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Its all about timing
Posted to Technical Discussion Forum on 3/17/2012 14 Replies

So heres a fixed car that I would like to share. It shows how important understanding computer inputs and how it relates to injector and spark sequence.

So heres a little back story to this car before it arrived in my bay. Vehicle had a timing belt, supercharger, and all oil seals replaced due to oil leakage. After being re-assembled vehicle wouldnt start.

The first thing I noticed while cranking was it tried to kick back now and again like a distributer in 180 off. Im thinking great this should be easy, a quick cam/crank sync search on IATN comes up dry. I pull cyl 1 plug (fuel soaked), drop a long screwdriver down the hole and roll motor to tdc. Once cyl 1 was at tdc I look at the crank pully and verify its at tdc mark, good the keyways intact and the crank pulleys on correctly. I then pull back the upper covers and check cam marks, hmm they're also correct. Now its time to hook the scope up and see what we can see, I grab cam, crank, and cyl 2 injector (easy to get to) and heres what i get.

[1999 Mazda Millenia S, ECM/Inputs/Outputs Waveform]

Now were getting somewhere. So we have 6 notches on the crank, one for each cylinder, and one reluctor on the cam to tell the ecm what stroke were on. The firing order on this car is a simple 123456 and im hooked up to the number 2 injector so why is it firing on the 3rd pulse after the positive cam pulse starts? Now its time to get invasive, ive got enough evidence to pull this engine down. Heres what i found.

[1999 Mazda Millenia S, Engine/Propulsion Photo] The timing mark was dead on for both cams, the only problem is this car doesnt have to right cams! Note the R on the left bank cam. I pulled the belt left the timing mark lined up and flipped the gear over.

[1999 Mazda Millenia S, Engine/Propulsion Photo] Now its a left cam gear! Notice how when you flip the gear its roughly 9 teethe out of time. I put things back together, hooked the scope up and fired her up.

[1999 Mazda Millenia S, ECM/Inputs/Outputs Waveform] Notice now that the number 2 injector fires on the second pulse of the crank after the low pulse of the cam sensor. I hope this helps someone out in the future, if nothing else we at least have a know good cam crank sync for a 2.3 miller cycle engine. But it also shows how important it is to understand how the pcm uses cam and crank inputs to time spark and fuel sequences.

Jonathan from Massachusetts

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car Vehicle Data

1999 Mazda Millenia S 2.3L

Engine2.3 L
Trans4-speed Automatic (Electronic)