Miss Who? Miss fire... still!

Doo · Jun 21, 2020

Most will know George, but for those who dont, 2000 V8 4.0.

Had misfire for ages and replaced a bunch of stuff before finally figuring out it was the Crank Sensor.

Anyway, it murdered the cats so I de-catted it until I discovered the cause as above.

I bought new cats and will fit them soon as my mate has a slot. BUT.... I notice I'm getting a poor throttle response almost to the point it feels as if I'm running out of petrol.

I hope it's because the car is running without cats so is running rich and when hot it doesn't "like" it

But to be honest, it feels as if it's the Crank Sensor again even though it's barely covered 200 miles since being fitted!

Is it possible it's gone faulty already?

RangeRoller dt · Jun 21, 2020

She letting you keep it now?

Datatek · Jun 21, 2020

Doo said:
Most will know George, but for those who dont, 2000 V8 4.0.

Had misfire for ages and replaced a bunch of stuff before finally figuring out it was the Crank Sensor.

Anyway, it murdered the cats so I de-catted it until I discovered the cause as above.

I bought new cats and will fit them soon as my mate has a slot. BUT.... I notice I'm getting a poor throttle response almost to the point it feels as if I'm running out of petrol.

I hope it's because the car is running without cats so is running rich and when hot it doesn't "like" it

But to be honest, it feels as if it's the Crank Sensor again even though it's barely covered 200 miles since being fitted!

Is it possible it's gone faulty already?

Anything is possible, lots of duff components on the market these days.

More likely the ECU doesn't like the lack of sensor input.

myfirstl322 · Jun 21, 2020

+1... fit the cats then see.

oakey · Jun 21, 2020

All the electronic stuff and sensors are designed for Cats. I would refit

oakey · Jun 21, 2020

Or reset adaptive values?

Mark Piercy · Jun 21, 2020

It's quite possible the lack of cats .
Does your have pré and post lambda sensors?

Henry_b · Jun 21, 2020

Fuel pressure.

kermit_rr · Jun 21, 2020

If it doesn't have post cat sensors then it won't know or care they are missing.
Anyways, pretty sure the post cat sensors only tell you if the cats are working and don't affect emissions/running

Mark Piercy · Jun 21, 2020

kermit_rr said:
If it doesn't have post cat sensors then it won't know or care they are missing.
Anyways, pretty sure the post cat sensors only tell you if the cats are working and don't affect emissions/running

If it does have the post cat sensors it can cause faults on the ecu side. As it is émission related its a priority system and will cause a code my mate.

kermit_rr · Jun 21, 2020

Mark Piercy said:
If it does have the post cat sensors it can cause faults on the ecu side. As it is émission related its a priority system and will cause a code my mate.

Agree on the faults, just wasn't aware they affected fuelling in any way

Mark Piercy · Jun 21, 2020

kermit_rr said:
Agree on the faults, just wasn't aware they affected fuelling in any way

The post lambda check the cats output. If the cat/s don't behave the way the ecu predicts it can effect fueling on some systems.

pwood999 · Jun 22, 2020

Was the old crank sensor bad output, or actually damaged ? Check the teeth on the flywheel, and make sure none are missing. I believe it should have 58 teeth on the Thor, with two missing at 60deg before TDC.

Doo · Jun 22, 2020

Thanks for all the replies. I was kinda leaning towards "it's because the cats are missing" but wanted a 2nd opinion.

It never occurred to me to check for missing teeth... But the new CS made a difference when I put it in. Granted it was a cold start, but the spark testers showed the sparks were now back in tune. I messaged my mate, but no reply as of yet so not sure when I'll get the cats on

I'm trying to not use the car as I want to sell it and have ordered a heap of new parts. Whole exhaust system, roof lining, new (well, used) wing and bonnet, etc. Someone going to get a decent motor all the same. I have lavished money on it over the 4'yrs I've owned it... Someone else's turn now.

Doo · Jul 16, 2020

Well, finally got it code read by the master and it showed one of the 2 O2 sensors is unhappy.

Sometimes it's working, but mostly it's not! Seems the last chap who code read it "isn't very good with older cars!"

Wait! What? An O2 sensor does the same job on a 2 year old car as on a 20 year old car

Anyway, ordered a pair and hoping they will be in today around lunchtime.

The same chap suggested my head gaskets are gone

I pointed out his boss fitted this engine not 22 thousand miles ago and it's been treated very well with a total of 5x oil changes (the original when the engine was dropped in followed by 4 more from me), it's never been allowed to overheat and doesn't get thrashed along motorways or tow heavy trailers. His boss agreed it's unlikely, but there is speak of it still being under warranty so if it "is" knackered, I may be covered...

However, I'm hoping it's just a dodgy sensor, but am replacing as a pair and will keep the "good" one as a spare for testing purposes.

kermit_rr · Jul 16, 2020

Doo said:
Sometimes it's working, but mostly it's not!
However, I'm hoping it's just a dodgy sensor, but am replacing as a pair and will keep the "good" one as a spare for testing purposes.

sounds like it could be a dodgy connection, it doesn't take much at all

Doo · Jul 16, 2020

kermit_rr said:
sounds like it could be a dodgy connection, it doesn't take much at all

Nah, the connections are excellent. We think it got cooked when the crank sensor cocked up the timing and fried the cat. It was switching properly, then it would drop then come back....

Henry_b · Jul 16, 2020

On live data the sensor should fluctuate between 0-5v if it is a static number the sensor is shagged.

Henry_b · Jul 16, 2020

Mind you when/if an O2 sensor fails the Thor will go into an open loop Rich mixture, it shouldn't misfire.

Mark Piercy · Jul 17, 2020

The first O2 sensor reacts to the engines emmisions.
if you have a post cat sensor as well, that reacts to the cat holding and releasing oxygène.
If the post cat doesn't respond or fluctuate, it could be either a dead cat (meaow) or a dead sensor.
By adding an external fuel via the air intake it will cause the both sensors to react, if they still don't react they are indeed dead... The fuel trims will also react and drop when the gas/fuel is added.

Miss Who? Miss fire... still!

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