TheSamba.com :: View topic

Thu Feb 17, 2011 4:01 pm

Hi everyone,

My loving and supportive wife just braved a hailstorm to pick up a digifant heated oxy sensor for me to install in my digijet equipped van. My plan is to tie the heater wire into the fuel pump circuit and just ground it to the engine block.

Are there any gotchas i should be concerned about? Suggestions on the place/method to tie into the +12V?

Thanks!
-Damon

<<<EDIT: just to put it on top, here is the wiring i've complete so far>>>

Here is the how to on how to wire in the 12V heater circuit:

After looking at the digifant wiring in the bentley (but not having a 86+ van to look at), it was pretty clear that piggy backing off the fuel pump relay was a good way to go. The purpose of the relay is to use a low power signal to flip an electro-magnetic switch that carries high power.

In this case the ECU powers terminal 85, which connects terminals 30 and 87 to let the big power flow.

For those of you who may not know, the fuel pump relay is this one:

Part of the problem is, things are pretty stuffed in that little relay box above the coil. So i needed to figure out a way to hook a wire up in there. To make things easier, i removed the relay box with the single phillips screw. It just slides out from under a little post on the other side side (i wonder why VW felt the need to make this so easy to remove?):

Then i removed the fuel pump terminal block by unhooking the little tabs top and bottom. The other relay terminal block is held down by tinnerman clips that would be a PIA to remove... :

Remove the horizontally oriented spade terminal by sticking a small poker in the little access cutout above the hole for the spade. This will bend a little tab down letting you free the terminal:

I did this because rummaging around in my parts box, i happened to have one of these:

Now, admittedly, it would be better if it had the little retention hook like the one i just removed had, but mine didn't. No problem, because i just cut the little center web and fashioned one out that material.

So i happened to have an old fuel injector connector+wires sitting around, so i used that and crimped a female spade on to that, and then added a bit of heatshrink to the exposed original terminal 87 female spade:

While it was a tight fit side-by-side, all together, it looked like this:

Then it was just a matter of stuffing it all back together:

and then route the power wire to where the O2 sensor wire is (back left of the engine - close to the ECU):

Of course, it isn't that simple because for some reason, VW swapped the male and female spades between digijet and digifant, which makes it kind of hard to plug the ECU (left) and the O2 sensor (right) together:

... and that is as far as i got. One gets tired working in the driveway at 10p.m. However, as i wanted, the circuit goes live when the van fires up and is running. My plan is to, just for now, get a little spade adapter to just stick the two female ends together and call it good... oh yeah, and struggle with the current O2 sensor to try and get it out of the exhaust (i currently smell like PB blaster).

So there ya go - i'll fill it out more if i get a chance to do more pictures and what not, but i have a big out of town weekend coming up, so not likely for a while.

Thu Feb 17, 2011 5:25 pm

What is the benefit over one wire?

Thu Feb 17, 2011 5:32 pm

It goes closed loop sooner and works better during extended periods of idling (the oxygen sensor needs to be a certain temperature to function properly - something you can't always count on with the 1-wire system).

My main impetus for this is making sure the O2 sensor is giving feedback to the ECU for my emissions test - part of which is an extended idle test.

Under normal driving conditions, it doesn't really matter at all.

Thu Feb 17, 2011 6:00 pm

I'm no expert but the O2 sensor is plugged into the exhaust pipe, super duper hot almost immediately when running and it stays super duper hot long after the engine stops.

Perhaps a different approach is needed to get through emissions?
How about a little bit hotter coil and plugs?

Thank you,

David

Thu Feb 17, 2011 6:15 pm

Yeah, you'd certainly think so, but I have a little box that shows what the O2 sensor is doing real time, and with the 1 wire, it is surprisingly often when it goes open loop (no signal to the ECU). I think to O2 sensor needs to be about 250*C (almost 500F) to work, and i think our vans don't really maintain that in certain conditions.

Don't get me wrong - i'm not relying on this as a crutch for emissions. I've been working pretty hard lately on getting the engine fundamentals sound by addressing vacuum leaks, ignition components, and fuel delivery.. I just figure a new sensor wouldn't hurt, and while i'm at it, improve the system...

-Damon

Thu Feb 17, 2011 6:46 pm

You might search for an not-too-long-ago post by 10cLife on this subject.

As I recall he suggested taking power off of the coil and using a relay.

Probably several ways to skin this cat but when someone with experience says a relay is a good idea I usually think 'A relay is a good idea'.

