454 Engine feels like its running out of gas

Rickf1985 · August 29, 2016, 09:50 AM

That 7 MPG is an average of light cruise where it is probably 12-15 MPG and acceleration where it is 2-3 MPG. I can assure you that at WOT it is in the negative figures at probably closer to 1/2 gallon per mile. Now think a half gallon jug of water and you are pouring it into a glass. Yup, about that fast!

BrianB · August 29, 2016, 11:19 AM

Quote from: kansascat on August 29, 2016, 01:35 AM

According to my math, it actually ismore than enough fuel delivery. At 7 mpg, even if you were running 70 mph that would still only require 10 gallons per hour. Slower speeds would be fewer miles in a hour and even less fuel per hour. Just saying.

And how far up a 5% grade would you get before the float bowl is empty?

tmsnyder · August 29, 2016, 11:28 AM

A fuel pressure gauge at the carb would be helpful.

Quote from: Froggy1936 on August 28, 2016, 01:24 PM
Your next move is to check the amt of fuel being delivered at the carb . If it is sufficient the problem is in the carb, Plugged fuel filter(inside carb ) Floats set way to low , Metering system inop ! Frank

kansascat · August 31, 2016, 12:34 AM

Quote from: BrianB on August 29, 2016, 11:19 AM

And how far up a 5% grade would you get before the float bowl is empty?

Perhaps our issues are a bit different then, because mine starves out of gas while cruising on flat and level once its hot and starts doing its thing, yes, pulling a grade will make it also happen, but not only on a hard pull. I just installed a second carb base gasket, the thick ones, so have two of them under it. I doubt it will help really, but for $4 its worth a try. Ill prob find out this weekend. If it shows any signs of helping ill invest the 40 bucks for a thermal barrier one. I also unhooked the vacume line that operates the heat riser valve on the RH manifold which if i understand correctly will insure it stays in the open position...and its not stuck, i checked that. This thing is putting so much heat thru the passage in the intake its all burnt and crusty next to the carb on both sides. Anyone know just where to look and what to do as far as a egr valve. Not sure if its got one or not as i dont see anything that looks like what i used to seeing on others that have one.

cook elandan · August 31, 2016, 07:29 AM

kansascat, Like I told Brian, You need to remove all of the pumps that don't belong you are just adding to a mix that might not be balanced to run correctly. set it back up the way it should be, It ran before like it should, so if it does not now, need to think what you did before this started. Tune up done with correct parts. Was the timing changed and is it correct. Any bad vacuum lines. Plenty of air flow through the radiator. Clutch fan working correctly. All the fuel filter are fresh. Oil and Transmission temps are OK. All fuel lines are good and not cracked also in tank tubing. I would get the block off plates that you can install to shut off the cross over port in the manifold, they make a complete closure plate or a plate that has a small restriction and then see if you are still having a boiling issue before going out and getting a new cam/manifold/carb. JMO.

tmsnyder · August 31, 2016, 08:13 AM

Just "T" into the fuel line near the carb and actually see what's happening with the fuel pressure as you drive. $27 at Hazard Fraught, probably a lot cheaper on sale.

http://www.harborfreight.com/fuel-pump-and-vacuum-tester-62637.html

Not for permanent use!! Don't hook it up and leave it though, you don't want to plumb a pressurized fuel line into the cabin, just to troubleshoot.

legomybago · August 31, 2016, 09:48 AM

Quote from: kansascat on August 31, 2016, 12:34 AM

Perhaps our issues are a bit different then, because mine starves out of gas while cruising on flat and level once its hot and starts doing its thing, yes, pulling a grade will make it also happen, but not only on a hard pull.

