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Discussion Starter · #1 ·
Today, I noticed for the first time the wagon running rough at first start. Then, my check engine light starts to "Blink". This is something that has never happened before. After about 10 minutes or so, the roughness went away & light stopped blinking, but stayed on. Has anyone had this problem before? I'll see what code came up @ home. Thanks for the help!!
 

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+1 on a possible misfire code. If it does end up being that try running a bottle or two of Chevron Techron fuel system cleaner through the car. An uncle of mine 96 Skylark had a similar issue, rough running combined with blinking CEL, I had him run a bottle of the fuel system cleaner through and problem was solved. After running the fuel system cleaner through you may want to replace the fuel filter(rear drivers side frame rail bolted to the frame with 2 quick disconnect connectors attaching the filter to the lines).

Also check for any damaged plug wires because one shorting out or broken can cause a misfire code as well. - Peter
 

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I've had a flashing MIL twice.

The first one was cured by removing, pinching and reconnecting each fuel injector connector. Apparently, they have a tendency to "yawn" open after a while.

The second time was when my Crank Position Sensor harness was being pinched between the Flo-Tech headers and the frame. It only flashed during one period, so it may have been something else.

HTH

-KP
 

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Discussion Starter · #6 ·
OK.. Sorry for the delay. It did it again this morning. Checked the code and it was P0300. Not sure what this is??:confused:
 

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Found this:


I have no first hand knowledge with this but from the manual, there is lots to look at.

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 CKP System Variation Learn Procedure .


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 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
 

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The P0300 is a random misfire dtc...since it's still OBD1 it will be a little harder to figure out which cylinder(s) is causing the misfire...does it misfire under "load" or at "idle"?
 

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Did you figure it out?

After a new AC Delco opti-spark (3200 miles), opti-spark vent harness (1755 mi), ignition coil (8431 mi), spark plugs (7819 mi), spark plug wires (7791 mi), 02 sensors (1755 mi), fuel filter & gumout tank additive (8329 mi), gas cap (1755 mi), PCV Valve and Optima battery, all done within under the last 2 years, my P0300 is back!
Driving it today has shown very early stages of what eventually the last go around led to a total crapout and replaced the opti-spark etc. The new opti actually had failed after 4600 miles (11 months later) and it was replaced under warranty - that was almost a year ago. So now the opti has under 3200 miles on it with I believe no warranty.
 

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After a new AC Delco opti-spark (3200 miles), opti-spark vent harness (1755 mi), ignition coil (8431 mi), spark plugs (7819 mi), spark plug wires (7791 mi), 02 sensors (1755 mi), fuel filter & gumout tank additive (8329 mi), gas cap (1755 mi), PCV Valve and Optima battery, all done within under the last 2 years, my P0300 is back!
Driving it today has shown very early stages of what eventually the last go around led to a total crapout and replaced the opti-spark etc. The new opti actually had failed after 4600 miles (11 months later) and it was replaced under warranty - that was almost a year ago. So now the opti has under 3200 miles on it with I believe no warranty.
Did you ever get your car fixed?

-KP
 

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I spent an afternoon going over everything over and under the engine bay. never found anything. funny thing is after that it hasnt acted up and the CEL has gone out. Still a mystery. Its been driven very little lately as we are being cautious. Our concern is when I get a/c working again (big hole in freon line) it gets to be driven in the hotter weather it could act up again and we will drive it a lot more now. The hot temp months is when it typically had issues, although never (the coolant system) overheated.
I kind of wondered if these "flukes" ever have anything to do with the fact that is has Hypertech Programming (Hypertech also programmed it for the GM dealer having flashed out the air pump for me), but thats all been on for many yrs. It also has a lot of new ignition system components & O2 sensors so its hard to say. That code we got apparently has a lot of possibles even for just temporary funky conditions.
 

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Since you first started this thread, Ive discovered a loose ground crimp at the ecm harness connector. Cured some very similar symptoms. The Purple 'common' wire for the MAP Sensor, ECT Sensor and some other (as yet undetermined) sensor. Plugged in to pin 16 of the Black ecm connector. The one you can see when you look down in to the connector while it's plugged in. It was still in the crimper, but was only occasionally making electrical connection.

Do you have a scan tool? That 's what fixed mine. I picked up an UltraGauge I could look and see which sensors were reporting to the ECM. the one's that weren't, were connected to the bad wire. The symptoms were so severe, and the cure was so simple, that the repair itself was rather disappointing.

Let us know.

-KP
 

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used transmissions for sale One of the most common misconceptions about rebuilding transmissions is that it will restore the transmission to a new condition, but this is definitely not true. Although it can help you restore the peak operating efficiency of the transmission, it is less effective in extending its lifespan. Rebuilding transmissions needs different parts of the transmission to be changed, making some of its parts older than or as old as the original parts.
This is the reason why you need to determine first the model and brand of your car before searching for a book that will teach you how to rebuild transmission.
 

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Blinking check engine light

Having the same problem. I can drive it but cel blinks on and off as I drive seems to be losing power amps goes down after car is warm.
Looked at the plug wires for breaks and burns but nothing sticks out. I guess Ill try to change the wires and go from their. 1996 caprice ss LT1.
 

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Many long stories short: this last time mine ended up being a partly frayed/cracked spark plug wire #8 maybe the worst one it could be since its hidden in back. someone had taped over the break but you coudnt see that. I am thinking maybe the A/C shop who replaced a broken freon line, thinking they were "helping me", but said nothing.
Even a mechnic shop could not find it & told me to take to the dealer. I got it home and tore into the car myself and found it.
The lesson here is do your own plugs and wires even if it takes days to get it done. The first shop that did the opti spark had also did plugs and wires. they routed my new Taylor plug wires badly and #8 wire even burned and some of my metal boot covers were missing so I had to buy new ones . I had to buy a whole new set of wires just to get that one bad wire since I do not trust myself to make up my own DIY wires.
Spark plugs all fouled, not gapped right, no anti seize on threads and no dielectric grease on either boot or plug tips. I had to buy a whole new set of plugs and start from scratch.
One mistake thye made led to other problems etc including lost gas mileage and then rough running.
The mechanics did not take time to do it right in the 1st place, and the next one did not do a thorough search for problems.
 

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Having the same problem. I can drive it but cel blinks on and off as I drive seems to be losing power amps goes down after car is warm.
Looked at the plug wires for breaks and burns but nothing sticks out. I guess Ill try to change the wires and go from their. 1996 caprice ss LT1.
While in there with wires - Pull the plugs and see if they are fouled! save later headaches. Swap ignition coil and see if fixes it. or Igniton module is expensive but worse Pray its not the opti spark.
 
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