Over 25 Years Later, Finally My 71 C-10 Truck Build

[hgs_notes]

Been trying to diagnose a problem with the new engine. It starts and idles fine and seems ok cruising but under acceleration it sounds aweful. Like it's misfiring. All of the EFI parameters seem to be normal. I had a bad plug wire, interference with the headers. I replaced all of the plugs with Accel shorty plugs and some of their best wire sets with porcelain boots. It didn't make much difference.

With the ignition system mostly ruled out I'm swapping out the EFI throttle body with a Holley carburetor. I had to get the fuel pump to run without the ECU connected and reduce the pressure. Unfortunately the old pressure regulator I had has a leaking diaphragm so I didn't get to try it out today. New parts should be here tomorrow. If it still runs the same with the carb I'm not sure what to do next.

[OneOffStroker]

Originally Posted by hgs_notes

Been trying to diagnose a problem with the new engine. It starts and idles fine and seems ok cruising but under acceleration it sounds aweful. Like it's misfiring. All of the EFI parameters seem to be normal. I had a bad plug wire, interference with the headers. I replaced all of the plugs with Accel shorty plugs and some of their best wire sets with porcelain boots. It didn't make much difference.

I don't think it was your EFI, or fuel related at all. Do a compression check, or use an infrared thermometer if you have one and take temps of each header primary right at the cylinder head. I bet you'll find one or more cylinders are much colder than the others or have lower compression. This is the exact scenario I have on my '72 at the moment. My case is self inflicted, and I bet yours is due to trust in brand new parts.

Your valves need lapped. They aren't sealing properly and creating leak-by, losing compression, and ultimately causing the engine to run like poo. It will start and idle fine, but worthless under acceleration.

A lot of budget heads are budget for a reason. They are assembled and seem ready to run, but a test as simple as filling the ports with water and looking for seepage around the valves will often show that they are not properly seated because they need lapped. That test should be performed even with expensive heads from Dart, Brodix, AFR, etc. Look at the reviews for Summit Racing's as-cast performance heads, which are just re-boxed Dart heads, and most reviews say that they need lapped right out of the box.

I did not test mine before I bolted them on, and sure enough...exact symptoms you're having. I went through three carburetors and never solved anything. After talking to a buddy, it clicked that I never lapped the valves after grinding them before assembling. Like I said...mine was self-inflicted.

[Palf70Step]

Truck still looks great. Glad she is running again for ya.

[hgs_notes]

Story time boys and girls. I took the day off for the longer weekend and took the wife out to do some of her favorite things, shop thrift stores and eat something we didn't cook. Another reason for the drive will come up later. We were at the 2nd thrift store and I spot an old boombox. You know the kind, 2 speakers, maybe 4, AM/FM/Cass, set it on your shoulder and walk the hall blasting some awesome 80's hair metal. First thing I said was "Oh that's coming home with us". A note on top says the radio works but the cassette player doesn't. No big deal. Although I still have a collection of 70's & 80's eargasm ecstacy on cassettes somewhere, I haven't pulled them out in years. I noticed the cord was missing but remembered seeing a few bins of miscellaneous cords at the previous store. We went back there and the first one I pulled out fit it. On closer inspection it's a Panasonic and if my old one from high school was sitting next to it I wouldn't know which was which after so many years.

Back then I didn't have much but I did have transportation and tunes, which was more than a lot of kids.

The boombox I had in high school was a big deal to me. It wasn't one of the big expensive hip hop break dancer mega machines. It was pretty basic but was a "good" brand. Not one of the extremely cheap store brand ones that might go a month before you blew the speakers and the antenna broke off. At the time I had minimal cash flow, no job, and was driving the hand me down beater truck that we hauled trash to the dump with and firewood from my grandpas woods for heat in the winter. It was only 12 years old but back then a truck over 10 years old in Minnesota was a well used, rusted beater by then. At least the heater worked. It was a 3 on the tree, with 307 sbc, remember those? And the only options was the heater, AM radio and the custom deluxe package so a cloth seat, vinyl door panels and lower body trim. That boombox radio was my sound system. Until it wasn't. Someone got into my truck in the high school parking lot through the rear slider (an option I installed after finding one in a junkyard).

A real kick in the nads. After the loss I think I installed one of those FM converters you could get but that single crappy dash speaker was not up for the challenge of AC/DC, Def Leppard, Dio, Scorpions, Ozzy, etc. Some time later I went to visit my cousin down by the cities (Minneapolis/St Paul for you non-locals) and we went to one of those mega sales for electronics they had at the state fairgrounds. I picked up a JVC head unit and some pioneer speakers with an amp/equalizer. The best of the 80s bargains I could afford.

On another note, I blew the engine doing burnouts in the parking lot that weekend. I should rephrase that. I damaged the engine doing burnouts in the parking lot. Not the original 307. That boat anchor had been replaced with a 283 built by a classmate in our auto shop class. I didn't use my own because I rebuilt a ford small block I think. I lived about 100 miles NW of the cities and tried to nurse that truck home just knocking like a sailor trapped in a sunken ship. I made it about half way. I was driving down US Hwy 10 and barely keeping it at the posted 55 with a ton of weekend traffic when there was a sudden bang and then silence and I drifted over to the shoulder. I managed to get the clutch in and keep my momentum enough to make it to a driveway for a farm field. It was not a good weekend.

Anyway, the engine teardown revealed the imprint of a bolt in the top of one of the pistons. Which resulted in the piston breaking and the rod coming loose. The rod did some further damage while the piston was up in the cylinder until it broke and was able to do a full rotation which removed chunks from the bottom of 2 cylinders. Something also managed to get up into the cam area locking it up and breaking it into 3 pieces. I was able to salvage the heads and 5 pistons/rods and the intake. The rest was scrap.

Oh my dad came with the 76 Oldsmobile cutlass supreme and towed me home the remaining 50 miles. My parents bought the engine from the school for me as a graduation present. When I showed the shop teacher the piston he refunded the money and I used it to build another 283, which I still have and it still runs in my racecart.

$8 for an old boombox at the thrift store.
The walk down memory lane, both good and bad, priceless.

The other reason for our trip today was to pick up a hood for my wifes first truck. A few weeks back I bought a 1999 Chevy S10 that was in very good condition. Never really winter driven, only 119k miles, 4 banger with automatic. Cloth seat and manual windows. It does have a decent radio and AC, PS, PB. It does have some rust showing above the rear wheel wells but otherwise it was mint. Until one of my stepsons friends backed into the front end one night. Less than mint. The kids found a grill and headlight. I found a good hood in the right color. It even had a bug deflector on it! It's almost mint again.

And to finish this very long post, and actual update on this particular truck. I got a new air cleaner to match the valve covers. I know, so what. But I drove my truck today and love it just like I did all those years ago when someone stole my boombox out of the cab in the high school parking lot.

[fatbass]

Great story, HG!
I still have the '70s era Pioneer Supertuner AM/FM in-dash cassette player from high school. I replaced the belts in it and it sits on a shelf in my garage waiting for me to repair the cut dash and replace the CD player in my '71.

[hgs_notes]

I installed a new torque converter lockup switch so I can manually turn it on and off. Works great!