Toyota truck diagnostics - Updated Some More

Here's a conversation I'm having with an expert at Just Answer. It's mostly for the benefit of the expert, because it seems like my replies are often too long for the space allowed at Just Answer, but some of you might find it interesting. I'm trying to determine exactly what's wrong, before I tear everything apart and install a new timing chain.

Dj :
Check B+ with the key on, it should have 12 volts.
Checked 12.26 vilts
Dj :
Check the large black plastic tube that goes from the throttle body to the air flow meter. It could have a split or crack in it or the clamps could be loose or out of place.
Checked for vacuum and intake leaks, as carefully and in as many ways as I could not find any major ones.  Closing off the air intake port on the airflow meter stops the truck immediately. The truck is loud enough that I may be missing a minor leak, but I don’t think a minor leak is the problem here.
Dj :
Now jumper B+ to FP in the DIAGNOSIS box. I just use a paper clip bent into a U shape. The greasy terminals are shaped like this O_O and the paper clip will fit right into the O.
I have a 1985 with the separate fuel pump connector harness.  It’s L shaped when looking at from the end.  Terminals position looks like this: l _   
Here’s a picture.  (not of my truck, but similar one found on web.)
Dj :
This will bypass the air flow meter and the circuit opening relay and run the fuel pump whenever the key is in the RUN position.
Fuel pump runs when jumped, fuel pump also runs during normal operation when contacts in airflow meter close.
Dj :
You should be able to hear the fuel pump running if you take the gas cap off and stick your ear to the hole.
I can hear it running.
Dj :
Please try this and let me know if the engine continues to run. If it does, I'll explain how the circuit works and what's wrong. If it doesn't keep it running, we'll try another path.
Engine runs, but only if I help open the air vane with my finger.

Dj :
With the volt meter ground attached to the negative battery post, measure the voltage on E1. It should be less than 0.2 volts.
I checked voltage on the smaller, round, two terminal diagnostic connector that you use a jumper on when checking timing.  Heres a similar picture of it: The one circled in blue.
I honestly don’t know what wire is E1 and which is TE1, but the voltage on green wire is 9.75 volts and the voltage on red wire is .01 volts. (with ignition key on)

Dj :
Check the vacuum line that goes to the fuel pressure regulator to make certain that it's not crimped or cracked.
If I am correct, the fuel pressure regulator is located on the back side of the engine, just below the air intake chamber, directly behind the no. 4 intake manifold runner.  There is a vacuum cannister on the fuel pressure regulator with a vacuum hose that leads to some type of electrical component on top of the valve cover.  Another hose leads from here to the air intake chamber near the back corner of it on the inboard side of it.  I visually checked theae hoses, and felt them with my fingers, trying to feel for cracks or breaks.  I also put the ends of the hoses in my mouth, and blew on them. (in the direction of the fuel pressure regulator) I could not hear, or otherwise notice, any air escaping.
Dj :
When you checked the timing, did you have a jumper between TE1 and E1? How far did you advance it to make it run?
I did not have a jumper in the first time I used a timing light, but I just repeated the procedure with a jumper inserted (into the connector pictured above and circled in blue) and the timing seems to be the same as when I checked it before.  The truck will only run with the distributor turned clockwise, as far as possible.
Dj :
What is the air gap between the pickup and the signal generator ring in the distributor?
I assume this below the rotor, and looks like a four pointed star.  The clearance between this and the pickup (has a red and white wire going to it) is .010”
Dj :
Is the check engine light on?
The only time I noticed a check engine light being on was after I one time, when I was pushing on the air vane really far in desperation to make the truck start.  I checked the codes and they were for faulty air meter reading.  I knew I caused that, so I cleared the codes.  One thing I might mention here.  I am using a remote starter switch, and must help the air meter vane to get the truck to run, so there is no way I can now see if the check engine light is on when the truck is running.

From Dj
Monday, October 20, 2014 10:10 AM EST
From your description it sounds like the timing could be severely retarded.

I've seen several vehicles where the outside ring on the front crank pulley slipped. So when you set the timing to the marks, you're actually retarding the timing. It happened on my own 1987 4Runner. It was about 20 degrees off.

