weird drivability issues... UPDATE

[dvdswan]

so my problem happened about 4 wks ago with an intermittent hesitation.  it seemed mainly going up hills with about 1/4 throttle.  well, it adventually stalled on me and would not restart.  the starter ended just clicking.

I didn't have time to look at the truck until this past Sunday when I was able to check the battery, clean the cables, and see if there was gas.  I hopped in the truck and it fired right up.  Knowing I still had a drivability issue I would take a look at it this coming weekend.  well, my DD had an issue yesterday so I took my chance with the truck today.  this morning it ran fine and only hesitated once going up a hill. 

well this evening I was driving home and again going up a hill it started to hesitate and backfire, as the road flattened out it started running fine but this time going down the hill it hesitated a little.  I was lucky to pull into a parking lot before it died.  I took a look and noticed that the vacuum advance for the distro at the carb was not on the tube, I connected it back together, check the carb to see if there was fuel couldn't tell.  I tried to crank it and it fired right up but stalled a few seconds later, tried again and the same thing but it lasted about 10 seconds longer.  well, I tried one last time and all it did was click. 

well the click issue I think is most likely the battery cable is corroded as well as an old battery.  I did rebuild the carb about 3-4 months ago and haven't had any issues until 4 weeks ago.  I've thought it might have been a float issue until it hesitated going down hill today.  I replaced the fuel pump 6 months ago, spark plugs, filters, and pcv also.  fuel is over a 1/2 tank in one and full in the other.

I'm mainly looking for advice on a direction to go when I look at it this Sunday.  I've looked through few drivability threads and I'm not sure if they really relate.  I'm wondering if I'm having a fuel and electrical issue.

any help would be greatly appreciated.

[rich weyand]

Backfire or afterfire?  Backfire is up through the carb, afterfire is in the manifold or exhaust pipe.  I'm guessing afterfire.  Sounds like a boom under the floor panel about at your feet.

One thing that can cause this is a loose distributor.  They seem to loosen up in warm weather, so if you clamped it in the winter....   Anyway, one thing to check is grab the distributor and try to rotate it.  Another is to check the timing and make sure it is where you think it is.  I say all this because it's acting like it's way retarded.

If they are older than ten years old, replace the battery cables, both the hot to the starter and the cold to the alternator bracket.  You need the negative cable with the extra smaller wire on it to go to the radiator support.

You don't say what engine, carb, distributor you have, but assuming a bit, I will offer the following as well:

Hook the distributor vacuum advance tube to manifold vacuum, not ported vacuum.  This could be the downhill problem.  Ported vacuum was used beginning in 1968 with AIR pumps.  Manifold vacuum has been used since 1930 without AIR pumps.  If you don't have an AIR pump on the engine (pumping air into the manifold), then use manifold vacuum.

Check the timing with the distributor vacuum hooked up and make sure it is stable.  At idle it ought to be at full advance, so it should be (stock distributor) 8* more than the base timing.  Checking the timing with the timing light with the vac advance connected allows you to check that it is working.  The vac advance could be sticking or leaking air, also retarding the spark compared to where you want it.

Make sure the centrifugal advance is working.  Check the timing with the vac advance disconnected and then gradually speed up the rpms to 3000 rpm.  You should see the ignition walk advanced about 20* (stock distributor) by 3000 rpm.  If there is any problem with any of this, open up the distributor and check it for corrosion, gunk, etc.  You can oil the gizmos in there very lightly to get them to free up.

Set the base timing (vac disconnected) at 15* BTDC minimum.  Recommended settings of 4 or 6 or 8 degrees BTDC once again for use with AIR pumps and other emissions equipment.  The 350 in a 78 K10 will take 16, 18, or even 20 degrees BTDC before it will knock.  Ignition advance is like a horsepower screw on those engines: more is better until you get to the point where it knocks at low rpm under heavy load, like accelerating from slow speed up a steep hill.  You should be able to hear it if it knocks.  But 15* BTDC is a safe setting for that engine.

It could be other things as well, but ignition is easy to check, and battery cables are easy to change, so I would start there.

[bake74]

If they are older than ten years old, replace the battery cables, both the hot to the starter and the cold to the alternator bracket.  You need the negative cable with the extra smaller wire on it to go to the radiator support.

You don't say what engine, carb, distributor you have, but assuming a bit, I will offer the following as well:

     I agree, replace both battery cables anyway, you suspect them now.  The other statement is very important to get the right advice, considering the advice would change for different carb's especially.

