A Late-Model Question...

[Bruce Dorsi]

This new-fangled technology has me scratching my head alot!  :oops:


My 1998 Chevy pu with 5.7 Vortec had the "check engine" light activate recently.  .....I used a code reader to retrieve the code for a misfire of #3 cylinder.  ....I cleared the code, and so far it has not re-appeared.

What I am confused about is, HOW does the computer know a cylinder has mis-fired, and WHICH cylinder mis-fired?  ....What sensors provide the info needed by the computer to detect the misfire, and pinpoint the offending cylinder?

I'm embarrassed to admit that I'm not up to date on late model technology, but I know some of you work on this stuff every day.

I tried to think these questions through, but I've failed to come up with a logical scenario.

Thanks in advance to anyone who will attempt to educate this dummy! :oops:  :oops:  :oops:

[Inprimer]

This new-fangled technology has me scratching my head alot!  :oops:
Join the club LOL but on 2 occasions it happened to me, on my old 96  318 Ram (turned out to be a bad wire) also on my kid's  Fierbird LT1 the * computer" showed" that #7 was misfiring ,long story short, the #7 plug was never changed so it had 107K on it, dont know the snake oil behind it, but it saved us a ton of "suspected parts" and found the source of the prob in a hurry I still have a love/hate relationship with 'puters but in this case it saved us a trip to the dealer

My 1998 Chevy pu with 5.7 Vortec had the "check engine" light activate recently.  .....I used a code reader to retrieve the code for a misfire of #3 cylinder.  ....I cleared the code, and so far it has not re-appeared.

What I am confused about is, HOW does the computer know a cylinder has mis-fired, and WHICH cylinder mis-fired?  ....What sensors provide the info needed by the computer to detect the misfire, and pinpoint the offending cylinder?

I'm embarrassed to admit that I'm not up to date on late model technology, but I know some of you work on this stuff every day.

I tried to think these questions through, but I've failed to come up with a logical scenario.

Thanks in advance to anyone who will attempt to educate this dummy! :oops:  :oops:  :oops:

[oiler]

This new-fangled technology has me scratching my head alot!  :oops:


My 1998 Chevy pu with 5.7 Vortec had the "check engine" light activate recently.  .....I used a code reader to retrieve the code for a misfire of #3 cylinder.  ....I cleared the code, and so far it has not re-appeared.

What I am confused about is, HOW does the computer know a cylinder has mis-fired, and WHICH cylinder mis-fired?  ....What sensors provide the info needed by the computer to detect the misfire, and pinpoint the offending cylinder?

I'm embarrassed to admit that I'm not up to date on late model technology, but I know some of you work on this stuff every day.

I tried to think these questions through, but I've failed to come up with a logical scenario.

Thanks in advance to anyone who will attempt to educate this dummy! :oops:  :oops:  :oops:

Short explanation is like this:
A misfire will cause a change in crankshaft speed
As the crank sensor and PCM are timing the crankshaft , the PCM can determine if the speed intervals are excessive.
It will time each speed interval and compare it with the previous one.
There is also as certain amount of crankshaft speed change on acceleration and decel. but that would be programmed into the PCM
The PCM will then determine what cylinder it is and set the appropriate code.
Probably one of the best scan tool parameters we have now.
Makes things much easier.
Jeff

[40cpe]

A '96 Cutlass we owned years ago kept setting the check engine light with a code of a misfiring cylinder. It would miss occasionally on start-up. A check of wires, plugs, coils, etc turned up negative, so I finally changed the injector. That stopped the problem until another cylinder set the light a few times. Changing that injector stopped the light from resetting.

Just another thing to consider if the problem persists.

[Bruce Dorsi]

Short explanation is like this:
A misfire will cause a change in crankshaft speed
As the crank sensor and PCM are timing the crankshaft , the PCM can determine if the speed intervals are excessive.
It will time each speed interval and compare it with the previous one.

Thanks, Jeff! ....It makes sense now.

I guessed the crank position sensor was involved, but I didn't know the intervals were compared.