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2001 silverado 2500hd 8.1l

Hi, I have a starting issue with my 2001 2500hd 8.1l. Started a few weeks ago, first thing I noticed is it took a few turns of the ignition to start then eventually during those few tries it backfired, then once it started to backfire before starting the engine the engine light apeared. At first it was code P3043 which was cam sensor high input. So I changed the cam sensor. I used one from oreillys bwt brand I believe. After that I erased the code but the code came back and the problem didn’t go away. Instead the code came up as p3042 cam sensor low imput. So I decided to get an AC Delco cam sensor. Code went back to p3043 cam sensor high. The next thing I did was check the pigtail or connector. That seems fine, then I changed the crank position sensor and took it to get a relearn. Still afterm all that the problem still exists, takes a few times to crank over, backfires at least once before turning over and I have an engine light reading p042. Any suggestions?

I couldn’t find any meaningful description for P3043 or P3042.
P042 is not a valid code.
Closest thing I could find is this:

I’m sorry I meant p0342 and p0343

Backfiring during starting might be caused by a stretched timing chain.

Since the ignition is COP type ignition, there’s no distributor. So a worn timing chain won’t have an effect on ignition timing.

But a worn timing chain can have an effect on valve timing.

Since the engine doesn’t have a distributor, you can’t use the old method of watching the rotor in the distributor to see how much slack is in the timing chain by turning the crankshaft.

Instead, you have to remove one of the valve covers to observe valve movement to check for a stretched timing chain.

All you do is turn the engine over by hand at the crank bolt in the normal direction while watching any valve movement.

Then turn the engine over by hand at the crank in opposite direction.

If crank can be turned more than five degrees in opposite direction before you see any valve movement, the timing chain is stretched.


I was thinking that myself but didn’t know how to check it without taking off the timing cover. Thanks

Also One More thing. Shortly after this problem started I noticed a new chirping sound coming from under the hood. Only makes the sound when I’m driving and only when I accelerate. If I put the truck in park and accelerate it doesn’t make the sound. Any idea what that is?

These websites show a list of things to check: