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Why is this thing shutting off $@#$%

K

K5_Fla

1/2 ton status
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Been battling a recent issue – driving down the road, no rhyme or reason the truck will decide to cut off. Very random ..not all the time. I have to coast off to the side of the road.. turn it over a few times and it starts back up again strong like nothing happened. Here the deal.. it’s not an immediate cut off, more like it’s running out of gas… kinda dropped RPM, splits, sputters and turns off all in about 5 seconds.

Ok.. so I’m thinking fuel delivery and that is where I start

1.Change fuel filter – no change.
2.Check and clean ground wire on fuel tank – no change.
3.Rebuilt the carb – edelbrock 1406 - I wanted a reason to do this so I could install the off road needles and seats. Did everything and changed the metering rods / springs around some too. Got the floats correct, etc. It runs stronger now than ever, but it didn’t cure the random cut off issue noted above.
4.Checked fuel pressure – nice constant 5 psi – no change
5.Adjusted the air/fuel mix screws – no change

Again, I think this is fuel related because it doesn’t shut off instantly – like it would with a spark / ignition issue. Its sputters for about 5 seconds before turning off.

Only thing else I can think of is two things –

1.the fuel pump is randomly shutting off - how do I test this?
2.Bad gas - the gas in the tank is around 6 weeks old (don’t drive the truck much) In addition, the last time I got gas it was Ethanol free – first time I have ever used it. Not sure IF this is related – but I DO think the gas could have already been old because people don’t use that pump often. But if it was bad gas – wouldn’t it just run bad all the time… and not just cut off randomly ??

Please tell me your thoughts…
 
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Also, the gas tank had just over 1/4 of a tank of the older gas in it. So I topped it off today with freash 93 oct Shell ...and also added a can of sea foam. Hasn't done it since.. but I have only driven it around 5 miles since doing this.
 
Distributor

My van did this once, doesnt have HEI, has the points setup, but new cap and rotor cured the problem. did the same thing, I would drive it, it would out of no where chug and die. then start right back up a few min later. The points on the cap were all corroded and the rotor was as well. $20 or so later, ran like a champ.
 
the Distributor, cap, rotor and fuel pump (really everything on this truck) is new and has less than 3,000 miles on it.

I did check everything around the distributor. But who knows...

BTW - motor is a newer TBI motor that was converted to carb a while back.
 
did you try and clean/blow out the fuel lines? was there dirty fuel in the filter?
 
I had a fuel pump act like that once. Stall, re start go, stall, repeat...
 
new fuel line from regualtor to carb. Carb is clean as can be...

anyway to test the fuel pump?
 
Check the easy stuff first man, just pop the cap off the distributor and look for corrosion.
 
yes, I was just thinking that. Even though it all pretty new, Im going to take a look.
 
Cap/ rotor all look fine.. no corrosion. Damn I hate these radom type issues!! When the truck is running, it runs like a bat out of hell.. has never ran better.

Still leaning toward fuel realated - pump (even though it's pretty new) or the gas I had was bad. I guess I just need to go for a long ride in the truck to really find out.
 
Next time I cuts off turn the key off immediately, pop the hood and remove the air filter. While looking down the carb pump the throttle a couple times. If it gives a full squirt each time the fuel pump is working fine.
 
that's a good point Chris...I'll keep that one in mind. I did notice tonight when looking at the carb that the accelerator pump is working and ports are shooting perfect the second I open the throttle. I dont think this is realted to the fuel pump.. or at least I hope not.

I really think it could have been bad gas or maybe some water in the gas. But again.. I would think it would run bad all the time. When it running it's perfect.
 
Intermittents are hard.

I am pretty good at finding them, because of long experience and lots of little tricks. In your case, we first have to isolate the problem.
It sounds like fuel, but ignition problems can mimic fuel problems.

Here is a trick I have used in the past. Not perfect, but quick and dirty. If you have an AM radio, either in the truck, or around the house, tune it off station and see if you hear ignition noise.
Not the whine that varies with engine speed, thats the alternator. I'm talking about the loud popping that varies with engine speed.
If you do, it should be fairly even. If one cylinder is louder than the others, or you only hear one, then you either have a bad connection to a plug, one of distributor ports, or a bad wire.
That is not your problem, just wanted throw that in.

If you can hear the noise, leave the radio on and go for a drive. When it quits, you should hear the ignition noise right up until it stops turning.
If you start hearing erratic bursts of static as it dies, then the ignition is failing.

If you can't hear the noise, try removing the ground wire from the body to the hood if you have one.
If all else fails, you can replace one of the spark plug wires with a copper spark plug wire long enough to check the problem.

A fuel pressure gauge like suggested, will tell you if the pump is bad, but this is easier, and more likely to be something you already have.
 
I'd wire up a bulb between the 12V lead to the HEI and ground and drive the truck--next time it quits,see if the bulb is still lit--if not,you lost the 12V feed to the HEI.that could be due to many things like a ignition switch going out,a corroded wire or one thats chewed bare by rodents grounding out,etc...

If it seems to be fuel related ,maybe the gas cap is not venting properly,and wont let air into the tank so the pump can draw fuel out of the tank..the wires at the plug on the fuel pump often corrode or burn up too,that can cause the pump to shut off without much warning,then come back on once the wire cools off again...I've seen a partially fried fusible link cause this problem a few times too...
 
Your sign says 84, do you have an electric fuel pump?

I was / still have a similar problem with my Jeep. When I got down to a Little less then 1/4 tank it would shut off when I'd go around a right hand turn. I think the tank needs cleaned out and it would go dry or suck up garbage off the bottom. It would always restart before it coasted to a stop.
 
I 2nd the question about electric fuel pump. If so, we used to have a common problem on ford explorers where the relay would go bad, shut off on a rh turn after warming up, and then restart if you tried.
 
If it's a tbi tank and sender, then the little rubber hose inside the tank could have corroded or have a hole in it. That would cause it to suck air when the fuel level got to the spot in the hose, then act normal after filling up.

My truck sits for many weeks at a time. 6 week old gas is not old. 6 month old gas isn't even old. 6 year old gas is old.


-Brian
 
Yes, the truck is an 84.. but has a tbi tank /elec pump/ sender in the tank.... all of which are pretty new. Im going to change some ingition parts this week.

Also - the problem has only happened when crusing straight.. not taking turns. The other day it happened after the truck was only running for 5 min... dont think anything had time to get too hot and cause the problem...
 
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