The Lotus Cars Community banner

1 - 9 of 9 Posts

·
Registered
Joined
·
467 Posts
Discussion Starter #1
So the car had been going perfect for a week. Today I started day dreaming about driving a Lotus and never having issues. Stupid me.

Then I get a CEL, misfire codes!

Cruising normally at 45mph
I was not in Sport mode
Traction control light was on (I am replacing the brake and clutch switch/sensor to try fix this)
Just as I was coming to a stop it started idling like crap and the CEL came up.
Then it went really rough. No power. CEL on all the time.

I pulled over.
Turned it off and checked the codes
P0300
P0301
P0303
P0305

Misfires all on the back bank.

I pushed every plug and erased the codes and everything is running fine.

In hindsight i shouldnt have erased the codes and instead started wigling plugs when it was running rough.

I have read a few posts about this exact problem. Seems reasonably common. Though I havnt found a definitive answer.

My questions are:
When the codes indicate an entire bank has misfired, is this actually true? Does it really know a per cylinder misfire or is it estimating it from the crank speed/position? Ie could it be 1 cylinder misfire and it trips a bunch of codes?

Lots of people saying its the throttle or MAF connector pins. If the indication of all 3 cylinders misfiring is actually true, why would an incorrect MAF reading only cause 1 bank to misfire? Why not all?

I have seen several posts about bank 1,3,5 going out and some with 2,4,6 going out.

Does anyone know if the ECU would shutdown an entire bank because of one weird reading? Or does it need a mechanical fault to shut a bank down. Ie wiring harness fault loses power to injects or coils.

I dont just want to clean and re plug things. Or replace engine harnesses without actually figuring out the problem.

Could this be something similar to the Elise idle stall feature? Not really a mechanical issue and you just have to deal with it? (though running rough and going into limp mode is a lot more serious than what the Elise would do)
 

·
Registered
Joined
·
467 Posts
Discussion Starter #2
I don’t like to start new posts on something that’s been talked about before. But what I’ve read hasn’t giving any proper answers. It’s all, new wiring harness, re plug things, better fuel.
 

·
Registered
Joined
·
878 Posts
I put up with intermittent stuff like that for too long when we had the '12 - Lotus finally solved the problems with a new wiring harness.
 

·
Registered
Joined
·
467 Posts
Discussion Starter #4
I put up with intermittent stuff like that for too long when we had the '12 - Lotus finally solved the problems with a new wiring harness.
Yeah it looks like that is a the common thing to do. Though some people have had multiple replacements to 'fix' it. So whatever the revision change was cant have been a lot. May purely be because everything is being re plugged and moved around during the process.

Anyone know what the changes to the harness were? From what ive read there are extra grounds to the engine and directly to the battery. Gold terminals?

Was that it or did they do more?

Would have taken an extra hour to replace when the engine was out! Now it doesnt look fun! Haha oh well.
 

·
Registered
Joined
·
288 Posts
I'm not sure how the Lotus ECM does misfire detection, but I know how Toyota does it. What Toyota does is look at the speed of the crank sensor for every cylinder firing event, obviously it will speed up and slow down depending. Since the computer knows when it should see the speed change since it commanded the injector and the coil, if it doesn't see that event occur, it logs it as a misfire. For Toyota's a P0300 is a misfire that can't be attributed to a single cylinder, but in your case it would appear that the even cylinders are not setting single cylinder misfire DTCs. This indicates to me that the ECM saw misfires on that bank logged the P0300, before getting enough single cylinder misfires to count up the individual sensors.

This doesn't help with the root cause analysis, but hopefully this helps with understanding how the ECM determines the misfire event. On transverse engines, they can be more prone to road variations inducing rogue misfires. I've seen it before where a single patch of rough road was transmitting enough speed variation to the crank sensor that it would set a P0300 every time, but were unable to duplicate it anywhere else. I'm not saying that is the case here, but it could be something to keep in mind.

