Burning smell, light smoke from engine bay

[theophile]

At least you got the hard part out of the way. Pulling the spark plugs will seem significantly easier after doing the VCGs

True.

I think I have narrowed down the issue. I'm able to use my OBD2 dongle and phone app to read the raw "Mode 6" data, which includes the per-cylinder misfire rate. The data reflects a consistent misfire rate at idle in cylinder 6, and a misfire rate of 0 on all other cylinders. Incidentally, within minutes of starting the car this morning to do this test, the CEL came on with a "cylinder 6 misfire" code.

The misfire rate for cylinder 6 is 6848, which is about 10 times the error threshhold of 644. According to the Ford spec sheet, this 6848 translates to a misfire rate of 0.10272%. Interestingly, this number tends to be lower at higher RPMs, such as when the engine starts and before it settles down to about 800 RPM at idle in park. After letting it settle consistently at 6848, I cleared the DTC, shut down the car, and started it back up again to get a clean reading. It settled at 6848 again.

The first thing I did was to swap the COPs on cylinders 5 and 6, but #6 continued reading 6848 and #5 continued reading 0, so I believe that rules out the COP.

Then I pulled the spark plug on #6. It was gapped narrower than .054" so I gapped it to .054" and reinstalled it. But the misfire rate remained the same. I noticed a small amount of oil in the well, but I think it's more likely residual oil I failed to completely clean out yesterday rather than new oil leaking through the gasket I just replaced.

I tried reseating the COP and the boot several times, and removed most of the dielectric grease from the bottom of the boot and spring just in case it had been inhibiting the connection, but it did not seem to help.

At this point, my next step will be to get a new plug, which would rule out the plug if that doesn't fix it. After that I will have to double check the wire harness to make sure the pins are seated properly and to make sure I did reverse the polarity on that plug. Failing that, I'll have to research other possible causes of consistent misfire.

 

[jjcool00]

Test the coil harness and the harness wires to see of it's they are not crimped somewhere or broken.

 

[theophile]

Test the coil harness and the harness wires to see of it's they are not crimped somewhere or broken.

Can I test the coil harness with a multimeter with the car running?

 

[joegr]

Can I test the coil harness with a multimeter with the car running?

You can test it with a multi-meter (resistance setting) with the car off, and the engine harness at the PCM disconnected.

You can test it with the car running with an oscilloscope.

 

[theophile]

I'm considering plugging the harness for cylinder 6 into the COP for cylinder 7 to see if the misfires follow the harness. I know this will mess up the firing order, so I have two questions:
1) Will doing this risk any damage to the engine if I only do it at idle for a few minutes at a time?
2) If not, will the fact of the "wrong" harness being on the COP look to the ECM like misfires, thereby defeating the purpose of the test?

 

[joegr]

I'm considering plugging the harness for cylinder 6 into the COP for cylinder 7 to see if the misfires follow the harness. I know this will mess up the firing order, so I have two questions:
1) Will doing this risk any damage to the engine if I only do it at idle for a few minutes at a time?
2) If not, will the fact of the "wrong" harness being on the COP look to the ECM like misfires, thereby defeating the purpose of the test?

This won't help you at all, and may do some damage. The firing would happen at the wrong time for each cylinder. It would prove nothing.

 

[theophile]

This won't help you at all, and may do some damage. The firing would happen at the wrong time for each cylinder. It would prove nothing.

Okay, I believe I have ruled out the plug and the 2-pin connector. I swapped plugs between cylinders 5 and 6 and 6 is still misfiring. I also verified continuity between the 2-pin connector and the PCM harness at the firewall. I need to check the injector harness to make sure it's secure. If it is, what would I look at next? I'm running out of ideas. :-/

 

[joegr]

...Then I pulled the spark plug on #6. It was gapped narrower than .054" so I gapped it to .054" and reinstalled it. ...

