GM MEFI Computer / Crate 502 Engine Computer

[dave w]

I'm wondering if anyone has information, links, write ups, or internet form posts about the GM MEFI computer used with a GM Crate 502 engine?

I've found MEFI Scan & Tune, which really stresses the budget. http://www.aldlcable.com/sc/toplevel.asp?cat=32.

I'm hoping to find wiring schematics, and how to pull trouble codes. The engine is up and running, but very poorly. Maybe something is wired wrong, but without schematics I don't know. I'm thinking I need to wire a SES light? I'm trying to figure out how to pull trouble codes, without an expensive scan tool.

Thanks,

dave w

[Buzz]

You didn't mention if this was a friend or a customer ... so some varying options are available.

If it is a friend ... then perhaps a referral ... high-end marina's or custom boat builders often have MEFI tuning software.

If it is a customer ... the easiest course of action for you is to treat this as an 0411 swap (just like with an older Vortec truck). The 502 as the plastic front timing cover - but the CKP hole will be plugged (or solid). Add a 4x CKP reluctor, CKP sensor, a Vortec style distributer, rework the wiring harness, and you are good to go.

The resultant tune will be 100% custom, but if you have a WBO it shouldn't be a problem. If you have a RoadRunner even quicker to do.

[dave w]

You didn't mention if this was a friend or a customer ... so some varying options are available.

If it is a friend ... then perhaps a referral ... high-end marina's or custom boat builders often have MEFI tuning software.

If it is a customer ... the easiest course of action for you is to treat this as an 0411 swap (just like with an older Vortec truck). The 502 as the plastic front timing cover - but the CKP hole will be plugged (or solid). Add a 4x CKP reluctor, CKP sensor, a Vortec style distributer, rework the wiring harness, and you are good to go.

The resultant tune will be 100% custom, but if you have a WBO it shouldn't be a problem. If you have a RoadRunner even quicker to do.

It's potential customer ... I'm wanting to pull trouble codes if possible. If I can't pull codes, I might as well leave with my tail between my legs.:yikes:

0411 swap seems like a distant option at this point in time.

Thanks,
dave w

[Nasty-Z]

It's potential customer ... I'm wanting to pull trouble codes if possible. If I can't pull codes, I might as well leave with my tail between my legs.:yikes:

0411 swap seems like a distant option at this point in time.

Thanks,
dave w

Dave ,

I have sent a few emails / texts to some people I know in the Marine field who might / might not deal with this.

If I can come across something I will report back.

TOM

[dave w]

I found this link: http://www.pirate4x4.com/tech/billavista/MEFI/

Has information for Trouble Codes.

dave w

[roughneck427]

Lyndon from westers had mentioned i forgot where on a forum that the interface is the same as the obd1 LT1 i was going to make a crossover connector to use on a mefi aldl setup but the guy never got back to tune it so i never pursued it. I did find some schematics online on some marine forums for the data wire and whatnot on the mefi aldl. I know on efi live forum a guy was building a def file to scan with efilive V4

http://forum.efilive.com/showthread.php?3418-MEFI-4-ECM-definition-file

http://www.marinepowerusa.com/download-delphi-mefi.php

[EagleMark]

I think they come with TunerPro RT definitions, so who ever bought that system should have the files needed? Cable is another story...

[1project2many]

Dave...

I had MEFI 2 in my Chevelle. I have some info. I have some software. I have some wiring diagrams.

Here's a page from my old site with info to get codes from MEFI 1 and 2. Might work with MEFI 3, 4, 5. Learned much since that page was put up.

lmk if this works. lmk which version of MEFI.
http://www.grolen.com/shannen/efistuff/

[dave w]

Dave...

I had MEFI 2 in my Chevelle. I have some info. I have some software. I have some wiring diagrams.

Here's a page from my old site with info to get codes from MEFI 1 and 2. Might work with MEFI 3, 4, 5. Learned much since that page was put up.

lmk if this works. lmk which version of MEFI.
http://www.grolen.com/shannen/efistuff/

Thanks 1project2many!

The question I have is about what to use for a MIL. Do you have manufacture / part number that will work with MEFI?

Maybe the LED light I've been using for a MIL with the '0411 PCM will work with the MEFI? http://www.k-four.net/Product.aspx?pid=68

dave w

[Nasty-Z]

Here are a couple of links I was forwarded . Marine based , but might be of some help

http://www.boatfix.com/merc/techbk/96/96hgd4.pdf

http://www.michaelstractors.com/forum/topic.asp?TOPIC_ID=199

HTH

TOM

[1project2many]

I used an expensive test light from Snap-On. It's only about $30!!!

