TheSamba.com :: View topic - 1975 t4 fuel injection wireharness unplugged & unmarked

Mon Sep 27, 2010 9:24 pm

fuel injection harness was unplugged from the motor and was not labeled, need to know what connectors go where, I looked at the bently and figured out a few connections but cant figure out all the connections, I searched but was un able to find the ansewer,
thanks

Mon Sep 27, 2010 10:08 pm

There are not that many connectors that can be accidentally interchanged, you can check continuity through the harness to figure things out if you need to. All the injectors fire together so they can be swapped without harm.

Tue Sep 28, 2010 8:32 am

A 35 year old harness will likely be so stiff it'll stand up by itself, throw it ontop of the engine with the big ECU connector to the right and most of the connectors will naturally fall in the area they go.

Tue Sep 28, 2010 9:30 am

busdaddy wrote: A 35 year old harness will likely be so stiff it'll stand up by itself, throw it ontop of the engine with the big ECU connector to the right and most of the connectors will naturally fall in the area they go.
lol yeah glue some leaves to it and call it a branch, ha

Tue Sep 28, 2010 11:48 pm

I was tracing out my wiring harness while chasing my Hot Idle Issue and came across this on the Guacamole Bus site (I hope it's ok to post it here).

Wed Sep 29, 2010 8:25 am

sorry to hijack, but...
all the injectors fire at the same time? I'm not saying that I don't believe this but I am pretty surprised by it. shouldn't they be timed to fire as the intake valve is opening? wouldn't that be more efficient.
I had an old 73 volvo 240 w/efi it had a bad brain and I had a spare one that was also bad. one ecu would fire injectors 1&3 the other ecu only fired 2&4 I rewired the injectors to share this signal with the two injectors that were not squirting, it worked, but not too well.
can some one give me the logic behind having them all firing at the same time with Ljet besides the obvious simplicity.

Wed Sep 29, 2010 9:50 am

Not sure if this helps you a whole lot, but here is my '75 harness hooked up:

Larger size at http://www.flickr.com/photos/ilikepeeps/4642295996/sizes/z/in/set-72157624141194528/

Larger size at

http://www.flickr.com/photos/ilikepeeps/4641684957/sizes/z/in/set-72157624141194528/

Patayres also has a 75 and might be able to help you out.

Wed Sep 29, 2010 9:59 am

59walkthru wrote: sorry to hijack, but...
all the injectors fire at the same time? I'm not saying that I don't believe this but I am pretty surprised by it. shouldn't they be timed to fire as the intake valve is opening? wouldn't that be more efficient.
I had an old 73 volvo 240 w/efi it had a bad brain and I had a spare one that was also bad. one ecu would fire injectors 1&3 the other ecu only fired 2&4 I rewired the injectors to share this signal with the two injectors that were not squirting, it worked, but not too well.
can some one give me the logic behind having them all firing at the same time with Ljet besides the obvious simplicity.
1/2 the required dose of fuel in each pulse, the first shot has a couple of nanoseconds to pre vaporize in the intake port until shot #2 comes along and they head for the cylinder.

Wed Sep 29, 2010 11:50 am

59walkthru wrote: sorry to hijack, but...
all the injectors fire at the same time? I'm not saying that I don't believe this but I am pretty surprised by it. shouldn't they be timed to fire as the intake valve is opening? wouldn't that be more efficient.
I had an old 73 volvo 240 w/efi it had a bad brain and I had a spare one that was also bad. one ecu would fire injectors 1&3 the other ecu only fired 2&4 I rewired the injectors to share this signal with the two injectors that were not squirting, it worked, but not too well.
can some one give me the logic behind having them all firing at the same time with Ljet besides the obvious simplicity.

With the earlier D-jet fuel injection they fired them in pairs. I guess when they got around to the L-jet they figured out it wasn't necessary and just fired them all at once.

Tue Oct 05, 2010 12:32 am

thanks for the answers busdaddy and wildthings.

Tue Oct 05, 2010 10:53 am

Wildthings wrote: 59walkthru wrote: sorry to hijack, but...
all the injectors fire at the same time? I'm not saying that I don't believe this but I am pretty surprised by it. shouldn't they be timed to fire as the intake valve is opening? wouldn't that be more efficient.
I had an old 73 volvo 240 w/efi it had a bad brain and I had a spare one that was also bad. one ecu would fire injectors 1&3 the other ecu only fired 2&4 I rewired the injectors to share this signal with the two injectors that were not squirting, it worked, but not too well.
can some one give me the logic behind having them all firing at the same time with Ljet besides the obvious simplicity.

With the earlier D-jet fuel injection they fired them in pairs. I guess when they got around to the L-jet they figured out it wasn't necessary and just fired them all at once.

Actually it is necessary.....or at least better...and its also why the D-jet always spanked early L-jet for tunability, emmissions and HP. Until the L-jet got 02 sensor control to do downstream fuel corrections. The rich/wet ports always caused (and still do) issues with passing emmisions...especially when the emmisions are tested at idle.

The very lean idle requiremnents of emmission testing were very hard to meet with early L-jet ....without running lean in other parts of the running spectrum. It alwasy was and still is difficult to get L-jet busses both running excellent AND passing emmissions. Its typical that owners lean out as much as possible to pass HC...and then fail NOX and CO because of it. Thats a function of wet, out of time injection in the ports with no downstream correction.

Its actually easier to get L-jet to pass emmisions on the rolling road dynos like they require now in Texas.
CIS had these very same problems. Its virtually impossible for many CIS Basic and CIS lambda to pass an idle sampled emmisions test on the first go araound because of the dripping wet ports.
Typiclaly having the idle up toward its maximum spec, a tweak to CO mixture and timing slightly retarded is required.

They went to batch fired on L-jet because it was simpler and cheaper...and was plenty adeuate and ran well (outside of emmissions testing).
L-jet was already through design and testing before emmissions testing came on board. Ray

Tue Oct 05, 2010 3:54 pm

I'm running 77 l-jet right now.
If I was to swap in a 79 ECU and add the cat and aft o2 sensor. is this all that would be involved in moving up to a stock 79 ljet system. i ask mostly because my bus is a 79 ca, that was webber when I got it. I moved up to FI from a 77. is the same AFM used? what else is not the same?