New to this forum ( just throwing that out there!)
i'm constantly getting the po340 code. It mostly comes on as soon as i start the engine. i will clear it and drive to town and back (about 10 miles) without another code until i shut it off and then restart it. and immediately i get the code again. i replaced the cam sensor two times (since they aren't expensive). I checked the wiring and found no shorts or open circuit.
I traced the signal wire all the way back to ecm and its good.. also once in a while i will get a 1406 code (egr) if i drive it more than 20 miles or so without clearing the p0340 code..
Could this be a bad ecm? Thanks for any feedback

 

Chances are it's not the PCM! Need to fix the P0340.

 

Is the alternator making any noises? Suggest checking the alternator output for excessive ripple.

 

no ripple , clean on scope. Would excess ripple cause erratic codes?

 

i found the p0340 explained page. i guess i'll try there first

 

Sorry for the lack of comments. It's just that 1995's are by themselves. 1 year before OBD2, they were a hybrid and very few people have equipment that will read them (outside of the dealer). Furthermore, fuel injection was mechanically different and computer is different as well. The P0340 explained page may or may not apply to your vehicle very well because of it's year and fuel injection differences. In other words people simply don't know! With what instrument are you reading the code? I will attempt to help.

 

Here is the wiring schematic and the P0340 diagnostic info from the factory shop manual. Wiring is for L35 vin W motor (there was another)

 

thanks for the info it will help . i am starting over from scratch. This has put a few more gray hairs on my head.
btw I am using 2 actron scanners a CP9035 and a CP9550 (this one is for a 1996 and up but it works on this 1995)
I didnt mention it before but when i get this code the engine will start surging when i;m driving but idles just fine.
I have changed the cap ,rotor ,cam sensor, timing chain and gears, plugs , wires (plugs were black) i found that when someone changed the egr valve they messed up the gasket , so i fixed that too.
I appreciate any help you all can give me.but for now its back to square one.

 

To answer your question if excess ripple could cause erratic codes; yes for those codes that relate to components that use a hall effect sensor. The voltage between the pulses should be very close to zero. If there is excess ripple present then the electronics become confused by "seeing" too many pulses or pulses out of sync. The source of the ripple is usually a bad diode in the alternator.

Was just a suggestion.

I had a '95 before the '02. The EGR valve gave me problems in that chunks of carbon would keep the valve open. But this caused a rough idle but was okay running.
You say the plugs were black....really rich fuel....cat is probably plugged-up.