L-16 intermittant stalling/shut off at idle

[Figbuck]

My engine has been running strong, starts and idles fine. I get good gas mileage... it just runs and runs. I drove around all day, stop and go, on and off the freeway. A few blocks from home I stopped for a light, then it died like it ran out of gas. It didn't want to fire off, even pressing the pedal pumping some gas in it didn't want to fire. I tried to hold the pedal to floor like it would normally start if I flooded it. Finally it fired, but ran really rough for a few seconds until it cleared out and it revved and ran fine.

 

I drove it into a parking lot then shut it off to look for loose wires, stuck linkage, anything wrong. It just wouldn't start or run. I left it for a while, came back and it fired right off. I shut it off and re-fired it a few times, the choke warmed up and idled fine. I drove it a few blocks and as soon as I came up to a stop it would idle... then start to die like it is being starved for fuel... but as soon as I blip the throttle, it just kills it like an electrical switch.

 

 

Then, I cant make it fire or run at all. I have a new Interstate battery and I'm pretty blown away how much I have cranked on it, and it still spins the engine like mad! Oh yeah, this is my daily driver... recent plugs, cap rotor... matchbook dist adjusted timing... oil change, coolant... I am on top of my maintenance. Except for the distributor up grade from dual points to electronic, everything else is stock. The carb is stock. The air cleaner and all the emissions stuff is still hooked up for a 49 state vehicle... it never had the California air pump bullshit.

 

A month ago when I was working on my brakes, I serviced a bunch of stuff like new fuel filter. I noticed that there was a ton of CRAP in the fuel filter. More than I have ever seen, black shit covering the pleats in the filter fabric and chunks of junk rolling around in the filter! So the other day I see the new fuel filter equally dirty!  I thought, there is the problem... horrible gas. There is probably junk in the idle circuit of the carb!  I know an easy way to find out...

 

... I have a spare Hitachi DCH340 that is the identical stock carb. I know it is a runner too...

 

I just got done swapping it out. The fuel pump is new and a new filter, just a couple cranks filled the float bowl. One step on the pedal to turn the choke on... Bang it fired right off!  It runs waay better than the carb that has been on there. Great throttle response... a few little tweaks to the idle mixture and throttle stop... took a test spin. Dang, the engine runs good!

 

I drive a couple of miles through the hills and when I stopped for oncoming traffic to turn, it idled right for a few seconds... then shut off.. like killing the ignition switch. I got it to fire again after cranking and cranking... seems like it would run as long as it was driving. Soon as I took my foot off the gas it would stall out... then it just wouldn't fire again. Crank and crank, nothing. 

 

That was two hours ago. Just now pressed the pedal one time, hit the starter and it fired off... idled with the choke on just like it is supposed to. I killed it and restarted it a couple times. Starts and runs... I am afraid to go somewhere and be stranded again.

 

Any ideas why it would be cutting off like this?

[datzenmike]

Either spark or fuel. You changed carbs so probably you can forget fuel delivery... for now.

 

Next time it cranks but does not fire, pull a plug wire off and check for spark. Maybe coil heats up and shuts off? Try slowly pouring cold water over the coil body (not the high voltage wire) Try a spare coil.

 

You said EI dizzy... do you have an EI coil? If yes, are you sure it's an EI coil and not a points coil by mistake? A points coil will draw too much current through it and it WILL over heat. If you kept the points coil, you need to run the ballast resister.

[hobbes_the_cat]

If the engine is always hot when this happens take a look at fuel line routing. Maybe when you put the new filter on the fuel line got moved to a hot area? It they're getting too hot it could be causing vapor lock in the fuel lines. I had it happen in an old Ranchero and the symptoms were the same as you describe. Insulated the fuel lines and that fixed it.

[banzai510(hainz)]

I do the basic chacks

timming light if dist is off time and then swap distributor if you have a spare

cam timming

valve lash

 

next ck the carb if old swap it out. or blow it out

 

 

was anything was changed like coil ect ,You might have wrong one. If coil hot then soemthing is wrong

 

 

 stop running at stop light is idle jet pluugged or vaccum leak or mixture screw adjustment

[racerx]

Maybe it was not posted but what is the history of gas tank?  Had a friend that had an old BMW and similar problems.  He changed the fuelt filter like 3x and would still die on him. Finally decided to check his fuel tank and lo and behold it was cruddy inside.

[banzai510(hainz)]

if fuel filter was bad I hightly suspect rust flakes in the carb and or idle jet.

 

If idles then cuts off when gas applied the main jet may be plugged. or the dist timming or condenser is bad if running a point distributor

[Figbuck]

Here is oic of my gas tank in 2009. I changed out the hoses at the filler neck, & for the vapor tank. The inside was pristine clean and shiney. The outside was dirty but not really rusty at all, so I prepped it, shot epoxy primer and Rustoleum on the outside. My Dad told me when I learned to drive;  always keep the tank filled and don't drive around nearly empty, sticking a bucks worth of gas in it at a time.  His reasoning was condensation could or would contaminate the gas. I always fill my tank and try to keep it filled... just a habit. There just isn't that many miles since this was done, so I doubt a crumbling tank is the problem.  It wouldn't be that hard to remove the drain plug and see what comes out.

