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| cold start injector ? (Page 1/1) |
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traceymac
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MAR 15, 02:29 PM
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i have an irractic high rpm idle, replaced all vac lines egr , solenoid, tps, egr ect. only thing have not replace cold start injector. what does this do ? any ideas on what is still causing high idle, low end 1300 to 2500 rpm. could i have a bad pcm ? bad brake booster thanks for any advice
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sanderson231
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MAR 15, 06:21 PM
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The cold start injector is not controlled by the ECM. It is controlled by a bi-metal switch. Allows flow in the cold start injector for 8 seconds when the coolant is below 95 'F. Too much fuel does not typically cause a high idle.
There could be a problem with the idle air control valve. To check this trun the key to "on". Jumper "A" and "B" on the ALDL connector (a big paper clip works). The ALDL is under the cover plate to passenger side of cigarette lighter. This should the idle air control valve to close. Give it a few to respond and then start the engine. If idle is around 800 rpm there is a problem with the idle air control valve or ECM (unlikely). If the idle is still high there is a vacuum leak or the idle air control valve is balky and didn't close when commanded. You can disconnect the brake booster line at the engine and plug it to eliminate a vacuum leak in that circuit
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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged[This message has been edited by sanderson231 (edited 03-15-2023).]
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sleek fiero
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MAR 15, 07:16 PM
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another couple of places to check. the cold start inj. has an Oring on it and it probably has not been changed for the life of the car. The second place to check is the injector lower Orings. I had one go bad and had the erratic idle. Easy to check with some brake clean sprayed around the base of each injector while idling. If an Oring is bad the idle will noticeably change. sleek
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fierofool
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MAR 15, 07:18 PM
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NOTE: When jumpering the ALDL be sure the ignition is OFF when inserting or removing the jumper to avoid possible damage to the ECM.
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sanderson231
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MAR 15, 07:48 PM
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| quote | Originally posted by fierofool:
NOTE: When jumpering the ALDL be sure the ignition is OFF when inserting or removing the jumper to avoid possible damage to the ECM. |
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A quote from the factory service manual. "Ignition "On". Ground diagnostic terminal."------------------
formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged
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fierofool
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MAR 16, 08:19 AM
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| quote | Originally posted by sanderson231:
A quote from the factory service manual. "Ignition "On". Ground diagnostic terminal."
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I just wouldn't do it and take the chance of damaging the ECM. A good number of people here over the years have reported that happening. You will get the same result if the ignition is OFF when the jumper is inserted then the ignition is turned to ON.
I do see one set of instructions for retrieving codes that says turn the ignition ON but not RUN and insert the jumper, then when removing the jumper the ignition must be in the OFF position. Don't know why.
Courtesy of GENERAL MOTORS CORP.
RETRIEVING CODES (NON-SCAN)
1. Turn ignition on with engine off. SERVICE ENGINE SOON light should glow. Locate Assembly Line
Data Link (ALDL) connector, attached to ECM wiring harness. Most ALDL connectors are located
under dash on driver's side of vehicle.
2. SERVICE ENGINE SOON light should flash codes. Each code is flashed 3 times. If codes DO NOT
flash, perform DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article. To exit diagnostic mode,
turn ignition off and remove jumper wire from ALDL connector.[This message has been edited by fierofool (edited 03-16-2023).]
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sanderson231
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MAR 16, 11:54 AM
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You can install the jumper with the engine running to put the ECM in "Field Service Mode" instead of "Diagnostic Mode". In field service mode the check engine light will blink out whether the ECM is in closed loop or open loop. There is nothing wrong with installing the jumper with the key on. You are just grounding a pin on the ECM.
I would do just as the FSM says turn the key to "ON" and install the jumper. The key thing is to cause the idle speed valve to close - not sure if that will happen if jumper is installed prior to key on
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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged[This message has been edited by sanderson231 (edited 03-16-2023).]
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traceymac
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MAR 17, 03:16 PM
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