I got my car out of storage, zipped in a bag with desiccant, and it's stumbling just off idle, running rough, then cleans up. Sometimes it's ok, sometimes not.

Smells rich at the back end. I can't id a single cyl miss. No CEL, but get a misfire code. Added fresh gas and a bottle of Techron, ran it up to high rpm and load to clean it out, no love yet.

Long term fuel trims show at 25% - does that mean rich or lean?
Short terms bouncing around 10%

Battery was disconnected for a time, started fine - no clue where to turn, was running perfect when I put the car away....

ideas?

 

I would start simple and disconnect the battery for a minute or two and reconnect. Any signs of mice under the fuel rail covers? Have you pulled the codes, is it one particular cylinder that is not firing? Have you had it out on the road, can you drive out the tank and re-fill with fresh fuel?

Mine is going to be "de-bagged" in the next couple of weeks, and this year I didn't top the tank as usual prior to storage. Hoping I don't have issues as well when I start it.

 

I did have the battery disconnected for about an hour. No mice anywhere, it was bagged. The code I got was just a misfire code, not cyl specific, but I had already been dicking around with it disconnecting injectors trying to isolate the miss. I did have it on the road, did put fresh gas in it (I parked it with less than half a tank). I'm going to run it again today, and then probably pull the plugs and see if I can isolate one cyl.

I'm thinking dribbling or bad spray from an injector, or maybe plug/wire or coil.

Sure wasn't what I expected on my first ride....

 

Be interested in what you find....just in case

 

Check the PCV Vacuum lines and the PCV boot. They are well known to rot and cause a severe vacuum leak.

Its on the passengers side of the intake manifold just aft of the TB

 

Get a different scanner on it and see which cylinder is misfiring, the DIC only shows P0300, not the 301-308 codes

 

I checked the PCV lines, looked fine, then I thought about my catch can, which might have had water in it and cracked. Turned the petcock, nothing came out. Looked with a mirror, nothing obvious. Took the bottom off the can and a bunch of oil came out, all over the AC compressor - damn!. Inspected everything, no cracks.

Pulled the codes with my OBD reader and still got the P0300 - random misfire code and also a P1626 which is the theft disable code - no idea where that came from.

Will be pulling the air cleaner and mass flow sensor tonight to take a look.

Is the P0300 code valid, is there another code reader that would give me some point at a particular cyl? right now I'm looking at generic stuff and grasping at straws.

Car is getting worse!

 

checked air cleaner for possible critters, no, tho was dirty (KN with a Vararam).
Mass flow sensor looked fine, hosed it off with MAF cleaner, also cleaned my Haltech screen.

Checked everything you can see - all fine.
Reinstalled the stock Predator tune.

Started it and it seems the same, won't know until I drive it and get the fuel trims reset.

 

P1626 Info for a 2004 model Year Vette
--------------------------------------------------------------------------------

DTC P1626
Circuit Description
The body control module (BCM) produces the theft deterrent crank relay and fuel enable signal when ignition is ON and the proper ignition code voltage value is detected. The powertrain control module (PCM) monitors the fuel enable signal during crank. If the proper signal is present on the Class 2 Serial Data Circuit, the PCM enables the fuel delivery in order to allow the engine to start. If the PCM determines that the fuel enable signal is not present or incorrect while the engine is running, DTC P1626 is set. The engine continues to start and run as long as DTC P1626 is stored. If the problem affects inputs to the VTD signal, the starter motor may be disabled.

Conditions for Running the DTC
The engine is running.

Conditions for Setting the DTC
The PCM has detected a loss of the state of health serial data message from the theft deterrent system.

Action Taken When the DTC Sets
• The body control module (BCM) send a class to message to the instrument panel cluster (IPC) to illuminate the SECURITY indicator.

• The powertrain control module (PCM) will not illuminate the malfunction indicator lamp (MIL).

• The PCM will store conditions which were present when the DTC set as failure records data only. This information will not be stored as freeze frame data.

Conditions for Clearing the DTC
• A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• The DTC can be cleared by using a scan tool.

Step
Action
Yes
No

1
Did you perform the Theft Deterrent Diagnostic System Check?
Go to Step 2
Go to Diagnostic System Check - Theft Deterrent

2
Important: If a loss of DLC data has already been diagnosed, clear this DTC and continue diagnosis with Diagnostic System Check - Engine Controls in Engine Controls - 5.7L.

Is DTC P1631 set as a current code?
Go to Diagnostic Trouble Code (DTC) List
Go to Step 3

3
Inspect for poor connections at the harness connector of the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 5
Go to Step 4

4
Important: The replacement powertrain control module (PCM) must be programmed. Refer to Programming Theft Deterrent System Components .

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 5.7L.

