engine dies in 15 minutes

[Shady Rascal]

You're either losing spark or you're losing fuel. Don't make it any more complex until you figure out which is the culprit.

When the thing dies, spray a spritz of carb spray or starter fluid down the carburetor. Does it try to start now ? If so, you have a fuel supply issue. If the spritz down the carb didnt cause it to try and start, pull a plug wire off and check for spark while cranking.

[bigjason]

When it dies look into the carb and see if the squirters are pumping fuel. Is the motor timed correctly? It could be getting hot due to poor timing and causing excessive heat that is vapor locking the fuel system. Are any fuel lines ran near the exhaust manifold?

[happy1970GMC]

When I had this problem before, I changed the fuel pump and had no problem for a couple years. That's why I changed the fuel pump again.

[Blakeman350]

I had the same problem, I tryed two different electric pumps and a mechanical pump and changed filters many times and it still died in about 15 or 20 miniues. I ended up pulling the tank to clean and coat it and found the filter sock on the sending unit pickup tube was plugged nearly solid and very rusty. So with a new sending unit and a clean tank she runs all day long.

[lyrikz]

Originally Posted by happy1970GMC

1970 GMC probably a '72 engine, 350, Q jet, auto tranny. Just replaced the mechanical fuel pump. It still dies at 13 to 15 minutes, and it will have to cool down for at least an hour, then do it again. Any help would be appreciated.

Seing posts like this frustrate me a little bit being a mechanic shop owner. This is a very simple fix. After 15 minutes and it dies do you still have fuel, spark, air, and compression. You are losing one of those.
Go spend 100 bucks and have a tech diagnose it for you.

[davepl]

Originally Posted by lyrikz

Seing posts like this frustrate me a little bit being a mechanic shop owner. This is a very simple fix. After 15 minutes and it dies do you still have fuel, spark, air, and compression. You are losing one of those.
Go spend 100 bucks and have a tech diagnose it for you.

Why would I pay to have a tech try to replace all those parts one at a time until it worked again? I could do that myself :-)




[This is too subtle even with the smiley perhaps, I agree troubleshooting is a lost art sometimes]

[MySons68C20]

You don't have to replace all the parts just the ones a PROPER diagnosis points to.

[MySons68C20]

Originally Posted by lyrikz

Seing posts like this frustrate me a little bit being a mechanic shop owner. This is a very simple fix. After 15 minutes and it dies do you still have fuel, spark, air, and compression. You are losing one of those.
Go spend 100 bucks and have a tech diagnose it for you.

This is what to do.

[davepl]

Originally Posted by MySons68C20

You don't have to replace all the parts just the ones a PROPER diagnosis points to.

Sigh. I knew it was too subtle. Even with a smiley. Even with a line of grey text.

My point was that a good technician doesn't just replace parts until the thing works again. He figures out why it's not working properly and fixes the problem. Which is why I said troubleshooting is a lost art...

But I wouldn't pay someone to look down the carb for me to see if fuel is shooting, or to check spark. Cover the basics at least!

[MySons68C20]

Originally Posted by davepl

Sigh. I knew it was too subtle. Even with a smiley. Even with a line of grey text.

My point was that a good technician doesn't just replace parts until the thing works again. He figures out why it's not working properly and fixes the problem. Which is why I said troubleshooting is a lost art...

But I wouldn't pay someone to look down the carb for me to see if fuel is shooting, or to check spark. Cover the basics at least!

Now I get it!

[Blakeman350]

One thing I forgot mention is I have a filter before the carb with a glass housing so I could monitor the amount of fuel I was getting when I first started it compared to when it would stop running. Since its before the carb I could tell I wasn't getting fuel to the carb and knew my problem was between the pump and tank. Since its a new pump that led to the tank. Cheap and easy diagnosing that I did myself.

[lyrikz]

Originally Posted by davepl

Why would I pay to have a tech try to replace all those parts one at a time until it worked again? I could do that myself :-)




[This is too subtle even with the smiley perhaps, I agree troubleshooting is a lost art sometimes]

Lol. I giggled. I feel you man. It should be a relatively easy diag.

[Grumpy old man]

With informative forums and you tube any problem you may have should be easy enough to diagnos and correct within hours not days weeks or months . Sometimes you can lead a horse to water but you can't make them drink .
Posted via Mobile Device

[67 chevelle]

Originally Posted by Shady Rascal

You're either losing spark or you're losing fuel. Don't make it any more complex until you figure out which is the culprit.

When the thing dies, spray a spritz of carb spray or starter fluid down the carburetor. Does it try to start now ? If so, you have a fuel supply issue. If the spritz down the carb didnt cause it to try and start, pull a plug wire off and check for spark while cranking.

excellent advise

[davepl]

I was watching a dyno session this week and they had a dead hole. The guy (the customer at home, not the shop or dyno guy) only put rings on seven pistons.

The exhaust port was clean as a whistle, never fired. Proof that you DO need compression, not just fuel and spark. But I doubt he loses compression after 15 minutes...

[happy1970GMC]

For anyone reading this thread: Had the truck towed to a mechanic highly
rated on Angie's list. He's telling me 'you can't find anyone to work on a
quadrajet carb anymore." "You need a $2500 fuel injection kit" Is it really that hard to find an honest mechanic? I can simply order a rebuilt quadrajet carb for as little as $270. Where do I go to get the "screw me" sign taken off?