As for your case, I'd pull up the wiring diagram (since harnesses are an issue with these) and start looking for common points that would isolate the banks. So if you have a power, ground, signal, etc. that only feeds the odd bank, start with those.

I hope that helps!
 
  • Like
Reactions: not-a-number

·
Registered
Joined
·
467 Posts
Discussion Starter #8 (Edited)
I'm not sure how the Lotus ECM does misfire detection, but I know how Toyota does it. What Toyota does is look at the speed of the crank sensor for every cylinder firing event, obviously it will speed up and slow down depending. Since the computer knows when it should see the speed change since it commanded the injector and the coil, if it doesn't see that event occur, it logs it as a misfire. For Toyota's a P0300 is a misfire that can't be attributed to a single cylinder, but in your case it would appear that the even cylinders are not setting single cylinder misfire DTCs. This indicates to me that the ECM saw misfires on that bank logged the P0300, before getting enough single cylinder misfires to count up the individual sensors.

This doesn't help with the root cause analysis, but hopefully this helps with understanding how the ECM determines the misfire event. On transverse engines, they can be more prone to road variations inducing rogue misfires. I've seen it before where a single patch of rough road was transmitting enough speed variation to the crank sensor that it would set a P0300 every time, but were unable to duplicate it anywhere else. I'm not saying that is the case here, but it could be something to keep in mind.

As for your case, I'd pull up the wiring diagram (since harnesses are an issue with these) and start looking for common points that would isolate the banks. So if you have a power, ground, signal, etc. that only feeds the odd bank, start with those.

I hope that helps!
Great info thanks.

So if you have enough variation in crank speed (from what its expecting) that would/could trigger a code. (assuming Lotus is the same as Toyota)
If the code is triggered does the computer shut those cylinders down? Ie inducing an actual misfire until the computer is power cycled?
Or if the engine is misfiring and in limp mode does it means there must be a mechanical fault?

Im guessing its the former?

In my case I have a light flywheel. When im in standard mode it sounds unstable and sometimes close to stalling when I come to a stop. Its like its having to work harder to control its speed when it initially slows down. This is when it did the misfire. It makes sense because whatever the control loop is for that now has a much lighter mass which is going to speed up and slow down quicker than it expects.

Would the ECM tune this control loop to suit a lighter mass or would it be fixed?

If I stay in Sports mode all the time the idle RPM is about 950-1000 (instead of 850?) and its perfectly smooth and doesnt have a variation when coming to a stop.
 

·
Registered
Joined
·
288 Posts
Great info thanks.

So if you have enough variation in crank speed (from what its expecting) that would/could trigger a code.
If the code is triggered does the computer shut those cylinders down? Ie inducing an actual misfire until the computer is power cycled?
Or if the engine is misfiring and in limp mode does it means there must be a mechanical fault?

Im guessing its the former?

In my case I have a light flywheel. When im in standard mode it sounds unstable and sometimes close to stalling when I come to a stop. Its like its having to work harder to control its speed when it initially slows down. This is when it did the misfire. It makes sense because whatever the control loop is for that now has a much lighter mass which is going to speed up and slow down quicker than it expects.

Would the ECM tune this control loop to suit a lighter mass or would it be fixed?

If I stay in Sports mode all the time the idle RPM is about 950-1000 (instead of 850?) and its perfectly smooth and doesnt have a variation when coming to a stop.
I'm not sure how Lotus controls it, but Toyota ECMs will continue to count the misfires during that one key cycle. If it determines that the cylinder is constantly misfiring, it will shut down that cylinder's fuel injector. The coil will continue operating so it won't saturate the cat with raw fuel (in the event of a leaking injector). Once it sets the DTC it will continue to try and run the cylinder, especially if the misfire isn't continuous.

As for the situation you're describing, it seems like the PID control loop is too aggressive, causing under/overshoots in RPM. A tune may fix this issue, but for the short term just run the sport button.
 
1 - 9 of 9 Posts
Top