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Help - 91 C4 does not want to go

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Old 01-12-2018, 03:53 PM
  #21  
aklim
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Originally Posted by wdsj View Post
Checked data with turner pro (version 4, I can't get version 5 to stay connected to my car)

Car has not run in days and coolant temp is reading 152 C. not good
TPS has no output. Stays at 0% then starts bouncing around. not good

added: is there a different temp sensor that sends temp signal to ecu vs the dash gauge? dash gauge shows temperature ok
IIRC there is the temp sensor under the TB that sends data to the ECM. There is another one in the head that sends info to the gauge. Higher engine temp, lower resistance. If you jumper the sensor pigtail, you should get 0 ohms which means your ECM sees a lot of heat from the engine and adjusts the fuel air mixture accordingly lean. If you have a lot of resistance, the engine is thought to be cold and more fuel is added.
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Old 01-12-2018, 06:11 PM
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I am not very familiar with Turner Pro, but version 4 seems to read the data.

Turner Pro indicates no output from TPS. Hand operate through full range and either reads 0 or output is erratic. I think TPS not functioning could explain my issues.

Removed the TPS and checked resistance. Ranges from approx 1 kohm to 7 and readings are smooth through full range. Sound reasonable?

No voltage detected at the TPS connector with the key ON. What voltage should be at the connector and which of the three terminals? 5V at top two terminals?
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Old 01-12-2018, 06:16 PM
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Originally Posted by wdsj View Post
I am not very familiar with Turner Pro, but version 4 seems to read the data.

Turner Pro indicates no output from TPS. Hand operate through full range and either reads 0 or output is erratic. I think TPS not functioning could explain my issues.

Removed the TPS and checked resistance. Ranges from approx 1 kohm to 7 and readings are smooth through full range. Sound reasonable?

No voltage detected at the TPS connector with the key ON. What voltage should be at the connector and which of the three terminals? 5V at top two terminals?
1 terminal should be 5V which is the reference. 2nd one should be ground. 3rd should be the signal.

https://www.autozone.com/repairinfo/...00c1528006c554
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Old 01-12-2018, 06:59 PM
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thanks, very clear information

I have nothing measurable at the TPS terminals. Appears tunerpro was correct.
any idea where this 5V comes from at the ECM? man I miss my FSM

In case its related; Tunerpro also indicated, with key to ON; no voltage at fuel pump. Key to crank, 12 volts and key back to ON maintains 12 volts.

added: TPS 5V reference at connector C c7

Last edited by wdsj; 01-12-2018 at 07:32 PM. Reason: corrected connector number
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Old 01-12-2018, 07:56 PM
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ECM terminal C7 reads 70mv with key ON

Do I have a bad ECM?
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Old 01-16-2018, 05:39 PM
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Monitoring fuel pump voltage; pump does not have power with key ON. Only gets power with key is on CRANK.

Voltage to pump only when key is in CRANK. Key ON after CRANK; no power.

Is there a pump relay somewhere that get bypassed when key is in CRANK?

add:
If I remember correctly, the pump only runs a few seconds when key is ON, once running the pump is sent voltage via distributor pulse; anyone confirm?
I have nothing to the TPS, checked at ECM, no reference 5V. Wouldn't the car run at idle even with 0v from the TPS?

add: Does the TPS signal have a delay? Watching scan, it appears the TPS signal comes in not long after the 5-6 seconds

Last edited by wdsj; 01-16-2018 at 06:52 PM.
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Old 01-16-2018, 08:45 PM
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Originally Posted by wdsj View Post
Monitoring fuel pump voltage; pump does not have power with key ON. Only gets power with key is on CRANK. Voltage to pump only when key is in CRANK. Key ON after CRANK; no power.

Is there a pump relay somewhere that get bypassed when key is in CRANK?

If I remember correctly, the pump only runs a few seconds when key is ON, once running the pump is sent voltage via distributor pulse; anyone confirm?

I have nothing to the TPS, checked at ECM, no reference 5V. Wouldn't the car run at idle even with 0v from the TPS?

add: Does the TPS signal have a delay? Watching scan, it appears the TPS signal comes in not long after the 5-6 seconds
Why would you expect it to have fuel pressure? You had the system primed, assuming it happened. So if you turn the key on for the first time, it primes. 2nd time within a couple minutes, it won't. That way, if you drive your car over a cliff and the engine stops, it won't keep pumping the fuel all over the hot engine.

I don't think so.

Absolutely.

Not sure. One of the 3 wires should have voltage with the KOEO.

I don't know about that. IIRC, it does NOT.
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Old 01-16-2018, 09:10 PM
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only obvious thing seems to the TPS, though I think the car should run at idle with 0 from TPS; so there is something else.

Thanks for your responses and knowledge
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Old 01-16-2018, 09:15 PM
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Originally Posted by wdsj View Post
only obvious thing seems to the TPS, though I think the car should run at idle with 0 from TPS; so there is something else.

Thanks for your responses and knowledge
wdsj
IDK about that. Never tried it before and mine is so not stock, I can't give you an accurate comparison. Still, the issue is that it is 0V at the reference. That is my issue. So the TPS might be perfect but here is the issue. On power on, the ECM sees a voltage it assumes to be base TPS. So, it might be confused.
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Old 01-17-2018, 11:54 AM
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Originally Posted by wdsj View Post
Monitoring fuel pump voltage; pump does not have power with key ON. Only gets power with key is on CRANK.

Voltage to pump only when key is in CRANK. Key ON after CRANK; no power.

Is there a pump relay somewhere that get bypassed when key is in CRANK?
Yeh, I still think you should be checking the fuel pump relay (see my post #8 for hypothesis on how the relay gets bypassed at crank) should be under the right side of the glove comp. carpet on the pass side. Look at this thread for reference: https://www.corvetteforum.com/forums...-location.html
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Old 01-18-2018, 03:56 PM
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Originally Posted by 91fora93 View Post
Yeh, I still think you should be checking the fuel pump relay (see my post #8 for hypothesis on how the relay gets bypassed at crank) should be under the right side of the glove comp. carpet on the pass side. Look at this thread for reference: https://www.corvetteforum.com/forums...-location.html
agree, will do and let ya know.

Out of town this weekend and next week; vacation .
More to come then.
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Old 01-18-2018, 08:15 PM
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Received new (rebuilt) ECM today and I'm all packed.
Did a quick installed and engine runs great.
I guess you need that 5V reference to the TPS.

Last edited by wdsj; 01-18-2018 at 08:16 PM.
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