The infamous diode mod!

[Outerfroggy1]

I have searched this forum extensively for any information regarding this controversial mod, and can only find passing mention of it in any threads. Kind of a 'I had a friend who's 2nd cousin twice removed knew a guy who tried that once'...

No concrete data, no DIY, no results or dynos, no pros-cons, nothing.

However, I have finally come across a thread from another Audi forum (I'm hesitant to post a link because I'm not sure about our forum rules on this). It's a fairly simple DIY that explains the mod, materials, and how it actually works. Its surprisingly simple!

Basically, part one of the mod consists of soldering a 4.3v zener diode between the signal output and the ground wire on the MAP sensor, this 'clamps' the voltage so that no matter how much PSI is produced by the turbo the ECU will only see ~11 PSI. This means you can build as much PSI as you want without the ECU saying 'WTF?!' and sending the car into limp mode.

Part two of the mod describes the installation of a MBC to take the place of, or run in series with the N75 valve that controls the wastegate signal pressure. This allows you to manually control the amount of boost the turbo produces (duh).

This all makes sense so far, however I have some concerns...
The OP claims that the stock ECU can adapt to higher levels of boost (and thus more air-mass measured in g/sec) by using the MAF sensor to adjust fueling levels. I will quote the OP.

16-17psi is safe on stock fueling

No, your not damaging the engine, the engine is stout and can hold way more than what a ko3 can throw at it

The ecu adapts the a/f with the readings from the maf and o2 sensor

Several concerns have been raised by other posters regarding proper fuel mapping, ignition timing and dangerous A/F ratios.
Has anyone here actually tried this mod? any major risks or drawbacks? I know everyone is gonna say DUHH GET A CHIP. But there are many reasons some of us don't want to blow 700-800 dollars on a chip. The nearest VW/Audi tuning shop is 2 provinces away, I plan to go BAT in the future and don't wish to waste money on a tune I'm not going to keep long term, and like most of us money is tight at the moment and bang for the buck can't be beat if this mod is possible. On paper it all makes perfect sense, but is it too good to be true?

(im prepared for old guy and diagnosticator to tell me 50 reasons why this is a bad idea hahah)

[b6nukka]

It sounds to good to be true I dont think you should try bypassing the system for the reasons you already mentioned fuel maps, ignition timing, A/F... as much fun as the high PSI is with out the proper tune behind it i dont think it will end up good either get a chip or wait till you go big turbo I wouldn't waste my time with this just my opinion

[pape]

I have done the zener diode mod on many chipped and non chipped VW's. its totaly safe aslong as you are running ~16psi
the problem is that the car dosn't have a fuel map writen in the ECU above 15psi.

go to vwvortex.com for the way to properly conect the diode. it goes on the 3 wires to the map sensor on the intercooler. you will need the 1watt 4.3v zender diode, soldering iron, solder wire and elecrical tape.

[drjonez]

I have searched this forum extensively for any information regarding this controversial mod, and can only find passing mention of it in any threads. Kind of a 'I had a friend who's 2nd cousin twice removed knew a guy who tried that once'...

No concrete data, no DIY, no results or dynos, no pros-cons, nothing.

However, I have finally come across a thread from another Audi forum (I'm hesitant to post a link because I'm not sure about our forum rules on this). It's a fairly simple DIY that explains the mod, materials, and how it actually works. Its surprisingly simple!

Basically, part one of the mod consists of soldering a 4.3v zener diode between the signal output and the ground wire on the MAP sensor, this 'clamps' the voltage so that no matter how much PSI is produced by the turbo the ECU will only see ~11 PSI. This means you can build as much PSI as you want without the ECU saying 'WTF?!' and sending the car into limp mode.

Part two of the mod describes the installation of a MBC to take the place of, or run in series with the N75 valve that controls the wastegate signal pressure. This allows you to manually control the amount of boost the turbo produces (duh).

This all makes sense so far, however I have some concerns...
The OP claims that the stock ECU can adapt to higher levels of boost (and thus more air-mass measured in g/sec) by using the MAF sensor to adjust fueling levels. I will quote the OP.