Wait, i"m awake now.
You set the V8 plug to 0.54"? The spec is 1.0mm, which is 0.039" The spec says that the maximum that you should allow the gap to wear to is 0.041"

 

[theophile]

Wait, i"m awake now.
You set the V8 plug to 0.54"? The spec is 1.0mm, which is 0.039" The spec says that the maximum that you should allow the gap to wear to is 0.041"

Wow, brain fart. I must have been looking at the spec for the V6 gap. I'll put it back. At any rate, the misfires don't seem to have followed that plug to the neighboring cylinder, and # 6 continues to read misfires with a properly gapped plug.

 

[joegr]

Wow, brain fart. I must have been looking at the spec for the V6 gap. I'll put it back. At any rate, the misfires don't seem to have followed that plug to the neighboring cylinder, and # 6 continues to read misfires with a properly gapped plug.

Just to be clear here, when you did get a misfire code, which exact one was it (five character code)? I curious as to if it was a misfire only, or a primary circuit problem (resulting in misfire).

 

[theophile]

Just to be clear here, when you did get a misfire code, which exact one was it (five character code)? I curious as to if it was a misfire only, or a primary circuit problem (resulting in misfire).

P0306.

Also, the several times I have cleared the code to reset the misfires counts while swapping parts between cylinders, that code will come back within a few minutes of engine start. And that is the only code I am getting.

 

[joegr]

Well, the PCM is not detecting any problem with the primary wiring. Is is possible that you bumped the wiring for the #6 fuel injector?

 

[Telco]

When you fix the plug gap, swap the COP from cylinder 6 to cylinder 4. Swap the plug from cylinder 6 to cylinder 2. If the code stays with 6 you can look at the injector, if it goes to 4 it's the COP, if it goes to 2 it's the plug, if it goes away it was the plug gap unless you positively identify a fuel injector plug issue.

 

[theophile]

Well, the PCM is not detecting any problem with the primary wiring. Is is possible that you bumped the wiring for the #6 fuel injector?

As a matter of fact, it is very possible. When I went out to work on it this evening, this was the first thing I checked and indeed, the #6 injector plug was dangling free. And looking at it again, I know exactly how it happened. The #6 injector plug is directly underneath the Shraeder valve I used to relieve the pressure in the fuel line before disconnecting it, and I put a rag under the valve to catch the dribble. Like a lot of the small plastic harnesses in the engine bay, this one had gotten a bit brittle and the plastic lock isn't catching consistently anymore. So I'm certain that when I placed the rag under the Shraeder valve, I accidentally knocked the injector plug loose.

However, incredibly, plugging it back in did not seem to solve the issue. I still get a slight shake at idle and cylinder 6 still seems to have a live misfire count (although it's not throwing the code anymore). I'm going to leave the battery unplugged overnight to clear the computer and start fresh, and tomorrow I'm going to try Telco's suggestion above of moving the plug and the coil to separate cylinders on the other side.

Anything else I should look at? I just can't believe the disconnected injector plug could have been a coincidence...

 

[theophile]

Okay, I think I'm progressing in a good direction. I left the battery disconnected overnight and reconnected it this morning. When I started it up, I think the idle smoothed out a little, though not entirely. I good news is that the Mode 6 data is now reading 0 misfires on all 8 cylinders and the CEL is staying off. I drove it around the block for a few minutes and it seems to perform just fine. Misfire counts stay at 0.

But there's still a gentle rhythmic shake at idle that I'm sure wasn't there before I did the VCG/plus/COPs replacement. Here's a quick video I took of the engine at idle:

[video]https://drive.google.com/file/d/0B0Z0bpkQXwBFVFZ6Y3liOXFESXM/preview[/video]

Please correct me if I'm wrong, but I think the car is "safe" to drive in terms of risk of damage to the cats. But I would really like to correct this little "jiggle."

