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Discussion Starter · #1 ·
Working on a 2002 3.0L OHV with an intermittent spark issue. A timing light on every cylinder wire shows a miss ranging between occasional miss to occasional fire. Some miss more frequently than others, but they all have an occasional miss. The engine always starts and stays running, but has low power. Even when missing it still idles fairly smoothly, but you can feel the miss under power.

So far, replaced the crank sensor, the cam sensor, plugs, wires, coil pack. It originally was throwing a crank sensor code which has gone away after it was replaced, however misfire remains. Is currently throwing P0303 and P0305 misfire codes (although timing light still shows misfire on all cylinders).

We've also reseated and cleaned battery terminals and all engine bay grounds.

Thinking maybe ignition switch or computer? What else could cause an intermittent spark? This is a charity repair for a family with some medical/financial issues so any help will be for a good cause. Thanks!
 

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Discussion Starter · #2 · (Edited)
Update:

I think we've now tried/checked everything! On top of Cam & Crank sensors, plugs, wires, coil pack, we did the following yesterday:

Compression: All in the 165-175 range. #5 is at about 162, but it was hard getting the tester in around the dipstick.

EGR: Removed, very clean for 100k+ miles. Black, but smooth. No deposits on the plunger or tube. Moves smoothly with external vacuum.

Fuel Pressure: Can get up to 60 PSI with engine off. Running is in the 35-39 PSI range. Significant needle shake at idle, smooths out at rpm. No significant leak rate when shut off.

PCM connection removed/reseated.

Started unplugging injectors one at a time and found #4 to have no effect on engine (all other injectors had drop in RPM when unplugged). Swapped #4 and #6 injector. Problem stayed at #4. Then swapped #4 and #6 plugs. Problem moved from #4 to #6. #4 plug was dark, but not badly fowled. Replaced plug (now in #6) and drivability was restored (jerking gone, power restored), however there is still is a miss at idle seen both on the timing light and felt at the exhaust.

At this point we're giving it back to the owner to let it be driven to see if problem resumes. Don't know what the next step will be. Wondering if it's a fuel pump issue (35 seems low) or a fuel pressure sender issue.

Edit: Was throwing a P0304 and P0316 this time. Scan gauge showed a difference in both short and long fuel trim between bank 1 and 2. Previously it had thrown code for Crank sensor (prior to that being replaced), and P0303 and P0305 (even after plugs were replaced).
 
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