'72 250 stalling, restarting, stalling

[rgnprof]

I haven't been here much lately as my '72 has been running pretty smoothly for a while now. But I have suddenly developed a problem where - while driving - the car just shuts down. If I let it sit it will restart and run, but if I try to restart it too fast, it will start but as I press the accelerator it will rev and then just die again. The first time it happened it felt like I ran out of gas. I shut it off, let it sit for 10 minutes or so and it started right back up and has run without incident for the next week or so - until last night.

It almost feels electrical to me - I installed a Crane ignition 20+ years ago and have never had any problem like this before. I just - less than 5k miles ago - installed new plugs, wires and the fuel filter is maintained although I will take a look at it. Zenith carbs have been cleaned and synched recently and the car starts right up w/o any trouble.

Any thoughts?

[Todd Miller]

I've never heard of a fuel filter that's been "maintained." Fuel filters get replaced.

You mention having replaced the plugs and wires, but you don't mention what brand, and you don't mention air filter, distributor cap, rotor, and whether the coil wire was replaced, or if the coil wire is solid core, or carbon core.

When the car shuts down, perform diagnostics to determine what you've lost: Spark or Fuel

I'm not a fan of any aftermarket ignition system. Points and a Bosch coil are bulletrpoof. I do have a Pertronix Ignitor and their matching coil on one of my vintage cars, and it's been both a great upgrade and completely reliable for 25yrs. My Coupe is still bone stock.

Your situation sounds like a clogged fuel delivery system, or failed fuel tank vent system. Easy to confirm either.

[rgnprof]

Poor choice of words - I do replace regularly, but I still need to check. I also recently (within the last year) replaced the in tank filter.

How would I confirm a fuel tank vent problem? I can check out supply issues..and spark.

My Crane has been running for 20 years - never had a problem.

[Todd Miller]

Drive with the fuel cap loose.

Don't rule out anything just because "it's been running 20yrs." In diagnostics, everything has to be looked at.

When the car dies, prove spark by removing 1 plug wire, putting a spare spark plug into it, and cranking the engine over. You should (of course) have spark at the plug.

To prove fuel delivery, remove a fuel supply hose from right at the carb(s), and crank the engine over. You should have fuel coming out of the hose.

It's not uncommon for there to be a fuel delivery issue where there's debris in the system, and it gets packed into a filter, or into a screen, and the engine runs out of fuel and dies. Then after a few minutes with the fuel pump not drawing on the system, the debris drifts away from where it's packed in, and the engine will restart... because there's now fuel flow. Then the process repeats, because fuel movement causes that debris to pack into where ever it's getting trapped.

When I purchased my Coupe in early 1992, it was doing just this, and it was being sold because none of the shops in the San Francisco Bay Area that it had been towed to, could figure out what was going on. The seller was tired of being stranded by the car, and then being told by a shop that it fired right up, as soon as it was taken off the tow truck. I actually drove the car home, 230mi, at night, with no problem, but it died and wouldn't restart, a week later. I had tools with me, because I knew the failure was pending. I quickly proved no fuel delivery (loosened the fuel line at the cold start injector, cranked the engine over, and watched for fuel spray), and went back to the fuel tank and found no fuel coming out of the electric fuel pump. I removed the hose from the tank to the pump and had good flow out of the tank. I stuck a screw driver down into the inlet fitting on the pump, and found a 1/2" thick slug of sandy grit was packed into a screen that was down inside that fitting. I dug the debris out of the fitting with the screwdriver, re-attached the fuel hose from the tank, and was back in business. When I got back to home, I removed that fitting, and cleaned it "for real." I've never had an issue since, and have driven the car all over CA, even 8hrs each way, to and from Tahoe.

[rgnprof]

Thank you - very helpful response. I just drove the car home - about 8 miles - and it ran fine. No issues at all...

I get the fuel possibilities and I will check, but both times it did this it really 'felt' like an electrical problem - I mean it just stopped - no sputtering etc.

I use good fuel and I just went through the Zeniths a few months back - cleaned all the jets, checked the filter at the front carb on the fuel inlet line etc

[Todd Miller]

The rule of solid diagnostics is to never assume anything. All systems that could be related to the problem being investigated, have to prove themselves to be functioning correctly, hence my statement of: Find out what you're losing. Don't assume, "...it feels like electrical, because no sputtering." Prove it.

Same goes for recent work. It all means nothing, because everything needs to prove itself to be functioning at the time of failure. What can't prove itself, is the failure.

My background as a tech is driveability issues and diagnostics. I can't tell you how many times a customer has said, "I've already replaced all that." "I've already rebuilt/repaired that/those." "My mechanic already checked that." "My mechanic already repaired/rebuilt that." None of that matters to me. Just tell me what the complaint is, and that's all I need to hear. I'm not going to avoid looking at a fuel filter because someone says it's been replaced, and then spend half a day chasing my tail, just to discover that a $5 fuel filter is actually the problem. I also see a lot of replica/wiz-bang parts being installed, and again, the claim is, "I already replaced those. They aren't what's wrong with it." Then I open the hood and find pretend spark plug wires, junk Bosch platinum spark plugs(or worse), carbon core coil wires, replica distributor caps and rotors that don't mate properly or have failed resistors, or the springs behind the carbon buttons... and the list goes on and on. Step 1: Remove all the junk replica parts and return the car to how it was built. If that doesn't solve the issue, dive deeper into the diagnostics.

[rgnprof]

I understand - I have only used NGK plugs, non-resistor, good wires, Bremi etc.

Cap and rotor are all OEM stuff - I still have the original zeniths while the only mod from stock being made was the Crane.