The LED should work. So should the same #194 bulb that's used in most dashboards. Even a low impedance light will work if you put some resistance in series.

My understanding of MEFI3 and up is that when the calibration is password locked it can't be read without the same password, although it can be overwritten at any time. I have a single calibration here for a 502 from a MEFI 1

MEFI controllers that I've tuned are different than automotive counterparts. They don't bother calculating airflow or AFR. You enter the desired injector on time based on MAP and RPM. The MEFI 1 BPW vs MAP and RPM table begins at 40 kPa and goes to 100 kPa in 20 kPa increments. There is not as much resolution for tuning. There are several safety switch options such as engine overtemp, low oil pressure, low coolant flow, and emergency stop that can all affect your success. MEFI controllers are able to use O2 sensors in closed loop and can receive input from a VSS. They also use a trim sensor although I have never considered how that affects off-water use or how it can be modified to help road going applications. AS&M used to charge big money to "convert" an open loop cal but as most of use know, there isn't much involved in flipping a bit and adjusting a temp setting or two. The big thing they offered was the schematics to connect the sensor. Again, this may not apply to MEFI 4 and 5.

In the 1 and 2 controllers, code is stored in the controller and only calibration data downloaded / uploaded for adjustment. I'm told the upload/download process is very similar to programming an OBDI LT1 or the 92-94 Cavalier 2.2 with manual trans. I'll upload some calibration data I have for a specific MEFI1 calibration as it should be with the caldocs data. This info could be used to make a very complete TP definition file.
http://gearhead-efi.com/caldocs/MEFI9321.pdf

[1project2many]

Here are some additional documents that apply to MEFI. The Mercruiser scan tool manual gives trouble codes and scan tool functions for anyone attempting to make an ADX for TunerPro. The two .jpg images are wiring connections for MEFI 1 and 2 showing, among other things, the connection points for an O2 sensor (J2-16 is LOW and J2-17 is Signal). Once upon a time, you could download TTS scantool software for MEFI. I don't know if it's currently available or if it works with other ecm's but it did allow a free trial period.

[dave w]

I visited with the MEFI 502 vehicle owner yesterday (56 Cadillac). I thought I'd share some pictures. The computer is either MEFI 3 or MEFI 4.

Thank you to everyone who helped me with information!:thumbsup:

I found two trouble codes, 34 & 81. I found the wiring for the stand alone 4L80E TCU was not correctly spliced into the MEFI harness (5 volt reference). The engine runs, but the idle is 2800 ~ 3200 RPM's!:yikes: I need better diagnostics. Maybe the MAP or TPS was fried with the incorrectly wired 5 volt reference.

I used one of the high speed printers from work to print the 300+ page .pdf files (2 minutes 14 seconds print time for double sided print) and gave printed pages to the Caddy owner.


dave w

[1project2many]

Wow... That's a nice looking project.

I have a copy of the free-to-download version of TTS Datamaster if there isn't one currently available. I've never tried it but if you need a copy lmk. There used to be a copy of the converter circuit used with the Diacom software. You can build simple circuits well enough... Old software works on DOS / LPT port if you have a machine that can run it.

[Nasty-Z]

I visited with the MEFI 502 vehicle owner yesterday (56 Cadillac). I thought I'd share some pictures. The computer is either MEFI 3 or MEFI 4.

Thank you to everyone who helped me with information!:thumbsup:

I found two trouble codes, 34 & 81. I found the wiring for the stand alone 4L80E TCU was not correctly spliced into the MEFI harness (5 volt reference). The engine runs, but the idle is 2800 ~ 3200 RPM's!:yikes: I need better diagnostics. Maybe the MAP or TPS was fried with the incorrectly wired 5 volt reference.

I used one of the high speed printers from work to print the 300+ page .pdf files (2 minutes 14 seconds print time for double sided print) and gave printed pages to the Caddy owner.


dave w

Wow , that's sweet :rockon:

TOM

[roughneck427]

as seen in the instuctions its the same cable used on the obd1 stuff all you need is serial and a ground crossover your obd1 scan cable. I tried to find the post but i think it was on monodax long ago that indeed the obd1 cable was same to flash as the obd1 LT1 stuff.

[1project2many]

I was asked several weeks ago where to find Datamaster for MEFI. I've had this on my laptop for years but I'm not sure if they support it any more.

