Popping/backfiring

[ajay]

car: AE93 sx corolla with cannon thing

 

problem: pops/backfires when throttle is let off and re-applied around 2500-3000rpm, burbles on decel from about 3500rpm

 

notes: when car was dynoed, AFR graph showed mix to be rather rich.

: have had the O2 sensor off and cleaned

: run 95 premium most of the time (98 sometimes, never 91/92)

: only happens when car is at/nearly at operating temp, and is worse when hotter

: happens almost every upchange

 

questions: what is the problem

: how do i fix it?

[love ke70]

the mix is too rich

too much fuel in exhaust = backfire

what motor is this?

just tune it properly

[ajay]

its a smallport 4age, the timing has been set at standard (10deg?) 3 times recently (cos the dizzy had an oil leak and was fixed on 2 occasions) and the car was only tuned about 2 months ago.

can the mixture be fixed simply or not? (no afm)

plugs and leads changed a few months back

Edited November 16, 2006 by ajay

[ajay]

how do i check the map sensor?

i've got a vacuum gauge and it always reads more than 22" (generally closer to 24/25"), which i think indicates that there's not enough air getting in but even if i take off the intake hose its still the same

[ajay]

this is my power and AFR graph from the dyno

[love ke70]

so its actually a map sensor, or you just removed the afm?

that does look rather rich...about the expected power, maybe a bit low if its in fwd trim...

whats your fuel economy like?

[ajay]

nah its map standard for smallports.

you can see the feint red lines on the graph too, they're the graph of the other smallport ae92 there on the day. he made less power but his mix is not as rich.

econ isn't *too* bad, i tend to drive pretty hard so its never gonna be great, around 10/100 in the city and about 7-8 on the open road

[love ke70]

in that case its just the bigger exhaust letting you hear the combustion completing in the exhaust.

 

try doing an ignition service as the popping would be caused my a miss in the idle circuit. i doubt it would be due to being too lean in the idle circuit but is possible...

Edited November 17, 2006 by love ke70

[ajay]

i know the exhaust makes it easier to hear but its only the muffler thats been changed, i can't hear any miss on idle, and it pops far too often and loudly to be normal. i'll try to get a sound clip of it over the weekend

[TheNOBBLER[RL]]

My ae82 twincam does the same thing... actually, its running rich enought to throw flames out the tail pipe when you back off from 6000 plus rpm! I have done the same thing as you ajay, replaced or checked everything I can think of and its still there.

 

Hope you get it sorted, maybe it will help my cause too as I'm out of ideas!

 

Jarrad

 

Actually, I just remembered. One suggestion my mechanic had was to get my injectors serviced to check they are working properly, they could be leaking to much when you back off causing the backfire. I'm not sure about this but it might be worth considering.

Edited November 23, 2006 by TheNOBBLER

[SoulSearcher]

hmm my old engine used to do that...I figured with the new engine it wouldn't but lo and behold it still does it.

 

So with a WHOLE new engine and turbo set-up, plus with it being tuned super regularly and well maintained, could mine be the MAP sensor???

 

Lesley

[mix13rolla]

Hi all i have the same problem with my ae82 (Carbie), all standard parts. Was told by my mech that its a valve seat prob what do yall think ? :jamie:

I'm getting it checked tomoro will let you know how it goes

[ajay]

lesley, it sounds like its something on you r car that wasn't changed when they replaced the engine, like maybe the map sensor or the ecu, intake sensors, that kind of stuff.

i would have thought the same prob on a carby would just be a tuning issue, but it would be good to hear what they say.

[mix13rolla]

Ajay i don't know if this is relevent but if you beast has a carburetor mine was just fixed, it was a combination of the base plate between the manafold and carburetor being out of shape and taking in to much air, and the electronics on the carburetor controlling the solonoid was giving the carburetor the werong signals.

After that mouthfull its running like a dream hope it applies to you and helps even in the smallest way.

Gool luck.

[ajay]

yeah, no carby for me, but i suspect somehow i have an exhaust leak, hmmmmmmm. i dunno, when i retarded the timing (twisted dizzy anti-clockwise) it stopped doing it, advancing it made it worse, but i've had it timed properly and its still going, dammit... i just haven't had time to sit down properly and work thru some stuff, altho i'm pretty sure its not the throttle body as i changed that a few weeks ago