ENGINE POWER LOSS:   ( Bogging, Hesitation
, etc.)            

Page 3 , bad sensor data to the ECU , the Engine controller ,or EFI brain.
EFI is Electronic Fuel Injection.

Prerequisites , Page 1 and 2 are done.

An Over view:   ( all sensors are here and some acuators, too)
The ECU has only the following inputs ( variables they are called to computer geeks)
Computers have Inputs (variables) and constants ( fuel pressure is a constant as is a working thermostat and good motor a constant !).

ECU Inputs:  (variables)  The 8valve and 16v EFI sytsems are very much differant !

MAF (16v)  Measures Air flow into the engine   ( a very difficult device to test)

MAP (8v) Measures maniflold pressures and with math can calculate air flow indirectly.

IAT  (intake manifold air temperature , helps adjust air flow calculations and is very critical on 8v motors)

ECT  ( must show the correct engine coolant temperatuere at all times. and this is just the thermostat function ) Vital this sensor is for cold and warm running.

Crank and cam rotation sensors ( both will DTC code if they fail)  So this is not it, and your CEL lamp is out , right? If not you'd already know whats bad.

O2 sensor,  very hard  to test but just get a new one for $50 and stop guessing if its good or bad but here is the test for the motivated.

The TPS sensor. ( if car bogs and catches up in few seconds this sensor is bad.)

The EGR is not a sensor but it is sensed INDIRCTLY , and there if IS an acuator and sensor.
If it malfunctions the ECU turns on the CEL lamp and sets code 51 or code P0400.

The EGR must be good and must never stick open or Bogging will happen.

The Old Pre 96 ECU's can not detect misfires, bad injectors ,or open acutators.
The old ECU's have very few monitors and monitors can be considered Sensors.
This is why I dont like OBD1 ECU's they lack most of the top monitors !  IMHO, YMMV.
So, If you have an old 95 Kick , you get stuck finding this bad sensor the hard way.  89-95 is old.

On newer cars, ignoring the CEL lamp ( all cars , all years ) is foolish.
Pull the DTC codes from the ECU memory and read up on them.



Top checks for bad sensors:

ECT , check the reading on the ECT , with a cold motor and a hot motor with an ohm meter with the connector pulled ( it has a lock don't force any connectors on car)
IAT  ,  same page as ECT check the temps cold then hot.

If the EGR main valve don't leak when relaxed ( idle) then it is ok for bogging.  Not the culprit.  ( you could block it and test for bogging)
If the TPS  if bad causes mini bogs,  the TIP_IN throttle response has a flat spot but catches up , this is classic bad TPS. WOT and steady foot power is good.
If the MAF is bad , the car will bog and blog hard and have no power at all and will never catch up and make power. clean it with "CRC MAF cleaner".
The Map sensor on the 8v motor almost never fails. but the hose to it does clog ( and its filter) and can crack this hose.
O2 sensor can drive you mad,  just get a new one and stop being a skin flint.  "PRIMARY SENSOR IT IS AND CHEAP TOO"

As you can see if the ECU is lied to, then it can in fact calculate too little fuel, but that is not the ECU's fault.
 GIGO "garbage in results in garbage out" applies to car computers too.
Lean means the  Air Fuel Ratio's are way greater thatn 14.7 : 1 .   (by weight:  Air to Fuel  Ratio).
We call this AFR.  Bogs are caused by LEAN AFR ,  16:1 is lean so is 20:1  ! and will bog like crazy if the O2 is bad.
  • Dirty or bad MAF ( 16v engines only , not found  on 8V) Clean the hot wire MAF with MAF cleaner,
  • on some cars the MAF is mechanical and looks like a toilet plunger , dont try to clean this Eurpean MAF.
  • A bad TPS  . This sensor gives car a boost in fuel, with a fast right foot , but causes slight and temporary bog   Where is this TPS?:
  • ECT sensors reading hot all the time, can cause bogging cold ONLY , The opposite ECT failure ,causes flooding , and this is not bogging. Smell that gas?
  •  The OPEN ECT connector or wires to it , causes flooding and MISFIRE
My MAF test page is here:  ( suspect it last)




Dead ECUs can't read Inputs and calculate correctly:

Facts: All early 90's era ECU's may need  the Capacitors (CAPS) replaced  IF NOT ALREADY DONE, OF COURSE !


  Bad sensor data input to the ECU.

