[FIXED] IGT1 The plain and simple fact.

The absolute fact is that I have no signal coming from IGT1. I've repeated the list of symptoms to people who know a little and people that know lot. And while I have received great advice about most things troubling my vehicle, IGT1 has not one answer. I've been addressing all the other symptoms, hoping IGT1 would get addressed at some point. If I'm wrong then someone please tell me so because what I believe I have is a 2nd computer faile PCM. Either that or a PCM that I'm unable to get out of limp mode. I run this diagnostic procedure from Mitchell and I had no results on IGT1.

If IGT1 circuit is being grounded at some point this could cause the PCM circuit to fail.
Let us know the outcome.

I'm going to assume for the sake of this discussion that;

1. Engine was running fine prior to any work being done by the brother.
2. Brother only replaced the timing belt.
3. Brother did not remove the cam or crank gears.
4. Brother removed the crank pulley.
5. Brother did not remove cam or crank sensors.
6. Brother did not alter the coils, igniters, wires or ECM.
7. Engine did not have low vacuum prior to repair.

Results of repair;

1. Car runs but has misfire on #1 & #4 cylinders.
2. Engine has low vacuum.
3. lGT1 has no signal.
4. lGT1 controls cylinders 1&4.

Additional repairs or test you have done.

1. Replaced igniter and ECM.
2. Swapped coils and plugs.
3. Tested powers and grounds.
4. Used an alternate wire for the lGT1.
5. Rechecked timing.
6. All above did not correct the problem.

If all that was done was to replace the timing belt and that altered the engine condition, we can directly infer the initial repair caused the problem.

Timing is critical to engine operation. If the timing is off just a little it can cause the low vacuum, engine misfire and related codes. With this engine it may be causing the lGT1 condition.

This all points to the repair and timing. I would go back and tear down everything to the point of the belt replacement. I would talk to the brother and find out every step he did. You assume he did it correct, but it is apparent something was done wrong resulting in the current condition. Their is no reason for the current misfire as no condition existed prior to the repair.

Liminy Snigett... an unfortunate chain of events...

I have to problem doing all I can to fix this but I can't find the answer to the IGT1 problem. The IGT1 wire has no short, it's been looked at a lot. How does any of the repairs done by the brother make only IGT1 stop working and why isn't IGT2 & IGT3 effected? In general what, if not a short that didn't seem to exist prior to repairs, would make that signal quit? I haven't undone the brothers work but I would if I knew exactly what along the way he could have done to shut off that signal. I understand the timing problem that can be caused by incorrect repair but given all the facts it doesn't make sense that it's only IGT1 is effected. Thanks for the help.

I agree the IGT1 issue has to be resolved. It works like this;

Each IGT circuit has four wires... 12v, 5v, a ground and signal IGF wire (B-Y to the ECM). The 12v supplies power to transistor in the coil, the 5v is from the ECM to a transistor in the igniter. The 5v is controlled by the cam and crank sensors via the ECM through grounding that turns on and off the transistor for the igniter which then lets the coil fire. The IGF sends an on off signal back to the ECM letting it know that the coil has fired.

Each coil/igniter has a common ground, 12v, 5v and IGF. If IGT 2&3 are working then one of the common connection to IGT1 has been compromised. I would look closely at the IGF wire.

You had brief circuit integrity then failure. Have you returned those to the other guy, are they working?

Ah...ok. What I have is an ignitor with a total of 10 wires.
3 IGT wires come into the ignitor from ECU and 3 wires go out of ignitor to the coils. Now please correct me if I'm wrong. The remaining 4 wires are the common wires shared by the 3 IGT wires. The coils don't have ignitors built in, I have just coils. The 4 remaining wires are 12v, 5, ground, & IGF. So if IGT#2 & #3 are pulsing @ 3.9v which in turn fire cylinders 2,3,5,& 6...then possibly those 4 common wires aren't the issues? You've got me thinking now. I performed a pull-up test on IGT1 at ignitor and at ECU. Both places fired corresponding cylinder plugs. (#1&#4) I tested cam/crank sensors (not under load) which were good. I assumed since IGT2 & IGT3 were working that it wasn't an input problem. Could it be a sensor failing under load? Doesn't make sense to me. BUT brother might have messed with or something happened to crank gear and or reluctor ring. ScannerJohn could you tell me if some kind of issue with either, especially the reluctor ring could cause a IGT no signal? Thank you sir for the conversation.

the wiring diagram I have is different from yours. The diagram is small, can you post a full pdf.

