I recently came back from running section 5 of the Oregon BDR. by came back I mean I made it back, and the truck broke down 153 miles from home. I noticed the engine wouldn't rev higher than 3,000 rpm when going up a hill and the check engine light flashed. I pulled over, checked the codes and P0301, P0316, P0171 came up. Originally thought it was the spark plug so I pulled that and replaced it but didn't fix it. On the trip we needed to use fuel cans and refueled in a dusty environment. I thought some dust or debris had gotten into the injector so at the nearest gas station I put some Seafoam in. After the treatment the cylinder 1 misfire stopped. It occasionally threw bank 1 low fuel pressure but it allowed me to hobble the car for 4 hours until I stopped for 10 minutes with the engine off. Upon restart it threw the same codes and check engine light flashed. I had to get it towed to home and when talking with fellow LR3 who were on the trip, suggested it may be a leaky injector. I took a look at the fuel trim, and O2 sensor voltages and found a possible hint. I'm not very familiar with fuel trims, what they mean, and what's good or bad. I did go through 3 water crossings, and went through several muddy trails if that may play a role. Water never went above the bottom of the headlights Or above the bottom of the door. What should I look at for diag and replacement? I was thinking of removing the injectors and sending them off to get redone and to replace coils and spark plugs anyways but not firm on that decision yet

 

With cylinder 1 misfires and bank 1 lean, a clogged injector on cylinder 1 is my first thought.

An intake manifold seal leak at cylinder 1 could also cause these same codes.

Low power also from running on 7 cylinders.

It’s good that you’re only showing lean on a single bank. It helps narrow your troubleshooting to that #1 cylinder.

 

Rereading your post, fuel pressure may be your root problem and it’s showing up on cylinder 1 first.

These rigs are difficult to setup a mechanical fuel pressure gauge.

 

You have a 2005, it should have a schrader valve on the fuel rail for checking pressure. A leaking injector tents to cause a rich condition, not lean. Even a misfire tends to cause rich condition since fuel is not being burnt... I guess, though, just to rule things out I would move the coil for #1 to a new location and see if the misfire moves. That is probably the quickest test you can at first before moving onto testing for vacuum leaks, etc.

 

Ah yes the thing I forgot to add. I did swap a new coil in as someone one on the trip was about to replace them before, but brought them instead. It was a new part so it may be faulty knowing how parts are these days. Spark plug was pulled and deemed clean. I assume a clogged injector would cause a lean condition on Cylinder 1? Another thing to note would be that it ran rough under 1k RPM and above 2k RPM but okay in between. It was drivable and the check engine would only flash when over 2k rpm.

 

Here’s what the book says.



Yes, a clogged injector will cause a lean condition. The computer will respond by adding fuel (increasing fuel trim) on the lean bank.

Everything in the book to cause lean, except a clogged injector, would likely show up on multiple cylinders or both banks. You can eliminate MAF or air leaks in the intake ducting because they would impact banks 1 and 2 evenly. Low fuel pressure would also likely show up as multiple cylinder misfires, not just #1.

I can’t think of a reason why you’re running good between 1k and 2k RPM. A flashing check engine light means you’re misfiring excessively. Spark related misfires, plug or coil, would show up as rich (low fuel trim) because unburned fuel is reaching the O2 sensor.

If you swap injector #1 to a different cylinder and the misfire moves with it, you found your problem. If the misfire doesn’t move, then you’re digging deeper to things like a manifold gasket leak, low fuel pressure, etc., or worst case, checking compression.