This is the old and infamous GIGO syndrome , Garbage in  EQUALS garbage out , GIGO:

You lie to the ECU , what do you expect?, (correcto ! , Der Garbage)
On all 96 and newer cars you can monitor all sensors live.   ( sorry no OTC scan tools for older cars)
This is called a full scan tool and can be had for $50 if you have an old laptop then you dont need  to buy one. 
Any old $30 beat up laptop will work. (needs 1 USB port and Windoz 2000 or newer , XP is best.)
You do NOT need a fast lap top to run SCAN tool software, any will work.
You are here, because your engine is perfect  (150PSI compression) and there are no air leaks into the induction system and you suspect bad sensors.

If either TPS or MAP are bad , they must be replace it  with new ones. ( used if you can find them?).  TPS can be calibrated , do that first.
I will now explain how each might fail and how each can behave bad.

The MAP (8v)  is almost a life time part, never seen one fail, unless hit by a tree or lightning.   The 8V engine does not have MAF sensor.
The MAP handles all load calculations on the engine. Keep its vacuum tube path free and not cracked or clogged ,and it will just work perfect.


The MAF will fail at medium to high loads  (up hills ,or passing) .
  ( the MAF works mostly at idle and off idle speeds  and is very important cruising and under load)  It is critical to making power UP ANY HILL.
My 96 pulls 55 grams per second up hill , WOT , in 3rd gear !  If that fails, I can not climb hills !

The TPS ( while running hot) is used for only 2 things,  Wide open throttle detection  and what I call a fast foot. (enrich mode)
One can accelerate 2 ways, gradual or sudden, the TPS is the detector of the sudden,  it allows the ECU to give a burst of energy (gas) .
If the TPS is bad ,some call this TIP IN BOG.   It is quite different then bogging during all accelerations.
Any bog that lasts for longer than  3 seconds is not a TPS fail.
If you have a vacuum leak the engine will bog from idle up to 1/2 throttle but MAY be ok from 1/2 all the way to WOT.  

The TPS , MAP   can't be cleaned.  but a  MAF sensors , can be cleaned quite easily. ( the pure mechanical MAF can not be cleaned)
The TPS has a TPS switch on some cars and it MUST be calibrated at idle, or the ECU will go crazy.  (surging ,  stalls)
DO NOT JUST SWAP the TPS OUT.  It MUST BE CALIBRATED.
TPS pot codes are code 21 and 22 ( Pot = variable resistor portion) (other codes for OBD2 cars and are obvious )
YOU MAY GET CODES for the switch being bad or being out of calibration, Code 44 or 45.

All sensors can be tested on the car with a simple volt /ohm meter.
The MAP sensor  can be tested with a volt meter.  ( there is a tiny little filter in the line that  can clog..

If the TPS Pot. goes open circuit (it can) the car may not START !  (ECU enters UN-Flood mode for ever  EQUALS = no start) {ie:Unflood mode}
If the TPS internal switch opens , the car will not idle. It will die.  It may also think car is idling while driving to work, and surge like crazy.
Surging feels like a demon is in the motor stepping on the gas pedal FOR YOU !  scary thing it is and very bad design practice. TPS idle switch opening too late does that.
If the TPS internal Pot. resistor shorts to ground , the car will not have en-richening on an aggressive right foot.   (tip enrichment mode will be dead)
Both sensors can be tested on car and off car.
The MAF must be tested on the car because you need air flow. ( I may do a leaf blower test some day just for fun)  (I need test MAF, not MINE !)
The 96+ cars I have MAF data , data logged and plotted here.

Hints: ( On the MAF)  16 V 92--95 engines and all newer engines (96+)
Do not touch the MAF internals, or remove screws in the device itself , just spray inside and wait and spray again. Keep any spraying back aways 6 inches !
It is ok, to just unplug it and remove the hose clamps and walk to an outside area and spray the heck out of it. I  keep nozzle back a foot.
Do not blast the hot wire to death, be gentle. 
I spray ,wait 15 minutes and then spray again, standing in fresh clear air spaces, outdoors.
That CRC cleaner is very good.  Try some? it won't  damage plastic.

Some MAF's have screens on filter side and some don't,  please never remove, that screen , as it is not a screen it is an AIR straightener!

A Dirty MAF sensor ( older 8 valve engines don't have it).  Use a special CRC cleaner for this sensor. This is very Common, & cheap fix. 
Keep in mind that crooked Mechanics  love to just throw away a dirty MAF and collect $600. 
Clean it for gosh sakes and save your money.   ( I am not saying all bad MAF sensor can be cleaned and fixed)


It is easy to test.


A MAF that reads too high (false air) will cause a rich running engine , even a tad more power, and O2 going very rich.
A MAF that reads low (false lack of air) all the time, under reports AIR, so car will go LEAN and BOG. 
If the ECU detects a grossly dead , MAF it will set the CEL lamp and mimic it by using RPM and the TPS. (just like a drag car).
Test the MAF with a simple voltmeter using back probing of its output pin to ground.   use 15-20vdc range of meter.
It must vary 1v to almost 5v range, at idle to WOT.  A linear progression, no bumps ,hicups , or other crazy action as you increase throttle.
The highest voltage is only obtainable on the road ,going up hill FAST !!!

