3RZ Misfire- advice needed

Hello all, I recently bought a 96 xtra cab 3RZ-FE 4x4 manual Taco and have been working through the minor issues. I am fairly well rounded when it comes to Toyotas (this is my 5th) and I have come across a problem that I can't seem to resolve on my own. I am writing this to ask for help/advice.

I had a misfire the other day. I drove about a half mile where it ran fine, parked it, and started it up to drive it home and it had a rough low idle and then limped it home. On the drive home the check engine light came on flashing. The code read P0304- misfire in cylinder 4.

I did a bit of research and found that the heads are fairly fragile on the 3RZ and mine has around 261k so I was worried. The first thing that I did was run a compression test. Here are the results in 1-4 order.



As you can see, these were very consistent readings. I checked each cylinder twice and they tested the same both times. I used this as a baseline to assume that I do not have a cracked head or a bent valve because these pressures would vary or be inconsistent.

Next I checked the coolant, it was not low. Not low in the reservoir either. I used this to make the assumption that the head gasket is intact because I am not burning any coolant nor does it smell like I am.

Next I pulled the spark plugs and wires (they all looked clean but it was time to replace them anyways). I went to the store and picked up a new set of wires and plugs. I cleared the code and swapped them in. Let it warm up- idling still rough and after about 5 minutes the code came back. Still only one code. Still misfire on cylinder 4.

Next I listened to the injectors with the old-fashioned screwdriver trick. Every one seemed to be firing at a consistent tik-tik-tik sound with no abnormalities.



I am now thoroughly dumbfounded. I don't know what to check next. Any advice is appreciated. Please let me know what you think.

 

@Taco critter

 

Check your coils.Your spark plug boot/sleeves going into the top of engine from your coil pack on one of your cylinders could have a bad spot and sparking outside of its self.The code reader should tell you what cylinder is misfiring I would imagine.One of your coil packs could also be bad.But if it’s got new plugs and wires I would imagine it’s something with one the coil packs or spark plug boots coming off of it

 

Thank you for the response, I don't think it has coil packs. It has a distributer

 

So the 1996 model has a distributor that also doubles as your cam position sensor, it's not entirely uncommon for that coil in the dizzy to age out and it's not too uncommon for the cap to wear out pretty bad as well. I've heard of the magnetic pickup getting weird and dropping cylinders but it's never happened when I had one. Anywho, I'd check the cap and rotor first and then consider checking the timing to see if it's wandering, theres a process to lock the timing advance to check it.

 

Hi, thanks for the response. I don't know how to check to see if the distributer (cap?... rotor?) is bad.. Also is this something that I can service or something is it something that I have to replace?

 

It's super easy, three screws and it comes off. It's not technically a serviceable part, they're only like $15 for a set of cap and rotor anyway. But if the contacts in there look burnt or corroded you can clean em up with sand paper or a scotchbrite. But if the cap is shorting internally (most likely cause for a dead cylinder) you'll have to replace it. They get carbon tracked internally from years of use and heat.

This is what carbon tracking tends to look like though it can appear lighter or darker too.

 

Thanks for the reply. I think we can rule this out. It looks pretty clean in there to me. My guess is it was replaced not too long ago... Any other ideas?

 

The cap looks decent but the rotor button has a lot of wear, how is it's edge? Also take some alcohol and wipe the base under the rotor

 

Oops I went ahead and snugged it back on because it's starting to rain. I will check the rotor tomorrow if the weather holds. How will I be able to tell if the rotor is done for?

 

They almost look kinda scorched. Sometimes the arcing makes craters on it too. The rotor and cap are good to change along the same interval with spark plugs and wires.

 

Again, thank you for the info. How do I remove the rotor without damaging the internals?

 

Pretty sure it just pulls straight off

 

Yeah I just read 3rz and assumed it was like mine.Yes it’s gonna be an ignition issue so the distributor will be your issue beings it is doing what my coil packs do except in a different way.May as well put a new one on truck and you will have changed it all to new at same time and should last you years to come without having to worry about that again

 

Here's what the front of the distributor rotor. Had a little corrosion so I cleaned it up. Still having the misfire. Still same cylinder.

I went ahead and ordered a set of new fuel injectors and the rubber gromets that go with them. They should be here on Thursday.

Anything else I can check in the meantime?

 

You should read up on the issues people have had with buying new fuel injectors if you're not aware yet.

Here are good threads, so you can be sure you ordered something worth your time. Cheap injectors are all over the place, and aren't worth replacing with.

https://www.tacomaworld.com/threads/thoughts-on-denso-fuel-injectors.651608/#post-22661570
https://www.tacomaworld.com/threads/caution-counterfeit-injectors.652261/#post-22697593

 

Hi, thank you for the warning. I read through that thread- there's some good info on there. I ordered a set of 4 from GB Remanufacturing in Long Beach California. I've read pretty good things about them, so I'll install them and give them a try. If I am uncomfortable with their product I'll send it back.

 

you check the secondary leads with an ohm meter. ohm meters vary on how they are used... some are auto ranging and others you have to set the upper limit. Put one lead on the nub inside of the cap and the other on the plug lead and see what it says, usually around a thousand ohms per foot + what ever the resistance is for the cable end. Twist the wire around and flex it and watch the meter... if it changes drastically or goes to 0, there is an open in the lead.
Lets hope it is something external...

 

Update: I have been told that when you replace injectors you should also replace the fuel filter as well. I will be getting a new one and swapping the injectors/f-filter sometime on Thursday

 

Hi all,

I got my new injectors and seals today. I got the fuel filter on and in place last night and went ahead and pulled the fuel rail today. The photo below shows what it looked like


Then I went ahead and pulled out and replaced the injectors. Here's a side by side of what they looked like new vs old:

I know that the old one looks bigger but it's not- it is just the lighting and the way I'm holding it I went ahead and installed them. No leaks. No misfire. A high idle, but I think that has more to do with the fact that the truck just had a major tune-up at 260K. It feels like the engine is getting a more complete burn and it blew a TON of smoke out of the tailpipe when it started back up. After it warmed up and blew out all the carbon from the misfires it seems to be running great!