LifeOnABoard

Has anyone measured the voltage on their crank sensor? I'm still dealing with a hard start issue. Takes up to 6-8 cranks of the starter usually. At first I thought it was fuel, checked that out, pressure is good and the coolant sensor is in spec. It's got new plugs, wires and fuel filter.

So I put a timing light on the wires and see that it doesn't spark immediately, when it does spark it finally grabs and starts up. So duh, I think crank sensor is either going bad or the ECU isn't responding fast enough. I tried an ECU from Ebay, no change. I tried an igniter from Ebay, no change. I pulled the crank sensor off to measure the resistance at different temperatures, that checks out fine too.

So I think alright, maybe there's interference in the engine harnesses that causes the starter voltage to interfere with the VR signal from the crank sensor.
So I put the trusty USB Oscilloscope on it. Everything looks good all the way back to the ECU harness! I'm lost here.

It's a 2 channel scope so my first measurement was to compare the crank sensor signal to the starter solenoid signal. As you can see the sensor responds as soon as the starter starts to suck juice. (This is measured at the starter relay).



I also compared the crank signal to the cam signal. I get the cam signal immediately after the first TDC missing tooth. All looks sync'd up but the only thing to note is that the crank signal voltage is smaller.



Can the dealer reprogram the ECU to respond faster or something????????? I hate delayed starts!

eddieleephd

First the crank sensor should be tested on an ac current.
Next it still could be your cam sensor, this must be sensed first before it will even try to crank!

lastly fuel pressure do not rule this out, do you turn the key and crank immediately or do you turn the key and wait a second then crank??

could be a slightly faulty fuel pressure regulator I would suggest seeing if there is any fuel pressure first thing in the morning by breaking the banjo bolt loose to see if any thing comes out and how far it squirts!!

LifeOnABoard

I hear ya Eddie. The Crank and Cam signals were tested for AC. In the second image you can see the red spikes for the cam signal, the first red spike occurs immediately after the crank passes TDC on its first revolution so I think this is OK (as seen in time block 1.987 - 2.074).

Ahhhh, fuel pressure, yes I have it, no the rail does not get primed with the key in the 'On' position. I've asked here before whether or not this is normal. Nobody seems to know, probably because checking pressure on the 3rd gen is a PITA! I had to solder together a custom banjo fitting to get a gauge on it. Not as simple as it looks, let me tell ya.
So as far as getting pressure prior to starting I have gone so far as to solder a jumper to the fuel pump relay! Basically I'm emulating what the ECU is supposed to do when the key is turned to the on position. I touch the end of the jumper to the cigarette lighter ground to turn the relay on for a couple seconds.
I tried a different ECU and it behaves the same way. The owner told me it came from his truck and it worked fine. Is he lying?? I don't know. Can anyone tell me if they get pressure with the key in the 'On' position?????????? This would be very helpful. Maybe I have 2 faulty ECU's here, I dunno.
I do have a bad FPR though, this is lame! It stays at 3 bar and doesn't drop with vacuum! Fortunatley, I still get 22 MPG.

I have a feeling that the tech at the dealer will look at me and shrug his shoulders.

eddieleephd

ok my next question is does it only do this at first start up or does it do it when warm??

Honestly this is one thing about our trucks is they turn over like 3-8 times before they start! and if there is no real issue with the truck you can not change this...
Mine does turn over more at first start then it does after warm, if this is not the case maybe fuel injector cleaner!

LifeOnABoard

It does take longer crank time when cold. I seriously think Toyota forgot to program the ECU's for a quick start. It should prime the fuel rail for a couple seconds and then open the injectors very briefly to clear them of air. This is the normal process for every other car on the road. Why the 4runner doesn't do this is frustrating to me. I don't want to change the battery and starter more than I have to.

Oh, I also tested the ignition switch for proper switching so it's not that either.

It's got to be the ECU. When I built my Megasquirt 2 ECU I had to adjust 2 potentiometers to get the processor to respond to the crank signal. I just don't think Toyota has addressed this issue properly so I'm reluctant to take it in.

eddieleephd

ok first the ecm looks for cam sensor for TDC, then it looks for crank sensor.
Once it finds both of those it gives spark and checks that it does then it gives fuel.

