1997 Range Rover loss of power, misfire

If it is missing that many cylinders, it is never going to accelerate. Since the coils are good, I assume you have good compression. The injectors are all that is left since you are already replacing the wires. Measure the resistance across the suspect injectors and compare with known good ones to se if there is a diiference

Clogged fuel filter will usually lean them out, not richen them up. Since you verified spark on the offending cylinders, use a meter to measure resistance across the injectors that are showing misfires and compare the readings to cylinders that are known good. How do the plugs look in the cylinders that are msifiring?

Usually a bad cat will give a random misfire code, not particular cylinders. You can try loosening the exhaust before the cat converters to see if it runs better. It will be loud, but if the exhaust can get out it will run better if the cats are the problem. May want to start at square 1 with th emisfire and do a compression test on the offending cylinders. Also if theinjectors are accessible, you can try swapping one from a cylinder that is missing to a known good one and see if themisfire follows it. Sometimes they will Ohm good but be sticking

Usually a bad cat will give a random misfire code, not particular cylinders. You can try loosening the exhaust before the cat converters to see if it runs better. It will be loud, but if the exhaust can get out it will run better if the cats are the problem. May want to start at square 1 with the misfire and do a compression test on the offending cylinders. Also if the injectors are accessible, you can try swapping one from a cylinder that is missing to a known good one and see if the misfire follows it. Sometimes they will Ohm good but be sticking

Hey.

Hope you don't mind me adding 2 pennies worth.

I would be rechecking or replacing the coil pack for cylinders # 4 & 7 .. I would also be checking the camshaft and crankshaft position sensor are not dirty or reluctor teeth dirty/gunked up ..

Ignition and spark distribution are controlled by DIS. DIS uses 4 double-ended ignition coils located at the rear of the engine. ECM provides internal switching of ground circuit for each coil, which operate on a waste spark principle. A spark is delivered simultaneously to 2 cylinders, one on its compression stroke and the other on its exhaust stroke. Coil No. 1 feeds cylinders No. 1 and 6. Coil No. 2 feeds cylinders No. 5 and 8. Coil No. 3 feeds cylinders No. 4 and 7. Coil No. 4 feeds cylinders No. 2 and 3. Failure of any coil will cause a misfire in 2 cylinders.
Ignition timing is controlled primarily as a function of engine speed and load. Engine load is sensed by Mass Airflow (MAF) sensor. Engine speed is sensed by a Crankshaft Position (CKP) sensor. ECM determines correct firing sequence and timing of ignition coils from input provided by Camshaft Position (CMP) sensor. An ignition coil fault is indicated by illumination of the MIL.

Camshaft Position (CMP) Sensor
CMP sensor is a Hall Effect sensor located in the engine front cover. CMP sensor produces 4 pulses for every 2 revolutions of the engine (one pulse is slightly longer than the others). CMP sensor signals are generated from 4 gaps on cam gear (one gap is smaller than the others). CMP sensor signals are used by ECM to correct fuel injector timing for fully sequential operation and for active knock control.
If CMP sensor fails, default strategy is to continue normal ignition timing. Fuel injectors will be actuated sequentially based on top dead center timing. Injection timing will either be correct or one revolution out of synchronization. A fault is indicated by illumination of the MIL.

Crankshaft Position (CKP) Sensor
CKP sensor is located on the left side of flywheel housing and uses different thicknesses of spacers for manual and automatic transmissions. CKP sensor provides ECM with information indicating that engine is turning, engine speed and crankshaft position. ECM controls fuel injection and coil firing based on signal from CKP sensor. Engine overspeed protection is set at 5500 RPM and is based on CKP sensor signal. There is no default strategy for the CKP sensor. A failure will result in an engine no start condition. A fault is indicated by illumination of the MIL.
CKP sensor output signal is obtained from the magnetic path being made and broken as the reluctor ring teeth pass CKP sensor tip. Reluctor ring has 35 teeth and one missing tooth spaced at 10 degree intervals. The missing tooth is positioned at 20 degrees after TDC.

Hope this helps

Did you replace the H02s, when you replaced the Catalytic convertor ? Also what type of new cats were fitted OEM/Aftermarket/universal ?

