Weak Fuel Fuel Flow on p30

Madtrap · February 09, 2014, 01:22 PM

Hi all,
I have a 89 chieftain with a 454. I'm trying to get some info on how the in tank fuel pump works. On my last trip to the track it was acting like it was starving for gas. So when we finally limped back home I disconnected the fuel line from the filter on the tank side and ran a line to a gas can to see if I had fuel flowing. I have no fuel flow if the ignition is on and engine is not running. When the engine is running there is a week stream. Maybe an 1/8 in diameter. Seems insufficient and might be my problem.

Is this pump load sensitive? Pumping more fuel as needed.

A couple years ago the regulator was leaking and I mixed up some jb weld and coated the outside and it hasn't leaked sense. Last minute rigging as we were going to the track the next day. Kinda wondering if the regulator has failed. Don't know if when they fail does it restrict the flow?

I'm going to drop the tank to change the reg anyway so I guess I should change the pump out as well. Any body know the pump part number?

Rickf1985 · February 09, 2014, 04:40 PM

I am not sure if the regulator can fail that way but another thing to check is the mechanical pump on the engine. The electric supplies the mechanical which in turn supplies the carb. At idle, unless there is a hole in the line, you should have a pulsing flow from the line. Another thing to check is the filter between the regulator and the front of the coach. I have not found mine yet but I have heard that these never get changed for that very reason. I am curious how you got to your regulator back when you worked on it. I can't even see mine. So far I have the tunnel that the fill tube runs through in the compartment out. I figure I will have to drop the tank but I can't see how to get the fill tube off enough to prevent damage. Getting it off is not a problem because I plan to replace it but I need to be able to get it back in one piece. I have not been able to do anything because of this exceptionaly bad winter.

Rick

pvoth1111 · February 09, 2014, 05:51 PM

The regulator should be in the frame, passenger side, back by the tank, I believe accessed in front of back tire....a rebuild kit is like 5 bucks.....maybe took me 15 minutes to do....if you don't move the adjuster (center bolt)...should have no trouble....

repairing it correctly easier that JB weld............relating to the PO post......PO put JB weld on regulator....

Madtrap · February 09, 2014, 07:06 PM

My regulator is in the frame behind the rear tires and half hidden by a side compartment. Could not get a screw driver in to remove the cover. Thus the half assed fix.

I was able to get the tank pump to operate by jumping the oil pressure switch. The rv had about 20 gallons of fuel in it. It took 30 minutes to fill a 5 gallon can. I did pull the filter and ran a hose from that point to drain the tank. The fuel filter was half way between the front tire and side door.

We'll got the tank out. I cut most of the fuel lines as they will be replaced with new ones. What a

. I'll get a pump and reg and put it back in next weekend. I'll Change the mechanical one on the engine as well.

ClydesdaleKevin · February 09, 2014, 09:04 PM

I went through most of this, except the regulator issue. 3 electrical fuel pumps later, a new mechanical pump, and I was still intermittently having the vapor lock fuel delivery problem. Then the last electrical fuel pump stopped running altogether, and I concluded it must be the fuel pump relay, an unobtainable obsolete part. I rewired the whole dang thing through a standard fog light relay using 10 gauge wire all the way back to the pump, and problem solved completely! I ran the relay to ignition 12 volts so the pump comes on when the key is turned on. Not the safest way to do it...it bypasses the oil pressure safety switch...but it works! I have a thread about it on here somewhere.

When working, if you disco the fuel line midship, the flow from the electric pump, while regulated, is a pretty substantial flow! Not just a trickle, so you probably do have a bad fuel regulator.

And its a good idea to invest in an inline fuel pressure gauge. I don't leave mine in place, but to check things I put it inline with the fuel line running to the carb...easy on mine since its an Edlebrock. Fuel pressure should be right around 4-5psi.

Kev

Rickf1985 · February 10, 2014, 12:29 PM

Kevin, Why didn't you tie the actuation wire into the oil pressure safety switch? I may NEVER get to mine! Last year we had one week below freezing, This year we are lucky to get even close to freezing from the other end of the scale. With snow every week too.

Madtrap · February 10, 2014, 09:02 PM

Thanks for all the good input. Now to find the time to put all back together. At least I don't have to worry about snow. 78 in Phoenix today. 88 is forecast for Friday.

Froggy1936 · February 11, 2014, 02:55 PM

@ Rick The oil pressure safety , Its only to shut off fuel supply in case of a roll over or serious frt end crash . Both unlikely events with a R/V But in case of impending occurance pump can be shut off Between Oh My God and Oh Sh--! The only other benefit is to allow oil pressure to develop before engine trys to fire up The main reason for not includeing it/relay and original wireing was to eliminate the possibility that they were causing the running out of fuel problem ! Frank

legomybago · February 11, 2014, 03:40 PM

I like the option of priming my carb with the electric fuel pump "before" turning the engine over..With the oil pressure switch in series you can't do that unless you incorporate some sort of over-ride I guess?

