Hi guys and gals! My first post here, but have been lurking for a while.
I was hoping to get some ideas on an fuelling issue I'm having.
The engine in question is an 1986 S4 6 port, but it's sitting in a 1985 GSL-SE chassis with GSL-SE engine management.
The emissions equipment has been removed, what I'm left with is the fuel rail vac solenoid and dissy advance solenoid.
The exhaust consists of a medium length 50ish" primary header 1.75" ID into two 2.5" resonators and 2.5" muffler.
I've installed a wideband O2 to monitor the mixture, and have tuned the AFM variable resistor to get a 14:1 at idle and 13.5 on throttle.
The issue is a heavy rich condition, about 10.5-11:1, on light 10% throttle deceleration.
Sometimes if the throttle is held for too long I will get a severe afterfire in the second half of the exhaust.
The question is: what controls fuelling at light throttle? Throttle sensor / variable resistor?
I understand that going rich on pulling throttle back is a normal condition,
but it seems to me that 10.5:1 is just dumping so much fuel that it can't combust in the engine.
I'd like to lean it out to 12.5 or so at 10% throttle. Maybe the afterfire will stop.

Any input on this will be great appreciated!

In the meantime I will look for possible vacuum leaks and exhaust leaks that could be adding to the issue and double check the timing to rule it out of the equation.

 

I can't see how the GSL-SE ECU can run a s4.....unless ALL the SE accessories were put on a s4 block? If you have anything s4 related to electronics, its not gonna mesh

 

Yes you're right the engine management has been swapped over from the SE to the S4 engine.

I think I've actually sorted the issue. I went poking around for vacuum leaks and found that a vacuum port plug had split.
We've has -25C temps the last week and it must have decided to let go because of the cold.
I've driven her twice and there hasn't been an afterfire since and the rich condition is now about 12.5:1.

Thanks for the reply anyway!