EE or ET help!!

[AJ77]

I have a TPI with an OBD1 computer. The system was working perfectly before I put my new motor in. After installing the motor I went through two heat cycles like the builder suggested and then changed the oil and drove it into town for a test. It ran good as long as I kept my foot out of it. If I tried to get on it hard, it would pop and sputter like it was out of time or something. After I got it home the check engine light came on and was giving me both high and low voltage @ the TPS. I got a new TPS and no change. I got another computer and no change except now it only says high voltage. When I put a meter on the signal wire coming out of the TPS with the key on it reads the same as the voltage going in--4.86VDC. I can take the TPS clear out of the picture and still get the same reading on the wires on the back of the computer. I have no continuity through the wires in the harness from supply to signal so I know the harness hasn't got a short. I can take the computer out of the car and when I check for continuity between the pin supplying the power to the TPS and the pin for the return signal. I get a momentary reading and then open circuit? If I had any hair I would be pulling it out right now!! Two TPS sensors and two computers and the same results? I'm lost. I could understand if the harness had a short, but it doesn't. :sos: Art

 

[Twin_Turbo]

5v is WOT for the TPS, idle should be adjusted to 0.25 +/- 0.025V

Sounds like you have a short to 5V somewhere.

Why not measure with the compiuter installed? Yiou can push a small DVM probe in the connector to probe the voltage.

 

[AJ77]

Done that. Everything os OK till I power up the computer. With the computer off the TPS works like it should, I think. With the meter set @ 20K ohms at idle it is reading 4.2 and at full throttle it is reading 1.1. It seems that would be correct? At idle there is more resistance so the voltage signal out of the sensor would be at a minumum. At WOT the resistance is less allowing more voltage through the sensor, correct? With the key off I have no voltage reading out of the TPS but as soon as I turn the key on it jumps to 4.87 or so volts. Should be approx. .4 to.5 volts. It sure points to an internal short to supply power to the TPS, but it's just too much of a coincidence for the exact thing to happen to two computers in a row. No one here stocks this computer, I have to order it each time. PITA! Art
As an after thought, if I unplug the connector that has the return signal wire from the TPS at the computer and turn the key on there is no voltage from the TPS till I plug the connector back in. Seems strange that there is no output at all from the TPS. Shouldn't I read the voltage signal whether it's plugged into the computer or not?

 

[big_G]

You are mixing resistance and voltage. Can't do that. Set the DVM on dc volts. Ground the black probe and with the key on, (engine not running) using the red probe check the voltage at the center lead coming out of the tps. Should be set to about .5 volts at idle. Then make sure it approaches 5 volts at full throttle. The tps needs to be plugged in to the harness to voltage test it.

 

[AJ77]

I know all that. I was checking resistence with the key off to see if I had a direct short in the wiring harness to the TPS. I actually just found the problem. There must be a thin or damaged insulator between the wires inside the conector. I've had the thing unplugged and plugged back in the computer at least 40 times today all with the same result. Out of frustration, I tried one more time before giving up and drinking myself into a stupor and all I did was gently move the wires going in to the connector where the orange and black and white wires to the TPS are with the key on and voila!!! .5 VDC @ idle and almost 5 VDC @ WOT. Painless Performance is just about 35 minutes away from me. I will call Monday and see if they will sell me the connector with the terminal inserts and the crimping tool. What a Fu**ing PITA!!!!
I've been at this all day. I waited 5 weeks to get my motor back and running and then this. I need a drink!

 

[big_G]

Glad you found the problem. A drink (or 2) sounds good right now!

 

[mrvette]

5v is WOT for the TPS, idle should be adjusted to 0.25 +/- 0.025V

Sounds like you have a short to 5V somewhere.

Why not measure with the computer installed? Yiou can push a small DVM probe in the connector to probe the voltage.

NO sir, just the opposite, I first would suspect a open GROUND on the lo side of the TPS....so just take a clip lead from that wire at the TPS and go to the engine block direct, or maybe trace it properly to prove the issue....all the way back to the computer, but it should work good with a jumper to engine block ....just to be sure, use the same terminal the computer uses to attach to the engine....could be the intake or heads, or block....same shit...different point....ground is ground on that chunk of metal....or damn well BETTER be....



what you reading at the puter itself off that input is a pulse integrator circuit to remove noise from the input to the A/D converter....i'ts a resistor and reasonable cap to ground to take out noise.....

I could go nutz about all that shit, but what's the point....

IF you unplug the computer, you will most assuredly remove the ground from the TPS....willing to bet, without looking at the wiring diagram directly on, once again....

:thumbs:

 

[AJ77]

Yea, what has me puzzled though is when the check engine light first came on, the computer was still tucked up neatly behind the pass side dash where it always lives. I hadn't moved it or anything. I jiggled the wires in that connector many many times today and not once did I get a correct readng. I can't see anything wrong with it but will get a new one anyway. I HATE ELECTRICAL WORK! I go through this at work on our oilfield equipment and don't like it any better there. So much for driving it to my wife's Christmas party tonight. Hey Big G, I was in your territory Wed. We went down to
San Antonio for a couple day getaway. We went right through Austin.

