Misfire 1995 TOYOTA AVALON

toyota
avalon

#1

My mother purchased a Toyota Avalon for my college age brother to use. With only a hundred and ten thousand miles comma we assumed that being a Toyota it probably would not break down. A short while later the engine began jumping and behaving erratically.

We attempted to have it diagnosed by the dealership. They did their $75 checkup and informed us it was time to replace a belt. I explained to my mom that they had charged her $75 to tell her what maintenance was suggested at the current mileage. We then took it to the nice people at aamco for a free diagnosis.

It IS misfiring on cylinder 4. First thing we did was replace spark plugs. This is no fun on a 6 cylinder… The one that was misfiring is actually in front but obviously I replaced them all. SAME PROBLEM

I replaced the ignition coils next. They were clearly beyond their expiration as you can see straight through to the red indicator.
SAME PROBLEM

And here I am now.

Logic says one of two things is occurring… But I may be wrong.

  1. fuel injector is not getting fuel to the cylinder. The line could be bad or the injector could be clogged

  2. the wire supplying power to the ignition coil could be bad
    MY PLAN TILL NOW

I plan on disconnecting the fuel pump relay, pulling the plug and coil, and checking for a spark. Obviously this is to see if the electric supply is the issue.

If anyone has any insight as to how to make this diagnosis any easier, or a step by step process in either/or most likely to least likely… Or least expensive to most expensive…

I would greatly appreciate it


#2

To find out if the injector is the problem, swap that injector with another from another cylinder to see if the miss moves with the injector.

To find out if the coil is firing the spark plug, plug the coil into a spark tester.

Tester


#3

I believe this engine has 3 ignition coils, on the front bank, with wires connecting the coils to the plugs on the rear bank

Have you also replaced those wires?

I’m not sure how accessible those injector connectors are on this particular model year engine . . . I suspect NOT

If you’re able to easily access all 6 injector connectors, hook up a noid lite to see if they’re being correctly pulsed

You might also want to perform a compression test. If low enough, you’ll get a misfire. I wouldn’t be surprised if the valve lash is seriously out of adjustment on this old vehicle. Tight valve lash will not make any noise, but will result in lower compression, which brings all sorts of associated problems with it


#4

"To find out if the injector is the problem, swap that injector with another from another cylinder to see if the miss moves with the injector.

To find out if the coil is firing the spark plug, plug the coil into a spark tester"

That’s good advice. That sounds like what I will try…

Thank you


#5

db4690
"You might also want to perform a compression test. If low enough, you’ll get a misfire. I wouldn’t be surprised if the valve lash is seriously out of adjustment on this old vehicle. Tight valve lash will not make any noise, but will result in lower compression, which brings all sorts of associated problems with it"

I suppose I will look into doing this if I don’t find the problem with either the wire or the injector. Compression test is more complicated if I remember from what I have read

Yeah…

Not easily accessible. Most dealerships go with removing the intake manifold, etc… Or they at least charge you for doing so. A tune up is $4-500…

At least of a woman (mom) goes to ask.

I have lots of different extensions and gadgets so I managed to wedge my hand into the tight spaces and remove and replace all 6.


#6

If you managed to replace all 6 plugs without removing the plenum, you should be able to perform a compression test. The results might be very telling


#7

An Avalon with 110K miles should be a pretty good bet, reliability wise. A 1995 may have a timing belt. If so and it is the original it needs to be replaced straight away. Major and very expensive engine damage could occur if that belt breaks while the engine is running, so double check about that. Is that the belt the dealership suggested to replace ? Still, even if the belt needs replacement, I doubt that’s the cause of your misfire.

You seem to be on the right track mis-fire wise. Spark plugs & coils were a good place to start. If a misfire is only occurring on one cylinder, usually you’d start by swapping things around, rather than replacing everything w/new. But replacing everything is an alternative method often used, no harm done. Misfire problems almost certainly has to be from among spark, fuel, compression, spark timing, or valve timing. Don’t start out by assuming the worse, it is probably something simple, like a bad spark plug, spark plug wire, dist cap, dist rotor.

If I had this problem and replacing/swapping the usual stuff didn’t fix it, and the compression tested ok, I’d seek out a well recommended inde shop that specializes in Toyotas or Asian cars and ask them to use the Toyota scan tool and an o-scope to check the ignition system.

I think you understand that assumption is overly optimistic. Choosing a car rated high in reliability increases your odds but doesn’t guarantee it won’t break down. At over 100K you not just dealing with Toyota’s abilities to design their cars well, but the previous owners inclination to keep Toyota’s recommended service schedule up to date. Which may or may not have happened. Still I think you are probably looking at something minor here, and any good shop should be able to diagnose and fix it for you. I’d stay away from the dealerships and national chains tho. Ask people you know, your friends, co-workers, etc, who they use to fix their own Toyotas, and go there.


