Hi all, was hoping I could get some help with a misfire issue on my 1996 Accord Ex. I started getting CEL codes p301, p302, p303 and p1300 (corresponding cylinders and random misfire codes) about 2 1/2 months ago. It gets terrible fuel economy (~15-18mpg) and bucks if I maintain a constant speed around town and at times, will sputter for ~10 seconds on start up. One thing I have noticed though, is that it runs better sometimes if it is cold outside or if I go WOT on the highway.

Since first getting the codes, I have done a tune up consisting of changing the spark plugs, spark plug wires, pcm valve, distributor cap, rotor, and air filter. The same codes came back on about 45 minutes later after on the highway after the tune up.

A friend told me to change the EGR valve, which I did. I swapped it with a new one and again, the same codes came on ~30-45 minutes later. By now, I am starting to get fairly frustrated and wanted to get some ideas from you guys before continuing to drop money on unnecessary repairs.

I was told by another friend to either change the MAP sensor, replace injectors, or run seafoam thru my intake and fuel tank. Anyone else have any ideas/suggestions?

 

Pretty much you need to got through the process of elimination before going any further. 4 things go into an engine and come out of an engine to make the combustion happen

Fuel
Air
Spark
Timing

Fuel:
Only thing that will cause misfiring is a bad/dirty injector. EGR, and basically every other emission system that car has, if it fails, will cause the car to run rough or not at all, but will not cause misfiring. The thing that will cause misfiring are bad hoses and wires if its an intermittent.

Air:
Intake won't do anything, but if the cam or rods are bad then that may cause misfiring. Pressure test the engine to ensure you're getting a proper seal on your exhaust and intake. Kit sets you back $30 at autozone and if its a 4 banger its easy.

Check your vacuum hoses; anything old and brittle replace.

Check your exhaust for a collapsed catalytic converter or intermittent leak. Easiest way is to set off a smoke bomb and throw a potato in tailpipe. If the amount of push the engine has to do to get rid of exhaust is not consistent it will cause the engine to spin too fast for a split second and throw off the timing.



Spark: Big potential for loose or faulty wires between the Electronic spark module or distributor and its power source or between ANY of the sensors and the ECM. Get a manual, start testing each part w/ a multimeter.

Check for oil in the cylinder; oil burns longer than gas and will cause misfiring.

Check for dirty or corroded contacts. Oil spills are ESPECIALLY nasty here.

Check your alternator and battery voltage. It's unlikely but it can happen.



Timing: Advanced/retarded timing, a loose-and-about-ready-to-go timing belt (which can cause the engine to read low pressure if it's super bad).

Check for oil in your cylinders.



Pressure test, exhaust leak test, checking your timing and 2x checking your wiring and hoses will probably find you your problem.