'89 Silverado Missing

'89 Original Stock, 350 ci TBI w/auto trans, 90,000 miles, spacer under throttle body is only performance part. New MSD plug wires, plugs, distributor cap, rotor, MSD coil, TBI spacer, fuel filter, & O2 sensor at 70,000 miles. New MAP sensor recently. Bad miss and loss of power during times of rain, mist, high humidity only. Starts missing after warm-up and continues for about 10-15 miles of highway driving, then quits. Runs well after warm-up and when no rain. Checked electrical connections. No OBD code. HELP!

'89 Original Stock, 350 ci TBI w/auto trans, 90,000 miles, spacer under throttle body is only performance part. New MSD plug wires, plugs, distributor cap, rotor, MSD coil, TBI spacer, fuel filter, & O2 sensor at 70,000 miles. New MAP sensor recently. Bad miss and loss of power during times of rain, mist, high humidity only. Starts missing after warm-up and continues for about 10-15 miles of highway driving, then quits. Runs well after warm-up and when no rain. Checked electrical connections. No OBD code. HELP!


I would disconnect the battery neg terminal and then clean and re-secure all grounds. check wires under the hood area for damage .


the ICM can be the problem when they get old the internal circuits begin to breakdown . the other item would be the ECT/coolant temp sensor to the computer could have connector or the sensor is defective.

check this wiring carefully.

use dielectric grease in the plug wire boots. always check the plug wire resistance. new wires does not mean good wires.

route the plug wires correctly . use loom and tie straps/wraps to hold plug wires correctly if the original plastic holder is destroyed.

I have the same truck and the same issue. I've always assumed that mine was because one of the ears for securing the distributor cap down is broken and I can't get a good seal around the cap. The one screw is stripped out. I've been wanting to replace the distributor, but money hasn't been flowing that great lately.

Also, my check engine light is on constantly. The code says that the catalytic convertor is not performing as it should. I guess it's getting clogged up since my truck is pushing 200K. I want to remove it, but the engine light would remain on.

I have the same truck and the same issue. I've always assumed that mine was because one of the ears for securing the distributor cap down is broken and I can't get a good seal around the cap. The one screw is stripped out. I've been wanting to replace the distributor, but money hasn't been flowing that great lately.

Also, my check engine light is on constantly. The code says that the catalytic convertor is not performing as it should. I guess it's getting clogged up since my truck is pushing 200K. I want to remove it, but the engine light would remain on.

use a reverse drill bit of a smaller size than the screw and drill out. place a self taping screw where the distributor cap screw is .

put some anti sieze on these cap screw threads.

missfires will destroy the converters.

use a reverse drill bit of a smaller size than the screw and drill out. place a self taping screw where the distributor cap screw is .

put some anti sieze on these cap screw threads.

missfires will destroy the converters.

The screw isn't broken off, the metal ear/tab that is molded into the dist. is half broken. There is already a larger diameter self tapping screw in there, but with the tab being broken, it just spreads further apart and the screw never really tightens down. Eventually, I will just replace the dist.

I appreciate your suggestions. Some I have checked, but you gave me some good ideas. I had not thought about grounds. And I'll check the temp sensor. I will follow up if I solve it.

The screw isn't broken off, the metal ear/tab that is molded into the dist. is half broken. There is already a larger diameter self tapping screw in there, but with the tab being broken, it just spreads further apart and the screw never really tightens down. Eventually, I will just replace the dist.

get a stick of metal epoxy . comes in a 9 inch tube. cut a piece off and mix it up till gray color . clean the broken ear with sand paper and wire brush . apply this product use a good amount then in an hour drill out a hole and try putting a normal sized screw. try to match the screw dia to the hole drilled.

you can use a dremel tool to shape it easy.