Nuked 3.2 EFI

[rolls 912]

Hi again

I thought I had finished my SWB resto...

The engine ran, but the wiring needed tidying after the auto electrician had partial rewired the car.

I asked my auto electrician to come back to finish off and tidy up and the following has occurred:

*the headlight switch needed replacing (was working okay previously)
*flasher can needed replacing " "
*he asked me to replace my fuel pump as it stopped working. Purchased a new one. Installed it. Now realized the old one was fine after all
*he now claims that the efi unit is cactus... It was working last time he worked on the car

What I am trying to get my head around is there seems to be a lot of sudden electrical failures. Is this a coincidence or is it something more sinister? If its the later, what do you think could be causing these issues?

Any help would be appreciated.

[quaz]

Check your battery terminals. I went through the same list of gremlins last year to discover my positive terminal was completely corroded. Visually it looked fine, but when I pulled it apart it was all rust and oxidation.

[rolls 912]

Thanks Kevin. Everything is brand new. So frustrating. Someone suggested it may have been damaged when I was doing some minor welding in the boot although the battery was disconnected.
Found a refurbished efi for 500 dollars.

[KTL]

Welding was going to be my question. Always a good idea to disconnect/remove sensitive electrical parts when doing any welding.

[rolls 912]

Have found a vendor for a new unit.

I have a 3.2 euro running with no cat/oxy sensor.

Can anyone tell me what's the difference between these two versions of the efi? Can the 082 which is the newer model runner without an 0xy sensor?

[rolls 912]

Bump

Anyone?

Need Help please.....

[scarceller]

You can run the USA 84-89 DME with the O2 disconnected without any issue.

But the chip code is different for the Euro cars. But any 84-89 DME should run your engine but the USA chip is slightly more conservitive.

Originally Posted by rolls 912

Bump

Anyone?

Need Help please.....

[ischmitz]

It's not that simple. The DMEs are electrically different between O2-sensor and non O2-sensor versions. For the later the comperator circuit is disabled and the inputs are grounded to make sure noise won't affect the mixture. Both the U.S. and the Euro chips will make mixture adjustment when the comperator is present in the DME.

Ingo

[scarceller]

Ingo,

After looking at DME pin #20 (o2 sensor signal) it does indeed feed the 2 comparator circuits but it looks like the 2 inputs would simply be pulled to ground on both comparators. I have the DME schematics and that's what they show.

Also I run my USA DME all the time in open loop and the code that looks at the O2 signals coming from these comparators indicates it does nothing.

I do agree that if noise is detected on the O2 signal line it could cause issues.

[ischmitz]

Hi Sal,

the non-O2 DMEs have the entire resistor network, the elevated calibration resistors and some capacitors removed around the comperator IC. The inputs of the comparator are grounded (wire instead of the small decoupling caps). The O2 DME's look like this:



And here is one without O2 functionality:



I checked both the late US and ROW code 357 and 358. Both react with mixture changes when running in a US DME with the comparator active. So you need to be carefull. The mixture will rail one way or the other with the input floating. Maybe the earlier 2k or 4k code versions are different where the ROW versions don't react to the O2 input.

Cheers,
Ingo

[scarceller]

Ingo,

100% with you on the code, both ROW and US code monitors the inputs from the comparators via the 8051 processor Port0 bit 6&7 they work like this in the code:

lean condition if p1.6=1 and p1.7=1
Rich condition if p1.6=0 and p1.7=0
Target if p1.6=0 and p1.7=1

If you ground the sensor input it will indicate lean condition, but I don't know what the code will do if it constantly sees lean condition from the comparators? I'll review the source code to see. As I recall the code expects a transition back out of each condition and I'm not certain what the code does if the transition does not occur. I'll check and see if I find out how it works.

[scarceller]

Ingo,

I looked at the schematic very carefully this time and it shows a voltage divider network of 4 resistors (R802,803,804,805) that setup 3 reference voltages as follows:

Rich - 0.63v
Target - 0.6v
lean - 0.57v

The rich ref voltage is wired to one comparator
The lean to the other

And the target is feed back to the O2 sensor input, doing this insures that if the O2 sensor is disconnected then the output from the 2 comparators is guaranteed to indicate target lambda. From what I see it's perfectly OK to disconnect the O2 sensor without any fear of the lambda control getting in the way. Simply if the O2 sensor is not connected the comparators will always indicate they are at lambda.

Hope this makes sense.

Also, this is from the 944 but the basics are the same in the 911 just the voltage divider resistors are slightly different values in the 911
http://www.the944.com/lambda.htm
Great write-up by frwilk
Also he took liberty to re-draw the schematic in a much more readable fashion than the 911 dme schematics.

[scarceller]

Back on the question for this thread:
Check and clean the ground strap at the battery (both ends)
Check and clean ground strap at front of transmission, this strap is the engine ground strap you'll find it near the area where the shift linkage leaves the center tunnel and the front of trany.
Check the grounds on cyl #1 intake runner just above the distributor. You'll see a bunch of brown ground wires all connected to the intake runner. This ground point is the main ground for all DME components as well as the DME.
Be sure all these grounds are clean and in good shape.

Also, to find out if the DME is alive simply turn the key to 'RUN' and then see if the IdleControlValve is humming and vibrating. It's located right near the throttle body. If it's humming then the DME has power and has properly booted up and the software is running. This test will help answer if the DME is even on? Report back the result of this test for further instructions.