Poor running condtion

Tiny
CADDYMAN85
  • MEMBER
  • 1985 CADILLAC EL DORADO
  • 85 MILES
Vehicle has gone through restoration mechanically, significant parts replacement has been done. New ac Delco, distributor, plugs, wires, map, baro, coolant temp sensors (both), New TPS, New ISC, New O2 sensor. New air pump, smog pump, all new ac delco AC system. New TB injectors, New ECM.

Car runs decent but seems to have slight miss all the time. Code 26 has returned consistently (Shorted throttle circuit)
Observations from Nemysis scanner OBDI
1. Car is in open loop all the time
2. Runs rich all the time
3. DTC Code 26-shorted throttle circuit
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Friday, May 3rd, 2013 AT 2:03 PM

5 Replies

Tiny
CADDYMAN85
  • MEMBER
Please contact me asap. Please
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Friday, May 3rd, 2013 AT 2:26 PM
Tiny
CARADIODOC
  • EXPERT
With the ignition switch on, measure the three voltages at the throttle position sensor. This has to be done with it plugged in by pack-probing the connector. You should find 0.2 volts on the ground wire, 5.0 volts on the feed wire, and between 0.5 and 4.5 (approximately), volts on the signal wire, depending on throttle position.
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Friday, May 3rd, 2013 AT 4:35 PM
Tiny
CADDYMAN85
  • MEMBER
The ground wire-(black) reads.057
The Feed-? (Blue) reads 1.9
The Signal-?(Grey) reads 5.1
My question is how to properly set the TPS sensor? The last 5 techs that have seen the car do not know how.
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Saturday, May 4th, 2013 AT 1:47 PM
Tiny
CARADIODOC
  • EXPERT
Your voltages are right but two of your labels are turned around. The 5.1 volts is the feed wire. The 1.9 volts is the signal wire, and that voltage will go up when you open the throttle. On all newer vehicles the Engine Computer learns the lowest voltage on the signal wire, which is at idle, and puts that in memory. Yours has slotted mounting holes and needs to be adjusted to a certain value. I don't know what that value is but around 0.5 volts is typical. If you have the service manual it should be listed in there. I'm trying to find the right manual but haven't had any luck so far.
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Saturday, May 4th, 2013 AT 11:53 PM
Tiny
CARADIODOC
  • EXPERT
I should have reread your first post. I was thinking you replaced the TPS but I see you're chasing a fault code. If the engine was running properly before and you didn't do anything to change the TPS adjustment, leave it where it is.

The fault code description leaves a lot to be desired. I come up with:

26 - quad-driver module (computer) circuit #1 fault

Normally that refers to the circuit in the Engine Computer that runs the injectors or ignition coil. I wonder if they're referring to the idle speed motor and they're calling it the throttle circuit. The voltages you found on the TPS would not set a fault code. Either there is an intermittent problem or we're looking at the wrong circuit. I need to do some more digging.
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Sunday, May 5th, 2013 AT 12:12 AM

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