This is exactly what I am fighting right now on my FMC. A completely different animal than your rig, but same fuel starving issue.
I would do the same as cook elandan mentioned about only running one electric pump, and make sure all your rubber fuel lines are new, or at least inspected. We cured our vapor lock problem on our P30 this way. The fuel we get to run these days boils to easy.

kansascat · August 31, 2016, 10:14 PM

I think ive pretty much covered the suggestions so far. Ill run thru it again for clarification. Fuel tanks have been removed...twice, and inspected for clean. EVERY rubber hose on the entire fuel system has been replaced with new, and good screw type clamps installed on every connection to insure air tight seal. Every filter was new, and now ive removed all of them ...including the one in the carb inlet, except one in line filter just ahead of the engines mechanicle fuel pump. One at a time ive tried only the mechanicle pump, and then only the big HD elec pump thats ahead of the mech pump, including bypassing the mech pump with the line. Ive replaced the fuel selector valve, and then bypassed it all together to see if it helped. It has fewer issues when running off the smaller aux tank which is just behind where the driver sits than it does on the factory mkain tank back behind the axle. It does better on the main tank since i put a in line elec pump back just ahead of it to push fuel forward, but still does it when hot. The exhaust system is in need of replacing as its got a few thin spots that leak as does the right side muffler. and the rear tanks fuel line runs inside the right frame rail which places it fairly close to the exhaust all the way forward. Its issues do seem to get worse the hotter the outside air temp gets, and its def worse in city traffic than on the open road. My current theory is the exhaust is heating the fuel coming from the rear tank as it travels thru the line so that when it reaches the carb its already pretty warm, and the rest of the problem, the majority of it, is the intake heat is over heating the gas once in the carb bowl. This is why i think its better on the aux tank as it reaches the carb a bit cooler than when on the main tank.
Everything on the engine was replaced when i first started restoring it from its 18 year slumber. All hoses, belts, thermostat, plugs wires cap rotor vacume lines filters and fluids. I removed the ac unit including the condensor so its getting great air flow thru the rad and usually runs below the center of the factory temp gauge and even on hard long pulls it rarely gets above mid point. Im running dual HD tranny coolers mounted just behind the grill and one of them i even added a elec fan on it so tranny seems to be running cool and happy. Ive made sure the heat riser valve is working freely, and now have it unhooked from vvacume even tho ive not seem it ever go to the closed position which is my understanding requires the vacume pod to pull it shut and that it defaults to open under its spring pressure with no vacume. When it has stopped running on me i have on a couple occasions coasted to a stop of wheezed to a pull off and shut it down and removed the air cleaner and witnessed the fuel boiling in the carb bowl by looking down the vent openings with a light, and noted at least on some occasions when i pumped the throttle it did not spray gas from the accelerator nozzles till a few pumps were made. Let it sit and cool a bit and it will retsart and run fine for a ways till things get heated up again.
Im running out of hair to pull out on this one. This weekend we plan to head out with it, and the only thing ive changed is to double up on the thick carb base spacer / gasket, and remove the vacume line from the heat riser, and adjust the timing a bit now that we are back to lower altitude. Sitting in the driveway its running great. It will actually spin the tires when power braked in my gravel drive. I think next will be a new exhaust since it needs it anyway. My only decision first is to install headers or not since it appears they will be needed to go along with the cam manifold and carb upgrade that will be coming. Any recomendations on a header model that fits and works well on these older P30's?

cook elandan · August 31, 2016, 10:47 PM

kansascat,
here is a quick trick that you might try, use this on my street racer. Make a coil of fuel line that you can get some good air flow around and attach it just before the mech fuel pump. so you are just making a gas cooler in a sense. some times at the track they are made where they fit in a large coffee can and you fill it full of ice just before your race. may be a way to cool your fuel down if that is an issue.

kansascat · August 31, 2016, 11:54 PM

Well i kinda did to some degree, i removed the steel fuel line that GM runs up the front of the engine and across the intake to the carb, and ran a rubber fuel line from the mech pump out thru the fender well and up above the engine over the side right to the carb inlet. This way the line is in a cooler area not being in the engine compartment. I also bent the aircleaner intake hose as much as i could so its drawing most of its air in from that same wheelwell area rather then right next to but still behind the radiator so its getting cooler air. Im going to get some flex hose the right size and run the air intake in from up just behind the grill so it will get cold air completely. Good input tho. Thanks.

