2.7l Cylinder 3 misfire

My truck recently started throwing a code for cyl. 3 misfire (P 0303).

Initially I started with the usual suspects. I installed new spark plugs, new coil (distributorless) on cyl. 3, and took the fuel injectors in to get cleaned and tested.

After this I was still getting the misfire. I ran a compression test and got the following results:
Cyl. #1 - 170 psi
#2 - 180 psi
#3 - 195 psi
#4 - 185 psi

These values seemed normal to me so I ran a fuel pressure test that read at ~46psi.

I then performed a noid test on the #3 injector which strobed indicating that it was firing.

To check for spark I took a spare spark plug and grounded it to the engine while connected to the coil and it looked like it was firing.

Last test was at the ECM injector terminals which all read ~8.3V for all 4 injectors. Toyota shop manual says these should be between 9-12V? Is this part of the issue?

I also replaced the MAF sensor to see if that would do the trick, no dice. Still throwing the code.

I don’t really know where to go from here, I believe the problem is some kind of electrical issue but do not know how to narrow it down, can anyone point me to some kind of testing that can narrow it down for me? I am not good with automotive electric so layman terms would help a lot.

Thanks guys

 

Boroscope the cylinders to see how they look? It’s a relatively cheap tool for what it allows you to see. Carbon build up can also cause increased compression depending on where it is. It’s easier to diagnose from knowledge than guess why they’re different. You might have already fixed the cause but not the consequences.

 

when was the last time you changed your plug wires. I had a misfire and the culprit was a bad spark plug wire.

 

How many miles on it? Have valve clearances been checked ?

 

M e too. Cylinder misfire was new plug wires. Our trucks kill wires

 

Check for control at Pin 1 (Red) of injector number 3 with a test light or plug a noid light into the injector 3 connector.

If you use a test light you need to connect the ground lead of it to battery positive.
With the engine running the light should flash.

 

Didn’t even know that was a tool, I like it. I’m guessing I just feed the scope through the spark plug insert?

 

I tested #3 injector with a noid light and the electric pulse seemed to be firing. Am I missing another type of test, I went through the shop manual diagnostic flow chart and am still stumped.

 

My 3rz has distributorless plugs so I don’t have plug wires.

 

My 3.4l has no distributer either, but it still has spark plug wires running from the Coils to the other side of the engine.

 

285,000+ miles, I just wanted to rule out all other possibilities before I start pulling the head cover

 

Seems like you have ruled out all the "easy" stuff, without getting into technical testing beyond DIY the only other thing I can think of is make sure the exhaust valve is opening.

 

I think it's time for an engine analyzer. A look at the spark pulse curve will tell you volumes, and only take a few minutes.
Let us know what you find.

 

Are they in a big loom? I looks like my spark plug wires feed into a loom that also has the fuel injector wires as well. Loom feeds to firewall on passenger side.

 

Perform a valve adjustment. Won't hurt to try.

 

Okay I think you guys have helped point me in the right direction. I will check valve clearances tomorrow and see if they need adjustment and report back. I think the boroscope was a good idea also so I’ll take a peek into the cylinders while I have everything taken apart.

 

You can look in the spark plug holes or look through the throttle body to see the intake valve tops.

 

I have a stupid question....since 2 and 3 fire simultaneously
cant you just swap those two coils including its wire with it and see if that follows to no.2....
rule out a global electrical problem...

and then go backwards from there....see if its the coil or the harness plug...


Also made me think for these coil over plugs.....since both piggy back on the same fire signal from the ecm......that if one of them is shorted, bad, or going out....it may affect the other....

The coil over plug is not a superior design....its a cheaper way for them to make em......so I'd keep a couple spares around if mine was a 2001 or later....


One of the first things I did when I got my truck was I ran a dedicated ground strap straight from the neg post to the engine block/head....
instead of depending on the round-a-bout hooky way they did it thru the body panels...

 

If swapping plugs and injectors does not transfer the problem to the test cylinder then it is mechanical in nature. Next step is do a leak down test. Requires a special tool and an air compressor. The 4 cylinder motors have a tendency to burn a valve and/or develop cracks in the head at that mileage.