What is EFI?

OMG ! OH MY GOSH , I don’t understand, any thing here , what is EFI?

This engine runs  by means of  a system, called the E.F.I. for Electronic Fuel Injection.   (includes spark in 1991)   (1989 to present) Gasoline engines, light cars and trucks only. A.k.a PCM power-train control module.(in later years)
EPA enforced Evolution (forced):
Almost all cars 1988 and newer,  have this system.  ( due to the USA EPA/ California laws) effective mandates, on the two major 1970 and 1990 SMOG laws.
Keep in mind, California operates as a country, they have their own EPA. ( called C.A.R.B), the FED EPA allows them to set their only tighter standards.
For obvious reasons, car makers soon, made all cars meet Calif and Fed standards with any model car/engine, ( to save everyones, money),
The first mandate was in 1977 Califonia, then the FED kicked in..  The laws regulate pollution per mile (not Carbs or EFI)  and were so strick, no carb on earth could do this. (but some did try) see the  examples below, of abominations.
One  wild exception (example) is a Jeep 4.3L YJ engine with ECU controlled Carburetter with oxygen sensor . See the drawing here.

After the year 1990 most CARB.S are gone in the USA , here is a 1980 Carb setup that passes smog,  no words need define the word SUCK here. Just look. “aka, Vacuum H3LL” EPA now says, this crazy setup actually made more smog.

See the 1990 to 1994 execptions here. The last Carb.here  was the 1994 Isuzu Pickup 2.3L 4ZD1 engine, with Hitachi carb.(but is electronic carb.)

As you can see there were some wild and brave, Rub Goldberg Engineers during this era.  (It is fun to study these guys and their efforts)
The smog rules are so strict here, that it became impossibleto make any Carburetter run clean for the  2 to 8  years mandated. (later mandates for smog part warranty, matter big time…on system design, even stainless steel exhaust parts…)

What replaced CARB.’S?:   
The EFI system seems daunting at first, until you realize it’s is only a small  simple dumb computer (smarter every year, and faster) that  only measures inputs and then calculates injection rates.  That is all it does. (Thanks to Intel’s invention, of the microprocessor)

But as  door prize, works 10x better, than any Carb made ! (except the 150 MPG  car myth )  (It’s the engine that wastes fuel, not the carb.!, and the wild driver action  and weight of car and hills… yes, hills)
The EFI systems, do improve fuel economy about 20% on average, and this fuel savings alone actually pays you back cash (math) ,each fill up and in fact, pays for that fancy EFI system. (making it a free upgrade  in a few years of driving.) EFI IS FREE!
The ECU has only a few inputs from very simple sensors.  The MAF/MAP sensors being the only complex sensors , the thermal sensors are just resistors. ( even Tesla had those.. a block of carbon…or carbon piles….)
The rules of computers are simple , if the inputs are wrong, so will be the output (injection,  spark ,etc…)  called GIGO, “garbage in , garbage out”

The EFI processor got faster in 1990 ,so the designers, scratched  heads, and goes. gee, lets kick vacuum advance  and the silly inaccurate, rusty centrifugal advance to the curb. (hark?, the ECU knowns RPM and load, so the inputs are already free !, of cost, and spark advance was born)
But the sad part is every country has a unique ECU, (hard fixed on board R.O.M), but later they got smarter,(flash memory happened) and one ECU fits all cars (same car /engine) and they upload the new tables to match your countries laws on smog. (saving huge costs)
Instead of 53 ECU’s , now one. (per engine)

This new Distributor  idea, made the distributor more simple and one distributor will fit any engine, needing only 4,6,8 cylinder versions now, and not one distributor per car /per engine, per country. VAST models to make and stock.
That is correct , the advancing system varies by engine./ country, and weight of car, smog laws too. (and more, load)
Later they kicked the whole distributor  to the curb. (D.I.S) was born, using COP coils. 1 per cylinder or a coil pack with 2, 3 or 4 coils inside, 2 per cylinder, called “wasted spark”.)  ( I had a 1975 Honda 4 that had this ,back when , in CB750)
The Advance system (spark), is now just a table in the ECU memory (fixed) and only needs to look up the proper advance is a split second. (same thing happens with fueling, same style table, based on engine air flow and load/RPM)
The early systems were very hard to trouble shoot. 1977 VW? analog EFI? (not digital) A true hard nut to crack ,if ever there was… (have lots of meters and gauges, to find problems)
The 1988 + systems were mandated here in USA to have OBD1 level smarts. (flash codes and mostly factroy only scanners)
In 1996 + systems here, in USA and 1998 in Canada we now have OBD2 (Fed laws) systems, that any can use any over the counter (OTC) cheap scanner, as low as $10  on ebay.  (any car owner can scan their own car, now)
These newer cars are vastly more easy to diagnose, ever try to talk (communicate ) with CARB? (well, some 1990 Jeeps you can (carb/ECU), if you can afford the $10000 Jeep DRB scanner)
The ECU can even send to the technician live streaming sensor data and live data for injection rates and spark advance. ( a huge clue of what the engine is doing)  (most 1990 plus cars all dealer shops could do this)
The ECU can even run the engine, with bad sensors, (limphome mode) unlike a carb that either starves of fuel or floods at the drop of a hat, the Carb can flood you, even with a tiny fleck of dust in the float valve! (even catch fire , for such a trival cause)

