Chrysler 2.2/2.5  Port Fuel Injection basics

 This page will cover a general overview of the Chrysler "speed density" fuel injection control system used on FWD 2.2/2.5 turbo cars from 1984-1993.  (The term "speed density" refers to speed of engine and density of air, or in other words rpm x map sensor = pulsewidth) Information found on this page are from Chryslers drivability & new model highlights books, Allen Institutes training program Chrysler EFI/Turbo book, Champion Tech*Knowlege Series, SAE technical papers 840252 & 900852 and my own personal experiences...

 To begin- The speed density system is a simple, low cost method of fuel injection. The system works by gathering information from the engines main sensors (tach, coolant, map, T.P.S.) and minor sensors (O2, baro read, battery temp, charge air, detonation) and generates an injector pulsewidth & spark curve. The main sensors are used to get the engine running, the minor used to "fine tune" the mixture & timing. This is different then a "mass air flow" system that directly measures the volume of air coming into the engine via "mass air flow" sensor. (A popular system on 87+ mustangs and most GM products)  Chryslers calculate the injector pulsewidth on the fly based on sensor information tables, something like this-

Map x RPM x (correction factors- coolant, charge air, baro & O2) = injector pulsewidth

This is an oversimplification but will suffice for our needs.  Chryslers do NOT have look up tables for pulsewidths, its all calculated on the fly- this has been verified in several pieces of factory literature I have.

System Inputs:

Distributor pickup (RPM)
Map sensor (also used to read outside air pressure known as baro-read)
Coolant temp
Charge air sensor
Oxygen sensor
Throttle Position Sensor (T.P.S.)
Detonation sensor
Brake switch
Neutral safety switch
A/C switch
Battery temp

System outputs:

Ignition coil
Auto Shutdown Relay (A.S.D.) power to coil and fuel pump
Alternator field control (charging system)
Idle speed (A.I.S.)
Fan relay
A/C cutout relay
EGR, Purge, Baro and wastegate solenoids
Power loss lamp
Information output to diagnostic connector.

84-87 used the logic module & power module system (think of it as brains and brawn, power module handled all the heavy amp loads controlled by logic module) in 88-89 this was replaced by the Single Module Engine Controller (SMEC) which had both units stuffed in a single "box" under the hood and in 90-93 it was simplified even more by the introduction of the SBEC- Single Board Engine Controller.  All this integration was done to reduce cost & wiring complexity (less connectors, less chances for failures)

System breakdown by year

1984-1987 logic module & power module

1984  A unique combo not wiring compatible with later years for several reasons; used a conventional pneumatic non-computer controlled wastegate set at 7.5 psi, charge air and coolant sensors had large "pin" type connections and were electrically unique internally (12,000 ohm fixed resister in parallel with NTC thermistor rated at 9,120-10,880 ohms at 77F) and used large "GM" style map sensor located near logic module.

LM is based on Motorola 6801U4 microprocessor and includes 6K ROM, 2K external PROM and 192 bytes RAM.

Injectors are "batch" fired in pairs (1+2 & 3+4) with cylinders 3 & 4 receiving "selective enrichment" due to them receiving more air because of the design of the "log" intake manifold.  In 1984 the power module fired the injectors based on sync signal from the distributor and was then fine tuned by the LM. Starting in 1985 ALL injector firing was handled by the LM/SMEC/SBEC

1985 debuted the computer controlled wastegate, map sensor integrated in logic module, GM "weatherpack" sensor connectors for electrically new charge air & coolant sensors (They are just NTC thermistors now, 9,120-10,880 ohms at 77F) and Logic Module fired injectors.

1986 the biggest change was the new larger diameter distributor and pickup- this was done for several reasons including to prevent 85 logic modules being used with 86 engines. The 85 logic modules had a much more aggressive spark curve that wasn't compatible with the new 1986 "swirl port" head.

