Hi,
I'm thinking of test-driving this car:
http://www.craigslist.org/eby/car/71421922.html
...but I emailed the dude and asked him what kind of fuel he uses, and he said he uses regular. I know Si DOHCs are spec'd for premium. Could the engine be worse for wear because of this?

Thanks,
-Dan

 

Odds are if it caused any problems, the ECU picked it up and retarded the ignition timing to compensate (gotta love a knock sensor). If it's not throwing any codes you shouldn't have any problems.

 

The problem here is detonation. With a compression ratio of 10.2:1, regular fuel is just not a good idea. As for 'riding the knock sensor', this is not a good idea, either. Running severely retarded ignition timing can cause the engine to run too hot. But as far as the condition of the engine, it is really hard to say whether the guy damaged it from running regular fuel in it. Does he live in a warm summer climate? The cooler the climate and the higher the altitude it was driven it, the less that chance that damage was done from running 87 octane for extended periods of time. In other words, I would feel better about the car if it was driven mainly in San Francisco or South Lake Tahoe than if it was driven in Davis or Sacramento.

 

Cool, thanks; that's useful information! I've basically ruled out this car anyway. It makes me feel sort of bad for leading the dude on though.

Dan

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StorminMatt &raquo;</TD></TR><TR><TD CLASS="quote">The problem here is detonation. With a compression ratio of 10.2:1, regular fuel is just not a good idea. As for 'riding the knock sensor', this is not a good idea, either. Running severely retarded ignition timing can cause the engine to run too hot.</TD></TR></TABLE>


Do you think this would make it hot enough to blow a head? If so -- I think I may have just found a possible answer as to why my head went...

btw --&gt; this was an H23

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Lewdin’ Incognito &raquo;</TD></TR><TR><TD CLASS="quote">


Do you think this would make it hot enough to blow a head? If so -- I think I may have just found a possible answer as to why my head went...

btw --&gt; this was an H23</TD></TR></TABLE>

It's hard to say whether it would get hot enough to blow a head gasket. But on the other hand, I don't think the H23A requires premium fuel.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StorminMatt &raquo;</TD></TR><TR><TD CLASS="quote">
I don't think the H23A requires premium fuel.</TD></TR></TABLE>
It is spec'd for premium. I don't know if by "require" you mean that what it calls for makes no difference, but that's what it calls for.

Dan

 

Yep, it does call out for premium fuel.....was trying to save a few cents.

Also, when we took off the head I saw that the knock sensor was broke off, was just laying on top of the block. I kinda understand what its purpose is and yes I have the replacement for it. What could that have done, if anything?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Lewdin’ Incognito &raquo;</TD></TR><TR><TD CLASS="quote">Yep, it does call out for premium fuel.....was trying to save a few cents.

Also, when we took off the head I saw that the knock sensor was broke off, was just laying on top of the block. I kinda understand what its purpose is and yes I have the replacement for it. What could that have done, if anything?</TD></TR></TABLE>

If the knock sensor is just hanging there, it would probably throw a check engine light.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StorminMatt &raquo;</TD></TR><TR><TD CLASS="quote">

If the knock sensor is just hanging there, it would probably throw a check engine light.</TD></TR></TABLE>

That's why I was surprised to see it like that, cause I haven't had the check engine light come on.

 

The purpose of the CEL is not to let you know about maintanence problems (for their own sake). It's there to let you know if there's something that would potentially make the car not pass smog.

If the knock sensor isn't detecting anything wrong, I'm not sure it would have a reason to throw a code.

-Dan