Fuel Problem 425 ci Caddy

48bill · June 16, 2009, 08:59:18 PM

The 1978 425 Caddy in my daily driven 48 F-1 pickup has recently started to stall as it isn't getting fuel. After a few minutes wait it will start and go for a 1/4 of a mile to several miles before it stops again. I changed the fuel filter into the quadrajet and it still did it. That is the only filter. The quadrajet was rebuilt two years ago. I had previously replaced all the rubber fuel lines with the ones that don't dissolve in alcohol.
I was told it was the fuel pump which I replaced yesterday to no avail. I have been told that my blocking off the return line from the pump to the gas tank is the problem and that I need that line. That doesn't seem right as it was blocked on the pump since 2003. I have also been told to eliminate a valve in the filter in the quadrajet.

Any experience / suggestions with these types of probs with the caddies??

Thanks for the help.

enjenjo · June 16, 2009, 09:40:15 PM

Does the outside temperature have any bearing on it stalling? Are you sure there is no sock filter on the pickup in the tank?

chimp koose · June 17, 2009, 01:32:07 AM

Had a similar problem with a friends truck some years ago. There was no rhyme or reason to the stalling . It would just stall with no particular driving condition or weather condition,just at any random interval. Turned out to be a piece of paper floating around in the gas tank that would cover the sock in the tank and cut off fuel supply.Have you got some kind of fuel tank coating that may be separating from the insides of the tank?I have heard that some types of fuel will strip the coating from inside of the tank.

wayne petty · June 17, 2009, 02:29:13 AM

great advice from the other guys..

i want to know.. if you have the HEI ignition... and if the last time you had the module out... if you put dielectric tune up grease under it...

dielectric tune up grease has property's that let it transfer heat... from the back of the module to the distributer housing... without this special grease.. the heat will buildup enough.. it will burn out the module in under 30 minutes.. in most cases...

the modules will shut down once in a while with heat... a few minutes ... they start back up...

got a timing light?

/ hook it over one of the spark plug wires... tape the trigger on.. take the truck for a short drive... with the timing light aiming at you... see if the ignition fails first...

taking the module out... to the local chain parts store.. have them test it 6 times... in a row... it will build up heat from the tests... may pass 2 or 3 .. but when they are going bad... never all 6...

the pick up coil could also be going south... look at the connector for green grease... if it has turned green.. the pick up coil will need to be changed soon..

testing the pick up coil with a digital volt meter on ohms... 2K ohm setting... should read between 500 and 1500 ohms... before you disconnect.. flip the meter knob to 2 VDC or 20VDC scale... see if when you spin the shaft... if the meter will read over 1 volt DC ...

you might also do a full flow volume fuel pump test... disconnect the fuel line at the carb... disable the ignition system... push a length of fuel hose over the end of the open line... into a plastic bottle... have someone CRANK the motor... you should get FULL pulses of fuel with each pulse.. if they start big... then get smaller and smaller.. you have a restriction somewhere... a kinked fuel line... a crushed fuel line... blockages...

you can also hook a pressure gauge to the blocked off return line to keep an eye on the fuel pressure ... but only for under the hood... not into the truck cab without an isolator...

48bill · June 17, 2009, 08:24:06 AM

Thanks guys for the great suggestions. I've infrequently posted but have checked the RRT over the years and have learned a lot.

Weather doesn't seem to be a problem, both days it happened were in the low 70's.

I cleaned the tank three years ago. I will look in there again. There is no "sock" filter or any type of filter in the tank it just drains to the fuel line. There is no coating in it either. Three years ago it looked like new inside.

It does have an HEI distributer. I have never changed or serviced it. It was on the motor when I swapped it into the truck in 2003. I'll have to check that out.

Thank you guys.

C9 · June 17, 2009, 08:36:03 AM

Replaced the gas cap lately?

If so, any chance you installed an un-vented one?

Or . . . the tank vent is blocked?

Charlie Chops 1940 · June 17, 2009, 10:20:15 AM

I chased a similar condition on a 350 Buick HEI daily driver for one of my boys when he was in high school. Wouldn't start for him, always fired a half hour or so later. Finally pulled the dizzy and took it apart. The pick up coil wire was broke inside and intermittently touched and untouched. New pickup coil and lead and that old Buick marched on for many more hard miles.

Charlie

48bill · June 27, 2009, 09:05:39 AM

A week and a half and three tows later of chasing this problem.

Fuel tank is clean, looks like new. When it dies there is fuel into the carb but no spark.

New cap, rotor, module (and grease) and the problem still persists. It's at the garage now and they got a new coil pickup but it is defective as it was made wrong. Waiting for another one on Monday. Not too many around these days.

