I'm working on a car that is coming up with standard diagnostic codes (OBD II) that certain cylinders are misfiring (P0300, P0302 etc).
I'm wondering, on what physical principle does the computer know that a cylinder is misfiring? Does it meter current to the spark coil, or what? Can it tell if misfire occurs because a fuel injector is clogged, no fuel enters, and the compression cycle just doesn't go bang, but there's a spark?
It's a bunch of things. Here's a discussion:
PS. We're still lovin' the seltzer. Everything's better with bubbles (TM)
The ECM watches the KPS. The crank actually accelerates and decelerates between firings. The ECM can tell if a cylinder misfires by measuring the time difference in these perturbations. Remember, a millisecond is an eternity for a microprocessor. For the ECM to watch the engine spinning at 4K, one revolution of the crank is like you watching the sweep second hand on a clock go around. JR Dweller in the cellar what's a KPS? sorry, college level instruction not provided
Richard J K> I'm working on a car that is coming up with standard diagnostic codes
Aha. Very clever. It actually detects the bang (or misfire) as translated into (an absence of) crankshaft acceleration at a N*rpm frequency for an N- cylinder engine.
Glad to hear that.
I assume this is a car where 2 cylinders per coil pack is the wiring scheme. Sparkplug tip - block - sparkplug tip is path. Firing across the cylinder that is not under compression is fairly trivial. I thought they were trying a restrike after the first firing to see cylinder pressure has risen.
I see answers that differ though. Many ways to solve a problem.
My answer is speculation,
Wes
-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
In this case it appears to be an OBD II standard method (measuring acceleration of the crankshaft between cylinder firings) which corresponds to the OBD II standard codes (P030x). It nicely detects the actual misfire, but can't by this method know whether it was due to ignition, fuel, valve, etc.
Richard,
I found these links (although you probably have found what you need):
Thanks, I knew this newgroup was frequented by the kind of guys that know these topics, or know how to find them out.
I've been impressed by your posts and have enjoyed the metalworking- related projects that you've described on your website.
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