I have owned this car since 2000 and know it pretty well and have never had it quit on me like this - unusual! It's been a daily driver for the past year or two, so it's not like it sits around.

[Todd Miller]

That's good info. Thanks.

The diagnostic path is always: Start with the most basic cause of the problem you're diagnosing, and move toward the most complex. Adding in, that nothing is assumed or over looked. If the plug wire set uses a carbon core coil wire, I would make or purchase a solid core wire. Carbon core coil wires are prone to failure, and they have a lot of resistance. Places like NAPA have bulk, solid core wire, and the ends, so you can make one inexpensively, and it'll last you decades.

If it were mine, I'd fire it up and give a little tug on the wires that are related to the Crane unit, the coil, and the distributor (the electrcal wiring, not "spark plug wires"). Sometime you'll create a stumble, or the car will actually die when doing that, and you have an ah-ha moment, because you find a loose connection, or maybe a wire that's broken inside it's jacketing. I would also start the car and wiggle the ignition key back and forth in the run position, in order to see if the contacts in the ignition switch electrical unit were failing and causing the issue. I'd also want to see how many keys were on the key ring, in terms of, does the owner drive around with 3lbs of janitor keys hanging from the ignition switch? Or is it just the actual car's keys and a house key(aka, no weighted load on the switch)?

If the quick wire tug test didn't produce a result, I'd loosen the fuel cap and go for a long drive. Or maybe remove the cap and squeeze a piece of foil around the filler neck, and slice a slot in it for venting, and keep the fuel cap with me, if I was worried that the fuel cap might fall off the car and be lost. I'd go 30min out and 30min back, with tools in the car, an see what happened. If it died, I'd jump out and test for spark and fuel, and see what I'd lost. If I could (sort of) remedy it there on the spot, I would. Otherwise, I'd wait that X number of minutes at which point it'll restart, and make a B-line for home. Then I'd fix it at home, knowing what I'd lost, and go out on another test drive to confirm that it was fixed.

[rgnprof]

Been looking over a few things quickly this evening and found that the rear carb accelerator pump injection pipe (the little calibrated 90 degree bend pipe that squirts fuel) had fallen out of the hole in the carb and was just lying in the barrel.

Replaced it and ran car for 20-20 minutes without problem. Not sure it explains my problems...

[Todd Miller]

Nice find, and lucky that it didn't fall through the carb and go into the engine.

If you don't have your accelerator pump discharge pipes aimed in a way that they spray onto the throttle shafts, consider doing so. Having them spray onto the shafts causes that solid (unburnable) squirt of fuel to hit the shaft and then be scattered nicely into the huge dump of air that is racing into the carb throat. You'll get much better throttle response, because you're creating a fuel/air mix that's easily lit. And if you haven't already done so, consider gapping the spark plugs out to .038". That wider spark, if the crane and your coil will fire the gap under load of compression and acceleration, will create a much better burn in the combustion chamber. Your seat-of-the-pants dyno will feel these improvement. You know when the spark plug gap is too wide, becuase it results in a little harder cold start. Narrow plug gaps are for customer satisfaction (really easy cold starting) and not for performance or fuel economy, especially with the 10-15% lower performance that ethanol based gasoline costs.

[rgnprof]

Yes - I'm pretty careful about directly the accelerator fuel pump flow (but it doesn't really matter if the pipe falls out!). And I did gap the plugs accordingly - in line with the Crane (been doing that since I installed the Crane in 2005).

I'm just trying to figure out if the detached injection pipe could have have been the cause of my stalling out. Not sure that it adds up...I did check the coil - primary and secondary resistances are good.

[cth350]

I like Todd's questions, but I would slightly change how to go about the answers.

I believe that a better way to test the spark is without moving a wire. I keep a timing light handy and clip it to the center wire of the distributor cap. Use for timing, but great to see if you have the steady rhythm that you expect from a happy ignition system. An erratic pulse of light is easy to see and means there is something wrong. (and you can do the test quickly on the side of the road).

For checking fuel delivery, a clear fuel filter added at the carb fuel return line can be looked at quickly and if it's dry, something is wrong.

Both tests, at "starter speed" should show results. That's especially useful if you can compare what it's like when you are stalled on the side of the road to what it's like in the drive way.

I am rather fond of the glass fuel filters that can have the element replaced, but they can leak and be a fire hazard, so exercise some caution with them.

-CTH

[Todd Miller]

The reason why I perform (and recommend) the "check for spark right at the plug" method, is because it doesn't matter if a spark signal that's able to be picked up by an inductive connection, is getting to the exterior, center connection, of the cap. What matters, (because it's what actually creates combustion) is that there is real spark, at a plug, that's sufficient to jump the plug gap. Even this test isn't perfect though, because a spark at a spark plug outside of the cylinder, doesn't mean there's enough spark energy to jump that gap under the squeeze of compression (hence why I recommend not using carbon core coil wires... too much resistance to current flow).

Regarding the carburetor that had the accelerator pump delivery nozzle fall out; I can see where this would cause poor acceleration, due to one pump delivering correctly, and the other pump just sort of flowing fuel down the carb throat, but I don't see how it could cause the engine to shut down and not restart. The accelerator pumps are only active when being triggered by movement of the accelerator pedal. When the pedal is held stationary, like at cruise speed, the pumps are not flowing any fuel.

[subforry]

I have a Crane ignition in car that sat a long time. The 3 wire connector between the box and distributor was corroded, thus no spark.

[rgnprof]

Haven't been able to replicate the problem - hard to diagnose when you don't want to drive it much...trying to avoid getting stranded anywhere!!