1987 introduced the Turbo II engine with it's 4 wire AIS motor and cruise control integrated into the logic module. Other changes where GM weatherpack connectors now being used on the TPS and AIS and the introduction of the 3 wire heated oxygen sensor. This was the last year of the LM/PM combo- one important quirk to note for the 1987 model year was that as a general rule of thumb the map sensor was now located under the hood except for all L-bodies (Turbo Omni & Charger) and early P-bodies (Shadows & Sundances)

All 85-87 are the same except for the software burned into the prom chip!  In short there is just 2 basic logic modules- internal or external map sensor units. This means you can take a Turbo I 86-87 internal map sensor LM and have GLHS Turbo II programming "burned" to the chips or you can take a Turbo I 87 external map sensor LM and have 87 Turbo II or 87 CSX programming burned to it. The 85-86 LM used 2 Motorola chips and the 87 and up used a single chip.

The 87 Logic Module used a Motorola 6803 microprocessor with a loop time of 22 milliseconds.

"Loop time" is the time it takes the processor to look at all it's inputs.

All power modules are interchangeable for the 85-87 model years.

1988-1989  Single Module Engine Controller (SMEC)

In 1988 Chrysler swapped over to the SMEC- it had less connections and did away with long wiring runs which could cause warranty problems-  It was cheaper and faster then the LM/PM combo.  It's based on a Motorola 68HC11 microprocessor and includes 6K ROM, 2K external PROM and 192 bytes of RAM.  This microprocessor was twice as fast as the 6807 at had a loop time of 11 milliseconds and can process 62,500 bits of information per second.

In 1989 Chrysler added 4-wire Oxygen sensor to all engines for more precise fuel control and changed the software code used in chip- 88 SMEC is based on 87 LM code! The SMECS are still interchangeable between the 88 and 89 model years however assuming the correct injectors and engine displacement is observed... And as before the Turbo I and Turbo II SMEC are the same units except for the software "burned" to the chip.

1990-1993 Single Board Engine Controller (SBEC)

In 1990 Chrysler came out with the SBEC, can you guess why? "simplification and greater reliability" here is a blurb from the New model technical highlights book:

"The single board unit has a new aerodynamically designed housing to improve air flow. The single board reduces the number of external wiring connections from 74 to 60 compared to the two board single module computer. Simplification is achieved by replacing standard integrated circuits with application specific integrated circuits. These ASIC's are both smaller and provide more functions then the standard IC's. One of these called Collage II replaces four separate input-output devices used previously."

In the late 89 model year Chrysler added sequential injector firing to the 2.2/2.5 engines for smoother idle and better emissions- previous years were "batch" fired.

In 1991 Chrysler introduced the Turbo III engine with DIS distributorless ignition- unfortunately a unique SBEC due to the coil pack driver circuit used on the 16V engine (It has more in common with the 3.3V6 SBEC then the common 2.5 TI SBEC). The Turbo III had the most precise fuel/spark calibration software of all the 2.2 liter family.

The Major Sensors

Distributor hall effect pick-up (HEP)

The most important sensor in the system- without it the car doesn't run!  Supplies TDC piston & camshaft location data to ECU for proper ignition timing and injector firing.

Manifold Absolute Pressure sensor (MAP)

The MAP sensor is the second most important sensor in the system, of all the sensors it has the most authority over fuel. It can starve or flood an engine.

The map sensor works on a 0-5 volt range, for a turbo 2-bar map at sea level use the following table...

30 inches of mercury = 0-.3 volts
0 boost/0 vacuum = 2.4-2.5 volts
15 psi of boost = 4.9-5.0 volts

This is why zenier diodes work to prevent overboost shutoff- For example most Turbo II computers are set to shut off the engine if map voltage exceeds 4.7 volts... however if you install a 4.6 volt zenier diode on the map sensor output line when the voltage from the map sensor hits 4.6 volts the diode shunts the extra voltage to ground. Hence preventing the computer from seeing boost over the 4.6 volt mark and keeping the computer from shutting the engine off at higher then stock boost levels.

1984 4.30 V 4.30 V Instant
1985 4.65 V 4.54 V 2 Sec
1986 4.88 V 4.65 V 1 Sec
1987 4.88 V 4.65 V 1 Sec
1987 TII n/a 4.65 V 1 Sec

Remember if you fool the computer into NOT seeing overboost over 14 psi via bleeds or diodes you must make sure you have plenty of fuel to keep from burning the engine up!

