I bought my 2003 Ex Limited V10 6 months ago with 258,000 miles on it. I am now up to 265,000 miles. It has been great so far and I have been really impressed, especially for a high mileage vehicle. The Ex developed a violent low RPM miss over the weekend. I should have known it was coming because I have been joking about it being more reliable with 265,000 miles than my wife's car with 12,000 miles.

I first noticed the miss driving on the highway when it shifted up to 4th gear and the RPMs dropped to idle speed. This produced a sputter that would go away when I accelerated and increased RPMs. A couple miles down the road I came to a stop and it idled like a big block with a big cam. The idle is violent enough that if not pressing the brake hard the Ex will jerk forward as it tries to run and even rocks the Ex side to side. No check engine light was on at this time, I did feel a loss of power throughout the RPM range at this point and hear a noise that almost sounds like a manifold leak that did not exist prior to developing the miss.

So my first thought was IAC Valve, PCV Valve, and vacuum hoses. I replaced the IAC and PCV and visually inspected vacuum lines. I removed the PCV vacuum line and blew in it while holding the other end to see if I could find a leak- none detected. After re-assembling it with the new parts I took it for a short drive. The miss was still there but not quite as bad at first.

I then headed to Autozone to check for codes that were possibly stored but not turning the check engine light on. During the drive to Autozone the miss became more pronounced again and the check engine light decided to come on. I did notice that this occurred after turning the AC on- coincidence? Maybe, but I believe it could be vacuum related. I turned the AC back off, but the miss stayed the same.

I had 8 stored codes (3 duplicates):
P1000- Cycle Test Not Completed
P0174- Bank 2 Lean
P0309- Cylinder 9 misfire
P0310- Cylinder 10 misfire
P0316- Misfire detected on startup (First 1000 revolutions)
P0174- repeat
P0309- repeat
P0310- repeat

With this information I guessed that a continual misfire on cylinders 9 & 10 would likely cause the unburned fuel and air mixture to pass by the 02 sensor and set the code for bank 2 running lean as it is seeing a higher concentration of 02 than it should.

I then decided a tune up is in line and I likely need COPs for cylinders 9 & 10 and all new spark plugs. I have no indication of what actual maintenance the previous owner may have had done (he claimed it was just a very reliable vehicle and he regularly took it in for routine maintenance and nothing more). Typically I would have already replaced the spark plugs but I have to admit I am a little uneasy about the spark plug issues that commonly occur on these motors and thought I would wait until I have reason to replace them.

So yesterday I ordered 10 Motorcraft spark plugs, 2 Motorcraft COPs, and 8 Carquest coil boots. After reading some about changing the spark plugs in these motors I also ordered some dielectric grease for the electrical connections, anti-sieze for the spark plugs, a magnetic swivel head spark plug socket, and an OBD2 scanner to conveniently check future codes at home.

This morning I noticed another issue that leads me to believe the underlying issue to my current low RPM miss is vacuum related. I was running behind and driving more aggressively than normal this morning. I began losing vacuum boost on my brakes when I would brake hard at low speeds. It appeared that when my engine RPMs would fall below ~1000 and braking heavily is when this would occur. I have been reading everything I can find about vacuum issues and believe I need to get a vacuum gauge and start actually testing the lines.

The only thing I am aware of that *could* be effecting my vacuum system is the vacuum lines going to my hubs. I replaced the ESOF hubs with manual hubs this winter and did not block off the vacuum lines. This however had not been a *noticeable* issue until now, if that is part of the issue now. My theory had been that, yes it would be best to block them off but they should not be receiving vacuum unless 4x4 was engaged.

So that's my long winded post. Any thoughts/suggestions?

 

Moved to the 6.8L V10 forum.

Stewart

 

You may want to check and clean the mass air flow sensor if it has gotten dirty it will make it run like you are describing if it has gotten dirty you also need to clean out the whole intake tube and get a new air filter. You may also want to go ahead and block off vaccum going to the hubs beings you you need it anymore and eliminate that as the source of the problem. After that I would start checking all the other vaccum line under the hood. Does your a/c come out the dash vents or out the defrost?

 

Thanks for the ideas. I looked at the MAF while I was changing the other parts and it actually looked clean. I didn't have MAF cleaner on hand though and didn't want to try brake cleaner or carb cleaner on it. Lol. I will be cleaning it though.

As for the air filter and intake tube they both looked pretty good. Air filter looks almost new still. Inside the throttle body did look kinda nasty though. I may decide to clean it up some. I may go ahead and pick up a fuel filter while I'm working on it. I doubt that's my issue but it's good to change it anyway.

