Put in a 408 stroker in last November, having a couple big issues with it, it seems pretty gutless compared to the mildly modified 360 I had in before, so I started testing everything to try and come up with an answer to why? The fuel pressure stays at 50psi at all times I compression tested it had 200psi across every cylinder. I did an injector shutdown test and every cylinder responded the same way. I have a snap on scanner and plugged it in and looked at all the sensor data everything appears normal as far as I can see. I reset the fuel sync with it also. Iv tried a bunch of different tunes on it and nothing has helped so far. The air fuel guage I have in it jumps all over the map. I thought it could be the guage so I replaced the whole assembly with the same results. To see the engine specs check out my other thread.

Some engine stuff:

eagle forged rotating assembly with i beam rods
comp cams camshaft part number 20-604-9
edelbrock aluminum heads
gibson stainless ceramic headers part number GP301S-C
hughes airgap intake manifold
fms 24# fuel injectors
march underdrive pulleys
sct tuner with a custom tune from hemifever

 

what pcm tuning method are you using? SCT or other? is it a 408 tune?

^everything you listed above is an excellent reading, and obviously not the cause of your problem. its probably the tune - either timing or fuel flow curve or both. your air/fuel gauge jumping around is probably indicating something screwy with the engine tune.

 

Unplug front O2 sensor, and see if things don't stabilize, and if they do, what your mixture looks like at steady-state cruise.

 

Some jumping on A/F is normal as the PCM makes adjustments. When I first installed mine it kind of worried me. If it pegs one way and never moves, there is a problem.

+1 on unplugging upstream and see what happens.

 

Way too many variables. For all we know you could still have a stock heads and stock cam, or some other bad combination of parts.

More details.

 

I have a 408 with about 30,000 klms on it. Other than some lean issues to start off with and some rotor and dirty fuel problems mine has been very reliable. I am running about 10.5 compression with big valve R/T heads(60cc chambers) and a stock cam with 1.7 RR's.
Many people have told me that the engine is over compressed with the stock cam. I am running 30lb Accel injectors with no black smoke at W.O.T. or any other time. It sounds very docile and is a daily driver. But when I hit the go pedal from stop it is a tire shredder.(posi rear)
I suppose what I am getting to is if some engine builders say my engine is over compressed ( I have 180lb cylinder pressure), what would they say about 200lbs per cylinder you have? Average pressures are around 150 to 160lbs. I have been told various times to get a longer duration cam with more lift. I don't know your engine but it could be something for you to look at.

 

It's sct tuned...it has ported edelbrock aluminum heads and a comp cam like I said the engine specs are in my other thread....ill try unplugging the front O2 sensor tomorrow morning and see what happens. I'm hoping its not over compressed that would be an expensive lesson...Iv tried a few different tunes on it and so far no luck...it also hangs at idle quite abit while coasting I don't know if this is a symptom or just because of the cam.

 

To see the engine specs check out my other thread.

Link ???

 

eagle forged rotating assembly with i beam rods
comp cams camshaft part number 20-604-9
edelbrock aluminum heads
gibson stainless ceramic headers part number GP301S-C
hughes airgap intake manifold
fms 24# fuel injectors
march underdrive pulleys
sct tuner with a custom tune from hemifever
Comp cams rockers and hardened pushrods

 

Get a 4BBL M1, and you didn't say what TB...Get a 58 F&B.
Gibson shorties aren't much better than a stock exhaust, you're choking that thing on both ends.

The small cam is hurting you too, you have the mods for a mild 360 on a 408.

Compression Ratio?