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Terrible Idle Exhaust Smell

Introduction to Engine Tuning

Discussion and questions related to the course Introduction to Engine Tuning

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Hi,

Searched pretty extensively but haven't been able to find any answers so I'm hoping for some help. I have an M20 Turbo motor with Megasquirt ECU and ID1000 injectors. I've went through all of the idle settings outlined in the course to amend the ignition table and fuel table to lean out the idle towards 14.0 - 14.5 whereas when I started it was idling around 12.1 - 12.-5 AFR.

No matter what the change the exhaust has a terrible odor which isn't common on any other car I have with a standalone and i'm trying to figure out why it's occurring. It's basically unbearable when at a stop or idling anywhere.

Hello James

Does it smell like the cat is on fire? the rotten egg smell? if so you may need to either take it for a long drive to try and clean it or failing that replace it

Regards Ross

Hi Ross,

No catalytic converter on the car. It almost smells like there is a ton of fuel being used but even after cleaning up the AFR at idle it's still similar. It has a 3" exhaust from the turbo back with a muffler. A few additional details that might help:

Stock Bottom End

Modified head with 272 grind cam (does make the idle hunt a bit)

ID1000 injectors

Distributor based ignition

Attached screenshots and msq

Attached Files

I suspect your mixture is actually quite a bit richer, but with your cam overlap, some uncombusted air/fuel goes out the exhaust. You might play with injector timing to see if you can get the mixture to indicate richer (ie, more of the injected fuel is being combusted), then lean the fuel table some more.

Thank you David. Does anyone have a reference of where injector dead time is covered in the practical stand alone tuning module? I don't see it referenced in the titles.

I am not talking about injector dead time -- I'm talking about when the injector opens (or closes) relative to the valve events. Often you see a table called injector timing, or injector phase, and can enter numbers from 0 - 720 degrees. You may have the option to use "Start of Injection" or "End of Injection" -- generally End-of-Injection is preferred as that is when the injection will stop, so you want that to be timed so most of the fuel makes its way into the cylinder on the input stroke. So with that in mind, and end-of-injection timing around 400 degrees is often a good starting place, and you should test in about 10 degree increments.

Look at the Fuel Configuration and Testing module in the Practical Standalone Tuning course, that talks about injector configuration (which includes dead times, but that's not the way it's represented in the m1 ECU used in the course).

As David said. There may be some air passing out the exhaust valve before it closed and that wasn't used to oxidise the fuel (burn it). As the lambda measures the oxygen content in the exhaust, that 'leaked' air may give a false lean reading.