- Sep 30, 2017
- Vancouver, BC Canada
Per the title, I am having some difficulty diagnosing an engine fault that would appear to point to the ignition coils. Per Haynes, the secondary resistance for these coils should be between 9,700 ohms and 16,700 ohms. Mine measure 12,300 ohms (each of the two coils) when cold, and 16,300 when hot. So, in the Hot condition, they are both just inside of the limits of rejectability. Let me explain further: there are two ignition coils on my '99 - and ea. ignition coil has two "towers" - onto which of each a high tension lead services a sparkplug. One coil caters for cylinders 1 and 4; the other serves 2 and 3. My fault codes are P0300, P0301, and P0304 - Random cylinder misfire detected; Cylinder 1 misfire detected; and Cylinder 4 misfire detected. The car would appear to faulter, just off-idle.... and only when beyond initial start-up / open loop operation. Truly, it feels like lean surge... cuz when you back-off the throttle when it surges, the surging reduces or ends. The pairing of the coils would appear to say that the coil serving 1 and 4 is suspect.... but it is within the limits of rejectability, and it totally maps what the adjacent coil does. Now I could pull the negative battery lead, allow the fault codes to reset to "zero"; and switch coils around. That MAY show new codes like P0300 (again), and P0302, P0303 - which would then nail it down as a bad coil. But that is a bit of PITA.... I note that all plugs look good. Plus, it'd be double jeopardy to have both plugs 1 and 4 bad, at the exact-same time. Ideas. PLEASE! I am really getting deperate! MAP is good, IAT is good, TPS is good, 4 wire O2 sensor is good, Coolant temp sensor is good. Did not check crankshaft position sensor or camshaft position sensor. PCV is good, and so is the grommet and the hose out of the PCV to the throttle body. All clear, no gunk, replaced PCV and grommet and hose. This model of Corolla does NOT have a hot-wire or other device... for measuring mass flow. Oh, one more thing: this car has neither a conventional fuel filter (only a "sock" on the in-tank fuel pump) nor a schrader valve to determine fuel pressure. However, I should note that it is ONLY at very little throttle opening that "lean surge" occurs. It does seem to be worse in 3rd and 4th gear of the automatic. Less so in first. And it does NOT correlate with how full the fuel tank is. Sometimes if a fuel filter is compromised... a full tank can operate adequately (i.e. sufficient fuel pump NPSHA)... but can fault at low tank conditions. No such correlation here.