C5natie

iTrader: (1)

Hey there. Im really stumped right now with this issue Im having with my C5. First of all let me list my mods.

2002 C5 Coupe
LS3, stock crank with forged pistons and rods 10:1cr
Stock LS3 heads with exhaust ports ported
Stock LS3 intake manifold
Vortech V2 8psi
Fuel system is dual in-tank Walbro 255lph
60lb injectors
LPE conversion box (working good, Light always green)
Closed loop speed density tune with 2 bar map

Heres the story...I rebuilt the motor after I broke the ringland on piston #7. Everything was basically the same except the pistons dropped compression from 10.5:1(L92 pistons) to 10.0:1cr. So the tune stayed the same. On the initial startup, we idled the engine at 3000rpm for 15min per the builders instructions. Everything was good, no leaks. Then we changed the oil of course. A few days later we start it up and after it warmed up it started missing really bad and was idling super rich, 10.0afr. Plugs got fouled, Autolite 103, so I changed the plugs to NGKTR6. The problem didnt go away. Then one day while idling in the shop bay it died. No fuel. Checked fuel pressure, nothing. Looked under the car and found that the weather pack connector from the main harness to the fuel pumps jumper harness had burned up, got too hot. Looked like the shop that had installed the supercharger and fuel system modified the stock harness vs using a hotwire kit. Looked like the small 18g wire couldnt handle the amperage. So I installed a hotwire kit from Caspers and replaced the oem harness. The car stared right up. It idled good when cold on the rack but as soon as it warmed up it went way rich and missing like crazy again. All temps are good, all relays and fuses are good.

So today we were trying to troubleshoot the issue. What was weird was that the last few days it was running way rich but a few times today it went way lean. Hooked up the pressure guage to the fuel rail. We got 64psi with the key on and just over 70psi while running. Also whats strange is it both was rich and lean with this fuel pressure. Something tells me both fuel pumps are always running but we didnt touch them and the car ran good before the rebuild. Also this issue existed with and without the hotwire kit. When you rev it up, say past 3000rpm, it sounds good and doesnt miss. Cant figure out whats going on here. The car has a closed loop speed density tune. I dont know if the O2's are an issue, maybe we criss crossed them, or the map sensor is going out. Idk, Im reaching here.

Plans are to hook up a scanner to see what the O2 and map sensors are doing. Also gonna disconnect the O2's to see if anything changes. The battery on the car was dead for weeks and we just replaced it. Can something like a tune or memory be wiped out? Not sure what else to do or check. I havent done much tuning and Ive never encountered this problem. I would like to figure this in house vs looking for a tuner. Everything should be exactly the same as before the rebuild so i dont know what could have changed. Any help would be greatly appreciated. Oh and the car is still using the stock fuel pressure regulator. I believe its on the side of the rail by the fuel tank.

C5natie

iTrader: (1)

No codes either. Only have an old one for the maf thats been there since the sd tune.

subeone

iTrader: (5)

disconnect the o2 sensors. it seems it runs better in open loop as per say that once it warms up it starts acting up.

C5natie

iTrader: (1)

Im going to do that tomorrow. Wasnt sure it would act that weird due to the o2's.

C5natie

iTrader: (1)

Took a cold start video. Idles good when cold.

motion427

iTrader: (1)

Check the STFT with a scanner.if one side goes lean and the other goes rich,the o2 wiring are crossed,will run like crap.
Usually the fuel pressure should be at 58 with 1 pump,the second pump should be set with a hobb switch to kick in under boost,let say 2-3 psi.

Old Geezer

iTrader: (3)

Running 2 pumps thru a stock filter/reg??????????

C5natie

iTrader: (1)

I'lllook for that. Also I know that's how the pumps are supposed to be setup but since day one I've only seen this hotwire setup. Unless they never installed 2 pumps. Lol. Wait hmm...

C5natie

iTrader: (1)

That's what I see under the car

motion427

iTrader: (1)

So your is a dual in tank setup,stock regulator and lines?
Could be wrong,but I think you should have 58psi at the rail.

The fuel system that I was talking about would be something from ECS or A&A

danieloneil01

My fuel pressure is around 64psi idling with the racetronix harness and pump. When I had the BAP hooked up wrong it made my FP 70 psi at the rail idling since it was running. I would start the scanner from cold to warm up while idling and see what the fuel trims and O2s are doing.

C5natie

iTrader: (1)

Thnx for the help guys. Turns out the o2's were criss crossed. They were fouled up too so i just replaced them under warranty. She runs great now. Seems like the relay on the hotwire kit closes when the ecu commands more fuel. Then the pumps see the added voltage. The harness to the pump has power ground and a signal to the ecu. At least that's how i understand it. Afr's are great so far. Idles at 14.7. Never thought the o2's would reek so much havoc.