well i was told instead of using a missing link i could just get a 4.7 volt zener diode. and put it with one side on the ground and one side on the signal output from my map sensor. making it cut voltage after 4.7V. so i did this today ( my turbo kit is not on yet) to prepare for putting my kit on soon. and i probed the wires. with the key on acc spot and one was 5V one ground and other like 4.5 V or so. so i put it on how i should and i took the car for a drive and it ran like crap. it stumbled until about 4K rpms then it got power. so i took it off to test and now its fine. . but i need that for my turbo setup so what could be the problem ? its a 97 RS. the diode i got has no stripes on it either so it can face either way. but can anyone help me? also . my CEL flashed code 61 which is not even in my book. i dunno if it has anything to do with it or not,.

61? It's not listed on the CEL page...sure you read it right? MAP codes are generally 13 and 14.

Turn the diode around, it's backwards. A zener diode is very similar to a regular diode, in that if you install it in one direction, it takes 0.6 volts to forward bias your diode, and create a path to ground, which makes your computer see the incorrect voltage, which makes it calculate your pulse width based on the wrong air pressure, which is why it's running crappy. The trick is to install it in the opposite direction, that way it will NEVER forward bias, but the trick with a zener diode is that it has a breakdown point (in this case, 4.7v). Once it hits 4.7 volts, it "breaks down" and reverse biases, allowing any voltage OVER 4.7 to be shunted to ground (aka, holding the voltage at a constant 4.7 even if it's higher). If your diode has no markings to indicate which direction to install it, then you can either run some simple tests with a multimeter, or install it one way, test, and then reverse it and try again. Hopefully installing it backwards didn't kill it, because it will then drop all but 0.6v rather than dropping all but 4.7v. I don't think it would hurt it, I beleive it's a very low current. Anyways, if you've got a multimeter, they normally have a diode check on it, in which it supplies ~.6v to test the direction of the diode. Anyways, just because it has no markings, doesn't mean it doesn't have to be a specific direction, I've NEVER heard of a diode that didn't have to be installed in a specific direction (and that includes LED's & zener's).

^^^^^^^ He's right.

I tested mine before I put it on the car with a 9V to make sure it bled off correctly.

Brian

Why don't you just spend the $70 and get a missing link rather than halfass something so important? Seems ridiculous to me to cut a corner like that, and then wonder why it behaves like shit.

Originally posted by DarkOne
Why don't you just spend the $70 and get a missing link rather than halfass something so important? Seems ridiculous to me to cut a corner like that, and then wonder why it behaves like shit.

Garbage in, garbage out. ;)

ok thanks. ill get a new one and try it i think i fried this one. and why spend 70$ extra on something that i dont need when a 25 cent diode will do the same thing.

Should have bought a 95. :P

Originally posted by 97grnRS
ok thanks. ill get a new one and try it i think i fried this one. and why spend 70$ extra on something that i dont need when a 25 cent diode will do the same thing.

Because it won't?

why wont it. what the reasoning.

The diode keeps the voltage from going to high and causing the cel. The other trick to use is a check valve that bleeds boost in one direction and not the other, this will make it so the MAP see's no boost, but can still read vacuum. It's about $2 at you're local walmart in the fish department (just make sure you don't put it on something to hot), and a t connection with a bit of tube. The basic idea is to install it so it won't let air in when it's under vacuum, but lets air out of it's under pressure (check valve only lets air flow in one direction). There is nothing wrong with the diode, just install it in the correct direction and you should be good to go. Also, make sure you're installing it properly, give a description on your installation to make sure you've installed it properly (I want to make sure you didn't put it in-line). You basically just attach one side into the line (without cutting it), and the other side to ground (this gives it it's path to ground when the voltage goes above 4.7).

--- Edit ---
Ok, here's a diagram of how you need to hook it up:

If it doesn't work properly, go to:
http://ready4dis.8m.com/2GNT/
and click on it. Warning, it's a free site and has pop-ups, so bring your pop-up blocker ;).

The right way to do it electronically is with two diodes and a variable resistor to adjust the cut. I can't find the damn schematic right now. But I do have Missing link for sale $30 shipped. ;)

well i think ill try the check valve approach. that should work right? i just take map sensor off and run vac line to it.. but the way i had the diode hooked up i did not cut any wires i just did it like u said.one side to grnd and other to signal. first time i tried car would shut off right away. so i reversed it and car starts but just ran badly. so maybe check valve is easier way .

That's really weird, are you sure you hooked to the correct line? I see no reason why it would affect the car if it was hooked up properly, but if you tried it both ways, something obviously isn't working properly. If you want to try the check valve, I will draw you a picture of how to hook it up. I will edit this post in about 5 minutes.


--- Edit ---
Here is the picture:

And if it doesn't work, check/click:
http://ready4dis.8m.com/2GNT/

The reason you do it like this instead of inline, is inline it would "block" boost, but once vacuum was applied it would actually hold vacuum as it wouldn't allow air to flow back in towards the sensor. Just make sure you hook the check valve in the direction noted in my picture (the side you can blow through gets connected to the T fitting).

not too but in here but i was looking over my ML today and noticed the filter is gone, what else can i use to put in it to use as the little filter you shove in the side? a cigarette filter maybe, lol?

