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Guys, I really need help please......

K

Kp

1/2 ton status
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Tucson
Ok,
truck is an 83 sub, 454, qjet carb.
I have been having problems with the mech. fuel pump. It was noisy(knocking), and vapor locking. (or so i thought.)
So I pulled it, and put in an electric pump this weekend. (Facet, 36GPH, 6 psi)
After I put it in, I test drove it, and it was perfect. Crisp throttle response, plenty of power, and I ran it up to 80mph with no problems. I also took it on a 15 mile trip in town, in 108 degree heat, and no issues. The knocking was also gone. Idled smooth. I was a happy camper.
So I leave my buddys house, and head home. A 20 mile drive on the highway at 65 mph. about 15 miles up the road, it starts to die. Acting like its running out of gas. I pull to the side, and let it idle, and it idles fine, but bogs when I hit the gas. Also, it actually does die when i shift into drive. Starts right back up though, and idles perfectly.
After a few minutes of idling, I shift into drive, and it accelrates just fine, for another couple of miles, and then does the same thing again.
Temp gauge never topped 200 degrees.
Anyone have any thoughts? I am at a loss.
 
I should also mention that this is the same problem I was having that prompted the change away from the mech fuel pump.
Also, there is a return line that comes off the in-line fuel filter, about 8 inches before the carb. I blew thru the filter, and it was not clogged. Very little resistance.
I did drive it to the store and back later that evening,(about 10 miles round trip), and it had no problems on that trip at all.
This issue only seems to arise after a long cruise at hwy speed.
 
sounds like a prob with the quadrabog, not the supply...
 
I'm no genius...maybe the electric fuel pump does not flow enough for the 454? Im running a 350 with a 45GPH pump...
 
Sounds like you could have a float problem. Next time it happens, pop the air cleaner off, leave the truck/key off, and see if there is any gas coming out when you work the accelerator pump. If there isn't, then there aren't many reasons you aren't getting fuel to the carb. Need to work back from there.

Won't hurt to do a GOOD physical inspection. All connections tight, hoses in good shape, etc.

"Vapor lock" is often cited as a culprit, but rarely the actual problem.

Didn't your truck have a fuel return line anyways? (maybe with 454 they didn't) That was implemented to ensure that vapor lock wasn't an issue.
 
The truck was originally a 350 engine. The previous owner had swapped in the 454, and i just put in a rebuilt motor a couple months ago.
There is a return line inside the framrail. That is what the return from the fuel filter is plumbed to. I am the first to admit that carbs are not my thing. The last carb I rebuilt was when I was 10, on my honda XR100.
To make sure the pump is working, just look down the throat of the primaries right? Push the lever for the pump, and make sure it squirts in there right?
 
I should also mention that this is the same problem I was having that prompted the change away from the mech fuel pump.
Click to expand...

it does sound like it could be a fuel supply issue, but you know the pump isn't the problem, or at least not the only one. have you checked your fuel lines for leaks?

how about timing?
 
I checked all of the lines, and they look good. No leaks that I can see at all.
I dont have a timing light anymore, so its timed basically by ear, but it runs really nice most of the time. I do get a little bit of part-throttle pinging at slow speeeds, but that goes away completely at hwy speed. No tach to say what RPMs its idling at, but it idles smooth, and has really good power.
My oil pressure reads a little low for my liking, BUT, my sending unit is on the drivers side of the block, at the bottom, towards the very front. I am pretty sure this is not the right location, and that may have something to do with the low readings. I have heard that other chevys have them mounted somewhere near the dist? I dont know exactly where it would go up there, and I dont have anything to compare it to. I just put it in the same spot that it was on the block I took out. But like I said, this truck came with a 350 originally.
 
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Yes, when it's stalled out. Should be a strong jet for at least a couple of pumps. If it hisses, spits, or doesn't throw any fuel out, you've got a supply issue into the float bowl. Could be anywhere in the fuel system BEFORE the float bowl, but at least it tells you it's not another issue like ignition.
 
AHA!!!
I did actuate the throttle by hand, and it did kind of hiss. Also, I heard what sounded like bubbling coming from the carb when I popped the hood. By the time I got the air filter housing off, it had stopped though, so I wasnt 100% sure. The ignition was off at that point, and it was not the fuel pump pumping gas. I am wondering if the FP I bought is too small? I actually asked the guy at the parts counter if it would be big enough to feed that big block, and he said as long as it was a stock motor it should be fine.
Is 36GPH not enough to keep pace with what the engine is using at hwy speed? Maybe I am using more fuel than the pump can supply, and its running the bowl dry, and I am basically running out of gas?
I guess that would explain why after sitting for a few minutes at idle, it recovers. It has time to fill the bowl again.
 
