So my 98 disco runs absolutely fine 99% of the time. Any time I get a heavy rain and more recently after a high pressure wash, it won’t want to rev out past 1600rpms. The truck idles just fine but when trying to accelerate it starts missing badly around 2k. I had it at the mechanic recently and they replaced the plug wires, they said the coil pack “looked” fine. Also the ecm under the hood, they said didn’t seem to be allowing water in either. Any experience with a similar issue? Should I go ahead and replace the coil packs to see if that helps? Thanks guys

 

Are you high pressure washing the engine?

 

No just washing the exterior at the local do it yourself car wash. The problem clears up after about 5 minutes of run time

 

If you are only spraying the exterior and not the undercarriage or the engine, and it happens when it rains, my only guess could be water getting into some sort of electrical component through the gaps in the hood or down where the windshield/hood meet through there. because it clears up, makes me think wherever the water is is being forced out through driving or evaporates and problem solved. I've heard of this happening before and involving the ECU box or an electrical issue. Maybe pop the hood and look at every connection, hose etc carefully. Maybe the MAF?

 

I experienced those symptoms under the same conditions plus add driving through a puddle. Mine ended up being cracked insulation on the wires leading to and down by the crank position sensor.

 

Almost guarantee that this is due to the placement of the ecu box directly on the fender bulkhead directly in front of the washer fluid reservoir. This is North American drivers side. There is a gap where the hood and fender meet and after heavy rains my truck wouldn’t even start. This metal box has a plastic cover, but after 20 years it’s brittle and no longer fits flush or actually covers the box well. I resituated it and gaffer taped it flush to the bulkhead and now water can’t flow directly into it. Problem solved.,, no longer will it refuse to stArt after heavy rain or misfire after a deep puddle.