TPS settings

[marc201]

I have just completed rebuilding and installation of my engine in a 84 SVO.
It will not idle.
it idles at around 750.
I purchased a new TPS & took it to my mechanic the put it on and said it was reading throttle 4.5 + open and he couldn't get it to come down. I am not sure if he set base idle first though.

He asked me to buy another one .
I did and the same thing happened.
I want to try it myself, because I think maybe he is doing something wrong.

but in case it is still werid what could it be.
Twice when i started it it ran fine at 1000 rpm
but when we rev the motor it drops down to 650-750 and stays there. It never did this before.
He said he hooked it up to a computer and it would not communicate.
What problems could it be.

any help is welcomed.

thanks.

[svobud]

Make sure you have the correct TPS and check the FAQ section on this forum. There's a tech tip on how to properly set your TPS and Base Idle.

[marc201]

How do I know it is the right one?

How do I know if it is the right one?

Is there a serial number on it somewhere?

is there a way to test it off the car?

could something electrical on the car effect the tps sending information?

[svobud]

There's a part number on it ...and I don't know it off hand. How bout you pull the TPS and check it - maybe one of the 'tabs' might be broken?

[SVOeric]

part # for new is

1985-86:

Motorcraft CX-1135
Ford E6ZZ-9B989-A

You should be able to test your old one with a analog volt meter, and just sweep it through the throttle range, and make sure it dont have any dead spots in it.

[GT350R]

The 85-86 Part number one will not fit. That is the same style that the all the later cars use. The 83-84 and mabey some of 85 use a different one. The difference is the plug. The early ones use plugs similar to those found on the EEC2 and 3. The early ones have fat male pins in the connector and the later ones have three small pins.

To answer your question, I am going to say it is a wiring problem. Very common for the TPS areas wiring insolation to rot off.

If you do not see an obvious problem with the wiring, (oramge wire touching the green wire and making metal to metal contact),,,,,,,,,,,,,,,,,,,,,,,,,,,

Try this. unplug your TPS sensor and then pull off your pasenger side kick panel. Use a 7mm socket to unbolt your computer and pull it out. Then use a voltmeter to with two needles to probe pin number 47 as positive and 46 as negitive. Turn the key on to test. It does not have to be running. You should not get any reading at all , since the TPS is disconnected. If you still get a high reading or any reading, you have a wiring short somewhere.

What is happening is that the Voltage referance (orange pin 26) wire is touching your (green pin 47) TPS return wire.

I had the same problem with an 83 Tc I owned. It had bouced around to differnt shops for over a year and a half. No one could figure it out, they just threw parts at it. It ran pig rich all the time and was not driveable.

Most of the sensor on our cars are potentimeters. They use a 4.5-5 volt referance volatge. The sensor uses "some" of the voltage for its sensor. Then it sends the left over to the signal return (ground or SIG RTN) So so the TPS or the VAM is open it will send the voltage that the sensor is spliting to the proper input on the computer. So say it is .8 volts of the VAM or 1.1 of the TPS at idle. The rest of the 4.5 goes to ground. BUT , when there is a short, the input see a full 4.5 and thinks you are at wide open throttle.
Since its your TPS, your computer is going to open loop and basing its fuel curve and igntion off of preprogramed info in the computer. With my VAM problem however it saw that it was getting as much air as it could flow and did not go to open loop because the TPS sensor was still under 4.5

Get it? If not, just ignore the last 2 paragraphs and do what a said above , LOL!

For anyone else. the pin outs and voltage readings can be a great tool to find problems you did not even know you had. Pretty much the only way to find things like bad temp sensors and such. The page is HERE

And can also be found on my mail wiring diagram page on my website.

[svono50]

I can give an update on Marc's car, since we worked on it in the balmy 96 deg heat / 110 deg heat index Sunday. His 84's harness has a few frayed wires in various spots. I began by hooking up my code scanner and trying a KOEO test, but it came back with an "EEC not responding". This result confirmed my suspicion that this car may have some wire harness issues.

We checked the TPS and didn't find anything wrong. It was set to 0.70 volts and didn't show any shorting when checked at the EEC connector. We then pulled off the IAB valve and the wires pulled out of the connector. The plastic connector has been softened by oil. The solenoid's resistance checked out OK. During our inspection over the motor I found the orange ground wire for the turbo/O2 hanging there, so I reconnected it. We then adjusted the idle screw up almost to its limit to keep it running and got it to idle at ~800 rpm.

We took it out for a spin and it ran decently, but we could not get it to pull more than 6psi. At one point the ignition cut out at 4K rpm and came right back. When you would push in the clutch the engine would almost die then bounce up and down in rpm before settling into a rough idle. On one stop it did die but re-fired right away.

After lunch we jumped back into the project. Marc spotted a vacuum hose off of the boost control solenoid, so we reinstalled it and secured it with a couple of pan-ties. We then tried playing with the ignition timing w/o a timing light and decided that it was pretty much on from the idle tone. The cam timing was also good. Next on the list was getting his cooling fan hooked up to a switch, since it had been removed from the fan control circuit and was running a bit warm. The harness connector was pretty burnt, so we decided to hook up the fan to a manual switch through a relay with some new connectors. We used a Bosch relay from his old Chapman alarm system as well a removed a bunch of old alarm system wires. We finished the fan switch, went to start the car and got nothing. It would crank and had spark, but didn't even try to fire as if it wasn't getting any fuel. You could hear the pump priming and could watch the fuel line move when you turned the ignition switch, so I know we had pressure. At this point we decided to disconnected the battery and take a break from the heat. We came back, hooked the battery back up and it fired right up. At that point Marc parked the car and I headed home.

I feel that we need to get the test connector working before we can really trouble shoot this car without shooting in the dark. Does anyone else have any input/ideas?

[GT350R]

I do not see that you tried to pull the codes after rehooking up the orange O2 wire.

So was the mechainic testing the wrong wires for the TPS????

You really might want to bump that TPS up a little more. They all seem to like between .94 and 1.0

[svono50]

Actually I did hook my scanner back up toward the end of the day and it still gave the same "no response", now that I think of it. The heat of the day smoked some brain cells that day.

Yes, the mechanic was obviously measuring across the green and orange wires, which gives you the 4.5+ volt reading. I almost can't believe there are guys like this still out there.

Once we adjusted the idle up to 900 or so rpm the TPS was showing about .82v, so it should be fine there. My 86 will almost choke you at idle if you go above .90v, so I leave it set at .75v and use that as a general rule of thumb.

[Shadow 27]

Which TPS wires to test?

Ok...I am new to this type of testing, and I am having almost the same problems that you are having, and I read that you are supposed to test across the green and orange wires- and of course I received the same result! So, what wires DO you test for the proper reading?

[SVOeric]

You should test across the green and black wires....

 

orange and black should be a constant voltage (roughly 5 volts)

[Shadow 27]

TPS Wires...

Well that makes a lot of sense, I am going to try that now. Thanks!

[GT350R]

Ok, now that you saw that first hand, go back and read my explaination of how almost all of the sensors work with the three wire set up and it will all come together.

[Shadow 27]

TPS / IAC

The same exact thing happened to me when I tried to disconnect the IAC last week! The wires pulled right out. Unfortunately I didn't pay attention which color goes where... anybody know? And by the way I adjusted the TPS and it runs a million times better... Thanks!

[SVOeric]

If you look in the FAQ, there is a pic of a TPS, with the wires.

 

You can probably figure it out from there..