A bad motor? (most topics here, can apply to no start bad motor , ignore running tests , in this case)
( include block , head and air leaks in the Plenum) and clogged exhaust.
Before Jumping all over sensors and bad ECU's and complex systems (EFI):
Do a compression test? 160 psi all 4 cylinders minimum. ( 16v can hit 180 psi easy)
Bad readings are, (reported) 90,120 PSI.
If any cylinder(s) are weak , do a leak down test to find out why?
Do a vacuum test? (19 inches HG at idle , no wiggling needle !) [can be done on a dead cranking motor]
If the engine runs, do an exhaust back pressure test at the 02 bung (remove 02) and get no more than 2psi at 2500RPM.
If engine don't run check exhaust back pressure cranking for over 1 psi.
A good motor has a good thermostat.
A good motor pumps air perfectly ( compression test pass 100%)
A good motor has no induction air leaks nor any exhaust leaks from the exh. valves to the front edge of the CAT converter element!
A good motor does not have damaged crank and cam keyways, and is timed perfectly as my two pages here and here show.
Valve lash set to zero lash or too tight, makes a bad motor. ( this is a service point, lash , and all timings, and Timing belt replacements)
TESTS:
Thermostat must be tested:
Your engine is warmed up to normal temperature, but it will not produce normal power. 180F or 82 C is normal.
180F to 195F is the normal water outlet temperature of the motor hot. Check it with an IR thermo-gun , hot.
170F is what I read on mine. ( temp drop is about 10 deg. through casing of STAT housing)
Compression:
You engine passes a full compression test or leak down test. (the cylinders are even in pressure and are over 150(8v) and over 170 (16) PSI)
The compression test must be done with the throttle blocked open (WOT) and the Distributor side connector removed (it has a lock DON'T FORCE IT)
WOT= wide open throttle or near.
if one cylinder is low it is bad.
if 2 cylinders are low ,the head gasket is blown.
if all are low , timing belt has slipped. 100 PSI on all 4 , means the Timing belt has slipped or the crank key (cam key too) has slipped. ( or the cam key is in the "I" slot and not the "E" slot)
If all read a tad low 140 (8v) or 160(16v) then add oil to the cylinders , engine oil , 1 teaspoon each cylinder and see if compression comes way up.
If it does?, then the rings are bad. Do A LEAK DOWN TEST to solve this riddle.
Running Vacuum:
Start motor, and attach the Vacuum gauge to the intake air plenum nipple.
The best place is the EVAP nipple going to the EVAP VSV solenoid valve, remove the hose and put our gauge host to the manifold nipple.
Start car and get it warm fully and the gauge will read 19 inches HG ,at 800 RPM normal idle speed . (All accessories off) NO FLUCTIONS allowed, a steady needle.
or
If you come here for a no start situation:
Here is my cranking Vacuum test :
Disable Ignition by pulling the Distributor side connect (or unplugging all COPS (1.8L) on each spark plug) [this kills fuel injections by ECU action)
Use a remote start jumper cable.
Attach vacuum guage.
Crank motor for 10secs (no more) at over 200 rpm (no weak batteries) and get about 5 inches HG (no Suz. spec.) ( I will put my data here later.)
The vacuum must be steady not pulsing. A retarded cam will show very low vacuum readings. As will other major engine failures ( stuck open valve?,etc)
Check the exhaust back pressure as follows:
- Remove front 02 (oxygen) sensor from its bung fitting a the
center of exh. header (8v) or at end of header (16v)
- Attach (vacuum gages (mech style) have a 0-15psi tests section) a pressure gauge to this bung. ( I have rubber nose fitting).
- Start motor and race it to 2500RPM ,if the pressure exceeds 2 psi ,the CAT Converter is melted inside, blocking the exhaust.
- Replace the CAT if pressure exceeds this factory SPEC.
Check the Whole intake system for air leaks. ( a daunting task ) ( I uses propane gas to find them)
( if here for a no start , I can start any motor with ANY air leak, with test fuel)
VACUUM LEAKS: (Look for Vacuum leaks if you are sure injectors are good and fuel pressure is good)
( Your induction is under a partial vacuum, any leaks are illegal AIR LEAKS)
[ On your old Sidekick 8V , a leak will cause your idle to be high all the time, but no bog, on newer 96+ you will get bogging and you get a hyper lean mixture, and any year .
The 16-Valve engines 92--98 MPI will bog if air leaks up stream of the MAF. (Rear of MAF itself)!!!
