Houston, we had ignition

Greetings all,

I've come to the well of knowledge and experience once again in search of clarity.

So I have a 1st gen Tacoma(03) and a 3rd gen 4Runner(96). Both 3.4L M/T. The 4Runner has a 1st gen S/C. My issue is with the 4Runner. I know this is the Tacoma forum but I wanted a larger pool of knowledge and it is a 3.4L issue.

So it started 2 months ago with stalling. I'm driving down the road or stopped and the engine just stops. No sputter or bucking. Just tach to zero. All other electronics stay juiced, speedo, radio, etc. If I'm rolling I just keep in gear and turn the key to off then on and I'm back to normal, not even a blip. In fact a passenger would never notice. Hell sometimes I don't notice unless I was in the process of accelerating and it does it. Then I feel the loss of power in my foot. But I just reach for the key, quick turn left then right, and I sail along. It's happening much more frequently with the passage of time, 2-3x/mile, whereas before it might not happen at all in a 40 mile trip and then maybe just a couple of times.

I have searched and tried multiple attempted fixes with loaners including swapping TPS, CrankPS, MAF, ignition module, testing IAC.

Had it scanned at Autozone:

P0171 System too lean (Bank 1)
P0100 Mass or Volume air flow circuit
P0110 Intake air Temperature sensor 1 circuit
P0335 Crankshaft Position Sensor A Circuit
P0505 Idle Air Control System

Now I suppose it could be a fueling issue like a pump or filter but I would think there would be a less abrupt ceasing of power. In other words more sputtering/bucking, etc. This is just all or nothing and then complete recovery with a simple turn of the key. I tried wiggling the key around in the ignition while drive to reproduce the symptom but nothing. And I don't lose electronics so I don't suppose it would be the key slot/ignition switch.

In my recent search I have turned my attention to the evap system. I tested the VSV valves with a 9 volt battery and i get a resounding audible click from the bypass but not so much from the purge. I took the truck for a short drive yesterday after replacing the TPS and I thought of checking the fuel tank pressure after several stalls. I pulled over and loosened the cap and there was a pronounced and prolonged hiss coming out of that thing, in other words a lot of pressure. It changed nothing but I thought I'd note it.

So I'm going to get a loaner purge solenoid next but I just wanted to post up my symptom here incase anyone else has had the same experience and hopefully resolution. In my search I haven't found this same type of stalling. Others are usually at idle only, or involve some lack of power just prior, or off and on power, etc.

Any help would be appreciated and as always, thanks for your time.

 

Check the ground for the ECM problems there will cause weird things to happen (left side of intake brown wires)

Now the Crank Sensor code will shut off the fuel when it trips The ECM thinks the engine quit running .

Loss of the MAF signal will shut off the fuel also.

Time to buy your own code reader because from all your codes your light must be on all the time.

You need the code that trips when it happens not when you can manage to get someplace to read it

happy hunting

 

So I took your advice and checked the ECM ground at the manifold(S/C). I first checked battery positive to ground with multimeter and would get 12+volts DC sometime and other times it would be erratic readings all over the place. Then I tested for continuity off of battery negative and that was consistent.

Next I cleared the codes and drove a bit and let the rig shut down a few times. Retested and came up P0335 Crankshaft position sensor. Cleared it again and again drove around for a few shut downs and once again, CPS.

So I removed the CPS and bench tested it. This is the CPS I swapped off of my truck. It had the proper resistance reading, it generated the proper voltage as I passed a wrench back and forth across, and the plug had a good ground wire. The pigtail was laying across a water passage(HOT) between the passage and the dipstick tube. So I pulled the tube and rerouted pigtail. I thought maybe the heat or flowing water creating current...wishful, I know.

Took it for a ride down around the block and stalling continued but just as I parked it shut down. Without ever turning the key to the "off" position I tried to start it back up. Cranked fine but would not start. Tried that three times. Then I turned the key to the off position and then cranked it and it started right up. So it appears that I may be clearing something by turning power off.

At this point I'm stumped. OBDII is telling me CPS but everything tests fine. Do you think the ECM is to blame and I reset it by turning power off and then back on?

Thanks

 

thought #1

with someone to start the truck for you I would watch the harmonic balancer pulley on start up. See if the crank moves forward or backwards. The PCM is telling you that the crankshaft position sensor is a symptom, hell it just might even be the problem... A Dorman unit is apx $50 and you have diagnosed it properly, at this point every diagnostic procedure I have ever read says "Replace with known good unit.", sometimes you just have to put a part in it to continue testing.

thought #2

with your scan tool look at both current and pending codes as well as readiness monitors completed and readiness monitors completed this drive cycle and make a note of which have completed and which haven't. When she cuts off the next time, rescan and compare. Sometimes when a PCM looses power it will reset all readiness monitors and it might even show a P1000 code whereas moments before the shut down she was "Smog ready", i.e. No Codes Present and all drive cycle monitors have run and passed. Is this a take it to the grave test, no, but it could point you in the right direction as to a power/ground loss to the PCM.

 

Update:

took URD module out of loop and plugged directly into stock ECU. Problem solved. It is issue with 7th module.

thanks to all