Several concerns have been raised by other posters regarding proper fuel mapping, ignition timing and dangerous A/F ratios.
Has anyone here actually tried this mod? any major risks or drawbacks? I know everyone is gonna say DUHH GET A CHIP. But there are many reasons some of us don't want to blow 700-800 dollars on a chip. The nearest VW/Audi tuning shop is 2 provinces away, I plan to go BAT in the future and don't wish to waste money on a tune I'm not going to keep long term, and like most of us money is tight at the moment and bang for the buck can't be beat if this mod is possible. On paper it all makes perfect sense, but is it too good to be true?

(im prepared for old guy and diagnosticator to tell me 50 reasons why this is a bad idea hahah)

You won't get a lot of information on it here, everyone will laugh you off the forum and tell you to just get a chip.

That said, I've been running the diode mod for some time now (6 months? I dunno). It is a cheap way to get a bit more power out of the pathetic K03. Here's some real info:

-The ME7 on the B6 1.8T bases its fueling and timing on mass flow as read by the MAF. This is what makes running the diode mod possible (and safe within reason)- increased boost = increased airflow, the MAF sees it and adjusts timing/fueling accordingly. Based on my logs, the fuel/timing maps do extend past the 11 PSI limit imposed by the MAP.

-I wouldn't do this without VAG-COM or some other way to log AFR and make sure your car is OK.

-Use a bleeder type MBC, ball + spring MBC + tiny K03 = MASSIVE torque surge (which is sort of fun I guess....).

[Outerfroggy1]

Thanks drjonez, Thats the kind of feedback I was looking for. Like I said I knew everyone was gonna say just buy a chip. But I have listed some of my good reasons for not wanting to do so.

I have access to VAG-COM and can log A/F ratios, but I'm a bit noobish on what to look for, and what is safe. I am a heavy duty diesel mechanic by trade so I'm comfortable tearing my car apart to a bare block, however I was educated on diesel fuel and not automotive gasoline.

What is a comfortable safe zone to run the boost at on a completely stock B6? From what I gather 16 PSI is perfectly safe while leaving a bit of headroom just for good measure. 18 PSI is about the safe maximum, and for the VW guys who can run a FPR they can push even more up to 21-22 PSI (pretty much maxing out the poor little K03).

I'm not out to blow up my motor, and even 10hp is worth it when you consider what this mod actually costs.

PS I have a buddy who's willing to guinea pig this for me first, so that helps in the willingness to go through with it lol

[drjonez]

Thanks drjonez, Thats the kind of feedback I was looking for. Like I said I knew everyone was gonna say just buy a chip. But I have listed some of my good reasons for not wanting to do so.

NP.

I have access to VAG-COM and can log A/F ratios, but I'm a bit noobish on what to look for, and what is safe. I am a heavy duty diesel mechanic by trade so I'm comfortable tearing my car apart to a bare block, however I was educated on diesel fuel and not automotive gasoline.

That's a good background...though there are few differences. ;)

There are several good VAG-COM writeups, take a look at those.

What is a comfortable safe zone to run the boost at on a completely stock B6? From what I gather 16 PSI is perfectly safe while leaving a bit of headroom just for good measure. 18 PSI is about the safe maximum, and for the VW guys who can run a FPR they can push even more up to 21-22 PSI (pretty much maxing out the poor little K03).

I'm not out to blow up my motor, and even 10hp is worth it when you consider what this mod actually costs.

Comfortable zone is totally up to you. You'll find there's no hard data out there as to where the the maps end, etc. Lots of conjecture and "my mom's counsin's friend told me..." but no data. I would do some logging- first stock to get an idea of where your car is at now and then slowly increasing the boost above 10 PSI. Settle on a number that you're comfortable with and that leaves a bit on the table in terms of injector duty and AFR. Personally, that number is 15 PSI...logs looked good and that allows me to run the timing bumped up a bit as well.

No luxury of messing with an AFPR for us....stupid returnless fueling. Curse you ULEV!

