intermittent random misfires
Thread Starter
New Member
Joined: 10-06-2017
Posts: 15
From: Toledo, OH
intermittent random misfires
Hoping someone may have a guess as to how to proceed. 2009 HHR SS (bone stock), approx. 56k miles. Car runs great, good acceleration and gas mileage. Even though it has no "noticeable" misfires, it will set codes P0300 (random misfire) as well as P0301, P0302, P0303 and P0304. No apparent pattern that I can discern to the code set, may run without code set for a week, then will set the codes every other day. Codes will sometimes also reset themselves after a few trips without me resetting them through the OBDII scanner.
Chevy dealer did the typical parts swaps:
New Plugs.
New Coils.
New VVT solenoids (intake and exhaust).
Dealer cleaned injectors and fuel rail.
New MAF sensor.
New Air Filter.
Told me to run a couple of cans of Seafoam through it. Did that.
This is the freeze frame data from the current P0300 cel:
DTCFRZF P0300
FUELSYS1 CL
LOAD_PCT(%) 23.5
ETC(C) 90.0
SHRTFT1 1.6
LONGFT1 3.9
MAP(KPA) 29
RPM(/MIN) 2605
VSS(KM/H) 88
SPARKADV 41
IAT(C) 17
MAF(G/S) 8.94
TP(%) 26.7
FRP(KPA) 4660
EVAP_PCT(%) 49.0
FLI(%) 14.1
BARO(KPA) 98
VPWR(V) 14.32
LOAD_ABS(%) 20.4
EQ_RAT 0.999
TP_R(%) 12.5
AAT(C) 11
TP_B(%) 27.11
APP_D(%) 21.2
APP_E(%) 20.8
TAC_PCT(%) 18.4
Any suggestions would be greatly appreciated.
Chevy dealer did the typical parts swaps:
New Plugs.
New Coils.
New VVT solenoids (intake and exhaust).
Dealer cleaned injectors and fuel rail.
New MAF sensor.
New Air Filter.
Told me to run a couple of cans of Seafoam through it. Did that.
This is the freeze frame data from the current P0300 cel:
DTCFRZF P0300
FUELSYS1 CL
LOAD_PCT(%) 23.5
ETC(C) 90.0
SHRTFT1 1.6
LONGFT1 3.9
MAP(KPA) 29
RPM(/MIN) 2605
VSS(KM/H) 88
SPARKADV 41
IAT(C) 17
MAF(G/S) 8.94
TP(%) 26.7
FRP(KPA) 4660
EVAP_PCT(%) 49.0
FLI(%) 14.1
BARO(KPA) 98
VPWR(V) 14.32
LOAD_ABS(%) 20.4
EQ_RAT 0.999
TP_R(%) 12.5
AAT(C) 11
TP_B(%) 27.11
APP_D(%) 21.2
APP_E(%) 20.8
TAC_PCT(%) 18.4
Any suggestions would be greatly appreciated.
Moderator
Joined: 01-23-2009
Posts: 26,484
From: Fredericksburg,VA
Don't go to that chevy dealer. There was absolutely no reason to replace any of those parts. Well, maybe the air filter.
Everything else was actual thievery.
Do you mean that you have P0300, P0301, P0302, P0303 and P0304 all at the same time? Or do the cylinders change each time?
P0300 does not mean exactly what you think. It means that the misfire doesn't happen often enough to identify which cylinder.
The obvious first tests to run would be compression and leakdown and fuel pressure.
P0300 and it's brothers will always reset after a cold start session without the misfire.
If you do indeed have all 4 cylinders misfiring on occasions, my first suspect is fuel pressure. i.e.: one or both of the pumps.
After that coking valves.
Everything else was actual thievery.
Do you mean that you have P0300, P0301, P0302, P0303 and P0304 all at the same time? Or do the cylinders change each time?
P0300 does not mean exactly what you think. It means that the misfire doesn't happen often enough to identify which cylinder.
The obvious first tests to run would be compression and leakdown and fuel pressure.
P0300 and it's brothers will always reset after a cold start session without the misfire.
If you do indeed have all 4 cylinders misfiring on occasions, my first suspect is fuel pressure. i.e.: one or both of the pumps.
After that coking valves.
Thread Starter
New Member
Joined: 10-06-2017
Posts: 15
From: Toledo, OH
Donbrew,
Thank You for your quick response.
Yes all 5 codes set at the same time. Is it viable to check fuel pressure through the obdii scanner looking at he FRP(KPA) variable? Or does a direct tester need to be hooked up?