 

[FDR]

Do you have what sounds like a ticking or single-cylinder exhaust leak? Coming from the center or the firewall or a little bit towards the passenger side? I have a ticking that seems to come from the throttle body... Definitely the back of the engine and not the front. I have an 02 V8. I'm just curious if its normal

 

[theophile]

Do you have what sounds like a ticking or single-cylinder exhaust leak? Coming from the center or the firewall or a little bit towards the passenger side? I have a ticking that seems to come from the throttle body... Definitely the back of the engine and not the front. I have an 02 V8. I'm just curious if its normal

I haven't noticed a ticking sound. Are you referring to something you heard in my video above?

 

[theophile]

So I drove the car around town for a couple of errands today. The rough idle is definitely noticeable. On the way back home, the CEL came on. I was expecting the misfire code, but it actually came back P0174 (System Too Lean (Bank 2)). I am hoping that this is due to a vacuum leak caused by my kludge fix for the crankcase vent tube I broke off while replacing the VCGs.

I will try to confirm that, but I'd love to hear alternative suggestions anyone might have.

 

[FDR]

I haven't noticed a ticking sound. Are you referring to something you heard in my video above?

Yes, but on a second listen, it sounds more like a normal V8 gargle than a tick. As for your lean code, a leaking vacuum line can cause it. All of the vacuum lines are "powered" by the pistons' intake strokes.

 

[theophile]

Yes, but on a second listen, it sounds more like a normal V8 gargle than a tick. As for your lean code, a leaking vacuum line can cause it. All of the vacuum lines are "powered" by the pistons' intake strokes.

I spent several hours today trying to hunt this down. I found that the TB-side connector on the passenger-side crankcase vent tube wasn't seated property and had a torn O-ring, so I replaced the O-ring and made sure the connector was seated properly. While I was at it, I replaced the TPS and cleaned the mating surface of the IACV and reinstalled it. It's still bouncing at idle, and still throwing the P0174 code (but no other codes).

I did the TB cleaner spray trick to check for vacuum leaks but I didn't get any surges indicative of a vacuum leak. (I confess I don't know all of the places where this issue might manifest itself, so I may have missed some spots).

While test driving this afternoon, I was using Torque to monitor the OBD2 data, and I set up a display array for the following data sources:
* O2 Volts Bank 1 sensor 1
* O2 Volts Bank 1 sensor 2
* O2 Volts Bank 2 sensor 1
* O2 Volts Bank 2 sensor 2

In general, while driving, the readings would hover around 0.7~0.9 for both Bank 1 sensors and for sensor 1 on Bank 2. But the Bank 2 sensor 2 reading was usually 0.0, though it would occasionally read 0.1 for a moment before returning to 0.0.

If I understand correctly, this is the sensor after the cat on the driver's side. I'm going to go take a look at it tonight to see if anything appears amiss. I will probably also clean the MAF since that seems to be a common recommendation for this rough idle issue. But overall, I'm stumped by why I would be getting this code and only this code. It seems that most people have this code with other codes that also tend to accompany these theories (bad O2 sensor, dirty MAF, etc.). As always, suggestions and ideas welcome!

 

[LS4me]

I spent several hours today trying to hunt this down. I found that the TB-side connector on the passenger-side crankcase vent tube wasn't seated property and had a torn O-ring, so I replaced the O-ring and made sure the connector was seated properly. While I was at it, I replaced the TPS and cleaned the mating surface of the IACV and reinstalled it. It's still bouncing at idle, and still throwing the P0174 code (but no other codes).

I did the TB cleaner spray trick to check for vacuum leaks but I didn't get any surges indicative of a vacuum leak. (I confess I don't know all of the places where this issue might manifest itself, so I may have missed some spots).

While test driving this afternoon, I was using Torque to monitor the OBD2 data, and I set up a display array for the following data sources:
* O2 Volts Bank 1 sensor 1
* O2 Volts Bank 1 sensor 2
* O2 Volts Bank 2 sensor 1
* O2 Volts Bank 2 sensor 2

In general, while driving, the readings would hover around 0.7~0.9 for both Bank 1 sensors and for sensor 1 on Bank 2. But the Bank 2 sensor 2 reading was usually 0.0, though it would occasionally read 0.1 for a moment before returning to 0.0.

