5.7 hemi idle and backfire

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1967GTXhemi

1967GTXhemi

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i was on my way to a cruise and my 67 gtx 5.7 hemi suddenly started idling very low and rough and slight backfire can anyone help me investigate this issue. its a new crate motor with less than 300 miles on it the fuel pump in intank and it has the corvette fuel regulator on it thanks
 
When do you notice it backfiring the most? Have you checked the spark plugs? What controller are you using and does it have error codes?

Please provide some more information.

Thanks,

Riddler
 
thanks for the reply riddler i notice the backfire mostly when i rev the motor; i have the plugs out right now and im using a reprogrammed ecu from hotwire auto. it only seems to backfire thru one side also it seems to be missing under idle and the idle is really low when i put it in drive it dies
 
Ok that's a lot of error codes.. lets see what they are?

P0038 - Oxygen Sensor (Heating Element)
P0053 - Same as above.
P0073 - Same as above.
P0043 - EVAP Purge Solenoid Valve 1 Control CKT
P0463 - Fuel Level Sensor Circuit High Voltage
P0480 - Cooling Fan Relay 1 Control Circuit
P0499 - EVAP System failure.

So lets start off with O2 sensor. I'm guessing the issue your having is a bad O2 sensor which is low idling your motor. I'd start with changing the upper O2 on the side that having issues.

The rest look to be emissions related. EVAP you prolly don't have so it could be shut off in the PCM. Not sure on the Fuel Level or Cooling Fan. Prolly both could of been eliminated when the PCM was flashed.

Riddler
 
Riddler said:
Ok that's a lot of error codes.. lets see what they are?

P0038 - Oxygen Sensor (Heating Element)
P0053 - Same as above.
P0073 - Same as above.
P0043 - EVAP Purge Solenoid Valve 1 Control CKT
P0463 - Fuel Level Sensor Circuit High Voltage
P0480 - Cooling Fan Relay 1 Control Circuit
P0499 - EVAP System failure.

So lets start off with O2 sensor. I'm guessing the issue your having is a bad O2 sensor which is low idling your motor. I'd start with changing the upper O2 on the side that having issues.

The rest look to be emissions related. EVAP you prolly don't have so it could be shut off in the PCM. Not sure on the Fuel Level or Cooling Fan. Prolly both could of been eliminated when the PCM was flashed.

Riddler
Click to expand...

Breaking down the 3 O2 sensor codes.

P0038 - Oxygen Sensor Heater Circuit High Voltage (Bank 1, Sensor 2)
P0053 - HO2S Heater Resistance (Bank 1, Sensor 1)
P0073 - Ambient Air Temperature Sensor Circuit High

Might have some wiring issues. What harness? I'd still try a new O2 sensor.

Riddler
 
thanks riddler i need to figure out where the o2 sensor on the right side is located and then which one to purchase my motor is a crate motor from a 2008 300c so im guessing that is what i should order the harness is also from hotwire auto
 
im fairly certain its no a wiring issue the car has been built for about three years and has always ran extrememly well and it was running great for about five miles when this issue occurred
 
ok i have located the o2 sensors and i only have the upstream ones on each exhaust so im going to replace both
 
Intake backfire, or exhaust?
I think you have an intake valve sticking or some lifter ain't liftin, or you hadda valve spring failure.
Does the engine have the MDS and variable cam timing stuff?
Is it hard to start?
 
no Dart it starts easily and the backfire is in the exhaust; Riddler i just replace both o2 sensors and im replacing all the plugs then i can try it and see if that solves the issue thanks for all the help
 
GOOD NEWS replaced the o2sensors and i came back to life thanks riddler and dart for all the help have a great day guys
 
well let me see if i can upload a pic for ya

10 004.JPG


car show 2013 011.JPG
 
i have changed some stuff since these photos it has a polished 6.1 manifold polished valve covers and coil covers now

car show 2013 009.JPG
 
Oh that's pretty. I really need to get a wiring harness and PCM flash and hear mine roar!

Glad we could narrow down the issues and get it fixed.

Riddler
 
Riddler you are very kind i appreciate this site it has been invaluable during the construction of my car. i have been watching your progress and i hope you get it done soon it will be a monster
 
So I'm guessing with the O2s went off-line, the ECU commanded a limp-in mode, went rich, and sooted up the plugs.Does that sound reasonable? Or do you suppose the engine was rich to start with and sooted up the O2s first.
The reason I wonder is; how long before it happens again?
Should the fueling be changed, or should the limp-in program be changed?
Or was it a fluke, never to be seen again.....
 
AJ i have thought about that same issue im not sure what happened it was running fine and just suddenly started missing and small exhaust backfires until i got it home about five miles or so. im thinking it may be too rich but im not familiar enough with the diablo system to know how to lean it up and i dont want to make it too lean that could be worse. the o2 sensors were not that bad when i removed them im kinda hoping it just might have been a sensor that took a dump and wont happen again but who knows
 
SSSSSSSSSSSSSSSSSSSSSssuper nice.

Since all plugs were sooted up, Ima thinking there is rich running issue that needs cleaning up. If you don't have an A/F on it,I would pop the plugs again after a short trip and see whats going on.
Sooted plugs do exactly what you describe, and are often irrecoverable.

It is also possible I suppose, that an underpowered ignition system could do that.. but I'm pretty sure I see COPs under that hood.
 
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