Random Multiple Misfire and Fuel Gauge fluctuates
12-08-2012, 06:41 PM
#1
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Random Multiple Misfire and Fuel Gauge fluctuates
So I've been dealing with a Random Multiple Misfire issue for a couple months now, its spiratic, does it whenever it feels like it, sometimes on two cylinders, or just 1 or it runs fine. Does it at idle and going down the road. Fuel gauge also reads lower than actual fuel level sometimes - will say it only has a 1/2 tank when full or even read empty when it has 3/4 or 1/2 etc etc.
Wondering if the two are related or not? Really need help with misfire issue.
I replaced plugs, ignition coils, throttle body and pcv valve. When I replaced plugs, the back 2 chambers had oil in them. When I replaced the pcv valve, it was covered in oil and the tube dripping oil as well. I also took apart the intake manifold and there was a thin layer of oil throughout it (assumably from the bad pcv valve). It ran signficantly better after I replaced the pcv valve, however, it shortly after started misfiring on one of the cylinders.
I don't think its valve seals because the tops and area around the valves are visably clean and clear of oil. Any help would be greatly appreciated! Thank you!
Wondering if the two are related or not? Really need help with misfire issue.
I replaced plugs, ignition coils, throttle body and pcv valve. When I replaced plugs, the back 2 chambers had oil in them. When I replaced the pcv valve, it was covered in oil and the tube dripping oil as well. I also took apart the intake manifold and there was a thin layer of oil throughout it (assumably from the bad pcv valve). It ran signficantly better after I replaced the pcv valve, however, it shortly after started misfiring on one of the cylinders.
I don't think its valve seals because the tops and area around the valves are visably clean and clear of oil. Any help would be greatly appreciated! Thank you!
12-09-2012, 05:26 AM
#2
Registered User
Well, looks like you've done a lot of replacing things.
I believe the two problems are unrelated.
First the misfires:
Multiple random misfires are pretty hard to diagnose because of the nature of the misfire. If its bad wires or bad plugs, the misfire will be confined to the offending cylinder. I.e if the plug/coil pack/wire related to cylinder 3 is/are malfunctioning, then the misfire will be limited to cylinder 3. Oh, and the oil you are seeing is a symptom of the misfiring, not vice versa.
Multiple misfires are usually caused by 3 things.
Vacuum leak
Excessive back pressure
Malfunctioning EGR.
1: vacuum leaks are a bear to pin down without a smoker, but there's a couple different things you can do if you are opposed to taking it in.
a. Buy a can of ignition fluid. Wait until the car is cold, start it, and before it has a chance to warm up (so you don't start a fire), spray the fluid around the gasket areas of the intake and around the ends of the PVC hoses. Spray and listen to the engine. If there is a leak, you'll hear the idle increase as the engine takes in the fluid and burns it. Where the engine revs when you spray the cleaner, is where the leak is.
2. Excessive back pressure is typically caused by clogs in the exhaust system. Usually, a plugged catalytic converter is the culprit. If you still have your cats, I would almost bet this is the problem. To diagnose this, you can unbolt the pre o2 sensor and run the engine. The open bung where the sensor is supposed to go is usually enough to release the pressure and stop the misfiring. If the engine seems ok at idle, and only misfires during acceleration, then that's even more indicative of a plugged cat. Also, obviously, new cats or test pipes will also solve the problem.
3. A malfunctioning EGR is also something else that can cause misfiring. But because of the nature of the EGRs functionality, the misfires will be limited to idle only. So if the engine is missing at idle and no other time, this is probably the culprit.
Multiple misfires are a pain to chase. I've been there.
Also, if your cats weren't plugged before this misfiring stuff started, then they are now for sure. The misfiring will plug a catalytic converter fast. So chances are you need new ones anyway. It ends up being a big spiral that plugs them completely. Slight restriction causing misfire, misfire makes restriction worse, eventually car won't run at all. I would start there. The last two misfire problems I had in two different vehicles were plugged cats.
I believe the two problems are unrelated.
First the misfires:
Multiple random misfires are pretty hard to diagnose because of the nature of the misfire. If its bad wires or bad plugs, the misfire will be confined to the offending cylinder. I.e if the plug/coil pack/wire related to cylinder 3 is/are malfunctioning, then the misfire will be limited to cylinder 3. Oh, and the oil you are seeing is a symptom of the misfiring, not vice versa.
Multiple misfires are usually caused by 3 things.
Vacuum leak
Excessive back pressure
Malfunctioning EGR.
1: vacuum leaks are a bear to pin down without a smoker, but there's a couple different things you can do if you are opposed to taking it in.
a. Buy a can of ignition fluid. Wait until the car is cold, start it, and before it has a chance to warm up (so you don't start a fire), spray the fluid around the gasket areas of the intake and around the ends of the PVC hoses. Spray and listen to the engine. If there is a leak, you'll hear the idle increase as the engine takes in the fluid and burns it. Where the engine revs when you spray the cleaner, is where the leak is.
2. Excessive back pressure is typically caused by clogs in the exhaust system. Usually, a plugged catalytic converter is the culprit. If you still have your cats, I would almost bet this is the problem. To diagnose this, you can unbolt the pre o2 sensor and run the engine. The open bung where the sensor is supposed to go is usually enough to release the pressure and stop the misfiring. If the engine seems ok at idle, and only misfires during acceleration, then that's even more indicative of a plugged cat. Also, obviously, new cats or test pipes will also solve the problem.
3. A malfunctioning EGR is also something else that can cause misfiring. But because of the nature of the EGRs functionality, the misfires will be limited to idle only. So if the engine is missing at idle and no other time, this is probably the culprit.
Multiple misfires are a pain to chase. I've been there.
Also, if your cats weren't plugged before this misfiring stuff started, then they are now for sure. The misfiring will plug a catalytic converter fast. So chances are you need new ones anyway. It ends up being a big spiral that plugs them completely. Slight restriction causing misfire, misfire makes restriction worse, eventually car won't run at all. I would start there. The last two misfire problems I had in two different vehicles were plugged cats.
12-16-2012, 01:38 PM
#5
any updates on this?? im in the same boat. multiple misfire code... this is after i fixed the steering angle sensor (reset) bad bank 2 cam sensor and replaced bank 2 (driver side) both o2 sensors. did a full ecu reset and car was running fine (except for the light misfire when idling) then as soon as i opened her up WOT the misfire came back and engine light came on.
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