Computer sent me on a wild goose chase

[Rizzo]

So I posted about the P0201 code I was getting with my service engine light. Hooked up OBD2 and it showed this code. #1 cylinder injector or injector wire. We did all the standard tests and found nothing. Wires all tested good, tested injector and it was good. tested connectors and they were good. With lots of help from Dan Lessor at Viper Specialties we narrrowed it down to a PCM. So I was all ready to order a PCM but thought I would test that as well. Over to my buddies place who also has a 98 and swapped PCM,s. Service light still comes on. We put my pcm on his car and it starts up and runs perfectly. PCM is good. ***????. Take car to dealer and explain situation. He has no idea and cant get car in until next week. Off to another mechanic buddy and this time we check everything again just to make sure. Everything checks out. Arghhhh, Frustrating. So I start thinking a different plan. We start the car and start taking off each injector connector to see if the engine changes tone. Take off the #1 connector and the engine stumbles which means its working. ***? We go down the line and every connector we take off makes the engine run rough....until we get to #2 cylinder. Take it off and nothing. Engine doesnt change. Test the wires on that connector. 12V power but no continuity to the PCM on the trigger wire. HUH? Computer said #1 cyl but in fact it was #2. Stupid computer. Found the wire broken and fixed. Problem solved. Car runs great again. What a pain in the as$ that was. I guess the diagnostics on the computer can even screw up..LOL. HUGE Thanks to Dan at Viper Specialties for all the calls and helping me out even at stupid hours of the night.

 

[steve911]

Holy Cow! Kudos to you and Dan for thinking outside the box in order to get your car fixed.

 

[Viper Specialty]

It might be worth a look to make sure the wires at the PCM connector actually correspond on the pins to the correct cylinder number. You never know- it could have been pinned wrong from Day 1!

 

[Vic]

Great find! That kind of stuff excites me. (No, not like that) I live for the hunt, find it intriguing.

Some weapons at your disposal-
Dual Trace Oscilloscope
Data Analyzer/Recorder (great for intermittant problem solving)
I/R themometer/imaging (for temperature sensitive issues)
As well as the typical DVM

Even a light bulb can work as sort of a make-shift oscilloscope, when you need to see either a pulse, or a drop in voltage, that is too quick for a digital meter's display update rate. You don't have to watch the light in the same way like you have to watch the meter. The light can catch your attention even out of the corner of your eye, when you are also checking other functions, wiggling connectors, etc.

Sometimes I make dedicated detector circuits, just to analyze particular functions. The detector can have as few as two input channels, or as many as needed. You could use TTL chips, but I just use small set-reset relays driving LEDs that trip in an ordered sequence to capture events chronologically. One advantage of these detector overlays is, that when there is an intermittant problem, I can secure it in place, leave the equipment running, and check the results later after a failure event, vs having a scope hooked up constantly.

Anyway, excellent find, great thinking "outside the box"

Much respect!

 

[Bandit3]

Excellent diagnosis.

 

[Rizzo]

It might be worth a look to make sure the wires at the PCM connector actually correspond on the pins to the correct cylinder number. You never know- it could have been pinned wrong from Day 1!

I was thinking the same thing and did check the wires. They are all where they supposed to be. Weird.