Gti6 Misfire

[jerseypug 1]

i have a 205 xs with a gti6 engine that runs fine when it is cold, when it warms up it cuts out when it is on about half throttle, it is like turning the ignition off. if i put my foot down it is like a switch and bursts back into life. if i put the clutch in and take my foot off the throttle it ticks over fine. it just seems to happen on half throttle when it is warm. if i leave it ticking over for a while, the engine starts missing, not sure if the two problems are connected. i have changed the tps and it made no difference. when it is missing on tick over i have pulled the plug off the cam sensor and the green temp sender on the thermostat which made no difference. Has anyone had this problem? i have done a search

[CaptainK 11]

I had a similar problem. Would drive fine and idle fine when cold. But after about a mile of driving or a few minutes of engine running it would act like the engien would want to cut out. Floor the throttle and it'd eventually come back and drive ok for a little bit then would repeat the process over and over.

 

I replaced:

Battery, cam sensor, crank sensor, map sensor, engine coolant sensor, lambda probe, stepper motor, TPS, the whole throttle body & TB warmer, inlet air sensor, new spark plugs, new coilpacks, even tried an earthing kit. Also reset the ECU many times as well. All to no avail.

 

Got it fixed in the end - it turned out the the lambda heater wasn't getting any power and thus the lambda probe wasn't warming up. So when the engine warmed up and switched from "open loop / startup mode" to "closed loop / normal running mode" the engine would die as the ECU was trying to control it via the lambda readings, which of course were wrong because it wasn't being heated.

 

The engine will recover when you got foot to the floor as the ECU doesn't use the lambda when you go "Wide Open Throttle".

 

So, in a nutshell, reset your ECU and see if it improves. Fail that, check out your lambda probe and its wiring.

[jerseypug 1]

thanks for the advice. how is the ecu reset? can the lambda probe be tested or will i have to get another one?

thanks again

 

I had a similar problem. Would drive fine and idle fine when cold. But after about a mile of driving or a few minutes of engine running it would act like the engien would want to cut out. Floor the throttle and it'd eventually come back and drive ok for a little bit then would repeat the process over and over.

 

I replaced:

Battery, cam sensor, crank sensor, map sensor, engine coolant sensor, lambda probe, stepper motor, TPS, the whole throttle body & TB warmer, inlet air sensor, new spark plugs, new coilpacks, even tried an earthing kit. Also reset the ECU many times as well. All to no avail.

 

Got it fixed in the end - it turned out the the lambda heater wasn't getting any power and thus the lambda probe wasn't warming up. So when the engine warmed up and switched from "open loop / startup mode" to "closed loop / normal running mode" the engine would die as the ECU was trying to control it via the lambda readings, which of course were wrong because it wasn't being heated.

 

The engine will recover when you got foot to the floor as the ECU doesn't use the lambda when you go "Wide Open Throttle".

 

So, in a nutshell, reset your ECU and see if it improves. Fail that, check out your lambda probe and its wiring.

[CaptainK 11]

thanks for the advice. how is the ecu reset? can the lambda probe be tested or will i have to get another one?

thanks again

Take the negative connector off the battery and leave for about 30 mins to an hour. This will ensure the ECU gets turned off and thus reset. Don't forget that you'll lose your radio stations and other stuff when you disconnect the battery.

 

Lambda Probe can be tested by doing an emissions test, or by using the ECU Diagnostics port to read what the ECU is doing (helpful to get any error codes the ECU may have). Fail that, you can just check the voltage the lambda is putting out when the engine is up and running. Mine was putting out a voltage of half what it should have been when it was faulty.

[maxi 36 1 Cars]

I would put money on it being a coilpack.

 

Maxi

[pj838 0]

If you reset the ecu, i read somewhere its an idea to start the car and then 'set the base load' by turning on all the electrics, fan etc for a while.. or is this just bollocks??

[jerseypug 1]

If you reset the ecu, i read somewhere its an idea to start the car and then 'set the base load' by turning on all the electrics, fan etc for a while.. or is this just bollocks??

