy fast. I really wish we could have figured out what was wrong with it before I left