Detergents and performance

[Falcon_LS]

My Grand Marquis calls for an octane rating of 91 RON, and does not have a knock sensor (although '03+ models do). Since I bought it, I have been using 98 RON because it contains more detergents than the available 91 and 95 RON, despite being a much higher octane rating than called for. It's actually imported here from state-owned Kuwait Petroleum's refineries in the UK. I reckon this type of gas is referred to as "Top Tier" gas in North America.

Yesterday, I finally switched to the recommended 91 RON, and after driving about 120 km (75 miles) noticed the car drove differently. This isn't a performance cars by any means, but acceleration felt much stronger at the ½ and ¾ throttle range, and naturally much better at WOT. The car just had get up and go, and didn't feel 'lazy' if that's the term to use. Just in case it was all in my head, I had a friend, who noticed and commented on my car's acceleration before, drive it and he also said it doesn't drive the same.

Octane wise, I know it isn't going to make a difference due to the lack of a knock sensor. So long as an engine doesn't knock, there's no need for higher octane fuel. But would detergent additives in the fuel really make any noticeable difference to an engine's performance? Thanks!

 

[willix]

I don't know how the fuels are rated in Kuwait but most large cars will noticeably benefit added performance/mpg with higher octane fuel.

91 vs 98 rating is a big spread with the fuel available nowadays.

I think the increased octane rating & not the additives are the reason for the performance gains.

American fuels are all basically 3 grades 87, 90, 93, any grades above that is difficult to find & very expensive.

 

[berniedd]

Willix, he said it performed BETTER when he switched to the lower octane fuel. About the only thing I can surmise is lower octane gas actually has more energy than higher octane gas. That's a fact. But it shouldn't have made the car perform like a different beast like Falcon described.

 

[Falcon_LS]

Sorry, to clarify - it performed BETTER with 98 RON. Performance dropped with 91 RON. In this section, I was describing my experience with 98 RON:

Originally Posted By: Falcon LS
This isn't a performance cars by any means, but acceleration felt much stronger at the ½ and ¾ throttle range, and naturally much better at WOT. The car just had get up and go, and didn't feel 'lazy' if that's the term to use.

 

[eljefino]

You do have a full feedback (with o2) fuel system right? I ask because in the early 90s GM made the "Saudi Syclone" hot rod turbo truck set up for leaded gas for export. They left o2 sensors in the manifold but cut the wires.

Maybe there's ethanol or something in your bum gas, even if you have a feedback fuel system it takes a while to adjust. Though I imagine through geographical availability to... cheap oil... and the politics of the region they don't use it as much.

Your two fuels could have radically different RVPs, but with pressurized fuel injection and warm temps either should vaporize fully.

 

[Falcon_LS]

I do have leaded fuel capability, but I'm still not sure about the oxygen sensors. The sensors are physically there with all the wiring. I emailed the Ford Customer Service Division, and have been told my vehicle is equipped with a 'regulated' fuel system and oxygen sensors, but that's confused me even more.

As far as I know lead and oxygen sensors do not go hand in hand.

 

[Spyder7]

My understanding of it is that the ECM will use feedback from the sensors to adjust its timing based on octane level so as to avoid pre-detonation and knock. If a lower octane fuel is used, the ECM will adjust ignition - there will be no knock but performance will be degraded.

All of this assumes the engine is designed to take advantage of higher octane fuel. If it isn't, then no benefit will be observed. In your case it seems like its designed to adjust to different octane levels, which is why you are seeing diminished performance from the lower octane (less energy in the fuel and the ECM is retarding the ignition accordingly so as to avoid pre-detonation and knock).

-Spyder

 

[Vikas]

Anybody wants to speculate when ECM decides to increase the timing again? How does it know you put the premium in the tank? Does it try it once every driving cycle? I have never gotten a skinny on it.

By the way, lower octane *technically* has higher energy albeit very slight.

- Vikas

 

[edhackett]

It could be due to the distillation cut of the 98 octane fuel. Back in 1986, while helping set up an FTIR for an emission study we ran a sample of Chevron 87 and a no name cut-rate 87. The Chevron contained a much higher percentage of aromatic compounds. Although both were sold as 87 AKI unleaded regular, the Chevron fuel contained more energy (would, and did, give higher mpg), and would have a higher actual octane rating.

The 98 that you are getting may be blended with a higher quality base stock.

Ed

 

[cp3]

Don't think it knows what you have in the tank, just that there is a pre-ignition condition. As for how and when it gets back to standard timing would be interesting to know.

 

[severach]

Originally Posted By: Vikas
Anybody wants to speculate when ECM decides to increase the timing again?

Some ECM watch for the tank to be filled and retry the tuning sequence. Other ECM constantly advance the timing until knock is heard then back off a set amount

 

[Vikas]

How can it be "constantly"? Then it will be pinging all the time on the standard grade gasoline. I can understand once per drive cycle.

 

[Falcon_LS]

Well, an update. I switched back to 98 RON and now I feel I'm actually driving my car again. It got a bit scary, as there was a weird rattling noise coming from the engine under partial load - the exact same noise you would hear if you put a manual transmission in 4th or 5th gear at low speed and bring the clutch back up to the biting point. Then it started becoming more frequent. I literally 'wasted' this tank of 91 RON by setting the cruise control on the freeway, which was the only way to prevent the rattling. Now with the 98 RON, there's no noise and it performs like before I'm extremely pleased to say.

 

[Vikas]

That is severe knocking :-( I am surprised that you would get it with regular gasoline. Mild pinging is understandable. I wonder if you have too much carbon build up in the cylinder which increases the octane requirement. Your vehicle looks like a prime candidate for commercial or home grown decarbonization. Seafoam, MotorVac, TerraClean, Chinese Water Torture come to mind.

 

[Falcon_LS]

To be honest, I use Liqui-Moly Valve Cleaner at every fill up and have been doing so for the past 9,000 km/5,625 miles. I also ran 2 double doses prior to an oil change. Also used Liqui-Moly Fuel Injector Cleaner and Gumout High Mileage Injector Cleaner at least 3 times, as well as TC-W3 and MMO in the fuel system.

The insides of the exhaust are now clean, and you can see some of the steel. When I first got it, you could barely see anything because it was literally caked in carbon!

 

[Spyder7]

Originally Posted By: Falcon_LS
To be honest, I use Liqui-Moly Valve Cleaner at every fill up and have been doing so for the past 9,000 km/5,625 miles. I also ran 2 double doses prior to an oil change. Also used Liqui-Moly Fuel Injector Cleaner and Gumout High Mileage Injector Cleaner at least 3 times, as well as TC-W3 and MMO in the fuel system.

The insides of the exhaust are now clean, and you can see some of the steel. When I first got it, you could barely see anything because it was literally caked in carbon!


I can think we can rule out any need to subject it to Chinese water torture

-Spyder

 

[Vikas]

Has somebody advanced the timing manually?

 

[Falcon_LS]

Originally Posted By: Spyder7
I can think we can rule out any need to subject it to Chinese water torture

-Spyder

Originally Posted By: Vikas
Has somebody advanced the timing manually?


Don't think that's possible.

There's even an information decal in the engine compartment pointing out ignition timing is electronically controlled by the PCM.

 

[ffracer]

Keep in mind that that most of the world uses RON (research octane number) for octane and the USA and Canada use R+M/2 (RON+MON (Motor octane number)/2).

91 RON ~=87 R+M (USA)
98 RON ~=93 R+M (USA)

Big difference.