#8

This has a 1MZ-FE V6 with a timing belt, and it’s non-interference

This engine never had a distributor. The early versions . . . such as this . . . had 3 waste spark coils, and the later versions had 6 coils


#9

So… The vehicle is at my mother’s. Finally I got to get into it.

On the last, hardest to reach coil, I have found fuel. I am going to check with the ignition/spark tester and see if power’s going to it.

If power is not going to it, I am going to attempt to find where the wiring is bad. Unfortunately this one is also the hardest to reach.


#10

All the plugs are indeed getting power. I am fairly certain it is indeed fuel and not oil in the plug.

It is plug 5 that is covered in fuel. It is receiving power… What is the next step?


#11

Might have a leaking fuel injector . . . I’m assuming #6 plug definitely smells like fuel?

Is there a strong fuel smell under the hood?

Does the engine take a particularly long time to start?

A faulty injector could certainly cause a misfire fault code

If you’re thinking of replacing the injector, I’d consider getting an inexpensive set of 6 rebuilt injectors. I’d hate to have you replace #5 injector, only to have another fail a few weeks later, at which point you’re pretty much doing it all again


#12

Yeah, I think you’re right.

I am getting the misfire message on what I thought (originally) was number 3. However, that was prior to replacing the plugs and coils.

So, I suppose replacing the injectors is the next step since I know the wires are getting power to the plugs.

ANOTHER OBSERVATION

There is a audible noise… I can hear the plug firing on number three when I have a tester hooked up to it, but not with the others. Maybe this is connected to 5 underperformed?


#13

You say the coil was covered in fuel, then later you say the plug is covered in fuel. Which is it? And for the plug, what part of it is covered in fuel? the part that sits outside the cylinder, the white part that the coil plugs onto? Or the part that screws inside the cylinder, the plug tip? If the former, that’s an external fuel leak, and you might have a leak at the fuel rail, an injector has popped out, an injector seal has failed, a leak in the fuel pressure regulator, something like that could cause an external fuel leak. If the injectors have ever been worked on, it can be difficult to get them all to reseat when you re-install them. So that’s a suspect here. If so, you might want to just have that injector install job re-done.

If you hear a noise coming from a plug, that is an unusual sitituation and needs to be addressed as a first priority. That is often caused by the plug not making an airtight seal with the engine for some reason. Might be loose, or cross-threaded. Get a discarded length of garden hose, use it as a stethoscope to narrow down where that noise is coming from. A cylinder that is pinging for some reason is a suspect too.


#14

The coil is covered in fuel. Primarily indicating where the plug and coil are connected.


#15

If the coil is covered in fuel, you got some kind of external fuel leak going on. Until this is resolved, suggest to carry a fire extinguisher with you in the car.


#16

“covered in fuel”… Let me clarify.

The seat, where the coil attaches to the plug has fuel on it. There’s not so much that it is on the external parts of any component. I’m going to upload two videos. The first is what every plug sounded like when I had the ignition tester hooked up.

As to the seal being broken, the noise is only there when the tester is plugged in, IE, the seal doesn’t apply. But it is different and more pronounced in real life than in the 60fps HD video

First video, this is what the five “other” tests looked and sounded like

Second video with the audible click/clack


#17

Are you sure it is fuel and not oil. The only way for fuel to get there is is there is a hole in the spark plug. If the spark plug well is filling with oil I could see how that may cause a misfire.


#18

Am I sure? Never 100%… But it smells like gas and so does the vehicle when driven.

Correct me if I am wrong… The plug ignites fuel in the cylinder… So, fuel is exposed to the plug regularly.

I assume, not fully remembering explanations from high school classes… That the injector emits fuel such that it fills the cylinder in gaseous form.

I can see build up occurring if the plug is not firing. Because that is not the case I assume (perhaps mistakenly) that the injector is sending too much fuel to the plug… The spark is not happening because liquid fuel is fouling it… And I am getting a misfire…

Does this sound plausible?


#19

I understand what you are asking/ what I am missing…

The plug is screwed into the cylinder. Fuel should not be exposed to the wires (coil). So… I am reading more. I’m guessing something more like a cracked cylinder as a leaky fuel injector would not send fuel to the coil


#20

So, without taking everything apart and doing a top end rebuild…

I am assuming the cylinder head or the gasket has failed between cylinders 3 and 5. Hence, why I hear the compression escaping through cylinder 3 and am finding fuel on number 5.

I also imagine the cylinder head is cracked… As a failed gasket is not going to cause compression to escape audibly…