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'02 Escalade
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Discussion Starter #1
OK...I've got a P0300 engine misfire code on my '97 SLS. The car shakes when at low idle and runs really rough. I got one new coil pack from autozone and tried it at all 4 spots. Problem is still there each time. So I was thinking maybe I had two bad coil packs, but instead of playing musical chairs with two new coils trying to find the two bad ones, I went ahead and got 3 more new ones and replaced everything. Problem is still there. So I took the new coil packs back to AZ and looked at my plugs. Well the first one I pulled off was shot...the electrode was almost non-existant so I replaced all 8 plugs. Good post in the tech section about what to remove (bar between shock towers, coil pack mount and one small vacuum piece to get the four plugs in back) to make the plug job quicker. So after I get the new plugs in, the problem is still there.

So next I get out the ohm-meter to check the resistance on my plug wires and here's where things got funny. I can't get a reading on any of the 5 wires I measured. I touched the two probes together and the meter read 0 ohms so its working (reads 'overload' when not touching so its not a problem with the meter). So I'm thinking there's got to be some sort of connection problem cuz there is NO WAY that 5 wires failed. So I plugged one of the old plugs back into the socket on the wire to ensure that I made good contact with the center electrode since the metal inside the end that fits over the plug is a little hard to get at and I still can't get a reading on these wires. Any suggestions here, guys? I felt like an idiot for not being able to confirm that a 2 foot long piece of wire is conducting.

So, lets put that aside and get back to the P0300 problem...the next thing I took a look at is the electrical connections between the pins inside the connectors on the chunk of metal that the coil packs sit on. There are two sets of connectors on either side of the mounting plate (as I'll call it). One has 3 pins, the other has 7 pins (if I remember correctly). I was guessing that there has to be some connectivity between the pins inside those connectors and the two posts that fit inside each coil pack. I was partially right. There is one pin inside one of the 3-pin connectors that connects to one of the posts for all of the four coil packs (1 pin shorted to 4 posts just to be clear). What I thought was strange was that the other post for each coil pack does not connect anywhere that I could find. It wasn't even connected to chassis ground. Does anyone know if that's how it is supposed to work? I figured there should be some symmetry/redundancy here since there are four coil packs working exactly the same, but that's not what I found. Can anyone look that up in a service manual? And those posts have to get an electrical signal from somewhere, but they don't appear to be connected to anything. Any help here would be appreciated. Let me know what you guys think.
 

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99STS,2004 Jeep Liberty Renegade,98 Deville RIP
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Good luck in tracking this problem, did you also replace the wires?, you might find that will come close to curing your problem, however have fun with the following




Document ID# 21970
1997 Cadillac Seville


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DTC P0300 Engine Misfire Detected




Circuit Description
This diagnostic test is used to detect misfires in any cylinder. A misfire occurs when there is a complete lack of or poor combustion in the cylinder. A misfire will cause a fluctuation in crankshaft revolution speed. The PCM uses the time between 4X reference pulses to determine when these fluctuations occur. At lower engine speeds, fluctuations in crankshaft speed are measured each reference pulse to detect misfire. At higher engine speeds, fluctuations in crankshaft speed are monitored over two engine revolutions and fluctuations in crankshaft speed at each half revolution are compared to compute a balance number. The 4X reference pulses originate in the ignition control module and vary with RPM.

Conditions for Setting the DTC
Test Conditions
DTC(s) P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0340 and P0502 are not current or have not set since last key ON.
Coolant is between -7°C (19°F) and 128°C (262°F).
Engine speed running for at least 3.19 seconds.
Engine speed is less than 6375 rpm.
Traction control is not present.
Cylinder shut down is not present
Ignition voltage is between 9 and 16 volts.
Throttle angle 0.3 degrees or more.
Vehicle speed is less than 45 mph.
During a 12.5 millisecond time period throttle angle stays between 0.6 and 1 degrees.
During a 100 millisecond time period throttle angle stays between 0.96 and 1.28 degrees.
Delta MAP diagnostic not in progress.
Number of consecutive positive delta revolution mode indexes less than 20.
Number of consecutive negative delta revolution mode indexes less than 20.
A/C compressor clutch has not changed states in the last 100 milliseconds.
Slip speed is at least -64 rpm.
18 engine cycles have occurred since any of above conditions and were not met.
Rough road indication is not considered present.
16 engine cycles have occurred since power-up.
16 engine cycles have occurred since both the reference mode and revolution mode were disabled.
8 engine cycles have occurred since a CAM error, or an ignition system error.
Diagnostic tool not connected.
10 engine cycles have occurred since desired torque less than 95.3%.
Failure Condition
A misfire has been detected.

Action Taken When the DTC Sets
The PCM will turn on the SERVICE ENGINE SOON MIL under the following conditions.