Thu Feb 17, 2011 7:22 pm

for any of the jetta I4 swaps I do I use a +12v from an Ignition triggered relay. it's stock like this in many older cars,
can't say how anything 2000+ does it.
but in digifant Jetta & Eurovana it's just a IGN relayed supply.

sounds like a decent plan to improve an older system..
let us know some emperical values if you gather data.

Thu Feb 17, 2011 7:33 pm

A three wire might give a slight mpg improvement ..is that your main reason for doing this mod?

Thu Feb 17, 2011 8:15 pm

reluctantartist wrote: A three wire might give a slight mpg improvement ..is that your main reason for doing this mod?

No he has been having trouble passing an emissions test.

Thu Feb 17, 2011 8:41 pm

Thanks for the input, dan. It sounds like adding a relay is recommended (vs just piggybacking off the fuel pump relay?). I haven't cracked open bentley or the engine bay today, so the exact approach is still TBD. The approach and tie-in points are the things I'm most interested in. Approach is suggested, but implementation might be up to my creativity (uh oh! :-) )

Regarding other points, I definitely do not expect an improvement in mpg (I've been hovering between 19 and 20 mpg since '84).

And I'll look for the 10C post.

Thanks for all the input!

Damon

Thu Feb 17, 2011 8:59 pm

Well, it sounds like you have a good plan going that will help all around.
For the smog maybe there needs to be a mod to the exhaust?
I can't remember which engine you have?
How about an extra pipe added to the exhaust to add a hose from the exhaust to th AFM or back to the intake?
It seems to me that giving it a little re-burn might help?
Just an idea, might not be a good one but an idea nonetheless.

Thank you,

David

Fri Feb 18, 2011 12:29 am

So i've added what i've done tonight by editing the first post.

I do have a question, though. Of course, after i did all the work, and came back in to make my post, i looked at the bentley again and in section 97.72, it seems the O2 sensor is NOT powered by the fuel pump relay, but rather by the main power relay (despite having the main power relay labeled "fuel pump relay".

Will this be a problem? Will i overload the fuel pump relay circuit? Personally, i like that the O2 heater only comes on while the van is running, and not while the key is on (sometimes i like to have the key on to listen to music, or whatever, and why have the O2 sensor going?). I think it should be fine since it is a 30A relay, but i just want a sanity check.
It wouldn't be too super bad to swap what i've done over...

Fri Feb 18, 2011 10:06 am

I ran into a similar problem with two femail conectors for the O2 sensor when doing a late night cat swap, look on your old O2 sensor and you might find the doble male conector there. otherwise hit the junk yard and look at similar vdubs.

Fri Feb 18, 2011 10:12 am

Another thing that has crossed my mind is a new charcoal can. Maybe yours is not working? I know you have an engine swap in there, larger then the stock. Perhaps there is a difference between the stock 1.9L and 2.1L charcoal cans?
Still just ideas, maybe no real help but it's worth exactly what you paid for it . . .

Fri Feb 18, 2011 10:12 am

Oh yeah... I think I have seen those. Good suggestion! For now, though, I'll just make a little adapter until I'm confident this is working just fine.

Fri Feb 18, 2011 10:21 am

camerahunter wrote: Another thing that has crossed my mind is a new charcoal can. Maybe yours is not working? . . .

Certainly a possibility - do you know how to check those? I do not know if there is a difference between a 2.1 and 1.9 canister (i have the 1.9)

Fri Feb 18, 2011 10:41 am

I know your van is for the 1.9 but don't you have something else in there?

Thank you,

David

Fri Feb 18, 2011 10:48 am

Yeah, it is a 2.3 (94 bore, 82 stroke), big valve heads, slightly off-stock cam (unfortunately can't remember which one), S&S headers...

It has 1.9 cooling and EFI, but the 2.1 intake mainfold/runners/throttle body (which is a rebuilt unit running on sealed bearing).

That's about it...

-Damon

Fri Feb 18, 2011 11:48 pm

Ok, does it have the 1.9 computer? Maybe it needs more 2.1 stuff?
Have yo read though the oldvolkshome.com write up on how to switch a 1.9 t a 2.1?
Maybe there will be some help there?
It seems to me that you just have a too much fuel situation. Somehow you have to get that reduced or get more of it to burn before it leaves the exhaust.

Thank you,

David

Sat Feb 19, 2011 12:23 am

I has passed smog a couple times before with this setup, so I know there is nothing fundamentally wrong with what's goig on.

However, to keep this thread on topic (adding a 3 wire O2 sensor to a 1 wire van), I'll make a little update on my smog thread and discussion (thanks for that, everyone!) can move over there...