MAF + Leak = Bog. ( lean city)
Look at the intake manifold and TB (Throttle Body) see all those small hoses and 1 big one for the brake booster and PCV hose. Don't forget to inspect that BIG main induction brake hose (pipe really).
My Leak test: I pinch each vacuum hose while the engine is idling and hot, to see if the RPM drops (bad). ( use fingers or pliers. or ?)
If it does drop idle speed? you have a problem? (see list of valid pinch points)
Investigate this leak. On 16V engine the pinch test is less effective and testing each hose and device with hand held vacuum tool is always best. Test all hoses and all Diaphragms and all VSV valves for leak down. Allow no leaks, period.
Top leaks are hose clamps missing, EGR gaskets missing or loose, IAC gasket missing or loose.
Injector gaskets, intake gaskets, Throttle body gaskets cracked.
Do not pinch the IAC/ISC top hose (as it uses LEGAL air to set proper idle ) nor pinch the PCV hose as the PCV valve always meters air constantly.
PVC air is legal air , note its path is measured by the MAF.
( The 16 valve car the IAC may be also called the ISC, idle speed control)
Don't forget to pinch that huge BRAKE VACUUM hose at the REAR, yes, it too can crack its internal diaphragm. (hard to pinch it is)
All hoses can be removed and vacuum leak down test them on the bench, or just look for any cracks in bright light. Pinch and look for cracking.
Hoses are dirt cheap so replace them all if they look bad or look weak or at end of service life.
Your PCV valve is, of course, new, as you just did a tune up. clean it and make sure it rattles.
If it's new, then it is ok. (one guy had the wrong one from a Huge FORD LARGE BLOCK V8, and it leaked too much. ). Amazing but true.
Pinch all the VSV tiny little hoses ( VSV equals Vacuum Solenoid Valves)
The there are up to 3 VSV valves total. EGR1, EGR 2, Dashpot (8v) and EVAP.
In fact, you can examine all the hoses. Both Visually and with a vacuum leak down device like the MityVac or clone.
There are many vacuum devices, that can leak.
Anything connected to the main induction Plenum can leak and cause lean running. Careful examinations are crucial.
Example Vacuum leak: ( The case of a failed pinch test)
( keep in mind 8v will not bog but will have a high idle speed , 16v will always bog with illegal air leaks.)
You discover the hose going to the EGR diaphragm is leaking, you check the hose and it's ok, but the now you discover that the diaphragm is leaking, and very badly. Use a MityVac type tool to measure leak down rate of this diaphragm. ( This tool, is great, to bleed your brakes, and test vacuum circuits)
This leak allows ILLEGAL air to enter the induction system of your engine and mess up the A/F mixture. (Air Fuel RATIO ). If it is an emergency , then, just plug up the hose , to get you home ,then fix it later . Same with the VSV hoses for the EVAP circuit.
On MAF 16V engines ANY LEAK is very bad .[ typical on all 16 valve SideKick's ]
BTW: this 16 V engine says 16 Valve right on top ! Huge letters. The 8 valve engines says nothing, just black painted thin steel valve cover.
In some locals , we have pack rats or mice , that eat the piping. Not good !
The main air tube from the MAF to the THROTTLE BODY must NOT be allowed to LEAK !!!
Make sure a fan belt did not slash a gash into this main top AIR pipe, during a belt failure.
On MAP only based engines [8Valve], you will get racing idle , however power will still be good. ( because the MAP detects the leak and informs the ECU of this fact ). 8-valve engines shout , hey, I am leaking !
The 8v motor that bogs is most likely to be found with low fuel pressure and never an air leak.
Injector O-rings can crack and leak air, as can any gasket on any part of the intake manifold.
EGR:
Lots of words on air leaks, but there are lots of ingress points a modern Induction system.
EGR LEAKS: ( THE EGR is and ECU actuator and is not a bad motor but it does ingress illegal gases to the induction)
Just be sure it is closing under its own spring power and is not leaking air or gas through its valve portion.
A stuck open EGR valve will make an engine bog real bad , the EGR starves the motor of oxygen and thus the bog. (only at low speeds)
Read about LEAKING EGR's.
Always check the EGR first ! EGR's are vastly unreliable devices. It can be cleaned. I have recovered incredibly clogged EGR main valves.
The MAP and the TPS can not be cleaned. ( they can be measured )
Most sensors can be tested.
Jargon and buzzwords confusing, here is my Jargon page.
rev 2 , bad motor page1.