Hey D2 experts. I've been battle a P0301 error for months now. My truck has 108,000 miles. Here's what I've done, but I can't seem to buff it out.

Head gasket, wires, plugs, coils, injectors, oxygen sensors. I did the head gasket first, when I first got the error, because I was concerned about infamous internal issues, but everything looked great. Rods were all straight.

After doing all the rest, I switched around plugs, wires, and coils, just to be certain it wasn't the ignition system. I guess I'll pull the intake again tonight to test the fuel rail pressure, but I've never seen an electric fuel pump partially fail before.

Any other thoughts? MAF sensor? Bad cam? The misfire wasn't consistent, but it seems to be now. So I'd ruled out the cam. MAF sensor or vacuum wouldn't stick to one cylinder, would it?

Thanks,

The Last One



I'm going to test fuel pressure yonight

 

None of those will be one cylinder only. Did you check compression? I had one truck with one low cylinder throw a code. Have done the swap known good for #1? Plug, wire, coil, injector

 

I swapped the plug, wire, and coils, all seperarely figuring it had to be one of them. Compression was good several months ago when I started this journey, suppose I could check again while I'm at it.

​​I thought if it's not ignition it'd have to be fuel. Number 1 is the last one on the rail. But, of course my fuel pressure tester doesn't fit this tiny Land Rover fuel rail access point.

Edit*** just tested compression. It's 150psi and mmatches the others very closely.

 

Misses are detected by the CPS timing between pulses of the reluctor on the flywheel. So if there was damage to a reluctor tooth, that should show up on two cylinders (e.g. 1 & 6) in a four-stroke engine, ruling that out.

There was a recent random mis-firing problem at idle caused by an uprated performance cam. So, possible could be a cam problem, but that would likely cause noticeable vibrations. How is the engine performance? Have you monitored O2 sensor trends and fuel trims?

 

Performance is decreased, especially at WOT. You can feel the misfire at about 2000 RPM and above.

I can monitor the sensors and trims with my readers, I wouldn't really know what to watch for. None of them are dead or 0.

 

Sure starting to sound like potential MAF or fuel delivery problem. Maybe try a different code scanner to see if different cylinders are involved. Some old scanners would only show one code at a time, and some act different, depending on interaction with the car make and model.

So, what to watch for real time: O2 (Upstream, or Sensor 1 each bank) voltages regularly modulating between low (around 0.1V) to high (around 1.0V). Both banks reacting nearly the same. LTFT near mid-range (-10 to +10%, zero is factory) not extreme (+/-25%). STFT near mid-range depending on engine demand, and not extreme. The both banks values for LTFT and STFT should be matching. If there's a big vacuum leak, STFT will rise at idle (when vacuum is high = more air) then drop down to normal on the highway. If the fuel pump (or maybe fuel pressure regulator, or filter) is weak, STFT will stay low at idle (when not as much gas is needed) then rise up on the highway calling for more fuel. Also real-time monitor the signal from the MAF to see that it rises smoothly as RPM and engine load increase.

 

Awesome. I wouldn't have thought of all that. Once I test fuel rail pressure I'll do a drive about and see how the stats look. My scanner is pretty good and has displayed multiple codes before, seems I just only have this one code. The live data works well. If I recall I can actually chart it on my phone as well.

I'll report back with my findings.

 

Off topic but could you share what kind of headlights those are and is it a 3D printed insert? Hard to tell if its the metal one from Australia?? I like the look and wanted to do something similar. Thanks

 

Hey man. No worries. It's not a 3d printed form or anything. I just removed the old lights, bought some seven inch bezels like on the Defender, and mounted 7" lights. Turned out pretty good.

You do have to drill some holes and make some cuts in the front body panel there. They plug right in tho.

I'll take a close up in a bit.

 

So, I'm trying to test the fuel pressure now. Should the fuel pump turn on with the "on" position? Because I only get a reading when I crank. I assumed it'd provide pressure with the ignition "on".

Either way, cranking it I only ever got to 45 psi.

Tested the power pin for the relay, it's getting 12v, but the signal pin (86) from the ECU is only generating 5.1. Guess I can inspect the ECU connector, if I can find the damned thing.