I've also see where the signal generator ring hits the pickup coil in the distributor and turns the ring on the shaft and knocks the timing out.

If the jumper isn't in place between TE1 and E1 when you set the timing, it will never be right. The ECU advances the timing. With the jumper in place, it cancels out the ECU advance.

I've gone ahead and very carefully either did or redid, everything you told me to do. Here's a link to what I have done.

I did things this way because I don't think there is enough room here at Just Answer to fit all I have written in this reply box. I've tried to write a long reply here before and ran out of available space. At least that's what I think happened. All I know is that I couldn't write any more. Please excuse any mistakes. I'm out in my garage, and my fingers are kind of cold. Makes it a little hard to type.

From Dj
Thursday, October 23, 2014 1:25 PMEST
I would like you to try advancing the distributor one tooth. When you take it out, keep a clockwise twist on the rotor. Pull it out slowly just enough to allow it to turn one tooth forward. It wouldn't hurt to mark the position of the rotor before you start to make sure you don't go too far and you can put it back in the original position if this doesn't work.

Set the distributor to the middle of it's swing (where it bolts to the engine and see how it runs. If it runs better, keep advancing the timing until the engine pings when you accelerate. Then back it off a couple of degrees.

Let me know what happens.

I haven't run into any restrictions on the website when I use this format. I've run into problems with the first format that we used.

I will do that after I tell you what I have done in the past hour and read your reply.

1) Determined TDC on cylinder no. 1 by turning engine over until compression gauge moved, then inserted a rod in spark plug hole and turned engine back and forth until I got to exact TDC.

2) Timing mark on crank pulley lines up exactly with zero mark on timing tab.

3) Distributor rotor is under no. 1 spark plug wire tower. The trailing edge, not the leading edge. (In respect to the way the rotor turns when the engine is running which is clockwise) In other words, the rotor has turned a bit further clockwise than I would expect it to have.

4) The distributor is turned as far counterclockwise, as it can go. Note that I made a mistake in what I told you earlier when I said that the distributor was turned as far clockwise as it could go. You could make the leading edge of the rotor be under the no. 1 tower if you turned it back, but this is the only setting where the truck would run.

5) I removed the valve cover and the timing marks are exactly at the 12 o'clock position and lined up with the bright link on the timing chain.

6) Just to make sure, I checked the valves on cylinder no. 1. Both are closed. i.e. they are not on any raised portion of the cam lobes.

You have received an Answer!

From Dj
Thursday, October 23, 2014 4:59 PMEST
So you're telling me that the timing is correct.

There are only a few inputs to the ECU. The ECU uses the information to determine how long to keep the injectors open. This determine how much fuel is delivered to the engine.

Air temperature. Doesn't have much input on the decision.
Coolant temperature. Has a fair amount of input.
Air flow meter. This has a significant amount of input. It measure how much air is delivered to the engine and the density of the air.
Throttle position sensor. Most input out of all of these.
Engine speed (from distributor) this either works or it doesn't.

So next I would start with the input from the TPS. The TPS is like a volume control on a radio. An analog potentiometer configured as a voltage divider.

It gets a regulated 5 volt input and a solid ground (zero volts). The output from the TPS should be between 0.5 volts and 4.5 volts. If it's below 0.5 volts, it doesn't have enough voltage coming in or it's completely disconnected internally or externally.

If it's over 4.5 volts, it's got an insufficient ground.

Here is a picture of the pins.

E1 is ground or zero volts. Be sure to have the negative probe on your volt meter on the negtive post of the battery.

VCC is 5 volts with the key in the RUN position.

VTA should swing between 0.5 volts (throttle closed) to 4.5 volts (throttle open) smoothly and should match the volt meter in movement. For example, half throttle should be around 2.25 volt.

IDL should be zero volts until you open the throttle a tiny amount. Then it should jump to 12 volts.

Here's a picture of the air flow meter.

VB should be 12 volts with the key on.

VC should be 5 volts, key on.

