News:

Due to a technical issue, some recently uploaded pictures have been lost. We are investigating why this happened but the issue has been resolved so that future uploads should be safe.  You can also Modify your post (MORE...) and re-upload the pictures in your post.

Main Menu

1979 cadillac fleetwood 425ci ecu fault?

Started by S M TAYLOR, September 21, 2021, 06:44:15 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

S M TAYLOR

Hi there, i have a customers 1979 cadillac fleetwood 425ci v8 efi. Runs terrible. Got auto sparky to have a look at it. He said it has no injection on group 1 and is over fueling on group 2 injectors. Has anyone come across this? We are both abit stumped. Cheers

TJ Hopland

I'm sure Bruce will be along soon to offer suggestions and if need be you can send the ECU to him for testing and repair.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

V63

Mercedes had this system first and injectors were triggered in groups of 2 however Cadillac did it in groups of 4? I had a 73 Mercedes SL and a circuit did 'smoke' on it and I did have it Successfully repaired by a television electronics shop.  So I would tend to think the dead issue of circuit one is causing issues with circuit 2.

bcroe

Quote from: S M TAYLORHi there, i have a customers 1979 Cadillac Fleetwood 425ci v8 efi. Runs terrible. Got auto sparky to have a look at it. He said it has no injection on group 1 and is over fueling on group 2 injectors. Has anyone come across this? We are both a bit stumped.

I am attaching a drawing of the Speed Sensor hookup, mounted on the
lower part of the HEI shaft.  On alternate crank revolutions, one or the
other makes very brief contact, causing a bank of 4 injectors to fire.  If
the contacts of the rotating magnets mess up, you might get something
like you described.  Hard to muscle the engine around, you might pull
the HEI (leave the cap and wires in place) and turn the rotor by hand,
observing a few degrees of each contact closing on your meter. 

HOWEVER, I doubt that is the issue.  IC6 has probably failed in the ECU,
messing up the firing signal.  I suggest you send me the ECU for what
is actually a simple repair, plus checking all, and upgrade of fuel pump
issues common to these cars. 

I am Bruce Roe CLC # 14630, have owned a 79 EFI Cad for 26 years,
and have been repairing these ECUs for quite a while.  DO NOT assume
you can just buy one of these pre digital ECUs, I keep hearing stories
of purchases that do not work, that because no one has the facilities
to test and repair the analog ECUs.  email for a lot more info at
bcroe@juno.com

bcroe

Quote from: V63Mercedes had this system first and injectors were triggered in groups of 2 however Cadillac did it in groups of 4? I had a 73 Mercedes SL and a circuit did 'smoke' on it and I did have it Successfully repaired by a television electronics shop.  So I would tend to think the dead issue of circuit one is causing issues with circuit 2.

The general operation of the 70sCad EFI was published with wiring, and
I have an 11 page schematic of the ECU internal circuit available.  The
bank trigger does not go straight thru, it gets modulated by temp, MAP,
etc to determine the injector pulse WIDTH required.  Things were simpler
in 1973, radios etc were built with discrete transistors, etc.  In 75 the
Cosworth Vega launched EFI using a couple very early Integrated Circuits,
silicon chip packages with lots of parts combined for a complete function. 

Cad built on the Vega design for 76-79, using more than a dozen ICs, an
all electronic MAP, and other improvements.  I do not see working on
these without a complete wiring diagram (not available from the General)
and a test set to provide/measure all signals.  Bruce Roe

S M TAYLOR

Quote from: bcroe on September 21, 2021, 04:56:35 PM
I am attaching a drawing of the Speed Sensor hookup, mounted on the
lower part of the HEI shaft.  On alternate crank revolutions, one or the
other makes very brief contact, causing a bank of 4 injectors to fire.  If
the contacts of the rotating magnets mess up, you might get something
like you described.  Hard to muscle the engine around, you might pull
the HEI (leave the cap and wires in place) and turn the rotor by hand,
observing a few degrees of each contact closing on your meter. 

HOWEVER, I doubt that is the issue.  IC6 has probably failed in the ECU,
messing up the firing signal.  I suggest you send me the ECU for what
is actually a simple repair, plus checking all, and upgrade of fuel pump
issues common to these cars. 

I am Bruce Roe CLC # 14630, have owned a 79 EFI Cad for 26 years,
and have been repairing these ECUs for quite a while.  DO NOT assume
you can just buy one of these pre digital ECUs, I keep hearing stories
of purchases that do not work, that because no one has the facilities
to test and repair the analog ECUs.  email for a lot more info at
bcroe@juno.com

Thank you for the reply Bruce.
Sparky has tested the HEI and everything is working in that aspect.  Have found a bad contact under neath the ic6. Sparky will re solder it to see if that fixes the issue. Does the ic6 need to  be replaced with same part number?  Im in New zealand, so would be a long wait and expense for the ecu to be sent to you for the repair.  Sparky is more than happy to replace the ic6 but availablity this side of the world is abit low. Cheers for your replys.

bcroe

S M TAYLOR, I have sent ECUs to most of the countries where there
are 70s Cadillacs, but it can take quite a while.  For this EFI generation
most of the failures are ICs, and most of of the ICs are very generic
and basic, pretty much available around the world very cheaply. 

The ECU ICs are only marked with a factory code, but my drawings
show the generic type for all but a custom type (peak and hold injector
pulse generator) IC5.  For example IC6 is a COSMOS family 4001 (easily
found on the internet) marked as IC6 in the ECU, but shown as a 4001
on my drawings on SH7.   If you will email me, I will return the entire
11 pages in high res, for the 1979 Cad ECU.  Using these and with a little
more info, you may succeed in repairing the ECU yourself. 

Also check out the first album of my PHOTOBUCKET, a bit dated and
definitely lower res (as the engineer in Poland told me). 
good luck

https://app.photobucket.com/u/bcroe

   click on an Album
   click on a picture to enlarge + description

​BRUCE ROE
5719 EAST SKINNER ROAD,
STILLMAN VLY, IL 61084-9215           Phone 815 234-8039
K9MQG since 1958            solar powered since 2013