tns1

My 98 ltd started idling poorly, and threw a code P0303 indicating a cyl 3 misfire. BTW, auto parts stores will often lend you the ODB reader at no charge. Years ago this was common, then it somehow became illegal for parts stores to help you read your codes, but now it is all legal again. The cause for this code can be a number of things such as clogged fuel filter, low fuel pressure (bad pump or fuel pressure regulator), bad or dirty MAF sensor, bad ignition coil, spark plug or plug wires, or bad injector. I first replaced the overdue fuel filter and ran some injector cleaner. When that didn't clear up the problem I cleaned the MAF sensor using electrical contact cleaner and replaced the plugs (also overdue). Next I checked the ignition coil primary & secondary resistance but it was OK. I have a neon bulb plug wire probe that shows when a coil fires, but it is less useful on the V6 since each coil fires two plugs at the same time. The light flashes too fast! I saw/heard no arcing from the plug wires, so it seemed the injector was the likely culprit. Since replacing them is a 2-3hr job, I was hoping for more confirmation.

The resistance of the injector winding is one good test, but the injectors are not all directly accessible without pulling things apart. There is a youtube vid showing how to pierce the wire loom to make these measurements, but there is a much easier method. Looking at the diagnostic section of the FSM shows the ECM terminals (#10,#20,#30,#40,#50,#60) that connect to the injector coils, and it only takes a few minutes to remove the glove box and expose that connector. There is no need to unplug the connector. By probing the terminal I found the resistance of injector #3 was way off compared to the others, giving me the needed confirmation. If you have an oscope, the FSM also shows the waveforms to expect if you probe those terminals while the car is running. I did this too, and I saw that the waveforms were fine despite having a known bad injector. This told me the injector wiring and injector drive circuit was probably OK.

I ended up installing a set of rebuilt injectors, which are incredibly cheap now. While it was apart I checked the fuel pressure using a banjo fitting and extended banjo bolt. These will just fit on the right hand fuel rail. The pressure was fine. It took a few days of driving before the ECM re-calibrated, but the car now runs like a dream.

tantacoma

Thanx for posting your trouble-shooting experience. I may have to use this someday.