VS should vary between 0.5 volts and 4.5 volts. But it's backwards from the TPS. Closed is 4.5 and open is 0.5 volts. It should be smooth and half open should be 2.5 volts.

E2 should be zero volts.

THA should be around 2 volts if the ambient temperature is around 60 degrees.

Let me know what you find.
Here are the results from my tests:
First the TPS test - after reading your answer, I began to wonder if these tests should performed on the harness alone, not plugged into the sensor, the sensor alone not plugged into the harness, or while the harness was plugged into the sensor.  Since I already have the cover removed from the air flow meter, I can test that with it plugged into the harness.  I will wait on the TPS until I hear your answer.
E2 = .02v
VCC = 5 V
VTA - .02 v @ any throttle position
IDL = 13.9 v @ any throttle position
Now, the air flow meter test - test performed on the harness, unplugged from the sensor, with the ignition key on.
Vb = 14.28 v
Vc = 9.14 v
Vs = 4.2 v @ any throttle position
E2 = .02 v
THA = 5 v @ 50 degrees
Here’s the airflow meter test while it is plugged into the harness -
Vb = 14.2 v
Vc = 9.14 v
Vs = 3.7 v @ any throttle position.
It was at this point where I began to wonder if you meant to check Vs at different air vane positions, rather than throttle positions so here is the results of that -
Vs = 3.7 v with air vane fully closed
Vs = 8.5 v with air vane fully open
E2 = .03 v
THA = 2.7 v @ 50 degrees
Here are the resistance test of the TPS in Ohms as per the Haynes manual.  The second and third test involving the IDL were difficult to do and know if I did them right because it’s pretty tight in throttle stop screw position and hard to get a feeler gauge in there squarely, but in general it seems to be OK - very few Ohms with throttle fully closed and quickly going up to infinity as soon as you open the throttle just a little bit.
VTA - E2with throttle closed = .683 KOhms
IDL - E2 with .022 between throttle stop and screw = .05 kOhms
IDL - E2 with .033 between throttle stop and screw = .068 kOhms, but goes up to infinity as soon as you open the throttle just a hair more.
VCC -E2 = 6.35 kOhms
As you can see, it’s not perfect, but close.

It appears that our problem is the voltage levels at the VTA and IDL terminals on the TPS harness.  The TPS itself, passes the resistance tests, kind of.

From Dj

The TPS reading still is way off. 

So where do I go from here? I suppose I should probe the TPS wires with the harness connected to get a true reading, then, maybe buy a new TPS and hope for the best.

From Dj

You are right. Probe the wires, and if the results are the same, replace the TPS. 

This is one of the most important inputs to the ECU, so this is really going to change things.

Out of 20 mechanics that work on Toyotas, only about 1 or 2 would have the skills to get to the point where you are at on this.

Most mechanics just can't or won't take the time to diagnose a problem. So my compliments to you for having the patience and the skills to dig this deep into this problem.

Thank you.  Of course, I have greater motivation:  Six years, about $2500 invested, snowplowing season breathing down my neck, and being at the point of no return.

One observation here, whatever it is that is causing this truck not to run, it can be at least somewhat compensated for by two things :

1) The fuel supply being enriched, via turning the air vane on the airflow meter further than it would normally go.  I can tell this happening because I noticed that the exhaust has been blowing black soot all over what was near the exhaust pipe.  I bet that this is not good for the O2 sensor.  Probably wouldn’t be very good for the catalytic converter, if it had one on it right now.  But it has not ran very long at any one time since I have had this problem.
2) The timing being very far advanced. Of course maybe It’s not.  All I know that the only way the truck runs is with the distributor turned fully counter-clockwise.  When I put a timing light on this truck, the timing is at about 20 degrees before TDC (my guess, it’s off the tab), but this may be a false reading because I forgot to disconnect the vacuum advance when I had the timing light on.  The timing seemed to be the same whether I had a jumper in E1 to TE1 or not.

So I will probe those wires on the TPS, and check the compatibility of this TPS with that of the one used on other vehicles.  Unlike the airflow meter,I think that this TPS is used on quite a few different vehicles.  I’d rather pay $5 for a junkyard one, (especially when I’m not going to be sure if that is the one and only problem I have until I have it installed.) than $80 or more, for a new one.