[FlatBlack77]

funny you should make this thread.

i had a very similar problem this morning while taking my 77 to get inspected for the first time in 3 years. only i didnt have the backfiring/afterfiring or the stalling. just some hesitation going up hills when i had to give it a little bit more gas. once it leveled out it was just fine under the same bit of throttle.

my timing numbers are all pretty spot on and this is literally the only running issue ive noticed so far. i had my distributor all apart recently and everything looks good inside and i installed  new cap/rotor/coil/rubber part/ignition module. BUUUUTTTT i have the vacuume advance hooked up to the carb where my old one was. after reading this i guess ill try hookng it up straight to the manifold

[bd]

Dave, install 2-gauge all-copper positive and ground battery cables.  Since you questioned fuel delivery, verify correct fuel pump draw, pressure and volume - and check the fuel filter; even if it is new.  I suspect the stalling is pick-up coil and module - replace the distributor.  Perform an Internet search for high voltage aftermarket HEI replacements - they're cheaper than repairing an existing distributor.

[dvdswan]

thanks for the replies.  I replace both the pos and neg battery (napa 4 ga.), cleaned all the connections including the 2 negs on the rad core support in front of the battery and on the frame.  as soon as they were replaced I tried to crank it and it turned over.  tried again and it fired up and drove it home. 

the carb is the stock quadrajet, distro looks to be very old and I have thought about upgrading it even before this.  I did check the timing when I rebuilt the carb so I will check that again this weekend.  as far as the backfire, it would be more of an afterfire as it was in the exhaust.  the batter will be replace this sunday as well as it's over 10 years old.

sad to say since owning the truck I haven't even popped the cap off the distro so that will be done this weekend as well.  I'm going do guess that its probably dirty and carboned up in there.  the PO had replaced the cap and wires so will be on the list as well soon.  he didn't tailor them to make them neat.  they are not arcing on each other so that's why I didn't touch them yet.

again, thanks for all the info.  one of the reasons I love this site.

[rich weyand]

Get the Taylor spiral wires.  A little more expensive, but not much, and much much better.

[dvdswan]

so, as it turns out, the right side fuel line (original hoses) ended up deteriorating and creating flap inside the fuel line creating a blockage and not letting the fuel get to the carb.  running out of gas.  I'm beginning to see a trend with this truck. lol.  I was about ready to drop the tanks to check for debris blocking the socks when I decided to just take it to the dealer and have them figure it out since I needed it to be my DD for a while starting next week.  not what I like to do but having to work 60+ hrs a week puts a hamper on working on your vehicle sometimes.  glad its fixed though. 

thanks again for everyone's input.

[dvdswan]

First off, I know this is an OLD thread, but the saga continues.

I started to have the same drivability issue again. so today I had time to replace all the rest of the original rubber hoses, dropped both tanks and replaced those, replaced the hose from the transfer valve to the main fuel line and the hose to the fuel pump.  The fuel pump is relatively new, replaced when I bought the truck when I thought I wasn't getting fuel, turned out the transfer valve was bad.  The carb has been rebuilt as well.  The truck will run great and performs well when it runs.

I started the truck and let it run for a bit.  It ran for about 10 minutes and stalled.  I pulled the hose off that feeds the fuel pump and it was dry.

I'm wondering if the steel lines are affecting this?  Or if something in the tanks themselves are causing this?  It will stall on either tank.  I'm also wondering if I let it warm up enough.  I thought I did. 

Any suggestions would be appreciated.

[Blazin]

Have you checked fuel pressure after the pump? Just because it is, or was a new part doesn't mean it might not have an issue. I have got bad parts right out of the box many times. Have also had new parts give problems a month, two or three, or a year into service. 

[WhiteHorse75]

I recently had the same problem. I spent over $100 changing all the goddies in the HEI distributer--with no improvement. I finally gave up and bought a new HEI, I was on the road in 30 minutes........

[dvdswan]

thanks for the replies guys. 

I did replace the distributor when I installed the new intake about 4 months ago.  I've had this issue off/on for a while now.  I'm going to blow out the steel line from the diverter valve to the fuel pump and pump to carb.  Just maybe there is a piece of deteriorated hose in there. 

Thinking back when I rebuilt the carb because the gas mileage was junk IIRC about 2 weeks to a month after that I started having problems.  I'm kind of wondering if the float was set right.  I'm probably second guessing myself but I might try rebuilding it again just to verify the float level.

I did replace the fuel pump Tuesday just thinking if the clogged hose wore it out.  It did idle for about 45 minutes before it died.  It would restart until the next day.  Then it fired right up.  Frustrating.

[dvdswan]

So a while back I bought 2 new tank sending units thinking the socks were deteriorated.  I dropped the tanks today and the socks weren't deteriorated like I thought but they were folded up against the pickup tube in the tank.  I'm hoping this is the reason for the fuel starvation issue.  The old socks were black nylon and the new ones were white.  The inside of the tank looked new as well.  Fingers crossed.

[Irish_Alley]

so 3 years later your still having issues?

[dvdswan]

I've been out of town for work the last 3 years.  so yes.  lol  I'm getting tired of traveling too.