Last november I decided to put a cam in the old LT1. So this winter I installed a custom grind cam ( comparable to the hotcam ) and had Lloyd Elliot port and pollish my heads. I also had Lloyd install larger valves ( Ferrea ) for me. When putting everything back together I installed a new LT4 ED timing chain set, new Optispark, Comp R lifters, new pushrods, comp pro mag 1.6 RR and 30 lb SOV injectors. The timing chain cam sprocket and crank sprocket were dot to dot. I reprogrammed the PCM for the injectors and bumped up the idle for the cam. The car fired right up when I was done with the installation. That's when the headachs started. To this day if I start the car up cold, it will run fine for about two minutes or so when a slight popping noise will start comming out of the exhaust. As the car gets warmer it begins to develop a hard miss almost. The motor actually moves when this happens and it is totally random. I checked the 02's on datamaster and they seem to look and act fine. I've adjusted the valves multiple times using every method known to man. I installed new plugs and wires for the heck of it. A couple of weeks ago I gave in and had her towed to the dealership I've been working on it now again and am still stumped!!! Can anybody shed a little light on the subject or direct me to a good f-body garage in the Delaware area. Thanks All

 

<---not a guru but...
isnt dot to dot wrong with the LT1?
i installed mine, crank gear dot at 12o'clock and cam gear dot at 12o'clock.......purrs like a lion

dot to dot (crank at 12o'clock cam at 6o'clock) (if i remember right) is #6 cyl firing?

 

ARE YOU SERIOUS??? I'll have to go and look at the pictures but I think that I installed mine crank at 12 o'clock and cam sprocket at 6 o'clock??? oh no

 

I will take a few guesses... Dot to dot is right...Sounds like possibly a coil or ICM problem....Ever do a compression or leak down test?

 

hehe oops N/M
short term memory loss

 

I thought the same thing. I proved the coil to be good and did the spaced it away from the heads to keep it from heating up so fast. I also changed out the ICM with a brand new one. I just keep throwing large bills at it with no improvment When I had it at the dealership I asked them to do a compression test on it but they were unwilling to help me there.

 

I still have a hypertech power tuning module hooked up to the PCM but I don't think that the module would cause something like this. Do you think that it would even be worth my time to take it off and run just the PCM by itself?? Everything looks good to me on my datamaster logs.

 

Dot to dot OR both at 12 is right... dot to dot is #6 fire and both at 12 is #1 fire. Either way the crank and cam are in time together.

EDIT: Whoops.. didn't see that it was already answered.

 

crossed wires are the #1 reason for a backfire

 

Did you change the optispark? Those darn things are crap if they get wet or get coolant in em. Sounds like a possibility to check. Otherwise I would get a good repair manual and check that plug wires are correct.

 

Sounds quite a bit like a problem I was having. Start it up cold and it's fine, but the longer it runs the progressively worse it gets, right??

If the cam gears in the timing set were off, it wouldn't run fine at initial cold start, it would be crappy from the first crank of the key.

What do your datamaster logs look like?? After the problem starts to appear, what are your fuel trims doing?? Are they taking a dump down to the bottom??

Honestly, I'd suggest a compression/leakdown test for knowledge and peace of mind. My problem turned out to be dropped compression on two cylinders with anywhere from 35-45% leakdown on said cylinders. I sincerely hope that this isn't your problem though. Good luck.....