FJ62 TPS Help

[Lead Head]

Thank you for the suggestion. I actually thought of this last Saturday and re-stabbed the distributor 1 tooth to the left. Not good, and barely cranked. I have set it to 7 degrees and played with the timing to try and get it to rev.

Do you think a failing ignition module could cause random misfires at all temps and failure to rev off idle?

I have pics of ignition waveforms at distributor, igniter input, and coil trigger wire, if anyone here would like to help analyze.

I do. Just seems coincidental, that's all. The igniters are also very expensive used, so it's not wise to just shotgun one in there. Toyota igniters are also prettttty reliable.

It just seems weird it would idle. Generally a weak spark will manifest as an acceptable idle, and you can very slowly bring the revs up. Putting too much load on the engine (i.e., whacking the throttle) will extinguish the spark. If you very gradually crack the throttle, can you bring the RPM up? Does it seem dependent on how hard you push the throttle, or does it cut out at the same RPM every time?

Like I was saying, there is a low-RPM rev limiter tied into the IDL and E2 circuit. Here's an excerpt from the manual:

 

[WrenchMagnate]

Yes, 100% according to the FSM.

I do. Just seems coincidental, that's all. The igniters are also very expensive used, so it's not wise to just shotgun one in there. Toyota igniters are also prettttty reliable.

It just seems weird it would idle. Generally a weak spark will manifest as an acceptable idle, and you can very slowly bring the revs up. Putting too much load on the engine (i.e., whacking the throttle) will extinguish the spark. If you very gradually crack the throttle, can you bring the RPM up? Does it seem dependent on how hard you push the throttle, or does it cut out at the same RPM every time?

Like I was saying, there is a low-RPM rev limiter tied into the IDL and E2 circuit. Here's an excerpt from the manual:


View attachment 4159785

Yes, it is somewhat of a coincidence. It was running super rich and fuel-fouling plugs, but revving ok. The random miss has been there, and I thought it was just over-fueling...so I went for the TPS resistance check (which it failed because the TPS would not mechanically return to zero position). Was hoping to lean the fuel and solve the missing.

Since the miss has been become more noticable while I have been troubleshooting this whole disaster, I figured I would look more closely at the spark, and that's when the ignition problem became obvious.

It will idle, but it idles like crap with the random missing on all cylinders.

It will not rev much at all, even when gradually increasing the throttle. Just falls off and starts mildly backfiring.

Attached are ignition signals...distro trigger, IGT at the igniter, and coil trigger output from igniter. The 3rd one is the one I am having trouble interpreting.

All these are at idle, with no throttle applied.

 

[Lead Head]

Your IGT and coil trigger waveforms look weird because you're using AC coupling, which filters out the DC component. You need to switch your scope to DC mode and try again. Also use the same time base for the coil output as you did IGT, that way we see more detail.

 

[WrenchMagnate]

Your IGT and coil trigger waveforms look weird because you're using AC coupling, which filters out the DC component. You need to switch your scope to DC mode and try again. Also use the same time base for the coil output as you did IGT, that way we see more detail.

I will try that, hopefully this afternoon. My thought process on the AC coupling was that it wouldn't be just a clean DC switch. I tried to use the same time base as the IGT for the coil...but couldn't get any sort of readable waveform. Maybe BECAUSE I had it AC coupled.

Thanks for staying with me on this! You guys are great.

 

[WrenchMagnate]

I will try that, hopefully this afternoon. My thought process on the AC coupling was that it wouldn't be just a clean DC switch. I tried to use the same time base as the IGT for the coil...but couldn't get any sort of readable waveform. Maybe BECAUSE I had it AC coupled.

Thanks for staying with me on this! You guys are great.

I will try that, hopefully this afternoon. My thought process on the AC coupling was that it wouldn't be just a clean DC switch. I tried to use the same time base as the IGT for the coil...but couldn't get any sort of readable waveform. Maybe BECAUSE I had it AC coupled.

Thanks for staying with me on this! You guys are great.

Ok, here are my DC coupled signals on 20mS time base. First signal is IGT, of course. The second signal is igniter coil trigger, approximately 5 seconds before the engine completely died, like someone turned the switch off. It cranked back up 30 seconds later.

I noticed when I attempted to rev it, the IGT increased in frequency slightly, then it just refused to respond and fell flat on its face. The IGT signal did not drop or become distorted.

I have videos, but not able to load here.