Hopefully that will solve the problem.

wayne petty · June 27, 2009, 08:20:27 PM

did you see my duraspark distributer testing link???

works on most electronic ignition systems

ohm meter 2K ohm setting... directly to the pick up coil...

should be between 500 and 1,500 ohms...

before disconnecting the leads... flip the meter setting over to 2 volt AC or 20 volt AC... spin the distributer shaft.... if the pick up coil and reluctor is good... you will see over 1 volt AC... this is the output signal to the module.. if there is not one volt AC of output.. it will not be enough to turn on the power transistor. no turn on... can't turn off... so there will be no triggering of the module to discharge the ignition coil...

this test only takes a few seconds to do after you have the meter on the pick up coil leads...

while the distributer shaft is out.. take apart the advance weights. pull the tiny C clips... pry up the advance plate... and slide the moving part down the shaft. clean and lube it... then put it back together...... i have had terrible problems with the advances hanging up and not returning fully...

and a tip for the viewers... pulling distributer shafts out of the housing...

turn it upside down.. fill the housing with carb spray or brake cleaner... work the shaft in and out while turning it... more and more till it will slide all the way without sticking... filing the burrs off the roll pin hole also helps...

48bill · June 29, 2009, 06:17:36 AM

Wayne, Did not get to try this as the new pickup coil had arrrived and was installed and all seemed well on Saturday afternoon.

Yesterday, Sunday, it stopped again less than a mile from home. Tried starting every few minutes and when it cooled a bit ( approx. 195 to 180) it started and I drove home.

Back to the garage again today.

I was told yesterday that a way to check the pickup coil was to see if they are magnetic.

Stumped

wayne petty · June 29, 2009, 09:22:47 AM

were you able to do a fuel flow test?

? having someone crank the engine for 10 seconds with the HEI unplugged... the line off at the carb a rubber hose pushed over the end and directed into a plastic bottle...

you should get over a PINT in 10 seconds.... FULL pulses of fuel each time... not smaller and smaller as you go...

another thing... do you have stock exhaust manifolds.....

??

is there an early fuel evaporation valve in the right hand exhaust .. (TRAP DOOR) that has gotten stuck closed... some later models were vacuum operated... without vacuum... the valve closed blocking exhaust and forcing it across the intake to warm the carb... if the actuator is broken or disconnected from a vacuum source the blockage will cause the carb to overheat... boiling the fuel .. baking the base gaskets... i have fixed more than a handful of big cads lacking power by replacing the vacuum hoses that feed this actuator and the thermal vacuum switch that controls it..

got a timing light..... hook it up ... tape the trigger on.... aim it at your windshield.. drive the truck... when the engine shuts off... see if your timing light is flashing when you crank it.. this will narrow it down to ignition system or fuel...

last thing this morning... did the ignition module get the proper Dielectric tune up grease under it?

this special grease has thermal transfer abilities.. the module will shut down when it gets hot if installed dry...

how it works... there are solids in the dielectric tune up grease.. these allow the heat buildup from the power transistor to be transfered to the aluminum housing where it can be dissipated.. the module switches 14 amps or so... about the same as your headlights on high beams..

and a warning... don't use dielectric tune up grease on threads... on sliding devices... the solids will swell and cause it to lock... tight.. like it had sand in it...

48bill · June 29, 2009, 04:40:25 PM

We think we have it. Wayne's fuel test got us back to the fuel system. After stalling out at the garage we checked for spark and it had it. Unlike last week when there was no spark. Cranked the engine for 10 seconds and only got an ounce or so of fuel. Pulled the fuel line below the tank and - drip drip. Blew air up the line to the tank and it flowed strong. Something in the tank.

Last week I pulled the gas inlet spout and the fuel gauge sending unit and looked in --- all looked clean. Apparently not so...

Two years ago I pulled and rinsed the tank when I found two cigarette filters and a strip of corrugated cardboard in there. We'll see what's there this time. May be time for a locking gas cap.

Thanks for all the help.

48bill · June 30, 2009, 04:21:17 PM

Pulled the tank today and hosed it out and blew it dry. Did not find any foreign matter in there. The inside of the tank has no rust and is the shiney grey of bare metal. Since the tank outlet has no filter/ sock or any thing I soldered a 1/2" long piece of 3/8's tube to it to stick up into the tank. I drilled 4 holes thru the tube so if a piece of film/ plastic/ foil or some such gets in the tank I might have a chance of still getting fuel. Who knows, it's worth a try.

Thanks again for all the help. This site is a great "fix it manual" for me.

THANK YOU ALL!!!!