Ignition timing retarded due to new exhaust.

[ml32]

Hope someone here can advice and give a second opinion.

My Turbo car is already ECU mapped, air filters, secondary Cat replacement pipe and cat back exhaust.

I changed the exhaust to another brand from a straight through to a multi chamber design and the 1st time WOT, it misfired ( I never experienced misfire before the new exhaust change). I thought it could have been the new exhaust is more free flowing hence the misfire. The new exhaust was a bit loud so I retro fitted the secondary cats but of big volume high flow version 200 cells. The noise is now tamer so I left it at that.

Now the issue, to my surprise when I run it on the rolling road it was down on power by about 25BHP from 5000rpm and the scary part was that from 5000 rpm, the ignition timing starts to retard from -2 to -8 degrees from the logs. The power graph is also very evident going flat from 5000 rpm.

The tuner advised that the power loss is due to the new exhaust being very restrictive not giving the top end power and I should change my exhaust again.

I'm not 100% sure so want to get a second opinion.

1: Car miss fired when I replaced the cat back exhaust and is not doing it now with the retro fitted 200 cells race cats instead of the cat replacement pipes. Does this mean, the car is more free flowing or restrictive when it misfired?

2: For the ignition timing to start retarding from 5k rpm, is the car struggling for air flow or fuel?.

3: Could a exhaust either more free flowing or restrictive can course the misfire and ignition timing to retard?.

Thanks in advance.

[stevieturbo]

None of what you're saying makes much sense. Or at least a bit more info is needed.

Throughout the entire spiel, not one mention if the car is even making the boost it is supposed to. Whether that's the same boost as before or otherwise.

Nowhere have you mentioned whether the car has been re-tuned to accommodate this new exhaust setup, which of course it should be

You then mention it is down on power. Compared to what ? when ? It's rather difficult to compare dyno figures from day to day, week to week, dyno to dyno etc etc. And that's not including the aforementioned things.

Then you mention a misfire. SO is the ignition system in good order ? Is it maybe some sort of overboost cut ? Or is it a definite misfire ?
Bad tuning could also lead to a misfire....so has the combo been tuned properly by someone competent to do so ?

Then the apparent timing retard. Timing doesnt just do this randomly. So why is it doing it ? Whatever you're using to make the claims timing is being retarded should also yield the information as to why.

So why ?

And you've been on a rolling road. Was this just for a blind power run, or was it more in depth ? And if so did the RR operator offered some insight ?
He would have a lot more information to hand than is being given here.

[ml32]

Thanks Stevieturbo,

More info for you.

1: The car is running the same boost as before and same state of tune.
2: The car did not received a remap for the new exhaust.
3: Car down on power compared to the last time it was on the same rolling road and from the average state of tune for my car across the broad.
4: Definitely a misfire being multiple cylinder 8,9 and 10 from a VCDS.
5: Retardation of timing from 5k rpm from logs from the rolling road session with all parameters.
6: Just wanted to run the car on the rollers to check if the exhaust has gain or lose power.

The car's ECUs are fine from scanning with VCDS and nothing has been changed apart from the exhaust.
Just really wanted to know IF a different exhaust can course the power loss and retardation of ignition timing?.

Thanks again.

[stevieturbo]

cylinder 8, 9 and 10 ?

How many cylinders does the engine have ?

Yes an exhaust can have an impact on the engines performance.

No it cannot cause timing to alter...not directly. But whatever is causing any timing retard should be apparent via the live data.

It could be knock, excessive air temperatures, bad tuning, a few things really.

If it's making the same boost, are airflow figures the same, boost solenoid duties etc ?

[ml32]

Thanks again Stevieturbo.

The car have 10 cylinders... Audi RS6 5.0 V10 twin Turbo.

Would excessive back pressure course the ignition timing to retard?.

My initial thought when it misfired before the rolling road was that the exhaust is more free flowing ( less back pressure) than of the old exhaust hence it needed more fuel to have the correct air/fuel ratio.

I will ask the tuner for more info.

Cheers.

[Heaveho]

Did you disturb the lamda sensors when working on the exhaust?

It's not clear from your post, so I'll just ask directly, have you tried returning the car to exactly the same spec as it was prior to the fault?

[ml32]

Yes, took the lamda sensors out from the cat replacement pipes and re fitted them to the new race cats.

No, have not reverted back to the former state because I have sold the old set up.

[ml32]

But the Lamda sensors were not disturbed when the car misfired after the cat back exhaust was fitted.

[stevieturbo]

ml32 said:

Thanks again Stevieturbo.

The car have 10 cylinders... Audi RS6 5.0 V10 twin Turbo.

Would excessive back pressure course the ignition timing to retard?.

My initial thought when it misfired before the rolling road was that the exhaust is more free flowing ( less back pressure) than of the old exhaust hence it needed more fuel to have the correct air/fuel ratio.

I will ask the tuner for more info.

Cheers.