Did you complete the replacement?
Go to Step 5
--

5
Use the scan tool in order to clear the DTCs.
Operate the vehicle within the conditions for Running the DTC as specified in the supporting text.
Does the DTC reset?

 

For a Stock 2004 Model year vette

DTC P0300
System Description
The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic converter (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.

Conditions for Running the DTC
• DTC P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0125, P0128, P0335, P0336, P0341, P0342, P0343, P0410, P0500, P0502, P0503, P1114, P1115, P1120, and P1220 are not set.

• The engine speed is between 425-3,000 RPM.

• The ignition voltage is between 10-18 volts.

• The engine coolant temperature (ECT) is between -7 and +130°C (19-266°F).

• The fuel level is more than 10 percent.

• The throttle angle is steady within 1 percent.

• The antilock brake system (ABS) and the traction control system are not active.

• The transmission is not changing gears.

• The A/C clutch is not changing states.

• The PCM is not in fuel shut-off or decel fuel cut-off mode.

• The PCM is not receiving a rough road signal.

Conditions for Setting the DTC
The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.

Action Taken When the DTC Sets
• The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

• The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
• Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration:

- Variable thickness brake rotors--Refer to Symptoms - Hydraulic Brakes in Hydraulic Brakes.

- Drive shaft not balanced--Refer to Vibration Analysis - Driveline in Vibration Diagnosis and Correction.

- Worn or damaged accessory drive belt--Refer to Base Engine Misfire without Internal Engine Noises in Engine Mechanical.

• There may be more or less cylinders actually misfiring than indicated by the scan tool.

• Spray water on the secondary ignition components using a spray bottle. Look and listen for arcing or misfiring.

• If there are multiple misfires on only one bank, inspect the fuel injector and ignition coil, power and ground circuits for that bank. Refer to Engine Controls Schematics .

Test Description
The numbers below refer to the step numbers on the diagnostic table.

If the actual CKP variation values are not within the learned values, the misfire counters may increment.

DTC P0135 or P0155 can be set because of a misfire.

Step
Action
Values
Yes
No

1
Did you perform the Diagnostic System Check-Engine Controls?
--
Go to Step 2
Go to Diagnostic System Check - Engine Controls

2
Important: You must perform the crankshaft position (CKP) system variation learn procedure before proceeding with this diagnostic table. Refer to Crankshaft Position System Variation Learn .

Start the engine.
Allow the engine to idle or operate within the conditions listed in the Freeze Frame/Failure Records.
Monitor all of the misfire counters with the scan tool.
Are any of the current misfire counters incrementing?
--
Go to Step 3
Go to Diagnostic Aids

3
Are any DTCs other than P0300, P0135 or P0155 set?
--
Go to Diagnostic Trouble Code (DTC) List
Go to Step 4

4
Can any abnormal engine noise be heard?
--
Go to Base Engine Misfire without Internal Engine Noises
Go to Step 5

5
Does the scan tool indicate that the HO2S bank 1 sensor 1 or HO2S bank 2 sensor 1 voltage parameters are below the specified value?
200 mV
Go to DTC P0131 or P0151
Go to Step 6

6
Does the scan tool indicate that the HO2S bank 1 sensor 1 or HO2S bank 2 sensor 1 voltage parameters are fixed above the specified value?
900 mV
Go to DTC P0132 or P0152
Go to Step 7

7
Inspect the following components:

• The vacuum hoses and seals for splits, restrictions, and improper connection--Refer to Emission Hose Routing Diagram .

• The throttle body and intake manifold for vacuum leaks

• The crankcase ventilation system for vacuum leaks--Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical.

• The PCM grounds for corrosion and loose connections--Refer to Ground Distribution Schematics in Wiring Systems.

• The exhaust system for restrictions--Refer to Restricted Exhaust in Engine Exhaust.

• The fuel for contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Did you find and correct the condition?
--
Go to Step 20
Go to Step 8

8
Turn OFF the ignition.
Disconnect the spark plug wire from the spark plug that corresponds to the Misfire Current counters that were incrementing. Refer to Spark Plug Wire Replacement .
Install the J 26792 Spark Tester to a good ground.
Start the engine.
Does the spark jump the tester gap, and is the spark consistent?
--
Go to Step 10
Go to Step 9

9
Remove the spark plug wire for the affected cylinder. Refer to Spark Plug Wire Replacement .
Inspect the spark plug wire. Refer to Spark Plug Wire Inspection .
Measure the resistance of the spark plug wire with a DMM.
Is the spark plug wire resistance less than the specified value?
700 ohms
Go to Electronic Ignition (EI) System Diagnosis
Go to Step 19

10
Remove the spark plug from the cylinders that indicated a misfire.
Inspect the spark plug. Refer to Spark Plug Inspection .
Does the spark plug appear to be OK?
--
Go to Step 11
Go to Step 12

