Feels like a misfire, but no CEL codes for it.

[Spawn]

Right, I’ve been having issues with the UAV for a few weeks now. Started off with when I was sitting at idle at a light, the engine would jump randomly and cough like a plug misfired. Was getting P0171 and P0174, so I thought it might be the O2 or MAF sensors. Took it to the dealership, who I have a VERY good relationship with, tech said that their computers couldn’t communicate with the ECU. Based on the symptoms, they suggest start by replacing the MAF, and told me to source it myself as it would be significantly cheaper. On the way home, the computer I have built into the truck was able to communicate fine with the ECU and read the sensors in realtime. Replaced the MAF, and it settled down for a bit (about 4 hours of driving, no issues.) Also no more P0171/P0174. Then the “misfire” started again, and this time threw out the P0303 for misfire on Cylinder 3. I replaced the NGK Iridiums that were 3.5 years old with new ones. Wires looked fine when I swapped the plugs so I didn’t replace them.

That solved the P0303 code, haven’t had it or any other CEL codes in 2 weeks, but the “misfire” action of the engine jumping and rough idling is still there. And now it’s getting MUCH worse. It isn’t all the time at a light, but when it starts, and I have to accelerate, it does it for a few coughs while it’s trying to get going. Last night, I noticed on the Volt Gauge I installed that there is a momentary drop in voltage (about a half to full volt) when it does the coughing. I am still trying to figure out what the issue is. My next line of thinking was replace the plug wires, and ignition coils, then have a look at the CKPS, but the voltage drop is making me think a loose ground somewhere. Anyone, and SBR711 I’m looking at you on this one , have any ideas? It would be appreciated.

[Spawn]

Seriously? No one?? Beuller? Anyone? Bueller?

[johnaauld]

Originally Posted by Spawn

Right, I’ve been having issues with the UAV for a few weeks now. Started off with when I was sitting at idle at a light, the engine would jump randomly and cough like a plug misfired. Was getting P0171 and P0174, so I thought it might be the O2 or MAF sensors. Took it to the dealership, who I have a VERY good relationship with, tech said that their computers couldn’t communicate with the ECU. Based on the symptoms, they suggest start by replacing the MAF, and told me to source it myself as it would be significantly cheaper. On the way home, the computer I have built into the truck was able to communicate fine with the ECU and read the sensors in realtime. Replaced the MAF, and it settled down for a bit (about 4 hours of driving, no issues.) Also no more P0171/P0174. Then the “misfire” started again, and this time threw out the P0303 for misfire on Cylinder 3. I replaced the NGK Iridiums that were 3.5 years old with new ones. Wires looked fine when I swapped the plugs so I didn’t replace them.

That solved the P0303 code, haven’t had it or any other CEL codes in 2 weeks, but the “misfire” action of the engine jumping and rough idling is still there. And now it’s getting MUCH worse. It isn’t all the time at a light, but when it starts, and I have to accelerate, it does it for a few coughs while it’s trying to get going. Last night, I noticed on the Volt Gauge I installed that there is a momentary drop in voltage (about a half to full volt) when it does the coughing. I am still trying to figure out what the issue is. My next line of thinking was replace the plug wires, and ignition coils, then have a look at the CKPS, but the voltage drop is making me think a loose ground somewhere. Anyone, and SBR711 I’m looking at you on this one , have any ideas? It would be appreciated.

Spawn,
If you haven't replaced your CKPS by now, you should just do it regardless of any other problems. I've seen a myriad of symptoms because of the bare copper wires that swing and short out. If you take off the starter shield by rotating it 90 degrees and pulling it off toward the driver side and then pull off the skid plate- you can see the CKPS from sighting beside the oil filter and looking back up toward the center of the engine above the starter. If you see three wires, the insulation that held them together has deteriorated over time and most likely the individual insulation on each wire has fallen off too. Takes a while to replace it if you are doing it on your back(be sure to use a 1/4 inch drive), but it can be done.
You can also look at your coils to look for gray-white discoloring. Of course it could also be your wiring- although I have an 03 2.7 with 113k miles and haven't had a problem with the wires yet.