Thank You for your quick response.
Yes all 5 codes set at the same time. Is it viable to check fuel pressure through the obdii scanner looking at he FRP(KPA) variable? Or does a direct tester need to be hooked up?
Moderator
Joined: 01-23-2009
Posts: 26,484
From: Fredericksburg,VA
OBD2 will give you the rail pressure, the final pressure, but not the low pressure pump.
I really don't know much about the SS.
All 4 cylinders misfiring sure does sound like fuel supply. Maybe if you can monitor a real time fuel rail pressure and correlate it to the misfire events.
exactly like a freeze frame
Except that:
The high pressure pump is variable; controlled by the ECM with input from the FRP sensor, So, the pump or the sensor or the wiring in the feedback loop could cause a problem.
Hopefully one of the turbo guys will pop in.
I really don't know much about the SS.
All 4 cylinders misfiring sure does sound like fuel supply. Maybe if you can monitor a real time fuel rail pressure and correlate it to the misfire events.
exactly like a freeze frameExcept that:
The high pressure pump is variable; controlled by the ECM with input from the FRP sensor, So, the pump or the sensor or the wiring in the feedback loop could cause a problem.
Hopefully one of the turbo guys will pop in.
Moderator
Joined: 05-01-2014
Posts: 8,509
From: California
Donbrew is on the money again. Without any other codes, you have to look at basics - spark, fuel, air, mechanical. Spark has been mostly ruled out by replacing plugs and coil packs. Not likely air. That leaves a fuel pressure test and compression test, possibly a follow-up leak down test.
Maybe some history? How long have you owned it? has it been run low on fuel often? Has it had regular oil and filter changes?
Also agree that dealer doesn't know how to diagnose.
Maybe some history? How long have you owned it? has it been run low on fuel often? Has it had regular oil and filter changes?
Also agree that dealer doesn't know how to diagnose.
Moderator
Joined: 01-23-2009
Posts: 26,484
From: Fredericksburg,VA
I'm always amazed at the high school kids that are in the SAE contests every year. Sorry they never make it to GM shops.
The guys at your shop must have flunked out of high school shop class. But who cares, the shop makes lots of money throwing irrelevant parts around.
The guys at your shop must have flunked out of high school shop class. But who cares, the shop makes lots of money throwing irrelevant parts around.
Thread Starter
New Member
Joined: 10-06-2017
Posts: 15
From: Toledo, OH
Not much history. My wife has been a little jealous of my Red SS so I bought her this one 4 months ago. We always run 91 octane in it, and we take good care of it. Changed oil and filter when we got it and the oil has remained suspiciously clean since then. Not burning any oil.
Car has 55k miles. Returned to Chevy dealer to ***** about the no diagnosis of this problem, they did ask if the crank sensor, engine or ecm had been changed out by pervious owner. His reasoning was that perhaps a crank variation relearn may need to be performed (the misfires may be just a calibration issue of the sensor). I would hate to take this back to this dealer or start over at another. What do you guys think?Once again, Thank You for your replies.
Car has 55k miles. Returned to Chevy dealer to ***** about the no diagnosis of this problem, they did ask if the crank sensor, engine or ecm had been changed out by pervious owner. His reasoning was that perhaps a crank variation relearn may need to be performed (the misfires may be just a calibration issue of the sensor). I would hate to take this back to this dealer or start over at another. What do you guys think?Once again, Thank You for your replies.
Moderator
Joined: 01-23-2009
Posts: 26,484
From: Fredericksburg,VA
Why go to a chevy dealer at all? They obviously don't know anything more than you do.
Crankshaft relearn would throw a code. Get away from those idiots and don't look back! They seem to be totally unaware of OBD2. They are either totally incompetent or actual criminals.
You have not mentioned any other CELs. Everything they have sold you would have thrown it's own code if bad.
Are you sure it is "bone stock"? If it has GMTU the crimped wire connections are suspect. Is there a "91 octane REQUIRED" label on the fuel filler door?
The wires for the sensor near the A/C sometimes bumps into the A/C.
Crankshaft relearn would throw a code. Get away from those idiots and don't look back! They seem to be totally unaware of OBD2. They are either totally incompetent or actual criminals.
You have not mentioned any other CELs. Everything they have sold you would have thrown it's own code if bad.
Are you sure it is "bone stock"? If it has GMTU the crimped wire connections are suspect. Is there a "91 octane REQUIRED" label on the fuel filler door?
The wires for the sensor near the A/C sometimes bumps into the A/C.