 

i should have mentioned that it is a rally car with no heater, minimal electrics and a batery isolator so every time i leave it all the power is disconnected. i might disconnect the lambda sensor and see what happens.

would it missfire with a coil pack problem rather than cut out?

[maxi 36 1 Cars]

i should have mentioned that it is a rally car with no heater, minimal electrics and a batery isolator so every time i leave it all the power is disconnected. i might disconnect the lambda sensor and see what happens.

would it missfire with a coil pack problem rather than cut out?

 

 

Coil packs breaking down can cause an intermittent misfire when the car is warm, similar to what you describe.

 

Maxi

[jerseypug 1]

just unpluged the lambda sensor and it runs like a dream now, i left it tick over for ages after driving and it continued to run sweet. it looks like the lambda was on its way out like captain k mentioned. i will leave it unplugged and see if anything else happens.

thanks for the help

[dcc 855]

what effects will this have upon performance?

 

Would this not make it over fuel?

[CaptainK 11]

what effects will this have upon performance?

 

Would this not make it over fuel?

Yeah, the ECU will be going into "safe mode" without the lambda reading and it'll be overfuelling a little to make sure the engine doesn't lean out. The car will still run, but performance, emissions and economy will be wrong.

[jerseypug 1]

Yeah, the ECU will be going into "safe mode" without the lambda reading and it'll be overfuelling a little to make sure the engine doesn't lean out. The car will still run, but performance, emissions and economy will be wrong.

 

it is going on the rolling road on friday so i can see what the power is without the lambda connected

[jerseypug 1]

just been on the rolling road and it made 164 bhp. this was with the lambda sensor unplugged and a standard 1.9 gti exhaust. the guy doing the rolling road said i would be loosing power as my k and n air filter is right against the rad and is sucking in hot air.

i am very pleased with these results. the rolling road was a new one that takes temperature and humidity into account and is Audi approved for reliable bhp results.

[maxi 36 1 Cars]

just been on the rolling road and it made 164 bhp. this was with the lambda sensor unplugged and a standard 1.9 gti exhaust. the guy doing the rolling road said i would be loosing power as my k and n air filter is right against the rad and is sucking in hot air.

i am very pleased with these results. the rolling road was a new one that takes temperature and humidity into account and is Audi approved for reliable bhp results.

 

 

What did it make with the lambda plugged in?

 

Maxi

[whizzer71 0]

Got it fixed in the end - it turned out the the lambda heater wasn't getting any power and thus the lambda probe wasn't warming up. So when the engine warmed up and switched from "open loop / startup mode" to "closed loop / normal running mode" the engine would die as the ECU was trying to control it via the lambda readings, which of course were wrong because it wasn't being heated.

 

Ive had this problem with two Gti6/205 conversions now,both had the same symptoms,one had a u/s lambda probe heater,the other had no feed to the lambda probe heater.

 

You just need to make sure the lambda probe has an Ign live to it via a 10A fuse If it hasnt been wired in already or correctly in the first place.

[jerseypug 1]

What did it make with the lambda plugged in?

 

Maxi

 

i didn't try it with the lambda plugged in. i should have to see if there was any difference.

[jerseypug 1]

Ive had this problem with two Gti6/205 conversions now,both had the same symptoms,one had a u/s lambda probe heater,the other had no feed to the lambda probe heater.

 

You just need to make sure the lambda probe has an Ign live to it via a 10A fuse If it hasnt been wired in already or correctly in the first place.

 

thanks, i will check that it has a live feed just out of interest but i will be leaving it unplugged as i am happy with the way it drives now and am putting on throttle bodies shortly and wont need the lambda sensor.

[whizzer71 0]

thanks, i will check that it has a live feed just out of interest but i will be leaving it unplugged as i am happy with the way it drives now and am putting on throttle bodies shortly and wont need the lambda sensor.

 

You should connect it up it'll run a hell of a lot smoother Its not rocket science should be easy after fitting the engine etc,If you're going for Tb's you'll need mapable management and a Lambda probe for sure to work out the AFR's.