JF1

Hello All,

This site is great!

For my first post, I am looking for troubleshooting ideas or feedback / solution from anyone who has experienced the same issue in hopes to resolve mine.

Here goes.

1996 4Runner LTD V6 5VZ-FE w/ Auto Trans A340F
158,500 on the ODO.

Four weeks ago this symptom showed up while driving back from the airport. I had been cruising at highway speed for 45 min and the check engine light came on as a light shudder began. I pulled aside to inspect. everything looked normal, temp was normal, fresh fuel, but it sounded like a cylinder was missing. The issue disappeared on its own before I arrived home.

Two weeks ago it began to misfire again.

It runs fantastically well with the new parts on it. The symptom is not present when the engine is cold, it only presents itself after driving around for a while to get the engine up to temp. Then the vehicle has to set shut off for 20 min or so before a restart to evoke the troublesome phantom like Cyl #4 misfire.

No MIL or check engine light for the most recent round of diagnosis.

I pulled the code to find P0304 (Generic Misfire Detected in #4 Cylinder)

Here is what I have replaced and attempted diagnostics on.

All fresh new Toyota OEM / Factory Parts.

(6) Plugs
(3) Coil Packs
(1) Set Plug Wires
(6) Injectors w/ new o-rings and seals
(1) Fuel Filter
(1) PCV Valve
(1) Air Filter
(2) Upper / Lower Intake Plenum Gaskets
(1) Upstream O2 Sensor (pre-cat)
(1) Downstream O2 Sensor (post-cat)

The compression test showed 176 Dry and 202 Wet on all 6 cylinders (well, within a few PSI of each other)

The Vacuum test showed perfect even at temp with the #4 Cyl Misfiring (20 in Hg)

No coolant in the oil.

No hydrocarbons in the coolant.

The new injectors all tested at 15.8 Ohm

The EFI relay tested at 92.8 Ohm

The fuel injection harness tested at perfect continuity.

ECM does not show any signs of "hot" or smell like anything.

The vehicle is extremely clean and is never abused and has not seen rain in a very long time.

The voltage at the fuel pump is 13.5V and is delivering plenty of fuel.

I have moved things around only to arrive back to #4 Cylinder Misfire??

Everyone that I have spoken to about this issue including the local dealership gives me the same "huh...never seen that one before"


I appreciate any feedback or ideas.

Thank you,
JF1

JF1

Hello All,

I finally went to my friends shop and had his technician run the full battery of diagnostics. Everything looked great except for....a very minor almost undetectable head gasket leak that was / is allowing the tiniest amount of coolant to seep into the cylinder.

They identified this by using what they referred to as a block test. Apparently here is a method / fluid of sorts that can detect hydrocarbons in the coolant. I must have screwed up the coolant test that I bought...I did not find anything. I am not a mechanic by day it is what I do for fun when we are not camping.

I have never added coolant after replacing my water pump and timing belt at 121,340 mi.

Trying to decide what to do. It is an expensive repair, but I could get another 150K on it if I do it. ??

Any thoughts?

maachine

yes definitely replace the head gasket. would totally be worth it whether you pay someone to do it or just do it yourself. you could probably do it yourself if youre careful and pay attention. do some research first so you'll have a basic idea of what you're diving into.

JF1

Thank you for giving your input. I have decided to replace the head gaskets as it looks to be a reasonable task, just many steps.

I will post how things go.

Several parts to order.

Any suggestions on Toyota OEM parts source ( hopefully not a dealership)?

Have a good one.

maachine

i'd hit rockauto.com for the parts myself. they do have some OEM parts available

JF1

Hello All,

Just thought I would post an update.

I have decided to repair the 4Runner. All of the parts were sourced and purchased from TEAM YOTA in the Pacific Northwest.

Of course there are a small handful of ancillary items that I have decided to refresh / repair along the way. The hardest part of the job so far was removing the exhaust manifold bolts and the crossover nuts.

With the help from others that have posted on the forum along with the FSM, the job is going well.

I plan to post the part list with factory numbers once I am finished.

Today I figured out that the radiator is fairly well plugged with gunk. I am not surprised given the condition of the intake manifold gaskets.

Hope all is well.

I will post as soon as I am finished with the work.