Cross-country mileage and other updates

[adamfgarner]

Hello all,

Thought you guys might be interested in some of these details...I could also use some help from the experts. I will try to keep it concise as it's been awhile since I've posted, so if you want the deets either reply, pm me, or you can call 805-698-1461....sooooooooo.....here's the saga:

My truck left me stranded at work....just wouldn't start again...would turn over, just no spark. Had it towed home...after some fiddling and such I replaced the module (HEI) and it fired up only to fail to do so after a couple of successes. My brother-in-law came to rescue me in my ineptitude and after a few tests/checks put in another module and corrected some of my blunders. Truck ran great.
This was right before a cross-country move necessitated by a high cost of living and divorce terms in California. I had bought a Dana 60 rear-end from a 1972 Chevy with 3.54 gears I had intended to swap mine out for (Dana 60 4:10 with positraction)...although the '72 wasn't a posi (bummer) I opted to change it anyway in favor of the bigger brakes and better highway gearing. I made the switch and headed out on the highway...
My previous mileage checks with the Holley 500, HEI, 4 speed, 4:10 gears and 31 inch tires resulted in a pretty consistent 11.5 mpg mostly highway miles..didn't vary much at all.
Once I switched the rear-end and figured out the odometer/speedometer difference by doing mileage checks and comparison to a companion vehicle I did mileage checks all across country from Southern CA to Southern IN (anyone know where I can get the right odometer/speedometer gear for the transmission now that I have changed gear ratios??)...worse mileage was about 12.5 - 13 going through the rockies, the best was just over 15 after I came through them...though there was some variance I did different legs at about 50-55 and 55-60....my rpm's dropped significantly with the gear swap (about 400 at speed) and my mileage was pretty consistently about 14 - 14.5 with one leg nearing 16 at best.
So I arrived in IN after four days of about 500 mile per day of driving with only some charging system problems (installed a Rebel wire 9+3 harness as my original ignition harness got melted from a bad ground in the starter??...) anyway the rebel harness and staff are great...it turns out my instrument panel cluster ribbon wasn't powering the alternator excitor...after an alternator/regulator change and figuring out the real issue the truck ran great for almost 2200 miles...then I got to Indiana and my ignition problems started again...really weird stuff : would turn over but not start...change module, start right up....run until I shut it off...failed to start again...change module start right up...after lots of whining to Irishbleueyes and some research, I still have the same problem...I have gone through 5 modules (later had them tested at Autozone 3 times each on their tester and they tested good...put one back in...starts a couple times then won't)...replaced the coil, checked the grounds, changed to a solid state one wire alternator, and more but still the same problem...did an ohms check on the magnetic pickup??? going to replace it tomorrow...just weird, weird problems with this ignition unit...any sage advice is appreciated. Also I would really like someone to tell me how to wire my 2 speed wiper motor back up...got 2 tabs on the switch and 3 on the motor...I didn't pay attention when I pulled it out when doing the harness swap...hope this wasn't too long or choppy and at least somewhat interesting as to how this old truck held up on the long haul. Any help in my current follicle reducing dilemma is appreciated. I now live in an area where internet service is hard to get so please feel free to call 805-698-1461 (eastern time) if you think you can solve my Scooby-doo mystery.

[bigblockv6]

It's possible that you're using the wrong module in Your HEI or the wrong coil. The Chevrolet HEI uses the coil with red and yellow wires while the Buick,Olds, Pontiac & Cadillac versions uses the coil with red and white wire, you have to use the corresponding module with it. I found this out some 22 years when I decided to use a fancy Chevrolet application Accel Super Coil in the Buick HEI on my 68 pickup, well within a month or so it burn up the module so I went back to the correct coil and the problem was solved.

[BarryGMC]

I am glad you made it. The mileage you experienced is about what I see with the 305 4 speed and 3.54 with the 3/4 ton trucks. However this is with stock ignition and Carb with about 4 degrees more advance on the base timing.