Hi guys,

My friend (2002 ep3) calls me one day and says he got a CEL. I tell him to go to honda and check it out and it turns out to be a code for a bad CAT. He swears its cuz of his AEM CAI, but i know he's full of it cuz he doesnt know jack squat about cars.

His car is completely stock, except for the AEM CAI, but the one thing i see him doing to his car ever since he got it three years ago was that he would ALWAYS fill up with 91 octane. I tried to explain to him numerous times about the adverse affects of running a higher octane than needed, but he swears that his CEL would always come on if he filled up with 87 octane. In fact, when i ask him why does he use 91, he simply says "its just habit..."

Ive done numerous hours of research here on ht, howthingswork.com, and other online forums on the topic of octane so i have a pretty decent idea of how it works. So my question is, would 3 years of running 91 octane on an engine that only requires 87 octane cause the CAT to fail so soon?

James

 

Running higher octane fuel on the K20A3 will not cause the cat to go bad. Not on that car or any other.

If he went to the track and decided to fill up on 110 octane, then it's possible he would damage his cat, because those fuels are not necessarily designed for street vehicles with full emissions control.

There is some apocryphal evidence that would seem to indicate that if you run premium fuel on your USDM EP3, that you will get a small extra spark advance that will make the car feel like it has a couple of extra horses. I understand the concept, but I regard the information as apocryphal because I do not believe that anybody has thoroughly tested this.

There is also information from people who normally run premium fuel that indicates they feel a reduction in performance after just one fill up on 87 octane.

I have been using 93 octane for quite some time with no ill effects, and <u>perhaps</u> with that little extra spark advance.

It could be all psychological.

But he's definitely not hurt the car with the single act of constantly filling it with premium fuel.

 

^^^this guy knoes everything y0...

 

it is possible the gas he was using had extra additives or a higher level of sulphur, which can cause the cat to clog abnormally. california/west coast fuel blends are not regarded for their qualities, particularly off-brands.

 

Shawn Church tested an EP3 on his dyno and found there was spark retard using 87 octane gas because of knocking, especially at lower rpm's. Let me see if I can find his quote:

Hello all!

Always hate to make my first post on a site on a controversial topic, but I was asked to chip in with what I know.

I own Church Automotive Testing, which is where Hondata does most of their development work on the K-series engine flashes. I work closely with Doug to help them identify what works and what doesn't. Lately, we've been working on the EP3 setup and noticed some interesting things.

When the test vehicle was first brought in, we were hearing detonation on the dyno at low rpm. The owner (rick77f) told us he was using 87 octane, as recommended. Hondata hooked up their Honda PGM-FI scantool (yes, a factory scantool, not an aftermarket) to datalog sensor outputs. We discovered that on certain runs (where the car was a touch hotter perhaps), that the ECU was pulling out up to 14 degrees of timing on the bottom end due to knock retard. At high rpm it was pulling out 4-6 deg in places.

Having had some previous experience dynoing EP's on different octane fuels, I knew that higher octane had shown more power on at least one example of the K20A3 (see VTEC.net test of a preproduction car for more data). So, we filled the car up with 91 after draining the tank and retested. Knock retard dropped a lot, 4-6 deg on the bottom end, and peak power went up by nearly 3 hp. This was done on a dyno that guarantees 0.3% repeatability, or about 1/2 hp on this car. The stock ignition maps for the EP3 run a lot of advance. The knock sensor pulls out timing in response to knock, which does occur more frequently on low octane gasoline. Note, same car, different gas, more power, less knock retard. So, you have two different sources of data corroborating the effect that a higher octane gas has (those sources being knock retard data from the scantool and the actual power output of the car).

Your car should come to no harm running 87 octane, but 91+ does appear to generate benefits, particularly on the bottom end where the knock retard can cost you up to 10 lbs-ft of torque. I believe Hondata will be tuning their flash only for 91 or better fuel as they didn't want to run more advance on 87 if it was knocking with the stock program. Anyone notice that their car feels slow or sluggish on a warmer day in traffic? That may not only be high temps, but detonation causing the the timing to retard.

Something to consider.

Rgds,
Shawn

 

Thanks very much for posting that. I guess our seat of the pants evaluation was not off target after all.

I just want to make sure that I'm understanding this correctly, though: His dyno that showed significant retard with 87 octane was on a car with the OEM computer?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by George Knighton &raquo;</TD></TR><TR><TD CLASS="quote">Thanks very much for posting that. I guess our seat of the pants evaluation was not off target after all.

I just want to make sure that I'm understanding this correctly, though: His dyno that showed significant retard with 87 octane was on a car with the OEM computer?</TD></TR></TABLE>

Yes, when Shawn referred to the ECU pulling 14 degrees of timing off the bottom end and 4-6 degrees off the top, that was with the stock ECU running 87 octane.

 

Honda has had problems with cats for years.

99-00 Civic Si's had lots of problems with clogging cats.

My 2000 Civic EX had that problem too, with 65k miles and the car was completely stock.

Luckily the Federal Government makes them warranty the factory emissions equipment for 80k miles or 7 years.