Bump-Starts and runs great, won't start with key - P0335 - ECU replacement fixed

Looks like it goes to the Clutch Start input.

What happens if you put the truck in NEUTRAL. Do NOT press the clutch and try to start the truck?

You need to use the clutch cancel switch. Or it wont crank.

 

Been tried, the ECM doesn't seem to "see" the crank signal (0 RPM), see post #49
But we have MAF signal so ECM is online.

 

No sure I follow, as you said: it will only crank if pressing the clutch OR clicking the "cancel clutch start" button. I nearly always start in neutral.

 

This is crazy.
We have confirmed we have a crank signal.
The truck runs as long as the key is NOT in the crank position.

WTF is going on here? LOL

 

That's the million dollar question lol, I'm really curious about those waveforms. Gotta be something we missed.

 

DO NOT DO THIS......

But I'm curious if the truck would start IF:

KEY - ON.
Transmission in Neutral.
E-brake - ON

Jump the starter relay.
And be QUICK.......Remove jumper quick when it starts.

That removes the ignition switch and feeds from the equation.

I mean.....Hummm..

Desperate times...desperate measures....

Again...Don't do it.
Not a "good idea"....

 

If I had a million dollars, I'd drive out there and help OP.
Worst case, we'd buy a new truck. LOL.......

IF....I had a million dollars.

 

You can buy (rent?) starter buttons that just jump the starter solenoid. I use one to run valves on my race car all the time. That way it’s way safer standing away from it a bit

 

Have we ever hit 4v + on the amplitude?

 

I'm pretty sure that will work, will give it a try and update accordingly.

And yes, desperate times in deed.
I mean, if jumping the starter work and we don't crack this down I may improvise a workaround...
Heck I even hooked the scope again suspecting that MTN signal to the 4wd ECU but all looks good:

 

Yes. you can.

But I'm a sketchy guy.
I do sketchy things.

 

Got +/-4V while engine running - post #6,
and +/-2V while cranking- post #8

The Toyota Mechanic, if he's to be believed, said there's fuel reaching the engine head (i.e. fuel pump fine) but no injection or spark while cranking, which makes me continue to believe the ECU is being "blind" to the crank.

 

But why is NOT "blind" while running?
That's the question.

And is 2v enough to start the truck? (doesn't look like it)
Is something pulling the amplitude down in the crank position?


Plus, you already tried a different ECU....
The chance of 2 being bad the same way, are slime to none....

 

@Dm93 what are your thoughts on the 2v during cranking?

I noticed this. And that's what gave me the idea to bypass the ignition by jumping the starter.

 

+/- 2V should be plenty, +/- 500 mV is typically minimum for the ECU to recognize the signal.

I watched a scanner danner premium video last night on a Camry with a weak crank sensor, it would start only with a jump pack connected but the crank signal was really weak (like +/- 300 mV cranking and like +/- 2v running).

 

So I thought it would be as simple as shorting the relay, but that didn't kick the starter.
I think it needs some other approach or maybe did something wrong.

When trying to jump relay connections with battery+ one of the "sensing"(silver coated) terminals turned on a humming noise I get once cranking. Not sure I noticed it before, probably because the engine would fire, but it's pretty strong.
Interestingly the noise stays on until I switch off (i.e. stays on during IGN) but won't start unless I turn to cranking (ST1).
Not sure what's that humm, sounds like a pump from the engine.

 

You gotta be careful what your sticking power to.
You would need to send power to Pin 3 of the STA relay to activate the starter.
I'm assuming you hit Pin 1 and the ECM saw the signal and turned on the fuel pump.

 

That's funny cuz I did try it (and all others, truly not wise) using the test light, maybe that's no good?

 

Not gona hurt anything poking around with a standard 150mA test light (I thought you were poking around with a jumper wire) but while that is enough to activate most standard automotive style relays it's not gona energize the starter solenoid, those typically need somewhere in the 10-30 amp range to pull in.

 

Thanks, tried again this time got a good crank just like with the key but darn, same issue.
I even "triggered" the fuel pump (humming noise on) using the relay prone #1 and tried again, but no difference... Maybe that would signal the ECU? Worth a try bypassing the fuel pump too/simultaneously?

Will get those bump-start scope readings soon.

*Another thing that crossed my mind:
Could the ECU have any other sensors that without them we won't get an injection or spark (e.g. engine flooded, compression)?
Maybe while cranking the voltage drops enough not to read?