[Spawn]

Thanks Johnaauld, I was thinking about the CKPS as well. It originally went bad in 2006 and was replaced. I'll have a look at the coils today before heading out. looking at the sensor might have to wait for to trip to the dealer.

[Spawn]

Well, she's fixed. Took it to the dealership yesterday. Tried again to connect with the laptop they are using to pull data, no joy. Then they pulled out the Hi-Scan tool, and low and behold, she connects fine with that. We were all ready to swap the CKPS, but the computer has just shown P0303 again.

First thing they ask me is did I change the intake gasket when I swapped out the plugs and wires. I say no, and correct them that I only swapped out the plugs, not the wires yet. They said I should have put a new gasket in, so they test for a leak, and there is none.

Now the fun part. They ask me to make it do the misfire, so I pull the parking brake, and with my foot on the brake pedal, put her in reverse. After about 5 seconds, she starts doing it. Now, I am gonna say that I have never heard of doing this, but it's apparently quite common and the easiest way to check for faulty spark plug wires. They pull out the spray bottle of water from the tint guy's bag, and start spraying down each wire. finally on the 4th wire (cyclinder 3 at the back), the engine starts stumbling like mad.

And that was it, seems it was the spark plug wires the whole time. I left her there to have the intake gasket and wires swapped out. Happy to say she is back to her sporty-clear-breathing-dual-exhaust-self!

[johnaauld]

Originally Posted by Spawn

Well, she's fixed. Took it to the dealership yesterday. Tried again to connect with the laptop they are using to pull data, no joy. Then they pulled out the Hi-Scan tool, and low and behold, she connects fine with that. We were all ready to swap the CKPS, but the computer has just shown P0303 again.

First thing they ask me is did I change the intake gasket when I swapped out the plugs and wires. I say no, and correct them that I only swapped out the plugs, not the wires yet. They said I should have put a new gasket in, so they test for a leak, and there is none.

Now the fun part. They ask me to make it do the misfire, so I pull the parking brake, and with my foot on the brake pedal, put her in reverse. After about 5 seconds, she starts doing it. Now, I am gonna say that I have never heard of doing this, but it's apparently quite common and the easiest way to check for faulty spark plug wires. They pull out the spray bottle of water from the tint guy's bag, and start spraying down each wire. finally on the 4th wire (cyclinder 3 at the back), the engine starts stumbling like mad.

And that was it, seems it was the spark plug wires the whole time. I left her there to have the intake gasket and wires swapped out. Happy to say she is back to her sporty-clear-breathing-dual-exhaust-self!

Well live and learn. Thanks for the tip as I haven't changed out the wires on mine yet(did just like you and only changed my spark plugs). Makes sense to mist the wires to check for a misfire. How many miles on the 04?

[Spawn]

Canadian, so metric it is 180,000 km

[Techsuperstar]

Funny I just saw this post. My car's been doing the exact same thing for almost a year now. Finally hooked up the computer and found out it was also Cyl 3 in the back. Was a plug wire as well.
It's really odd that it can misfire all the time while sitting at a light but there are no codes unless the engine is stressed (hard acceleration) which causes the check engine light to come on.

[johnaauld]

Originally Posted by Techsuperstar

Funny I just saw this post. My car's been doing the exact same thing for almost a year now. Finally hooked up the computer and found out it was also Cyl 3 in the back. Was a plug wire as well.
It's really odd that it can misfire all the time while sitting at a light but there are no codes unless the engine is stressed (hard acceleration) which causes the check engine light to come on.

It must be some real high amounts of bad data to trip the cel light. I know when my car started having problems with the CPS, it would almost kill the engine at high speed momentarily and would never set a cell. It also used to kill at stop signs occasionally. Never bad enough data for it to set a cel. Did that for over two years before I figured it out.