Bad misfire under load
09-14-2018, 10:37 AM
#1
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Bad misfire under load Changed plugs and wires over the weekend and the car was running fine. Made a 50 or so mile drive, shut off the car and let it sit for a while. When I got back in the car an hour or so later it was misfiring bad under load. Like if I put the pedal to the floor it would miss bad about 2k to 3k rpm. It's like it has a 2 step lol. When driving an you put the pedal to the floor it just misfires and pops and backfires. Car also takes a while cranking to fire over (like 5 to 10 seconds of cranking) Put another set of plugs and wires on it today and the same thing. The plugs I pulled out that were only a week old were all black. Only thing I can think of is maybe I jostled something while working on the car maybe. A ground or something?. Cant seem to think of anything. Thoughts? Car is full bolt ons and cam car with a T56. Car is nearly un drivable it misses so bad. No codes. I have a more in depth scan tool that I'm going to put on it tomorrow (its at a buddys house)
09-14-2018, 04:45 PM
#2
Was it running ok before changing plugs and wires? If so you can try putting the old plugs back in. Are the new plugs black from fuel or oil, should be able to smell a difference. And were the old plugs fouled the same? Check to make sure all the wires are seated into the coils and plugs. How tight did you screw the new plugs in? If they were over torqued a plug could have been damaged causing a misfire.
09-15-2018, 09:35 AM
#4
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Did you remove coil packs to change stuff out? Possible bent pin in connector
09-20-2018, 08:31 AM
#6
This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles. Although generic, the specific repair steps may vary depending on make/model. Essentially the same as P0136 and P0137 and P0131, a P0151 code refers to the first oxygen sensor on Bank 2 . P0151 means the O2 oxygen sensor's voltage remained low for longer than 2 minutes.
The most likely cause is a bad ignition coil which caused contamination on the O2 sensor.
Direct an infared temp gun on each exhaust outlet on the passenger side (bank 2). The one of the four exhaust outlets that is cold will identify the misfire or non-ignition. Cold is about 100 - 110 degrees if the engine is cold/lwarm and not heat soaked. The cylinders that are firing will have temps over 170 - 240 on start up.
Pull the plug from that cylinder and test if it is firing. If it is firing, you want a nice blue spark.
If the plug is NOT firing then one of two things - 1) bad plug or spark plug wire 2) bad ignition coil or coil wire or ignition coil ground.
All of the above requires that the ground for the coils is securely attached to the back of the heads. Some cars the ground goes to both heads. On my 98 there are three ground wires on the back of bank one (driver side).
Or:
Not likely but if cylinder is dead with no heat then not getting fuel meaning a bad injector or injector plug connection for that cylinder.
The most likely cause is a bad ignition coil which caused contamination on the O2 sensor.
Direct an infared temp gun on each exhaust outlet on the passenger side (bank 2). The one of the four exhaust outlets that is cold will identify the misfire or non-ignition. Cold is about 100 - 110 degrees if the engine is cold/lwarm and not heat soaked. The cylinders that are firing will have temps over 170 - 240 on start up.
Pull the plug from that cylinder and test if it is firing. If it is firing, you want a nice blue spark.
If the plug is NOT firing then one of two things - 1) bad plug or spark plug wire 2) bad ignition coil or coil wire or ignition coil ground.
All of the above requires that the ground for the coils is securely attached to the back of the heads. Some cars the ground goes to both heads. On my 98 there are three ground wires on the back of bank one (driver side).
Or:
Not likely but if cylinder is dead with no heat then not getting fuel meaning a bad injector or injector plug connection for that cylinder.
Last edited by dlandsvZ28; 09-20-2018 at 08:38 AM.