Figured I would post up and see if anyone can toss ideas of things to look at. I've had my 4runner since I bought it new in '96, I'm at about 200k miles now. Edit: It's '96 SR5 4x4, 5VZ-FE and Auto trans, all stock.

Problem is yesterday out of the blue I was leaving the house and the engine started cutting in and out going down the bumpy driveway, seemed electrical. After about 2 miles on smooth pavement it quit and wouldn't start. I noticed when it was cutting in and out the check engine light and the A/T temp light flashed on whenever it cut out and flashed back off when the engine picked back up again.

Towed it back home, put it in park, engine started up and ran fine so Shut it down and went to bed.. Tried again today and 2 miles from home it died again, wouldn't start, towed it back home again. This afternoon it starts intermittently, will idle for a random amount of time, then die. It started up several times, ran enough to get up to temp, but then went dead and just turns over fast but no start.

It is throwing no codes, and when I was on the side of the road my laptop OBDII reader lost connect to the ECU and couldn't connect to the ECU with the key on, so I thought maybe wiring or bad ECU, but now it connects up just fine, no codes, engine will spin over but will not start. Gonna try it again once it cools down and see if maybe it's temp related.

I have never had to dig deep in the systems on this truck, and don't have a service manual, it has been 100% reliable all these years with never a break down so I never needed to dig into it or buy a manual and have only had to replace brakes, batteries, ball joints and other wear items. I do also live in high dust environment of Texas dirt roads.

Any ideas? Does this issue sound familiar to anyone?

Water/ Bad gas?

More info, went back out after it cooled off and it started right up, ran for 10 secs and cut off hard. Started back up, held it at about 2500rpm and connected the laptop.. I put it in raw data mode where it just spits out lines of data as it gets it from the ECU..

The engine would cut out and then come back and every time it cut out the raw data feed from the OBDII port spit out a couple of lines saying NO DATA, and started spitting lines of data again when the engine started firing again. It lost connection altogether and couldn't connect, but less than a minute later it started back up and the laptop connected again just fine.

Bad ECU? I kinda figured when an ECU dies it just dies, not cut on and off like that. I unplugged the ECU plugs and plugged em back in a few times, swapped out the EFI relay, same problem.

Hmm, couldn't find correct pinout on the ECU to save my life, so I can't check the power going in.. So ebayed a used tested good ECU, if that isn't it I guess I'll just hold onto it as a spare.

Have you changed your fuel filter? If that services is current I kind of sounds like a fuel pump.

I have been told of a thread that discusses a specific chassis ground for the ecu causing all kinds of headaches for 3rd gen owners. I haven't seen the thread for myself but a friend of mine read up on it and insisted that we install a dedicated ground wire for the ecu chassis on our 3rd gens. Maybe you can find that thread or someone can link it. Sudden "NO DATA" certainly screams of a ground loss to me since the ecu takes all the signals to ground and acts as the ground switch for many systems.

That would have been the first thing I looked for, except when it died on the side of the road I had my laptop scanner hooked up while driving it and when it died the scanner lost connection to the ECU. I had the key on and the scanner would not reconnect at all, it tried all it's protocols and popped up a box saying "can't connect, make sure the vehicle is OBDII compliant"..

I must have tried to reconnect 10 times. Next morning the scanner connected right up with the key on, read fine, no codes, truck started fine.. And when I hold it at high RPM and it just stops firing for just a second but doesn't die and picks back up instead, the scanner is saying it isn't getting any data during the second it cut out. I really can't see the pump or fuel pressure causing the OBDII port scanner to stop receiving data unless I'm missing something.

That's what made me start looking for whether power to the ECU was bad, or maybe a bad ECU. My first thought was maybe a mouse had chewed into the ECU wires or something, but it looks ok from what I can see. We do have mice that get into cars out here in the sticks, I killed one in there just a few months back that was moving into my dash..

But since I have to wait till Monday for the ECU anyway I'll probably replace the filter anyway and check the fuel pressure this weekend, been a while since filter was replaced.

That sounds like a possibility, I can certainly ground the ECU box to chassis and see if it changes anything. Whatever it is it's getting noticeably worse. I'll search for a thread on it. This forum doesn't seem to accept ECU as a search term though, vbulletin forums by default won't accept three letter search terms I believe.

It would be real nice if I could find an accurate wiring diagram. I downloaded the 1996-2002 FSM from here but it shows a 5 plug ECU when mine only has 4 plugs.

How to search: https://www.toyota-4runner.org/1470647-post1.html

Here are the terminal and ECU diagrams.

ps if you would be so kind as to list your truck's specs in your sig, it saves time
for anyone who might reply.

Attached Images

	1996 4Runner.pdf (55.2 KB, 66 views)
	1996 4Runner-ECU.pdf (151.7 KB, 61 views)

Thanks for the links, I don't see a place to add a sig in my profile page..

Anyway it's a '96 SR5 4x4, with a 5VZ-FE engine and automatic trans.. Any other specs that would be applicable?

It has a 4 plug ECU, part # 89661-3d150


Edit: Those diagrams look much closer to what I have, and a lot of good system info. I'll be going out in the morning with a meter and maybe my oscilloscope to make sure they match and start testing voltages and signals. Thanks again

You're certainly welcome.

The diagrams should be what you have. Hope it helps.

to edit sig:
further down the same menu
"Settings and Options"
"Edit Signature"

Year, model, engine, and transmission, at least. Anything else that might
matter- mods, paint, I don't know. Maybe check out what others have listed.

Yeah I found it, I'm the original owner and mine is bone stock 100%, right down to the cassette deck in the dash. Now lemme see if the sig works...

I had a very similar issue just recently. From some help here I tried an easy fix first. I replaced the fuel filter and has been running good for a few weeks now.

Had the same symptoms. Break up right before it died. Would not restart for a few minutes. Then when it would run it would die.

Just a thought but it has helped me out.

This could help you diagnosis the problem If you have a small container to safely keep some gas or get a can of starting fluid. When it stalls on you pull the air horn off and splash or spray a small amount of fuel into a open throttle body (just open it with your hand). Replace the air horn and try to start it. If it does not try to start right away then it's a spark problem if it starts and dies then you have a fuel problem then work from that point looking for a cause.

Went through something similar with mine. 1996 sr5 4x4. Would randomly just shut off. Pull the ECU out and pop it open. Mine had a bunch of ruptured capacitors. They had leaked out onto the board and messed it up. I bout new ones and soldered them in and cleaned the board with alcohol. Has not missed a beat in 3 years. Was having issues with overdrive and cruise control as well. It's a problem with more Lexus cars from the mid 90s.