 

[mrvette]

Sorry I shot off without reading the whole thread there, but I still think you found a bad ground at the puter.....

I have no comment except to say I do my own wiring....

and had once thought some time ago, that maybe I found a error that when corrected SEEMED to fix a erratic idle....the final solution on that one is still out to the jury on that one though....

:beer::flash:

 

[big_G]

Yea, what has me puzzled though is when the check engine light first came on, the computer was still tucked up neatly behind the pass side dash where it always lives. I hadn't moved it or anything. I jiggled the wires in that connector many many times today and not once did I get a correct readng. I can't see anything wrong with it but will get a new one anyway. I HATE ELECTRICAL WORK! I go through this at work on our oilfield equipment and don't like it any better there. So much for driving it to my wife's Christmas party tonight. Hey Big G, I was in your territory Wed. We went down to
San Antonio for a couple day getaway. We went right through Austin.

I worked for Welex/Halliburton in the early to mid '80's, EET on down-hole well-logging gear. Next time you're in the neighborhood look me up.

 

[Bullshark]

Gene is on the right track. You have an open on your TPS signal ground. Without that ground. the TPS signal input looses its resistor divider circuit path and floats up close to the 5v signal source voltage. It will be slightly lower due to a small voltage drop based on the small current flowing from the 5v reference source into the TPS input. I would not screw with the whole connector. Just remove the signal ground pin and check for a loose connection in the connector. Replace just that pin if it is damage beyond fixing. If you replace the whole connector harness by re-terminating all the wires, I think you are asking for more trouble. A picture is worth a thousand words. Here is a Megasquirt schematic which is probably close to what you are dealing with. Of course the connector pin numbers are different so don't let that screw you up. It's just a sample circuit diagram

It just dawned on me you were probably talking about replacing the TPS 3 wire connector. That might be easy if the bad connection is in that pin.




Bullshark

 

[AJ77]

It just dawned on me you were probably talking about replacing the TPS 3 wire connector. That might be easy if the bad connection is in that pin.




Bullshark[/QUOTE]
I wish that was the culprit. It is in the multi pin connector on the back of the computer. Easy enough to find the ground pin, just not easy to work on it. I don't have the little tool to safely remove that type of pin. I'm not sure what the proper name of that type of connector/pin is so I don't know what tool to ask for at maybe Radio Shack? The pin is sort of flat with a locking tab on one side to hold it in the plastic connector. The side that makes contact with the pin in the computer is square. Takes a special tool to remove it without damaging it. I'll find one no later than tomorrow and hopefully be back on the road with my new (old with new cam and valvetrain) motor. Thanks to all for the replies, this kind of crap makes me insane. I looked at that connector at least two dozen times to make sure there weren't two wires touching where the insulation was cut back to crimp into the pin. I never thought to look and see if they were all making contact with the pin in the computer. Kind of hard to look for. I can read a schematic easily enough, just not ttrained in electrical to know where the symptoms point.

 

[mrvette]

Yea, what has me puzzled though is when the check engine light first came on, the computer was still tucked up neatly behind the pass side dash where it always lives. I hadn't moved it or anything. I jiggled the wires in that connector many many times today and not once did I get a correct readng. I can't see anything wrong with it but will get a new one anyway. I HATE ELECTRICAL WORK! I go through this at work on our oilfield equipment and don't like it any better there. So much for driving it to my wife's Christmas party tonight. Hey Big G, I was in your territory Wed. We went down to
San Antonio for a couple day getaway. We went right through Austin.

I worked for Welex/Halliburton in the early to mid '80's, EET on down-hole well-logging gear. Next time you're in the neighborhood look me up.

Oil field gear eh??? one of the things our little company had a patent on was a little cutie we called the OWIS board, nothing but a probe into the surface of the vortex of a floating drum platform....big as hell, lowered overboard and had like a 5000 hp electric motor on it....don't remember the real power, but it was LARGE.....anyway, it ran a fan/paddle arrangement that would create a vortex in the middle, like a whirlpool and so there the oil off the water surface would flow down and into the pump pickup for recovery....our little thingy was used in refinery settling ponds, or overside in harbors....

the comment in the ME dept was that unions in this country limited use of our machine so they went with more labor intensive booms and floats to contain spills....and recover the oil....but our units were shipped overseas primarily.....where naturally enough some idiot left on on the dock overnight in Indonesia.....by morning it was stripped clean and useless....so I had to build another bomb proof control box, wiring harness, OWIS board, cable set and sent it over to be rebuilt.....fine kettle of fish THAT was....one of the engineers who had the passport went to oversee the rebuilding.....

:crap:

 

[AJ77]

Congrats to Gene and Bullshark!!! I managed to get the pins out of the connector for the TPS and found that the one for the ground somehow had opened up and wasn't making good contact with the pin in the back of the computer. Closed it up a little, put everything back together and took it for a test drive. At least that problem is solved. Now I just have to get the guy who buile my EFI system to burn me another chip. It seems the program he burned in for the new cam has it leaning out at WOT. Not a problem, he's going to send me another chip and I'll go from there. :beer:to all! Art

 

[mrvette]

HEY HEY HEY, when in doubt over a bad connection, use a soldering iron,....or a TORCH if necessary.....:crap::beer::drink: