RJR

If you've got a laptop with a mic input and a copy of Audacity or some other sound capture program, it shouldn't be too hard to make a little attenuator box (maybe 1Meg into 10K) and make a simple waveform capture tool that way. Amplitude accuracy will be just relative, but timing should be excellent. I may try to cook something like that up, since the traces on the CRT on my ancient HP oscilloscope are completely invisible anymore, and there's no chance of ever getting a replacement tube these days.

My interpretation of the paragraph about the changing pulse width is that it is the dwell angle that increases as rpm goes up, even though they used the word time. If my conjecture is correct that the pulse width is around 2 mSec, that works out to about 10 degrees of crank angle at 800 rpm, and 50 degrees at 4000 rpm. It has to fire every 120 degrees for a V6, so those numbers seem in the ballpark.

I'll see if I can gin something up tonight and get some pictures. You've got me interested now.

scope103

Interesting. Back in the day (with mechanical points), the rotor both open and closed the points so the dwell really was an angle. The points-closed time was inversely proportional to engine rpm, so the dwell had to be set to be long "enough" to charge the coil at full rpm.

Now, with a hall-effect sensor driving the ECU, I would expect Toyota to use something like a schmidt trigger to give a constant length pulse. Which length could be played with by the igniter. Perhaps the authors of the article I cited are just re-using old terminology when they talk about dwell "angle," when all they mean is "pulse width."

Let me know how your oscilloscope works out. You might have better luck with "designed" sound-card oscilloscope software, like http://zelscope.com/ or http://www.zeitnitz.de/Christian/scope_en (I haven't tried either). The problem you will run into may be bandwidth. The IgT signal runs about 40 to 200Hz, a typical soundcard is ac-coupled and may not work well that far down.

oldblue

wow thats over my head. my hillbilly ass just looks for a flash on the light haha

RJR

And you probably get your answers faster, too! But, for us engineers, analyzing the problem to death is far more interesting than ever getting it fixed.

[In my business (electronic test and measurement), I have an incredible amount of respect for the technicians who can find and fix problems while I'm still trying to reverse engineer the schematic.]

Scope, I've thought about the ac coupling, but I think your numbers are a decade off. At 800 rpm, a 6 cylinder should give 40 ignition pulses/second, going up to 200 pulses/sec at 4000 rpm. At any rate, the edges are fast enough that it should be easy to observe the timing and pulse width, even if the tops aren't flat or accurate.

I've downloaded the Zeitnitz oscilloscope. Looks pretty good.

scope103

'cause you're just too darn quick. Don't you have anything better to do on a Friday afternoon?

I realized the typo as soon as I posted it, and promptly fixed it. Just not promptly enough to beat you.

RJR

I've been sitting on the sofa for the past 3 days nursing a terrible cold and fever. Yotatech is one of the few things keeping my sanity.

RJR

Here's a "scope" shot of the IG pulse at the diagnostic connector, which appears to be the same as the negative side of the coil (I measured both). A couple of notes
- Engine is idling at about 850 rpm
- The waveform is upside down. My PC sound card apparently has an inversion in it, so the waveform should be flipped over so that the leading pulse is negative going.
- Vertical sensitivity is not calibrated, but is about 7 volts/div based on other signals I measured with the same settings.
- It's ac coupled, so the "zero" line in the middle is more like +12 volts than 0 volts,
- The large negative-going (on the picture, positive in real life) spike is the flyback of the coil when the igniter shuts off the current flow. It's that spike that generates the spark.
- The pulse width, as you can see, is about 3.2mS. That does not change at all as rpm varies, so the coil charge time appears to be constant, which makes sense from the physics of it.

None of this probably helps the OP, but it's interesting nonetheless.

oldblue

engineers, that explains everything!!!!

RJR

Chainbrain01, did you ever get your truck started? How's it going?

chainbrain01

So I ordered a new ECM from a local parts store on Saturday and was told they had one in a local area store and it'd be ready on Sunday. No call Sunday... Monday comes and I'm told it's in stock so I go check it out, I asked the clerk to double check the computer matches what I need (4x4, standard, federal emmisions) and of course the girl who took the order put in a 4x2 instead of 4x4! Now I have to wait until this Friday to pick it up. Once I get it plugged in I'll let you know if it starts up! **Fingers crossed**

chainbrain01

Update - Just plugged in the new ECM and tried starting the car. STILL NO START! Haven't had a chance to try a spark test again but I'll try that tomorrow night.

