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Misfire Troubleshooting
Since this is Asked frequently. I thought I would a do a write up on Solving the dreaded misfire. This could be use to diagnosis most engines. From L3-W16
Recommended tools: scanner with engine data read out, Digital test meter, stand hand tools, a standard magnet, (universal joint sockets would be nice but not required)
First isolate the misfire. P0301, P302, P0303, P0304, P0304,etc……
1. Check for spark by removing the IDE cover using a known good plug hook it up to the boot. Have someone crank the motor over and check for arcing. On cable check by disconnecting and hooking plug to wire
Good move on
Bad - check coil pak -there are 2 coils swap the order and recheck to confirm misfire in different boot. If misfire in the same boot replace Coil pak housing. On V6 there are 3 coil pak swap those. (Common cause is a bad ignition module on both Q4 and V6(3100,3400, 3800)
2. Check MAF - hook up test leads and using a hand held fan check restance to see if changes occurs. Plug in connector , turn to KOEO, and see if MAF is responding.
3. If spark is good. Check fuel pressure (52-58psi) must hold for 2 minutes.
Good - move on
Bad - You got an injector leak or check valve bad at the fuel pump. Confirm bad check by test for fuel pressure at the fuel filter, if bad, change fuel pump (This is a rare case). If pressure is as stated and holding , next Dead panning (restrict the return flow) using a duck-billed visa-grip and restricting the return. Recheck pressure should hold for 2 minutes. If failed change injector (rare case as well).
4. If pressure is good pull injector harness and test using LED diode. If pulsing confirm. Move on.
No- pulse, do some wiring tracing, make sure engine harness not rubbing on block. Check pin-out at PCM.
Good - move on
5. Compression must disconnect injector to prevent injector releasing pressure. Crank and confirm pressure (100+ psi)
Good - move on
Bad - use compress air and hook up into cylinder, ensure piston is TDC and check for air leak at the throttle, exhaust, and oil fill. (Throttle - intake valve might be bent or rocker need adjusting, exhaust same as intake, crankcase - piston skirt worn).
6. Check for coolant in cylinder
Good - move on
Bad - common cause (head gasket, intake gasket, cracked head) If coolant in cylinder also check for coolant in radiator, Your vehicle should boil in about 5 minutes.
7. Check for air leaks around the cylinder using carb cleaner. Lightly spray around the cylinder and isolate the air leak. (Common cause vacuum lines.)
Good - move on
Bad- repair and retest
The following step requires more in-depth knowledge on motor (I WILL NOT BE RESPONSIBLE FOR YOUR MISTAKES FROM THIS POINT ON)
8. Check on Crank Position sensor (Lower front end of motor) remove and test for conductive. Hook up a test lead to contacts and pass a solid steel by-and-forth over the sensor. Do the signals change?
Good - move on
Bad - replace and retest
9. Check Cam-position sensor using above method
Good - move on
Bad - replace and retest
10. Since our cars use timing chain use you hear a know or grind I would leave this alone. But just in case someone things it the case. Align all the mark up. Check to see if #1 cylinder is TDC.
Good - move on
Bad - (Q4 - head job, at least 8 new valves, and have machine shop do a pressure test) reset timing, I recommend new guides, and new seal since you in there. Timing kit runs about $160.00 Do the water pump if you a Q4
Hopefully this will be enough. There are many minor things I may have left out. But those should be simply. Could a Mod make this a sticky.
Last edited by super white alero1 : 04-22-2008 at 12:48 PM.
Reason: Could a Mod move this to the DIY section.
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