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Misfire at part throttle... fine at WOT.... fixed page 2 

 

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 Post subject: Misfire at part throttle... fine at WOT.... fixed page 2
Posted: Sun Feb 17, 2008 9:31 am 
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Hi, ever since ive had a new timing kit fitted, ive had strange problems with the car on cold starts.

Every morning on a stone cold start, the car will misfire, and surge real bad when cruising in 4th gear..... this lasts for a few minutes till its warmed up.

But, then for the rest of the day it will be fine, even if the car has been sitting for a few hours then started again. It only runs like a pig in the first cold start of the day.

Ive tried new plugs, and tested the resistance of the leads and all seems fine..... i dont exactly wanna spend another 50 bucks on these leads if i dont have to? Have also swapped different coil packs over, and injectors were replaced for new ones not long ago. Fuel filter has also been done

What could it be?

Last edited by FordFairmont on Fri Mar 07, 2008 9:50 am, edited 2 times in total.

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Posted: Sun Feb 17, 2008 9:35 am 
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maybe your hego/oxygen sensor has crapped it self..???
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Posted: Sun Feb 17, 2008 9:40 am 
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TROYMAN wrote:
maybe your hego/oxygen sensor has crapped it self..???


i was thinking that too, but i replaced it not long ago as well?

i might see if i can find my old one and see if it helps tommorow morning,
cheers
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Posted: Sun Feb 17, 2008 2:00 pm 
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i doubt it'd be the oxygen sensor. these aren't used while the car is cold. to be sure just unplug it and go for a drive.
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Posted: Sun Feb 24, 2008 5:59 pm 
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ok now the misfire happens whilst the car is warm too. But at full throttle, the car runs beautifully.... even ran 156kw a few days ago getting my chip dyno tuned, but at part throttle it seems to miss.

The misfire is most noticable when holding the revs at 1600rpm, f@rt and burps badly. I have measured the voltage using 2 different o2 sensors and both had a big voltage drop, even negative -0 on my multimeter whenever the car can be heard misfiring, especially at 1600rpm.

So the o2 sensor is picking up the misfiring, but something else must be causing the miss?. Ive measured voltage at each injector, tps sensor, new coolant sensor, tried two different coil packs, plug leads resistance BUT EVERYTHING MEASURES FINE :?

The only thing i cant measure is the map sensor, even if i had a frequency meter, my workshop book doesnt tell me the specs to measure. And even though the plug leads' resistance was fine, could they still be buggered?
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Posted: Sun Feb 24, 2008 9:06 pm 
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i found something interesting tonight which might be the cause of the misfire. I measured voltage at 5 ecu pins which all earth together.

Pins 24, 51, 76, 77 and 103.

The manual says there should be 0 volts at these pins, but i found 0.05 volts at each pin with ignition on, and 0.1 when car is running. And surprise, surprise one of these earth wires run to the o2 sensor :idea:

So im thinking i should cut all these earth wires, and run my own wires to a stable earth, and run another wire to the 02 sensor and hopefully fix this.

Does this seem like a good idea? Can i earth these wires to the same place where the main ecu earth wire is?

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Posted: Sun Feb 24, 2008 9:13 pm 
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If it only happened after you put in a new timing kit, then I would have thought it's got to do something with timing? might be a couple of degrees off and that could have a lot to do with the bit of misfire.

I always thought the O2 sensor has more of an effect on fuel economy rather then misfires.

phong =P~

 

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Posted: Sun Feb 24, 2008 9:18 pm 
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have you checked your crank angle sensor for dirt or grease between the sensor and toothed wheel?
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Posted: Sun Feb 24, 2008 9:46 pm 
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phongus wrote:
If it only happened after you put in a new timing kit, then I would have thought it's got to do something with timing? might be a couple of degrees off and that could have a lot to do with the bit of misfire.

I always thought the O2 sensor has more of an effect on fuel economy rather then misfires.

phong =P~


well yes its only started like this after timing kit was fitted, but ive measured tdc, and dialed in the cam to the millimetre, timing is spot on.

