Multiple system failure at 27 years

My truck is a 1995 2.7L 4WD single cab. It has around 193k lightly driven miles on it. My dad owned it from 1999 to 2019, and I've owned it since. In June of this year, it broke down with severe misfiring, rough running, and low power. I had fixed similar issues the previous year, which turned out to be a combination of plug wires and battery corrosion. I took it to an auto shop, and I still haven't gotten it back. I've been communicating constantly with the mechanics, who have been very helpful, and they say they've never seen such a spectre of a problem on a Tacoma. They have found issue after issue, and the engine has improved, but the misfire remains. So far they discovered my ignition coil was weak, my condenser was blown, my harmonic damper was ruined, they tried swapping out my ECU to no avail, and now they believe my timing chain and balance shaft need replacement. Their current theory is that fluctuation in my timing assembly is causing inconsistent signal timing from my pickup coil, which is ruining the fuel injection pattern. All of this was exacerbated by the previous issues.

I'm not asking for repair advice - I want to know if such hard-to-track issues and multiple component failure have occurred for anyone else. These trucks are supposed to be some of the most durable and reliable vehicles out there, but mine has given me grief for around half the 3 years I've owned it. Do I just have bad luck or is this more common than I know?

 

Its a 27 year old vehicle, who knows what its been through or how its been maintained. That matters far more than the brand name.

Have they done a compression test?

 

Yeah they've done a compression test and all the standard stuff. I'm actually a bit reassured by how long it has taken because they're really running out of stuff that even could be the issue. I have an idea of how it was driven and maintained since my dad owned it for most of its life. He changed the oil regularly and drove it lightly. The only engine related issue it ever had under his ownership was the MAF sensor. To be fair, he never did much more than the oil (e.g. checking sensors, fuel filter, plug wires, etc.), but even so it's a bit surprising that all of this seems to fail at once.

 

Is it a 1995 or a 1995.5?

Difference being a Diag port vs OBDII port for diagnostics.

In short what are the codes?

Is the missfire active? (Flashing CEL) or intermittent? (Occasional miss or stumble)

When does the missfire occur? Anytime the engine is running, only when cold, only when hot, only after sitting overnight etc?

As much specific information you can provide will be beneficial.

The only thing I am sure of is I would get my truck out of that shop because it sounds like they aren't doing diagnostics and have no idea what's wrong and just unloading the parts shotgun at your expense.

 

It's a 1995.5 and there are no codes and no engine light. The misfire occurs usually upon throttle application that tips the engine into load territory and above a certain RPM (I think it's around 2500 but I don't have a tachometer). It's almost never up a hill or in any of the other "misfire under load" situations. The mechanic showed me the scope of the crank position sensor signal and pickup coil signal and showed that the pickup coil signal moves about and is earlier than it should be. What happens when it misfires is that two of the injectors (second and fourth I believe) fire twice and put too much fuel in, while the other two don't fire at all.

 

Okay, that's much better information, and if he's showing you oscilloscope readings then he just might know what he's doing.

However, I have never heard of a balance shaft going bad.

As a matter of fact the balance shaft isn't even necessary, LCE (Land Cruiser Engineering) makes a balance shaft delete kit as well as at least one or two other performance shops, it's not necessary for the motor.

The description you're giving, the occasional misfire when throttle position changes, sounds a lot more like a throttle position sensor to me.

I've had this issue and it was much as you described.

Have him use a sewing needle on the wires at the throttle position sensor and move the throttle through its range and get the resistance from that to see if it's bad.

I had a similar missfire issue and my throttle position had a dead spot of a few degrees where it would not transmit any signal, the resistance would read 1kΩ.

 

I had a stumble/dead rpm issue. I replaced TPS and fixed it.

Out of curiosity, I took the old one apart and found contamination in one section of the travel path. It's basically a rheostat. If crud interrupts the signal along the path, bad things happen.

2.7L Stumble - Throttle Position Sensor Impact and Disection | Tacoma World

 

Did you ask the previous owner (aka dad) what he thought about what the shop is feeding you?

Why did they jump to replacing the ECU? Pricey I bet.

Condenser blown?
Harmonic dampener ruined?
Timing chain and balance shaft need to be replaced?

Now they are telling you about fuel injectors not firing?

I'm with @Key-Rei. Time to get out of there.

 

It's honestly quite the dilemma. The fact that they're using an oscilloscope and showing you the captures means they're light years ahead of the grease monkey down the road. If you take it to another shop you're going to be spending a lot of extra money for them to start from scratch and likely start throwing parts at it. Yet, it sounds like you're at the point of questioning the original shop. You really need to find a good diagnostician but it's not like they advertise in the phone book...at least not in these parts and if you truly have some bizarre situation the forums are just going to lead you down a rabbit hole - especially if what the original tech said turns out to be true. What state do you live in?

 

I stopped reading after seeing a complaint that any 25+ year old vehicle with over 175k miles isn’t reliable.

 

This almost points to the crank pulley starting to break down.

Key way starting to get loose.

When your looking at the scope do you understand just what your seeing??

 

My thoughts exactly! I mean, really???? 27 years old (the vehicle, not the owner) and you're complaining about the reliability!

 

A bad ground or grounds can be easy to miss. Some people even run their trucks missing the back ground wire at the firewall near the heater core hoses.

I’d ask them how many grounds they verified were tight, and where they were in the engine bay.

 

I have yet to every see a Toyota in person that had that tiny ground from the valve cover to the firewall.

I never even was aware it was there till the internet.

 

Lol you and I have gone over this before, too funny. Mine is there and I sleep better at night, I’m convinced.

 

You know the strange part it is never shown in any of the EWD`s That I have found.

I forgot it was you to be honest!