Crank, no start

[Down by the Water]

'96 4x4 Automatic: ran fine until it just didn't run at all.

No rough running, no CEL; it was running fine, I parked it and a couple hours later it wouldn't start. The battery, fully charged, turns the engine over fine. Lights on the dash seem normal. No blown fuses. No clicking relays.

Two things, when the key is in the ACC position there is a loud clicking coming from somewhere around the throttle body/valley of the engine? It goes away when I pull the EFI relay. I've tried a new relay and swapping the AC relay (same part number) with the same results. The other thing is the ECU will not communicate with my code reader.

I noticed there was no rpms on the gauge when cranking so I pulled and tested the crank position sensor, it is good. Visual inspection of the ECU and harness are good. No loose connections or broken wires I can see. If I hold the throttle open while the engine is being cranked it will try to start just a little, push some white smoke out the tail pipe. I can smell a bit of fuel too, not overpowering though. I backed the nut off the engine side of the fuel filter and fuel passes through.

At this point I'm just trying to figure out what I can test and how to do it. Has anyone experienced anything like this before?

 

[giovannie23]

Try looking at the maf sensor

 

[Down by the Water]

Maf

I see it. It definitely has a MAF sensor. All jokes aside, the MAF sensor wouldn't be clicking. Also, unplugging the MAF sensor doesn't stop the clicking. Also, if the MAF sensor is bad it would start and die.

Try looking at the maf sensor

 

[phattyduck]

Since you have a non-communicating ECU... It may be bad internally (leaking caps). The visual check for that is to actually remove the ECU - since you already inspected the wiring, you now how to get to it - just the two 10mm bolts and it'll just pull out after unplugging.

Open it up and see if you can see leaking caps on the board.

-Charlie

 

[Down by the Water]

more info

Thanks for the reply, Phatty.

I pulled the ECU and inspected. Looks fine, no loose pins, the inside looks clean and new, no corrosion or burn spots, no loose parts or debris.

The OBD port has 4 wires. Two grounds (pins 4 & 5 - tested good,) power (pin 16 - tested good, batt voltage) and a signal wire (pin 2.) I measured 0.44v at pin 2 with the key on (ACC position.) The voltage never changed and the scanner would not link with the ECU. I am assuming this means the scanner and ECU are not talking to each other because bad ECU or broken wire? The internet says the signals should vary between 0 and 8v. I did not observe that. I wasn't able to figure out what the comm wire was at the ECU so I haven't been able to check the voltage on the ECU side or jumper the scanner and ecu to see if I can get it to communicate that way.

The IAC valve was the source of the clicking. I unplugged it and the clicking stopped. I was able to start the engine with it unplugged by holding the throttle body open a bit by hand. It would only run for a moment before dying. Later I plugged the IAC valve back in and got it to run for a bit longer but it was definitely running rich (a bit of white smoke out the exhaust) and it smelled like fuel, would pop and sputter a bit. It did not run well.

I may just buy a used ECU and see if it helps, return it if it doesn't? I have no idea why the IAC valve would be clicking like that? Possible bad ground? Possible the ECU is getting bad info and commanding it to open and close like that? No idea.

Since you have a non-communicating ECU... It may be bad internally (leaking caps). The visual check for that is to actually remove the ECU - since you already inspected the wiring, you now how to get to it - just the two 10mm bolts and it'll just pull out after unplugging.

Open it up and see if you can see leaking caps on the board.

-Charlie

 

[phattyduck]

The OBD-II VPW data line 'idles' in the low state, so 0.44V is normal unless there is active communication happening.

Not sure why the IAC would be making noises - that does seem like a smoking gun - but it may be a red herring too.

You may want to pull the upper timing cover back (just move the rad hose clamp, no need to remove the hose yet) and make sure the intake cams are at 0* when the crank is... (you may need to rotate the crank 360 to get to TDC intake stroke)

-Charlie

 

[2TH4IST]

Was the intake boot attached when you unplugged the IAC? If so reattach it and leave the iac unplugged. See if I will stay running. Have you checked all fuses inside the car and in the engine bay? All grounds good? Is the ground wire from the batt negative to the body (about 4 inches long) still attached and in good condition?

