Spitfire557

Got my LE2 all back together finally (le2 heads, le2 cam, pro mag 1.6rr's, etc., stock 350 internals) and it's not running right. Under load (ie: driving it), it'll backfire like a mother, even when at a constant 25% throttle. If it's not's under load, it'll idle fine, and even rev out pretty clean, with little to no backfiring. What could this be? I'm thinking it's picking up false knock and pulling timing. Could it be the O2's? We haven't let it run long enough to put it in open loop (or is it closed loop? whichever it goes into when warm). Any other idea's? Sounds good otherwise though!

Thanks!

http://smg.photobucket.com/albums/v3...nefinally2.flv

Steve0

Do you have a tune? I would think that that motor definately needs some type of tune before you try drivign it. You dont want to damage your new motor.

Zigroid

it has a madz28 tune

Spitfire557

Yep, it's got a LT4 KM and a MADz28 tune.

526 SS 96

Check the valve adjustment. This usualy causes the problems you described. Or it could be a leaking or bad injector. If it still has the problem with the valve adjustment, find a local place and have the injectors cleaned and flowed. Also, hook up a vacume gauge and see what you have. If this stuff doesn't turn anything up you may have the cam a tooth off., or even the opti. It is also possible that the tuner entered the wrong size injector, not common but we are all human. Remeber to recheck everything you did, even if you are 'sure' you did it right.

Spitfire557

But would any of those make it run fine when not under load? Here's a quick vid of it.

http://smg.photobucket.com/albums/v3...nefinally2.flv

nosfed

It sounds like it's going lean. You might watch the fuel pressure and O2 readings when it starts popping.

526 SS 96

You said little to no popping at idle, so I assumed that it's popping all the time. Nosfed could be right, maby it is way lean check FP.

93yellowta

well it could be the tune, I have a similiar setup... a cc306 cam p&p heads.. and bigger, injectors/t.b.. and many other mods.. had a madz28 tune, for my mods. it was leaner than crap. hopefully you can get it on a datalogger/scanner, and if it is lean he will re-tune the chip. but good luck on that, he wouldn't even take mine back to re-tune, kept on saying it was the car, ended up getting a live tuner to do it,what a difference. ended up it was Ion's tune... car runs awesome now... nothing beats a dynotune...

Zigroid

I set the valves at half turn past zero lash today. I even reset some of them after it was started due to a noise we thought was the valves. I can always go back and reset them. getting good at it lol.
Im not sure how the cam could be off a tooth. the cam gear can only go on one way. its lined up with the crankshaft gear dot to dot. the opti can only go on one way. I just hope it doesnt get that far that the front of the engine has to come back apart

thanks for all the help.

Zigroid

also, does it sound like the car's idle is "hunting"?

seems like the rpms are fluctuating rapidly up and down.

526 SS 96

What type of lifter is it? OEM?

Here is a short write up I did on adjusting valves.

Adjusting valves is easy. This is my method.

1) Install pushrods and rocker arms

2) By hand install all of the locking nuts (do not install locks at this time, compleetly remove them and set them aside).

3) Turn the engine over untill some of the valves are in the open posion. Keep rotating the crank untill you observe maximum lift. You don't need a dial indicator here just close 'nuf.

4) You are now ready to adjust the adjasent rocker arm of the same cylinder.

Note: Step #3 insures that the lifter is on the base circle of the cam. If the lifter is any where on the lift part you will adjust the rockers wrong! This is because you are now tightening against the valve spring and lifter, this will make the rocker higher than it needs to be. You will notice that on the next engine rotation that particular rocker will not be adjusted right. Step #3 also assumes that the intake is on the engine and you can't see the lifters.

5) Loosen the adjusting nut untill the rocker just flopps arround.

6) Begin tightening the nut by hand while lifting up and down on the rocker arm on the push rod side. (forget that spin push rod garbage )

7) Continue tightening by hand untill the rocker arm has no vertical movement. This is zero lash.

8) At this point a decision needs to be made with regard to your preload setting. A stock hydraulic lifter takes between 1/4 and 1/2 turn, still other lifters require less like 1/16th tun, and some lifters either run at zero or with lash in which case you would need a feeler gauge. Consult the lifter manufactureure for this part.

9) Install the nut lock. Thread them in by hand.

10) Grab a box end wrench and hold back the nut while you tighten the lock. Use a medium length allen wrench and snug it down pretty tight. I typically use my thumb untill I get some wrench deflection.

11) Lastly take the box end wrench and tighten the nut another degree or two. This will ensure that the locks are set.
NOTE: When removing the nut (for any reason) don't break them loose at the lock. Instead, loosen the nut first then hold back the nut while you remove the lock. This will help preserve the threads on the locks and nuts.

Thats it! Then continue down the line roating and adjusting untill you run out of locks.

Spitfire557

OEM lifters, and we followed that method when setting the valves.

Zigroid

yeah, they were OEM lifters. but I like your way of setting them better than I did. tomorrow I guess we'll try some things out and I'll hook up my pcmscan up to the car. its not a datalogger but its better than nothing.

seawolf06

Hasn't been mentioned, so double check the plug wires and the plugs.