While burning a high octane gasoline, will it cause higher (richer) numbers when they stick the sniffer in your exaust pipe?

I'm not sure if any of you have seen my failed emissions thread but now I'm wondering if the gasoline could be a factor in it as well.

Ofcourse it is a new engine & needs to be broken it. I've tested it twice since the new engine went in.
The first test it blew some outragous numbers that caused me to fail.

The second test (after driving it awhile, maybe a month ~ no repairs even attempted from the first test.) Blew half of the numbers of the previous test.

Now I have to get it tested to renew my tag (previous testing was just trying to get it to pass before it's time). Tonight I realized that I've been running the highest octane fuel the station have to offer. It is a high performance motor, so I want to feed it what it deserves.
But if the lowest octane will help me lower my numbers to pass emissions, I will be happy to run a couple tanks of low octane to pass, then buy the well deserved fuel afterwards until inspection time again.

 

What compression ratio are you running? What type of engine (fuel injected, etc.) If you engine is computer controlled, you have to program the computer for a higher octane fuel if it wasn't set up for it. A lower octane will drop emission because it burns quicker.

 

Can't remember the compression ratio. It is not fuel injected or computer comtrolled. It used to be, but with all the changes the computer & fi went bye bye & the carb was slapped on.

So a lower octane will give lower burn numbers??
I'll have to buy a tank of low octane tomorrow to burn. I'm going to retest once again on Monday so I guess I'll find out soon enough.
I've been burning 92 or 93 octane. I think the station I frequent has 87 octane. I'll try that just to pass emissions.

 

Yes, running high octane fuel can make you fail smog if your motor doesn't need it. I had the same problem trying to smog my 67 mustang. I tried carb and timing adjustments, but nothing helped until I switched to 87 octane. If your motor doesn't ping on the 87, than thats all you need. THere's no point wasting money on 92 octane fuel if you vehicle doesn't benefit from it. Run the 87, if it passes the test and the motor doesn't ping, then stick with it.

 

A lower octane fuel may give lower numbers, it may not. Some high octane blends burn faster some slower than lower octane counterparts, it depends on the formulation (which is basically impossible to find out on a constistant/relialbe basis, if at all). You can NOT look at octane numbers alone to tell. Octane rating is resistance to exploding, explosion and burn are not the same thing.

If you are borderline give it a try, it may and probably will change slightly, but if you're way out still, don't expect any miracles. I forget what vehicle you're dealing with, but carbed motors seem to be more sensitive to the specific gravity differences between the fuels (in a positive way for your situation), so give it a try. That's not a fact, just a trend I've noticed. I wouldn't worry about running tankfuls through, just run it low and fill it up with the cheap stuff,it should be a fairly instantanious change.

Maybe you could run a heavier oil for the test? It sounds like maybe it's just oil getting past the rings still, ie. not broken in. Any other problems/oddities? What was high? HC, NO..? Low temp thermostat or anything else?

 

Yeah, report back what thermostat you put in, and the numbers from the testing.

What year, motor, etc?

 

Sycostang Why did you have to smog test a 67 Mustang????????????

 

Running higher octane means the mix will (hopefully) only fire off when it is supposed to, a lower octane might pre-ignite and could cause the engine to burn more thoroughly but it would be better to run the correct octane (whatever that is) and adjust your timing for the best and most complete burn in the cylinders.

If you wanted to get way deep into it you could reduce:
1) the idle mixture.
2) the main jet size.
3) the metering rod height adjustment if it is a carb that has them, such as a quadrajet.

Theoretically, you can create your own vacuum leak to thin out the mixture the cheap way, but this is not something you want to do unless you can change it back quickly - as in right after leaving the test station.

 

Because Idaho sucks! The smog exemption applies to vehicles built in 1964 and all previous years. I only had to do it once though. I soon learned that if I registered my mustang as a classic, I wouldn't have to smog it. A vehicle has to be at least 30 years old to be registered as a classic, but they assume you don't drive the vehicle much. My stang only gets driven when its warm anyway, so it works out.

 

The #1 thing you can do to help pass the tailpipe sniffer test is to retard the timing. I know this is counter-intuitive but true, especially for CO. As someone else mentioned, a higher temperature thermostat also helps. It needs to be run lean, yes, but lean misfire will cause HC to skyrocket.

Jim

 

Well I'm not smogging it tomorrow now anyhow.

Just dropped the transmission about 30 minutes ago. 3 times in one year...... Thank god for warranties!!!!