Misfires on all cylinders only in cold start mode - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

Nutbutt · 10-20-2013, 07:27 PM

Getting misfire codes on all cylinders when car is started and in cold start/catalytic warm up mode. As soon as it drops out of this mode and idle drops, immediately no more misfires and car runs fantastic at idle or WOT. Not a misfire at all. If I start it up and the car is warm enough to not enter warmup it's also fine.
Is there a specific sensor that effects the timing when in warmup mode and system is open loop ? MAF was changed and all plugs removed and look great !
Looking at engine temp, and iat and both look good.

Sikoriko · 10-20-2013, 07:48 PM

Was the car actually misfiring?

TooCool5 · 10-20-2013, 07:57 PM

Try a bottle of Dry gas, ethanol is Hydro-phonic and collects water in the tank.

Nutbutt · 10-20-2013, 08:43 PM

Quote:

Originally Posted by Sikoriko

Was the car actually misfiring?

Yes, ran like top fuel dragster with a hairy cam. The obd shows the counters counting up. But as soon as the cold start is ended car immediately, and I do mean like someone flipped a switch all the misfires stop !
I get misfire codes on all cylinders and multiple misfire code.
Definitely not a gas issue. If I reset the ECU the first cold start mode is good. Then the ECU seem to be learning and next cold start it gets a little worse. By three cold start modes the misfires are back.
I am leaning to a sensor only used to control timing during open loop cold start is driving the timing off ???? O2 sensor ? Coolant sensor ? Engine temp sensor ?
Thought maybe MAF IAT sensor but I replaced the MAF.
Once off cold start mode the timing is perfect. The car performs great. Also may try go get a tune without the cold start /cat warmup disabled but I feel like I'm covering up another problem.

MagnumForceGB · 10-20-2013, 09:13 PM

What are your LTFT's at start up? You may be running too rich at that point.

Nutbutt · 10-20-2013, 09:35 PM

I'll check the LTFT, I thought they were slight negative. But there has to be something driving the ECU when in the open loop cold start mode. I have been doing more searching and it seems the coolant temp sensor drives a lot of the tune during cold start. Need to figure out where on the block it's located and see if this could be an issue.

menendez1293 · 10-20-2013, 11:25 PM

Wired it wasn't on my Camaro but on my cruze Eco I experienced something very similar. It ended up being a cracked spark plug and the coil pack had broken on two of the four cylinders so for some reason only at cold start it would misfire but not enough to trip the computer.

Do you by any chance have a AFR gauge?

Nutbutt · 10-21-2013, 08:26 AM

I am throwing misfire codes on all cylinders. CEL is lit. The amazing this is that as soon as the car jumps out of cold start mode all misfire stop. No AFR on the car. For a broken plug or coil the stopping of misfires would be this repeatable on stopping when I get out of warmup.
Bringing the car in later this week if I can't figure it out. I wonder how they will react to the SC sitting there

Sikoriko · 10-21-2013, 03:02 PM

could be an O2? Do you have the new MAF senser in? Can you put in the old one back in and see what happens? Or did it start with the old MAF senser in?

Sikoriko · 10-21-2013, 03:05 PM

Cold = Crappy, Warm= Smooth, sounds like a Ford.

Nutbutt · 10-21-2013, 04:28 PM

Started with old MAF, cleaned it, still the problem. I replaced with a new one I had the mechanic at dealership ohm out to make sure it's within spec.
I was thinking O2 heater in the sensor during cold start. But I just got off the phone with a GM tech who was reluctant to talk but said during cold start the MAF and O2 is not used for scheduling. During warmup the coolant temp sensor is used.
Since I'm at work I can't check but does anyone know where the coolant sensor is located on the LLT block ??

Nutbutt · 10-22-2013, 08:57 AM

Anyone know where the coolant sensor is located on the LLT.
I'm use to seeing it next to where the coolant hose enters the block. Couldn't find it ?

Sikoriko · 10-22-2013, 03:03 PM

Most are located on the heads.

Ventmaster · 10-22-2013, 04:42 PM

Is it possible an air leak is causing the misfires and when things warm up and expand a bit you're regaining a seal?

I'd try re-torqueing the intake manifold just to be sure.

More likely you're right about it being electronic

but sometimes we get lucky and its something more simple.

Keep us posted.

