so my problem is pretty much summed up in the title. ive had this problem for over 9 months and ive been reluctant to post on a forum because i didnt wanna get a bunch of bs. like "your distributor is off a tooth". i swear if i hear it one more time im gonna put a bullet in my head. ok to the setup.

1991 formula, 327, .030 over, world sportsman2 heads, holley projection tbi intake, holley 670cfm tbi with 90lb injectors, fuel pressure is 28 lbs.
rockers, pushrods are stock,
camshaft: RPM Range 1500 - 6200 Duration @ .050 Lift 224 / 224 deg int/exh.
Valve Lift .450 in / .460 in int/exh. Lobe Separation 114 deg
i am running a stock distributor and ecu is a megasquirt2.

some things ive checked: obviously tried alot of tuning to fix the problem. air fuels are great, maybe on the rich side even. replaced the distributor and coil (no its not a tooth off or 180 out im no rookie!!) checked the camshaft with a degree wheel all the specs match within 1 degree and .001 inches. compression checks great, leakdown test is incredible. removed the heads and
checked for cracks. thats all i can think of off the top of my head im sure when i start 2 get replies ill be like oh yeah ive checked that too. im really pullin my hair out here. so i appriciate the help!

my current thought is maybe the cam isnt a good grind for a fuel injected engine. the motor will actually make some power at a high rpm if you advance the ignition 50 or 60 deg. thats the only thing thats made any difference, and theres no way an engine should run with the ignition like that. anyway thanx in advance and im really lookin forward to what you guys think.

 

Clogged cat?
Rocker arms over tightened?
#90 injectors @ 28psi thats a hell lot of fuel, hope you have a VRFPR.
What is the cam brand and part #?

 

seems like way too much fuel.that much unburned fuel will heat them pipes up in ahurry.im assuming back fire is when you let off?

 

usually egt's will increase with retarded timing and less fuel.

 

I had a similar problem when I first started up my Camaro. Probelm wound up being that I was running very rich and didnt have enough timing. What was happening was that the fuel wasnt being completely burnt up in the cylinder and was continuing to burn as it went into the exhaust.

 

it backfires only when i accelerate hard.(backfires as in: if the hood is off it shoots a 4 ft flame out the throttle body) the wideband reads between 12.00 and 13.5 at pretty much any time. the leaner i try 2 run the hotter the exhaust obviously. aside from the header being scorching hot this thing has no ***** at all. there arent any cats and just 2 make sure the exhaust wasnt too restrictive i removed it at the y pipe. i did try resetting the valves. and rather than using 1 full turn after all the lash was out i used 1/4 turn, it is a hydraulic lifter btw.

oh and the cam is sold through pbm i think eglin is who actually manufactures them. grind # E110036

 

turning the timing up as i said does help the problem. headers arent quite as hot still kinda red, still not nearly the power it should have. and cmon 65 degrees? and it doesnt spark knock? wft? keep the wheels in your heads turnin guys im really hopin to get this figured out!

 

i know its stupid but have you checked for a STRONG spark output from coil.in my experience intake backfires are usually valvetrain related or due to weak secondary output.remote but possible.

 

by strong do you mean. have i measured it in some official way? no. it seems 2 be nice and hot/blue. new coil, new distributor, new cap rotor and wires. its a stock replacement hei 8 pin, the same that would have come on that car in that year.

 

...
I have a friend who recived a defective cam for his BB some time ago. Although he did not let it run long anough for an exhaust to glow, it appeared that with crazy timing advance it would run slightly better. The exchange cam worked well.

 

i think the cam will be my next try. when you say lt1 i think 98 and l8er firebird camaro. define what exactly you mean by lt1 cam?

 

Before swapping the cam out, I would get another timing gun to make sure your gun isnt off. Also I know some motors had the timing mark at the top of the timing chain cover (12 o'clock) and most have it kinda off to the side. You do have the correct balancer for where your timing mark is correct?

 

Sorry, I was thinking the 93-98 LT1 roller cam but that does not work with flat tapped set up.

 

Drop your fuel pressure to around 14 lbs. Give that a try. If your FP spring disallows that purchase one from TopDownSolutions. Regardless of other mechanical issues your FP is crazy high. Is your intial spark timing in .bin matching up to physical setting at dist?

 

i have used another light. and the timing tab is adjustable and i set it myself to TDC with a dial indicator on the #1 piston

 

initial spark does agree with what the light is showing. before i upped the fuel pressure it was having the same problem. the 60 lb stock injectors were running 90% duty cycle at around 4500 rpm and i was still leaning out. hence the 90lb injectors cranked 2 28psi. keep in kind this is not a stock ecu i have complete control of pulse rate so 90lb injectors or not my ecu is tunable so it really shouldnt matter. and still i was having the problem on stock injectors on stock fuel pressure with the stock ecu.

 

know this might sound stupid but i had a similar problem with my tbi,turned out to be the distributer modual.

 

lol didint see the post about the 4 ft flame. yikes!!!! probly not the modual.....

 

When you set initial timing you do have the timing connector disconnected?

90 lbs injs @28 lbs FP at 80% DC at .45 BSFC will support 453 HP. That is a lot of fuel to control at idle and lower loads.

 

ive got a question for you! lol well what intake did you go with and how much power do you have now?