runnin rough in rain

Ive got a 99' Chev 1/2t 4x4 with the 327 in it.. Everytime it rains, the truck runs like shit.. I dont know if it's gonna get me home..
The engine light comes on so I put it on a scanner and it comes up with "random misfire"
I tried cleaning all the coil harnesses and wires on the top but it doesnt help.. Is there anything near the bottom of the engine or underneath the truck that could be getting wet and causin this??

any ideas??

update.. its raining out now and truck is running rough again, but now my fuel gauge wont work either?? Could someting in the fuelpump or fuel system wiring be getting wet and shorting out? would that cause a misfire?

I dont think it's got to do with the rain it's more of a short circuit going on.

Humidity or something, i am pretty much having the same problem, according to alldatadiy the following information might be helpful.

Some customers may comment on rough idle after start-up, especially if the vehicle has sat overnight. These symptoms may be intermittent. The Service Engine Soon (SES) light may also be illuminated. Current misfire or history misfire codes may be detected with the Tech 2 scan tool.

Cause

A deposit build-up on the CSFI poppet valve ball and/or seat may cause the poppet ball to stick open or closed. In either case, the specific cylinder will be mis-fueled, resulting in a cylinder mis-fire condition.

Correction

A new injector unsticking and cleaning process has proven to be effective in restoring poppet valves to an "as new" condition. CSFI injector replacement should NOT be considered as a correction for this customer concern.

Check the vehicle history to determine if the vehicle is returning for a second fuel system repair for this condition. If the fuel system has been repaired for this condition previously, then inform the customer that an alternate fix is available. A new MFI fuel system has been developed that will back service the CSFI fuel system. The MFI fuel system eliminates the CSFI poppet valve ball and seat. The CSFI fuel system will need to be replaced as a unit. Refer to Central SFI to MFI Conversion instructions in this bulletin.

Notice : Individual CSFI injectors can not be replaced with MFI injectors. The entire CSFI fuel meter body will need to be replaced. The bracket used to retain the injectors in the fuel meter body is different between the CSFI and MFI unit. The unit may not seal if you mix injectors. Severe engine damage could result.

Cleaning the CSFI injectors is the preferred repair. The CSFI unit should not be replaced until cleaning has been attempted. If the vehicle should return for the same repair, then the CSFI unit can be replaced with an MFI unit. If the vehicle is out of warranty, the customer should be given the option of which fix to pursue.

Important : "GM of Canada" dealers require District Service Manager approval prior to replacing the CSFI unit with a MFI unit under warranty.

The first step of this process is to use the J 41413 Evap Pressure/Purge Station, in conjunction with the J 44466-10 pressure regulator/hose assembly, to provide the required high pressure (150 psi) source to perform the unsticking procedure. The J 39021 fuel injector tester and accessories provide the means to "energize" the injector. Some later model-year vehicles may utilize the Tech 2(R) to "energize" the injectors.

The second step of this process is to run the engine on a solution of 10% Top Engine Cleaner and 90% gasoline. This will effectively clean any deposits from the ball and seats of the poppets. It is very important that the engine fuel system is separated from the vehicle fuel system. Top Engine Cleaner may have detrimental effects on the fuel pump.

well so far its done it twice.. Both rainy days..
on saturday, then again today..
And today also the fuel gauge stopped working???

ok.. SO now Ive got a really wierd problem.. three of the gauges and all of the indicator lights stopped working, BUT they will turn back on if I hold in the trip odometer reset button.. as soon as I push that... Everything comes back to life, as soon as I let it go, my tach, fuel and temp and indicator lights will shut off.. This is F$%# up! Also, my daytime running lights (the ones under the headlights) DOnt work.. all the fises are good and the bulbs are good.. before Just one didnt work.. I think this might have something to do with the short in the wiring.. It all started after a 1 1/2 hour trip on a rainy day..

Check your computer wires that are directly connected to the ECM, it could be loose or wet, get yourself a contact cleaner that dry type ones, spray on, and spray them on all the possible contacts that run from the ECM and the main fuse blocks get the fuses checked one by one and main selonoids, this might help

I had similar problem when I had my 96 chevy only rain was not the only time it happened i found the wire harness connection loose to the fuel pump dont remember if it was on the drivers or passenger side of truck but was by the frame. at times it would not even start up after shutting off

I think I found my problem.. I decided to check all my fuses one more time and the very last fuse I pulled.. (out of the 200 in the truck) was coated in some greasy substance.. After i cleaned it out and put a new fuse in everything worked fine! And the truck doesnt stumble or run rough anymore..

But my engine light wont go off???

That could be related to your mass air flow sensor, check that also.

If it still does not go off get yourself a scanner for DTC error codes they help to identify things more easily. A worth while investment that serves both purpose is having a reprogrammer like the Hypertech programmers they can put extra HP as well as scan for DTC's error codes, but you will need a reference manual of some osrt or verify it on the internet for what the error code number stands for.