For sure the ECU has weakness, it will go very crazy with a bad 02 0xygen sensor or exhaust leaks near it.  (it usually causes say 40% rich running and 2 times fuel consumption, but it still runs)
Newer cars 1996+ run even better  , when the 02 OXY. SENSOR READS  WRONG. (and warns you to boot)
The inputs on many cars with ECU are the AIR meter(s), RPM , Vacuum and at least 2 thermal sensors.
Once you learn how EFI works, you will see its just smarter carb , that is now modular, all layed out with distributed parts on the engine, That  is all it really is… (fuel/spark).
No more chokes to stick.
The Carb with any plenum vacuum leak goes lean or even stalls.
The EFI (about 1/2) Just cause  fast idle with vacuum leaks (over spec  higher RPM) and with FULL POWER. (Most Jeeps and all TBI Suzuki’s do this, or most TBI)  How ever, the MAF engines, go lean if the leak is too much….(single failure only)

The EFI system.  is way simpler than any Carb. with all its fussy , complex needles , jets, power valves, sticking chokes, or air bleeds and the like !


If  EFI don’t ring a bell ?, please  check out my  page below:
The presumptions are,  you have engine and drive line  mechanical/electrical(electronic)  maintenance, skills.  (can do compression tests. vacuum tests, and fuel pressure tests and a full tuneup, all are basics.)
A full set of tools and or the desire to buy more.
You can NOT fix a car, with out tools and Tools are free, that is, all tools net DIVIDENDS , to the point of payback!

The desire to dig in and get to the problem, will overcome any hesitations (yes a pun).

If you want magic or expect to fix a car with no tools or money, then you need a reality check.(I’m sorry all machines break and need humans to keep them running, and not one machine on earth has “zero costs of ownership”)

I refuse to guess.  (as do all ASE mechanics)  See this master say that clearly, to the students, DO NOT ask me to GUESS!
If you want to throw parts and guess,  then do so, it is your nickel , and wasted time, I can not help you guess.  In the end, it is your car and your cash.

There is but one  Silver bullet . (but yes, do tune up the engine)  (The Lone Ranger, magic silver bullet, refr) (spark parts and filters do not last over 60,000 miles, ) Don’t be Tonto and skip tuneup’s ! (lol)
Imagine paying a mech to fix your car at  $100 and hour + 2x price on parts ,and all that was wrong ?,were bad spark plugs or a clogged fuel filter,  (you can do that service (just those 5 parts) for $25 at home)
Not only that, the dealers charges $15+ for $2.50 spark plugs. (same exact part too.)  (earning the name stealerships, well earned? huh?)
What do you think  $25 new spark wires cost there,  400% more. 800% < ask them and cry.
You can not burn all the fuel , if spark is bad. CAN’T.  It just  spews out the end of the tail pipe wasted.

The EFI will not function correctly with a bad engine (dead cylinder(s)?) dead spark or  bad sensors or actuators. ( or bad gas).
The compression spec is about 170 to 200 PSI, The EFI lower limit is about 100 PSI. But will run real bad there, and the engine is doomed there. (ignore posters telling you 100psi (lawn mower) compression is OK, IT’S NOT.
The ECU will try hard , very very hard to run a bad engine, (low compression?, Air leaks? etc) but will not do so on a dead engine or one with dead cylinders.
I call these LIES,  if anything lies to the ECU,  it can malfunction.  Bad sensors, or leaking or clogged injectors will result in bad fuel control.
Keep in mind the ECU usually can only detect dead sensors, not weak or off calibration. !! Keep this in mind at all times,  to see this fact , see that dirty weak MAF sensor, cause weak engine power and no DTC codes !
(However the ECU/PCM  can adjust to normal wear and compression losses over time and altitude like no CARB ,ever could by itself. Heck we had to retune the carbs for Denver, Co. altitudes)

Bad (out of spec.) fuel pressure,  is one form of a vary BIG lie. (bad means out of spec, (short for factory specifications) 30 PSI is minimum ,but if the FPR fails and pressure is 55psi , all hope is lost !!! or at 10 psi. lost.

