Jeep Grand Cherokee

1993-1999 of release

Repair and operation of the car

Jeep Grand Cherokee
+ Cars of the Jeep Grand Cherokee brand
+ Settings and routine maintenance
+ Line six-cylinder engine
+ V8 engine
- Procedures of the general and capital repairs of the engine
   General information
   Capital repairs of the engine - the general information
   Check of compression pressure in cylinders
   The diagnostic checks made by means of the vacuum gage
   Methods of removal of the engine and necessary precautionary measures
   Removal and installation of the engine
   Options of restoration of the engine
   Order of dismantling of the engine
   Dismantling of a head of cylinders
   Cleaning and check of a condition of a head of cylinders
   Service of valves
   Assembly of a head of cylinders
   Removal of conrod and piston assemblies
   Removal of a bent shaft
   Cleaning of the block of the engine
   Check of a condition of the block of the engine
   Honingovaniye of cylinders
   Check of a condition of conrod and piston assemblies
   Check of a condition of a bent shaft
   Check of a condition of radical and conrod bearings
   Engine assembly order after completion of its capital repairs
   Installation of a bent shaft and check of gaps of radical bearings
   Installation of piston rings
   Installation of conrod and piston assemblies and check of gaps in conrod bearings
   The first start of the engine after capital repairs
+ Cooling systems, heating and air conditioning
+ A power supply system and production of the fulfilled gases
+ System of electric equipment of the engine
+ Systems of decrease in toxicity of the fulfilled gases and engine management
+ Manual box of gear shifting
+ Automatic transmission
+ Transfer case
+ Coupling and transmission line
+ Brake system
+ Suspension bracket and steering
+ Body
+ System of onboard electric equipment
+ Governing bodies and methods of operation

The diagnostic checks made by means of the vacuum gage

Measurement of depth of depression gives valuable information on a condition of internal components of the engine. There is an opportunity to estimate degree of wear of piston rings and walls of cylinders, to reveal leakages of a head of cylinders and the inlet pipeline, violation of passability of system of production of the fulfilled gases, jamming or a burn-out of valves, weakening of valvate springs, violation of installation of a corner of an advancing of ignition or distribution of operation of valves, and other problems with ignition.

Unfortunately easily it is wrong to interpret results of vacuum testing therefore it always should be made together with other checks which general analysis of results allows to draw unambiguous conclusions.

Are important for adequate assessment of the situation both absolute indications of the vacuum gage, and relative size of a deviation of an arrow of the device. The majority of vacuum gages measure depression depth in mm (inches) of a mercury column (all results and indicators are lower will be given in metric system). All references given below are made on the basis of the assumption of conducting check at zero height concerning sea level. Raising of a point of conducting check (or decrease in atmospheric pressure) leads to the corresponding decrease in instrument readings. For a binding we will note that increase in height of a point of carrying out tests by each meter after a mark of 610 m gives understating of result on 83 mm of mercury.

Connect the vacuum gage directly to the entrance union of the inlet pipeline - not to port of the case of a throttle. Track that no hoses during check remained disconnected - it will lead to violation of reliability of results.

Before starting check let's the engine be warmed completely. Block (wedges) of a wheel and cock the parking brake. Having transferred transmission to situation "P", start the engine and leave its working at turns of normal idling.

Before starting the engine attentively examine fan blades on existence of cracks and other damages. You watch that during the procedure not to touch the fan and not to allow contact with it of vacuum hoses. After start of the engine it is not necessary to become directly in front of the car or in the plane of rotation of the fan.

Consider indications of the vacuum gage; for reference, on average, the serviceable engine has to create depression from 431 to 559 mm of mercury in depth. At the device arrow situation of stability. Results of check can are interpreted as follows:


  1. The stable low indication of the vacuum gage usually speaks violation of integrity of laying between the inlet pipeline and the case of a throttle, existence of "leakages" of vacuum hoses, delay of the moment of ignition or violation of distribution of operation of the valvate mechanism (camshaft). By means of a stroboscope check installation of a corner of an advancing of ignition, then carry out all diagnostic inspections listed in this Chapter before starting removal of a cover of a distributive chain and check of correctness of combination of distributive tags.
  2. If instrument readings are lower than norm on 75 - 200 mm of mercury. also are unstable at this level, the probability of existence of leaks through laying of the inlet pipeline around an arrangement of inlet port or malfunction of an injector of fuel is high.
  3. If the arrow of the device regularly falls on 75 - 100 mm of mercury., steadily keeping on these values, it is possible to suspect leakage of valves. Make check of compression pressure or testing of the engine for leaks.
  4. Irregular falling or deviations of an arrow can be caused by jamming of the valve or admissions of ignition. Make check of compression pressure or testing of the engine for leaks, also check spark plugs.
  5. Frequent trembling of an arrow at the level of about 100 mm of mercury. during the operation of the engine on single turns, accompanied with the smoke-filled exhaust speaks about wear of the directing plugs of valves. Make testing of the engine for leaks for confirmation of this assumption. If trembling arises at increase in turns of the engine, check laying of the inlet pipeline or a head of cylinders for leaks, estimate extent of weakening of valvate springs whether make sure valves burned through and whether admissions of ignition take place.
  6. Insignificant fluctuations within 25 mm can demonstrate existence of problems with ignition up-down. Make all usual settings, in case of need start the engine for work with the ignition analyzer.
  7. In case of an essential deviation make check of compression pressure or testing of the engine for leaks for check of degree of wear or failure of cylinders or violations of integrity of laying of a head.
  8. If the arrow of the vacuum gage slowly "walks" in the wide range whether check the system of the operated ventilation of a case (PCV) is corked, estimate quality of fuel-air mix and also check for existence of signs of leakages of laying of the case of the throttle/carburettor and inlet pipeline.
  9. Make check on slow recovery of indications after "revival" of the engine by bystry opening of a butterfly valve and an otpuskaniye of the frequency of rotation of a bent shaft, its after rise, in 2500 rpm. Usually indications have to reduce practically to zero, rise above norm (approximately on 130 mm of mercury.) and then to return to former value. If depth of depression is restored slowly and does not form peak when closing a butterfly valve, it is possible to speak about wear of piston rings. If the considerable delay takes place, check passability of system of production of the fulfilled gases (the muffler or the catalytic converter is often blocked). It is the simplest to check such assumption having disunited sections of system of production of the fulfilled gases above the place of alleged obstruction.