P1404 P0300 codes 2001 century custom

[banjeman]

My car had the SES on and after changing the Air filter (which has always cleared the problem in the past) the SES did not clear, seeing how it had 93,000 miles on it. I changed out my spark plugs (bosh double platinum) I purchased at AutoZone and the Cables purchased at O'Reillys. I started the car and the service engine light was still on, but my vehicle was running horrible now(missing constantly, loping) I decided to go around the block with it. It was sluggish and the service engine light would start flashing whenever I accelerated. I went to AutoZone and they put a OBD II reader on it and the codes returned were P0300-multiple misfires, P1404-EGR Closed position performance. I used a gap tester to ensure that my spark plugs were gapped at .060 mm. I used a spark plug wire tester to ensure all plugs were firing. I ohmed out the spark plug wires and they were within specifications. I tripled verified spark plug wires were correctly installed. I tested my EGR and the coil ohms was in range. The 5V to the EGR was there. I was wondering if there is any other possibility as it appears I have a bad EGR valve. Has anyone else experianced this fault combination or have any other Ideas on troubleshooting this problem or an explanation of what P1404 code means is the EGR closed and won't open or is it being commanded closed but isnt?

[BNaylor]

Welcome to AF.

The P0300 is probably being caused by using the Bosch spark plugs. It is highly recommended to use the OEM AC Delcos made for your engine. A flashing SES light indicates misfire most likely due to spark plugs or ignition wires. With that mileage you might consider the wires too. Also, use only the AC Delco wires.

The P1404 DTC error code means that the PCM has detected the EGR valve is stuck open when commanded to close. Try removing it and doing a visiual inspection. Make sure the spring loaded pintle moves freely. If that doesn't work then you may need a new EGR valve. Also, most EGR codes will need to be reset with a scanner after corrective action and will not clear on their own. Good luck!

[banjeman]

Thank you for the information. I did change out the wires at the same time. I purchased them from O'Riellys. I have just ordered a scanner interface that will allow me to use my laptop to read and reset codes. I will change out the spark plugs with the OEM AC DELCO and remove the EGR and give it the once over. Is there anyway that the EGR being stuck open would cause the misfiring problem? Or am I looking at two different problems.

[BNaylor]

Originally Posted by banjeman

Thank you for the information. I did change out the wires at the same time. I purchased them from O'Riellys. I have just ordered a scanner interface that will allow me to use my laptop to read and reset codes. I will change out the spark plugs with the OEM AC DELCO and remove the EGR and give it the once over. Is there anyway that the EGR being stuck open would cause the misfiring problem? Or am I looking at two different problems.

It sounds like two different problems but a stuck open EGR could cause misfires because hot exhaust is being introduced/recirculated into the intake system at all times when it should not be. I've seen a stuck open EGR cause a very poor idle.

On the plug wires were they aftermarket brand or AC Delco?

[banjeman]

I am sure they are after market. I looked up AC Delco parts and found there is only one retailer in my area that carries AC Delcom parts and OReilly's was not it. I changed the plugs and wires out because my wife was complaining of intermittent idle problems. I being an Electronic Technician though look at what was changed last and that would of been the plugs and wires. I guess I will have learned my lesson about after market products. I had two toyota's that I did all the routine maintenance and minor repairs with aftermarket stuff never had a problem. Thanks for your help I will report back on my findings.

[BNaylor]

Originally Posted by banjeman

I am sure they are after market. I looked up AC Delco parts and found there is only one retailer in my area that carries AC Delcom parts and OReilly's was not it. I changed the plugs and wires out because my wife was complaining of intermittent idle problems. I being an Electronic Technician though look at what was changed last and that would of been the plugs and wires. I guess I will have learned my lesson about after market products. I had two toyota's that I did all the routine maintenance and minor repairs with aftermarket stuff never had a problem. Thanks for your help I will report back on my findings.

The 3.1/3.4 GM engines are nitpicky when it comes to spark plugs and wires. The OEM/AC Delco ignition wires have the lowest resistance figure per foot of any plug wire and will handle up to 6500 rpms or more with no problems. Good luck and let us know how it turns out.

[banjeman]

Alright been awhile but I finally got my code reader and have removed the EGR valve to clean. My question is after I replace the cleaned EGR valve is it OK to reset the trouble codes or will this completely screw things up if the misfiring is still occuring? If I dont reset the trouble codes will I notice a difference if cleaning the EGR valve worked?

[BNaylor]

Originally Posted by banjeman

Alright been awhile but I finally got my code reader and have removed the EGR valve to clean. My question is after I replace the cleaned EGR valve is it OK to reset the trouble codes or will this completely screw things up if the misfiring is still occuring? If I dont reset the trouble codes will I notice a difference if cleaning the EGR valve worked?

EGR codes will normally not clear after a few drive cycles and should be reset with the scanner. Then you will see if the problem is resolved. Good luck!

[banjeman]

Success! well sort of.

I reset the fault codes and started the engine back up. It was still missing horribly. I checked the DTC and found in the potential codes P0301 #1 cylinder misfire (much easier to troubleshoot than the P0300).

I had saved the old spark plug cables as I had only really broke a couple of them when removing during spark plug change out.

I pulled of the spark plug wire that was on the car and tested the resistance against the old wire to my astonishment it was about a 2500 ohm difference.

I installed the old #1 spark plug wire and started the car and PRESTO! no more missing.

I gave the car a test drive and toward the end the SES light came back on checking the code I found the P1404 code was back (which I now believe was the original SES problem before the changing of the spark plugs and wires.)

Needless to say car is running good except still have P1404 I have already cleaned it, tested the voltage to it and read the coil ohms all appear to be good. Guess I just need to change the EGR valve.

Thanks everybody for your help. In conclusion the misfire issue was a faulty spark plug wire from set I had bought from O'Riellys (to bad I lost the reciept ).

[maxwedge]

Good work retracing your steps here, rather than jumping off into random parts replacement.