Throttle Position Sensor (TPS)

The TPS sensor is the third most critical sensor in the system- The TPS has different types of authority. If the throttle is opened slowly the TPS has very little authority over fuel, however if the throttle is "snapped" open the TPS has as much authority over fuel as the map sensor as long as the TPS voltage is increasing!

Other functions of the TPS sensor...

1) Recognizes idle- SMEC will use AIS and timing to control idle speed once it see the TPS at idle position.
2) Recognizes off idle condition- Timing is added as soon as min TPS voltage is exceeded by .02 volts.
3) Dashpot function- AIS motor is kicked open a slight bit in preparation for decel, this also happens when min TPS voltage exceeds .02 volts.
4) Flooded engine- If more then 2.43 volts above min TPS the computer will go to 0 pulsewidth while cranking assuming a flooded motor.
5) WOT- at 1.8 volts over min TPS the computer recognizes this as WOT and the system will go into open loop and shut the a/c off as well.

Coolant sensor

The forth most important sensor in the system- the coolant sensor has a lot of authority over fuel when the engine is cold but not very much when the engine is hot.  Think of it as a choke on a carburated vehicle.. And of course it provides data to the ECU for the cooling fan schedule!

Resistance values of a good coolant sensor
(all the coolant sensors are the same- Turbo, N/A & V6, except for '84 with the funky pins)

32F Degrees =  29,330-35,990 Ohms
77F Degrees =    9,120- 10,880 Ohms
212F Degrees =          640-720 Ohms

Charge temperature sensor

The fifth most important sensor in the system, the CTS has a limited authority over fuel and this only happens when it senses very cool air in the intake manifold. Temps over 220 degrees the sensor has no authority over fuel at all.

Resistance values of a good charge air sensor (yes it's the same as coolant sensor but plastic!)

32F Degrees =  29,330-35,990 Ohms
77F Degrees =    9,120- 10,880 Ohms
212F Degrees =          640-720 Ohms

Oxygen sensor

The O2 sensor "tells" the engine controller that the fuel mixture that was just burned was rich or lean- The ECU then uses this information to "fine tune" the mixture. The only time the ECU ignores the O2 sensor is first start up and at WOT.

Battery temp sensor

The battery temp sensor is a 10,000 ohm resister that varies its resistance opposite of temperature. The colder the battery the higher the charging system voltage will have to be for the battery to be properly charged.
Inside the power module/SMEC/SBEC casing there is no way to test aside from interrogating ECU with a scanner (it's mounted to the printed circuit board).

Detonation sensor

The detonation sensor is a piezoelectric crystal that outputs a a/c sine wave when squeezed or "flexed" in the 6,000 to 6,300 hertz range. The output of the sensor may go as high as 6-8 volts under severe detonation- This voltage sine wave happens so fast that an oscilloscope is needed to "see" the actual output. The computer will "dial back" the distributor timing in 2 degree increments to a maximum of 14 degrees (This figure is for WOT).

In 1984 this was for all cylinders; 1985 and up it was just for the one that's detonating based on the sync signal from the distributor.  Also on the 1985 and up engines the electronics will alter the duty cycle of the wastegate solenoid to reduce boost to also retard detonation.

Software bit's and snits. (otherwise knows as weird stuff my mopar does)

1)  Chrysler uses the map sensor to check outside air pressure using the baro read solenoid, basically it just exposes the map sensor line to outside air for a second to take a reading. Some years the computer checked while the car was on a decel when the throttle was closed and some checked when you turned the ignition key right before cranking.

2) Most cooling fans come on at 210 degrees, shut off at 200.  At speeds over 45 mph, 220 on, 210 off.

"The ECU will close the fan relay based on engine temperature (coolant sensor) and car speed (speed sensor). The ECU will turn the fan on at any speed when the temperature is above 240F. The ECU will turn the fan off at any speed when the temperature is below 210'F. In between these temperatures the fan may be on or off depending on the coolant temperature vs. car speed. For example, if the coolant  temperature is 215'F and the car speed is 55 MPH, the fan is off. If the car slows down below 45 MPH the fan turns on. If the coolant temperature is 230F and the car speed is 30 MPH the fan is on. If the car speeds up above 35 MPH, the fan turns off."