10-20-2013, 07:27 PM	#1
Nutbutt Drives: 2011 RJT 2LT/RS Convertible Join Date: Nov 2009 Location: Western Massachusetts Posts: 3,381 View My Garage	Misfires on all cylinders only in cold start mode Getting misfire codes on all cylinders when car is started and in cold start/catalytic warm up mode. As soon as it drops out of this mode and idle drops, immediately no more misfires and car runs fantastic at idle or WOT. Not a misfire at all. If I start it up and the car is warm enough to not enter warmup it's also fine. Is there a specific sensor that effects the timing when in warmup mode and system is open loop ? MAF was changed and all plugs removed and look great ! Looking at engine temp, and iat and both look good. __________________ 1st IPF Supercharged 2011 2LT/RS RJT Convertible

10-20-2013, 07:57 PM	#3
TooCool5 Drives: 2010 Camaro 1LS 3.6 LLT V6 325 HP Join Date: May 2009 Location: LS Posts: 4,244 View My Garage	Try a bottle of Dry gas, ethanol is Hydro-phonic and collects water in the tank. __________________ 2010 Camaro Auto, Inferno Orange, Titanium Interior, Gearhead Wheels AIRAID CAI

10-20-2013, 09:13 PM	#5
MagnumForceGB Drives: Fastest 2010 Camaro V6 Join Date: Apr 2010 Location: Newcastle, OK Posts: 3,571 View My Garage	What are your LTFT's at start up? You may be running too rich at that point. __________________ Camaro V6 = 11.268 @ 120.11

10-20-2013, 09:35 PM	#6
Nutbutt Drives: 2011 RJT 2LT/RS Convertible Join Date: Nov 2009 Location: Western Massachusetts Posts: 3,381 View My Garage	I'll check the LTFT, I thought they were slight negative. But there has to be something driving the ECU when in the open loop cold start mode. I have been doing more searching and it seems the coolant temp sensor drives a lot of the tune during cold start. Need to figure out where on the block it's located and see if this could be an issue. __________________ 1st IPF Supercharged 2011 2LT/RS RJT Convertible

10-21-2013, 08:26 AM	#8
Nutbutt Drives: 2011 RJT 2LT/RS Convertible Join Date: Nov 2009 Location: Western Massachusetts Posts: 3,381 View My Garage	I am throwing misfire codes on all cylinders. CEL is lit. The amazing this is that as soon as the car jumps out of cold start mode all misfire stop. No AFR on the car. For a broken plug or coil the stopping of misfires would be this repeatable on stopping when I get out of warmup. Bringing the car in later this week if I can't figure it out. I wonder how they will react to the SC sitting there __________________ 1st IPF Supercharged 2011 2LT/RS RJT Convertible

10-20-2013, 07:48 PM	#2
Sikoriko Drives: 2011 V6 IOM Join Date: Jul 2012 Location: San Diego Posts: 1,385 View My Garage	Was the car actually misfiring?

10-20-2013, 11:25 PM	#7
menendez1293 Emerald Coast Camaros Drives: 2010 Camaro 2LT/RS M6 Join Date: Nov 2009 Location: Tallahassee FL Posts: 9,686 View My Garage	Wired it wasn't on my Camaro but on my cruze Eco I experienced something very similar. It ended up being a cracked spark plug and the coil pack had broken on two of the four cylinders so for some reason only at cold start it would misfire but not enough to trip the computer. Do you by any chance have a AFR gauge?

10-21-2013, 03:02 PM	#9
Sikoriko Drives: 2011 V6 IOM Join Date: Jul 2012 Location: San Diego Posts: 1,385 View My Garage	could be an O2? Do you have the new MAF senser in? Can you put in the old one back in and see what happens? Or did it start with the old MAF senser in?

10-21-2013, 03:05 PM	#10
Sikoriko Drives: 2011 V6 IOM Join Date: Jul 2012 Location: San Diego Posts: 1,385 View My Garage	Cold = Crappy, Warm= Smooth, sounds like a Ford.

10-21-2013, 04:28 PM	#11
Nutbutt Drives: 2011 RJT 2LT/RS Convertible Join Date: Nov 2009 Location: Western Massachusetts Posts: 3,381 View My Garage	Started with old MAF, cleaned it, still the problem. I replaced with a new one I had the mechanic at dealership ohm out to make sure it's within spec. I was thinking O2 heater in the sensor during cold start. But I just got off the phone with a GM tech who was reluctant to talk but said during cold start the MAF and O2 is not used for scheduling. During warmup the coolant temp sensor is used. Since I'm at work I can't check but does anyone know where the coolant sensor is located on the LLT block ?? __________________ 1st IPF Supercharged 2011 2LT/RS RJT Convertible

10-22-2013, 08:57 AM	#12
Nutbutt Drives: 2011 RJT 2LT/RS Convertible Join Date: Nov 2009 Location: Western Massachusetts Posts: 3,381 View My Garage	Anyone know where the coolant sensor is located on the LLT. I'm use to seeing it next to where the coolant hose enters the block. Couldn't find it ? __________________ 1st IPF Supercharged 2011 2LT/RS RJT Convertible

10-22-2013, 03:03 PM	#13
Sikoriko Drives: 2011 V6 IOM Join Date: Jul 2012 Location: San Diego Posts: 1,385 View My Garage	Most are located on the heads.

10-22-2013, 04:42 PM	#14
Ventmaster Drives: 2017 1SS 6spd Join Date: Jan 2011 Location: Utah Posts: 3,016	Is it possible an air leak is causing the misfires and when things warm up and expand a bit you're regaining a seal? I'd try re-torqueing the intake manifold just to be sure. More likely you're right about it being electronic but sometimes we get lucky and its something more simple. Keep us posted.