Engine Cranks But Won't Run - '86/'87 3.8L Turbo

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CHART A-3

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ENGINE CRANKS BUT WON’T RUN “TYPE I C³I”

3.8LTURBO “G” SERIES (PORT)

Circuit Description:

The C3I uses a waste spark method of spark distribution. In this type of ignition system the ignition module triggers the #1/4 coil pair resulting in both #1 and #4 spark plugs firing at the same time. #1 cylinder is on the compression stroke at the same time #4 is on the exhaust stroke, resulting in a lower energy requirement to fire #4 spark plug. This leaves the remaining high voltage to fire #1 spark plug.

The Sequential Fuel Injection type of fuel delivery system utilizes 6 separate injector driver circuits to activate the 6 fuel injectors. While cranking, the ECM activates all 6 injectors simultaneously (all at one time). After a calibrated engine rpm is reached and a good Cam signal has been received by the ECM, the injection mode of operation is changed to Sequential (timed separately).

Test Description:

Step numbers refer to step numbers on diagnostic chart.

Identification of "TYPE I” or "TYPE II” ignition system is very important, because the “TYPE I” diagnostics will not work on "TYPE II” systems. Identification can be made by comparing the position of the coil towers with the drawing at the top of the chart. This step verifies “SES” light operation, TPS and Coolant Sensor signals are normal. A blinking injector test light verifies that the ECM is monitoring the C3I reference signal and attempting to activate the injectors.
Both the Cam and Crank Sensors have been verified as functioning properly as is evidenced by the blinking injector test light. A fuel pressure test, at this point, will separate the diagnostic path into either a fuel related fault, or ignition system malfunction.
The 8 terminal injector harness connector must be disconnected to avoid flooding of the engine and fouling of the spark plugs. By testing for spark on plug leads 1, 3, and 5, each ignition coil’s ability to produce at least 25,000 volts is verified.
By testing the problem coil’s control circuit with a test light, a determination can be made as to the problem coil being faulty or the module’s internal driver for that coil being the source of the complaint.
An injector, with a resistance value of less than 10 ohms (shorted), could cause repeat ECM failures.
Tests for battery voltage on CKT 639. If voltage was present, the light off’ test result was caused by no activation pulse reaching the injector connector from the ECM.

NOTICE: FUEL SYSTEM IS UNDER PRESSURE.

1 •Verify type of ignition system (Type I or Type II)
•Fuel quantity OK
•Ignition on, throttle closed.
•"Service Engine Soon Light" should be on. (If not, that must be rectified.)
•If Code 41 is displayed, start test at step #9 on Page 2 of this chart.
•TPS should "scan" less than 2.5V. (If not, click here.)
•Coolant Temperature should "scan" between -30º & 130º C
•Disconnect any injector connector and install injector test light J-34730-2 or equivalent in injector harness connector
•Crank engine and observe test light. It should blink. Does it?

Module & coil assembly (top view)

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Yes No

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2 •Ignition "off", install fuel pressure gauge and note press. after ignition is turned on for 2 seconds, pressure should be 34-40 PSI. Is it? Steady Light Light "Off"

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Yes No ê 6 •Remove test light.
•Probe injector power harness power terminal at inj. with a test light to ground.
•Test light should be on. Is it?

│ ├ ── ── ─┐ ê

3 •Disconnect 8-terminal inj. harness connector.
•Check for spark with spark tester (ST-125) J-26792, or equiv. on plug wires 1,3 & 5, (one at a time) while cranking, with remaining plug wires still connected. No Pressure Incorrect Pressure ê

ê

ê ├─ ── ── ─┐

ê No Yes

│ ê │ │

├─ ── ── ── ── ── ── ── ┬─ ── ─┐ ê CKT 639 from ign. feed is open or shorted to ground See page 2 of this chart

No spark on one or two wires. Spark on all. No spark on all. ê

│ ê

│ ê ê ê

4 •Verify that plug wire resistance is less than 30K ohms. (If not, replace)
•Remove 6 coil screws and tilt coil assembly back.
•Disconnect the affected coil's control wire from the module.
•Connect a test light between the common feed (blue) and control wire for the coil being tested.
•The test light should blink while cranking engine. Does it? Check for fuel wet spark plugs. Check CKT 839 to C³I term. "M" for open. If CKT is OK, it's faulty C³I module connection or module. 5 ê

•Check injector driver circuit for a short to ground.
•If circuit is not shorted, check resistance across injector.
•Resistance should be over 10 ohms. Is it?

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Yes No

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No Yes Faulty ECM Faulty ECM and injector

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The C³I module is faulty. Also check primary coil resistance. If resistance is not between .5 and .9 ohms, replace the coil and the C³I module. Faulty ignition coil connection or coil

* Inspect crank sensor for proper gap (approx. .025"), or signs of rubbing. If rubbing is evident, determine cause and replace sensor.
Clear codes and confirm "Closed Loop" operation and no "Service Engine Soon" light.

11-25-86