Here's the results of my TPS tests while connected to truck. First off, I didn't want to take off the tape and covering on the truck's wire harness, so I made this cool little test extension cord out of an old junkyard TPS and harness that I plugged in between the truck's TPS and harness. Here's a link to a picture of it:

This made it easy to touch the multimeter probe to the correct wire without shorting across two adjacent terminals.

Here's the results.

E2 = .02 v

VCC = 4.98 v

VTA = .46 v with throttle closed and 3.72 v with throttle wide open

IDL = .03 v with throttle closed and 12.98 with throttle wide open

Not perfect, but close. The VTA reading at full throttle is about .8 v low. I also scored another TPS from the junkyard and did the resistance tests as per the Haynes manual. Results: Again, not perfect, but close. I'm beginning to think the TPS is not the problem either.

Should I swap in the junkyard TPS and hope for the best?

From Dj

The readings are close enough that the problem isn't the TPS.

Did you try to start the truck?

Well, it's kind of a pain in the ass to get to that bottom screw without tearing a bunch of stuff apart, so I haven't done anything yet. I suppose that I could just plug the other TPS in, and let it dangle from the harness. Wouldn't this be the same as actually being on the truck when the throttle is fully closed? I was thinking of getting a longer screw, cutting the head off of it, and jamming two nuts together on one end and using locktite on the nuts. Kind of like a homemade bolt. I think it would be easier to install a small bolt with a wrench, than a screw with a screwdriver, and I don't think that I could ever find a bolt with a six sided head in that size. I know that I could order allenhead screws that size, but I would be paying an outrageous price for them with shipping, and I would have to wait for them.

For the time being, what could the problem be if it is not the TPS?

I was sitting and thinking, what happened to this truck between the time that it last ran well and when it no longer started. The only thing that I can come up with is this - I installed snowplow lights. I didn't do any cutting or modifications to the factory wiring except for one thing. The plow lights, both high and low beams, are run off of relays, and I bought pig tails to plug directly into the factory headlight harnesses. I tapped into the marker and directional lights by installing a small homemade extension cord, kind of like the one I made for testing the TPS, between the factory connectors for the turn signals and running lights. This truck shouldn't even know that those snowplow lights are there. The only place where I may have compromised the factory wiring is where I tapped into a source for power to run the plow light relays. I used a scotchlock to tap into a heavy wire, (as I remember, it was black with an orange stripe) that ran with millions of wires up the steering column. Is it possible that the scotch lock actually severed this wire, or worse yet, somehow my snowplow light installation, shorted out the ECM? I was very careful installing it, and those relays take hardly any juice. Please don't tell me that you think that that is where the problem stems from.

I just take off the throttle body, then there is great access to the TPS. I've got an entire drawer full of air tools. Zip zip zip. It it's in the way, zip it off. Zip it on, move on to the next job.

The first test results indicate that the TPS is faulty and this could certainly cause your symptoms. 

I think the only wire in that area is the black-red ignition wire.

I won't use Scotchlock connectors. They cause too many problems. Also I never tap into a circuit that I need to run the truck. 

I also use relays. Take a wire off the battery with a fuse, run it to a relay, then run small wiring to the switch. This is for a couple of reasons. It delivers more power to the load, with less load on the switch and the circuit I tap into. Heavy gauge wire has gotten so expensive it can be cheaper to buy a relay than 10' of 12 gauge wire.

The Scotchlock connector may have cut into the copper which would deliver less current to the injectors, coil and ECU. 

I doubt that you've nuked the ECU. But if you've got a buddy with a the same setup, you could try swapping it out.

I do have a spare ECU that I got years ago, when I thought I had a ECU issue, but didn't. That ECU was good back then, and I just recently swapped it in to see if it made any difference and of course, it didn't. The reason I tapped into that wire, is because it was the only one I could find that I could easily find that became hot only when the ignition key was turned on and looked heavy enough to rob some power from.

I try swapping in the other TPS tomorrow.

