GM S10/S15/Sonoma Pick-Ups 1982-1993 Repair Manual



The special edition 1991-92 Syclone was equipped with a high performance 4.3L MFI-Turbo engine. The Turbocharger and multi-port fuel injection are special to this vehicle and require some service procedures which are unique to the rest of the S/T truck series.


Proper maintenance practices MUST be followed in order to prolong the performance and life of the turbocharger. Failures in the turbocharger system are often caused by oil lag, restriction or lack of oil flow, dirty oil or foreign objects entering the turbocharger.

When working on or around the turbocharger system always follow these precautions:

DO NOT allow dust, sand or other foreign material to enter the turbocharger. Dust or sand will erode the compressor wheel blades, while uneven blade wear can produce shaft motion causing bearing failure. Large or heavy objects will completely destroy the turbocharger and could cause severe damage to the engine.
The air cleaner system must be properly maintained. A plugged or restricted air cleaner will reduce air pressure and volume at the compressor air inlet. The pressure drop will lower turbocharger performance and may cause oil pullover during idle. Oil pullover is a compressor end oil seal leak without seal part failure.
The oil lube system must be properly maintained. If dirt or foreign material is introduced into the turbocharger bearing system by lube oil, the center housing bearing bore surfaces will wear. Contaminants act as an abrasive cutting tool and will eventually wear through bearing surfaces causing turbocharger noise and poor performance. Excessive noise and/or oil smoke may be noticed. Remember that oil will completely bypass the filter if the element becomes clogged. Adhere closely to oil and filter change intervals on turbocharged vehicles.
DO NOT allow sludge to build up in the turbocharger. Sludge may occur if oil oxidation or breakdown occurs. Possible causes would include, engine overheating, excessive combustion products from piston blow-by, non-compatible oils, engine coolant leakage into the oil, incorrect grade/quality of oil or improper oil change intervals. If turbine end oil leakage is noted, check the turbocharger oil drain tube and the crankcase breathers. Remove any restrictions and check again for leaks.
The charge air cooler system must be properly maintained. Only use the proper type and quantity of coolant in the system. If coolant becomes dirty or contaminated, the system must be flushed and refilled with fresh coolant. For system draining and refilling procedures, please refer to Chapter 1 of this manual.


See Figures 1, 2, 3 and 4

  1. Drain the engine cooling system, then remove the air intake duct and the turbocharger air intake duct.
  3. Disconnect the negative battery cable, followed by the positive cable from the battery. Loosen the battery hold-down clamp and remove the battery from the vehicle.
  5. Remove the battery tray and vacuum tank.
  7. Remove the nut and disconnect the turbocharger oil feed line, then disengage the electrical connector from the solenoid.
  9. Loosen the turbocharger coolant return line clamp nut, then disconnect the coolant return line assembly.
  11. Raise and support the front of the truck safely using jackstands.
  13. Remove the right tire and wheel, then remove the wheelhouse panel retaining screws and remove the panel for access.

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Fig. Fig. 1: Turbocharger oil return line assembly

  1. If necessary, disengage the oxygen sensor electrical connector, then remove the nut from the turbocharger and the bolt from the outlet pipe support bracket. Remove the clamp from the catalytic converter and bolts from the converter support, then remove the turbocharger outlet pipe.
  3. Remove the retaining bolts from the turbocharger oil return pipe, then remove the return pipe and gasket from the turbocharger assembly.
  5. Remove the turbocharger mounting nuts.
  7. Disconnect the coolant feed line from the turbocharger, then remove the turbocharger assembly.

To install:

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Fig. Fig. 2: Turbocharger assembly mounting

  1. Inspect and clean the turbocharger and manifold mounting surfaces.
  3. Position the turbocharger, then connect the coolant feed pipe with gaskets and loosely install the bolt.
  5. Loosely install the turbocharger mounting nuts followed by the oil feed pipe line fitting. Tighten the coolant feed pipe bolt to 26 ft. lbs. (35 Nm), then the turbocharger mounting nuts to 33 ft. lbs. (45 Nm) and the oil feed line fitting to 13 ft. lbs. (16 Nm).
  7. Connect the turbocharger oil return pipe and gaskets, then tighten the line bolt to 35 inch lbs. (4 Nm).
  9. Connect the turbocharger coolant return line assembly and tighten the line nut to 16 ft. lbs. (22 Nm). Secure the coolant return line clamp and tighten to 16 inch lbs. (1.8 Nm).
  11. Install the turbocharger outlet pipe to the catalytic converter and turbocharger. Install the nuts to the turbocharger, then clamp to the converter, the bolts to the converter support and the the bolt to the outlet pipe bracket. Tighten the turbocharger nuts to 41 ft. lbs. (55 Nm), the converter clamp nuts to 42 ft. lbs. (57 Nm), the support bracket bolt to 22 ft. lbs. (30 Nm) and the converter support bolts to 25 ft. lbs. (34 Nm).
  13. If disengaged, connect the oxygen sensor wiring to the harness.
  15. Install the wheelhousing panel, then install the tire and wheel assembly. Remove the jackstands and carefully lower the vehicle.
  17. Engage the turbocharger solenoid electrical connector.
  19. Install the battery tray and vacuum tank.
  21. Install the battery and secure using the hold-down clamp.
  23. Install the air intake duct and the turbocharger air intake duct.
  25. Connect the positive cable, then the negative cable to the battery.
  27. Properly refill the engine cooling system.

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Fig. Fig. 3: Turbocharger coolant feed line assembly

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Fig. Fig. 4: Turbocharger coolant return line assembly