A bad MAF usually is indicated if the bog happens only on medium to heavy loads , and NOT on a lightly loaded engine.

I now  have  calibration data on this device,   including full power full load WIDE OPEN THROTTLE PLOTS !


TRICKS for DISCOVERING ( proving) Motor is  running too lean)

OVER DRIVE the system.  Trick 1:  (the best way)

If you THINK car is starving for fuel then add EXTRA !

THIS IS MUCH SAFER.  It is designed to exactly what I am reporting here.  IT COMES WITH INSTRUCTIONS, TOO.
A OTC: model 7148 propane test injector.   ( DYI: make one  from and old propane torch , just remove old nozzle and add plastic tubing, see?.)
    A simple and much safer device. 
The test:  ( Please conduct your tests in a safe place away from people , pets and traffic, off road is the best.)
I connect the above tube to the  EVAP VSV intake manifold nipple.  ( pull hose, replace with above, simple)
Connect to the Manifold side not the valve itself.
Attached any propane cylinder to the above valve assembly. Then your plastic tube to the induction port on your engine.
( do not pull and use the Brake booster hose, you need brakes, right?).

When you detect a power loss, just crack the valve and give your engine a quick shot.   ( note the results )  (Truckers use this to boost over hills too)
Alternate connection:
Take out the air cleaner and feed this hose in to main induction, .  Be sure to not let air leak in to your (after maf) connections that you make.
Try testing with foot steady on gas and with more pedal.  (wait for bog then.. Open the Propane main VALVE hard..)
If car takes off like a banshee? ,then you have an air leak in the induction (you were lean !)
Give your engine some more throttle , see bog, hit it with propane again, see bog vanish.  YOU  ARE LEAN.
Find the air leak or the injection problem.  ( you have a fuel loss problem or you have way too much air in the induction and is not passing through the MAF sensor)

Finding out why you are lean , can be hard.


More Tricks of the trade, and works on may cars:
Trick 2:
Pull the MAF CONNECTOR ELECTRIC, and car will be forced to run using only the TPS and RPM , note the results. "CALLED MIMIC MODE"
This trick should force the car to rich and lower spark advance (retarded maybe). [ limp home mode ]
This is a good trick for  when you suspect the car is running, too Lean.
On the 8valve engine i can pull the MAP and car will run, badly but it will run and can be used to find problems.
I pull MAF connectors all the time to see if MAF removed makes the engine produce more power up a hill.
Not all cars will work perfectly with the MAF pulled, others work pretty good.   
The hardest of all is a weak MAF and bogging. Pulling the MAF connector may improve the power.
IF it does, you have the source of the problem.
(note: trick 1 will wreck idle RPM so use right foot to compensate)

TRICK 3 is to pull the OXYgen sensor plug , this can? cause a slightly richer mixure and the results can tell you if you are lean, or not.


My Last trick #4 (a radical test but can be helpful)
The water temperature sensor , (engine coolant Sensor) ECT connection ,can be pulled.
{ warning, this may flood an engine so tread carefully)
By pulling this conn. , you send a HIGH resistance reading  to the computer.
This tells the ECU, that the  engine is freezing cold.  Forcing  the A/F mix to be  very rich.   ( it may be way to rich , so be careful)
If your car is hot and it is bogging  and you think, gee this car seems lean, just pull the ECT.  ( I tend to prefer the OXY test or MAF test)
Bingo, instant rich mix, and power comes back.  ( keep test short to save your CAT ).
A better test is to put a 250 ohm resistor on the ECT connector.  This tells motor it is at perfect temperature.
note any improvements in running.

In the case of all tricks above do not do this and drive long distances, only short runs,  5 miles or less, I would say.
I don't want you to hurt the CATcon.  Lots of fresh air and gas are bad for it.

This by no means identifies all sources of a Bog, but is a start.
That is the end of my BOG page.   I hope is helps someone fix their car or helps them save lots of money.  Cheers.!

parting comment.
a dead or weak maf is hard to test.
That is because you need it to function perfectly to make power under load.  If you can not drive up the hill fast , you cant test the MAF.
The chicken and egg issue.
How ever , if you can feed propane and go up a hill and then measure the MAF with a volt meter or scan tool , you can find a dead MAF.
For sure !
They are expensive. Above $600 at Suzuki dealers.


Jargon:
Please go here to see the meaning of the common 3 letter abbreviations used here.  It's standard SAE , jargon.


ver 1 ,page3  Input bad to ECU.




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