3) The cooling fan comes on to blow steam under the car! I'm not making this up! Ever wonder why your car would suddenly turn the fan on while sitting at a light and it wasn't even hot? It seems that an engineer at Mopar noticed that under certain conditions condensation on the radiator would "boil off" as the car was warming up and to a customer it looked like the radiator had a leak and was steaming! The fix? Turn the fan on when the car stopped moving under these "certain conditions" and blow it under the car out of sight!

"This system also has an anti-steaming feature. This feature prevents moisture from rising up from the radiator when the car is stopped. When the coolant temperature (as  indicated by the coolant sensor) is below l00F and the ambient air temperature (indicated by the battery temperature sensor in the power module) is below 60F, this "tells" the logic module that conditions are right for radiator steaming to happen. If the engine is started under these temperature conditions, the logic module will start a 2 minute timer when the coolant temperature is 180'F. After 180'F, if the car is stopped (as determined by the speed sensor) while the 2 minute timer is running, the fan is turned on for a maximum of 2 minutes or till the car starts to move. If the car is driven the whole 2 minutes while the timer is running, ram air will evaporate the condensation on the radiator."

4) GLHS LM turn the cooling fan on as soon as the car sees 3-4 psi of boost. This was done to head off overheating- the GLHS had very small radiators and fans.

5) Stock GLHS LM limits the boost at peak torque of the 2.2 engine so the transaxles limit of 175 ft/lbs isn't exceeded.

6) The 89 2.5 Turbo SMEC limited boost to 7 psi till 4000 where it was raised to 11 psi- this was so the engine never exceed 180 ft/lbs of torque which was the limit of the automatic transaxle.  Later "high torque" 2.5 turbo motors with the manual transmissions had normal boost scheduling and revised fuel and spark curves.

7) All 2.2's had fuel cutout at 6650 RPM, 2.5's were 6200 RPM.

8) Speed limiters were incorporated into the SMEC's in 1988,  118 mph for the Turbo I automatic cars. This was done mostly due to tire speed ratings from the factory.

9) Same thing with the 88-93 cruise control, for safeties sake it will set no higher then 85 mph.

10) Speaking of cruise control- why it works with some controllers and not others? Because not all controllers have the cruise control circuitry built in them! Basically Chrysler saved money by only including the circuitry only in the SMECS/SBECS on cars that were ordered with cruise control. That's why some Mopar Performance modules have functional cruise control and others do not- they are reman units that the remanufacturer has no idea if the unit has cruise or not.  That's why in the MP catalog they state cruise control may not function.

11) Computers generally go into O2 feedback as soon as the computer sees the oxygen sensor is up to temperature- the exception to this is if it's very cold out (below 40-50 degrees) it will wait till the engine hits a predetermined temperature (roughly 80-95 F depending on application and year) before going into feedback mode.

12) At WOT the computer ignores the oxygen sensor.

13) If you hold your gas pedal to the floor and try and start the car it wont- computer is programmed to shut the injectors off it sees WOT during cranking because it assumes the engine is flooded. (this works most of the time)

14) The smec/sbec cars increase the fuel pressure 10 psi during a hot restart (engine over 176 degrees) It does this by grounding the purge solenoid which blocks off all vacuum to the fuel pressure regulator hence raising the pressure during cranking.

15) 2.2/2.5 TBI TPS sensor rotate BACKWARDS compared to Turbo/V6/V8 TPS- installing one from a 2.2 TBI car will give you a no start because the computer things it's at WOT during cranking!

16) Did you know Mopars had a battery temperature sensor? YUP! it's right inside the 85 and up Power Module /SMEC/SBEC casing! It's used to adjust the charging rate of the battery. (cold batteries are harder to charge so need more voltage)

17) At WOT the computer shuts off the a/c compressor.

18) Map sensors- If the part number is in black it's for a TBI controller, a red part number is for a turbo.

19) Injector flow rates and applications; all the below injectors are low impedance, 2.4 ohms.

