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Junkyard MPI
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Junkyard MPI

Date Created: 04/22/2008
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I couldn't afford the $2000 kit from Hesco, but Hesco will actually sell individual pieces. You can even download their intallation instructions, so the details I leave out can be found in there. I got all of my junkyard parts off of a 95 Cherokee 4.0.

Here is what you will need.

- Intake manifold w/ throttle body, fuel rail etc.

- Engine wiring harness w/ PDC( I found the wiring to be easier with the PDC)

- ECM (Computer)

- E200 Fuel Pump (From some Ford trucks)

- Coil

- Distributor

- Fuel pump block off plate (For a big block Chevy)

- O2 sensor

- Thermostat housing and temp sensor

- Throttle cable

- Map sensor

Then I placed an order to

- Dampner

- CPS mounting bracket

- Diode from Hesco to hook to alternator wire

I then started removing all of my stock parts I did not need:

- Vacuum lines and other emissions equipment (thank God)

- Carb and Intake Manifold

- Engine wiring harness and computer

- Pulse air system (the holes on the cat and exhaust need to be closed)

- Distributor

- Coil

- Exhaust to replace the gasket

The only real modifications I had to do was to the intake manifold (had to grind down some areas of it to make it fit with my stock 258 exhaust) and of course the wiring harness needs to be weeded out and modified, but I will get into that later.

It cost me $169 for the damper, $7.95 for the diode and $75 for the bracket from Hesco. The intake etc I found at my local pull a part and ebay I found new cps and o2 for $5 and $10. I took my time to shop for parts and got them all really cheap!

The hardest part was figuring out the wiring. You want to be sure to get the complete harness, from the bulkhead to the PDC. This was actually a pretty fun and easy project.

You can find anything on Ebay cheap I got an almost new intake w/ all the sensors etc for around $5 I forgot how much I paid for shipping but my budget never passed $400

A few Part numbers:

CPS #56026884

The VSS or vehicle speed sensor is something I have not installed yet because you dont actually need it to run, but it will supossedly run better and get better fuel mileage with one. The part number is 56027015

There is also a plastic adapter I think we will need for it to work with our original speedo cable.

The plastic speedo adapter changes the thread from the 5/8 male thread to a 7/8 male thread so the original cable will still fit. It can be found on a '87-'90 Jeep XJ/MJ, on the black plastic cruise control speed sensor that is under the dash. It's mounted on the speedo cable, about 8" down from the speedometer head. Unthread the large cable end and remove the adapter.

I have not done this yet so dont consider this fact.

Here is the link to the MPI Installation instructions. Remember they wont be exactly the same, but they will help with removal and installation steps. They are in PDF format:

Here is a pic of the intake manifold. I just had to cut down some of the "ribs" between the ports and I hand to shave a little of the lip that bolts to the head on a few ports. I used and angle grinder and a dremmel tool to do all of this. You do however want to be carefull not to cut into the ports. And be sure to get any shavings that might get into the ports out before you bolt it on. I dont think you will be able to put the 4.0 exhaust on a 4.2 head. The ports on the heads are not the same and I dont think they will bolt up, so "shaving" the 4.0 intake is probably your best bet. You can see the "ribs" Im talking about between the ports that have been cut out. You can also cut off the power steering bracket that would be on the right of this manifold. I just would cut a little off and then try it on my jeep, you will see what needs to be cut as you go. You will also need to cut your Cjs power steering bracket.

This is what your harness will resemble.

Notice the PDC (the rectangular black box), the plug for the PCM, and the bulkheads. You want to make sure you have a complete harness (even though you will cut out most of it.)

Now comes some wiring. The pics are of the bulkheads on the cherokee harness.

Here is part of the bulkhead.

You need to keep H2 on this one.

Here is the other part of the bulkhead:

You need to keep:




Now for even more wiring:

If you are looking at your engine management plug in the face, the upper left pin is number 1 and the lower right pin is number 60. THe middle row is 21 to 40, left to right. The alignment tabs will be on the bottom. The Number refers to the pin.

