Model: Toyota, Tacoma Prerunner 2.7
Year: 2002
This is what I have: DTC P0300 and P0301 with a random blinking engine light. Truck isn’t smoking, not using oil and Radiator water hasn't drop. It does have a rough idle and gas mileage is bad. I have change the Fuel filter, air filter, OS sensor plugs, cleaned PCV valve, Replace EGR Valve, Sea foam the intake added to gas also, replace fuel filter, replace Cylinder 1 & 2 fuel injector, air filter, clean MAP sensor, unable to detect any other vacuum leak.
The vacuum on the engine at idle and at 2000 rpm is steady 17lb. Last night I did a pressure test and here are my numbers. 1 2 3 4 Dry Test 130 163 175 185 (PSI) Wet Test 150 190 200 215 I did order a Air Fuel Ratio sensor I was going to try, but these numbers have me worried. From cylinder 1 through 4 is a different of 55 PSI. I was trying to do a leak down test, but it was too difficult to get a wrench on the fly wheel without pulling the radiator.
Things I have thinking about trying are trying to re shim the valves if any are burn or pulling the head and buying a rebuilt online. There are no machine shops in my area the would rework this head. any ideas would help

 

Hopefully you will get more experienced feedback.
Did you get the valve clearances? If an exhaust is way tight and you are lucky it is not burnt, then a shimming might be all you need.
Could it be ignition on one cylinder? Have you pulled caps to see if one cylinder has less effect then the others once pulled?

 

Did you replace the spark plugs and wires?

 

First thing I did was replace the spark plugs and change the wires around to see if the the miss would change cyl. I did go ahead and replace number 1 with a new wire. Cyl 1 does have a change when I unplug it. More of a change on the other three. I haven't taken the valve cover off yet to attempt to check the clearance. The truck is driven every day and I am still trying to find any other option be before digging that deep into it. I have never check valve clearance before and wanted to do my homework going that route.

 

Valve clearance could effect it but only if too tight and quite a bit past spec.

Are you getting a CEL?

 

And, adding to Texas Ace, if a valve is way too tight you are risking burning a valve. This is very real and happens rather often. Sorry to worry you but check it real soon. Check it cold. For everything you have done, checking the valve clearance is not a biggie!
Good luck, let us know what you find.

 

What is a CEL?
The Valves have shims that are original. Never been check that I am aware of. Again, the truck has 170k miles. In my mine if the shims are harden, that the valve would wear down and make it lose not tight. So would I assume that the valve is burn or lose. What do you think?

 

CEL = Check engine light.

170k miles is nothing. Although yes most of the time the valves loosen up it is not unheard of for them to tighten up as well (valve seat wearing ect).

 

I have a engine light that stays on and blinks random. The engine code is P0300(Random Miss fire) and P0301(miss fire 1) with a random blinking engine light(Catalyst over heating) .
I found this on link on how to check the adjustments and will try it when i can afford some time on the truck. I also need some shims, it would be nice to have some of different sizes. Still not sure where to find them.
https://www.yotatech.com/forums/f128...t-tech-226997/

 

There are a boat load of different sized shims. You wont know what you need until you take the clearances and measure theses shims (not on the center dot hotspot). You then you do math to figure what size shims you need, then look up the part number and order the shims.
Not a easy done in a day job. If your daily driver you may have to reinstall old shims until the new ones come. I called my area dealers, they did not carry stock on shims.

 

I would try running some fuel injector cleaner though it and might consider a seafoam treatment as well (search my threads for the writeup).

Also check the cat, make sure it is not clogged, seems someone else had this problem not long ago and that was the problem although he was supercharged but still worth a check.

 

Your #1 Compression doesn't look good. Could very well be a valve, but you need to check the clearances and post your results. if its too tight, you likely have a burnt valve. Normally your intake valves will check out in the normal spec range and the exhaust will tighten up over time.

 

I pull the heads off. It was no easy project. I took pictures of everything to make sure I remember how it when together. I found a machine shop close by. The guy recommended to just replace the number 1 exhaust valve and he clean it up and he did a light skim cut on the base. I when ahead and replace all my hoses, water pump, thermostat, and belts. Put it back together and found I could not get the .010 feeler gauge under the valve. I figue out what Differences I would need to get to the .010 and took the shims back to the machinist. He use a belt sanded to bring them to size. He work out great, Truck is running better then it every has.