I'm about to order a new ECM for my truck in a desperate attempt to fix a problem, but thought I'd ask for help before I do. I'll spare you the details of how I slowly learned the following things about my problem, but here's what I know:

• the truck misses and smokes when it experiences the problem, indicating excess fuel
• the problem only happens after the truck has been parked in rain
• the truck will run perfectly when driving in heavy rain as long as it hadn't been sitting in rain
• the #8 injector pulses too long when the problem occurs. I had suspected this for a while after seeing a wet #8 plug a few times, but I recently confirmed it using a breakout box to watch the injector pulses while the engine was running poorly
• the #8 injector has been replaced twice and the problem continues
• using the breakout box, the circuit for the #8 injector shows the same kOhm resistance to ground as all of the other injectors. this was tested when the truck was experiencing the problem after a rain
• when the truck was experiencing the problem I couldn't seen any water on the fuel injector wiring harness. there was some water sitting on the firewall wiring harness connector near the ECM, but it has been greased with dielectric grease

Here are some of the things I have done trying to fix the problem:

• the distributor cap and rotor button have been replaced
• the plug wires have been replaced. the plugs have been inspected
• the coil has been replaced
• the cowl has been resealed with seam sealer. the foam dam under the cowl has been replaced above the ECM. the weatherstrip across firewall has been resealed to the firewall. a couple of windshield leaks have been repaired.
• there was some water in the floormat after the truck had been sitting in rain recently. however, the ECM was connected to the breakout box and was sitting in the floorboard. it was near the wet spot, but I didn't see any water getting onto the ECM or the wiring to the ECM.
• dielctric grease was added to ECM connector & TFI connector
• foil tape was added over the ECM to firewall seal
• fuel injector wire harness (MAF conversion) has been wrapped with harness wrap to prevent water getting in
• plug wires have been routed according to the service manual recommendation to ensure proper spacing and 90 degree crosses. watching the plug wires in the dark and misting water on them showed no arcing.

There's probably some other things I've done but that's all I can remember now. I really thought I was going to find a lower resistance to ground on the #8 injector wiring, but now that I've checked that with no problem found I'm at a loss. The only other thing I can think to do is replace the ECM, but that really doesn't fit the problems I'm seeing. The ECM doesn't seem to be getting wet, and the problems seems to be related to water running in somewhere, not just humidity in the air.
This isn't a daily driver, and it stays in the garage most of the time, but I've been dealing with this for a while. I've gotten some great help here previously. Any suggestions?

 

How exactly are you measuring injector pulsewidth?

 

I used a breakout box and digital multimeter to measure voltage between the injector pin and ground. The meter isn't quick enough to measure the actual pulses, but it seems to average the voltage. The displayed voltage corresponds to pulsewidth. At idle running normally the voltage displays about 0.8 volts. Giving it throttle will increase to displayed voltage up to about 1.5. When I experienced the problem I was reading around 9 volts on injector 8 but normal (1-2 volts) on all the other injectors.

 

aaaaand what are the codes that are being thrown, if any?

don't overcomplicate things, these are crude machines that don't need excessive diagnostics 99% of the time. not saying you shouldn't break out the break out box (pun intended), but you should start with the bare bone basics first.

pull codes, check fuel pressure, report back.

 

There are no codes. I haven't checked fuel pressure, but one thing I didn't mention was that it runs great most of the time. When the problem shows up it starts immediately, and when it goes away it is immediate, like someone flipped a switch. I've done the simple stuff like plug wires and distributor cap. The injector circuit is also pretty simple outside of the ECM, so I can't figure out why it's going haywire.

 

And you're 100% sure theres no wires chafing?

 

No, not 100%. I thought if there was chafing I could detect it by checking the injector circuit resistance to ground while I was experiencing the problem. All the injector circuits showed the same resistance. I don't remember what it was, but it was up in the kOhms.

 

Check the computer inside for signs of water intrusion or damage.

 

I will. I've been in the computer before. You may have noticed from my signature the I've got a quarter horse on it. Also I've replaced the capacitors on the ECM before I realized my problem was moisture related. I sealed the ECM seams with foil tape to keep moisture out, but you're right that I should open it up again to double check.

 

I had previously seen no codes when I used my scanner. However, this morning I did the KOEO test using a jumper wire. It gave me two codes, 15 & 67. I probably need to clear them and see what comes back. I have a feeling that the code 15 may have been stored from when I had the adaptive tuning turned off via Binary Editor. I'll update y'all with any checks I get a chance to do. Thanks for everybody's help so far.

 

I really doubt code 15 has anything to do with disabling the adaptive. I suspect you either have an intermittent power fault (losing power to pin1/KAM memory power) or an internal fault with the PCM.

 

Thanks. The intermittent power failure to pin 1 is worth checking. I seem to remember a damaged terminal in the ECM connector that I had to repair when doing the MAF conversion. They could be related. I took the ECM apart last night. It had a little rust on the outside from contact with its supporting bracket, but looked ok internally. I'm going to put it back without the quarter horse just to make sure that isn't causing problems.