No start on 2000 Infiniti I30t – open to suggestions

[gene.s]

A little background. I bought this post-flood car from a dealer in 2005, figuring I could fix most of the problems that will come out of that. And it was true … until this January that is. One day after a cold night it just would not start. ..

After some tinkering with it in the cold I figured out that the computer did not give the ignition pulse to the coils. Actually, it would give one or two and that was it.OBDII (connected to my laptop via Elmscan) did not produce any complaints at all. I decided that this should be easy enough fix for a dealer. Boy was I wrong…

In short, they told me that ECU needed to be replaced (I got a used one off the net and they put it in), claimed to have fixed whole bunch of corroded wiring… And nothing to show for it. The new ECU behaved the same way. In the end they said their Consult II could not communicate with either ECU, but they restored good power and ground to it. That the next step would be to replace the whole engine wiring harness, at $2k for the part and some ungodly labor charge. So, $600 and two weeks later I got my car back in the same shape I left it.

With this development, I put the car in the garage until warmer days were here. When they arrived, I started my quest on finding where the problem may be. I have the shop manual for A33, I have an OBDII scanner, a good Fluke , a dual trace oscilloscope, and decent enough knowledge of electronics.

By now I checked most of the inputs/outputs of the ECU I thought were relevant to ignition. Checked power and ground (redid most of the ground just in case); checked the signals from camshaft, crankshaft position sensors. All appear to be OK. I started thinking that maybe even this ECU is now somehow fried; but, at one point after some serious starter cranking the car actually started and ran! OBD reported all OK except for the O2 sensors that must have died after being doused in gasoline from all the starting attempts.

Of course it did not start after that. It seems that I can reliably get one or two sparks. After that the engine kind of chokes and there are no more sparks and no spikes in the ignition signal. The starter seems to slow down when the engine ‘chokes’ and then continues to rotate at good RPM. This choking appeared before, but the car would actually start after that.

So at this point I am open to any suggestions. There are a few warm months ahead so I can test a theory or two on this matter.

One more thing. It appears that in addition to repairing the wiring (I actually saw evidence of just one ground wire being fixed) the dealer set the NATS code for the new ECU.

[DevonD]

How did you determine that the coils werent getting an igniton pulse? are the coils just fried?

[gene.s]

The ECU gives out ignition pulses to the coil transistors; normally these pulses are seen as periodic voltage spikes on the terminals 21,22,23,30,31,32. I used an oscilloscope to check them and saw no pulses after the initial one or two (if there were any). Thanks

[gene.s]

Plus if the coils were just fried the car would not run at all; however it did run at some point, as I described in my post.

[gene.s]

Did some connectivity testing at the ECM. A little into the endeavor found one unreliable contact (91, Throttle position sensor). Did not continue testing everything, decided to replace the ECM plug. It was a suspect from day 1, although before this I could not reliably find a fault.

So here's the question - are 2000 Maxima's and I30 ECM plugs the same? I found a bunch for Maxima at car-parts.com, and just a couple for I30. The price difference is substantial. Please comment.