PS I have a buddy who's willing to guinea pig this for me first, so that helps in the willingness to go through with it lol

Sounds like a plan! Be sure to have him set his MBC @ 40 PSI so you can get some 1.8T rebuild experience. ;)

One thing that I just thought of was the divertor (bypass, blow-off, whatver your favorite name is) valve solenoid. I seem to recall at some point the ECU opening it to try to stop the overboost condition....I can't remember if that was before or after the diode mod. Just something to keep in mind.....and if you run into it, simply plug the valve's vac line into any post-TB vac source (and not a solenoid controlled one).

[TurboAudiGuy]

I ran the diode mod on my B5 for 10K miles and now on my b6 for over 15K miles. No problems except the occasional over boost code but i don't have my diode soldered in yet(long story). I have my boost controller set to 15psi. No complaints and no problems. I have over 135K miles on the stock turbo. An upgraded DV is a must also. The stock ~166HP is just not enough in these cars.

[CoreyRS]

WTF is the diode mod?

[drjonez]

WTF is the diode mod?

Limiting the output of the MAP sensor via a diode, allowing you to circumvent the ECU's overboost safeguard.

[rbj325]

I've been running a 2.2V diode with my APR chip forever. Gets rid of the overboost code until I write it out.

You will not see any gains above like 14psi with a k03s anyways.

Basically what you'll find out is, the car will run and the AFR above 3500 rpm will suck. If you push too much boost it will slow the car down at lower RPM because it over compensates with fuel on the top end(4000-5500rpm).

[Outerfroggy1]

Personally, that number is 15 PSI...logs looked good and that allows me to run the timing bumped up a bit as well.

Yes 15 sounds like a good maximum. How much of a boost in power did it produce for you? (I just might find out how much my buddies makes at 40psi for about 5 seconds lol)

One thing that I just thought of was the divertor (bypass, blow-off, whatver your favorite name is) valve solenoid. I seem to recall at some point the ECU opening it to try to stop the overboost condition....I can't remember if that was before or after the diode mod. Just something to keep in mind.....and if you run into it, simply plug the valve's vac line into any post-TB vac source (and not a solenoid controlled one).

Thanks for the tip, I already have the n249 bypassed! I'm planning on a forge DV or BOV undecided just yet.

[JEENYUS]

WTF is the diode mod?

guess you didnt read the first post?

[kwimberly]

Where's texasboy? He was the diode mod's #1 fan.

[champion]

WTF is the diode mod?

guess you didnt read the first post?

^^^THIS^^^

[mattro]

subscribed !!
heard of this mod for a long time but wasn't sure how safe it was and if I wanted to try it. sounds good so far though.
I don't mind the power of the car stock, so i'm sure i'll be happy with around 14-15 psi with the diode mod.. and for the price of it !!

[EErie B6]

subscribed !!
heard of this mod for a long time but wasn't sure how safe it was and if I wanted to try it. sounds good so far though.
I don't mind the power of the car stock, so i'm sure i'll be happy with around 14-15 psi with the diode mod.. and for the price of it !!

the amount of people i see on this forum that have been around for a long time and still have a bone stock car boggles me.

[champion]

the amount of people i see on this forum that have been around for a long time and still have a bone stock car boggles me.

cuz alot of the ppl use the forum for the DIY repairs and such. its all good(for them)lol

[drjonez]

Yes 15 sounds like a good maximum. How much of a boost in power did it produce for you? (I just might find out how much my buddies makes at 40psi for about 5 seconds lol)

I would say it's fairly substantial (then again I have custom TIP and 3" DP...), certainly a nice kick in the pants.

[mattro]

the amount of people i see on this forum that have been around for a long time and still have a bone stock car boggles me.

i'm surprising myself too, i'm trying to keep this car as reliable as I can, as weird as it can sound for an Audi A4.
I had a mk3 VR6 turbo that I built and had my share of fun and break downs, this audi is my family car and told myself i'll never mod it performance wise.
and I know myself, if I start i'm done. my mk3 started as a 2.0 gti

I have to do the diode mod though, and hopefully i'll stop there for performance

[drjonez]

...I have to do the diode mod though, and hopefully i'll stop there for performance

Famous last words....

