Stumble? at 60+

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HTMLmopars

HTMLmopars

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Was driving my Valiant on the freeway yesterday when I noticed that the tach would drop a couple hundred rpm kinda suddenly and then recover. I noticed a bit of a vibration in the car when it was happening, but at 65 there's a lot of vibrations in that car, so I'm not convinced I wasn't making it up. Pulled off the freeway and finished my trip on the highway, kept it under 60 the whole time and never had that problem.
It didn't sound to me like the engine was missing, and didn't feel like she was down on power when the tach was dropping. I think maybe the ground on the tach was vibrating loose, but unsure, I'm gonna go check it out today, pull a couple spart plugs and double check the grounds to the ign box and the tach.
Running FBO ign box, and a cheapo sunpro tach.
Any input on what this could be would be great.
 
Had something like that happen to me once, I disconnected the tach and it went away.
Try disconnecting the wire to the coil from the tach and re-drive the same drive.
Could be anything from water in the fuel to skip from bad wire.
Need more info.
Joe
 
Just went out to look and it looks like the ground wire on the ign box/chassis ground from engine is a bit loose. This is the one on the firewall, it won't tighten up, it seems like there's a nut-sert in the firewall that isn't held in place anymore
 
Yeah, it's not a nut-sert its just the firewall. New ground bolt drilled and tapped. Didn't get to test drive because I got distracted with cleaning the car. Hopefully fixed today
 
Hopefully that was your issue - the only incident I had like that was when a customer's car was dropping fuel pressure during high duration freeway cruising.
 
66 Valiant wagon said:
What is vibrating? My 66 Valiant 225/903 with a rebuilt front suspension feels really solid at speeds up to 80mph?
Click to expand...
I should probably change my username, the car is a 318 now. The front of the frame isn't exactly straight, which is responsible for some of the vibration. Also I put in a 8.25 axle and am not conviced that the pinion angle is exactly on. Learned a lot from the swap and I need to get back underneath and pretty much re-do the install to get it perfect
 
I know that this thread pretty much died, but I drilled and tapped a new bolt into the firewall ground from the engine. That is also where the ignition box has its own dedicated ground. (i don't trust it to ground reliably through the chassis of the box). So far, no indicated stumble, seems much happier at high speed.
 
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