Hello all. This is my first post here, and as a fairly competent wrencher and recent Navigator purchaser, I wish that I didn't have to make it.

Backstory: To make my car hobby jive with my family life, I've made a habit of buying cars in various states of disrepair and fixing them, and those become our cars (and we sell whatever we were driving prior to that). My most recent move was to buy a 2003 Navigator 4WD with ~160k miles on the clock. The truck was running very, very poorly, along with having a handful of cosmetic and convenience issues. So far I have just been trying to make it run well, but it has been a battle.

The truck: I bought it with codes reading cylinder 8 misfire, bank 1 lean, and bank 2 lean, along with a horribly rough idle and a nasty tick from the passenger side of the engine.

I expected vacuum leaks, and found one, but repairing it only solved the bank 1 lean. Driving it, it would miss and start to die if you tried to give it any serious gas, but would idle forever. I checked the fuel pressure (this was sounding like a bad pump) and saw that it had 15psi at idle, and 20psi with the vac hose removed. Bad regulator, so I replaced that and have 30-35psi at idle now. No more missing under throttle, but codes remained the same.

I should mention also that the misfire counter would go up and up at idle, very fast (8-12 more per refresh), but would stop going up as soon as it was revved off idle. Held at 1500rpm, the misfire counter would never move. Drop to idle, and it would go back again.

Staring at the Torque app long enough, it occurred to me that the upstream O2 on bank 2 was saying that it was lean only at idle (not revving), but the downstream O2 was pegged at 0.9V at idle. On a whim, I disconnected the upstream O2 sensor, and the idle smoothed out to what I would call 90% of normal. The misfire counter slowed to 1-2 more misfires per refresh at idle, and still none off idle.

Now, misfire codes for cylinders 7 and 8 started coming up, despite not feeling like a misfire (wife drives a Town Car, so I've gotten familiar with the feeling of a coil going out). I pulled the plugs on bank 2 and they all looked normal, but I changed them anyway, as well as the coil on cylinder 8 just for kicks. Exhaust smells normal. No leaks at the manifolds that I can find, but the exhaust has a pulse (where pressure is much less) that has a cadence that matches the tick up front. Using a stick of 1x1, I listened around for the source of the tick, and it sounds loudest touching the forward and lower-most valve cover bolt on the passenger head. No abnormal noise from the timing chain cover on either side, or from the driver side head. The tick happens at about 300-350ish steady beats per minute at idle, and changes frequency proportional to engine speed, so I'm relatively sure it is valvetrain related.

The truck runs reasonably well except for that tick, and except for the fact that it will throw misfire codes at idle or under heavy load (uphill on highway, for example). Uphill on the highway, it will actually start flashing the CEL and it feels like it kills at least a few cylinders until it stops flashing.

I work a lot, so I won't have a chance to dig further into it until this weekend. My plan is to pull the passenger valve cover off and figure out the source of the noise. I'm guessing it's a collapsed lash adjuster, bad follower, or bad oil flow to the lash adjuster for one of the valves on cylinder 1. I'll also check the timing chain slack while I'm in there. I have new upstream O2 sensors ready to go in on both sides, though I don't expect that to solve anything, and a new thermostat since the truck never gets above 170 degrees.

My question/confusion is trying to correlate the valvetrain issue on cylinder 1 with the misfire codes. If I have a completely collapsed HLA on one valve there, would the restriction of only having one valve open be enough to slow down the crank and throw a misfire code? Could I have a bad crank sensor causing this? I suppose that I should do a compression test across all cylinders, but I would like to sort out the valvetrain issue first, lest the cylinder 1 result be affected by whatever is going on there.

I am completely open for opinions and theories. Ideas?

If I can't figure it out without pulling the heads off, I will probably just swap in a junkyard motor to use while I sort this one out. Speaking of which: does anybody have a running list of changes to the 5.4 dohc over the years? They look identical for the whole run, but parts searches imply that very few years are interchangeable. (ie: a 2001 engine is not interchangeable with a 2003)

Thank you guys for any help you can give (and sorry for the novel). It's not often that I can't make sense of something, but sorting out this poor mistreated Navi has me perplexed.

 

If you have a compression tester available, I'd do a quick one of the suspect cylinders plus a couple on the opposite bank to see how it is. Does this Navi have the 4v Intech engine?

 

Yes, it's a 4V. I don't know whether to be scared of dropping valve seats, or thankful that it doesn't have cam phasers.

 

The 32-valver uses an ITMV (Intake Manifold Tuning Valve) which basically shuts down the intake flow on one of the two intake valves below ~2800 rpm. So if the collapsed HLA is on the intake valve that is full time functional and the other intake valve's intake port is shut down, yeah, ICould see it cause a misfire.

Also, the 32-valve is known to crack exhaust valve seats from excess heat on the rear cylinders. And low fuel pressure plus P0171/174 could cause excessive cylinder heat. I suspect that may cause an exhaust pulse.