Misfire with lower than 1/2 tank of gas

[slider701]

I’ve been chasing what I have thought is an ignition misfire and the more I’ve been driving my truck as a daily driver it seems that the issue starts to happen when the tank is below 1/2 tank. It seems to get worse the lower I get on fuel.

For reference the truck is all stock original 1970 C10, fuel tank in cab, big block (not that should matter), 62k miles, been garage kept most of its life and never left non-running for more than a month or two (like it didn’t sit for 20 years with same gas in the tank like my dad’s Pontiac did when I inherited both this truck and Pontiac when he died. My dad actually drove the truck and kept it running with fresh gas in it)

Question is gas anyone experienced this and was it a fuel pump issue or or sending unit in the tank? Could the sending unit have hole in pick up tube causing this? Or is fuel pump just too weak to pull the fuel from a tank that is low on gas?

[Sheepdip]

Originally Posted by slider701

I’ve been chasing what I have thought is an ignition misfire and the more I’ve been driving my truck as a daily driver it seems that the issue starts to happen when the tank is below 1/2 tank. It seems to get worse the lower I get on fuel.

For reference the truck is all stock original 1970 C10, fuel tank in cab, big block (not that should matter), 62k miles, been garage kept most of its life and never left non-running for more than a month or two (like it didn’t sit for 20 years with same gas in the tank like my dad’s Pontiac did when I inherited both this truck and Pontiac when he died. My dad actually drove the truck and kept it running with fresh gas in it)

Question is gas anyone experienced this and was it a fuel pump issue or or sending unit in the tank? Could the sending unit have hole in pick up tube causing this? Or is fuel pump just too weak to pull the fuel from a tank that is low on gas?

The pick up tube/sender is a real easy pull and check.

[slider701]

Originally Posted by Sheepdip

The pick up tube/sender is a real easy pull and check.

My seat back does not fold forward. How do you get it to fold without removing whole seat? I thought I’ve seen it posted that there is bolt you need to remove. Question is where ?

[sick472]

The first and easiest thing to check would be the fuel filter/s. A clogged fuel filter can cause the symptoms you are describing. A slight clog in a filter along with the reduced head pressure from a full tank may be causing fuel starvation. Look for any inline filter and your carb may have one internal to the inlet line.

[HO455]

Both of your thoughts are good ones. I would try disconnecting the fuel pump from the tank and try running the truck from a portable gas can. Obviously you will have to be careful and do this safely but it should show which one of the two items may be the problem. The fuel pump is likely the problem as the diaphragm is a wear item.

[slider701]

Well I was on my way home from work (beautiful day here in Texas and I’m working 1/2 day from home). Stopped to fill it up and it kept acting same way.

Then she blew up about a mile from the house. Really feels like it sheared the timing chain teeth the way it’s spinning over. Would make sense. If I rev’ed the engine up fast it felt like an ignition misfire. If I reved it slowly it was fine up to 4500. Timing chain flopping around would explain it.

Waiting on tow truck to get me home. I guess I got my weekend project picked out

[AussieinNC]

Pull the dist cap and hand turn the engine over...

If the rotor doesnt spin it means either the distributor drive gear has sheared off or the cam chain has broken.

BB engines are interference engines meaning there is the likely hood that a broken timing chain has also caused some bent valves / push rods. It is also possible there could be some damage to piston tops....

If you don't see the rotor turning, remove both valve covers and check for loose rockers and bent push rods...when a valve bends it doesn't seat correctly, opening up the valve clearance

If the cam is not turning, the fuel pump wont be pumping.

65000 is not a lot of miles on a chain but I have seen them grenade at 30000...

Re fuel pickup tube....these are known to crack or rust through about half way up the tube allowing the tube to draw air instead of gas.

[sick472]

That's a bummer...sorry to here about that. Hopefully your new found project will prove to be on the minor side of things.

[slider701]

Well it got even worse. Tow drive had my 17 yo son get in truck to steer the truck as he let it down off the truck in my driveway. Didn’t realize he took the cable off it and as soon as my son popped the emergency brake it rolled off the truck right into the front of my house destroying the brick and smashing the bumper.

I’m beyond pissed at this point. And completely spent for the day. I guess the good thing is it didn’t die while I was going down the freeway 65 mph and get me killed.

But if what AussieinNC is true that it’s zero clearance then this isn’t going to be a weekend fix. I’m into pulling the engine and having it rebuilt. F#%k!!

[sick472]

Dang it man! Feeling for you, my daughter put my car in drive when she was 4 (while it was running) and drove it through the garage...buggared the car up bad and knocked the wall off the foundation, It was a nice 67 GTO. She learned her first cuss word that day (nothing too horrible, but her mom did not appreciate it). Of course, it was my fault...first and last time I left the kids in the car with it running. I learnt this lesson on the first go around. It usually takes me a few knocks to the head for them to sink in.

I'm not saying your tragedy was anybody's fault, just saying I know how it feels. Stuff happens.

Keep hanging here with the forum and we'll get the motor diagnosed once you recover from the shock of it all.

[3767]

Good thing here is no 1 is hurt. Truck and house can b fixed. Kid will feel bad more than u about all this. Walk away from this thing for a few days. Just let it sit while u fix the house. Dont think about working on it till u take stock of it all. If u work on it while u are pissed, it will only make matters worse.like slick said...it happens to us all.

[slider701]

Originally Posted by 3767

Good thing here is no 1 is hurt. Truck and house can b fixed. Kid will feel bad more than u about all this. Walk away from this thing for a few days. Just let it sit while u fix the house. Dont think about working on it till u take stock of it all. If u work on it while u are pissed, it will only make matters worse.like slick said...it happens to us all.

Considering I almost ran my dad over with the same truck when I was about 14 it’s kind of fitting or ironic that my son crashed it into the house. In my case we were checking trailer lights and he was on the ground between the truck and trailer with test light. He turned me to turn the key on to test the turn signals. I bumped the starter with it in gear and truck jumped about 3-4 feet. It was enough for him to decide time to teach me how to drive a stick

[Myself]

You better name that truck Christine, lol!

[HO455]

A bit of bad luck for sure. Good advice from 3767. One thing for sure is you and your son have a good story for the future. And when you pass the truck down to your son you might want to warn him about the dangers with that truck and sons.
Keep us posted on how things go.

[Boog]

Oh man. That reminds of a neighbor's accident. He was standing between two cars after hooking up jumper cables and had his daughter turn the key, of a standard trans car. Broke both his legs and had him pinned until she could get help.

[Happy_dan]

Sorry to hear about the circumstances but nothing that can't be resolved. I am thankful for that but I know how you feel. We have all been there. Seems like some days are just better skipped. Another day and everything will fall into place.