WIRING ISSUE AND QUESTIONs

turns out this info was based on a mistake i made. more accurate discoveries are below this post

 

bump

 

Godspeed

 

Do you have the Factory Service Manual with wiring diagrams? Usually $15 on ebay as a download. Then you won't be guessing.

I would be surprised if the ECU is not grounded to chassis ground in some way.

 

Looking at the 2002 FSM Wiring Diagram, I have 4 pins for the TPS, not 3 so probably not much help.

I'm not seeing that any the pins should be grounded, unless it's internal to the ECM or any of the other little "black boxes" its wires go to.

 

Thank you for responding. one issue is that both digital versions of the FSM are Calif regulation specific. The VOM troubleshooting of the TPS connector, which has 3 wires, gave me the center as reference 5v, then with the ohm meter it gave me a pin with an ohm readout, which should be the ECM, or a leak to ground somewhere, and the third pin, which should be direct to ECM ground, is open, so that wire is broken somewhere. it goes from the connector to the engine wire as it is famously called. the problem from there is that, so far, I have only seen wiring for the Calif Regs.

I was able to verify the IAC motor works and turns both ways, it appears to be OK.

I tested the TPS and its circuit seems OK.

My trouble shooting proposal is to back probe the ungrounded pin, which I believe is the pin to the ECU that doesn't go all the way there, and ground it. I could jump that pin all the way to the ECU, but in my truck it is basically out of reach, and to have good access I would have to remove the whole dash on that side, which I would gladly do if someone could talk me through it, because I don't want to mess around with the air bag.

Thank you very much for taking time to discuss this. If I don't get this rig running soon, I might miss a family reunion, and I might have to find another vehicle...

Hopefully someone with wiring swapping experience will chime in.

Regards,

Michael

 

Well, keep us posted. There have been known cases where the wiring harness under the dash rubs on a support and grounds a wire.

If you have the battery disconnected, the air bag shouldn't have an issue going off.

Has anyone messed with the wiring under your intake manifold? The protective wiring harness conduit have all gone brittle by now and people just throw the protection away and don't put anything back. It just hastens a possible wiring failure. One of the worst design decisions TOYOTA made was to run wiring on top of the engine block.

 

THANKS. I agree, it's stupid. you can't imagine how much I miss my '45 Dodge flatbed truck with flathead engine and a granny gear that the youngsters refer to as a crawler. Easy to work on. Reliable. better clearance than any of the "lifts" I see online . . . ran it from the southern US border to Alaska, with the overload springs loaded flat. no complaints from that rig. just day dreaming. I put a 55 gallon drum under the bed on each side, 110 gallons of fuel. At 23c IIRC. I'M laughing out loud.

thanks for your input

seems this issue would have a 'standard' solution by now.

 

Well, from what I can see in the schematics, which unfortunately show a 4 pin connector on the TPS, the TPS is grounded via pin E2 of the ECU. Pin 1 of the TPS. E2 of the ECU is grounded via pin E1 of the ECU. IIRC, E1 goes directly to BODY (not chassis) metal right where the ECU is mounted. Ensure the wire from E1 to the body metal is in good shape, and the connection point to the body sheet metal is clean, and free of corrosion. It only takes a small amount of corrosion to cause BIG problems.
You also need to ensure the connection from the body sheet metal to the battery negative terminal is in good shape. No corrosion at either end, and the wire itself is in good condition. The cables that are connected direct to the battery terminals, can get acid mist down inside the insulation, causing the copper strands to corrode and break inside the insulation, with no external signs. Best way to check them is to pull the cable off the battery, and ohm it end to end, while flexing the cable along it's length.

If you're going to be working on anything that might, possibly, involve anything having to do with the air bags, the secret is to pull the battery leads, or at the very least the negative lead, then wait 90 seconds or more before doing any kind of work. The air bags have a backup power supply, that's viable for 90 seconds, max. Once that's bled off, the air bags are fairly safe. I would, however, avoid doing anything with the meter in OHMs. The meter uses a very low voltage, very high impedance, source to read ohms, and there's a very faint possibility it could trigger an air bag. A very, very low possibility, but batter safe than sorry.