Should I go out and buy this?

in the hope that it has some part we need?

In the meantime, I'll go swap in my junkyard TPS.

You have received an Answer!

From Dj

That's a great price but it's got it's own set of problems. 
I don't think you're going to spend $150 to get your truck running.

Here's what I did this morning. I rechecked those TPS voltage specs you gave me, as well as the static resistance tests on both of my TPS's. The one that was originally on the truck is with in spec on the Ohms test, the one that I got from the junk yard is not. I retested the voltage on the TPS on the truck while plugged into the harness with the key on. Everything is within spec except the VTA terminal is only 3.75 v (.8v) low.

Just for the heck of it, I plugged the junkyard TPS and let it dangle off of the harness. I think that at closed throttle, (the normal start and idle position) this essentially the same as having the TPS mounted on the truck correctly. Anyway, the truck would not start with things like this.

In desperation, I tore apart the steering column cover and checked that scotchlock that I installed. I took off the blue plastic cover and everything looks good. The wire is centered exactly in the notch on the metal piece, and the wire that I tapped into seems to be intact. (It seems strong and doesn't stretch at all when I pull on it from either side of where I installed the scotchlock.

WTF? This truck will start, and run, but only if I help the air vane open with my finger. Sometimes, I have to use starting fluid to get her going.

I think somehow it's not getting enough fuel. It seems like the cold start injector should be squirting enough fuel to start without me using starting fluid.

I'm getting close to throwing in the towel here.

You have received an Answer!

From Dj

Do you still have the jumper in place for the fuel pump?


  1. Disconnect your lights!!

    Take what you put in back off, repair any damaged wiring or insulation and see if it is fixed!

    Computerized rigs are extremely sensitive to voltage drops and EXTREMELY sensitive to grounds.

    Make damn sure your engine to body and battery to body grounds are clean and tight.
    If you are robbing your ignition wire by tapping into it, do the relay trick.
    A small buss bar for connecting extra electrical loads are cheap and can be mounted just about anywhere.
    Run a hot wire with an inline fuse to a buss bar and connect your plow light relay to that power source.
    You can use that for extra stereo crap and such as that too.

    Your timing is still suspect from what I see also.

    Restore your electrical system and start from there.

    Good luck, sounds like you are going to be as bald as I am before you are done.

    1. The power I am using from tapping into this wire only runs my relays, not the lights themselves. These relays take very, very little juice. Even if they were the cause of the problem, how come the problem still exists when the switch that allows the power to flow to them is turned off. When this switch is turned off, it should be the same as if I never tapped into that wire at all.

      At any rate, I must somehow have these plow light relays get power from some source that is only present when the ignition key is in the run position, so I am not feeding power to them when the truck is unattended. There is no way that I am going to remember to turn a switch that is hooked directly to the battery, every time I get out of the truck.

      Out of desperation, I will remove the scothlock and wire I installed, but I can't imagine that this is going to make any difference.

      Why do you still think the timing might be off when the timing mark on the cam sprocket is at 12 o'clock and lined up with the bright link in the timing chain, and the timing mark on the crank pulley is lined up with zero on the timing tab while the piston in the no. 1 cylinder is at TDC on the compression stroke?

  2. Run the hot wire to the buss bar directly from the battery.
    I see I forgot to specify that.

    1. I did just remove that scotchlock and the wire looks fine, however it made no difference with the problem I'm currently having. Thanks anyway, I'm so desperate now that I'm willing to try anything.

    2. I am sorry that I am not being more helpful, it is hard to diagnose something with out being able to see exactly what is going on, you know? I don't have a ton of experience working on Toyota's, I was a factory trained Ford tech for ten years and have been a mechanic for thirty though.

      From what I have read and your comments I am wondering if your distributor gear its self might not have slipped somehow..
      If you have had it out, do you know if it has a roll pin or something holding the gear to the shaft?

      It sounds like the timing chain is correct but the rotor not being in the right position and it only running with the distributor cranked all the way makes me want to look at that thing very carefully.