 

[Lead Head]

The IGT signal looks fine. Whenever the IGT signal goes to 5v, it turns the igniter on. Whenever it goes to 0v, it turns the igniter off, firing the coil.

Your primary waveform doesn't look right. Here's what it should look like. I've added some annotations:

Here's what yours looks like with annotations:

What has me perplexed, is the very long time it takes for the voltage at the (-) post of your coil to climb back up. It should be at or near 14v right after the spark fires, but it doesn't. I think there are two possibilities here:

• Something in the igniter has gotten "leaky", meaning it either never fully turns off, or it turns off slowly. A slow transistor turn-off would cause the coil to not fire (or fire weakly), and explain the gradual increase in (-) voltage. It may also explain why the igniter and coil get hot, as never turning fully off will cause a lot of heat to dissipate in both the coil and igniter.
• The coil +12v feed is high resistance. It provides just enough current to appear +12v to a multimeter, but when the igniter grounds the coil, it drops to near nothing. This would explain a weak spark (as there would be low coil current and low spark energy). It would also explain the slow building back up of the voltage at the coil (-)

I would scope up to the coil (+) wire, and see what it does. If it's pretty close to steady +12v the entire time, I'd start leaning towards a failing igniter. I think you could confirm the "leaky igniter" theory if you have a current probe for your scope.

 

[WrenchMagnate]

The IGT signal looks fine. Whenever the IGT signal goes to 5v, it turns the igniter on. Whenever it goes to 0v, it turns the igniter off, firing the coil.

Your primary waveform doesn't look right. Here's what it should look like. I've added some annotations:
View attachment 4160383

Here's what yours looks like with annotations:

View attachment 4160384

What has me perplexed, is the very long time it takes for the voltage at the (-) post of your coil to climb back up. It should be at or near 14v right after the spark fires, but it doesn't. I think there are two possibilities here:

• Something in the igniter has gotten "leaky", meaning it either never fully turns off, or it turns off slowly. A slow transistor turn-off would cause the coil to not fire (or fire weakly), and explain the gradual increase in (-) voltage. It may also explain why the igniter and coil get hot, as never turning fully off will cause a lot of heat to dissipate in both the coil and igniter.
• The coil +12v feed is high resistance. It provides just enough current to appear +12v to a multimeter, but when the igniter grounds the coil, it drops to near nothing. This would explain a weak spark (as there would be low coil current and low spark energy). It would also explain the slow building back up of the voltage at the coil (-)

I would scope up to the coil (+) wire, and see what it does. If it's pretty close to steady +12v the entire time, I'd start leaning towards a failing igniter. I think you could confirm the "leaky igniter" theory if you have a current probe for your scope.

Man, I am in awe of your analysis. This is teaching me so much!

I will scope the + side of coil and post it.

Thank you for this!

 

[WrenchMagnate]

Man, I am in awe of your analysis. This is teaching me so much!

I will scope the + side of coil and post it.

Thank you for this!

Looks like it's holding steady to me. Do you see anything concerning with Coil +?

 

[Lead Head]

Looks like it's holding steady to me. Do you see anything concerning with Coil +?

View attachment 4160435

Looks pretty normal to me.

One thing I noticed, is that the coil (-) voltage never seems to fully get to ground. Now, that could be because of a failing igniter, or maybe the igniter itself has a poor ground connection? Something to investigate.

I would ask you to scope the coil (-) at an even faster time base. Get as much detail as you can. Just 1-2 firing events.

I'd feel better with a current measurement of the coil (-) wire before condemning the igniter, but if you don't have one...

 

[WrenchMagnate]

Looks pretty normal to me.

One thing I noticed, is that the coil (-) voltage never seems to fully get to ground. Now, that could be because of a failing igniter, or maybe the igniter itself has a poor ground connection? Something to investigate.

I would ask you to scope the coil (-) at an even faster time base. Get as much detail as you can. Just 1-2 firing events.

I'd feel better with a current measurement of the coil (-) wire before condemning the igniter, but if you don't have one...

I have checked the igniter body to chassis ground in multiple places, and checks fine with multimeter (1 or 2 ohms). What is the best way to perform the current test on coil negative?

I will also re-scope coil- at faster time base and post.

 

[WrenchMagnate]

I have checked the igniter body to chassis ground in multiple places, and checks fine with multimeter (1 or 2 ohms). What is the best way to perform the current test on coil negative?

I will also re-scope coil- at faster time base and post.