And what keeps pointing me back to the sensor is the fact that the o2 sensor is ignored at full throttle and the car happens to run fine at full throttle

TROYMAN wrote:
have you checked your crank angle sensor for dirt or grease between the sensor and toothed wheel?


yeah i tried cleaning the best i could, without removing the balancer and crank sensor itself. There was alot of grease....... but you would think it would affect the engine at all rpms, as opposed to below 1600?

thanks for the replies so far
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Posted: Sun Feb 24, 2008 11:06 pm 
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FordFairmont wrote:
i found something interesting tonight which might be the cause of the misfire. I measured voltage at 5 ecu pins which all earth together.

Pins 24, 51, 76, 77 and 103.

The manual says there should be 0 volts at these pins, but i found 0.05 volts at each pin with ignition on, and 0.1 when car is running. And surprise, surprise one of these earth wires run to the o2 sensor :idea:

So im thinking i should cut all these earth wires, and run my own wires to a stable earth, and run another wire to the 02 sensor and hopefully fix this.

Does this seem like a good idea? Can i earth these wires to the same place where the main ecu earth wire is?

Image




That earth wire(ECU PIN 103) to the oxygen sensor is for the heating element that brings the sensor up to operating temperature in about 30-60 seconds. The sensor output is from (ECU PIN 35). I wouldn't be cutting any wires!!!


Cheers..

 

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Last edited by EL__Fairmont on Sun Feb 24, 2008 11:09 pm, edited 1 time in total.

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Posted: Sun Feb 24, 2008 11:07 pm 
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air temp sensor, could be burnt out or covered in s**t

 

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Posted: Mon Feb 25, 2008 7:19 am 
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Hi There

Air / intake leak ??

Voltages on TPS ??

Any chance of a diagnostic for error codes ??
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Posted: Mon Feb 25, 2008 11:09 am 
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EL__Fairmont wrote:
[
That earth wire(ECU PIN 103) to the oxygen sensor is for the heating element that brings the sensor up to operating temperature in about 30-60 seconds. The sensor output is from (ECU PIN 35). I wouldn't be cutting any wires!!!


yeah but according to the diagram they are all connected and earth out together.

I cut those 5 earth wires and earthed them myself and ran one wire to the o2 sensor, so ive fixed the bad earth. But the misfire still remains, it seems the first couple minutes of a cold start the readings from the o2 sensor are fine, but once the car warms up it shows 0 volt readings whenver the misfire can be heard, which could mean leaning out

Also the air temp sensor, is showing nearly 40 deg heat on a cold morning?
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Posted: Mon Feb 25, 2008 1:24 pm 
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FordFairmont wrote:
EL__Fairmont wrote:
[
That earth wire(ECU PIN 103) to the oxygen sensor is for the heating element that brings the sensor up to operating temperature in about 30-60 seconds. The sensor output is from (ECU PIN 35). I wouldn't be cutting any wires!!!


yeah but according to the diagram they are all connected and earth out together.

I cut those 5 earth wires and earthed them myself and ran one wire to the o2 sensor, so ive fixed the bad earth. But the misfire still remains, it seems the first couple minutes of a cold start the readings from the o2 sensor are fine, but once the car warms up it shows 0 volt readings whenver the misfire can be heard, which could mean leaning out

Also the air temp sensor, is showing nearly 40 deg heat on a cold morning?


what resistance is the IAT showing in the morning???
how did u take the reading, its nearly impossible to reach the thing

 

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Posted: Mon Feb 25, 2008 1:31 pm 
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i took the measurment at the ecu pin.

it measures 2.8volts and according to the book, 2.2 volts is 40 degree

ive already rewired the 02 sensor and coolant temp sensor as they had slight earth leaks. Now it seems the tps sensor has a similar earth leak, but im not f**k around with wiring again for nothing

Im f**k sick of this f**k car.....
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