Sorry I'm not more help...
Pat☺

 

Pat thanks so much. I MADE A BIG MISTAKE IN DIAGNOSIS. My connector to the TPS is 3 wires. I had measured with the key off yesterday. Aaa rrrgh.

looking at it plugged in, the top wire is blu, the middle wire is grn+blk, and the bottom wire is yel+blk.

center pin is B+ 5v. the top and bottom pin read 0.038 and 0.039, which makes my former theory bogus bologna... and should mean that comms with the ECU are present and accounted for

the 99 with Federal regulations has different emission controls and different engine controls. The one you looked might be the hybrid that has one cable to the throttle body. Later ones are completely drive by wire.

my diagnosing memory starts way back a long time ago, and i still make rookie mistakes.

thanks everyone, it really helps to type it out. hopefully my error-trapping skills will come out of hibernation. i am waiting on the IAC gasket to reassemble the induction business and roll off to a real mechanic. i hope.

kind regards,
Michael

 

Can you post a pic of this? I can't figure out how to see that E2 and E1 are related.

In the diagram I have, I see E2 is connected to the 4-wire TPS and E1 is ground from the ECU. I don't see the connection between E1 and E2 though?

I'm still learning how to read schematics. Please enlighten me?

 

it is, of course. i used a ground point near the plug with the battery hooked up AND the key "on".

 

I turned the schematic sideways. The red tick on the TPS plug is my mark for B+, 5v. two views that show different wire colors, but the schematic is looking at the ECU connection, not the cable end. and that schematic has the 4 pin plug that Pat mentioned. The colors on my plug look different to me. also I dona' ken what the circles represent near the ecu connection on the schematic. fuse values? as soon as the gasket arrives i can wire this up and try try again.

sri, already asked and answered,

THANK YOU BOTH VERY MUCH, THIS IS HELPING. it's difficult when there is only one grey cell available for me to wrap it around this?

 

The pic I posted was for a 2001-2002 4Runner. Prior years have a three terminal TPS and a different schematic that I don't have.

 

I caught that. Thank you. at this point i just want to get to a mechanic who has the big scanner and toyota experience.

 

I finally found a schematic of a 3 wire TPS, circled in red.
You can see that E2, both in the ECU and in the TPS, is ground. It's ground for a number of things, as you can see, simply by following the Blue-Black wire around.
It goes into the TPS plug on Pin 1. Vc comes from the ECU, and goes into pin 2. Vta goes to the ECU, and comes out pin 3.
Looks to me like they used a voltage divider network in the TPS. With the entire voltage from the ECU dropped across the TPS, from Vc to E2. IOW, Vc, is +5 VDC, created in the ECU. It goes into the TPS, and across the resistor to E2, where it should be 0 VDC, as E2 is ground. The wiper, Vta, moves across the resistor as the throttle plate is opened and closed by the throttle pedal. It picks a voltage off the resistor, depending on where it is on the resistor, and that voltage goes to the ECU, to tell it the position of the throttle plate.
The resistor in the TPS is known for getting dirty and corroded. It doesn't function properly then, as when it gets dirt and corrosion on it, the wiper doesn't receive the correct voltage for the actual position of the throttle place, sending inaccurate info to the ECU.

Long rambling, but I hope it helps a little.
Good luck to you!
Pat☺

 

thank you So Much Pat. I really appreciate this info. I wonder if a shot of electrical pot cleaner could "fix" the TPS. it used to work in radios to fix scratchy audio pots. I still think there is a harness issue, but will know more later today.

Is there a digital copy of that wiring available? sure would take some guess work out of these setups.

Thanks again !!!!

 

Electrical Contact Cleaner might do wonders. Then again, if the resistor has gaps, or worn down spots, IOW, if the resistor the wiper rides on is physically damaged somehow, wear and tear type stuff, just cleaning it won't help much. You'll need to replace the TPS entire.
If you do replace it, it might not hurt to clean the new one out a it, just to be safe. At least take a look to see if it does need cleaning before you install it.

I don't recall just where I found that schematic. Somewhere on this forum, but just where I don't recall. Do a Google, or Duck duck go search for something like that. If you want, I can post the PDF I took it from. It's just a small section of the wiring portion of the FSM. Sorry I'm not more helpful...

Pat☺

 

put the wheel back on and started up, watching the scanner. it warmed up properly, slowed idle down as the temps came up, O2Sensor graphed a saw tooth pattern governing the fuel mix, AND NO ROLLING SHAKING MISS. 1st time since I bought it. There might be some life left in the old boy after all.

Thanks VERY MUCH to everyone who chimed in. Next chores are to replace all the rest of the wear items and do a deep discovery to see if I can run this guy through the desert southwest in the peak of the summer. just to see my kids again...