Rb25 leans out when it rains

[redline racer510]

I have been having this problem for quite some time now and can't figure it out. Everytime we have a period of rain my car starts to run like crap. If I put any kind of load and as it approaches boost it starts to lean out like past 17 afr and if I just floor it from a dead stop it accelerates somewhat normal. I have been having this problem for a while now and can't seem to figure it out. Please any help would be freakin awesome.

[redline racer510]

I am starting to think there is some kind of short i just don't know how to go about figuring it out especially when the symptoms only appear while the car is under load/in boost.

[JAStirrett]

MAF? MAF wiring? Is your MAF in the bumper? How's the filter?

I just had an issue where I had about 16in of pipe going to the front driver's side corner with my MAF attached. I didn't have enough room for a filter, so I just put a screen on it to get the car running properly. Under WOT the car would literally hit a brick wall and would run lean all the time, sputter, etc. Martin @ RS Enthalpy told me I needed a cone filter on the MAF and sure enough, that fixed it. I am still in disbelief. Dude I was checking voltages, chasing wires, replacing fuel pumps, and the whole time it was not having a damn filter on the MAF. The ECU didn't know how much air was coming in, so it kept leaning out and as soon as I installed the filter, the AFR's were perfect.

I'm not saying that you have the same issue, but I just wanted to share my experiences. What I have learned is that the MAFs on our cars are extremely important for these motors to run correctly.

Hope you get it figured out man, I know how frustrating it can get.. Oh and btw, I had this issue on a Blacktop SR20DET w/ Z32 MAF

[supersayianjim]

when this happened to me when I had my rb20, it was a maf issue.

[redline racer510]

The car has a z32 maf and enthalpy tune to accommodate the bigger maf.

[redline racer510]

No check engine light

[JAStirrett]

The car has a z32 maf and enthalpy tune to accommodate the bigger maf.

My car is also tuned with a Z32 MAF and usually a MAFS issue won't turn on the CEL. When it is dry out, under WOT what does it do?

[redline racer510]

It drives normal but as soon as you get close to 0 vacuum it leans out past 17 afr and it's starts sounding like a subaru

[JAStirrett]

It drives normal but as soon as you get close to 0 vacuum it leans out past 17 afr and it's starts sounding like a subaru

Ok, it leans out in a dry climate and a wet climate. It doesn't seem to be related to the rain, but I may be reading it wrong. Like I mentioned previously, my car basically stayed lean all the time because the MAFS didn't have a filter on it.

You're not even getting in to boost, so I wouldn't suspect spark blowout...

Does the car build boost with 50-70% throttle to redline? Is partial throttle smooth? Or does it also sputter with partial input?

Do you have a stock fuel pump or an aftermarket fuel pump like a Walbro? Have you hard wired it yet?

Does it idle rough or have hard starts? I can't imagine it starting fine, running fine just cruising around, and then under WOT it starts to stumble and cut out. That certainly sounds like a MAFS issue to me, but hopefully someone else will chime in.

What I would do is:
1. Install a fuel pressure gauge and run it up to your windshield and put it under a windshield wiper to see if you're losing fuel pressure under WOT (if you have an aftermarket pump, if not I would consider one)

2. Make sure your MAFS wiring has good connections and is not shorting, etc. Also make sure you have a clean filter on it. I'm not sure about RB25's, but on a SR20DET, you have to have atleast 12in of intake pipe between the MAFS and the turbo. (I'm pretty sure this applies to RB25's w/ a Z32 MAFS also because a Z32 has like 4ft of intake tube before the MAFS!)

3. Check for boost and vacuum leaks.

4. If all of this checks good, you probably want to start looking at your timing in relation to cam timing, etc. You want to check everything you can check first before tearing in to it.

Hopefully this helps and a lot of the times man, it's something simple, but we always tend to over think things.

[redline racer510]

Only wet climate hence the title

[JAStirrett]

When it is dry out, under WOT what does it do?

It drives normal but as soon as you get close to 0 vacuum it leans out past 17 afr and it's starts sounding like a subaru

Hence your last response, I answered accordingly.

[redline racer510]

When it is dry it drives normal. On wot it drives normal

[JAStirrett]

Your car is allergic to harsh driving conditions! Jk

Sounds like something is getting wet that shouldn't be. Hopefully someone else has had this issue.

[redline racer510]

Lol it actually feels good spinning 255 section continental DW, but yeah I'm thinking a short or open of some type.

[redline racer510]

Anybody know proper method for finding shorts or opens?

[redline racer510]

I just went to go Start my car and when I try to hold the rpm at say 3k rpm after a second it just falls flat on its face and leans out and sounds like a ignition or fuel cut

[dee242]

Put your o2 sensor bsck in i had the same problem

[Drake_fist]

I had a similar issue with my rb25 when it rained but i also run a map sensor. I used dielectric grease on every single one of my wire plug in points and grounds along with battery, aem ems and I used it on everything note relays and all anything in engine bay area that makes a connection It never happened again Hope this helps ur problem.