# Help! Diode mod issue



## TT_Power (Apr 5, 2006)

I put a MBC in my car a few weeks ago, and the car would boost up to ~18 lbs in 1st, 2nd, and 3rd and be fine, but highway pulls in 4th+ gear, the computer would reduce the boost to ~7 lbs. I did the diode mod yesterday, and the engine ran like total garbage: backfiring, no power, putting up all kinds of codes. As soon as I disconnected the diode, all was back to normal. The diode I put in is a 4.7v 1w, zender diode. The car is an 01 225. Any ideas?


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## 20v master (May 7, 2009)

Its been a while, but sounds like you put it on the wrong wires. It shouldnt affect anything at idle. What codes is it throwing?


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## TT_Power (Apr 5, 2006)

Honestly, I didn't save the codes, or pay close attention to what they were. The 2 wires I put the diode between are: purple/blue & brown/blue....the 3rd wire that I did not use is purple/green



20v master said:


> Its been a while, but sounds like you put it on the wrong wires. It shouldnt affect anything at idle. What codes is it throwing?


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## 20v master (May 7, 2009)

TT_Power said:


> Honestly, I didn't save the codes, or pay close attention to what they were. The 2 wires I put the diode between are: purple/blue & brown/blue....the 3rd wire that I did not use is purple/green


I believe thats right, but the codes arent random, you should pay attention to them.


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## poopie (Feb 22, 2005)

i bet those are still over pressure codes cause you are using the WRONG diode. You are using a 4.7v diode making your ECU actually read 17psi. You actually want to trick the ecu to think its just maxing out at 10psi so it doesn't cut back fuel/spark. 

the 4.7v zener is for people that are chipped and want to make more boost than specified without throwing a code.


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## 20v master (May 7, 2009)

poopie said:


> i bet those are still over pressure codes cause you are using the WRONG diode. You are using a 4.7v diode making your ECU actually read 17psi. You actually want to trick the ecu to think its just maxing out at 10psi so it doesn't cut back fuel/spark.
> 
> the 4.7v zener is for people that are chipped and want to make more boost than specified without throwing a code.


Ahhh yes, didn't read. You want a 4.3w diode, but the car still should have idled and ran fine with the 4.7.


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## TT_Power (Apr 5, 2006)

The idle confuses me as well. Many of the write-ups I found online recommended the 4.7, so that is incorrect? Does it make a difference that I have a 225 not a 180?

I really appreciate your guys help!



20v master said:


> Ahhh yes, didn't read. You want a 4.3w diode, but the car still should have idled and ran fine with the 4.7.


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## 20v master (May 7, 2009)

TT_Power said:


> The idle confuses me as well. Many of the write-ups I found online recommended the 4.7, so that is incorrect? Does it make a difference that I have a 225 not a 180?
> 
> I really appreciate your guys help!


No, doesn't matter. What matters is if you're chipped or not. If not, you want a 4.3 = ~11 psi max boost reading. 4.7 = ~17 psi max boost reading. If you're not chipped, the ECU will still see 17 psi with the 4.7 diode and think you are overboosted. Again though, the car should have idled and drove fine other than limp mode when you overboosted. I'd reinstall the diode (or just hold it to the wires while someone else cranks the car) and record the DTC codes this time.


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## Marcus_Aurelius (Mar 1, 2012)

TT_Power said:


> The idle confuses me as well. Many of the write-ups I found online recommended the 4.7, so that is incorrect? Does it make a difference that I have a 225 not a 180?
> 
> I really appreciate your guys help!


You probably had the connection of the diode done improperly. As stated, if you don't have remap/tune that raised the boost limits, you want the 4.3 diode that clamps the pressure signal at 4.3 volts or 11 psi. 

With the increased boost achieved with the MBC, what are you doing to increase fuel accordingly? Also, are you monitoring IAT and timing corrections? These are necessary steps that goes along with the process of raising boost. :beer:


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## 20v master (May 7, 2009)

Marcus_Aurelius said:


> You probably had the connection of the diode done improperly.


Now that I think about it, aren't they directionally oriented? Aka, if it was running poorly, reverse the diode?


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## Marcus_Aurelius (Mar 1, 2012)

20v master said:


> Now that I think about it, aren't they directionally oriented? Aka, if it was running poorly, reverse the diode?


Yes!


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## 20v master (May 7, 2009)

Marcus_Aurelius said:


> Yes!


Damn, I'm getting old when I start forgetting more than most people know about 1.8t's. :laugh:


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## TT_Power (Apr 5, 2006)

Oh....I had no idea that they were directional. I have ordered a 4.3, and will make sure to reverse it compared to how it is now. Also, I try to avoid cutting wires whenever possible, and have tapped into the wires using something similar to the pic I attached. Is this okay? I have one of these on each wire, and the diode is in the other inlet of each.












20v master said:


> Now that I think about it, aren't they directionally oriented? Aka, if it was running poorly, reverse the diode?


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## 20v master (May 7, 2009)

Should be fine. :thumbup:


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## steve-o 16v GLI (Jun 26, 2005)

That will work but I'd recommend soldering n heat wrapping it. A tap like that works but it will corrode. I only use them on interior things like my boost gauge light n wot box but when it comes to electrical connections in the bay I'd prefer to know my wiring is solid n waterproof. I'm running the 4.3 in my 225 n running around 18psi with a 4 bar fpr, stock tune right now. I did this cuz my n75 sucked n was causing spikes that would put me in limp mode so I figured while doin the MBC might as well slap a diode in n crank the boost a bit. Def pleased with it for the $5 it cost for the diode.