A single igniter works the same, the common connections are in the unit. The 3.9v has me concerned. Should be a 5v on off signal. The IGF circuit should be the same. Unplug one coil at a time and see if you get a 5v signal. I'm thinking the 3.9 is pulling down the IGT1 circuit. You used a good known ECM and igniter and still had the same readings, can you check voltage on your friends system and compare readings.

The crank and cam sensors supply a chip in the ECM with a on off signal that powers a transistor to power the each igniter and coil circuit. If the sensors were bad IGT2&3 would not be working.

The low vacuum can be the result of cam and crank mistiming. Cant figure why brother would have taken off the cam gear for belt change. If he moved the crank position and did not align that can be a factor.

I keep going back to the same reasoning... if it ran before the belt change and all that was done was a belt change, how can that relate to the IGT1 problem. Timing, cam and crank. If you are able to scope the engine you could determine if timing was correct without tearing down the engine. The timing must be off just a little to allow 2&3 to fire but not 1. You can manually fire 1 so the circuit is good forward of the ECM.

Here you go. I have a Power Probe knockoff, the Kzyee KM10, that performs a max/min showing the wave form a single wave at a time. I can get an idea if the wave is square or not. I also have an oscilloscope with no skills which to use it. I though I might start with the sensors and examine their wave, see if anything jumps out unusual. I going to have to learn how to use that oscilloscope, I can tell that this is where it's all leading. I was wondering how serious this would get, little did I know it would involve an oscilloscope. It might be easier to break down the engine. 3.9v is the right voltage, I'll find the info that talks about it and post it.

Here is the Manuel, I have the 5VZ-FE with automatic trans. www.markofshame.com/fsm/03_Tacoma/

Here is the info about IGT voltage on page 5. It one of the diagnostic sections from the manual link I posted. If I didn't know about the timing belt repain this diagnostic procedure would have me buying a new computer. I remember some where in all the research I've done seeing that 3.9v was the magic number I'm fairly confident.

the procedure on page 2 is where I was headed... even though this is for a P0351 (coil problems) it explores the IGT circuits. You do not have a P0351 code and you can manually fire the coils so they are Ok. I believe the problem is still in wiring and you're shorting out the transistor in the ECM. On your loaner ECM you had 3.9v to start then if dwindled to 2.7v then 0v. This suggest it was heating up and shorting out not turning off.

Do the tests on page 2 and let me know the results. You have a scope so the waveform on IGT1,2,3 and IGF will tell all. Back probe each pin at ECM. Use 4 channels and set scope to 20msec and 10v.

I performed the whole procedure and of course it led to a bad ECU. This was the very last thing I did and what made me concede to not being able to fix it. I can't fix a computer but the problem is they don't include sensor or wires as part of the testing. Right? Sensor are still a question? If so could you explain how they might be suspect so I can keep an eye out for it. I asked brother and crank gear, the washer behind it, and pulley of course were removed. It's not a procedure that he's extremely familiar with. I don't discount mistakes but problem is I'm not familiar with timing belt replacemen either. I almost wouldn't recognized a mistake just by inspecting it. That's why I ask for a short explanation. On page two, was it the checking for open short? It had no shorting/grounding issues with a good 12v on IGF. I can do it again if there was a particular thing you were looking for or a way that you want me to do it, no problem. A list of things in an order you think I should do them would be helpful. Today I put back together the truck, second ECU will be sent back and installing original. Figure since the problem wasn't computer that the original would be best. I plan to do oscilloscope tomorrow on a fresh vehicle. Thanks

Well if scanner John has known good cam crank correlation waveforms for this engine you can scope cam and crank sensors to see if the timing is off. Also try cutting the wire at the pcm where you can repair it and put a scope on it to see if ya get the waveform like in your pics from service information. Also leave scope hooked up then clear codes start engine see if ya get the waveform on igt 1 and make sure it isn’t doing something funny like shutting the driver off

I'm trying to answer all your questions, but so much conversation has taken place, I find that I have missed some things and skipped to answering a question that I felt was more to the point or important. I will try to answer better.

to the question of sensor or wires as part of testing for ECM;
When you do testing for a specific problem such as a code#, in this case the P0351 as that is the procedure you were using, the procedure is based on what engineers have deemed appropriate for that component only. They include small nuggets in footnotes that directs you to other procedures to check other related components. A novice and many advanced DIYers miss this. Its frustrating to say the least. Inputs basics for the computer are the cam and crank sensors.

Sensors are still a question;
In this case your inputs are verified as the injectors are firing, they work off the cam and crank signals via the ECM. I questioned before but you did not reply, the tach, is it working normal, abnormal or not at all. The tach is part of the same circuit as cam and crank and IGT. If the cam and crank signals were absent, the engine would not start.