11
Exchange the suspected spark plug with another cylinder that is operating properly. Refer to Spark Plug Replacement .
Operate the vehicle under the same conditions that the misfire occurred.
Did the misfire move with the spark plug?
--
Go to Step 18
Go to Step 15

12
Are the spark plugs oil or coolant fouled?
--
Go to Base Engine Misfire without Internal Engine Noises
Go to Step 13

13
Are the spark plugs gas fouled?
--
Go to Step 16
Go to Step 14

14
Do the spark plugs show any signs of being cracked, worn, or improperly gapped?
--
Go to Step 17
Go to Step 15

15
Perform the fuel injector coil test. Refer to Fuel Injector Solenoid Coil Test .

Did you find and correct the condition?
--
Go to Step 20
Go to Base Engine Misfire without Internal Engine Noises

16
Perform the fuel system diagnosis. Refer to Fuel System Diagnosis .

Did you find and correct the condition?
--
Go to Step 20
Go to Base Engine Misfire without Internal Engine Noises

17
Replace or gap the spark plug. Refer to Spark Plug Replacement . If an improper gap is found, be sure to gap the spark plugs using a wire type gage.

Did you complete the replacement?
--
Go to Step 20
--

18
Replace the faulty spark plug. Refer to Spark Plug Replacement .

Did you complete the replacement?
--
Go to Step 20
--

19
Replace the faulty spark plug wire. Refer to Spark Plug Wire Replacement .

Did you complete the replacement?
--
Go to Step 20
--

20
Was the customer concern the MIL flashing?
--
Go to Step 21
Go to Step 22

21
Operate the vehicle at the specified value for 4 minutes.
Operate the vehicle within the Conditions for Running the DTC P0420 or P0430 as specified in the supporting text. Refer to DTC P0420 or P0430 .
Does the DTC run and pass?
2500 RPM
Go to Step 22
Go to DTC P0420 or P0430

22
Clear the DTCs with a scan tool.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?
--
Go to Step 2
Go to Step 23

23
Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?
--
Go to Diagnostic Trouble Code (DTC) List
System OK

 

Have you checked the plugs for any that are sooty? If you can scan for individual cylinders you can start swapping plug wires, etc. When my daughter's Envoy had a miss I swapped two coils and the miss moved with the coil. New coil fixed the problem.

 

I agree with vettenuts. Some of the better OBD II scanners will tell you specifically which cylinder is misfiring, which will narrow things down for you to look at.

I'm in northern CT, close to Springfield MA, and would be happy to scan it with my AutoXray 6000, which has that capability. PM me if I can help.

 

I would try something easier to begin with...load it up with a double dose of Techron, and top it off with fresh gas.




You DID put some fuel stabilizer in it last fall, right??

 

Had the car on the analyzer this morning and it showed something like 2500 misfires on cyl 3, 700 or 800 on cyl 2, with the same number on another cyl, don't remember which.

they looked up the firing order and found that the two lower count misfires were on either side of 3 in the firing order, so concluded that it was probably some kind of carry over and 3 was the issue.

Looking over 3 while the engine was running they found arcing between the metal heat shield on plug wire to the exhaust - bad plug wire.

So, the car is running correctly now.

LTFT - why were they off?
Reading the LTFT while driving to the shop today they were moving down and are now about +10-12%. Why are they changing? The only thing that I did that might make a difference is the PCV was pretty goopy, so I cleaned it - but this is before the wire was fixed.

Would the LTFT be off from a misfire?
Maybe two problems at once?

Just want it to stay fixed for a while and start to drive it now that the good weather is here!

 

Good to hear you got it fixed and it was something simple.

 

I'm very happy to have it running again w/o worrying about it.

I'll ponder what happened for a while, but at least I'm back in the car.
Gave it a bath tonight, tomorrow should be restarting the love affair for 2013.

 

All engines have misfires, it the number that's important.

 

The reason your LTFT were up is because a plug that doesn't fire results in the unburned fuel/air mixture hitting the O2 sensor, and because it is unburned, it is loaded with oxygen, and when an O2 sensor sees a lot of oxygen, it says the engine is running lean. As the STFT runs up to it's limit, the LTFT has to start to run up as well compensating to let the the STFT come off it's upper limit and can fluctuate enough to keep the cat happy. Engines with vacuum leaks exhibit this same behavior.

Fix the misfire condition and the oxygen is reduced at the O2 sensor, the LTFT starts to reduce while still letting the STFT have some fluctuation. Eventually the LTFT and STFT come into balance and all is well again.

The best explanation I've seen of this:


Long video, but good stuff in there.

 

I am way behind due to clean up from all the storms this winter but hope to have mine out within the next week or two