My 07 Quest 3.5 is in need of help and I am out of ideas. Here is the rundown.

About five months ago it started running rough with a cylinder 3 misfire. A mechanic diagnosed it as a bad injector and was set to replace it but said he couldn't get things apart to get to it.

So my wife and I watch some YouTube videos and take on the job which took about four hours. We replaced all six injectors, spark plugs, PCV valve, and I swapped the #3 coil pack to cylinder 4 before closing it up. After firing it up, cylinder 4 misfire. Replaced the coil pack and everything was great for four months and 4,000 miles.

She calls me, check engine light blinking and running rough a month ago. Hook it up, cylinder 5 misfire. Luckily with long thin arms I could replace that one without tearing everything apart again. Van was again running fine for 1,000 miles.

Now this week. This time it is running rough, check engine light blinking, and white smoke from the tailpipe. I suspect the head gasket and start looking at it. No coolant missing, and the smoke from the exhaust smells of oil and gas. Scan reveals cylinder 2 misfire and a P0151 for the A/F O2 sensor right below that cylinder.

I pull the coil and swap it, doesn't fix it. Pull the plug and it is wet but I test it and it has good spark but I change it anyway. I change out the o2 sensor and no change. Finally I pull the injector and test it and spray choke cleaner goes right through it so I suspected it was stuck open. I get a new injector and put it in, not fixed.

It is however different. Although it is a little rough, it isn't as rough. I ran it and let it get up to temp at idle and revved it a bit and although it threw the misfire on #2 code again I cleared it and ran more and it didn't do it again. There is also far less smoke and the smoke that is coming out is the smell of burning oil and no gas odor.

Testing with a meter and test light I can see pulses on the front three injectors and can also feel them ticking with my finger when it is running. The only thing I noticed that seemed a little off was that with the ignition on there was only 9.5v at the injector wires and not full battery voltage.

Last, I used a block tested with the radiator and there was no color change in the fluid indicating that there was no combustion gases present in the coolant which would happen with a head leak of coolant.

I am at a loss on this one, no idea where to turn. It almost seems like it is something simple that I just have no clue about.

Can anyone assist with some ideas on where to look or what to check? I really appreciate it. Buying another vehicle is just tough as well as a big repair bill with all the crud going on lately in the country. My young daughter also wants "Nessy the Quessy" feeling good again.

Thank you.

Sounds like you've done some good diagnostics thus far and are conveying them very clearly. Thank you, and welcome to NICO.
I tend to agree with your first assessment of the open injector. If it was stuck wide open, that can certainly cause other issues such as rapid piston ring wear (you're washing away all of the oil in there and diluting it), or even bending a rod if the injectors are big enough... which hopefully they aren't.

I'll think about this one, but I would suggest doing a compression check on that cylinder and comparing it to some of the other ones around, and also look at the plug when you pull it to make sure it isn't still wet.
You can also just unplug the battery for 15 or so minutes and then plug it back up to reset the ECU. Maybe the open injector caused some sensors to drift pretty far away from normal operating and they need to be set back to home

Have an update on this with improvement but not resolved.

I unhooked the battery overnight to fully reset the ECU, and pulled the injector and reseated it. Once the van was started I could feel the injectors ticking with my finger indicating opening and closing.

The idle is a little rough but it smooths out above idle, even had it up to 80mph on the back country roads and it was smooth and sounded good. Under deceleration it would get a little rough again.

The CEL was not coming on after 10 miles of driving on two different tests about an hour apart however there was a pending P0302 code after the first test drive which I cleared, and P0300 and P0302 after the second test drive which I also cleared.

Unfortunately I don't have the necessary tools to check compression, nor have I ever done it, and need to know if it can be fixed and at what cost or if it needs to be replaced. At this point I have to admit that it is past my skill set and it is at a mechanic today. I hate throwing in the towel but also know when to step away and bring in an expert. When I drove it the four miles to the mechanic it was the same as the previous two test drives but the CEL did come on when I arrived but was not flashing. I didn't check the codes.

