Hey all,

I've come to this forum in the past and fixed many problems without posting, but now I'm officially stumped on what to do.

My 97 F-150 has 208,000 miles on the original engine. It started misfiring originally on just 2 cylinders, 1 and 8, after pulling the codes. I also get a P0420, catalyst system below threshhold bank code being thrown, but I think it is because of the misfires.

To remedy this I've done the following:

1. Spark plugs are relatively new and were changed completely a few months prior to issues.
2. Coil Packs were changed on both sides. Additionally, Cylinders 1 and 8 are on separate coil packs.
3. Spark Plug wires were changed
4. Did a resistance test on each fuel injector and they all passed.

None of this has worked. Am I missing something obvious? From my friends I've heard everything from my exhaust is plugged to I need to change all my injectors. Injectors are costly and I'm not even sure how to check if my exhaust is partially plugged, but it seemed to be flowing fine. Also, I pulled plug one since it was simple to get to and noticed it was slightly brown, like it had oil on it.

I got frustrated and continued driving my truck until the problem degenerated into severe misfiring and now I cannot get it started at all (Wrong move). I bought a car and haven't drove it since, and have it sitting behind my house. Now the cops want to tow it because the registration is has expired so I've decided to move it into my garage so I can work on it. Part of me wants to junk it, but I've put a lot of time, money, blood, sweat, tears, and curse words into this truck and am motivated to get it back up and running since the transmission and front suspension had been replaced recently.

What to do!?!?

1. Go to the Ford dealership and have them diagnose the issue and then try to fix it? (I have little confidence in them from the stories I've heard)
2. Pull the engine, tear it apart, and rebuild it?
3. Drop a used/rebuilt engine in?
4. Call me crazy and say junk the truck and buy a different one?

Currently leaning towards option 3, but I would like some advice for a young guy who is probably too cheap and stubborn to know any better. Thanks in advance.

 

I'd drop the exhaust or at least unbolt at manifolds and see if it'll run. If you've had severe misfires the catalysts may be melted and blocking the pipes.

 

I would do a compression check on all cylinders and see what you got motor wise... possible intake leak in front? either way it's a good check to start out with.... keep us posted! good luck!

 

If your thinking of a bad injector, trade places with injectors from cylinders you know are good.
Just because the plugs were changed recently, pull them and check them anyway. A spark plug can tell you a lot. Make sure it is firing. See what kind of deposits are on the plug. This can tell you if it is running rich, running lean etc.
Do a compression check on all cylinders. To have cylinders 1 and 8 missing, it if probably not anything in the intake, but possibly an intake gasket leak.
Those are the first things I would check. I have had new plugs go bad after a couple hundred miles before, so check them first. Make sure they are sparking, then move injectors around and see what you have.

 

Once you get a 420 code the cats have to be changed.
Before you spend on cats, the misfires absolutely have to be cleared or you lose the cats again.

 

Thanks for the advice. Tonight I will start compression testing each cylinder to see if that is the issue. I doubt it's the plugs since I also tried to start the engine while having plug 1 out and grounded and saw a strong blue spark, as I expected since they are so new. I'll keep everyone posted!

 

there is plenty of info in this forum related to misfires and people with extensive knowledge, start again with a cold head and look for that misfire cause.

 

When you replaced those spark plugs, did you gap them? There is a good chance the gap is to big and the spark cant make the jump.

 

what spark plugs and COPS are in use?




also how long was it misfiring before you ruined the cats?

 

I used motorcraft plugs I think, though I didn't gap them. I used to check in the past though they always seemed to meet their gap specs. My '97 uses coil packs not COPS.

I'm assuming the cats are ruined but I don't know for how long. As soon as I pulled the codes for the misfire I also was getting a code for my cat as well. I'm assuming the misfire itself was causing the bad cat code.

 

So I ripped out my old engine and put in a junkyard engine a few months ago and thought I would provide an update. While swapping out components and taking off the intake manifold, I noticed clear damage to the intake manifold gasket which was causing antifreeze to flow into the cylinders. This was confirmed after taking out the spark plugs on cylinders 7 and 8 and noticing the gunk that was caked onto them. So, a little preventative maintenance would've gone a long way if I would've just rechecked my spark plugs (which I had replaced only a few months before) so I could've replaced the gasket and I may have been able to salvage the old engine. Hindsight is 20/20 I guess, but at least the junkyard engine is running like a champ.

 

Grats bud, knowledge and wisdom are worth more then gold. The better we learn how to 'think intelligently about problems' the easier they become to solve, universally speaking. Gather all the data you can reasonably gather before attempting to 'fix' the problem, will save money and unnecessary headache.


Cheers,
Van