Hey,

Service engine light was on so took it in and replaced all they recommended. 4 main O2 sensors, spark plugs n wires. Light came back on as soon as I left the shop.

It's running rough a s smells like gas. I took it to a Land Rover shop a s they think it's in the electrical harness. My question is -- will a fault in the wiring harness cause such misfire lack of power and high smell of gas? Could this be the fuel filter?

Thanks

 

I would start by checking the wire order. If the previous shop crossed the wires that would absolutely do it. Also what are the codes before and after?

 

The ECU bases fueling on oxygen sensor voltage readings. O volts means lean, 1 volt means rich. If the ECU reads zero volts because the wiring is cut, or the sensor is dead, or an injector is plugged, or there is a vacuum leak, then it will command more fuel until it richens up or reaches the max enrichment. If the voltage reads high, due to a leaking injector, then the ecu adjust until leans out.

When the truck is cold, it starts out rich for a few seconds until the ECU decides it needs to go to closed loop fueling and starts using the 02's. When it uses the 02s for closed loop fueling, the ECU drives the fueling until it reads close to 1 volt, then reverses until the voltage gets close to zero, and then the cycle starts over.

The best way to troubleshoot is to chart the voltages, and use a known good 02 sensor.

 

I have the same problem, been troubleshooting it for a year now...no luck. Like you I've replaced plugs/wires/sensors.

 

Could an intake leak cause this?

 

Charting the O2 sensor voltages can help pinpoint the problem, like Extinct says above. Charting O2 sensor voltages from idle to highway can also help determine if there's a vacuum leak.

 

To answer your question, all based on experience w/ D2s of mine:

-- Doesn't sound like a fuel filter issue (unless it's punctured or physically damaged and maybe leaking under the truck and you're not getting enough fuel). A fuel filter issue would result in clogging / less fuel most likely and not super common on D2's.
-- A massive intake leak could cause this -- but I think you would see it or hear it if you at all know your way around the engine. You could spray carb cleaner around your running engine (delicately - don't blow yourself up on hot manifolds etc please...) to confirm. Definitely check the PCV hoses, but on my 4.0 / 4.6 V8's, they still run pretty decently even if a large hose is disconnected, this is unlike many cars which will barely run with a big intake vacuum leak.
-- Check every fuel injection component -- MAF sensor plugged in. ? Each injector plugged in? etc
-- Yes, a massive wiring harness issue could cause pretty much *anything* to happen, including this. Massive overfueling might point to an electrical issue with something in the fuel injection system or it's wiring harness. One thing to watch out for -- if you drive it like this too much, you're probably over diluting your oil with fuel which can be very bad for an engine long term. (I bought a RRC with an overfueling issue that was result of bad EFI ECU, and the oil was essentially gas consistency (watery) when I drained it -- oops -- )

Step 1 of what I'd try: Did they 100% put the plug wires on the correct terminals on each cylinder and on each coil pack? You should verify as someone else suggested. Diagrams are around that you can compare too with a bit of looking.

Step 2: You said Engine light is on. This means codes are being stored. Do you have ability to pull and write down those codes via a code reader? If not do this. List codes here. I suspect it probably is throwing a bunch of codes.