GM Chevy Mid-Size Cars 1964-1988 Repair Guide

Injection Timing

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CHECKING



A special diesel timing meter is needed in order to check injection timing. There are a few variations of this meter, but the type desirable here uses a signal through a glow plug probe to determine combustion timing. The meter picks up the engine speed in rpm and the crankshaft position from the crankshaft balancer. This tool is available at automotive supply houses and from tool jobbers; it is the counterpart to a gasoline engine timing light, coupled with a tachometer. An intake manifold cover is also needed. The marks on the pump and adapter flange will normally be aligned within 0.030 in. on the V8 and 0.050 in. on the V6.

  1. Place the transmission shift lever in PARK, apply the parking brake and block the rear wheels.
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  3. Start the engine and let it run at idle until fully warm. Shut the engine OFF .
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If the engine is not allowed to completely warm up, the probe may soot up, causing incorrect timing readings.

  1. Remove the air cleaner assembly and carefully install cover J-26996-1, or equivalent. This cover over the intake is important. Disconnect the EGR valve hose.
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  3. Clean away ALL dirt from the engine probe holder (rpm counter) and the crankshaft balancer rim.
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  5. Clean the lens on both end of the glow plug probe and clean the lens in the photoelectric pick-up. Use a tooth pick to scrape the carbon from the combustion chamber side of the glow plug probe, then look through the probe to make sure it's clean. Cleanliness is crucial for accurate readings.
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  7. Install the probe into the crankshaft rpm counter (probe holder ) on the engine front cover.
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  9. Remove the glow plug from No. 3 cylinder on the V8 engine and from No. 1 on the V6 engine. Install the glow plug probe in the glow plug opening and torque to 8 ft. lbs. (11 Nm).
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  11. Set the timing meter offset selector to B (99.5) on the V8 engine, and to A (20) on the V6 engine.
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  13. Connect the battery leads, red to positive, black to negative.
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  15. Disengage the two-lead connector from the alternator.
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  17. Start the engine. Adjust the engine rpm to the speed specified on the emissions control decal.
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  19. Observe the timing reading, then observe it again in 2 minutes. When the readings stabilize over the 2 minutes intervals, compare that final stabilized reading to the one specified on the emissions control decal. The timing reading will be at ATDC (After Top Dead Center) reading when set to specifications.
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  21. Disconnect the timing meter and install the removed glow plug, torquing it to 12 ft. lbs. (16 Nm) on the V8 engine and 15 ft. lbs. (20 Nm) on the V6 engine.
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  23. Engage the generator two-lead connection.
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  25. Install the air cleaner assembly and connect the EGR valve hose.
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ADJUSTMENT



  1. Shut the engine OFF .
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  3. Note the relative position of the marks on the pump flange and either the pump intermediate adapter (V6 engine) or pump adapter (V8 engine).
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  5. Loosen the nuts or bolts holding the pump to a point where the pump can just be rotated. Use a 3 / 4 in. open-end wrench on the boss at the front of the injection pump on the V8 engine and a 1 in. open-end wrench on the V6 engine. You may need a wrench with a slight offset to clear the fuel return line on the V6 engine.
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  7. Rotate the pump to the left to advance the timing and to the right to retard the timing. On the V8 engine the width of the mark on the adaptor is equal to about 1° of timing. On the V6 engine the width of the mark on the intermediate adaptor is about 2 / 3 degrees. Move the pump the amount that is needed and tighten the pump retaining nuts to 18 ft. lbs. (24 Nm) on the V8 engine and 35 ft. lbs. (47 Nm) on the V6 engine.
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  9. Start the engine and recheck the timing as described earlier. Reset the timing if necessary.
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  11. Adjust the injection pump rod on the V8 engine. On both engines, reset the fast and curb idle speeds.
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Wild needle fluctuations on the timing meter indicate a cylinder not firing properly. Correction of this condition must be made prior to adjusting the timing.

  1. If after resetting the timing, the marks are far apart and the engine still runs poorly, the dynamic timing could still be off. It is possible that a malfunctioning cylinder will cause incorrect timing. If this occurs, it is essential that timing be checked in cylinders 2 or 3 on the V8 engine and 1 or 4 on the V6 engine. If different timing exists between cylinders, try both positions to determine which timing works best.
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