Tampa 928s

86 S/C 5-speed

Having an issue with closed loop mode my Lh maybe not the one that came with the car. Cover has been off and may have been mixed up with another Lh.
My numbers 928-618-123-04 bosch 0 280 002 503 which I believe is correct as far as the cover shows. On the mother board it has a yellow sticker # 2 284 486 516, Any way to Id the actual mother board?

It has a 14 pin EPROM receptor on the mother board and a 12 pin chip.
Does any one have a chart showing Lh for 85-86? The four extra pins must be there for a reason.

I have access to an 85 euro will this allow me to change the chip and test the Lh to see if it will go into closed loop?

Tampa 928s

From an old thread, never received an answer.

https://rennlist.com/forums/928-foru...1812304-a.html

This was Mikes board I tried to repair his the swap was a mistake.
I found that the difference between the 24 versus 28 pin is that the 24 pin keeps 8k of code 1/2 in the eprom 1/2 on the controller. The 28 pin keeps all the data on the eprom.

danglerb

I don't think if I understand closed loop to be be using feedback from the O2 sensor that a Euro runs in closed loop at all, no O2 circuit.

US 85/86 very commonly have aftermarket chips in them.

John Speake

The box part # 928 618 123 04 is correct for your car. 05 & 05 would also be OK for US 32v 85/86.

Personally I've never seen a board with the 28 pin chip - all were 24 pin.

If you swap in a Euro LH (only /02 is acceptable) then that LH has none of the O2 loop or idle controller circuits that the 32v have. But if the car is stock and has no problems an /02 should run OK in your car for testing AFAIK.

You car is modified with larger injectors so a stock LH chip won 't run correctly.... with a standard EPROM

Tampa 928s

Update:
With open loop chip my voltage on the NB is .907 12.2 A/F approximately.
With closed loop my voltage on the NB is .013 16.04 A/F

Again from previous research:
I found that the difference between the 24 versus 28 pin is that the 24 pin keeps 8k of code 1/2 in the eprom 1/2 on the controller. The 28 pin keeps all the data on the eprom.

That said I need to aquire a correct 85-86 LH to test it so far no one I know has one. The problem may be how my LH processes the memory but need confirmation from you. You mentioned you have never seen a 28-pin LH well I have one.

John Speake

The WSM procedure is to set the open loop O2 to 14.7, then close the loop. The loop needs the open loop set accurately to retain control.

PorKen

The 28-pin must have been very late '86 production or replacement brain. I've never seen one.

All the S2/S3/S4-up 928 brains have all the code on the EPROM. No ROM on the ECU.
S2/S3 uses a 8039 no-ROM version of a 8048 processor, S4-up use a 8032 no-ROM version of a 8052 processor (=8051 w/extra mem + timers).

The LH 28-pin holder is wired so that only one 4K bank is accessible.

(The EZ-F uses a 4K 24-pin 2732 chip, but can only access 2K, as it was designed for a 2716. Fun fact - CASIS shift light tach uses a 8039 w/2716.)

Tampa 928s

Should I be looking in a different direction is the 28 pin a non issue?

I found a 86.5 LH I am going to use to test the closed loop chip today this should put the LH issue to rest.

John Speake

Ooops ! Sorry I made a silly mistake in my post #24 re LH EPROM pin count which I have now corrected :-(

When you run open loop with O2 volts ca 0.9v then your gauge should read around 14:1. If not something is wrong with the display.

You could try running closed loop and adjusting the MAF 3mm hex adjuster a few turns clockwise to see if he can get the loop volts to cycle up and down, hopefully around 1 v. and the mixture nearer 14:1

danglerb

Could the brain be from an 84 which doesn't have a socket from the factory and might have had one added.

John Speake

I have only ever seen socket-less EPROM on '84 Euro EZ-F ECU, never an LH.

Tampa 928s

I have the correct 04 LH loaner for testing.
Using a breakout box this is what I have.

Pin 6&7
At idle 2.85 volts A/F 12.8
At 2K 3.84 volts A/F 11.6

Pin 14&25 pot set to 291 ohms

This all looks correct.

Tampa 928s

Open loop:
288 ohms base line 12.4
339 ohms 14.9-15.7

Closed loop:
361 ohms 17.1
340 ohms 17.8
300 ohms 17.5
276 ohms 17.2

The last three closed loop will allow my NB A/F gauge to move back and forth between rich and lean.

Tampa 928s

Will adjusting the Maf while using the open loop chip affect the rest of the tune? I was thinking about setting it for a little leaner at idle.

John Speake

The main goal is to get it running within the control range of the O2 loop. You seem to be getting closer to that. But the A/F values your display shows seems suspect. Are you sure it is OK ?

The open loop values at idle are less important. Adjusting the idle pot has a rapidly diminishing effect at higher rpm/loads, even though the LH may well have gone open loop under those conditions. So you can be adventurous with your adjustment range.

As well as the NB system, do you also have a WBO2 system on the car ?