I understand the reason for this is that with out TDC it does not where to give spark,
and if there is no spark it will not ignite so no fuel is necessary, otherwise it would flood!

most other cars still use a distributor and do not check if there is spark.

now if there is an issue with the Pressure regulator then you may need to fix that.
However if it is 6 cranks or less then you will probably not be able to change this, since it is designed that way...

LifeOnABoard

Hmmmmm, I went back and looked at the signals from the Ford EDIS crank sensor I have installed on my Corrado. I get a strong 2+ volts from the sensor during cranking. Maybe the sensor on my 4runner is getting weak although it passes a resistance check. Further investigation to be done tonight hopefully.

This is from the Ford sensor:

eddieleephd

they are cheap enough to replace so If I was I would go the cost of the both of them and see if I was so inclined to make it happen...

LifeOnABoard

I replaced the crank sensor with a brand new unit, not sure how much voltage it puts out but there is no change in starting performance. I'm just gonna give up on this one and accept it as normal.

Thelast83inNJ

You wouldn't be able to scan it and look at the fuel trims for possibly a dirty MAF or one on it's way out? Negative numbers indicate lean condition. Could add little propane on crank to see if better?

LifeOnABoard

Well, I'm thinking that it's not fueling as the spark seems to be what is delayed. Actually, the injectors are probably slow to open as well. I haven't put the scope on the injector harness yet but a quick view of a timing light shows that it won't start until it starts sparking. It just seems like the ECU is slow to respond.

Also, I have a perfect idle and consistently get 22 mpg in the summer.

NicCantDecide

Sorry to hijack, but I'm working on an ignition mapping project at my university for kart racing that uses the same crank sensors from the toyota trucks.

I don't have a kart engine to test with at my current location and Denso/Toyota won't give me tech specs on the sensor.

I was wondering if you could post readings on the sensor throughout the RPM range, I just need to know how high the voltages get towards the upper RPM ranges so I don't blow out my microcontroller.



But more along the lines of this topic: your fuel pump should be priming when you turn the key to ON. I had a similar problem because I had a fuel leak above my sixth injector so it would lose pressure overnight and take a few cranks to start in the morning. I found that if I let the fuel pump prime by leaving it a few seconds in the ON position it would start fine. If yours isn't priming it could be the problem.

But anyway, if you could help me out that would be great and I'd really appreciate it. Send me a PM if you don't want to fill up this thread with unnecessary stuff.

LifeOnABoard

Hi Nic. To get an accurate idea for the VR output, you can always mount a 36-1 tooth wheel to a power tool of some sort on a bench. Boost Engineering can hook you up with cheap hardware from Fords, the T4R happens to use the same amount of teeth. But I take it that you're not part of the hardware group.

For a quicker answer; "At idle the output is approximately 0.6 volts, at mid-RPM it is close to 3 volts, and at very high RPM it can go as high as ~50 volts."
- http://www.megamanual.com/ms2/pickups.htm

I've only tested my sensors at cranking speed which is anywhere from 200-300 RPM. The Toyota sensor puts out 1 volt at that speed, whereas the Ford sensor puts out 2 volts. Hence, the reason why I thought it might be the sensor's fault. I am not prepared to test at operating speeds as that would require further wire work.

As far as the fuel pressure goes, I totally agree. The ECU is responsible for grounding the fuel pump relay before starting. I've tried a different ECU and that one didn't prime either. So I've gone so far as ground the wire at the ECU to manually prime the rail. But it still doesn't matter, the engine won't catch unless the injectors open and the plugs spark.

I guess there's an unknown that I don't know how to find. I'm giving up at this point. I love the truck and will just have to replace the battery & starter prematurely.

NicCantDecide

What I'm trying to do is simulate the crank sensor for the system I'm building, so I was hoping to stay with purely solid state electronics.

Looks like I'll have to go with a toothed wheel on a motor and the crank sensor in the system now though, since I can't simulate an analog signal like this inexpensively with digital components.

Thanks for the help though! Great article.

Good luck with your truck.

LifeOnABoard

FYI ,put a reman'd starter in from Napa and no change. Bought it at 84K and now at 128K miles. It's been a trusty truckie. Almost used to the long start at this point.