Here's to hoping. I'll update when I know more.

Also, thank you for the compliment on my description. I work in IT on server infrastructure on very complex systems and recognize that auto mechanics is equally as complex and takes exceptional skills. When people come to me with issues on systems they don't always share on the information or what to give just enough to lead you to a solution they desire. I try to be straightforward, factual, and give all the info I can when asking for assistance from that experience.

Your descriptive skills are very noticed and appreciated
Compression checks aren't really that hard to do, but you do need the equipment. Its about 50 bucks. I used to just bum it off buddies, but finally bought my own compression checker set.

Let us know what the mechanic finds!

Got a call from the mechanic and they are stumped. After two hours of looking at it they cannot find a cause to the misfire. All the injectors, coils, and plugs test fine as well as electrical. They see ECM signals that look good as well.

At this point they wanted another $250 over the first $125 for just diagnostics and I declined, too much money to just find a problem that the cost is unknown.

They did say there are three suspected things they wanted to look at. 1. Excessive carbon or sludge buildup 2. ECM issue 3. Camshaft issue but they didn't know if it would be the sensor or something else related to it.

Not sure what I will do at this point with it.

Did they mention if they did a compression and/or leakdown test?
Sorry to hear about the troubles

Yes, forgot that. He did and said compression was good on the cylinders.

I had printed a one page history of everything I had done admitting I may have done something wrong. The tech said he checked all of it, and it all looked good, and was exactly what he would have done to the vehicle. He was really stumped.

I am baffled too. It starts up fine, idles a bit rough, then is smooth under acceleration be it mild or heavy all the way to 80mph. You can feel it when coasting down from speed but not horrible. Don't get it.

I drove it home and put the tank at just under half of premium, it was almost empty, and added a can of Seafoam to it. Tomorrow I plan on getting it warmed up and slowly running Seafoam into the intake vacuum hose from the brake booster (after check valve) while it idles or just above and then shut it down and let it hot soak. I'll also pull the plug out of #2 and spray some in there with a squirt bottle then put it back and let it hot soak. After that, fire it up and drive it like it owes me money and see what happens.

Good deal. Hilarity will ensue haha. Smoke screen the neighborhood.
https://www.nicoclub.com/archives/how-t ... t-way.html

I have done two Seafoam treatments now by removing the brake booster vacuum line and adding it in there slowly while the wife held the RPMs up.

After each one I let it sit for 30-60 minutes then took it for a drive. Although I accelerated very briskly and drove at 55 for miles, no change. I was surprised based on what others say that I got very little smoke when adding it while running regardless of how fast I added it. I also didn't get very much at all during the driving and it was gone after 1/4 mile of driving.

I'm at a total loss and the wife has decided it is time to throw in the towel and get a replacement vehicle without putting more into it. Naturally when sold the buyer will be made 100% aware of everything and that the vehicle could die the next day or last years, and possibly be an easy fix when found.

Still mystified that although it runs a little rough I can still squeal the tires and it still MOVES and feels smooth. At this point it is just pending codes and running rough but still, just done. Wondering if there is possible internal damage on that cylinder from when it stalled out on my wife and she tried to start it, possible hydro lock or something.

Bummer. "Nessy the Quessy" as my daughter calls it is going away.

Yeah you could totally just keep driving it.
That's wild that you didn't get a smoke show from the seafoam though. That's gotta be a first.

Hoping you got the issue resolved by now. Can you share the fix?
If not fixed yet, did the mechanic consider that one (or both) Camshaft Position Sensors are not operating correctly? You may not have a CPS error but the sensor could be failing. CPS is critical to proper ignition timing, and are very easy to replace.

Never did get it resolved and sold the vehicle about a month later. I did change those sensors with no change though. Ended up selling it to some folks for $1800 with absolute full disclosure of everything and test drive. Never heard from them after the sale.

Interesting. My 2004 may eventually meet the same fate, and that's being optimistic. I do enjoy the ride though.