DTCS P0130-P0133, PO136-P0139, P0150-P0153, P0156-P159, P0171-P0172, P0174-P0175, P1137-P1139, P1157-P1159, P1171-P1172 & P1185-P1196: HO2S CIRCUIT MALFUNCTION

There are 4 Heated Oxygen Sensors (HO2S) located in the exhaust system. Primary HO2S-1 "A" is located before left side catalytic converter and secondary HO2S-2 "A" is located after left side catalytic converter. Primary HO2S-1 "B" is located before right side catalytic converter and secondary HO2S-2 "B" is located after right side catalytic converter. Secondary HO2S-2 measure oxygen content after catalytic converters to monitor operating efficiency of converters.
Each HO2S is electrically heated to ensure sensor achieves operating temperature as quickly as possible after start-up. ECM energizes HO2S heater using a Pulse Width Modulation (PWM) signal which starts low and increases within 30 seconds to desired heater temperature. Primary HO2S heaters are wired in parallel and secondary HO2S heaters are wired in parallel for synchronous ECM control of each heater pair.
If front HO2S wiring is crossed, vehicle will operate properly until sensors reach operating temperature. ECM will then cause one bank of cylinders to run very rich and the other bank to run very lean. This will cause engine to misfire, idle rough and emit black smoke, with possible catalytic converter damage.

Diagnostic Aids
Indications of HO2S failure may be a strong smell of rotten eggs until default condition is initiated, high CO readings and/or MIL is illuminated. Check for contaminated sensor, poor connections, loose terminals, and open or shorted wires. Ensure wiring to primary sensors is not crossed.
With engine running at normal operating temperature, measure HO2S output voltage between HO2S 4-pin connector terminals No. 1 and 2. See Fig. 7 . Output voltage on primary HO2S should change between approximately 0.2 volts (rich mixture) and approximately 4.7 volts (lean mixture). Using a Snap-On Personal Automotive Computer (PAC), compare wave pattern with known-good wave patterns. See Fig. 8 . Oxygen content of exhaust gases after catalytic converter should be nearly constant, causing little voltage change in secondary HO2S.
Measure HO2S heater resistance between sensor connector terminals No. 3 and 4. See appropriate WIRING DIAGRAMS article. See Fig. 7 . HO2S heater resistance at 68 °F (20 °C) should be approximately 5.7 ohms.
Fig. 7: Identifying 4-Pin Sensor Connector Terminals

Fig. 8: Identifying Known-Good HO2S Wave Patterns

Is the timing chain noisy (rattling) I don't see how a timing chain can give misfire codes for 3 cylinders or driveability issues @ high RPM only. The car would misfire all the time on all cylinders?

Did you do a compression check? Remove and clean the CKP, CMP and the MAF. You said he checked the sensors. How did he do this? With engine running hooked up to a scanner?

Ignition and spark distribution are controlled by DIS. DIS uses 4 double-ended ignition coils located at the rear of the engine. ECM provides internal switching of ground circuit for each coil, which operate on a waste spark principle. A spark is delivered simultaneously to 2 cylinders, one on its compression stroke and the other on its exhaust stroke. Coil No. 1 feeds cylinders No. 1 and 6. Coil No. 2 feeds cylinders No. 5 and 8. Coil No. 3 feeds cylinders No. 4 and 7. Coil No. 4 feeds cylinders No. 2 and 3. Failure of any coil will cause a misfire in 2 cylinders.
Ignition timing is controlled primarily as a function of engine speed and load. Engine load is sensed by Mass Airflow (MAF) sensor. Engine speed is sensed by a Crankshaft Position (CKP) sensor. ECM determines correct firing sequence and timing of ignition coils from input provided by Camshaft Position (CMP) sensor.

If the timing chain was stretched or had damaged in some way, I would expect a rattle of some sort and also rough running all the time, not just at high rev's or under load. Ask the mechanic to check fuel pressure at WOT (wide open throttle) and also to check the readings from the TPS (throttle position sensor) also if your mechanic has the scanner to read these sensor's output signals he could read them whilst doing a drive cycle test upto 3,500 rpm to check all readings are good or what changes at this speed. I'm thinking TPS may be bad. Also check the wiring for PCM and if it looks like it got wet?