Forum Chat #32 – Can misfire be detected by OBD2 Reader?

Back to videos

Welcome to Bamford Rose and his forum chat. Before we start, it really helps us if you can like, subscribe and hit the bell button for notifications. So, you always get our latest videos when we release them. This week, it’s something I’ve picked up from a Facebook group and its, ‘Will an OBD2 reader detect misfire on a V12?’ I’ll cover OBD2 readers’ detected misfire for VA as well. But in direct answer to this question, there’s quite a few subtleties to understand before simply answering the question.

So, firstly it’s really important to check for misfires on a V12 to check that misfires, if they’re occurring, are not putting the stat catalyst at risk. Because if they were the unburned fuel that goes onto the catalyst as a result of the misfire, it could cause the countess to break up being jested back into the engine. And then that ceramic debris caused untold misery. Now even if the system is working fine and we’re talking about the misfire detection system, which is basically looking at the flywheel teeth and looking at rates of change of speed. Angular acceleration between certain points for certain cylinders to detect if the engine is running roughly.

That system is calibrated by the manufacturer to pass OBD legislation that each onboard diagnostic legislation. So, this is a legislation that forces the maker to ping up a check engine light if the emissions performance of the car is put at risk. So, this system is there to comply with legislation, which has got certain parameters. Engine speed, engine loads, rate of misfires at which it must be compliant with in. Contrary to popular belief, the light and the warning system isn’t there as a helpful friend to tell you the owner something’s wrong. Because the maker doesn’t want to do that. They never want to do that; they never want to put the light on if they don’t have to if they’re not forced to by legislation.

So, on the V12, you can be a very low engine speed cruise and this would be the lowest engine speed in 6th gear cruising down the motorway. And the misfire detection system isn’t very sensitive there. So, totally allowable by legislation. You can’t have a certain rate of misfire in that region and not put the lie on the dashboard, and that’s fine. So as an owner, you want to check that you haven’t got misfires. So, that separate from the car’s warning system, you’re reassured that your car is functioning fine. Now really as an owner you shouldn’t be doing that because that should be done by your garage at point of service.

And at each annual service every 3- 5,000 mile, it’s unlikely that a real serious catastrophic problem is going to creep in between each annual service at that interval. So, really these are checks that your garage should be doing, but not every garage does. A service to some garages is simply an all-in filter. Have a quick look around and that’s it rather than a bit detective work with a laptop to try and find the stuff that’s wrong. Well anyway, we want to plug into the car to see if it’s going to tell us anything about any misfires that will be happening. We can do that with a factory laptop, the MDS. And we can look at each individual cylinder and look at the real time at misfire that’s counting up.

This is going to say if any particular cylinder is misfiring, and for cylinder 1 to 12 there will be a P0301 to P0312 for all 12 cylinders indicating if any misfire is triggered. So, separate from the MDS laptop, you could potentially plug in a fault code reader and read any of those codes being present. There’s a couple of care points there. Firstly, a generic fault code reader is most of them apart from the really expensive ones, only going to read the primary ECU. So, this is the ECU for cylinders 1 to 6. So, you’re gonna read the fault codes for that ECU. It’s not gonna be able to read the ECU for cylinders 7 to 12. You need the proper factory kit for that.

So, that’s one of the care points. You could plug into a car, see that it’s got no fold codes and think that everything’s okay. But it’s not, because misfires are occurring on secondary side of the engine and you’re blind, your kit is blind to them. The next is that for the system to detect misfire, it needs to have been put through a drive process that teaches the engine management system what a reference engine cycle is. So, this is where you get it in sixth gear, no electrical load whatsoever. So, no headlights, no aircon, no radio and you have to get it into sixth gear. I would say start from 65-70 mile-an-hour and you have to do a Coast down in sixth gear in Top Gear, all the way down to 39 now.

It’s actually 35, but you place it to 30. And after a few cycles of doing that, the engine management system is going to be taught or a reference engine cycle is, and misfire detection is enabled. So, you’re not going to be able to tell with a generic OBD2 reader, if the misfire enable cycle has been run. Again, that’s gonna mean that you’re going to put your fault code checker in the car, read there’s no codes while they’re on. Because your systems are not active and you’re not going to be able to tell if the system is active unless you’ve got the proper factory laptop looking at that enable parameter for the process.

So, those are a few concerns on V12 and really the answer is, as an owner you shouldn’t have to worry about this yourself, should all be taking care at point of service. V8 is exactly the same in terms of it needs to learn its process. But when you plug into a V8 you can read because there’s only one ECU all cylinders, so you’re not blind to anything. But separate from an OBD2 reader, if you were worried that your V12 was exhibiting any misfire. The easiest thing to do is to find a nice gradual hill, nice gradual incline somewhere. Doesn’t have to be too steep but just nice and gradual. So, that you can accelerate up it, say get it into fourth gear and then at that lowest speed point at which it wants to change down into third gear. Obviously, it’s an auto.

Then just play with the throttle slowly increasing the throttle loading up the engine and it’s at that point that if there was a misfire and typically it’s a coil related misfire. You’re gonna feel the whole chassis shudder, because the engine is misfiring. And that long drive up an incline, fourth gear low engine speed typically 2,000 RPM playing with a throttle load. You know you can be happy that there are no misfires by doing that drive better than any single pretty unintelligent fault code reader that you could put into the car. Obviously, if there is a misfire, this is where the more intelligent equipment is going to sass out to exactly watch the cylinder it is. So, you don’t unnecessarily replace all 12 coils instead of one or two which are clearly defective.

Hope that helps. If there’s any more on the subject, then please comment below. And let’s see if we can detect misfires to prevent the horrors of having to repair an engine from catalyst ingestion. That’s what it’s all about.

Want more videos? Subscribe to our YouTube channel for regular updates!

Our channel