2.2 Turbo 1 injectors flow 27 pph
2.5 Turbo 1 injectors flow 33 pph
2.2 Turbo 2 injectors flow 33 pph
2.2 Turbo 3 injectors flow 33 pph
2.2 Turbo 4 injectors flow 33 pph
Super 60 Injectors flow 52 pph

20) injector duty cycles of the various engine packages;

2.2 Turbo 1  85% at 5200-5600 @13-14psi.
2.5 Turbo 1  85% at 5200-5600 @13-14psi.
2.2 Turbo 2  85% at 5200-5600 @13-14psi.
2.2 Turbo 3 100% at 6144 rpm @12-14 psi
2.2 Turbo 4  85% at 5200-5600 @13-14psi.
Super-60      80% at 5800 rpm @ 18 psi

Mopar Performance Computers including the S-60 SMEC

All M.P. computer are re-manufactured units that have been reprogrammed for additional boost and raised map sensor cutoff.  They do not have a raised rpm limit nor do they supply additional fuel (your stock computer supplies just as much fuel at 13 psi as a MP unit does).

Except for the the two "Shelby" L.M.'s none are CARB (California Air Research Board) emissions exempt- As a matter of fact some have no O2 feedback at idle and run quite rich at idle! The non-CARB exempt units seem to have random programming at times- people have reported no problems at idle using one while others had to swap back to a stocker to pass state emission testing. (I have seen this in several units, we have emission testing here in the Northeast)

The S-60 unit is a 88-89 SMEC that has been calibrated for 52 pph injectors & 28 psi General Motors MAP sensor. (GM part number 16040749) Stock Turbo I injectors flow 27 pph and stock Turbo II & the 2.5 Turbo I injectors flow 33 pph.  Important things to remember before moving on-

1)  GM map sensor WILL NOT WORK with any other SMEC besides the S-60 unit.
2)  52 pph injectors will not just "drop in" and work with any stock SMEC either.
3)  This is a 89 Turbo Trams-Am part- it is NOT the same as a Grand National.

Remember the Chrysler electronics are built around a "speed density" system- they have some room for corrections but not enough if things get to far out of spec! The S-60 package is based around a certain cylinder head, cam, intake, turbo, intercooler combination.  It makes 300 crank hp at 18 psi of boost. (Stock Turbo II is 174 hp at 12 psi, Turbo III's however make 224 hp at 10-11 psi) You can run a S-60 computer around in a stock combo but it will be very, very rich- Speaking of rich, guess what? S-60 has NO O2 feedback AT ALL. Not at cruise nor idle, it was considered a race only package so the O2 software was left out. So if your engine package is a little out of spec the computer has no way to compensate and will be rich.

Another feature of the S-60 SMEC which is unique is a dual boost setting- grounding one of the pins going into the SMEC switches the boost from 14 psi to 18. The S-60 SMEC has been internally modified for this feature.

The boost cutoff point for the S-60 computer is 22 psi. The 52 pph injectors cannot support hp levels over that point. (approximately 320-340 hp at stock fuel pressure settings)


1) The 84's were SUPPOSED to have the internal map sensor setup like the 85-86 cars... The logic module has the cutout for the sensor and examination of the Logic Module circuit board clearly shows spots where the map sensor wiring was to be attached... perhaps Motorola could not supply the required number of sensors in time hence that's why mopar used a GM style map sensor this one year?? (I'm just speculating)

2) key delay programing- This one I'm fuzzy on because it's been a long time since I have read about it... Basically Shelby had a few computers in the road test cars that if you delayed cranking the engine over 15-30 seconds AFTER turning the key on the computer would select a different engine calibration with hotter spark and more boost... anyone have more info on this or a link to the information??

3) Tim Pettijohn answering a question on the SDML mailing list about SBEC with an odd extra connector that was purchased at the Shelby auction ...

"To answer Joe Anderson's question about the Development SBEC's "mystery wire" the answer is: These computers were equipped with "DUAL" E-PROMS. Chrysler has a name for them but, I'm drawing a blank right know. Anyways, (my 1990 Prototype has one of these) the purpose of the computer is to help the Driveability Engineer in the development process while he is using the "Interrogator Tool". He can make changes on the fly to one E-PROM, pull over and connect the "wire" to check the base "E-PROM's" program. Sounds pretty cool except......when the battery is disconnected.....the "on the fly" program is erased !

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