1996 3.4 Dies and Goes into LIMP Randomly

Hey fellow Tacoma owners new guy here. I have a 1996 Tacoma 3.4 5VZ-FE with 128,000 miles.

My truck has been dying randomly and sometimes going into LIMP mode.

This all started last year, but has progressively gotten worse.

Recently it has been dying after it is warmed up and has just started going into LIMP mode randomly. I have a code reader and NO codes are being thrown, when it goes into LIMP I lose connection with the OBDII and can see no readings. If I stop while it is in LIMP the truck will die and won't start till you give it a few minutes. The part that is really strange is when it dies the Check Engine light will "flicker" not flash but the light is dimmed and you can just barely see it has a small flicker to it, but will stop (as seen in video) and the truck will crank and run till it happens again. I will attach a video link at the end.

Things I have changed/checked since this has started:
O2 Sensors
Removed Cat Convertor(was bad, went with straight pipe, seemed to solve the issue for awhile)
Cam Position Sensor
Checked readings on Crank Position Sensor (was to spec according to service manual)
Coolant Temp Sensor
Checked all grounds in the engine bay(had one bad that I will explain below)
Fuel Filter & Fuel Pump
Tested and replaced MAF (did not fix issue and returned the replacement MAF, original was to spec)
Valve Cover Gaskets, O rings, Spark Plugs, & Wires
Checked all fuses and relays (all read to spec)
Ive went through all wiring that I can find inside and outside the cab doing "wiggle" tests, but can't mimic the issue.

The one bad ground was from the back of the block that runs to the firewall passenger side. After cleaning up the area and getting a reading the truck ran like new for about 2 days, then the issue came back. The MAF and plug gives readings to spec according to the service manual for this year and motor. It seems to be electrical or possibly (Hopefully not) ECU related. I have checked the temp on the ECU and all seems to be normal.

All of my live readings are great until the LIMP starts and I lose all communication with the port/scanner. Again NO codes are being thrown for the issue pending or active.I am at a complete loss on where I should go next. I have scoured the forums here and any I can find related to this issue, but have had no luck solving.

Any help would be appreciated!

Video Link:
https://youtube.com/shorts/Vz5SaQdqd7M?si=L0WmzFSuMRqx4Qk9

 

I would strongly consider sourcing an ECU.

 

weeeeeeeeeeeeeeird.

any chance you could pull code/communicate with the 'Diagnosis' OBD port under the hood?
or u have tried both ports to no avail?

what was the last OBD code you could read?

 

My worst fear, I will look into to finding one.

 

Unfortunately I don’t have the tool/reader to try the diagnostic under the hood.

The last code I had was the MAF but it was from it being unplugged during the change. So I know the ECU will throw codes it’s just not throwing them for whatever this issue may be.

 

It sounds like you really did a through job troubleshooting, and there's just not many more things it could be.

On second thought- have you tested the battery, alternator, and cables? maybe some corrosion in the cables is resulting in an intermittent ground? clutching at staws, but worth a thought while you hunt for an ECU.

 

I did a very tedious job cleaning the terminals and cables for the battery. Getting normal readings on those as well. I will check the alternator now. Possibly order a cheaper (returnable) one to test incase it’s a problem with the alternator itself getting hot once the truck warms up. I appreciate your time. I’m about neck deep into searching for this problem, and the motor is to young to die on me now.

 

Hmmmm
During your ‘flashing CE’ light searches
What most common cause?

 

Pretty much all the things I went about replacing in my original post. Unfortunately, it seems like its not a true "flashing" like I have seen others deal with. Seems to be a short of some kind somewhere in the wiring or the ECU/ECM its self. I checked the alternator as well, readings were to spec and the truck did the same thing while it was unplugged so I have ruled that out.

I have found an ECM and will hopefully be going to get it this weekend if it doesn't get purchased before I can get there. I will also be checking all the wiring underneath the intake manifold tonight. That is the only wiring that I haven't been able to inspect due to whats involved to actually get to it.

 

glad u found one

 

I think this guy was recommended for ECU repair, if you have time.
https://www.ebay.com/itm/223971438280

 

You can check the voltage on the +B wire to the ECU when this happens, before replacing the thing. If it's not close to battery voltage, it's a wiring issue

 

I will try and attempt this when the problem happens. Being quick enough to it will be the issue. Thanks

 

Hey man, did you solve the problem? I'm having the exact same issue on a 96 with the 4 cyl motor; and since I lose comm with the ECU when it happens figured replacing that is the starting point for diagnosis.

Edit: I have pulled the ecu and opened it up; there is a blown capacitor with a melted resistor next to it, so I'll need to replace or repair it either way, but truly hoping this was the fix for the random dying and limp mode.