Make sure no feul lines are close to the exhaust that will vaporize your feul in the line and starve it. Also hindsight is 20/20 but i usually recomend people use a feul pressure regulator when they switch to an elec. pump. Old carb+new high pressure=carb problems.

Balzer
 
OK I might be noob but when was last time you replaced fuel filter? Also if the carb is boiling gas, might the gasket under it need replacing? Could it be some thing in the tank that when he is going slow it sloshes and when he is at highway speed it is smother so it draws it to the pickup???

I ask because I do no know and wonder myself. Flame on!
 
On the Q-jet I had on my car engine (403) I noticed the lack of enough fuel flow under hard acceleration from a dead stop.

If your pump isn't enough (which I have no idea how many GPH a stockish 454 needs) a full throttle run as long as you can hold the pedal to the floor should tell you. Should also be 100% repeatable. BUT if you lift from the throttle, and the problem doesn't go away, then it's probably not a delivery issue. When you get off the gas, fuel demand goes to almost nothing, and since an electric pump isn't governed by whether the engine is sputtering or not like a mechanical pump, it should recover almost instantaneously.

You may not be able to keep it at full throttle long enough to suck the bowl dry, but it's worth a try.

Fuel filter could certainly be an issue, as could crud in the tank. Both would probably also be pretty consistent in showing a problem.
 
dyeager535 said:
Fuel filter could certainly be an issue, as could crud in the tank. Both would probably also be pretty consistent in showing a problem.
Click to expand...

Dirt was the first thing I thought of , having had a piece of charcoal get into my original carb from the original vapor can .

However mine ran fine at WOT , stalled at stoplights , and made slight acceleration difficult on a trip back from Tucson . It would come and go until I finally figured it out and got rid of the vapor can .
 
Hey cowboy, no flames, I appreciate any help.
Well, for the fuel filter, I did the highly scientific method of blowing thru it. Didnt seem clogged, but its cheap, so I 'll try replacing that. The only reason I havent yet, is because I was hoping to find a clear one. Unfortunatly, I need one with one inlet, and two outlets, and I havent seen a clear one like that.
I'll also get a new carb base gasket. Again, its cheap, and I didnt do it when I put in the new block, so it can't hurt.
My dad also mentioned debris in the gas tank. He said that his old willys did something similar, and it turned out to be crud in the tank. Apparently, driving in town kept the gas sloshing around enough to keep the sock around the pick-up clear. But when he'd go on a long straight-a-way, it would accumulate at the pick-up, and clog the sock.
Dropping the tank will be my last resport. Its not gonna be very easy to do.
 
You live in Tucson, somehow I doubt you'll have much problem getting the tank down. :)

I've had a BUNCH of tanks apart, never yet seen one with enough crud in it to cause a problem. I guarantee it has happened to some people, but that would take a lot of crud! I've also heard of the sock coming apart and causing problems.

Boiling in the carb seems to be a normal condition. Even my lawnmower will boil the gas if you turn it off. If it were a heat issue alone though, you would expect it to be worse at idle, as that's when heat soak will be the worst. Load on the engine moves more fuel, giving the fuel less time to pick up the heat, and gives the carb more cooling.

If you have a return, it's even less likely an issue, because the carb is ALWAYS getting a supply of cooler fuel. I don't believe the stock steel line even touched the block, heat was probably the reason. If I were you, I might look into other BBC pumps, see if you can find one with a return. That would alleviate the fuel filter issue.

Would be interesting to use one of those temp guns on the tank after it's been running for awhile. :)
 
Yeah, I'd really like to figure out a better way to configure that return line.
Right now the filter is just above the water pump,(the metal hard line routes behind it, against the block), and the return line kind of drapes down over the pass side valve cover.
I dont like the idea of that rubber hose full of gas hanging above the ex. manifold.
Plus, it looks pretty ugly too.
 
Well, I havent been able to find anything that says how many gph are needed to feed a big inch motor. Anyone know what the stock mech pump flows?
 
UMMM the return is hanging over the exh. manifold???? Could it be vaporizing the gas in the return and forcing it back into the carb. the vapor would want to go up and to the path of least resistance (I.E. shortest way out). I could be wrong but its definatly something i would look into. Drive it till it does it again and feel the return line. You could also wrap it in alum foil (loosely) to try to keep the heat out. I just thought of another thing, is this carb elect. controlled? They have an elect. conection just above the inlet. That controls the "economy" valve, witch shuts down the flow during constant RPM, they often get sticky and shut off too much. If this is in fact the way your carb is, you can simply unplug it. Unplug it b4 you drive it, if this is the problem and it shuts down on you then you unplug it it will stay shut.
 
...........that could be a problem. return line near exh manifold. I had a Holly red feeding my last 454 crewcab @ 96 gph . never had a problem like that.
 
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