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Engine Cold start problems due to sensor? But which one, no parts cannons!

  • Thread starter Thread starter beeduckworth
  • Start date Start date Aug 20, 2023
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    closed loop cold start open loop
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AeroCoupe

lube between the nut and the face. I know my lubes
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Oct 28, 2001
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Claremore, OK
Aug 26, 2023
#21
  • Aug 26, 2023
  • #21
You need to check the 5v ref wire to see what the voltage is when the sensor is plugged in. You commented that all the sensors are off brand so it literally could be a bad sensor causing the problem.
 
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beeduckworth

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Socal
Aug 26, 2023
#22
  • Aug 26, 2023
  • #22
I've since changed all to motorcraft, still have the same problem. Figured better off to have legit quality sensors even if they aren't bad. I have 5 volts when plug is unplugged. Then when plugged in and coolant is 80 degrees I was around 2.6v so that all checks out.
 

vferrizz

Member
Oct 23, 2020
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Fleetwood, PA
Aug 27, 2023
#23
  • Aug 27, 2023
  • #23
beeduckworth said:
I checked vacuum leaks with a smoke machine, nothing. Yes it does still have an egr but maybe it's not functioning well. What confuses me the most is while running poorly, if I unplug the ect then the car runs perfect during cold start/ warm-up. I don't see egr as an issue or it would be an issue with ect unplugged....correct?
Click to expand...
If you unplug the ECT, voltage output is 0VDC to the signal return path to the ECU pin 46. Low voltage out of the ECT correlates to warm engine temperature. The TPS, ACT, ECT and EGR outputs all go through the white salt and pepper shaker pin 1, which is the signal return to ECU Pin 46. The way I understand this is all 4 sensors have their output voltages summed together and the total voltage signal goes to ECU pin 46.
 
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beeduckworth

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Aug 27, 2023
#24
  • Aug 27, 2023
  • #24
vferrizz said:
If you unplug the ECT, voltage output is 0VDC to the signal return path to the ECU pin 46. Low voltage out of the ECT correlates to warm engine temperature. The TPS, ACT, ECT and EGR outputs all go through the white salt and pepper shaker pin 1, which is the signal return to ECU Pin 46. The way I understand this is all 4 sensors have their output voltages summed together and the total voltage signal goes to ECU pin 46.
Click to expand...
Ah I see ok, well the only problem I see here then is the egr voltage being an issue because it throws a code. That must be the missing voltage back to the ecu to run correctly. The tps, ect, and act are all correct in spec, only egr is not working, I have no vacuum to the egr so I'll have to sort that out and see what vaccum lines are incorrect.
 
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beeduckworth

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#25
  • Aug 27, 2023
  • #25
Well I found that the egr is activated on cold start and this is what's causing the bad idle. When disconnected it closes and runs well so I'll need now figure out how the vacuum is routed to fix that up. Is it supposed to be open on cold start open loop?
 

AeroCoupe

lube between the nut and the face. I know my lubes
Founding Member
Oct 28, 2001
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Claremore, OK
Aug 27, 2023
#26
  • Aug 27, 2023
  • #26
Does the car still have the two solenoids on the back of the passenger shock tower? If so the source of the vacuum for the EGR comes from them:
 
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beeduckworth

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Aug 27, 2023
#27
  • Aug 27, 2023
  • #27
AeroCoupe said:
Does the car still have the two solenoids on the back of the passenger shock tower? If so the source of the vacuum for the EGR comes from them:
Click to expand...
Yes but there is another relay above those that has a line running to egr. Looks like the computer opens and closes that relay based on pintal valve on egr reading. I had the rgr off and it can press it in with my thumb so it's not stuck but maybe the sensor doesn't read right and miss informing the computer. I have a new one anyway to throw on and see what happens.
 

vferrizz

Member
Oct 23, 2020
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Fleetwood, PA
Sep 1, 2023
#28
  • Sep 1, 2023
  • #28
beeduckworth said:
Well I found that the egr is activated on cold start and this is what's causing the bad idle. When disconnected it closes and runs well so I'll need now figure out how the vacuum is routed to fix that up. Is it supposed to be open on cold start open loop?
Click to expand...
EGR should be closed at idle when cold and at WOT. Below are some vacuum routing diagrams:


 
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beeduckworth

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Sep 1, 2023
#29
  • Sep 1, 2023
  • #29
vferrizz said:
EGR should be closed at idle when cold and at WOT. Below are some vacuum routing diagrams:


Click to expand...
Yeah the evr controls vacuum to the egr, it does close when car gets to operating temp(closed loop) why the valve is told to be open by the computer I don't know, so I'll have to figure out what tells the computer to open that. Then I should be good to go.
 
Last edited: Sep 1, 2023
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Sufarry

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Nov 5, 2025
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Atlanta
Nov 5, 2025
#30
  • Nov 5, 2025
  • #30
Hey! Really reviving a 2 year old post but I'm dealing with similar issue as you. Cold start runs terribly but if I unplug the ECT or an O2 Sensor, itll snap to a default closed loop and run great. I have the same codes as you too! My EGR has been bypass and blocked off but the electrical connector is just dangling there with nothing plugged into it. What ended up fixing your issue?
 

AeroCoupe

lube between the nut and the face. I know my lubes
Founding Member
Oct 28, 2001
5,891
4,015
183
Claremore, OK
Nov 6, 2025
#31
  • Nov 6, 2025
  • #31
I’m just gonna throw this out there. Start a new thread and tell us what year the car is, which motor is has and any modifications, what the issues are (cut and paste above), and anything you have done to fix it.

It’s a lot cleaner this way and you can keep track of your progress in one thread.
 
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