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Discussion Starter #1
I have a 2003 IS300 (230K mi) that won’t start. I was doing some maintenance (I’ll describe below) and when I put it back together it idled rough. I narrowed the issue down to the fact that the third coil (from the front, though weirdly these connect to “C1” on the igniters) was not firing. I discovered this by disconnecting the coil-to-plug wire while running and noticed that that coil wasn’t sparking/arcing like the others. If I gave it some throttle, it started to arc & run smooth above 1500 rpm or so. Weirdly, I can’t find the reason for this. After tinkering, it’s now not starting at all.

I’ll list the other things I’ve tried below, but everything seems normal. My only thought is the ECM. I verified it’s sending a signal to the igniter for all 3 coils (in accordance with manual, each of the ECM wires is sending a signal as signified by positive voltage). But, because the signals are +5V or zero over time, my cheap multimeter doesn’t sample that fast and it shows .7-.8V on the first two coils and .2V on the third (I assume it’s picking up some average of signal and null). Does this mean the ECM is sending a signal to the ignitor for each coil but a lower voltage to one, hence failing to trigger the ignitor)? I don’t have an oscilloscope or fancy multimeter that can give faster peak reads. Any idea why it would start working at higher rpm? Any other ideas? Do I have to tow this to a dealer to fix/repair?

What I’ve checked/done that hasn’t worked:
  • All 3 coils show 12V input so they’re getting juice.
  • All 3 coils have continuity with the ignitor.
  • All 3 ECM ignition signal wires show continuity with the ignitor.
  • I’ve tried a junkyard ignitor too
  • Other ignitor wires are working (battery is 12V, ignition from ECM is 5V with ignition on, ground is 0)
  • I’ve tried a new throttle position sensor
  • I’ve tried a junkyard accelerator pedal position sensor
  • Timing belt marks are correct
  • Cam & crank position sensor impedences within spec
  • Battery is 12-13V off and 13-14V running. My battery is 3 years old so I also jumped it to a second battery to make sure it was getting enough juice.
  • I disconnected the battery and pressed the brake to try to reset the ECM.
  • Pulled the ECM to see if there were any obvious burn marks but it looks brand new. No bent pins either.
  • No obvious vacuum hoses or wires I forgot to connect. Note: it is an old IS and all the connector secure tabs have broken off. Still, connections seem solid.
  • I don’t think it’s compression or fueling since I’ve actually observed the ignition problem.
The maintenance I did before this:
  • Compression test. Most cylinders are 125psi dry/150 wet, though a couple were below. That’s below spec, but should be enough to fire and it was running smooth before I tore it down.
  • Valve clearance checks. Original cams were still in spec.
  • Cams and front crank seals replaced. I didn't replace the belts because I did that recently and only went back in when I realized it was leaking oil.
  • VVTI rebuild (for that seal)
  • I did replace the intake cam with a junkyard unit because I damaged the original position pin/key for the cam gear when reinstalling VVTI. Original cams were within valve spec, but the new one is tighter (intake clearance of .1mm on some cylinders instead of .15-.25mm spec). I didn’t bother to change the shims since I needed to finish.
Please help. Thanks guys.
 

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You can check the resistance of the primary and secondary coils too. I posted the specs somewhere around here.

What exactly does it do when you turn the key?
 

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Discussion Starter #5
You can check the resistance of the primary and secondary coils too. I posted the specs somewhere around here.

What exactly does it do when you turn the key?
When I turn the key now it cranks but doesn't fire. Prior to some fiddling it would start but idle rough and then smooth out above ~1500rpm.
I checked the resistance on the coils. Primary coils are 1.5 ohm, secondary are 11kohms. I know the primary is suppose to be .33-.52 so, in theory, I'm out of spec, but it's the same on the 17 year old original ones and the brand new ones (amazon, not oem), so I'd be surprised if that's the issue. It might be my multimeter struggling to be accurate at that level. The running behavior is the same with the new or old.
 

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Discussion Starter #6
You can check the resistance of the primary and secondary coils too. I posted the specs somewhere around here.

What exactly does it do when you turn the key?
I just learned I have to subtract the resistance of the lead wires, so 1.5-1.0=.5 ohms or within spec on the coils.
 

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Cherisher
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If I were you, I would just double check all my plugs and make sure they didn't wiggle loose. I have a broken plug or two on my wagon with wire ties holding together.

If you're confident you have spark, it wouldn't hurt to pop up the rear bottom seat cushion and bang on top of the fuel pump a few times just to check. When my fun pump went out, I was out in public and banged on it with my lug nut socket to get back home.

edit: I saw the autocorrect to "fun pump". I'm not changing it.
 
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