[alpinestar180]

cuz alot of the ppl use the forum for the DIY repairs and such. its all good(for them)lol

or they are poor...for audi owners anyway. (me) =)

[Coyote USP]

Where's texasboy? He was the diode mod's #1 fan.

This ^^

If you want a diode mod fanboy shoot him a PM, I'm certain he will gladly spout off all of the beautiful intricacies of the mod. I personally think it's quite brilliant, although I haven't done it myself. Guess it just sounds reasonable in theory.

[Outerfroggy1]

I would say it's fairly substantial (then again I have custom TIP and 3" DP...), certainly a nice kick in the pants.

I have a 3" test pipe sitting in my closet waiting for install after my warrenty runs out (bought the car from the audi dealer last year and still have 20,000kms warrenty left). Also going to eliminate the vaccum hose mess under the hood and fabricate a custom smooth aluminum TIP.

Would anyone reccomend the larger 3" MAF on a stock turbo with intake and intercooler piping?

[widgget]

^^ 3" maf on a stock turbo wont' make any difference at all.

[Outerfroggy1]

^^ 3" maf on a stock turbo wont' make any difference at all.

Didn't think so... I'll just wait for a year or two until I get a 2nd vehicle and tear this thing down for a BAT build. Run a MAFless setup with one of those sexy mushroom filters hanging right off the turbo. A man can dream lol

[EErie B6]

i'm surprising myself too, i'm trying to keep this car as reliable as I can, as weird as it can sound for an Audi A4.
I had a mk3 VR6 turbo that I built and had my share of fun and break downs, this audi is my family car and told myself i'll never mod it performance wise.
and I know myself, if I start i'm done. my mk3 started as a 2.0 gti

I have to do the diode mod though, and hopefully i'll stop there for performance

im not knocking it at all. in the end, dumping cash in a car is a losing investment... your only compensation is the fun you get from it.
when i bought mine, i told myself i was going to keep it stock, i didnt care to change it at all...etc. lol

its an addiction and i have hardly scratched the surface. ...and some would argue thats a lie.

[texasboy21]

I ran the diode mod for years, never had 1 issue. Got REVO and had problems since day one.

I think the diode gives better performance than a chip. PM me if you have any questions

[Outerfroggy1]

Thanks texas, will do!

UPDATE: My buddy had located a 3rd party supplier of VW electrical parts (plugs, terminals etc). We are going to attempt to build a short harness with a MAP plug on one end (to plug into the map obviously) and a custom plug that will accept the stock MAP plug on the factory wiring harness. The diode will be soldered in this short harness.

That way you can add or remove the diode in 10 seconds without hacking up the stock wiring harness and returning to completely stock at anytime. (except for the removal of the MBC of course.)

[drjonez]

Thanks texas, will do!

UPDATE: My buddy had located a 3rd party supplier of VW electrical parts (plugs, terminals etc). We are going to attempt to build a short harness with a MAP plug on one end (to plug into the map obviously) and a custom plug that will accept the stock MAP plug on the factory wiring harness. The diode will be soldered in this short harness.

That way you can add or remove the diode in 10 seconds without hacking up the stock wiring harness and returning to completely stock at anytime. (except for the removal of the MBC of course.)

That's pretty slick. I actually was able to tuck the diode inside the boot on the plug....STEALTH!

[Outerfroggy1]

That's pretty slick. I actually was able to tuck the diode inside the boot on the plug....STEALTH!

Nice! mine will be heatshrinked, loomed and ziptied out of the way nice and neat of course. I am ANAL about wiring. I've seen too many hacked up rats nest wiring jobs in my time. How anyone can think twisting two wires together and a patch of black tape will actually last is beyond me...

[rbj325]

I ran the diode mod for years, never had 1 issue.

http://www.audizine.com/forum/showth...uel?highlight=

http://www.audizine.com/forum/showth...ted?highlight=

http://www.audizine.com/forum/showth...683?highlight=

That way you can add or remove the diode in 10 seconds without hacking up the stock wiring harness and returning to completely stock at anytime. (except for the removal of the MBC of course.)