    3. Nothing to be sorry about. You are being extremely helpful. I hope that I didn't come across as not being grateful for you advice. I am grateful. Plus you are the only one who responded. That says a lot right there. You were the only one who took the time and trouble to try and help me.

      I was being inquisitive, not critical. Since all indications that I knew of, led me to believe that the timing was OK, I wanted to know what other possibilities may exist. Your last comment here, answered that for me.

      Thanks for everything so far, and I will check into the things you mentioned this weekend.

    4. It's all good Bud!
      I am rooting for you big time, I know what a nightmare some of this stuff can be, I did it for a living.

      I'm just thinking out loud here, trying to figure the damn thing out.

      That Air flow meter problem is bugging me too but I'm fairly certain you have some kind of distributor issue.
      That rotor being off and it only running with the distributor cranked over is definitely an ignition timing issue though.

    5. I'm going to beat this thing. I've already checked the obvious stuff. Now, I'm going to check out the not so obvious, if I still don't find anything, I'm going to start taking things apart, (namely the intake system) and check the injectors. If I still can't fix it, I'm going to shelve the project until next summer and drop a Chevy 350 in it. No matter what happens, this truck is gonna go. It just might take a little longer than originally anticipated.

    6. Phil - I have updated this post, starting at where I have a red dotted line going across the page. My comments are highlighted in pink. The Just Answers comments are highlighted in blue. Maybe you can figure out what's wrong with this truck with this added info.

    7. Something just occurred to me that I have only run into a couple of times over the years.
      Is your exhaust system plugged up?!!!

      If your exhaust system is plugged up the thing won't be able to breathe, your air vane won't open properly and you won't have any power at all.

      Try undoing your exhaust pipe where it comes into the exhaust manifold and see if it doesn't run better.

    8. Phil - Thanks for suggestion. My truck however, has a super simple exhaust system. Just four foot of straight pipe with a straight through muffler. I installed it about two years ago and has zero miles on it.

    9. Humor me and check it anyway.
      I have a cousin who bought a Model A from the widow of an old guy that had had it in running condition and stored in a garage a couple years after his death.
      My cousin had a hell of a time getting that thing to run despite the widow's insistence that it ran fine the last time her husband had parked it.
      It also had a straight exhaust pipe with a Glass Pack muffler.

      A bunch of wasps had built a freaking nest inside the muffler.
      My cousin finally got it fired and floored it out of frustration and that nest popped out the back end.
      Ran like a champ after that.

      I'm just sayin', ya never know.

    10. I will do that. I am willing to try anything at this point. In the meantime, please check out this post again. I am going to update it in the next few minutes with a theory I have. I will put a green dotted line where the new stuff starts. Obviously, the update is going to be near the very bottom.

  3. Makes sense.

    The very best fuel system/injector cleaner I have ever run across is called Sea Foam.

    It comes in a white can with red lettering and any decent parts house should have it.
    I get mine from NAPA.
    Dump it in the tank and do whatever it takes to keep the engine running for fifteen minutes or so.
    I kid you not, this stuff works wicked good.

    I put some in a 95 Ford pickup with the fuel injected straight six I used at work with 200K+ miles on it .
    After it had run for about ten minutes it started to smoke out the tail pipe.
    Three minutes after that I had to open the garage and back it outside because it filled the entire shop with smoke.

    Another ten minutes and all the smoke cleared up.

    It not only cleaned all the crap out of the injectors but scoured the intake system and combustion chambers too.

    One other thing you might look at is whether or not the temp and or air intake temp sensors might not be bad.
    If either is bad the computer will think it is -40 degrees out and run the injectors full rich trying to get it to operating temperature all the time.

    It sounds like you are on to the problem though.

  4. Excellent!
    Now take it out and run the shit out of it!!

    1. Still gotta put the rest of it together. I put the box on it today, assembled the snowplow blade and rebuilt the hydro-turn cylinders today. Now, I got to put together all the stuff I tore apart trying to make it run. If I'm lucky, I'll have it on the road by Thanksgiving.

  5. Hey Neil - just trying to get in touch. Could you send me an email when you get a free second? Thanks.

    rebelmississippi at gmail

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