If I understand correctly, this is the sensor after the cat on the driver's side. I'm going to go take a look at it tonight to see if anything appears amiss. I will probably also clean the MAF since that seems to be a common recommendation for this rough idle issue. But overall, I'm stumped by why I would be getting this code and only this code. It seems that most people have this code with other codes that also tend to accompany these theories (bad O2 sensor, dirty MAF, etc.). As always, suggestions and ideas welcome!

From Google......

A code P0174 may mean that one or more of the following has happened: The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters can cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry. There could be a vacuum leak downstream of the MAF sensor. Possible Solutions Possible solutions include: In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling Inspect all vacuum and PCV hoses, replace if necessary Check for a dirty fuel filter and proper fuel pressure

Read more at: http://www.obd-codes.com/p0174
Copyright © OBD-Codes.com

 

[theophile]

I wasn't able to clean out the MAF tonight because the T20 is the only bit missing from my set of security drivers. Go figure. I'll get some specific mAF cleaner while I'm at it too. But I think there may be something else going on too. I found another cracked/brittle vacuum hose, the one connected to the "back" of the IACV. Until I can get the replacement part, I wrapped the cracked parts with electrical tape followed by a layer of HVAC foil tape to seal it up, but it's still bouncing at idle.

Now that I'm listening for it, I can definitely hear a hissing sound from the engine bay with the car running. But I can't locate it specifically, and I'm not sure whether it's nornal or not. I did a second round of the throttle-body-cleaner test, but didn't find any hot spots.

I'm starting to think that the issue is probably traceble to something I disconnected or disturbed (whether accidentally or on purpose) during the VCG replacement process. Assuming I do have a vacuum leak somewhere, is it correct that the "Bank 2 too lean" code means that the leak would be somewhere on the driver's side of the engine bay?

 

[joegr]

...Now that I'm listening for it, I can definitely hear a hissing sound from the engine bay with the car running. But I can't locate it specifically, and I'm not sure whether it's nornal or not. ...

Not.

 

[theophile]

I grabbed an OBD2 log from my commute to work this morning, specifically the O2 sensor and MAF readings. If you want to take a look at it, you can see it here.

My understanding is that the O2 sensor will output about 0.45 V when the air:fuel ratio is the optimal 14.7:1. From my log, I calculated the average voltage output from the "sensor 1" sensors on both banks as follows:

Bank 1 sensor 1 = 0.4850384763 V (average)
Bank 2 sensor 1 = 0.4740090926 V (average)

So it looks like the pre-cat sensors on both banks are registering a pretty much optimal air:fuel ratio. Now here are the averages from the "sensor 2" sensors on both banks:

Bank 1 sensor 2 = 0.6730510695 V (average)
Bank 2 sensor 2 = 0.0527801105 V (average)

So bank 1 is running a little rich and bank 2 is running extremely lean.

Does this indicate a problem with the cats? I may be interpreting these numbers wrong but it looks to me like the air going into the cats has the proper air:fuel mixture, but the air coming out doesn't.

I understand a vacuum leak can cause this symptom, so I'm still barking up that tree (unsuccessfully so far). Does anyone have a "map" of the vacuum system so I can just check every single hose and connector? I really need to get this straightened out. Thanks all.

 

[Telco]

The sensor 2s are after cats, and their primary function is to make sure you don't remove the cats. Their secondary function is to make sure the cat itself is working correctly. I would suggest swapping the sensors from side to side. If the sensors continue to read the same as in the readings remain as they are, then you have a cat issue. If the sensor results follow the sensors, you have a bad sensor.

On the vacuum leak, so far you have found two brittle lines. This says that all your lines are likely brittle and leaking. So far they are leaking badly enough that the car knows there is a problem but not badly enough that the car can't compensate since the precat sensors are more or less reading a correct mix. You're just going to need to find them and fix them. No idea if you are going to find the parts or not though. Parts are getting to be hard to find for the LS. Your local Jag dealer may be a source for hoses and fittings though, since they are still using the AJ engine. They aren't going to be all that different.