1. DG/RD Map Sensor - Located on the Manifold

2. TN/BK Engine Coolant - Thermostat Housing

3. RD Fused (+) current (Constant Battery Power)***

4. BK/LB Sensor Ground

5. BK/WT Ground (ground this!)***

6. VT/WT 5 Volt Supply - From Computer

7. OR 8 Volt Supply - From Computer

8. ___EMPTY___

9. DB Ignition Switch Output (Key On Power)***

10 VT Power Steering Sense Switch (used only on 4clys)

11 BK/TN Ground

12 BK/TN Ground

13 LB/BR Injector 4 Driver

14 YL/WT Injector 3 Driver

15 TN Injector 2 Driver

16 WT/DB Injector 1 Driver

17 ___EMPTY___

18 ___EMPTY___

19 GY Ignition Coil Driver**

20 DG Generator Field Driver**

21 BK/RD Intake Air Temp (On the Manifold)

22 OR/DB Throttle Position Sensor (On the Throttle)

23 ___EMPTY___

24 GY/BK Crankshaft Postition Sensor (Back of Engine or Crank)

25 PK SCI Transmit (Tranny(AW4) or Diagnostics, if needed)***

26 VT/BR CCD BUS (+)(Tranny(AW4) or Diagnostics, if needed)***

27 LB A/C Cycling Switch

28 LG A/C Pressure Switch Output

29 WT/PK Brake Light Sensor (I never hooked it up?)***

30 BR/YL Park/Neutral (I never hooked it up)***

31 DB/PK Radiator Fan Relay (I would reccomend an aftermarket)***

32 BK/PK Check Engine*** (neutral switched)

33 TN/RD Cruise Control Vacuum Relay

34 DB/OR A/C Compressor Relay

35 ___EMPTY___

36 DG/YL Generator Lamp Driver (I run a voltmeter...)***

37 ___EMPTY___

38 PK/BK Injector Number 5

39 GY/RD Idle Air Control (Throttle Body)

40 BR/WT Idle Air Control (Throttle Body)

41 BK/DG Heated O2 Sensor (Exhaust Manifold)

42 ___EMPTY___

43 GY/LB Tachometer Signal***

44 TN/YL Camshaft Postiton Sensor (distributor)

45 LG SCI Recieve (Tranny(AW4) or Diagnostics, if needed)***

46 WT/B CCD Bus (-) (Tranny(AW4) or Diagnostics, if needed)***

47 WT/OR VSS (Trnasfer Case)**

48 BR/RD Cruise Control Coast

49 YL/RD Cruise Control On/Off

50 WT/LG Cruise Control Resume

51 DB/YL Automatic Shutdown Relay*** (should be with fuse block)

52 ___EMPTY___

53 LG/RD Cruise Control Vent Solenoid

54 OR/BK (2.5 Auto Olny)

55 ___EMPTY___

56 ___EMPTY___

57 DG/OR Automatic Shutdown Relay Output*** (Should be in fuse block)

58 LG/BK Injector 6 Driver

59 VT/BK IAC Driver (throttle body)

60 YL/BK IAC Driver (throttle body)

This is the plug that goes through the computer. You can weed out everything you dont need, It should be self explanatory of what you need but be sure to double trace your wires so you dont accidentally cut something you need.

From the bulkhead the wires should go like this to the cj:

Cavity E4 (10G Red) to cj 12V Constant (I used the pos side of starter solenoid)

Cavity H2 (14G Yellow) to Cj (+) during crank(I spliced to the red wire that went to the old coil)

Cavity B6 (12G Dark Blue) to Cj (+) crank and run (I spliced to the red wire that went to the old spark control module)

Cavity C4 (14G Dark Green) to (+) side of E2000 Fuel Pump

Notice the pdc on the left fenderwell.

Where I cut the power steering bracket

Here is the stuff for reading the check engine light:

I dont think this is all of the codes, but some of them should be correct.

Start with the ignition off. Within five seconds, switch the key on, off, on, off, on. ("On" is NOT "Start" and "Off" is NOT "Lock"). The "check engine" light will flash. Count the flashes. Each code is a two digit code, so a (for example) 23 would be FLASH FLASH (pause) FLASH FLASH FLASH (long pause). It will never flash more than 9 times, so watch for those pauses!