 

[Down by the Water]

Hey, yeah, I am going to check the timing. When it cranks it sounds normal but you never know. The timing belt isn't broken. If it has slipped a couple teeth I would think it would still start and run, even if poorly, but that is a good suggestion.

I was measuring the ECU communication line voltage while my OBD reader was trying to connect with the ECU. I'm assuming there would be some variation in the voltage while the two "talk," no?

Thanks,
Andre

The OBD-II VPW data line 'idles' in the low state, so 0.44V is normal unless there is active communication happening.

Not sure why the IAC would be making noises - that does seem like a smoking gun - but it may be a red herring too.

You may want to pull the upper timing cover back (just move the rad hose clamp, no need to remove the hose yet) and make sure the intake cams are at 0* when the crank is... (you may need to rotate the crank 360 to get to TDC intake stroke)

-Charlie

 

[Down by the Water]

I did reattach the intake before trying to start it with the IAC valve unplugged. I didn't want the MAF to kill the engine with low readings by leaving the boot off.

I've tested all the grounds I can find. Both brown wire grounds on the ECU (there might be more?) both grounds on the OBD plug and the grounds on the air intake are all good. There are no blown fuses on the panel in the engine bay or inside the cab and the fuses have power. The body ground is attached and I can get to ground from inside the cab by touching an unpainted screw on the body. I tried that when testing grounds inside the cab with a line straight from the battery positive. Also, test light lights up when testing the ground on the air intake so I'm assuming the engine is grounded.

Was the intake boot attached when you unplugged the IAC? If so reattach it and leave the iac unplugged. See if I will stay running. Have you checked all fuses inside the car and in the engine bay? All grounds good? Is the ground wire from the batt negative to the body (about 4 inches long) still attached and in good condition?

 

[Down by the Water]

Update: 2/27/26

I've verified the mechanical timing. The belt is good and the timing marks are good. The cam and crank sensors are good, clean, clear of obstruction.

Definitely think the ECU is bad, but I’m baffled as to why or how? Other than the 'Linking Error' and the IAC valve clicking, everything seems normal. I opened up the ECU, there is no apparent defect, no corrosion, no burn spots, no loose pins or parts, no bulging capacitors… It is very clean. I checked the engine grounds again, on the air intake and along the firewall of the passenger side, both tested perfect.

I have a used ECU coming in the mail. Strange, if this ECU starts and runs the engine, this will be the third ECU I've had in this 4runner.

 

[Down by the Water]

ECU fixed it

It was indeed the ECU. Used one I bought on ebay came in the mail yesterday. The truck fired up with no hesitation. It's running really well.

Couple things I've learned: the OBD to ECU communication line will "idle" at 0.45V (as you indicated, PhattyDuck.) When the ECU is talking to the OBD scanner the signal will move between 0.45 and 1V. You can actually see it on a multimeter. I was using the DC 2V scale and it was obvious. The other thing, almost every year of the 3rd Gen 4Runner has a different wiring layout. You have to find the diagram for your year, full stop. For instance, I have a '96, the '97 and '98 layouts will not work for me.

My concern is that this is the third ECU this truck has had in it. When I bought it, maybe 10 years ago, it had a shifting problem. I could not diagnose it. One day it just died while my wife was driving it. We had it towed to a shop and they diagnosed a bad ECU. After that it shifted well and ran strong, until last week when it died again. Either the ECU's aren't as bulletproof as some might think or there's something else going on.

Next I'm going to see about having the old ECU tested and refurbished. I lucked out finding one on ebay for $250, they were mostly in the $500-600 range. Yikes!

 

[phattyduck]

I have seen some correlation with project vehicles that stay parked with the battery disconnected for long periods of time and ECUs going bad - it may seem counter intuitive, but electrolytic capacitors can last LONGER when they have voltage applied to them regularly.

May not be the case for your truck, but...

-Charlie

 

[Down by the Water]

Charlie,
Do you have any idea if there are companies out there that will refurbish my old ECU. I'd love to have a spare.

Andre

 

[phattyduck]

Charlie,
Do you have any idea if there are companies out there that will refurbish my old ECU. I'd love to have a spare.

Andre

Nope. I've repaired a few ECUs myself over the years, but it was all for obvious leaking capacitors (friend's cars - I've been lucky with my own vehicles).

-Charlie