My scope won't measure current. I have forgotten so much since the last time I used a scope in '86.

Take a look at these:

 

[Lead Head]

I have checked the igniter body to chassis ground in multiple places, and checks fine with multimeter (1 or 2 ohms). What is the best way to perform the current test on coil negative?

1-2 ohms can actually be pretty high resistance for certain circuits. With the vehicle running, I would measure the voltage between the igniter ground and battery ground. Should be close to 0v.

Anways, to my untrained eye, it appears that igniter is unable to "release" the negative onnection to the coil fast enough,, and is just allowing the voltage to slowly climb up. Either that, or the coil is faulty and very high impedance. Was the coil known good?

Anyways, without being able to measure coil current, and assuming it's a known-good Coil, I think it's looking like the igniter. Unfortunately the FJ62 igniters are hideously expensive used ($250-400). They're expensive enough that I think I'd be willing to give a different Toyota igniter a try. For example, you can get an LS400 igniter for $35 with a harness connector: https://www.ebay.com/itm/1171765003...pid=5337589904&customid=&toolid=10001&mkevt=1

 

[WrenchMagnate]

1-2 ohms can actually be pretty high resistance for certain circuits. With the vehicle running, I would measure the voltage between the igniter ground and battery ground. Should be close to 0v.

Anways, to my untrained eye, it appears that igniter is unable to "release" the negative onnection to the coil fast enough,, and is just allowing the voltage to slowly climb up. Either that, or the coil is faulty and very high impedance. Was the coil known good?

Anyways, without being able to measure coil current, and assuming it's a known-good Coil, I think it's looking like the igniter. Unfortunately the FJ62 igniters are hideously expensive used ($250-400). They're expensive enough that I think I'd be willing to give a different Toyota igniter a try. For example, you can get an LS400 igniter for $35 with a harness connector: https://www.ebay.com/itm/1171765003...pid=5337589904&customid=&toolid=10001&mkevt=1

Thank you for the time you have taken for analysis.

I think I will try the LS igniter if ok with Dryfly43 (the owner of this beauty).

Will post back here with results!

Have a great night, good sir!

 

[Lead Head]

Looks like it's holding steady to me. Do you see anything concerning with Coil +?

View attachment 4160435

Thank you for the time you have taken for analysis.

I think I will try the LS igniter if ok with Dryfly43 (the owner of this beauty).

Will post back here with results!

Have a great night, good sir!

Yeah I looked at the pinout of the LS400 igniter, and it appears to have all the same signals and voltage levels. So at a surface glance, it appears to work exactly the same. You will have to adapt the wiring of course. I would just right something up with jumper leads before cutting anything of course.

 

[WrenchMagnate]

Yeah I looked at the pinout of the LS400 igniter, and it appears to have all the same signals and voltage levels. So at a surface glance, it appears to work exactly the same. You will have to adapt the wiring of course. I would just right something up with jumper leads before cutting anything of course.

Yep, I checked the pinouts also. Should be a quick check! Plus LS400 units should be very robust for that 1UZ.

 

[WrenchMagnate]

Yeah I looked at the pinout of the LS400 igniter, and it appears to have all the same signals and voltage levels. So at a surface glance, it appears to work exactly the same. You will have to adapt the wiring of course. I would just right something up with jumper leads before cutting anything of course.

Update: LS400 igniters arrived Saturday.

Got one of them wired up yesterday....RUNS FINE!

My TPS problem was actually the igniter the whole time.

Thanks, Lead Head, for all the help.

Hopefully I can pay it forward!

 

[Lead Head]

Update: LS400 igniters arrived Saturday.

Got one of them wired up yesterday....RUNS FINE!

My TPS problem was actually the igniter the whole time.

Thanks, Lead Head, for all the help.

Hopefully I can pay it forward!

I think you could pay it forward would be doing a little write up about the igniter swap, with a wiring diagram explaining how to hook it up, so someone searching in the future can find it.

As these vehicles age further, being able to substitute components will be very important. Knowing A $30-40 super common igniter can be subbed in place of a rare $250-400 igniter is super useful.

 

[WrenchMagnate]

I think you could pay it forward would be doing a little write up about the igniter swap, with a wiring diagram explaining how to hook it up, so someone searching in the future can find it.

As these vehicles age further, being able to substitute components will be very important. Knowing A $30-40 super common igniter can be subbed in place of a rare $250-400 igniter is super useful.

I thought about that last night. In the coming days, I will do just that!