Timing belt placement;
If the cam and crank are not aligned "timed" correctly the signal from the sensors will be reported to the ECM at the wrong time and the engine will no run or run poorly, not to mention internal damage to the engine in extreme cases. In the engine you have with overhead cams, one on each side, the two cams have to be timed together then timed to the crank. Its not that easy and even an experienced mechanic has done it wrong.

page 2 checking for opens or shorts;
Yes, both.
Just noticed, you say you have 12v on the IGF circuit... that's a 5v circuit. I have to check to make sure.

I can do it again;
You gave values for each IGT. The procedure was for an accumulative reading, but in the long run it does not matter as you have no signal from IGT1. The procedure is to point to a coil or igniter problem. The scope is great, it shows the wave forms and actual values where a DVOM only shows an average value in waves forms. In this case, IGT1 will show no value, but it could show a low value that the DVOM could not read. This would indicate a short.

Put truck back together;
The ECM is the problem in that you're not getting a signal from IGT1. I'm very interested in knowing if the returned ECM works. If it does then your system is pulling down that signal somewhere, maybe that 12v IGF. If its not working, your system is shorting out the IGT1. But why only IGT1 and not 2&3. Maybe a Toyota design fail safe not to blow the entire ECM (limp mode)

Your Toyota works off of three IGT's. In your case, two are working one is not. All three work off the same inputs. Those inputs control transistors for each IGT circuit that control each coil.

I wrestle with the fact one transistor is not working and why. Other than just being an old or bad transistor what caused the failure and why the alternate ECM suffered the same fate, if it did. And how this relates to the timing belt change.

All I can give you. Hopefully, someone with more knowledge can chime in and give more insight.

Update: IGF signal voltage should be 4.5 to 5.5 volts

So more info on the IGF signal. The IGF signal is generated each time an igniter/coil event occurs by an igniter and is sent to the ECM to confirm ignition. The ECM receives input from the crank sensor as to the next cylinder in the firing order and activates the corresponding IGT. If the ECM does not receive an IGF confirmation signal from an igniter within 9 firing cycles, the ECM shuts down the injectors for that coil. This stops the flow of fuel and prevents unburned fuel from entering the CAT.

You asked if the ECM shuts down an IGT. No, it shuts down the fuel injector for the non responsive coil on that IGT. This bring me back to the crank gear as the crank sensor feeds the ECM the signal as to crank position for cylinder firing.

I appreciate the time you took to explain all that out in detail. As far as testing ECM, sensors, P0351 procedure. That makes total sence and at the time if I wasn't frustrated or would have taken the time to think about it I may have realized it was issue specific. Thanks for pointing that our to me.

The voltage on IGF was 5v or there abouts and not 12v. I wrote that wrong. Also sorry for not answering your question about the tachometer, I some how missed that. Yes at start up the tach bounces before registering RPM. I will check to see what's on the wire still. A good spot to examine.

Brother returned second ECU and I installed the original ECU last night. It exhibits the same symptoms as before, as same as the second ECU did. Afterwards I attached my generic Power Probe that has a signal wave analyzer. The time duration is really short in what it shows you but it was enough. Pulled out my oscilloscope today and tried to get it working before I was off to work but with no luck. I quickly hooked up my Power Probe again and recorded with my phone. I back probed crankshaft sensor signal wire using a tpin, attached a wire to it to gain some separation from the moving belts, and rap the bare wires on the other end around the probe. Hoping that use of a wire lead like that wasn't causing the "scope" to show falsely. So this is the same Power Probe used to view the good square single waves on IGT2 & IGT3. I attached screenshot from the video and a zip file with a video in it. Interested to know your thoughts.

Not looking good to me... check this pdf from your manual. www.markofshame.com/fsm/03_Tacoma/Repair...g2rzfe3/cip0335p.pdf the sensor wave form should be like this.

What I'm looking for is a missing signal. Should have 11 signals the same then the pattern starts over again. If you have a missing or distorted signal, I believe this would be the #1 crank signal for IGT1. This suggest to me that the crank gear may be damaged. This would be consistent with working before timing belt repair and not after.

SOLVED! One of the teeth on the crankshaft pulley gear was broken off. The brother who did the timing belt replacement remembers dropping the tensioner and so thought it possible that he might have dropped the pulley gear.
I was a little heated but what can one do? It definitely reminds you to never trust the customer. Not an actual photo of my pulley gear

Great news!!! Good work!

the repair supports the crank waveform and all other testing done.

Fantastic! Thank you very much for following up with us about the fix!

Having the whole story from start to finish helps make this forum a great resource for anyone who needs help.