Any more thoughts, ideas, voodoo magic??

RJR

Sorry to hear it's still not working, but... you haven't done the tests on the coil and igniter I asked you to do. Go back and do these tests to look for...

- An open primary on the coil. Pull the connector off the coil and measure the resistance from + to - on the coil itself. It should be an ohm or less. If it measures an open circuit, the coil primary is open.
- A blown ignitor. With the connector off the coil and the ignition off, measure the resistance to ground at pin 5 of the igniter. If it's a dead short the output transistor on the igniter is blown.
- Measure the input to the igniter. With the connector off the igniter, measure the resistance to ground on pin 2. It should be > 1K ohm or so, I think.

Do all of those tests in boldface type and let us know what you find out.

chainbrain01

Ok, just got done checking the coil, .7ohms. I tested the igniter and it tested within your range for both the pin 5 and the pin 2. Plus I plugged in a new igniter in order to rule it out (going to return it once the truck starts up). No fire still.

I got a little curious about the VAF so I pulled the on-vehicle inspection from that factory manual and noted the VC-e2 read 0 ohms. The VS - e2 read just under 200 while the THA - E2 read about 2.6 (being close to 70 outside). Could this have any affect on the ignition system to not spark?

I also found a test light I'll give a shot with tomorrow when I have more time. Any thoughts on the latest information?

RJR

At this point about all that's left are the timing signals coming from the distributor to the ECU. The article that I attached to post #16 of this thread has a thorough trouble-shooting procedure for "no-spark" conditions on page 12, and I think you'll need to go through that carefully. You can measure the resistance of the pickup coils in the distributor and compare them to the values on page 13 of that article.

If the the ECU does not see an Ne signal or G signal from the distributor, it will not attempt to fire the igniter to create a spark. I don't think the ECU looks at any other sensors to determine if it should fire, at least while starting.

It still seems strange to me that you are seeing very close to 0 volts on the - terminal of the coil. The "normal" voltage at that point should be 12V if the ECU is not trying to fire the igniter. If that point is stuck at ground and the coil is good, there would be upwards of 15 amps flowing through the coil (and about 180 watts of power being dissipated in it), which is not a good thing.

Check out the signals in and out of the igniter with your test light, and see what you find there.

Hope you find the issue soon.

chainbrain01

I just read through the troubleshooting guide and realized I didn't bolt in the new ingniter! It's not getting ground if it's not bolted in... Crap. Another question: does the ECU need to be mounted for grounding purposes? I haven't mounted that either just in case I needed to return either item. I'm going to try mounting both tonight to get a good ground on the igniter at least. If that doesn't work I'm going to start through with the test light to check the wires throughout the system as you mention above.

RJR

Not grounding the ignitor will certainly gum up the test results. I think the ECU gets its ground through the wiring (at least there are ground pins on the connector), so I doubt that was an issue for you.

Here's hoping it fires up with the ignitor properly installed.

ginger.yota

Just a side note here but I had a similar problem on my 95 couldn't get spark after replacing head gaskets. Long story short but the Volume air meter (thing on top of air box) went bad basically no air ecu says no spark I spent days going through the coil igniter distributer plugs and wires when that was bad. From you saying it cut out while driving I would think that was the problem. Good luck chainbrain

chainbrain01

I have a 4runner again, no more no-runner...! @ginger.yota was spot on, I dug into the VAF and found the 3 foil connections to the circuit board were torn. After an afternoon of soldering I got 2 of the 3 connections soldered which happened to be enough to get it to start!

After going through the entire checklist for the ignition system from the previous posts (thanks to everyone who contributed) I was about to give up until ginger.yota gave me something new to try.

A good lesson learned here is the VAF has to have a complete circuit in order to let the ECU to give the signal to spark/start. At least at this point I've replaced the spark plugs and rotor which needed it anyway. Time to see if I can return the new ECU and ignitor and purchase a rebuilt VAF since I couldn't get a good solder on the 3rd connection. I'll try to post pictures of the connections once I find a way to get them online (suggestions welcome).

So relieved... Again, thanks to everyone who contributed to this post!

RJR

Congratulations, and thanks for sharing the final fix!! I had not seen anywhere that a valid VAFM signal was necessary for ignition, but apparently it is. That's good information.

ginger.yota

Yes Congratulations nothing better then driving your toyota after a long repair