Need Help with Electrical Problem

[Kristi]

We just installed a brand new engine in our 1986 T-Type. Since the installation, the ECM does not read the TPS sensor as it changes (Scanmaster displays idle setting of .42, even at WOT - engine off), the O2 sensor is lazy and generally reads lean at idle and cruise, and O2 cross counts are also lazy or unchanging. We've replaced all sensors, the chip, and the ECM. We've confirmed that the TPS is producing the proper output (with a voltmeter), and confirmed that the grounds at the back of the passenger side cylinder head are properly attached.

What do the TPS and O2 sensor circuits have in common? What could cause this problem? Please help!

 

[Steve Wood]

Did you ever verify the ground at the pin number on the ecm that I gave you once before? The ground from the battery to sheet metal as well?

 

[Kristi]

We have not had a chance until today to try to determine the problem as the weather has not been very cooperative.

We checked the major grounds at the back of the passenger side cylinder head today (hoping that we'd missed one), but they were all attached.

We did check the battery ground, and that is fine. How do you check the ground on the pin number?

Thank you!

Kristi

 

[Steve Wood]

I believe you can verify that ground under the hood. Put your meter on volts, touch one lead to the black wire from the tps and the other lead to the blue wire from the tps....and you should be able to read the tps voltage. This may be the way you did it before.

Putting one lead on black and one on the grey wire should give you 5.0 volts. Key has to be on the run position for both of the above.

If you read voltage correctly on the above, then the ecm is making the connections properly.

I don't see any relationship between the o2 and tps which leads me to believe something else is wrong. The o2 gets its ground thru the up pipe. Assuming the cylinder head grounds, battery cable to turbo bracket, and battery to sheet metal on the fender are all good...which I understand have been verified..

Now, having said that, the o2 ground goes from the cylinder head to the ecm thru a tan wire that connects to pin D6

And, the power ground for the ecm goes to the head via a blk/white wire from pin D1. I think I would go to the ecm, find those two pins and check the ground on each one individually. When I say pin, I actually mean the connector side, not the ecm. Put the meter on ohms, put one lead in the connector and touch a ground such as the chrome strip in the doorway that holds the carpet down. See if the meter goes to near zero verifying the ground. Do the same for the other wire. If both of these wires shows a ground, then it is probably time to talk to Bob Bailey or John Spina.

 

[Kristi]

Thank you very much....I truly appreciate all the step-by-step directions, as I have never had this type of problem before. We will run this test first thing tomorrow and post the results.

I love this board......

 

[Kristi]

Steve...Please Help!

Here's the latest...We (again) visually verified the battery ground to the turbo bracket (new battery cable), the battery ground to the fender, and the firewall ground. These grounds are clean and tight.
With the key in the run position, we probed the TPS: Probing the tan wire and the black wire resulted in 4.60 volts, regardless of throttle position. Probing the blue and black wires resulted in .38 volts (.40 shown on the Scanmaster) and 4.2 at WOT.
We moved inside the car and disconnected the harness from the ECM. With the voltmeter set at 20 ohms, we put the positive probe on pin D6 (pale orange-colored wire) and ground the other probe to the doorsill. The voltmeter displayed a fluctuating value around 7. With the positive voltmeter probe on pin D1 (black wire with white stripe) and the negative probe on the doorsill (voltmeter set at 20 ohms), we again saw a fluctuating reading on the voltmeter of 7 ohms or so.

Any ideas? We're in over our heads here, and really appreciate any advice you may have.

Thanks, Steve.

 

[Steve Wood]

What does the meter read while on 20 ohms and you touch the two probes to each other? What ever it reads then, is what it should read when probing the two wires and going to ground.

Also, go back under the hood and probe the black wire on the tps and put the other probe to a good ground on the engine....with the meter on ohms again.

I don't seem to be helping much...more like a circle....

 

[Kristi]

It looks like we may have a problem with our voltmeter. (It figures) We are going to re-run the tests as soon as possible, and will let you know what we find.

Once again, Steve, we really appreciate your help on this.

Kristi

 

[Steve Wood]

Wish I felt like I was helping more. I keep beating on the circuitry because the tps seems to be working at the sensor and you have changed the ecm.....