Cause of 1996 Tacoma 2.4 #3 cylinder misfire? Help.

1996 Tacoma, 2.4, 5 speed. Truck has 262,000 miles. Has been running great. Developed a #3 cylinder misfire. Was driving it about a week ago and it started running rough, check engine light come on, then light started flashing. Would run better at higher RPM, check engine light would stop flashing. Was able to drive it home. Pulled the code and it was P0303 "#3 cylinder misfire". Checked plugs, and plug wire, they were fine. Starts fine, after idling for about a minute, the #3 cylinder will quit firing (rough running), you can pull the plug wire and there will be no difference. Raise the RPM and it will start firing on all 4 cylinders. Pulling the plug wire will then cause the run roughing again. I did read one other post where it turned out to be a water leak into the combustion chamber caused by a cracked head letting water into the cylinder. Has anyone else had this issue, was it a cracked head or bad head gasket? I have not checked the injector yet, need to rule that out. Don't really want to pull the motor apart until I a sure of the problem. I looked into the cylinder with a bore scope camera and did not see any signs of coolant. Thanks

 

Well you want to solve this before you destroy the catalytic.

Is yours the distributor version? If so check the cap and the point alignment, points might be corroded. Plug wires might be going bad.

When you looked down the scope, was cylinder #3 cleaner than the others (sign of long term misfire)? Might want to do a compression check, it could be a bad valve as well as a HG leak or cracked head.

 

I stopped driving the truck after this happened. I will change the plug wires and check the cap. I did not look in the other cylinders, but I will. It did look pretty clean inside #3 cylinder. Its been a great truck, this just came out of the blue. Does not burn any oil between changes, get 28 mpg. It was my daily driver.

 

did you get into any water before the misfire started, wash rack engine cleaning... large puddle or something like that? this happend to me, and i ended up having to replace the plugs, wires, and one coil pack (3.4L) mine was cylinder #5. the total was around $300 for the repair and worked like a charm. good luck, hope this helps.

 

I did not get into any water, so its nothing external that is causing the misfire. I replaced the fuel filter and swapped out injectors #1 and #3 and it made no difference, I still have the misfire on #3. So it is looking more like a water leak into the combustion chamber, hopefully just a head gasket and not a cracked head.

 

Do a compression check. If #3 is low then pressurise #3 with a air compresor and watch for bubbles in the radiator. I had the same thing but on #4. Pulled the heads and found three cracks on it. The guy I bought it from must of put a cheap remanufactured head on it because the machine shop was pointing out the what not to dos on heads. I am buying a new bear head and seating the valves and putting it together myself. Hope its just a head gasket good luck.

 

I did the compression test today, Warmed up the vehicle, pulled the plugs and tested with the following results, #1 - 180psi, #2 - 170psi, #3 - 180psi, #4 - 165psi. Variation was more than I would like (15psi, manual says 14psi). Cylinder #3 was 180psi, which is very good (260K miles). With #3 pressurize to 180psi, I checked for bubbles coming out of the radiator and nothing. Held pressure. When it is first started, it runs fine, then in about 30-60 seconds starts to misfire at idle, if I raise the RMS I an get the missing to stop, if I then lower the RPM the missing will return, very strange. Would sure like to pinpoint the issue.

 

You have to pressurise the cylinder with a air compressor. It only took about 60 psi of constant pressure to show bubbles in my radiator. I would try a new cap and rotor. The cap might have a small crack or something.

 

got a timing light? hook it up to #3 and #1 to see if they are sparking the same way.

 

Swap #3 plug wire with one of the others & try that. I would not start taking the head off til some other tests were done. Make sure your ign. points are opening wide enough.

 

Not sure if you figured it out, but my '99(2.7) had a misfire in #3 and it ended up being a stretched valve.

 

honestly theres a myriad of situations that cause a misfire. intake leak, exhaust leak, intake valve leak, exhaust valve leak, coolant leak, oil leak, leaks in other cylinders, TPS, cam sensor, crank sensor, mass air flow sensor, O2 sensor 1 or 2, bad computer, bad wires, bad coils, bad coil boots, bad wire boots, aaaand ill leave it at that

the issue is that you really need to know how to diagnose an engine when a misfire occurs. you cant just say, "i had the same issue and XXXXX is what it was". mainly because that's only 1 of the possibilities that could cause a misfire.

But thank you for your concern and well wishing for the OP. you do care at least.