What are the causes of missing/backfiring?

[ChaosAD]

Got my car started today after being rebuilt and it goes good, except for once it warmes up it misses/backfires a bit even on light throttle at 100km.

It did that with the old engine but that had a blown headgasket and I was running on the dregs of the tank.

I filled the tank up with 96 and a bottle of octane boost as it has a compression ratio of 11:1 (same as blacktop) and set the base timing to 5-8 degrees.

It has new dizzy cap,rotor,leads&plugs but I dont know how well the plugs are gapped.

could it be my fuel pump or filter? or is it caused by not enough octane?

Any help will be appreciated.
Thanks

[ChaosAD]

Took it for another drive and a few fault codes popped up. 2, 5 & 9.
2 is listed as an airflow meter fault
5 is listed as an oxygen sensor fault.
and 9 is listed as 'not used'. WTF?

It says the oxy sensor fault could be caused by a lean mixture, maybe the ecu cannot compensate for the additional compression.

I suppose by AFM they mean MAP sensor, would the extra compression make too much more vacum?

It will miss to the point that you cannot drive it. But if I turn it off for 30sec it will be fine.

[vvega]

in a fueling sense backfireing is normally lead
and bogging down and blowing black is lean

could be a faulty lead or plug :d

v

[matt dunn]

Ign timing?

[vvega]

Took it for another drive and a few fault codes popped up. 2, 5 & 9.
2 is listed as an airflow meter fault
5 is listed as an oxygen sensor fault.
and 9 is listed as 'not used'. WTF?

It says the oxy sensor fault could be caused by a lean mixture, maybe the ecu cannot compensate for the additional compression.

I suppose by AFM they mean MAP sensor, would the extra compression make too much more vacum?

It will miss to the point that you cannot drive it. But if I turn it off for 30sec it will be fine.

2 is listed as an airflow meter fault

if there is a faulkt wuith the map sensor you wont get good fueling and no you r motor mods wond affect it its ethier wireing or the sensor is rooted..or perhaps the line to it is crimped

wireing been the preferable :d

v

[atmosports]

Usually a miss or backfiring is an electrical problem of some sort. Else if not it could be timing or fuel but this is usually not as common as electrical faults.

Check all the leads,connectors etc are on the right place, check all the plug/leads/connectors you've had off since last time, lots of work but easier to rule them out straight away.

Then I'd pull the plugs out, if they are new, then havea good look at them & clean if necessary, then regap them probably down to about 0.8mm(30 odd thou in the old terms) as any compression is gonna do wonders for blowing out sparks.

If the above doesn't sort it then it could be either fuel/timing related or else maybe even though they are new you could have a dude lead or a plug that breaks down under load, see this all the time on the dyno even with new stuff. We run road motors on 96/98 on the road with no octane boost on 11:1 or higher compression without problems so I doubt fuel quality is an issue. Quantity on the other hand could be, you've obviously bumped the compression which will need more fuel, have you changed cams etc??? as the majority of 4age 16v's I've seen on the dyno have bigger injectors/pumps or else need them to get more power as there doesn't seem to be that much room in the stock setup to increase power.

[levinwreck]

how do you get the fault codes?? ive got two 4agzes. wudnt mind seeing if everyhting is runnign smoothly

[ChaosAD]

Thanks guys. I pulled out the plugs and they have a red/orange coloured deposit on them. Same colour as the rusty water you find in an old car that hasnt had antifreeze used in it.

So should I regap them to .8mm as opposed to the standard 1.1mm? are the standard heat range plugs ok? might have to go for a 'colder' plug.

All my leads and plugs are new. Havnt tried changing my ignitor/coil with a spare one but I might have to give it a try.

I set the base timing with the engine cold, would the ecu advance the timing once the engine gets hot?

It runs fine when its warmed up but after 3-5 mins driving the missing/detonation or whatever kicks in, it doesnt actually backfire but im only taking it up to 4,000rpm. It then gets progressivly worse til your bunnyhopping down the road.

under the MAF fault code it states that one of the wires going to it is open circuit, can I test the map sensor with a multimeter? or could it just be that the ecu is recieving inconsistant values from it?

Does anyone have any idea what the fault code 9 is about?

Ive got some big cams for it but its just been freshly rebuilt so im waiting for a bit b4 they go in. Injectors and pump are standard but its doing this even on light throttle, cant even idle properly once the missing has set in.
The engine runs fine again after a little break for a minute or so, could it be the fuel filter?

[vvega]

lol your running octzne booster
hence the color

v

[matt dunn]

I set the base timing with the engine cold, would the ecu advance the timing once the engine gets hot?

Pretty sure that the 4AGE's used ignition advance to help raise the cold idle speed, so it may affect it.

You have made sure the TPS is set and bridgefd out the check connect to set the timing right??

Matt

[ChaosAD]

Yea its pretty hard to read plugs with todays fuel/additives.
Im thinking maybe the map sensors buggered causing lean mixtures which is messing with the oxy sensor.
Ill change it tonight and see what happens.

I set the timing with the check connector bridged but diddnt touch the tps and the engine was cold. I set it with the engine cold so I could take off the water pump belt as its pretty hard to see the timing mark with the belt in the way.

How do I tell if its detonating or just missing?

[matt dunn]

How do I tell if its detonating or just missing?

I think you'll struggle to "feel" detonation while you drive.

If you can feel it, it's probably a miss.

Matt

[ChaosAD]

I changed both the sensors and those fault codes are now gone and it runs fine. The wire was broken off the oxy sensor but the insulation was still holding it there.

Ive still got the fault code9 though. What the hell is it? also got a fault code11 which is something to do with idleup, my a/c is removed and turned off.

How do I tell if it is knocking without taking it to a dyno? (which im going to do soon anyway)

Anyway, that prolems fixed. Thanks for the help.

[ee904age]

http://www.mr2mk1club.com/repairsp76.html

Show a set of general Toyota codes not specific to any particular engine. Code 9 on that list is Speed Sensor, if so I wouldnt worry about it.

Cheers
Shay