11 No ignition reference signal detected during cranking OR timing belt skipped one or more teeth; OR loss of either camshaft or crankshaft position sensor.

12 Battery or computer recently disconnected

13 MAP sensor or vacuum line may not be working

14 MAP sensor voltage below .16V or over 4.96V

15 No speed/distance sensor signal

16 Loss of battery voltage detected with engine running

17 Engine stays cool too long (bad thermostat or coolant sensor?)


17 (1985 turbo only): knock sensor circuit

21 Oxygen sensor signal doesn't change (stays at 4.3-4.5V). Probably bad oxygen sensor

22 Coolant sensor signal out of range - May have been disconnected to set timing

23 Incoming air temperature sensor may be bad

24 Throttle position sensor over 4.96V

25 Automatic Idle Speed (AIS) motor driver circuit shorted or target idle not reached

26 Peak injector circuit voltage has not been reached (need to check computer signals, voltage reg, injectors)

27 Injector circuit isn't switching when it's told to (TBI)

OR (MPI) injector circuit #1 not switching right

OR (turbo) injector circuit #2 not switching right

OR (all 1990-) injector output driver not responding

- check computer, connections

31 Bad evaporator purge solenoid circuit or driver

32 (1984 only) power loss/limited lamp or circuit


32 EGR gases not working (1988) - check vacuum, valve


32 (1990-92) computer didn't see change in air/'fuel ratio when EGR activated - check valve, vacuum lines, and EGR electrical

33 Air conditioning clutch relay circuit open or shorted (may be in the wide-open-throttle cutoff circuit or normal on early 80's models if you don't have air conditioning)

34 (1984-86) EGR solenoid circuit shorted or open


34 (1987-1991) speed control shorted or open

35 Cooling fan relay circuit open or shorted


35 idle switch motor fault - check connections

36 (turbo only) Wastegate control circuit open or shorted

37 Shift indicator light failure, 5-speed


part throttle lock/unlock solenoid driver circuit (87-89)


solenoid coil circuit (85-87 Turbo only)


Trans temperature sensor voltage low (1995 and on)

41 Alternator field control circuit open or shorted

42 Automatic shutdown relay circuit open or shorted


42 Fuel pump relay control circuit


42 Fuel level unit - no change over miles


42 Z1 voltage missing when autoshutdown circuit energized (The Z1 voltage is the voltage of the circuits fed by the autoshutdown relay. This typically includes fuel pump and switched-battery feed to the ignition coil)

43 Peak primary coil current not achieved with max dwell time


43 Cylinder misfire


43 Problem in power module to logic module interface

44 No FJ2 voltage present at logic board


44 Logic module self-diagnostics indicate problem


44 Battery temperature out of range

45 Turbo boost limit exceeded (engine was shut down by logic module)

46 Battery voltage too high during charging or charging system voltage too low

47 Battery voltage too low and alternator output too low

51 Oxygen sensor stuck at lean position (this may be tripped by a bad MAP sensor system causing a rich condition. If you get hot rough idle and stalling, especially on deceleration, accompanied by flooded engine and difficulty restarting, that can be a bad MAP sensor causing the O2 sensor to try to compensate. If you get poor cold driveability, stumbling and bucking, and acceptable warm driving with poor gas mileage (a drop of 10 mpg or more), that is usually the O2 sensor.


51 Internal logic module fault ('84 turbo only).

52 Oxygen sensor stuck at rich position


52 Internal logic module fault ('84 turbo only)

53 Logic module internal problem

54 No sync pickup signal during engine rotation (turbo only)


54 Internal logic module fault ('84 turbo only) - or camshaft sensor/distributor timing

55 End of codes

61 "Baro" sensor open or shorted

62 EMR mileage cannot be stored in EEPROM

62 PCM failure SRI mile not stored

63 Controller cannot write to EEPROM

64 Catalytic converter efficiency failure

65 Power steering switch failure

Just another pic of the cleaned up engine bay.


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