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## poopie (Feb 22, 2005)

steve-o 16v GLI said:


> That will work but I'd recommend soldering n heat wrapping it. A tap like that works but it will corrode. I only use them on interior things like my boost gauge light n wot box but when it comes to electrical connections in the bay I'd prefer to know my wiring is solid n waterproof. I'm running the 4.3 in my 225 n running around 18psi with a 4 bar fpr, stock tune right now. I did this cuz my n75 sucked n was causing spikes that would put me in limp mode so I figured while doin the MBC might as well slap a diode in n crank the boost a bit. Def pleased with it for the $5 it cost for the diode.


a proper splice is probably better in this situation. OP seems like he lacks the basic electrical skills and using improper solder techniques will corrode faster.


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## steve-o 16v GLI (Jun 26, 2005)

poopie said:


> a proper splice is probably better in this situation. OP seems like he lacks the basic electrical skills and using improper solder techniques will corrode faster.


Are you joking?! Doesn't take an expert to buy some flux core solder n do the connection right. If he/she can find the map sensor n install a MBC they can handle a simple solder job like this.


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## poopie (Feb 22, 2005)

steve-o 16v GLI said:


> Are you joking?! Doesn't take an expert to buy some flux core solder n do the connection right. If he/she can find the map sensor n install a MBC they can handle a simple solder job like this.


I'm an IPC certified trainer for joints, rework/repair, cabling, and inspection. I've seen some crappy repair jobs from and people using low quality flux or flux that is too aggressive just destroy wires in no time. He already screwed this up and he wants a cleaner solution that can be undone. A wire splice can just be pulled off. If he solders it and wants to remove it, he's gonna have to go back and patch up insulation.


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## steve-o 16v GLI (Jun 26, 2005)

I honestly have no automotive training other than hands on work but I've soldered every electrical connection I've had to add in my car n I've never had a single failure. Maybe I'm just good. . Can't say the same for the taps I used over the yrs that corroded or stopped making good contact. Just saying.


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## Marcus_Aurelius (Mar 1, 2012)

steve-o 16v GLI said:


> I honestly have no automotive training other than hands on work but I've soldered every electrical connection I've had to add in my car n I've never had a single failure. Maybe I'm just good. . Can't say the same for the taps I used over the yrs that corroded or stopped making good contact. Just saying.


That's consistent with my experiences! I had multiple tap failures over the years, but I have yet to experience a bad soldering job. Maybe we're just lousy crimpers with ninja soldering skills


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## 20v master (May 7, 2009)

Marcus_Aurelius said:


> That's consistent with my experiences! I had multiple tap failures over the years, but I have yet to experience a bad soldering job. Maybe we're just lousy crimpers with ninja soldering skills


Ditto.


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## poopie (Feb 22, 2005)

20v master said:


> Ditto.


haha might be. crimps have their place. I try and keep most of the solder on boards. If you look at any OEM cable or harness there isn't a drop of solder on them.


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## poopie (Feb 22, 2005)

Most importantly, use a good quality water soluble no-clean flux. Flux is designed to clean the surface of copper so eventually it could wick down into the insulation and eat down the copper if you use the wrong kind. 

NEVER use acid core solder or ANYTHING you would use on plumbing. I think there is where people get into trouble just using stuff they have laying around.


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## 20v master (May 7, 2009)

poopie said:


> NEVER use acid core solder or ANYTHING you would use on plumbing. I think there is where people get into trouble just using stuff they have laying around.


I think so as well.


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## TT_Power (Apr 5, 2006)

alright, here's an update. I have put a 4.3v diode in (and reversed the direction of it), and the car runs fine, but as soon as I get above 15-ish lbs, it goes into a ~9 lbs limp mode. The code that comes up is P1297. When I run without a diode, it will sometimes let it boost higher, sometimes not. When it doesn't let it boost higher, I can let go of the gas, and when I hit it again, it lets it go higher...it doesn't seem to go into limp mode w/o the diode, but is inconsistant.  any ideas?


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## 20v master (May 7, 2009)

1297 is pressure drop between turbo and throttle, check DV. Test you DV to make sure it's working. Also, you'll get better results if you spell out what the DTC code is for instead of just listing the code. For instance, most are too lazy to Google P1297, like I was on my phone last night, the first time I read you post.  Anyhoo, that code has nothing to do with your diode.


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## TT_Power (Apr 5, 2006)

Thanks for the info. I upgraded to a Forge 008 about a year ago, and haven't had any problems. The car runs great without the diode, and at regular boost. The only issues are with the diode and when I try to turn up the boost.



20v master said:


> 1297 is pressure drop between turbo and throttle, check DV. Test you DV to make sure it's working. Also, you'll get better results if you spell out what the DTC code is for instead of just listing the code. For instance, most are too lazy to Google P1297, like I was on my phone last night, the first time I read you post.  Anyhoo, that code has nothing to do with your diode.


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## 20v master (May 7, 2009)

Could be the hoses, not necessarily the DV itself.


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## TT_Power (Apr 5, 2006)

Alright guys, looks like I got it squared away. I had originally put the 4.7 diode in backwards. That caused the car to barely start, and ran horribly. When I installed the 4.3 in correctly, it kept going into a limp mode as soon as I got into any real boost. On a whim, I put the 4.7 diode back in the correct way yesterday morning before work, and I am now getting up to ~18 lbs of boost, and have not had any issues at all. No limp mode, no check engine light, and lots of fun!  Thanks for all the advice. I really had no idea that diodes could only be put in one way.


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## 20v master (May 7, 2009)

A diode bleeds off voltage over a set level, and sends it to ground. Definitely directional. :thumbup:


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