I just replaced the computer.

Daburn I LOVE my Cjs No computors ...

 

I turn my jeep on everything seems fine for about 30 sec then the tach starts to move all over the place. The engine does not change then, about 30 sec after the tach starts to jump the engine starts to choke. This is all while not moving. I'll go drive it around the block and see what happens.
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Well that was fun I drove it to the next street started the turn in a coldasack (or however you spell it) and it stalled. I could not get it to start so I push/rolled it home. Tryed again once home and did not turn over but tach jumped. I think my jeep loves me...... hahahaha ya right.

 

Check the basics (Leve must be asleep)
Air, Fuel and Spark. I would check spark first though.
Post what you find.

 

I had the same tach problem on my YJ with a 4.2 and shortly after the tach started jumping I started having alternator problems. Turned out the brushes in the alternator were worn out. After replacing the alternator the problem went away. May have been a coincidence. Don't know. Check ALL the wiring especially the grounds and get the alternator checked (hopefully the tach will be jumping while the test is being done).

 

If anyone can't seem to find a computer for their jeep in Cali blame me. Mine was filled with water (again) only after one day of rain with the soft top on. This new one I'm picking up at Napa later today is not going straight in... it's going to get covered in silicon!!!!!! Then put in.

Anyone have any idea how the water is getting to my ECU?


As for the basics those are all new.... but the puter was only 4 days old so maybe they died at 4 days old also... might as well check...........

Dang it Napa hurry up with that comp I need to go to work on the other side of town!

My jeep Hates me. Ok I'll stop...

 

Be careful with the silicone. Put it on too thick and it will hold the heat and kill another one.

 

I really should have thought of that thanks. I'll be careful.

 

Might be better to fabricate a cover that keeps water from dropping into the computer but allows the heat to rise out.

 

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Be careful with the silicone. Put it on too thick and it will hold the heat and kill another one.

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Some also have a strong reactents(?) that outgas chemicals that will attack the circuit board. We use a special type of silicon coatings that we actually mix ourselves to coat our boards.

 

A very good point that I should have mentioned.

The hardware store variety silicone caulk produces acetic acid - the vinegar smell - when it cures. Circuit boards, with their lead, tin and copper, don't like acid. Dow Corning, and probably others, produces a clear RTV silicone developed for the space program that is OK to use on most electrical stuff, but they're proud of it. Last time I got some I think it was close to $10 for a tube about the size of a toothpaste tube.

If you think that water entry is really the problem you should look for electrical potting or electrical sealing compounds. Also investigate moving the device to a place where it won't be exposed to water in the first place.

 

IMHO... you're over thinking the problem. The water's pouring into the area above the heater box (where the ECU should be located) and destroying the ECU. So, why not stop the water?

You should drop and caulk the air intake plenum between the cowl and the plenum. While you're there, make sure it's drain, and the heater box drain is not full of leaves, dirt, mice, pine needles and clogged.

Then make sure the cowl seal between the windshield and cowl is intact and working. It may need replacement.

Start there...