Hi All,
My car has recently started misfiring really bad, it started all of a sudden during a drive a couple months ago. It sounds like a harley now.. when i start the car it just stalls out unless i keep giving it some gas.. and it looks like it runs really rich when i'm giving it gas according to the AFRs

a bit of history...
the motor is built but i'm not 100% sure on the compression (i believe its low compression 9:1). it has upgraded valvetrain, Brian crower cams, skunk2 camgears, upgraded fuel pump (340) with upgraded wiring, stock fuel rail, 850cc injectors. Its supercharged with a vortech supercharger and a 3.8" pulley. upgraded heat exchanger as well.

Last year i had the car in and had a shop check the compression and check if its healthy and install the camgears and retune. it ran amazing after the tune but then my relay for my fuel pump died. i originally thought it was my fuel pump..pulled it out and tested it and it worked fine. so i changed the relay and it ran fine again this year until this misfire.

So far i've done the following
changed spark plugs
tried a new set of coilpacks
had my injectors cleaned and flowtested and those all are fine now.
tried pulling the aftercooler off to see if there was an air blockage and it ran the same
i swapped the fuel pressure regulator with someone elses and it performed slightly better but was still dumping way too much fuel into the motor (rich AFRs).

It really seems like a fuel problem since its running really rich and all the sparkplugs were all black but I can't seem to figure it out.. i really thought it was the FPR

my next thing i'm thinkin is to tap the fuel rail and put a fuel pressure gauge and see if that tells any stories.

Anyone else had similar issues or have any ideas?

 

Try swapping out the o2 sensor, if you have one.

 

What's the car tuned on? How rich is it idling? Is the vacuum reference hooked up to the FPR?

After swapping FPRs and still having the same issue I'd assume fuel pressure was correct. Reading through your description it makes me wonder if you're running a piggyback on the stock ecu and either something got reset or you've got a loose connection. If the car thinks those 850cc injectors are the stock 360cc's it would certainly be dumping a ton of fuel and running terribly.

 

Im running an aem ecu

 

my aem ecu runs off my wideband. So i dont have a stock o2 sensor being used.

 

That sensor can go bad causing similar symptoms that you’re describing. O2 and wideband are similar. Wideband reads a wider range.

 

if the wideband shows its rich wouldn't the ECU compensate? based on the readings it shows its really rich

 

100% o2 sensor, mine goes bad after about 3 years.
Taking out and cleaning on regular basis can prolong it but yeh it will run super super rich if it fails.

 

This sounds almost exactly like the problem I had. It ended up being overheated/burnt wires leading into the fuel pump hanger. I replaced the fuel pump relay three times and replaced the fuel pump twice which every time led to a short and temporary fix. My idle would fluctuate up and down when nothing was altered to the tune. After closer inspection I noticed the connecting prongs both on top of the fuel pump hanger and inside where the actual pump connects to were burnt. It weakened the connection to the point it was probably fuxing with the voltage going to and from the pump which would cause your tune to run rich/lean and give very inconsistent afr's.

Consider upgrading your wires directly wiring the pump to the battery. My wires overheated even using the upgraded kit offered from science of speed. Since then I bought a new fuel pump hanger, changed the wires out to even bigger wires and quadruple checked to make sure my crimps were perfectly done.

 

Also just to add, i also got rid of my fuel pressure gauge on the fuel rail because it had the tiniest leak which fuxed up my fuel pressure and was also causing all these weird afr fluctuations that took forever to diagnose. You really only need to check your fuel pressure once then no real need for it.