matt_ls1_z28

My 1999 Z28 Camaro is missing when it rains, if its dry the car runs fine. I think that it may have something to do with my coil paks or plugs...any suggestions please....my car has slp longtube headers and a full slp loudmouth, it has no cast on the exhaust....excecpt the the Y pipe it appears to be custom, which i need to purchase a Y-pipe from slp but...ive checked for leaks and they arent any...i bought the car and all that was on it...i also have a slp ultra Z hood on it and ram air is functional...the egr is off and has like a "freeze plug" in the whole...im not a mechanic, just a body man...this one guy told me they call it a freeze plug...he is suppose to be really smart mechanic, i just hate asking him for advice because he talks to you like your dumb.

99ls1bowtie

iTrader: (1)

I would check your O2 sensor connections. They can get water in them and the car will run like absolute ****

matt_ls1_z28

Ive checked them and i dont think that is it...ive hooked a obd scanner to my car and it pulled all the 02's but i figured that is just from the aftermarket exhaust system...and it also pulls up P400 Multiple Cylinder Misfire after i reset the codes it will pop up the 02 codes right off the bat but takes it a second on the multiple cylinder misfire...any ideas on what that means? Ive thought about taking a spray bottle full of water and spraying on my coil paks and plugs...will that hurt anything? Of course im gonna do this when its dry to see if that makes it cut out

Monello

iTrader: (1)

Replace your front o2 sensors. Problem will go away.

matt_ls1_z28

If it was my 02's wouldnt it do it when it was dry to?

dman

iTrader: (5)

my 87 turbo buick had a similar problem when it rained. after lots of hair pulling i read somewhere that the grease in the electrical connections dry out over time and become suceptible (sp?) to moisture. I bought a extra large tube of dielectric grease and filled every connection i could find from o2's to coil pack. never had the issue again!

CoastieWS6

iTrader: (1)

It could be the spark plug wires, if they are old or haven't been changed. If they are old they could be cracked and the moisture will make it run like ****.

LSxPwrDZ

iTrader: (4)

My guess is o2 sensors. Aspecially if you reset the computer and its the first codes it throws. Once the o2's arent working properly it will cause cylinder misfires as long as you are running in closed loop. If you floor it and get into power enrich mode the car should run normal. If it does then it has something to do with the fuel control in closed loop and that would be the o2 sensors.

jsteele90

iTrader: (13)

its either water getting on your o2 sensors or your o2 extensions. for me it was my o2 extensions. i just disconnected them, packed them with dialectic grease, reconnected them, wrapped them with electrical tape, and called it a day.

SSpdDmon

iTrader: (10)

Also check the top of the PCM. You may need to buy/fabricate a cover for the top of the PCM as water running off the windshield may be getting to the unit.

Monello

iTrader: (1)

I had this exact same issue with my car, thats why I beleive its the o2s.

When I installed my headers, I extended the o2 sensor wires. Whenever it would rain, water would get into them and misfire like crazy.

I ended up buying new o2's and getting the right extensions. The problem went away.

john shea

I have the exact same problem. I'll try some dielectric grease in the spring.

00silver6

iTrader: (4)

if your getting a p0400 that is exhaust gas recirculation flow fault not a multiple miss (p0300) which one was it?

stormsracing10

my 99 is doing the exact same thing. except im all stock no headers or 02 extensions. and when it rains i pick up a miss

rjkZ28

i would check wires and coils.

TURBO6.0L

iTrader: (1)

I would get it up in the air and start selectively hosing things down to see if you can get it to come back. A spray bottle might work like you mentioned but you will probably have to pump it a whole bunch to get enough water out. I would spray the O2 connections, plug wires and coils as well as the PCM. Make sure you do it separately so you can figure out what item it is so we can all stop guessing. How many miles are on the plug wires? Does the miss start as soon as you start the car after it has rained? This might indicate the PCM since it is likely the only thing to get wet while the car is parked. Once you start driving down the road the O2 sensor wires would really be the only thing to get really wet. The plug wires and coils should stay pretty dry.