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Old 09-12-2003, 04:10 PM
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ECU wiring 5.7 L TBI

hi i am new on this forum and basically i need help.

i have an 1981 Chevy K5 silverado, i installed a 350 V8 5.7 L TBI engine i am did the wiring by my self but i still have 4 problems :

1- idle speed is high
2- i dono where to conect the " Crank In " wire from the ecu
( supposed to enrich fuel during ignition ? )

3- i dono where to conect the " P/N indicator " wire from the ecu
i have a 1990 suburban steering wheel and my car is A/T 3 speed t350

4-i changed the dash board to a new digital one but unfortunatley i have no speed sensor on the car.
i have to change the back cover of the gear and install the newer model that comes with a VSS or install a THM 700R4 with VSS.

5- Service engine light is always on while driving.

Thanks in advance for any help

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Old 09-17-2003, 05:02 AM
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no one knows any answers ??
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Old 09-17-2003, 11:45 PM
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have u checked to see what u have for codes? u probly have a code for a speed sensor code 24 that will cause the light to come on. the p/n wires should go to a switch at the bottom of your steering colum.
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Old 09-18-2003, 12:13 AM
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thnks man for your reply
i checked the flash codes and i do have the vss code on

on the other hand where exaactly on the steering wheel is the p/n switch ?
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Old 09-18-2003, 12:19 AM
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They should require automakers to precisely and accurately label each individual connector to make things easier, but oh well..

Did'nt you take picture, or label the connectors from the donnor car before you pulled everything? Otherwise if you can find someone with the same engine like in a mid-80's IROC-Z or something you could retrace all the wires that way. I've had to do that before.
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Old 09-18-2003, 03:36 AM
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actually i have mitchell on demand but i dono what to look for
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Old 09-19-2003, 12:04 AM
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the p/n switch should be at the bottom of your colum towards the fire wall
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Old 10-02-2003, 08:17 PM
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An incorrect or non existent VSS signal is needed for idle control, as well as emissions controls, and trans controls. We've seen folks run without vss, and inconsisten idle does happen. The crank wire is to inform the ecm when the motor is cranking, yes.
PARK/NEUTRAL is also a culprit in idle control, emissions, and trans control. Desired idle speeds are higher in neutral than drive, usually about 100rpm, which would typically put it around 650-700rpm. If you have to, wire it so that it always sees a DRIVE condition, and know that N idle will be slightly lower than normal, but should not be a problem with a stock motor. Check the state with a scantool. To default to drive, leave the circuit 434 open, not grounded, and it will see a drive signal all the time, which is the better option, not having a switch. Keep in mind that the PN switch is different then neutral safety switch, and NEVER should be used for PN . If your motor has a vacuum leak, it will idle high. If the motor is non-stock(cams, etc), it will idle rich, and idle high to compensate. If your transmission is a cable drive, than the correct speed sensor to supply your ecm is 130.00, and hooks up simply with two wires. If your transmission has a 2 wire speed sensor, then the solution will be different, and I can tell you how, if necessary. The crank wire input affects cranking fuel and timing. Hope this helps.
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Old 10-03-2003, 01:04 AM
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Thanks alot for your reply i really appreciate it.

Where should the cranck wire be conected ? a crank sensor ? where ? or to ignition as mentioned in mitchell on demand ??

The P/N wire is not grounded but eventhough on a scan tool its always on N

my transimmion is a THM-350 with no electrical wirings and a cable
i have no speed sensor yet i am willing either to change the transmission to a 700R4 or change the gear ( VSS in transfercase )

where can i get a VSS for a cable drive transmission as u mentioned 130.00 ?? is it mountable on the thm-350 ???

Thanks alot and awaiting ur reply
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Old 10-03-2003, 11:51 AM
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The crank wire, which is ppl, and circuit#806/906, goes to pin C9, is supposed to battery hot in start only. Ground the PN wire, and see if the state changes to D. If so, leave it there, and see. The vss we sell is designed to sandwich between cable and tranny, at the tranny, grounds one side and other goes to + vss term on ecm. You can reach me at programming@ccsmotorsport.com.
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Old 10-03-2003, 05:27 PM
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thnks alot for this info, i just need to sort things out
the cranck wire which is ppl goes to battery hot + in start only
what about while driving ??
is the + DC signal only on start up ??
or remains + all the times ??

regarding the VSS i will mail u later this week i might go to montreal Canada i hope u ship there
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Old 10-06-2003, 04:45 PM
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It's hot, only while in the crank mode-tells ecm when it's in crank mode.
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