P0304 after gassing up the night before

I've owned this 1997 2.7 Tacoma for almost 3 months. I've done a lot of work to get this truck in good mechanical shape. During this time, my check engine light went on twice. On both occasions, I overfilled my tank with gas and then drove 10 miles home. The next morning, I experienced rough idling for about 2-3 seconds when I started the truck, then everything smoothed out, but the P0304 code was thrown (misfire in cylinder #4). The CEL resets easily. This truck purrs like a kitten and the temp gauge stays on the cool side at all times. I don't burn any oil. This doesn't happen if I drive 15 miles after filling up the tank. Gas mileage is excellent (compared to my old 22re). I do notice that my coolant slowly goes down, and I can't find any leaks. There is no coolant in the oil. I'm thinking the problem may be a small leak in my #4 injector or a leaking head gasket. I'm in the process of building a leak-down tester to check for a potential head gasket leak.

Has anyone experienced these symptoms before? Do you have any other suggestions of something to check, other than what I've already mentioned? Any and all help would be appreciated.

 

First ( if you haven't already ) pull the plug and "read" it. Black sooty running rich, light brown to brown normal, white either new or running really lean, Noticeable white or brown deposits ( dirt/dust ) = leak somewhere in the intake or insufficient air filter. Also check the gaps. Always check the gap even on new plugs.

 

One of the first things I did when I bought this truck was to install new plugs,wires and air filter, along with adjusting the valves. I gapped the plugs before installing them, but I'll remove that plug tomorrow and look at it. What surprises me is how well this truck runs other than this little glitch.

Other work I've done on this truck:
replaced cracked exhaust manifold, shocks, inner CV boots, missing line from air filter canister to the charcoal canister, all fluids, O-ring/gasket for oil filter bracket and some broken body parts

lubed and torqued everything, along with throttle body cleaning, fuel system cleaning and engine oil flush (prior to changing the plugs)

I'll recheck what you mentioned and get back to you tomorrow.

 

I pulled all the plugs, checking their condition and gaps, and all checks out fine. Any other suggestions?

 

Ok the plug reading came out ok.

I am starting to lean towards bad gas as in water in the tanks at the gas station. If it was a coolant leak, reading the plugs would have shown that.

One time I put gas in from a station that I didn't go to very often and got a stumble while going down the road after leaving and a CEL as a misfire. Cleared it and never went back to that gas station. Talked to a guy that worked there the following weekend that said they have been having problems with water at the bottoms of their tanks and they are trying to correct the problem. Something to think about.

 

I only use Chevron gas, though the station I used wasn't the station I normally go to (just the closest Chevron to my home). It seems to me if the gas was bad I would have experienced problems for the entire tank, not just the next morning for 2-3 seconds.

 

Since oil is lighter than water, water settling to the bottom of the tank over night or while sitting still could cause what you experiencing.

 

Are you saying the solution is just to avoid this station... or accept the occasional CEL? It seems too simple, but it works for me. I'll still do the leak-down test this week to see if anything is leaking, along with borrowing a radiator pressure tool from Autozone to check that out.

 

yep, avoid that station is all you need or mainly avoid it after anytime it rains which is when most stations with leaky tanks have water in the gas issues because the fill valves have leaky or poorly fitting caps.

I used to work at a refinery and the trucks that came fill up from the exact same filling station were amaco, exon, mobile, chevron, Texaco, and a few others I cant remember but the important lesson there is all gas is the same from the same place no matter the name on the pump. some addatives like detergents or shells famous techron are just poured into the trucks after its filled like you would be adding any fuel addative to your car.

gas is gas and you get the same gas anywhere from any station so the important thing is make your regular gas station one that is up on a hill with no low spots where water collects during heavy rains and then you greatly reduce the chance of ever getting watered down gas.

now all that said, some gas addatives may help keep your engine cleaner then others but the extent to which they make any difference at all is questionable so picking a brand that you feel makes your car run best is a smart thing to do but I have never found any difference (other then price) between name brand stations and non name brand stations like circle k or quicky mart

 

After doing a leak down test, I can't understand how this truck runs so well.

Cylinder #1 showed a drop from 100PSI to 20PSI, with much pressure coming out of the exhaust pipe.

Cylinder #2 showed a drop from 100PSI to 0PSI, with air coming out of the throttle body (I could hear sounds in the exhaust pipe, but there was no air coming out).

Cylinder #3 showed a drop from 100PSI to 0PSI, with air coming out of the throttle body (I could hear sounds in the exhaust pipe, but there was no air coming out).

Cylinder #4 showed a drop from 100PSI to 0PSI, with air coming out of the throttle body, exhaust pipe and radiator. This must be the cause of my loss of coolant and P0304 code.

I'm sensing the head gasket is bad and the head needs to go to the shop to have the valves re-worked. Since the truck runs so well, I'll put this on hold till next summer. Any other suggestions any of you might have?

 

once you go that far it makes sense to have the head reworked but I wouldn't assume the valves are leaking, its probably all just the gasket

 

If you are HEARING the pressure in the radiator.........The problem is a lot worse than I thought. The problem going to only get worse as time goes along.
Start doing research and ordering parts. Buy a manual and study it. Once you have all the parts gathered, pick a weekend that your not busy and attack it. Saturday disassemble and cleaning, Sunday reassemble and testing.

 

I'm afraid it can't be a weekend job, as it will take time for the machine shop to rework the head. The coolant leak is very slow, and it isn't going into the oil.