DaveVA78Chieftain · February 11, 2014, 04:04 PM

Quote from: laygomybago on February 11, 2014, 03:40 PM
I like the option of priming my carb with the electric fuel pump "before" turning the engine over..With the oil pressure switch in series you can't do that unless you incorporate some sort of over-ride I guess?

To pre-prime would require an override say push button. When you place key in start, signal from starter solenoid is used to energize relay and turn pump ON. Oil Pressure builds up turning the pressure swtich ON so when you turn key back to ON the relay remains energized. If engine stops (Key OFF or due to an accident), oil pressure switch turns OFF and De-energizes the relay.

legomybago · February 11, 2014, 05:02 PM

Good thinking Dave....so key on, push/hold fuel prime button (4-5 seconds), start engine (engine running now), oil pressure switch pumps up, and wall-la, fuel pump turns back on...

DaveVA78Chieftain · February 11, 2014, 10:18 PM

Yep, that is the standard fuel pump circuit design minus the prime button. Some installations, like Ford and Oskosh, also have a collision detector circuit that shuts the pump off if it detects a collision has occurred.

Fuel Injected setups, being computer controlled substitute a prime/start timer (approx 12 seconds) for the starter signal. Thats why you can turn the key ON and you hear the pump run for a short bit. They still monitor oil pressure to detect engine stop to shut pump off.

Dave

Froggy1936 · February 11, 2014, 10:40 PM

Laygo The desired operation is for oil pressure to be up before engine fires on dry crank bearings . One of the bonuses with carburators if you dont touch the acc pedal before cranking up oil press It wont start till you touch acc pedal to close choke ! Frank

legomybago · February 12, 2014, 10:27 AM

I can see your point on the dry bearing start up, So what we need now is an oil pressure pre-prime button!!

Just kidding Dave....

Rickf1985 · February 12, 2014, 03:22 PM

The oil pre-luber is out there. I had one on my 428 SCJ. I am still at a loss for why you have to prime a carburetor? Unless it has sat for many months and the gas has evaporated then there should be enough gas in the carb bowl to start the engine and run for a bit. Unless the vehicle does not have a regular mechanical pump I just do not see the need for a prime. The only time I would see an advantage is if the line from the mechanical pump back to the tank went empty due to a bad valve in the pump or something similar. Even then the gas in the carb would fire the engine or worst case scenario, 15 seconds of cranking will give enough oil pressure to turn on the pump. After that the electric pump would fill the line to the carb and the carb itself.

Rick

legomybago · February 12, 2014, 04:32 PM

Thermoquads are notorious for losing/evaporating all the fuel out of them when they set longer than week or so, even with a fresh set of X-rings and rebuild....rather than cranking and cranking til the fuel appears...prime with fuel for a sec. Then start the sum-bitc*.

I like the option of having electric pump to use when outside temps are hot, and vapor lock is prone to happen climbing that big hill....I dont need to have an electric pump ALWAYS on when the mechanical pump 98% of the time works great on my rig. So I like the off/on electric pump, with the by-pass check valve.

ClydesdaleKevin · February 12, 2014, 07:24 PM

In response to the weather, we are also near Phoenix right now, and its was balmy in the high 70s all day here in Gold Canyon...beautiful blue skies, and at 5:30pm right now, its still around 70 degrees and I'm sitting in the SHADE cuz its still pretty warm in the sun!

Okay, back to the topic...lol!

I thought about going through the oil pressure switch, but decided to super simplify the circuit. If I drive this motorhome off a cliff, the last thing I'm really worried about is the fuel pump still running...lol! But if you feel safer tying it into the oil pressure circuit, then by all means do.

Which leads to the priming switch. With my setup, as soon as you turn the key to "On", the fuel pump comes on and primes the line. With the oil pressure switch in the circuit, you might want to add a primer switch.

That said, most RVs do sit for weeks, sometimes many months, at a time. It makes sense to prime the line, since gas doesn't stay in the float bowl forever!

Kev

Madtrap · February 16, 2014, 07:45 PM

Found the culprit. Broken rubber hose joining the pump to the outlet.

Stripe · February 16, 2014, 08:01 PM

good find!

pvoth1111 · February 16, 2014, 08:14 PM

there's yer problem right there...that's broken

ClydesdaleKevin · February 16, 2014, 10:21 PM

That would do it! Good job finding it!

Oh yeah...its was near 90 degrees today...glad we were in the shade!

Kev

Madtrap · February 23, 2014, 10:44 PM

Tanks back in and running good. I think there's been a leak for some time. Seem to pull much better.
Damn will the Daytona 500 ever end?