The ECU (EFI) brain, is not Deity like or Omnipotant  it is really, brick stupid, and has no inputs to true reality at all, therefore, it can never make a comparison to truth. (dual sensors (2x all) is a cure, but no takers,  it’s too expensive they say)
The CEL:
The CHECK Engine LAMP; or CEL: (service engine soon or MIL lamp, maintenance indicated lamp….) Your glove box operators guide states, get engine serviced soon .
The false illusion that my engine is ok, if the CEL lamp is not glowing ,engine  running , IS NOT TRUE at all.  It’s mostly a SMOG fail light.
(The ECU will report SMOG is bad, or gross sensor failures.)
This lamp can glow, for all catastrophic sensor  failures.  (shorted or open)
This lamp on newer cars does not glow, for the 1000+ DTC errors reported today. IT DOES NOT.
Even Canada cars , mask or block the CEL light for misfire and for EGR failure. (unlike USA cars)
There is only one rule here, Scan it.  and see the FULL TRUTH.
I will repeat for effect ,SCAN IT now.
Going on Vacation soon?,  SCAN it before the trip.
The other sad fact, is the CEL glows (1996+) if the automatic transmission fails. (and the smog station fails you in a blink of a eye lid) DANG ME! my TCC lock is bad….

On topic reading links are here:
You might get help here.

Even better, is Wiki

If you don’t have a scan tool, you must learn to test your sensors and learn to  convert the readings to human terms. .

Take one example, the ECT,  the hot engine with ECT unplugged will read about 250 ohms.  250 ohms is 180 degrees F. (revised 2015 with Excel plots )

Here are my sensors test page.

Consider the below block diagram for EFI. (I made it up as a universal system for TBI and MPI and the adding of spark in 1991, SEE BLACK “X” for that addition)
My drawing is crude , I’m no artist or writer , only a retired mechanic.  (I did only electronic controls, last 10 years and PLC’s, and computers and chip testing for over 50 years.)

The system is simple , if you just look at the whole system engine with EFI.

Suzuki ECU History: (USA evolution only)
The below shows a basic fuel system,  (The 89/90  year, there is only 1 injector and the ECU don’t create or control spark, but it DOES monitor spark  and cut fuel if  spark goes bye-bye)
1989-90′ EFI is a fuel only system.!
The 89/90 has a stand alone Distributor (old school, mech. vacuum and advancement weights) , and a coil, the ECU does not create or regulate spark, in these 2 early years.
In 1991 the TBI 8v ECU, now creates and controls all spark and advancement of same.

For EFI skeptics , if you drove 2 cars for 20 years both 1.6L  the gas savings (10,000 miles per year) 1990 to present  would be a fuel savings of  $5000.00    (some of the V8s SBC/ LBC Chevy’s  report gains over 20% ! (more savings if carb quadrajet needle sickness! )
The savings can be more , as many drivers of carb engine cars, run it for 5 years with a carb bad, or choke stuck on.(partially) or a leaking float valve.  etc, etc…
Carb.s have  huge cost of ownership, do to rapid failure and expensive and frequent need of cleaning and parts change outs, (the old Boilout and kit jobs)

Digging in to EFI:  ( ECU is Engine Control Unit)
The ECU is a processor and as such has inputs , outputs and if the inputs lie , the outputs lie.

If any input goes bad (detected it) the ECU will attempt (very poorly) to mimic that bad sensor ( simulate is the correct word and works better starting in 1996+, that is, less crude)
If the ECU knows what is wrong it will throw DTC errors and glow the CEL lamp.
The ECU can do 4 things, work perfect, run in Failsafe, run in Backup mode, and be LOST.
See Backup and  Failsafe here, this  will kill economy  and power and RPM limits.  (spark retraded, and 15MPG horrid fuel economy
What does lost mean?, it means that something horrid is bad, but the ECU does not know what it is, (like fuel pressure at 60PSI) and the ECU can not control fueling at all, it just runs rich. (do to lack of sensor command Authority)
The ECU is NOT all powerful and knowing , it is not Artificial Intelligence as some think.
It  can’t be , “because it has little to no redundancy in the sensors., and lacks necessary quantity of sensors to do that., for example, it has no wide band oxygen sensor”

