Late model engines overfueling at WOT

[Truckedup]

Some guys claim a late model gasoline fuel vehicles, especially a truck, will run rich enough to push out black smoke when working hard...They claim turbo engines, like Ford Eco Boost trucks, will smoke like a Diesel when wide open....To be honest I have not noticed this... Is this true ? It would seem to me with all the sophisticated engine management controls that fueling would be spot on at about 12-1 A/F...Or am I missing something here?

[Orr89rocz]

Seen some 5th gen camaros run in the 11's air fuel ratio wot. They pick up alot with a proper tune

[user-23911]

Proper tune.....lol.

It's probably a built in safety margin so it doesn't detonate under sustained WOT when the temps start to creep up.


A "proper" tune can't do anything other than remove safety margin.

[pamotorman]

once it get into pinging the timing retards and it stays retarded till you refill the tank. this is in case you get a bad tank of gas. i have been on road trip with my corvette club and the guys who ran regular instead of high test always needed more at the fill ups because their timing was retarded by the computer

[Ron E]

Proper tune.....lol.

It's probably a built in safety margin so it doesn't detonate under sustained WOT when the temps start to creep up.


A "proper" tune can't do anything other than remove safety margin.

A proper tune will make more power. But, it requires a driver who is intelligent.
A safe tune assumes the driver is less so. And, many are.
We all know the "drivers" who speak with pride about how many engines, transmission, etc. they've destroyed.

[Zmechanic]

once it get into pinging the timing retards and it stays retarded till you refill the tank. this is in case you get a bad tank of gas. i have been on road trip with my corvette club and the guys who ran regular instead of high test always needed more at the fill ups because their timing was retarded by the computer

I've heard similar thing to this. Someone told me once GM retards indefinitely until you redo the tune up, others say it's constantly chasing an optimal value. Even though the engine is rated for the lowest octane, using higher octane will allow you to keep the timing in it and get an edge on the tune up.

[Truckedup]

I understand the engine management fattening the fuel/air mixture as a safeguard when the engine is pulling hard....But to the point of visible black smoke ?

[Orr89rocz]

Proper tune.....lol.

It's probably a built in safety margin so it doesn't detonate under sustained WOT when the temps start to creep up.


A "proper" tune can't do anything other than remove safety margin.

Well duh. Ofcourse its a safety thing. Proper tune as in lean it out for max power it Will pick up. I see it quite often, i tune some cars

Most of the late model guys drag race. 11.0 air fuel aint gonna run hard

[MadBill]

My Premium spec fuel '97 3800SC* Park Avenue (*with undersize driven pulley) would ping lightly at part throttle for a short time if I tanked up with mid-grade but would then switch to its low octane spark table and go quiet. It and all US-certified road vehicles were/are mandated to run frequent function tests while being driven, including checking the knock sensor(s) by briefly advancing the spark until knock is detected. Each such test would re-establish the degrees of knock margin and allow an immediate return to the more aggressive spark table.
I'm very confident that twenty years on cars are much smarter.
Also, many vehicles are calibrated to go rich after 'X' seconds of WOT to keep converter temps down.

[Ed Wright]

once it get into pinging the timing retards and it stays retarded till you refill the tank. this is in case you get a bad tank of gas. i have been on road trip with my corvette club and the guys who ran regular instead of high test always needed more at the fill ups because their timing was retarded by the computer

I've heard similar thing to this. Someone told me once GM retards indefinitely until you redo the tune up, others say it's constantly chasing an optimal value. Even though the engine is rated for the lowest octane, using higher octane will allow you to keep the timing in it and get an edge on the tune up.

GM computers run an octane test at startup. It does not stay retarded until tuned again. Why in the hell would any fool put low octane gas in a Corvette?? What would be the point? Save two dollars on a fill up?

[Brian P]

Direct-injection gasoline engine are next in the spotlight of the emission control regulators - due to particulate-matter emissions.

"Particulate matter" is pretty much carbon.

And, lots of them do run rich under load (beyond the loads seen during emission control testing).

Just take a look at the inside of the tailpipe. Black! That's carbon ...

[Orr89rocz]

once it get into pinging the timing retards and it stays retarded till you refill the tank. this is in case you get a bad tank of gas. i have been on road trip with my corvette club and the guys who ran regular instead of high test always needed more at the fill ups because their timing was retarded by the computer

I've heard similar thing to this. Someone told me once GM retards indefinitely until you redo the tune up, others say it's constantly chasing an optimal value. Even though the engine is rated for the lowest octane, using higher octane will allow you to keep the timing in it and get an edge on the tune up.

GM computers run an octane test at startup. It does not stay retarded until tuned again. Why in the hell would any fool put low octane gas in a Corvette?? What would be the point? Save two dollars on a fill up?

Lol you'd be surprised at what ppl do

[DaveMcLain]

My Premium spec fuel '97 3800SC* Park Avenue (*with undersize driven pulley) would ping lightly at part throttle for a short time if I tanked up with mid-grade but would then switch to its low octane spark table and go quiet. It and all US-certified road vehicles were/are mandated to run frequent function tests while being driven, including checking the knock sensor(s) by briefly advancing the spark until knock is detected. Each such test would re-establish the degrees of knock margin and allow an immediate return to the more aggressive spark table.
I'm very confident that twenty years on cars are much smarter.
Also, many vehicles are calibrated to go rich after 'X' seconds of WOT to keep converter temps down.

Running it over rich is certainly not going to keep the converter temps down it will make them get MUCH hotter.

[MadBill]

EGT peaks at ~ 15:1 for gasoline and goes down as the AFR drops or rises from there. Running rich, there is no oxygen in the gas stream to ignite the excess fuel, so it acts to cool the converter.

Here's a quote I lifted from another forum:

"....The most I can find in GM manuals is :

Converter Protection Mode: The PCM constantly monitors the engine operation through inputs such as the oxygen sensor, and estimates conditions that could cause the catalytic converter to reach excessive temperatures. If the PCM determines that a converter overheat condition may occur, the system returns to open loop, and enriches the fuel mixture which, in turn, cools the converter.

Thus if you use your scanner and see the PCM go out of the norm of being in closed loop ( once engine is at normal operating temps) then you know COT has been triggered and then I would suggest tuning COT table, if you do not see a switch to closed loop I would not muck with COT for it could cause damage to cats."

[DaveMcLain]

EGT peaks at ~ 15:1 for gasoline and goes down as the AFR drops or rises from there. Running rich, there is no oxygen in the gas stream to ignite the excess fuel, so it acts to cool the converter.

Here's a quote I lifted from another forum:

"....The most I can find in GM manuals is :

Converter Protection Mode: The PCM constantly monitors the engine operation through inputs such as the oxygen sensor, and estimates conditions that could cause the catalytic converter to reach excessive temperatures. If the PCM determines that a converter overheat condition may occur, the system returns to open loop, and enriches the fuel mixture which, in turn, cools the converter.

Thus if you use your scanner and see the PCM go out of the norm of being in closed loop ( once engine is at normal operating temps) then you know COT has been triggered and then I would suggest tuning COT table, if you do not see a switch to closed loop I would not muck with COT for it could cause damage to cats."

The catalytic converter's job is to consume unburned hydrocarbons in the exhaust stream. An over rich mixture will make the converters glow red hot and they have been known to catch stuff on fire. Maybe the thought is that if the EGT can get low enough it'll drop the converter temperature enough that it isn't hot enough to "light off" any more and thus cooling it. It seems like once it wasl hot enough it would keep itself hot enough.