On a car of that level...I really would not believe 25hp difference is measurable when dyno'ing on different days

Yes they should be accurate and they should be repeatable....but that is a relatively small number compared to what the car should be making.

So more info on this misfire. Are you simply reading codes that say there is a misfire, or is there an actual misfire ? Fault codes arent always correct and reliable.

But again no, in general I would say excessive backpressure would not cause a timing retard.
But you dont know if there is excessive backpressure. There will be data that informs you why ignition is being retarded though. It doesnt happen for no reason.

Max Torque if he appears would know better the intricacies of the modern high end OEM ecu though, and the things they can do when confronted with strange situations.

[ml32]

Stevieturbo, I actually experienced the misfire at high rpm and confirmed it with multiple cylinder when I scanned it with VCDS. I also experienced another misfire the following day after the initial one but that was at idle....the car was cold and I revved the car hard and it did it... I had to stop start the engine to stop it from being very lumpy. Scanned it with VCDS and again, multiple cylinder misfire.

However, the car did not misfire after the retro fit of a pair of 200 cells race cats and on the rollers. The power curve just didn't make sense going flat from 5k rpm when it should be still climbing for my car and that's where it starts to retard. So, there must be something that's coursing the ECU to preform the way it does from 5k rpm.....

I will change new Lambda sensors just in case.

[stevieturbo]

Your tuner needs to be looking at the data when the problem is happening. As said, timing just doesnt retard for no reason. But yes the timing retard could cause the drop in power at higher rpm for sure.

Misfire could be down to basic things like plugs, coils, wiring issues. Or it could be other.

I'll presume that car does use wideband sensors with the OEM ecu, so if there are issues there it could cause problems. But again your tuner should be keeping an eye on all those things and be able to see if there is a problem in that area. Although sometimes yes it can be difficult to spot problems.

[Heaveho]

I agree that the 25 hp difference is negligible at that power, even if it has actually lost that, you just wouldn't feel the difference on the road. As stevieturbo says, there's a variety of reasons for it pulling timing, poor fuel is another to consider. I'd be checking to see if it's making target boost, if not, consider looking for boost leaks.

Is it a single coil per plug setup, or is it possible that the misfiring cylinders are controlled by one particular coil? Clutching at straws a little here, as the number of cylinders seemingly affected is an odd number.

[Pumaracing]

I presume English is not your first language so there may be something getting lost in the story telling here. I've had to read it through a couple of times to try and work out what's being said and am still not entirely sure.

If the engine is misfiring then there's an ignition or other mechanical fault. Changing the exhaust, assuming it's actually in good condition with no leaks, won't cause a misfire. It may create a slightly rich or lean mixture, and or a small loss or gain in power, but not enough to stop the engine running properly.

However I'm confused about the ecu. I assume this is still the stock one which if it is clever enough to detect misfiring and retard the ignition should be amply capable of adjusting the mixture to suit small changes in the air flow or exhaust restriction. Which also begs the question why did it need remapping in the first place just for an exhaust change if in fact this really was done? Modern ecus can cope with 15% or 20% change in power output easily enough after a few miles to learn the new fueling settings required.

[ml32]

Pumaracing, thanks for your info. The misfire only happened twice when I retained the secondary cat replacement pipes after the NEW exhaust change and has not done so since I have retro fitted the secondary race cats. I'm now thinking along the line that the Lambda sensors could be at fault here because they were disturbed and could course the timing to retard.

The car was mapped to stage 2 a while back to gain extra power and has been running perfectly fine until this issue. I guess changing the Lambda sensors and checking for exhaust leaks might solve the issue or at least eliminate them.

Fuel wise, I always use Shell Nitro+.

[stevieturbo]

Pumaracing said:

Modern ecus can cope with 15% or 20% change in power output easily enough after a few miles to learn the new fueling settings required.

Whilst I agree, coping and optimising are not the same thing.

[Pumaracing]

By "mapped to stage 2" I assume all this involved was raising the boost limit. I very much doubt any actual mapping in the true sense of the word was done unless you have more information. The ecu will still just be using the MAP sensor and other inputs to determine fueling and ignition timing from its standard parameters.

So the misfire has gone away now. The ignition retard was no doubt done because the ecu detected knock or some other problem and this may be the only cause of the power loss. It's too early to say the new exhaust is better or worse until the ecu reverts to standard settings. Maybe just give it a few miles and see if it settles down.

[Heaveho]

Again, doubt it's the solution, but if the new exhaust was close enough and/or able to touch another part of the car when on the move, or even revved hard, when the engine moves on it's mountings, the knock sensor(s) would pick that up and retard timing.

[ml32]

Thanks again guys.

The car was never pushed past 5k rpm since the misfires and fitment of the Cats so the rolling road session was the 1st time with W.O.T.

I will check the exhaust for knocks underneath the car, exhaust leaks, change the Lambda sensors and run it on the rollers again.

Thanks again so much for all your help and advice.

[Heaveho]

Let us know when you find out, always useful for future reference.