I like to think of the below drawing as a  FLAT carburettor or distributed..,, with the parts all laid out and easy to test and replace. because it IS.
The 89/90′ just controls fuel  see that “X:” the X path was added in 1991 to NOW.
So as you can see , only the 7 inputs below control injections.
If the 7 inputs(counting CMP (CAS) are good, then the output (injections) will be good.  The 7th input is fuel pressure , it must be in the specified range.
The word CAS below is for either or both the CMP or CKP sensors (cam and crank) that I show as ONE sensor. CAS. (crank/cam angle sensors)
CKP started in 1996 for SMOG and misfire detection, the engine runs with the CKP unplugged 1996-98. (not tried later)
The ECU brain, will mimic all detected dead sensors.
(but never can it mimic a dead CMP (cas) CAS means cam angle sensor here.
if the CMP dies , RPM is 0 and there can be no spark or injection timing ever  with a dead CMP)
The ECU can get lost if any sensors are wrong (weak) or fuel pressure wrong. or VUCUUM bouncing like a mexican jumping bean.(or a 10 year old kid on a Pogo stick)
If the spark is bad, the engine can not burn fuel correctly and NO EFI system can cure that.(not yet)
The injectors must not leak or be clogged.
IF the exhuast leaks (cracks?) near the 02 , the 02 lies, and the ECU goes , NUTS.
IF the air meters (MAF/MAP ) are not dead but lie?  AFR will suffer. (but will run in most cases) (on a carb car, if the Carb can’t feel (if you will) air flow?, the engine dies)  (AFR means the Air/ Fuel  flow ratios.)
Case in point, unplug the MAF/MAP engine runs but real rich. Try to run engine with each sensor unplugged and learn what happens?

The below, is the 8 valve TBI system total;  ( the 89/90 Kick, only does injection those years, never does it do, spark, how ever all ECU’s monitor spark on the tacho line.)
But all ECU’s do  cut all fueling, if the tacho signal, brown wire from the ignition noise suppressor,  goes dead.)
All Suzuki ECU’s kill injection if spark is lost. No exceptions , laws for fire safety, etc.. (same with CMP sensor dead, or  a dead Tachmeter signal  as seen  here more clearly.
Starting in 1991 the ECU took over FULL spark generation duties.  see that below. (91-95 USA)

This newer EFI system will run your engine , even if the motor is old and tired.

It will not run your engine correctly,  if the engine has dead cylinders , or you have bad sensors, actuators or  bad fuel pressure. Nor clogged injectors or leaking ones.
A bad engine is discovered by poor compression, weak or bouncing vacuum at idle.  (or up to 50 engine parts bad, say  broken valve springs, stuck valve stem/guides. or pistons with gaping holes on top)
It can not run the engine right with the cam belt slipped,  (It might run and make noise and black smoke but almost no power, and constant stalling)
The ECU can NOT adjust for dead cylinders, nor  gross cam timing issues or gross Ignition timing errors.
It can not tell you the spark coil output is weak but in 1996 , you will get P0300 errors, (ransdom misfire) The ECM can not see the spark plug voltages, directly. (on my 2008 car it can see spark plasma currents…a 3.8L Jeep)
The older engines, all need vacuum tests, and compression test first to see if the engine has any viablity at all.
180,180,100,180  PSI, sorry the baby is not ready for prime time. (no guessing why, its 100% inspection time)

Here is the 16v 1992-95 (N.American) ECU. with my markup’s It has 3 more injectors and the MAP  is  replaced with a MAF.

More engine EFI schematics. (to run and more)

Here are my sensors test page.

end basics,  G16 EFI.

The Jargon is not made up , it is SAE/ASE  standard terms. (Society of  Automotive Engineers)

I made a very short list of  40 of the 4000 terms or Jargon used by SAE.

We use Jargon, because nobody wants to read, or type, Engine Coolant Temperature sensors 1000 times. over and over…. it’s ECT  (every technology has its Jargon , or worse latin, ask your Doctor that…. omg)

Best place for asking questions is FixKick forum.

1 thought on “What is EFI?”

  1. Hi bro, I’m Jose from Mexico

    I like your trip and I have a cuestiones about ingnition circuit.
    I’m devolvement a system of direct ignition in a Suzuki samurai 87 swap 1.6 8v tracker 94.
    The system works good, but now I want integration between my ignition system and inyección system.
    In actuality the two system working separately but no more, I want ECM controller the ignition timing.
    (And I need to now what doing the pin A1 (Tacho) apart of cut combustible)

    If you want to now more about of my protect I’m here bro, you information it’s gold


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