![]() Fuel pressure with an old reliable gauge showed normal pressures, ruling out fuel issues. A spark test, several times seemed to reveal nothing wrong with the coil pack (coil pack laid out over the engine, plugs in place, bases wired to engine block ground). I suspect the schrader valve on the loaner tool is worn and cannot use a tire valve as replacement. My very old compression gauge with a press on rubber cone still works (holding pressure) when I used a paint compressor and inflator nozzle but it can't fit into the long passageways of modern engines. I tried to make repairs to the loaner gauge but I gave up - I anticipated loaner tools wear and tear. I didn't want to waste any more time explaining a faulty compression gauge and borrowing another one from Autozone but I went ahead and ordered a low cost replacement coil pack from rockauto and waited. A compression check would have helped but I went on the fact that the engine was fine under my ownership. Compression after 104k miles isn't an issue as the engine ran with perfect idle since I bought the car back in '05 until this misfire popped up. Spark plugs were already exchanged to rule out a faulty plug. I borrowed a compression gauge from Autozone and promptly found it useless as it couldn't hold any pressures from any one of the three cylinders. The rear coil pack requires more removal of upper engine parts before the coil pack can be measured for comparison purposes. I checked coil resistances and found nothing unusual. Suspecting the coil pack, I removed the front intake runners before removing the coil pack. My V6 uses a pair of ign coil packs, one for the rear cylinders (135), one for the front cylinders (246). I drove around slowly with the engine misfiring and after some agonizing blocks decided to go home and put it in the garage for further diagnosing. Flashing cel means unburned fuel entering the exhaust and can damage catcons if driven this way. I pulled out my OBD II diagnostic reader, plugged it in while parked two blocks from home and read P0304 - cylinder #4 misfire. A few days before Xmas, I went on an errand for lunch and as soon as I left my driveway, sudden check engine light with severe engine hesitation occurred. Just so you appreciate where some of us may or may not have similar experiences, here's my recent issues with my 元00. Examining it for blockage, rubber seal for deterioration and allowing vacuum leaks, and substituting it is far easier than attempting to measure it without prior experience and knowing what's expected in normal operation. A chart is needed with known values at certain vacuum levels. Measuring it requires a vacuum, 5v supply and multimeter to measure voltage signals as vacuum varies. The easiest way to eliminate map sensor issues is removing it for examination and/or substituting it with a known good one. This is part of EFI system operation along with other sensors. The map sensor is used as a load sensor for the pcm to determine what part of the fuel map to use as loads change. A spray test will show how well they've held up over thousands of gallons of fuel.Īmong many things contributing to hesitation are clogged fuel filter, dirty/clogged/intermittent egr valve, erratic fuel pressure fluctuations, intermittent spark from worn/corroded ignition coils, disintegrating catalytic converter guts blocking exhaust flow, damaged spark plugs, damaged intake manifold gasket allowing vacuum leaks, etc.Ī piece of carbon sticking into the map sensor may block off its ability to detect varying vacuum as engine rpm changes. Removing injectors for bench testing is another way to determine if injectors are worn, clogged, intermittent. ![]() Wet black deposits indicate cold range or oil burning. Removing plugs to examine them may show dry black deposits, indicating excessive fuel leaking past a worn injector. Not only fuel pressure is checked but a leaky injector will lower pressure (ignition on, bleed off occurring quickly). Mileage? Presuming the coolant sensor is the flat nosed brass one to rule out rich fuel mixtures, worn injectors are possible.
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