BUMP

well i bought a wal mart check valve the key would be to face it so it sucks air in at vacuum but when i boost no boost can push through right? also . how strong are they? can it stop 8-9 psi from pushing through? if so ill use it.

What's your aversion to a Missing Link? It's tried, true, and known to be a good part.

I mean, seriously... are you going to trust your motor to a fishtank checkvalve?

No wonder we get no vendor support. :rolleyes

Well Ner, a few others, and I have trouble with smooth transitions and getting fuel cut with the ML. Ner solved his problems with the diode solution so, theory states that the diode might be the solution for me... I just haven't gotten the motivation to try to figure this thing out. Ner are you there? Post some pics man!

here's the link I used to make mine.

http://www.fwdmopar.com/sites/dennis/howto.html

It's adjustable, and cost only a few bucks.

I haven't put it on my car yet though, since I ran out of time last year. ETX, you still have that missing link? Since I'm running the MS, I shouldn't have to worry about fuel cut, or smooth transitions, right? Well, unless the computer plays with timing.......


Brian

First of all, if done properly, an electronic cut on the MAP output will work perfectly. I know cause I ran mine for as long asI've been boosted. In fact it's still on there...

Anyway, all you need is a resistor and a zener diode.
I don't remmeber exactly the values I used, I will take a look todya thougha nd draw a circui tup for it later.

Don't mess wiht a check valve to do the job. Either do it the (right) electronic way, or use a ML.

Originally posted by ForceFed420a
here's the link I used to make mine. http://www.fwdmopar.com/sites/dennis/howto.html It's adjustable, and cost only a few bucks. I haven't put it on my car yet though, since I ran out of time last year. ETX, you still have that missing link? Since I'm running the MS, I shouldn't have to worry about fuel cut, or smooth transitions, right? Well, unless the computer plays with timing....... Brian

Ah ha! That's the link I was looking for. I have two lieing around the Garage if anyone want's one it's theirs for $5, assembled in a case and everything. I don't need to use them with the megasquirt.

Yeah I still have the Missing Link, but with the megasquirt you shouldn't need it.

well . i tried a cheap check valve and a stock eclipse check valve and they dont work. the car bucks around during normal driving without my turbo even on. so i guess ill use the 4.7 V diode again .

im glad i have a 95. :P

Originally posted by etx

Originally posted by ForceFed420a here's the link I used to make mine. http://www.fwdmopar.com/sites/dennis/howto.html It's adjustable, and cost only a few bucks. I haven't put it on my car yet though, since I ran out of time last year. ETX, you still have that missing link? Since I'm running the MS, I shouldn't have to worry about fuel cut, or smooth transitions, right? Well, unless the computer plays with timing....... Brian

Ah ha! That's the link I was looking for. I have two lieing around the Garage if anyone want's one it's theirs for $5, assembled in a case and everything. I don't need to use them with the megasquirt. Yeah I still have the Missing Link, but with the megasquirt you shouldn't need it.

hehehe, you're welcome :)

Well, I have a 97, so i have to do something just to prevent a CEL. I've already made this contraption, and I've heard mixed stuff about the ML, so I'll just stick with this electronic version.

Glad I could help.

Brian

Originally posted by ForceFed420a
here's the link I used to make mine. http://www.fwdmopar.com/sites/dennis/howto.html It's adjustable, and cost only a few bucks. I haven't put it on my car yet though, since I ran out of time last year. ETX, you still have that missing link? Since I'm running the MS, I shouldn't have to worry about fuel cut, or smooth transitions, right? Well, unless the computer plays with timing....... Brian

I have a couple of these sitting in the garage also if anyone wants one. Work much better than the damn missing link. That piece clogs up and gives you problems. Dino commented on its not so perfect operation not too long ago.....

Terry

Have you tried to run and drive the car witout any FCD or check valve on, just to be sure it runs like it should?(dont boost it) Almost sounds like the motor isn't running right to begin with..or maybe I'm not reading this correctly..

ya the car runs fine without the valve or the diode. but with either it bucks or loses power at the beginning of each gear.

Originally posted by XtremeRS
Have you tried to run and drive the car witout any FCD or check valve on, just to be sure it runs like it should?(dont boost it) Almost sounds like the motor isn't running right to begin with..or maybe I'm not reading this correctly..

The way I read it was he doesnt even have the turbo kit on yet. which would be irrelevant to it causing those problems. It has to be installer error. There is a link a few replies above that teaches you how to build and setup the actual FCD unit using the zener diode. I did and have been running with no problems for about 8 months.

How exactly are you connecting the diode, and which MAP wires are you connecting to?? The actual color of the wires...Also, from the links, you need to go to the sensor's ground wire, not chassis ground.. The yellow/black wire is the MAP sensor signal wire. I'm pretty sure the black/green is the ground wire, and the orange/yellow is the sensor 5v+ wire.

i connected it how it should have been. the stripe facing the signal wire yellow W something, an the other side to grnd of sensor. i dunno if 4.7 V is the wrong diode but it runs bad like that. i will try to build the more complex one from that link to see if it works. but i dunno why the diode works for some ppl and not me, i did install it correctly. not like its a hard thing to do.