7afe Misfire

[THE.ALB]

hi guys, new to forum and had a good look round.looks good

some thing for anyone technical......i have a kind of misfire on my avensis 1.8 7afe 1999. it only misfires (i say misfire but its sort of a surging rarther than misfire) but this only happens on very light throttle at 30 - 40 mph...... no faults under acceleration..no warning lights....here's wot i done so far..

plugs,leads,coils,no air leaks,oxy sensors looks ok and is cleanish,cleaned throttle body,checked compressions,took inj out and sprayed into 4 seperate cups-same amount- iknow ist was only on crank but spray patterns all looked good,plugs all same colour.

please help ....... where do i go next ????????

[jamesholden]

Did you use the correct spark plugs? The 7AFE runs at quite a high temperature and some normal spark plugs can't take the heat.

[THE.ALB]

hi james, yep serviced with new plugs 4 months ago and suspected that so as i kept the old plugs incase of a misfire i swopped them back but no change ;-(

[Q.S.]

hi james, yep serviced with new plugs 4 months ago and suspected that so as i kept the old plugs incase of a misfire i swopped them back but no change ;-(

Doesn't sound like a misfire from your description, more like a flat spot. Definitely no air leaks? Check for air leaks on inlet manifold pipework, both main inlet tract and small vacuum pipes etc. Have you cleaned the air flow meter (MAF)?(I presume it has one on this model)

[THE.ALB]

yeh your right it is more of a flat spot....but like a jerky flat spot... it dont have an air mass on it unless its the type in an ecu ?

as for air leaks deff is none as i forgot to mention i took the inlet manifold off and cleaned /checked the little butterfly valves for the eco running so mitty vaced all the pipes then ??????????????

i really am lost where to go from here.....

there are a few little valves around the engine that i dont know what they are and wonder if any of these could cause it ???????

[PhilGee]

Have you actually checked for any fault codes? I've seen vehicles with fault codes but no warning lamp illuminated. Might be worth checking. Not dealt with many of these engines. Normally run without fault.

[THE.ALB]

ah ha.................another tale.........i do have a vas5051 diagnostic machine (for vw/audi etc) but it wont !Removed! communicate with it in obd but when i plug it in it does put the eml on and blinks 14 and 15 to be..........but seaching the web i cant tell if this actualy means owt ???

[Beagh1958]

To THE.ALB,

You seem to have pretty much covered everything regarding misfire. I don't like guessing, but maybe cam or crank angle sensor ? Cam sensor by coil unit & crank sensor behind cambelt cover. Also coolant sensor showing up as possible cause of misfire. Hope this helps rather than confuses the matter. Sorry, as suggested cannot locate MAF sensor anywhere.

Regards, Beagh.

[Beagh1958]

To THE.ALB,

Flash code 15 on 7A-FE showing up as potential ignition coil amplifier wiring circuit to ECM ?

Regards, Beagh.

[THE.ALB]

i think the ign coil may be me playing about with it as i've tried diff ones on it.

i have tried today disconnecting the cam sensor thinking it would default back to a basic setting and thus getting rid of flat spot/misfire......nope still same ;-(

also disconnected temp sensor and still no difference apart from eml coming on.....! even tried blanking off evap pipe still no diff

i mean what the hell is left to cause a stutter/flat spot/misfire......... i dont think and have not heard of a crank sensor doing this but suppose i could be wrong..but guess it wont run with that disconnected unless it see's open circuit then takes off cam sensor ....dunno....

a booking into dealer is getting closer....... :-( :-( :-(

[Beagh1958]

To THE.ALB,

See private message for info. Will leave it with you.

Regards, Beagh.

[Beagh1958]

To THE.ALB,

See follow up PM.

Regards, Beagh.