Impending catalytic converter damage
If a cylinder misfires at a sufficiently high rate for at least 200 engine revolutions, a catalytic converter damaging misfire level is considered present and the Service Engine Soon MIL will flash until the catalyst damaging condition is no longer present, at which time the MIL will remain on steady.
Disable TCC if either the number of emission misfires or number of catalyst damaging misfires exceeds 2.
Excessive exhaust emissions
If a cylinder misfires 15 times in 200 revolutions for 5 out of 16 200 revolution tests in each of two consecutive trips (engine run cycles which meet specific criteria), an excessive exhaust emissions condition is considered present and the Service Engine Soon MIL will be turned on.
Disable TCC if either the number of emission misfires or number of catalyst damaging misfires exceeds 2.
PCM turns ON the ENGINE MISFIRE message.

The PCM will record operating conditions at the time the DTC sets. This information will be stored in the Freeze Frame and Failure Records.

Conditions for Clearing the MIL/DTC

The PCM will turn the MIL OFF after three consecutive drive trips within the same driving parameters that set the DTC and the diagnostic runs and does not fail.
A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
A History DTC will clear after eighty drive cycles within the same driving parameters that set the DTC with no failures of any emission related diagnostic test.
Use a scan tool to clear DTCs.
Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation.
Diagnostic Aids
If more than one cylinder showed a history of misfire, look for something in common between the cylinders such as, shared coil, etc. If only one cylinder showed a history of misfire look for a possible vacuum leak at that cylinder, etc.
If fault cannot be duplicated, wet secondary ignition system and operate vehicle under conditions that the DTC set.
It is possible to set DTC P0300 if the vehicle has run out of or is very low on fuel.
To quickly determine the cylinder(s) that are misfiring, use the scan tool and observe Misfiring Cyl. in the Misfire data list. This will display the primary and secondary misfiring cylinders.
Due to the potentially destructive nature that engine misfire has on the exhaust catalyst always check for proper catalytic converter operation after a misfire has been repaired. This can be accomplished in the following ways:
Drive the vehicle under the Test Conditions for DTC P0420 and ensure that the DTC runs and passes.
In IM240 areas (or those properly equipped) perform the Catalytic Converter Service Bay Test.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.

If other DTCs are set, diagnose them first because other problems may be causing the misfire.

Checking if multiple cylinders are misfiring. If there is a single cylinder misfiring, the diagnosis is much easier.

Checking for causes of a single cylinder misfire.

Step
Action
Value(s)
Yes
No

1
Was the Powertrain On-Board Diagnostic (OBD) System Check performed?
--
Go to Step 2
Go to A Powertrain On Board Diagnostic (OBD) System Check

2
Connect a scan tool.
Turn the key ON.
Are any other DTCs set?
--
Go to DTCs that are set
Go to Step 3

3
Start and idle the engine.
Observe the Misfire Cur. counters in the misfire data list (there are 8 counters, 1 for every cylinder).
Are any of the counters incrementing?
--
Go to Step 4
Go to Step 15

4
Turn the Ignition to OFF.
Connect spark tester J 26792, to the ignition wire(s) that indicated a misfire.
Ground the companion cylinder(s) plug wire.
Idle the engine.
Does spark jump the tester gap and is spark consistent?
--
Go to Step 5
Go to Step 9

5
Turn the key to OFF.
Remove spark plugs from the cylinder(s) that showed a misfire.
If the Injector Coil Test Procedure finds no fault, review diagnostic aids and refer to Engine Mechanical for diagnosis.

Do the spark plugs appear to be okay or are only gas fouled (not oil or coolant fouled)?
--
Refer to Fuel Injector Coil Test
Go to Step 6

6
Are the spark plugs oil or coolant fouled?
--
Refer to Engine Mechanical for diagnosis
Go to Step 7

7
Do the spark plugs show any signs of being cracked, worn or improperly gapped?
--
Go to Step 8
Refer to Fuel Injector Coil Test

8
Replace or re-gap spark plugs.

Is the repair complete?
--
Go to Powertrain Control Module Diagnosis for Verify Repair
--

9
Turn the key to OFF.
Using DMM J 39200, measure the resistance of each plug wire which had an intermittent or weak spark or did not fire the spark tester.
Is the wire resistance less than the value shown?
15K ohms
Go to Step 10
Go to Step 13

10
Remove the affected coil(s).

Is the coil free of carbon tracking?
--
Go to Step 11
Go to Step 12

11
Switch position of the coils at the problem cylinder.
Idle the engine.
Does spark jump the tester gap and is spark consistent?
--
Go to Step 12
Go to Step 14

12
Turn the key to OFF.
Replace the faulty ignition coil.
Replace any wires that show carbon tracking or damage.
Is the repair complete?
--
Go to Powertrain Control Module Diagnosis for Verify Repair
--

13
Replace the faulty wires.

Is the repair complete?
--
Go to Powertrain Control Module Diagnosis for Verify Repair
--

14
Replace the Ignition Control Module. Refer to Ignition Control Module Replacement (Assembly) .

Is the repair complete?
--
Go to Powertrain Control Module Diagnosis for Verify Repair
--

15
Turn the key ON, engine OFF.
Review the DTC P0300 snapshot data.
Check the conditions that the vehicle was operating under when the DTC set.
Start and operate vehicle under conditions noted.
Observe the Misfire Cur. counters in the misfire data list (there are 8 counters, 1 for every cylinder).
Are any of the counters incrementing?
--
Go to Step 4
Go to Step 16

