Lean condition??

[C5GTO]

I just welded in new sidepipe mufflers (longer version of story here: Question about rattle in CR sidepipe ) where the original mufflers were CR1 (very, very retrictive) and the new mufflers are Flowmaster Slimline sidepipe. I took the car for a test drive and the change in performance was phenomenal with the mufflers being the only change.

I took the motor up to 6,500 RPMs for gear changes 3 times over the 15 minute test drive. Upon returning home, the sidepipes looked like this:







The mild steel portions turned blue (before and after muffler), ceramic coated (collector and turn out) and stainless steel (new muffler) portions had no appearance changes.

Is the blueing a sure sign of a lean condition or is it "expected" that the proper A/F ratio would turn mild steel blue under this sort of test drive? The motor is a 5L Ford with EEC IV EFI, mass air meter, and injectors sized for up to 450HP. The motor and ECM were dyno tuned a few years ago (producing ~ 300 HP) and "chipped" to provide proper A/F. I have made no changes to motor or ECM until this muffler change. I'm worried that these new mufflers flow so much better that I've now introduced a lean condition.

[spdbrake]

It does look to be lean. But I doubt the exhaust is the issue. The condition was probably already there and the un-coated mild steel exposed the problem.

Typ the VI EFI runs in open-loop when cold and switches to the closed loop feedback once up to temp. AFR feedback being the o2 sensors. And the the system will try and compensate for rich or lean conditions. Are you running O2 sensors? I've seen chipped cars running in Open state full time and that can work but won't respond to AFR changes. I'd get the car back to a Tuner since Bluing that far down the pipes is pretty extreme.

Some helpful info on the Mustang EFI
Mustang FAQ - Wiring & Engine Info
http://www.veryuseful.com/mustang/te...erWorkings.pdf

Last question, that was exhaust tubing that was used and not something like Chainlink fence tubing? Had to ask...

[Gaz64]

I would think that the engine is still richer than stoich, which it should be especially at 6500 rpm.

If it was lean, the engine would be down in power, and lean is high oxygen, all the fuel is consumed and no further combustion occurs.

I would be looking at the ignition timing is late (ie: 30 where the engine wants 34), for the power produced.

Combustion is then still occurring while the exhaust valves are open instead of almost ceased, and the exhaust runs hot.

What induction system is on your motor?

Can you have the whole second half HPC coated, after the first join, collectors, muffler, and turn out as an assembly?

I've seen brand new HPC coated pipes glow red in the dark, then return to normal finish once they cool.

Many engines have glowing pipes under heavy load.

Gary

[C5GTO]

Originally Posted by spdbrake

It does look to be lean. But I doubt the exhaust is the issue. The condition was probably already there and the un-coated mild steel exposed the problem.

Typ the VI EFI runs in open-loop when cold and switches to the closed loop feedback once up to temp. AFR feedback being the o2 sensors. And the the system will try and compensate for rich or lean conditions. Are you running O2 sensors? I've seen chipped cars running in Open state full time and that can work but won't respond to AFR changes. I'd get the car back to a Tuner since Bluing that far down the pipes is pretty extreme.

Some helpful info on the Mustang EFI
Mustang FAQ - Wiring & Engine Info
http://www.veryuseful.com/mustang/te...erWorkings.pdf

Last question, that was exhaust tubing that was used and not something like Chainlink fence tubing? Had to ask...

Yes, the car has O2 sensors. In second pic, you can see the sensor just after the collector.

The tubing is exhaust tubing. Specifically, Schoenfeld Exhaust Reducers, 3530. The blue color is on the newly added reducers through the weld and onto the existing sidepipe tubing where I removed the ceramic coating to weld.

[vatdevil]

Steel with straw color....450f.....purple.....500f.....blue.....575 f. Consider that header temps can exceed 1000f, those color aren't unusual. Best to pull a few plugs and read them, if you don't gave access to a sensor.

[1795]

I would suggest doing a load test on the plugs when you check them to see if it is lean. Find a large parking lot with plenty of room, get the car up to speed (i.e., expected rpms that you will be operating in) and then while at speed turn the ignition off and coast down to a stop. Then check your plugs for color and determine if you are running lean or not. You do not get an accurate representation of A/F status if the engine idles for long as it may be richer at idle than under load and that will alter the appearance of the plugs when you pull them.