[happy1970GMC]

Sorry guys, I forgot, this isn't dear abby.

[Grumpy old man]

http://www.allamericanautolongmont.com/ here is a repair shop with an A+ BBB rating in your town , Bite the bullet and drop it off . The only other best bet would be to contact some of the local car clubs and ask for some help .The fuel system in these old trucks is not rocket science .Have you ever tried to pull the sending unit in the tank ? your problems started years ago and got better when you replaced the fuel pump .You may just need to clean the fuel tank and lines ? And get rid of the glass fuel filter it's a fire hazard .

[67 chevelle]

Are you using a ballast resistor , or the white cloth covered wire to your coil ?

with the truck running , or key in the run position , you should have around 9 volts to the coil positive , if its 12 you may be overheating the coil , it will wear your points quickly also

[swamp rat]

Originally Posted by happy1970GMC

1970 GMC probably a '72 engine, 350, Q jet, auto tranny. Just replaced the mechanical fuel pump. It still dies at 13 to 15 minutes, and it will have to cool down for at least an hour, then do it again. Any help would be appreciated.

Under the cab there is a 3" length of hose separating the gas tank tube and the fuel line running to the pump, if the hose is the original hose it could be collapsing and causing a starvation issue.

I still don't know after reading this threadif you were ever able to determine if its fuel or spark...

[davepl]

Originally Posted by happy1970GMC

For anyone reading this thread: Had the truck towed to a mechanic highly
rated on Angie's list. He's telling me 'you can't find anyone to work on a
quadrajet carb anymore." "You need a $2500 fuel injection kit" Is it really that hard to find an honest mechanic? I can simply order a rebuilt quadrajet carb for as little as $270. Where do I go to get the "screw me" sign taken off?

Run away!

You need a mechanic who specializes in pre-1972 vehicles, probably. I'm fortunate to have 3 old veterans who work from a huge rural home shop so when I can't figure it out, they do. But that's all they do - classics and old stuff.

A basic Q-Jet tuneup is something a respectable tech should be able to do before falling out of bed in the morning. But not many current techs, working on modern vehicles, will know much about them.

Find a good local tech. Then buy him a Christmas present at Christmas, send them a card, pay your bill promptly, and hope they live forever. Odds are they will be over 50 already, one foot on a banana peel and the other....

[lyrikz]

Originally Posted by davepl

Run away!

You need a mechanic who specializes in pre-1972 vehicles, probably. I'm fortunate to have 3 old veterans who work from a huge rural home shop so when I can't figure it out, they do. But that's all they do - classics and old stuff.

A basic Q-Jet tuneup is something a respectable tech should be able to do before falling out of bed in the morning. But not many current techs, working on modern vehicles, will know much about them.

Find a good local tech. Then buy him a Christmas present at Christmas, send them a card, pay your bill promptly, and hope they live forever. Odds are they will be over 50 already, one foot on a banana peel and the other....

The $2500 dollar fuel injection is pretty funny. We just went through something similar.

On my 71 i had a quadrajet on it. It would run great, then run like ****, then run great. My tech, who is an old timer. Completely tore it down, rebuilt it and it ran great, then started running like crap again. Turns out that the pinhole passages everywhere in the carb were getting this corrosion of some kind and i think the ethanol in the fuel wasnt helping. I slapped an edelbrock on it and never looked back.
No one, not even me is going to want to rebuild your carb, but we would offer a already rebuilt unit. Slap a new carb on it and call it good. You can do it yourself and its not very expensive at $270 bucks.

[happy1970GMC]

So I got my truck home, carb's in pieces in a box. $300, including towing both ways. For all you who make a living at working on cars, it just got a little tougher to prove you are honest. This is a town of about 100,000 people, many mechanics. I'm looking into buying an ad in the local paper to tell people about this. No names of course, the justice system protects the guilty, not the victims. I'd like the honest mechanics to know why people may not trust them.

In Colorado, small claims court doesn't cross county lines, since I moved a few
miles recently, there's no help there. Angie's list says these people are great, who bought them off? Maybe they are doing their own reviews. Since I got into this I've done more research about these people. There are horror stories about the owner, including flipping customers off in his parking lot, on Main street. There will be one less classic truck on the streets for the foreseeable future.

[happy1970GMC]

Just wanted to thank you all for your help, I'll get back to working on it sometime.

[lyrikz]

Originally Posted by happy1970GMC

So I got my truck home, carb's in pieces in a box. $300, including towing both ways. For all you who make a living at working on cars, it just got a little tougher to prove you are honest. This is a town of about 100,000 people, many mechanics. I'm looking into buying an ad in the local paper to tell people about this. No names of course, the justice system protects the guilty, not the victims. I'd like the honest mechanics to know why people may not trust them.

In Colorado, small claims court doesn't cross county lines, since I moved a few
miles recently, there's no help there. Angie's list says these people are great, who bought them off? Maybe they are doing their own reviews. Since I got into this I've done more research about these people. There are horror stories about the owner, including flipping customers off in his parking lot, on Main street. There will be one less classic truck on the streets for the foreseeable future.

So basically you paid a diagnostic fee plus towing. Where are they in the wrong? You towed them the vehicle, they stated you need a new carb, or go fuel injection. You said no, then towed it home. Did you expect them to diagnose it for free???
You cant tell me they didnt tell you there would be a diagnostic fee for shaking it down? Tell the whole story.