Also, here's a list of pinouts that was posted to Monodax years ago.
MEFI CONTROLLER CONNECTIONS

MEFI 1

J1 Connector:
J1-1 Knock Sensor Input
J1-2 Coolant Temp. Sensor Input
J1-3
J1-4 I/O Fluid Level Switch
J1-5 Master/Slave (twin engine application)
J1-6 Oil Pressure Switch
J1-7 Diagnostic Output (blink light)
J1-8
J1-9 MAP Sensor Input
J1-10 TPS Sensor Input
J1-11 12V Ignition
J1-12
J1-13 Sensor Ground
J1-14 ECM Ground
J1-15 5V Sensor Reference
J1-16 12V Battery
J1-17
J1-18 Serial Data
J1-19 Water Flow Switch
J1-20 Oil Level Switch
J1-21 Emergency Stop Switch
J1-22 Trans Temp / Trim Set
J1-23
J1-24 Intake Air Temp. Sensor Input
J1-25 Trim Sensor Input
J1-26
J1-27
J1-28
J1-29 Sensor Ground
J1-30 ECM Ground
J1-31 5V Sensor Reference
J1-32 12V Battery

J2 Connector

J2-1
J2-2
J2-3
J2-4
J2-5 Injector Driver
J2-6 Distributor Reference Low
J2-7 Port Fuel Jumper
J2-8 Distributor Reference High
J2-9 Fuel Pump Relay Driver
J2-10
J2-11 Coolant Lamp Output
J2-12 RPM Reduction Warning Buzzer Output
J2-13 Idle Air Control Coil A Low
J2-14 Idle Air Control Coil B High
J2-15 Fuel Injector Ground
J2-16
J2-17
J2-18
J2-19
J2-20 Fuel Injector Ground
J2-21 Fuel Injector Driver
J2-22 Port Fuel Jumper
J2-23 Ignition On Control (Spark Out)
J2-24 Ignition Bypass (For Timing Set)
J2-25
J2-26 I/O Fluid / Water Flow Lamp Output
J2-27 Oil Pressure Lamp Output
J2-28 Idle Air Control Coil A High
J2-29 Idle Air Control Coil B Low
J2-30 Oil Level Lamp Output
J2-31 Malfunction Indicator Lamp Output
J2-32

[1project2many]

MEFI 2 Controller Pin Outs

J1 Connector:
J1-1 Knock Sensor Input
J1-2 Coolant Temp. Sensor Input
J1-3
J1-4 I/O Fluid Level Switch
J1-5 Master/Slave (twin engine application)
J1-6 Oil Pressure Switch
J1-7 Diagnostic Output (blink light)
J1-8
J1-9 MAP Sensor Input
J1-10 TPS Sensor Input
J1-11 12V Ignition
J1-12
J1-13 Sensor Ground
J1-14 ECM Ground
J1-15 5V Sensor Reference
J1-16 12V Battery
J1-17
J1-18 Serial Data
J1-19 Water Flow Switch
J1-20 Oil Level Switch
J1-21 Emergency Stop Switch
J1-22 Trans Temp / Trim Set
J1-23
J1-24 Intake Air Temp. Sensor Input
J1-25 Trim Sensor Input
J1-26
J1-27
J1-28
J1-29 Sensor Ground
J1-30 ECM Ground
J1-31 5V Sensor Reference
J1-32 12V Battery

J2 Connector

J2-1
J2-2
J2-3
J2-4
J2-5 Injector Driver
J2-6 Distributor Reference Low
J2-7 Port Fuel Jumper
J2-8 Distributor Reference High
J2-9 Fuel Pump Relay Driver
J2-10
J2-11 Coolant Lamp Output
J2-12 RPM Reduction Warning Buzzer Output
J2-13 Idle Air Control Coil A Low
J2-14 Idle Air Control Coil B High
J2-15 Fuel Injector Ground
J2-16
J2-17
J2-18
J2-19
J2-20 Fuel Injector Ground
J2-21 Fuel Injector Driver
J2-22 Port Fuel Jumper
J2-23 Ignition On Control (Spark Out)
J2-24 Ignition Bypass (For Timing Set)
J2-25
J2-26 I/O Fluid / Water Flow Lamp Output
J2-27 Oil Pressure Lamp Output
J2-28 Idle Air Control Coil A High
J2-29 Idle Air Control Coil B Low
J2-30 Oil Level Lamp Output
J2-31 Malfunction Indicator Lamp Output
J2-32

[1project2many]