16
Turn the key ON, engine OFF.
Observe the Misfire Hist. counters in the misfire data list (there are 8 counters, 1 for every cylinder).
Do more than 3 cylinders show a high misfire rate?
--
Go to Step 18
Go to Step 17

17
Record the cylinder numbers that show a higher number of misfire.
Check the affected cylinders for damaged or high resistance plug wires, vacuum leaks, damaged spark plugs, etc.
Did any of the checks require a repair?
--
Go to Powertrain Control Module Diagnosis for Verify Repair
Refer to Diagnostic Aids

18
Check the vehicle for proper vent operation, vacuum leaks or an intermittent rich or lean condition.

Did any of the checks require a repair?
--
Go to Powertrain Control Module Diagnosis for Verify Repair
Refer to Diagnostic Aids



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Document ID# 21970
1997 Cadillac Seville
 

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'02 Escalade
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Discussion Starter #3
Thanks for the post. I'm not quite sure what the first 1/2 of your post means, but it might be useful as I dig further into this. No, I have not replaced the plug wires. The connections/boots are free from rust and the wires look to be in good shape. I just misted some water on the engine tonight and didn't see any "light shows" as others have described so I think those are OK. I'm not sure why the test procedure states look for a wire with resistance under 15k ohms. I'd think you'd want less than a few ohms so you're not losing power in the wires. Maybe I'll test those again tomorrow with a higher setting on my ohm meter to see if I can figure out whats up.

A little more info. When I pulled the plugs, there was quite a bit of oil on the threads. A couple of posts said that this isn't a big problem, but I thought I'd include that info. Also, the guy at Autozone said I don't need to gap my 41-950s. Is that true?

So things I need to try. I need to get a scan tool and see which cylinder is misfiring. No other codes are tripped indicating a specific cylinder, but maybe a scan tool will give some more info. I don't have a spark tester to verify if sparks are getting to a particular wire, but I could probably pick one up. Isn't it bad to run the engine without the wires connected though? You prolly want to do that test quickly.

Please post if you have any more info. I read about possible fuel injector troubles. I might read some more about that.
 

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99STS,2004 Jeep Liberty Renegade,98 Deville RIP
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A couple of things, first off, there is no codes for a specific cylinder, only a control circuit which is from 0201 thru 0208, this only tells you if the injector is getting its power and if the pcm is controlling it properly. If you run that test without the wires connected you will come up with the code for misfire again and your check engine light will start to flash and it is saying that the cat converter will start to overheat. Which scan tool do you plan on using?
 

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White Diamond '03 DHS (with DTS floor shift)
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Always check the gap on new plugs. Then stop :banghead: and change the wires. Do a search for my thread "Stutter, engine or trans".
 

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1997 Polo Green Cadillac Seville STS
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If you have covered the coil paks, wires, and plugs... My next thing would be to look for a bad injector. in my opinion the P0300 code is very general and can be set due to a number of issues.... Sometimes more then one. It's a bitch to track down. I would not rule out the ICM either. Have it tested.
 

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'02 Escalade
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Discussion Starter #7
A friend has a scan tool. I'm not sure what the model is though.

Ranger, yea I figured I should prolly test the plug gaps. The guy at autozone just acted like he didn't want to go through the trouble of doing it...lazy bum.
 

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'02 Escalade
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Discussion Starter #8
So after searching some more I decided to change the plug wires. The resistances were all 8-9k ohm which is not over the 15k limit, but I thought this might be the problem. However, the car still misfires.

So to recap, I've got a P0300 Engine Misfire that is not due to coil packs, spark plugs or plug wires. Anyone have any other suggestions? I read some place where someone had to clean out their EGR to fix this kind of a problem. I might have to do that. Let me know what you guys think.
 

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'02 Escalade
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Discussion Starter #9
OK...so after looking at a couple other posts, someone said they fixed this problem by cleaning the EGR valve. I took that off and it wasn't stuck open or closed and wasn't that dirty, but I cleaned it anyway. That didn't fix my problem. Anyone have any other suggestions?
 

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1997 Polo Green Cadillac Seville STS
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Have your fuel injectors checked. I would have a tech scan it so they would be able to tell WHICH cylinders are mis-firing.. Then pull the injectors from those cylinders and have them tested.


Also, Did you have the ICM tested. That is the Ignition Control Module thats at the bottom of the coil paks.
 

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'02 Escalade
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Discussion Starter #11
It was the fuel injectors. I called my mechanic and he said take a flat head screwdriver and hold it flush against the body of each fuel injector. Then stick your ear against the handle while plugging your other ear and listen for click, click, click. I know it sounds strange but its REALLY easy to tell if the things are working. If one injector isn't clicking, it may be clogged and simply tapping it with the screwdriver handle, a small hammer or anything else (I used a 6" extension from my socket set) might clear the clog. That worked in my case. I wasted 3 days and spent $110 on parts that didn't necessarily need to be replaced, but new plugs and wires can't hurt the car. She runs good again and I avoided a trip to the stealership...time for a cold one.
 
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