 

 

I keep a maintenance log in my glove box. I'm at 257K miles now.  At 230K (Jan. 2012) I blew a head gasket towing the trailer. So fresh head and new radiator. I remember re-torquing the head and cam towers after a thousand miles.... adjusting cold and hot. And At 240K I swapped the dual point Dist. to a Matchbox set timing and dwell, adjusted valves (only 2 intake valves were a tad tight), new plugs, cap, rotor, wires. The coil came of the donor truck. It's never hot or even warm. I personally have never had a coil go bad on any vehicle... how can I say this... I have been driving the fuck outta it with no problems.

 

About 240K I was getting some oil in my air cleaner, so put in a new PCV valve. The other thing that happened at 240K was installing a 70amp internally regulated alternator from a hardbody, then cleaning up all my circuits, lights, switches, so everything worked again. Added grounds, re-did my trailer wiring, fixed a bad headlight relay, etc.

 

In January I changed the oil, air, fuel filters... then drove 800 miles to the Bay Area. 26mpg at 70mph. I blasted around down there for a month, then towed my utility trailer with job boxes full of tools back to Poortland, getting 22 plus mpg at 60mph. I never popped the hood! The only entries in my log after that are oil, air and fuel filter changes.

 

I know it has to be something stupid simple... seems electrical more than fuel. I wondered if the Boost Controlled Deceleration Device was not working... but I changed the carb out.

 

I have a rebuild kit, so I'm going to thrash on the one I just pulled off. The boot for the accelerator pump is fucked, plus it's off and just as likely a candidate. oic  to follow... i hope

[banzai510(hainz)]

accell pump not working is a possibility But this is ez to ck and assume this was a cheaked already.  just cycle the gas and see if squirts good. I mean good.

 

since you got a mqtchbox I assume its good and its carb related as what I said.

 

Unplugged the choke if its electric(pull the choke if manual). so the choke stays on. Now if you get the truck more drivable then the main jet is plugged and your running on the 2nd barrel.

[datsunaholic]

My 510 would do this, even with filter changes rust particles got into the carb bowl and eventually lodged in one, the other, or both main jets or the idle circuit.  So the symptoms changed- sometimes it idled fine but wouldn't accelerate unless you really got it going into the secondary, sometimes it ran fine unless you got into the secondary, and sometimes it ran OK but wouldn't idle at all.  Sometimes shutting it off and letting it sit, the flakes would fall out of the jet, so it would run for a while until it got sucked back up to the jet and problems all over.   Cleaning the carb fixed it for a while, then more flakes.  Changed the carb, same issue. 

 

Turns out there was rust in the lines BETWEEN the filter and carb, and every so often it would flake off and into the carb it went.

[Figbuck]

Thanks for the advice and help guys. I just now got it running after two weeks of fucking around. In the end it was the matchbox module that failed. But there were other wires, clips and connectors that were funky too. It took me a while to trouble shoot each component. Y'all were pointing me in the right direction from the beginning.  When it wouldn't fire and run, there was no spark either. Took me a while to connect the dots there.

 

Part of my problem is that I don't have a good place to work, I can't see well anymore, my back doesn't like bending over an engine compartment. I got stranded about five of six times where I thought I found a short or open. I would fix it and try to go somewhere. One night I had to call AAA to get towed home. The next morning I hit the gas and fired it right off, ran fine. Until I drove it a ways then wouldn't idle just die with no re start. Until the next day when it would start and run again.

 

When I could make it run and idle, I wiggled / tugged on wires and clips, to see if I could make it to stall out. Just as I was about to give up because I wouldn't stall... a metal cover popped off back of the matchbox module. Then it died. A spare matchbox did fall into my tool kit a few years ago at the P 'nP... hahaha fuck you fuggers. So two minutes to swap the spare matchbox... bang it starts, warms up, idles well.

[datzenmike]

This is only the second time I have heard of a module fucking up and yours came apart.

[banzai510(hainz)]

well most L motor guys should have a spare carb and distributor , at least for trouble shooting. Most my issues are distributor related. I just wear them out(distributors)then valve lash falling out and or getting tight.

[Figbuck]

 

???...

[datzenmike]

Looks just like mine...

 

 

[Figbuck]

Is the chip and circuit board covered in a clear jelly like, silicone like, sticky goo? I don't see why it won't work just like that, cover or not. Seems like if the chip was fried, it wouldn't run the engine at all. What would make it intermittent? 

 

The spare I put in has a different case that looks sealed.

 

How can I bench test it?

[datzenmike]

Yes a somewhat sticky clear 'jelly'? The cover just protects it.

 

That Black thing at the bottom is likely a power transistor and needs to be solidly against the metal backing as a heat sink.

 

 

 

So is the back clean of oily grime so air can circulate around it?

 

Is the module directly exposed to exhaust heat?

 

Hot air from the rad doesn't matter, all modules are exposed to some under hood heat. But if insulated with grime or turned towards the exhaust manifold, radiant heat might cause intermittent operation.

 

 

You want to see another module?...

 

 

Same 'jelly' covering but this one works with EFI and adjusts the ignition advance

[banzai510(hainz)]

soem people clean out the broken box and use at as a feed thru to a GM EI module. so you can still use the trigger part of the distributor