Click the image to see a simulation of the engine, live.
Before tearing the motor apart into 100's of pieces, consider the below.
Before buying $900 MAF sensor. (a new Suz. price) sensor or the like , consider the below.
Given:
The motor must pump air, if it can not do so, for any reason, it is bad. ( vacuum tests and compression tests find this out in about 30 minutes work) (This is JOB 1, besides fresh fluids)
Look down the oil filler cap hole , does the cam spin?, cranking?, does the the Dizzy rotor, spin while cranking (cap off). The problem is obvious ,right? (the belt or cam chain is snapped)
Attempting to tune or repair any vehicle with a dead , bad or very sick motor is a very costly mistake. The EFI system can not make a bad engine run. (worn yes, bad, no)
The engine is an air pump, and worse, is has 4 air-pumps and each can be bad , if one is weak they can interfere with each other. (vaccum bouncing is real bad for the EFI system )
Keep in mind the 4 cylinders are ganged, but share common resources, the Induction Plenum and the Exhaust collector and the common connection at the crankshaft ! (a common EFI too)
Think of the crankshaft as a team of 4 horses all pulling together, and if one gets sick the others have to drag the dead horse around all day.
If the engine can not pump air efficiently the EFI ( Electronic Fuel Injection +spark) may malfunction. (due to bad MAF/MAP readings and reduced , effective displacement)
The ECU is programmed to ignore some vacuum, or air flow bounce but not severe.
The EFI system can compensate for old tired and weak motors ±25% , so that is not at issue here , what is at issue here, are gross engine defects or gross intake or exhaust faults.
No Tools , no Joy.
First off, buy a compression gauge and a vacuum gauge or you will never be able to diagnose any ICE vehicle. (internal combustion engine, Otto cycle type)
You can also kill the fuel pump on any EFI car then use test fuel to listen to the engine run, (short times lasting 3 seconds or longer with practice) and hear noises? and just the sound of a normal engine.
Backfiring? , is bad timing ,cam ,dizzy or both, if the cam slips?, so does the dizzy they are daisy chained , check Dizzy timing if way off, the cam has slipped, (do not correct this dizzy slip, fix the cam)
The PIT FALL LIST:
- Vacuum weak or bouncing
up and down
violently , just one burned or simple stuck open intake valve and
the
EFI system goes nuts. (idle spec: 15.7-19.7
inches HG @800 rpm
warm)
- A slipped timing belt.
(with gross cam timing errors causes,
compression as low as 80 PSI) (low compression and weak
vacuum) You never did the 60,000 mile tune up ,did you!
- A stripped crank
(#1 killer here) keyway , key and cog , at the end of the crank
shaft. (Low compression and weak vacuum)
- A
Broken valve spring is tricky, it can be opening and closing ok (or
not) and still have good compression (or not) and only fail due to
faster RPM valve float, very hard measure this , best is to
just look at each spring with eye balls.
- The above or a flat cam lobe, on say one cylinder,
and shows perfect compession, but a very weak motor. Failure of
proper valve lift. (just a fast look while cranking and looking
cam rockers , it become obvious, it's bad.
- Bad head gasket , or a holed piston. Low vacuum
bouncing and weak compression. (2 cylinders only with low
compression is sign of a bad head gasket.
- Cracked head, cracked block. ,bent rod , broken cam
shaft
or related parts, lifters, cam sprocket broken., Cam/crank keys
sheared.? NOISE, fix noise first or the damage will cascade. $$$$
- A Melted Catalyst Converter element totally
blocking
the
exhaust and rendering the Engine Air pump useless. (can not pump
air , it will never run and may not even start up) LIMPHOME loves to melt CATS.
- Gross Induction
Air leaks. Find them and cure
them. The Induction must have only the valid air sources,
especially on the 16v motor with a MAF sensor. (the IAC and ISC must
not be jammed open)
- Distributor can't spin? Look at the under dizzy cap,
rotor.
Cam failure will cause a distributor to not spin. (look down oil
filler cam, does cam spin at all?) Check timing.
- No oil pressure ? No Oil In engine.? oop's.
- No coolant?, ever heats engine , and lost power
- A missing thermostat, or thermostat is bad or the rubber
surround gasket is missing.( under cooling is
just as bad as over cooling as it make the ECU go nuts)
- Forgot to put antifreeze in the Coolant loop last fall? ( cracked head and block).
- A stuck open EGR main valve will make a motor gutless.( and stall at idle)
- Something allowed the valve
lash to be too tight, it is a
service point ignored by most. at 60k miles. Weak compression is
the result and burned up valves.
TOP TESTs:
Checking Compression with out the throttle blocked open, is a waste of time. CUT FUEL INJECTION !
Then Minimum compression "warm" is 170 PSI @400 , is caused by many things, but a slipped cam belt is tops, as is a stripped crank key.
Cold compression will be less, but not alot.10 PSI less?
Max. allowed differential pressure is 14.2psi /cyl to cyl.)
Induction Vacuum Plenum:
Bouncing Vacuum is never good. The MAP or MAF will send grossly varying signals to the ECU and the ECU will just go, nuts.
( can be detected on OBD2 cars ,with a full SCAN TOOL, the Monitors never complete and MAF signals look crazy?)
EXHAUST BLOCKAGES:
Maximum exhaust back pressure is 2 psi at 2500 RPM. use the O2 front sensor bung port to measure pressure. (eg: remove O2 and test the pressure?)
Most vacuum gauges come with a 0-15psi side.
Check the induction carefully for air leaks ,see my racing motor (fast idle) for details on leaks.
Our EFI and MOTOR Jargon, can be seen here.
Almost all tail chasing happens due to not checking the above 3 things.
The Top fails based on real data:
Slipped timing due to bad cam timng belt.
Blown headgasket. (allowed to over heat due to lack of cooling system maintenance, or not repairing a bad EGR function)
Crank key sheared at the crank cog wheel , and will make the timing markes USELESS ! (not following the 1996 TSB on crank cog bolt torque , 94ft/lbs) [retroactive spec. too!]