496 Position Sensors (Cam & Crank) Question
 

I just got done dressing & installing (2) new 496 HO long blocks. One engine has a sensor issue that I suspect is either the Cam or Crank Position Sensor. When starting the motor, somethings it will start/run normally and other times it will start but only idle (bogs out if any throttle is applied), while other times just an occasional back fire out the exhaust (will not even close to starting). I can cycle through these various conditions as fast as you can shut off the key and turn the key back on, which leads me to believe the PCM is having difficulty determining where the internal rotating assembly is orientated to sync the ignition.

Luckily I have a perfectly good set of sensors on the other motor, but before I start swapping parts I thought I would ask the community rather than flipping a coin. Given this presentation, would you swap the Cam or Crank first (my guess is the cam)?

Having had a Crank P.S. go bad on 496HO before, go with that one.

Whichever one is more expensive and or harder to get to, thats the on it will be.

read the below and especially post # 11 and read the whole thread including anything I put a link to.


http://www.offshoreonly.com/forums/g...1-496-a-2.html


The new reluctors will not work with older cam and crank sensors properly and visa versa. Not saying this is your problem but have no idea if your rebuild included the new crank / crank reluctor and the new cam reluctor. Just saying to pass on the info. Post 11 might explain your problem but there might be more to this as your engines were rebuilt. The older cam sensors are NLA and will not work with the new reluctors. The crank sensor / reluctor went from 24 x to 58x and then to 63 x.

I'm suddenly getting a sinking feeling in my stomach...both long blocks arrived with timing chain covers (newer style sensor) and oil pans (dipstick wrong and oil level sensor ports). I didn't think twice, bought new gaskets and swapped covers and pans...thinking now my sensor is fine, but the cam gear is set up for new style? What puzzles me is why one engine from the same supplier, configured the same (wrong pan and timing chain cover) yet my old sensors work fine?

On your post when you said I have a running problem and will post a new thread - I knew you were going to say cam and or crank sensor NO bull I knew you were going to say these sensors.. Anyways I posted the info I did so possible for you to figure it out. I will try to find the post exactly explains this and post that below.

post 38 in the link explains all of the changes.

http://www.offshoreonly.com/forums/g...400-rpm-4.html

ALSO swap your cam & crank senor one at a time out to see what happens from the good running engine to the bad running engine

It still can be a bad crank and or cam sensor or both. Also the connectors can become bad.

Next engine builders are not up to speed with the 496 and the reluctor changes thru out the years. That cam reluctor was changed 4 times thru out the years to read differently - the crank reluctor was change 3 times thru the years. I have seen in the past 5 to 6 years actually it can be a 50 / 50 deal depending who rebuilt it if your old sensors will work or not for the current rebuild.

Again keep in mind just throwing it out for a possible. Never can rule anything out plus what was really thrown into the mix from the engine builder.. Good luck with it. . .

So the issue was the Cam Position Sensors, and after getting some good information from BUP, Raylar's website and Performance Trucks Website, I began to investigate what I had. As it turns out, the builder installed 2004+ Cam Gear and a 2004+ Cam Gear cover, but when I dressing the motors I reinstalled my 2003- covers because these were what I had sensors for :mad: I notified the builder and they didn't offer any words of wisdom about the sensor change like the TSB Jasper has on their website: Jasper Technical Bulletin

After all the knowledge dump of the internet, it appears the changes in the cover where to accommodate the taller sensor. After looking at the face of my sensors it also appears the newer cam gears are a little taller as you can see contact rubbing marks from on the face of the sensors in both motors. The obvious solution would be to put the matching timing chain covers back on, change to the new sensors and install the harness adapters...but now that the engines are installed, this is not a decision to take lightly. Suspecting an unconventional solution wasn't far off, I decided to shim the mounting of the 2003- cam position sensor to account for any end play in the cam shaft. This might not be the solution long term, but it costs nothing to try and might save a lot of additional labor (not to mention the potential to cause a problem somewhere else in the process of fixing this issue)

http://youtu.be/_lKTHMNcxJU

you need to run the engine and scan it if you think you got your cam sensor shimmed correctly.

Like I said not many engine builders are up to current info for the 496 8.1 about the changes with sensors and reluctors that are needed to properly set up these areas. Been there, seen it and fixed many of them. .

You will need the correct cam sensor and connector if this will not shim out correctly to have a properly running engine.

the newer reluctors do not work with the old NLA cam sensors depending on which you have as a set up. Just saying

We will see, I've got nothing to loose. As a contingency plan however I did order:
(2) SENSOR PIGTAIL: HP4240
(2) CAMSHAFT SENSOR: 12591720
(2) TC COVER GASKETS: Fel-Pro TCS46007
(2) OP GASKETS: Fel-Pro OS30714R

as already installed is the 2004+ timing set and I have the 2004+ (GM 12589846) TC Covers. Had the motors not already been installed and plumbed, this would be an easy decision :(