I agree entirely on going ahead and blocking off my ESOF vacuum lines and should have already.

The AC blows out the dash vents. That confuses me if its a vacuum issue because I have read about people having vacuum issues that set it to defrost.

Parts should be landing tomorrow. Hopefully I will have time to actually work on it some tomorrow evening. Driving it like this is terrible.

 

You are going in the correct direction with the coil boots, they do dry out and crack or even let water down into the spark plug hole with time. I wouldn't get overly excited about the lean code until you've done a tuneup, with two cylinders not firing and pumping only air into the exhaust I wouldn't be surprised to get a lean code.

Edit added. The loss of break boost vacuum that you described sounds pretty normal with a multiple cylinder misfire.

 

Dose your truck still have a Catalytic converter? If it dose and is driven with a multi cylinder misfire for any distance it will destroy the converter. I hate to be the guy with the bad news but Dads 00 V10 destroyed the converter in under 20 miles with three misfiring cylinder's from water getting in the spark holes from snow and dried out plug boots. His truck had pretty much the same codes and running conditions as yours.

 

How is the elbow from throttle body to PCV hose?

 

Granted that is a problem but I'm not sure as how it's related to the misfire. The misfire needs to be fixed before vacuum leaks are addressed, if there are actually are any.

 

Lean codes is where I was going with it. Check the hose and see if it is in fact intact. Mine wasn't so I replaced it and the lean codes went away. Lean codes could be contributing to the misfire as well.

 

It does have a converter on it. I thought I could be damaging the converter but I need to drive it. I've probably driven it 80 miles like this so far so mine will probably need replaced also. That's awesome news. Lol

 

I am going to go over the hoses again. I checked the PCV hose when I put the PCV valve in and could not visually detect a leak or by plugging one end and blowing in the other. I'm not ruling out a vacuum issue contributing to the lean codes.

I do have a question related to that though. I have a code for bank 2 being lean. If it is drawing enough air through vacuum lines to cause it to throw a code, shouldnt both bank 1 and bank 2 have lean codes? To me that would be logical but I dont know if it happens on just 1 bank sometimes.

 

So I changed the spark plugs for 6-10, new Motorcraft COPs for 9 & 10, new boots for 6,7,8. I plan to do the other side tomorrow. I cleared the codes and took started it up. Still has a miss but not as bad. It still idles rough but better. I also receive my OBD2 adapter today so I checked the codes after driving. It is still setting codes- P0174, P0309, and P0310.

I did notice a pending code for P0305 prior to erasing codes so I guess I will be buying a COP for cylinder 5 as well.

Plugs 6-9 all looked rough. The electrodes were burned down pretty well. Plug 10 doesn't look bad. Maybe it hasn't been firing right for a long time? I thought the Ex ran good before...but it is the only V10 I've driven and Sunday is the first time I've checked the codes on it.

I will try to post some pics of the spark plugs from a PC tomorrow. Not sure how to upload them from my phone.

 

I believe I figured out how to attach photos from my phone. I had to switch to the mobile site. I used to use the Autoguide App for another forum I used to frequent (TundraTalk). I checked and didn't see this one on there. That sucks because I really like that App.

Here are my spark plug pictures.

Cylinder 10 spark plug



Cylinder 9



Cylinder 8



Cylinder 7



Cylinder 6



Edit- resized pictures

 

I finally got the time to mess with it some more. I must have a valve stuck open on cylinder 9. Before putting the new spark plugs in cylinders 1-5 I decided to pull all of them and do a compression test.

Cylinder compression test

1- 140 psi, 140 psi
2- 140 psi, 140 psi
3- 140 psi, 140 psi
4- 140 psi, 140 psi
5- 140 psi, 145 psi
6- 138 psi, 139 psi
7- 140 psi, 140 psi
8- 145 psi, 148 psi
9- 0 psi, 0 psi
10- 140 psi, 140 psi

Not sure if I want to pull the valve cover and take a look or just plan to pull the engine in the near future.

 

I would pull the valve cover off for a look before considering pulling the engine, it would suck to go to all the work of pulling the engine only to find a broken valve spring.... 260K+ miles is definitely in the high mileage range but just going off of your spark plugs (lots of miles on most of them) and your description of how it used to run it doesn't appear that it's burning an significant amount of oil. You are checking all the right things, keep going in that direction and see if the engine is healthy enough to justify fixing it before pulling it out.