Just use black electrical tape and you'll never even notice the diode on the wires of the MAP sensor. I can remove and install the diode in less than a minute. Put it like 3-6 inches away from the sensor on the wires.

[Outerfroggy1]

http://www.audizine.com/forum/showth...uel?highlight=

http://www.audizine.com/forum/showth...ted?highlight=

http://www.audizine.com/forum/showth...683?highlight=






Just use black electrical tape and you'll never even notice the diode on the wires of the MAP sensor. I can remove and install the diode in less than a minute. Put it like 3-6 inches away from the sensor on the wires.

Black tape will never stand up to the salt air enviroment in newfoundland. Even a pin prick in wire insulation will corrode and break the wire in a few weeks/months. Properly applied heatshrink and sealed weather proof connectors (with lots of dilelectric grease) are the only solutions. Even then wiring has a tough time to stand up to the weather over the years.

PS thanks for the links!

[texasboy21]

http://www.audizine.com/forum/showth...uel?highlight=

http://www.audizine.com/forum/showth...ted?highlight=

http://www.audizine.com/forum/showth...683?highlight=

Okay, so I had an issue or two here and there...lol

Really though, those issues could be expected bc of what I did to the car - acceptable in my book. What I am not okay with is the funkyness thats been going on ever since I got REVO'd (MAF readings too high thusly affecting other variables)

[Outerfroggy1]

Okay, so I had an issue or two here and there...lol

Really though, those issues could be expected bc of what I did to the car - acceptable in my book. What I am not okay with is the funkyness thats been going on ever since I got REVO'd (MAF readings too high thusly affecting other variables)

What did you do to correct these issues? I've read that simple tweaks from lemmiwinks (which I can't get to work grr) are not enough to compensate. Did You ever get the car running satisfactory?

[texasboy21]

What did you do to correct these issues? I've read that simple tweaks from lemmiwinks (which I can't get to work grr) are not enough to compensate. Did You ever get the car running satisfactory?

You are correct, lemmi wont help you out too much.

The car ran better with the diode mod than it does now with REVO thats for damn sure, however, you must remember that my car is autistic ...

I havnt dropped this little tidbit in a while and now seems like a good time. I ran a 15.278 quarter mile with no mods other than the diode, mbc set to 19psi, and a K&N drop in filter. Thats as fast as chipped cars, big injector file cars, and some k04 cars.

http://www.mjbmotorsport.com/sitebui...medatabase.htm

Bout that

[pape]

You are correct, lemmi wont help you out too much.

The car ran better with the diode mod than it does now with REVO thats for damn sure, however, you must remember that my car is autistic ...

I havnt dropped this little tidbit in a while and now seems like a good time. I ran a 15.278 quarter mile with no mods other than the diode, mbc set to 19psi, and a K&N drop in filter. Thats as fast as chipped cars, big injector file cars, and some k04 cars.

http://www.mjbmotorsport.com/sitebui...medatabase.htm

Bout that

I have seen dyno days were 1.8t's with diodes run more WHP than chipped 1.8t's (vw)

[alpinestar180]

so do you NEED an MBC to do the diode mod? or is it just to add controlability?

[pape]

the diode just fools the ecu into thinking its not boosting over ~14psi

you do need a MBC or EBC to up the boost.

[rbj325]

Black tape will never stand up to the salt air enviroment in newfoundland. Even a pin prick in wire insulation will corrode and break the wire in a few weeks/months. Properly applied heatshrink and sealed weather proof connectors (with lots of dilelectric grease) are the only solutions. Even then wiring has a tough time to stand up to the weather over the years.

I've been running my diode using Labatt blue grip tape that came in a 24 pack of bottles in the salt belt of NY without issues. The diode is up near the intake manifold...

[Outerfroggy1]

I've been running my diode using Labatt blue grip tape that came in a 24 pack of bottles in the salt belt of NY without issues. The diode is up near the intake manifold...

Must be the beer tape! lol