Camshaft retard and ignition timing are not the same thing. However, camshaft retard will affect ignition timing. The crankshaft position sensor relearn sync's the sensor so the PCM knows exactly where the crankshaft is in its rotation. Adjusting camshaft retard does the same thing for the camshaft position sensor, it tells the PCM exactly where the camshaft is in its rotation. That's why they're called position sensors. The ignition timing readout on a scan tool tells you how much advance the PCM is applying. It is not adjustable, it is what it is. The PCM will apply a given amount of advance for each cell, (set of parameters). When camshaft retard is off, it limits the amount of advance the PCM can apply by the amount that camshaft retard is off. For example: if the PCM is programmed to apply 30 degrees of advance in a particular cell, and camshaft retard is -20 degrees, you end up with 10 degrees advance. On the other side, if camshaft retard is + 20 degrees, and the PCM applies 30 degrees of advance, you end up with 50 degrees of advance. The engine will misfire and most likely encounter spark knock, in which case the knock sensor will detect it and the PCM will retard ignition advance. Either way, performance and mileage both suffer when one or both sensors are not reporting correctly.

 

Thanks for clearing that up captain. I thought it might have been just different terminology.

 

Ok i think i might have figured something out. I bought this truck from Ohio and drove it down here to Georgia. When i got the truck i never had any cat codes but then come to realize that whoever had it before me removed the cat and just had a straight put. Now ive installed spark plug foulers on the front o2 sensors to try and stop the flashing ses light. Well i noticed after i installed them the vehicle idles smoother and the light only flashes a couple seconds and stops now. Im wondering if the person who had it before me had the ECM tuned to have the cat deleted so it wouldnt set check engine lights. Now that i have a cat on it and performace muffler its seeing different backpressure and changing the air/fuel mixture and putting to much fuel in causing a misfire, plus my gas mileage is horrible. I havent sat down and figured the exact number but ive always had v8's and this drinks gas as bad if not worse than most v8's ive ever had. Does sound logical to anyone?

 

The downstream 02 sensor doesn't affect mpg or driveability. I had my pcm tuned and had them delete the downstream 02 sensor since I have a hi flow cat it set the ses light. Have you done a fuel pressure and leakdown test?

 

No its got a new engine and new fuel pump and new injector system. Its only on deceleration between 75 and 80 and will stop shortly after you start slowing down or start accelerating again. Thats why i think it has something to do with the ECM module because everything has been replaced on with this vehicle. It has a K&N intake system also and i checked the filter its not over oiled. There was barely anything on it out of the box when i installed it and it did this with the factory air cleaner system as well.

 

I believe the front 02 sensors need to be in the stream to work correctly. Can your scan tool show the 02 sensor readings? Maybe they are just getting lazy and need to be replaced. Have you done a compression test?

 

o2 sensors are new "delphi", and yes compression check is good. well its running better with them out of stream thats whats making me think towards what i suggested.

 

The upstream O2 sensors, (in front of converter) need to be in the exhaust stream: remove the anti-foulers. The downstream O2 sensor, (behind converter) monitors the catalytic converter efficiency, that's all it does and will not affect engine performance. Without a converter, it will set DTC P0420 and turn on the light, (unless the PCM has been reprogrammed). As for exhaust backpressure, the PCM has no means to monitor it, there are no backpressure sensors. The flashing SES light is indicating a misfire, and there should be a DTC in memory. If the DTC is P0300, it's more than likely due to a fault in secondary ignition: plugs, wires, cap, rotor, ignition coil. Worn distributor bushings and or low fuel pressure can also set it.

 

Well ive replaced the o2 sensors and ign module and coil and it still flashes on and off at highway speeds. Im running out of options but im wondering if the Crank Position sensor could be sending wrong signals back to the ECM because i never changed it, it came with the junkyard engine. Also wondering if the knock sensor could be incorrect. Ive also had the valve springs changed on cyl. 1 and 4 because thats where i was getting the misfire counts. Im really in need of help.

 

Have you done a crankcase relearn? When I received a tuned pcm, I had to.
Edit, nevermind, just re read the thread lol