MotorPro · September 01, 2016, 07:34 AM

Time to stop throwing parts and find the problem. You have. no idea if your problem is fuel or electric. Put a pressure gage and find out if your getting fuel or not. If as I suspect (based on everything you have already done) you are getting plenty of fuel. Then you have to determine if the problem is in the carb or in the ignition.

tmsnyder · September 01, 2016, 07:37 AM

So you're not trying to pull fuel through dead in-tank fuel pump? Thought I read that somewhere.
Could it be a heat induced ignition problem?

lemortede · September 01, 2016, 09:56 AM

So I tried to read through all this to see if this was covered, but did you check the fuel filter in the quadrajet? When in first got my mh some one had put that fitter in backwards. The only way it ran was when there was enough fuel pressure to push the whole filter forward against the spring. It's also possible that it's just plugged...

legomybago · September 01, 2016, 10:54 AM

He removed it already

lemortede · September 01, 2016, 11:06 AM

Thanks. I must have missed that.

cook elandan · September 01, 2016, 11:33 AM

I still say put everything back to factory. It worked that way in the past. so now there is a problem that is in the engine area. Kansascat stated that he has leaky exhaust. I would put a heat shield down the frame rail to protect the fuel line. So for the most part with all that has been done to his RV the engine is good so the middle man is the carb. have it rebuilt.
Just had a quick thought, Kansascat could you exhaust be plugged up causing your engine to over heat more. That could put more heat near the fuel line and more heat internal through the crossover in the manifold. JMO.

kansascat · September 01, 2016, 10:10 PM

I rebuilt the carb in order to get it running in order to bring it home when i got it. It shows no signs of having a plugged exhaust, in fact its got enough holes in it that id say its overly free flowing. LOL
I went ahead and ordered a set of hedman headers for it yesturday. Will install them and then it goes to the muffler shop to get a new Y pipe made for the headers where it will run down the left side to a muffler and then turn out ahead of the rear wheels. This way it wont even be close to the fuel line or main tank.

kansascat · September 01, 2016, 10:57 PM

To address your question regarding it being electrical. I guess the main reason im thinking its fuel and not electrical is when it quits running, and i look in the carb bowl vent i see it boiling,AND it dont spray fuel when i pump the throttle like it should. Pump it several times and it will eventually start spraying fuel as it should.

Mike_Rosoft · September 02, 2016, 09:07 AM

Well, might as well drop in my 2p..

My 87 Chieftain 26RH had a very similar issue, felt a bit like a VW bus when she warmed up or was going uphill. As there aren't that many RV shops over this side of the pond, this little community helped a lot. Reading through many posts, I discovered that I had a couple of problems.

1st the 'auto retarders' .... not the ignition, but the exhaust valves, do stick closed (probably the cause of so many header issues) ... surprising how different she is, once that green idea was wired back at first, then removed when an exhaust specialist made me some custom connectors.. now that helped with the flow, but made the starvation a bigger issue.

The answer was to replace the fuel pump relay (NOT MANUFACTURED OR AVAILIABLE ANYMORE!!) so I had no choice but to disassemble it in its entirety.. This little beast from the 80's is a safety relay! very interesting! When you turn on the ignition it has a 10 second priming ON action then it turns off the pump. Then it waits for the oil pressure to rise whilst the engine is running, then turns on the pump again. The relay shuts off the pump if the oil pressure drops (i.e you have an accident). all of this is done using discrete components! so after fitting the reconditioned electronic relay I can hear a very quiet motor at the back when I turn on the ignition. Not only does she start a lot better when cold, she now pulls like a train..... but only when I can afford it over this side of the pond(almost $10 US gallon)!!!...... next project is to connect a 12" red lamp to the top of the dash flashing and sounding the alarm on the opening of the 2nd throttle!

tmsnyder · September 02, 2016, 09:35 AM

Sounds like another case where a gauge would have been handy to troubleshoot the problem.

