The Truth About Cars » efi http://www.thetruthaboutcars.com The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. Wed, 01 Oct 2014 10:00:16 +0000 en-US hourly 1 http://wordpress.org/?v=3.9.2 The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars no The Truth About Cars editors@ttac.com editors@ttac.com (The Truth About Cars) 2006-2009 The Truth About Cars The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars » efi http://www.thetruthaboutcars.com/wp-content/themes/ttac-theme/images/logo.gif http://www.thetruthaboutcars.com Piston Slap: MAP-ping Engine Load http://www.thetruthaboutcars.com/2014/08/piston-slap-4/ http://www.thetruthaboutcars.com/2014/08/piston-slap-4/#comments Mon, 18 Aug 2014 12:55:25 +0000 http://www.thetruthaboutcars.com/?p=893722 TTAC regular David Holzman writes: When my scan gauge says my engine is under 99% load, and I’ve only pushed the gas pedal about halfway down, does that mean, as I suspect, that I can floor it and I’m not going to get more than a drop more power out of it?  And, in a […]

The post Piston Slap: MAP-ping Engine Load appeared first on The Truth About Cars.

]]>

(photo courtesy: www.8thcivic.com)

TTAC regular David Holzman writes:

When my scan gauge says my engine is under 99% load, and I’ve only pushed the gas pedal about halfway down, does that mean, as I suspect, that I can floor it and I’m not going to get more than a drop more power out of it? 

And, in a modern car (’08 Civic, stick), will the computer control prevent me from wasting gas by pushing the gas pedal beyond the point where I’ve reached 99% load?

Sajeev answers:

I’ve wondered this myself, just not enough to research until someone posed the question to TTAC.

Since the dawn of carburetors, vehicles used engine vacuum to measure engine load under the guise of a fuel economy gauge. Earlier EFI machines implemented fuel injector duty cycle to spit out a fuel economy reading. It’s cheaper/easier/simpler to use the fuel injection computer’s powers to calculate an approximate number, but many (all?) newer models use the mass-airflow sensor (MAF) and/or the manifold absolute pressure (MAP) sensor as the basis of these calculations.

As per SAE standard J1979, there are two engine load values: calculated and absolute load value. I suspect absolute load value is used in more customer facing interfaces, as it’s a normalized figure that might be easier to apply across multiple engines, platforms and operation parameters sans re-work. And it probably neuters the data as to not cause end user confusion, warranty claims, lawsuits, etc.

If reading this hamfisted analysis upsets you, methinks you’re a pretty frickin’ brilliant engineer.  Distilling this into an easy to digest blog post isn’t easy, as I was more of a Collegiate SAE wonk. But let’s get it down to one sentence:

Load values are a normalized calculation of engine airflow, which isn’t a 100% accurate measure of the load on your vehicle’s engine at any time.

How’s that for not answering your question and giving me a headache?  I console myself with this Hot Panther Looove:

Click here to view the embedded video.

Oooooh yeah, muuuuuuch better.

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice. 

The post Piston Slap: MAP-ping Engine Load appeared first on The Truth About Cars.

]]>
http://www.thetruthaboutcars.com/2014/08/piston-slap-4/feed/ 34
Piston Slap: Playing Super Breakout by Itself? http://www.thetruthaboutcars.com/2012/01/piston-slap-playing-super-breakout-by-itself/ http://www.thetruthaboutcars.com/2012/01/piston-slap-playing-super-breakout-by-itself/#comments Mon, 23 Jan 2012 14:00:21 +0000 http://www.thetruthaboutcars.com/?p=427725   C.V. writes: I am a mechanical engineering student looking to learn how to work on cars. My friend has given me the opportunity to take his 1988 Mazda B2200 extra-cab 5-speed. When I drove it, I saw why. The catalytic converter has broken off, and apparently pieces of it are in the exhaust. Would […]

The post Piston Slap: Playing Super Breakout by Itself? appeared first on The Truth About Cars.

]]>
 

C.V. writes:

I am a mechanical engineering student looking to learn how to work on cars.

My friend has given me the opportunity to take his 1988 Mazda B2200 extra-cab 5-speed. When I drove it, I saw why. The catalytic converter has broken off, and apparently pieces of it are in the exhaust. Would it be possible to just replace the catalytic converter, or should I replace the whole exhaust?

Also while driving it, there is a weird problem. About 10 or so minutes after startup and driving, it starts bucking back and forth as if I was engaging and disengaging the clutch. Any idea as to why that is happening? Theoretically the truck could drive even with this problem, but I don’t think it’s safe or good for the truck. What should I do?

Sajeev answers:

It wasn’t long ago that I was an mechanical engineering student looking to work on cars.  Hell, it’s way more fun than a semester of Thermodynamics, Solid and Fluid Mechanics! So what’s my advice?  Join the Society of Automotive Engineers (SAE) as a student and join the local chapter in your college.  The SAE chapter at the University of Texas changed my life, in a good way. And if you don’t have a chapter?  MAKE ONE!

Oh wait…you wanted advice on the truck, not your career. My bad.

The first problem is pretty easy, replace the convertor. Or not: eventually the loose bits of honeycomb inside will stop playing Super Breakout with itself, exit stage left, and it still might pass an emissions test.  If not, any exhaust shop can slap in a new one, and I just Googled one for $270 that’s a direct replacement.  I am sure you college kids use Google all the time, why not for a sweet little truck?

The second one is usually a combination of a poor gear change technique and a lack of fuel.  Or maybe too much fuel.  Does it buck less if you give it more gas and take more time to let out the clutch?  Problem solved. If not, I’d recommend rebuilding the carb, seafoaming the motor (at your own risk, see YouTube for reasons why), and testing the fuel pressure.  Actually not in that order: start with fuel pressure, then maybe learn how to work on a carb.

Or convert it to a later-model EFI setup! Or even better, LS1-FTW!!! You are an engineer for a reason!

Send your queries to sajeev@thetruthaboutcars.com . Spare no details and ask for a speedy resolution if you’re in a hurry.

The post Piston Slap: Playing Super Breakout by Itself? appeared first on The Truth About Cars.

]]>
http://www.thetruthaboutcars.com/2012/01/piston-slap-playing-super-breakout-by-itself/feed/ 12