1990 F150 Custom / 4x4 / 4.9 liter I6 300 / Manual Transmission

Water is coming into the cab near the ECU / computer and I'm wondering if anyone else has had this issue or knows how to fix it.

To be specific: If you are facing the pedals / front of the truck (from the inside of the cab), the ECU is mounted horizontally and there is a metal mount / access plate of sorts that mounts to the left side of the wall of the cab to the left of the ECU, just above the 45 degree angle of the floor. I don't think that it's the windshield leaking since water would be all over the place, but anything is possible. I opened the hood and noticed that water runs down the inner firewall of the engine well, right around where the ECU plugs into the wiring chassis. Also, water flows down "somewhere to the right of where the ECU is.

Any ideas?!

Thanks,
Nabor J

 

ok, i have one for you to check out. the bracket that holds your clutch pedal and where it sits against the firewall. one the cab could be split on the firewall around this area or the slave master to firewall seal could be leaking

 

It's not the bracket. The leak is coming into the cab on the left side of the wall right behind the ECU.

 

I've had windshields leak.

 

is all the seam sealer there? and are your cowl drains clear? you may have to remove your inner apron to see that.

 

seam sealer looks ok, but from the amount of water coming into the truck, it could just be a very small weak point in the seal. is the only way to clear the cowl drain by removing the apron? seems that ford would have designed it so one could access a drain that needs maintenance.

 

Yes I have a 95' F250XL 6cly manual with a leaking cab on left side. The floor mat is always wet. I thought it was the windshield but now Im not sure. I'll check behind the ECU and keep you updated.

 

Yeah, I bet you have the same issue. I've taken up the entire floor mat since the insulation will never dry out. I figure I will fix the leak then install better insulation then the factory crap they used and then install a new rubber floor mat. Let's keep in touch and figure out the issue!

 

There is a foam/rubber gasket behind the flange & frame that the ECU slides into that may have dried out and cracked thus allowing water to flow through the firewall. The problem can be exacerbated by the fact that as you are driving you may have a negative air pressure in the cab relative to that under the hood. This can actually siphon the water through such a crack.

It is many times possible to locate a leak by closing all windows/doors & running the heat/vent fan on "High" using a soap & water solution applied to the engine side of the firewall with a pipette or straw to the suspected leak location. You will know when you've found the leak(s) by the bubbles that develop. To best seal the leak it is best to pull the flange loose from the firewall and clean the surfaces to be sealed, taking care to remove any and all loose and dried out sealant or old gasket material. Apply a suitable sealant - one that will remain soft and pliable.

dn.