New post about the same ECM topic

[JoeKansas]

I got 5 trouble codes. These codes are from "troublecodes.net" To refresh you on this vehicle and its no spark problem, this is an '89 sentra. Fuel pump will run, engine turns over, distributor rotor spins, coil and ignition module are ok (tried them on another car) -just no spark from the coil.ECM was under passenger seat. When finished I didn't clear trouble codes. I let the ecm run thru the codes a couple of times to be sure I got them all right. I am positive I didn't get any of them mixed up- but it sure would have been easy to mistake 12 and 21- with 21 being "ignition signal". Now, I am starting to doubt myself......but here they are.

12 -air flow meter/MAF sensor23 -idle switch off (on/off diagnosis)34 -knock sensor45 -injector leak51 -injector circuit

I don't recognize anything there that would keep me from getting ingition spark. But, as far as 12 and 23............where is the MAF sensor and does it only perform a funtion when the engine is running, and what would the idle switch do- and where is it located for a visual check. I am going to post this under another thread, and maybe start a new one also, so more chances of it getting viewed and answered.

[510SX]

I would ignore the codes for now.Did you check if you have battery voltage going to the coil when the key is in "ON" and "Start" position?

[JoeKansas]

I pulled the plug on the coil itself and put the voltmeter probes in the socket feeding the coil. From wire to wire, with the key on, I had right in the 12 volt range- with the voltmeter on the 25 volt range. I didn't check voltage from either wire to ground, though. I figured one was the power in, and the other would be a ground? With the probes in, cranking the engine, the voltage would drop from 12 volts, to around 8 to 10 volts. But, I think that is normal because of the cranking current draw. What I did notice was that there was no pulsing of the voltage as the engine turned over. It just went down to 8 to 10 volts as the engine cranked. I thought there should be a pulse of voltage for each time a cylinder should fire, right? Something else I checked was what looks like a ballast resistor. It is mounted right about up to the top of the firewall halfway in from the fender. It has two wires coming out of it going to a wire loom. The thing is white porcelain itself, and has a metal shield covering it. It has continuity, and when I pulled it's connector from the wire feeding it, the input wire has 12 volts. So, whatever it is, it is good. I would like to check the plug connected to the distributor. It has a 4 pin socket, and if I knew what I should have coming out of each wire, I could do that.

[Tech12]

I dunno if this will help, but check your grounds throughly. If you are getting power to the coil and dist, the reason it may not be sparking is that it has no where to ground too. Have you tried the "take out a plug and lay it on the valve cover to check if it sparks" test? You can also try this by connecting the wire that goes from your ignitor to the middles of the dist to bypass the distributor in a way. I'm just throwing ideas out here. Seriously though, check your grounds, or re ground some points on the engive and intake manifold (Do you hgave an intake maini? Never worked on a 89 sentra, and if you have a filter attatched to throtle body and it injects right there... I dunno) Keep us informed and good luck.

-Lech

[510SX]

I've never worked on sentra, either. Tech12 is on the right track. The distributor ground circuit need to be checked. There is another thing you need to check, JoeKansas. Assuming you have an electronic distributor, there should be some sort of device to trigger the spark. Usually, magnetic cam on the dist and a pick up coil. If the gap of the cam lobe and the pick up are wide or too close, you are not going to get signal to trigger the ignitor. Also, there might be the pick up coil is bad (burned or bad ground).

[JoeKansas]

I have tried a whole different distributor from the salvage yard, just pulled the old out and put in the new, and nothing- again. I haven't had the distributor all the way apart, but from what I see, there is no star wheel and a pickup coil. There is something I have read about -on another thread- called a chopper wheel in it instead. It is a thin wheel- about .030"- , approximately 2 1/2" diameter, perforated around its' outside diameter with real small rectangular holes. This wheel is in the place normally occupied by a star wheel on any "normal" USA" electronic distributor I have had apart.

This wheel rotates- it's sandwiched- between halves of a small, black, rectangular plastic gadget mounted at the outside edge of the aluminum distributor housing. It is the same as a disc brake rotating in a brake caliper. This black plastic thing evidently senses the interuption of some sort of a magnetic field or light beam that this wheel chops up. Man, I wish I had a digital camera to post pictures. But, I think I will go wiggle some ground wires, or make a nice new one and ground the engine to the body to the battery, to be double safe. I am off googling for "nissan optical pickup" and am finding hits, so maybe there is something to look for there...later

[JoeKansas]

Optical Triggering

Optical triggering has seen very little use by automotive manufacturers (one or two years of the Nissan Sentra come to mind). The basic construction is an infrared LED (Light Emitting Diode) facing a phototransistor separated by a small gap. Thru this gap a slotted wheel passes which alternately blocks and un-blocks the light, generating position information. Since light will pass through a very narrow slot, a high degree of positional accuracy can be obtained. So why doesn't everybody use this method?

A couple of reasons, the optics of the LED and phototransistor must be kept fairly clean, particularly as the windows in the trigger wheel get smaller. Failure ranges from a subtle timing shift to complete inoperability. Also, LED's and phototransistors that are rated for the automotive temperature range are not available in low cost (required in cost sensitive applications).

Optical triggering has been used primarily by aftermarket ignition manufacturers. It was the only viable alternative to magnetic back in the 1970's when most of the aftermarket ignition companies were founded. It was attractive chiefly because a simple trigger wheel could be fabricated out of plastic or other household materials and the output required minimal signal conditioning, unlike magnetic.

[JoeKansas]

I was in the process of checking for bad grounds. None, all good. I was about to put a test probe into the coil plug and then the ignition module plug, when I came across a broke wire that was down in the taped up part of the wire loom that feeds those two items. About 3 inches down from the plug itself.

I stripped the insulation off of the two ends, clipped a jumper on the two bare ends, and turned the key.

Started right up......So, all is well in Kansas and the girl has driven off in her car. I have learned more about electronic ignition than I ever thought I would need to know, and most of it I learned here. Thanks.........

[Tech12]

Right on. That optical iginition is some crazy isht. I wonder why nissan decided to test it out on a sentra...