MEFI 3 Controller Pin Outs

J1 Connector:
J1-1 Fuel Injector Driver A
J1-2 Ignition coil
J1-3 REFLO
J1-4 ECM Ground
J1-5 ECM Ground
J1-6 EGR
J1-7 CKGAGE/GOVOVS
J1-8 RPMCNG
J1-9 MALF Lamp
J1-10 EST
J1-11 IAC Coil B High
J1-12 IAC Coil A Low
J1-13 N/C
J1-14 Knock Sensor 2
J1-15 N/C
J1-16 N/C
J1-17 Injector Driver B
J1-18 EGRIGN
J1-19 O2 Sensor Low
J1-20 ECM Ground
J1-21 GW1LMP/TROLLMP/CNP
J1-22 GW1LMP/TRAN/GOV
J1-23 Fuel Pump Relay
J1-24 BYP
J1-25 Oil Level Lamp
J1-26 Warning Buzzer
J1-27 IAC Coil B Low
J1-28 IAC Coil A High
J1-29 N/C
J1-30 Knock Sensor 1
J1-31 N/C
J1-32 Serial Data

J2 Connector

J2-1 Battery
J2-2 N/C
J2-3 Sensor Return
J2-4 5 Volt Reference
J2-5 ESTOP
J2-6 BOOT
J2-7 Oil Pressure Switch
J2-8 GW2/GOVMOD
J2-9 Load1/Shift Interrupt/LOCKLO
J2-10 Distributor Reference
J2-11 Coolant Temp Sensor
J2-12 Fuel Pressure Sensor
J2-13 N/C
J2-14 N/C
J2-15 N/C
J2-16 O2 Sensor High
J2-17 N/C
J2-18 Sensor Return
J2-19 5 Volt Reference
J2-20 Load Anticipation
J2-21 Master/Slave
J2-22 Diagnostic Test Terminal
J2-23 Oil Level
J2-24 GW1/FCAL
J2-25 VSSVF
J2-26 TPS Sensor
J2-27 MAP Sensor
J2-28 EGRFB
J2-29 OILP
J2-30 MAT Sensor
J2-31 ESC
J2-32 Ignition Power

[1project2many]

MEFI Read/Program Connections:

To read or program the MEFI1 and 2 controllers, you need to make the following
connections:

J1 – 11 Ignition
J1 – 14 Ground
J1 – 16 Battery
J1 – 18 Serial Data
J1 – 30 Ground
J1 – 32 Battery

To read or program the MEFI3 controllers, you need to make the following
connections:

J1 – 4 Ground
J1 – 5 Ground
J1 – 32 Serial Data
J2 – 1 Battery
J2 – 32 Ignition

RS232/MEFI Converter
The RS232 to MEFI converter used to connect a PC to the MEFI controller for
reading and programming is the same converter as that used for the ‘94/95 LT1
PCM.

[dave w]

1project2many,
Thank you for the updated information!:thumbsup:

I think I'll make an adapter plug MEFI / ALDL and see if I can communicate with the MEFI 3 / MEFI 4 computer (I don't know which type it is) that is in the Cadillac. The vehicle is about 70 miles away, so it might be several weeks before I get out that direction.

dave w

[delcowizzid]

anyone working on adx and xdf for this have a mate just cammed his boat on engine builders advice and now the ecu is having a sad LOL 7.4L bbc mercruser

[Munchies]

So whats the deal with the e67 ecus?
Supposedly MEFI5 is the E67 with a different OS.

What kind of secret sauce does mefiburn use? Sounds like the MEFI is a hell of an ecu. can run cable or dbw, 24x or 58x, distributor even..

[roughneck427]

I just bought a 1969 Vdrive flatbottom and has a mercruiser 7.4 it has a mefi I'n it ill be tweaking it here in a few weeks on the water

[delcowizzid]

thats the same engine we have

[roughneck427]

thats the same engine we have


My friend has mefi burn and going to test it out ive never tuned one before and from what I hear its all injector bpw and no ve. I have a mefi 3 controller on it from what I can see im not sure if im going to run it as I looked at the return system of the fuel lines they dumped it back to the suction side of the ext fuel pump I don't know how it affects the tuning ill install a fuel gauge and see what it looks like this weekend in the driveway. What camshaft did you guys run??

[roughneck427]

Well I decided to just buy mefi burn myself. I talked to the owner and nice guy should have it in a couple days ill post the file that I read out.

[delcowizzid]

i dont think you can read out the tune can you.i heard the ecm's are locked from factory and that you have to flash a new tune in to begin playing

[roughneck427]

When I talked to Bob he said when I get the cable try and read it out it will give me a checksum number and he has all the passwords for the mercruiser mefi stuff. I had asked him the same thing he said not an issue

[roughneck427]

I got tts datamaster posted above working using an LT1 cable and a crossover connector