T in the gauge, verify that it has no pressure at the carb. Maybe it's the fuel relay? --> Jumper the relay to force the pump 'on' --> Pressure at carb? Y? ---> Bad relay.

But without seeing the pressure at the carb you're just shooting blind.

cook elandan · September 02, 2016, 03:07 PM

It may not be the pressure but the flow. They all say that the unit runs fine for awhile then the issue happens. There is a loss of fuel some where. Maybe there is a clog in the hard fuel line. Are you able to clean it out. With kansascat he has three pumps in the system, they may be working against each other. Didn't see where he say anything about a fuel regulator. Brian was trying to pull through a dead pump and regulator.
but I agree with tmsnyder along with put the unit back to factory and test the flow and pressure and that will take all of that out of the issue. I had said that on my 85 elandan, only had the mech pump with two tanks main behind rear wheels and aux mid driver side. no electric pump. PO kept good logs and never saw any comments about fuel issues. unit has 113k miles with dual exhaust headders and is 34' long. Air flow under the RV should be enough to keep heat away from fuel lines in the rail.

bluebird · September 04, 2016, 10:54 PM

Quote from: kansascat on September 01, 2016, 10:57 PM
To address your question regarding it being electrical. I guess the main reason im thinking its fuel and not electrical is when it quits running, and i look in the carb bowl vent i see it boiling,AND it dont spray fuel when i pump the throttle like it should. Pump it several times and it will eventually start spraying fuel as it should.

Are you sure you have the correct size needle and seat in the carb? They do have different sizes. Is the float adjusted correctly? You need to run that bowl as full as you can because the Qjet has a rather small bowl to begin with. You also need 6 to 6.5 lbs of fuel pressure at the carb. You really should take the time to pull the top back off the carb to be sure the bowl has the correct amount of fuel in it.

Rickf1985 · September 05, 2016, 08:43 PM

I have already added my 30 cents but 6-6.5 lb.s of pressure is pushing the upper limits. It is doable but could possibly cause flooding under some circumstances.

tmsnyder · September 06, 2016, 11:11 AM

A pressure gauge will indicate whether the flow is sufficient at all times and at all loads. And as Rick said, 6 psi is too much, carbs only want like 3psi.

Quote from: cook elandan on September 02, 2016, 03:07 PM
It may not be the pressure but the flow. They all say that the unit runs fine for awhile then the issue happens. There is a loss of fuel some where. Maybe there is a clog in the hard fuel line. Are you able to clean it out. With kansascat he has three pumps in the system, they may be working against each other. Didn't see where he say anything about a fuel regulator. Brian was trying to pull through a dead pump and regulator.
but I agree with tmsnyder along with put the unit back to factory and test the flow and pressure and that will take all of that out of the issue. I had said that on my 85 elandan, only had the mech pump with two tanks main behind rear wheels and aux mid driver side. no electric pump. PO kept good logs and never saw any comments about fuel issues. unit has 113k miles with dual exhaust headders and is 34' long. Air flow under the RV should be enough to keep heat away from fuel lines in the rail.

bluebird · September 06, 2016, 04:09 PM

Quote from: Rickf1985 on September 05, 2016, 08:43 PM
I have already added my 30 cents but 6-6.5 lb.s of pressure is pushing the upper limits. It is doable but could possibly cause flooding under some circumstances.

Depends on what size the needle and seat are. If they are the stock .110 they will handle 6 psi. If they are the .125 he can get by with 5 psi. A big block should have a .125 needle and seat, but I don't know what comes in the kit now a days. Needles and seats used to be available up to about .150, not sure they're available any more. The float setting is very critical on the Qjet.

tmsnyder 3 psi is too low on fuel pressure for a Qjet, cant fill the bowel fast enough for a BB engine.