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  #16 (permalink)  
Old 03-28-2005, 01:15 AM
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it sounds like you possibly have something hooked up not quite right.i saw an article in chevy hi perf. about a yr. ago about using a toggle switch on your elec. fuel pump to run around with low voltage and lower pump performance until you really need to stomp on it ,witch helps your gas mileage,then you flip the toggle switch to full power and full pump performance witch kills your mileage.if you go to mad electricl or 12 volt .com you will probably find the answer.if its only a mild 350 though why do you need an elec. fuel pump?sounds like over kill.
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  #17 (permalink)  
Old 03-28-2005, 04:48 AM
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Power swamp

Doc here,

HAPPY EASTER TO YOU AND YOURS!

From reading this thread, it sounds like your swamping the fuel pump of power When the Fan cuts in......

You need to monitor Voltage to the pump when the fan cuts in...I'll betcha it drops below 14.4 volts....Which would cause the pump to S-L-O-W down, work twice as hard to do half the work.

If that's the case...get a relay, hook the coil up to the line already going to the pump and ground, then get some 10 gauge or even 8 gauge wire and run a wire straight from the positive battery terminal (after the fusible link) to the Normally open side of the relay. Hook the center wiper directly to the fuel pump.If it's a current swamp, that should cure it.

One other thing to check is the ground wire from the in tank fuel pump/fuel gauge sender to frame ground...It may be bad...picking up ground through the fuel lines instead.

Is The Fan Relay controlled? It should be!

If so where are you getting relay fan contact power from? You may be taxing a circuit by getting power from an undersized source.

I would leave the relay coil connections alone, but move the power wire for the fan that goes to the relay contacts to the same place you hook up the fuel pump relay pump power contact (Battery Terminal past the fusible link) Because it sounds like that fan is loading something down hard...and obviously no fuse has blown...so you could be heading for a harness meltdown the way it is.

Hope It helps!

Doc
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Old 03-28-2005, 01:01 PM
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So venting is okay, I looked at an 83 ranger setup, and the vent is in the right place. So the pressure goes up after the fans cut out?
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Old 03-28-2005, 01:29 PM
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yea try to bypass the mechanical fuel pump and see what happens.

and maybe try bypassing the relay and hard wire the elec. pump and try that as well because thats kind of a wierd problem and i really dont know what to say but just troubleshoot possibilities
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  #20 (permalink)  
Old 03-29-2005, 07:33 AM
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Fuel pressure changing.

Palmtrees57chevy,

It sounds like you've actually had one problem, and one ghost. The problem being your fuel pump was not keeping up with the demand of your engine. From what I've read now since you've gone to an electric fuel pump the performance does not change even when you see a change in fuel pressure. Now for your ghost, the fuel pressure is most likely not acutally changing!!! The liquid filled fuel pressure gauges are filled with glycerin. As Gylcerin gets hotter, it gets thinner. This is causing a false reading. If you try a non liquid filled gauge, your problem will probably go away.
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Old 03-29-2005, 07:51 AM
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Quote:
Originally Posted by Tech @ BG
Palmtrees57chevy,

It sounds like you've actually had one problem, and one ghost. The problem being your fuel pump was not keeping up with the demand of your engine. From what I've read now since you've gone to an electric fuel pump the performance does not change even when you see a change in fuel pressure. Now for your ghost, the fuel pressure is most likely not acutally changing!!! The liquid filled fuel pressure gauges are filled with glycerin. As Gylcerin gets hotter, it gets thinner. This is causing a false reading. If you try a non liquid filled gauge, your problem will probably go away.
I would agree except he claims the engine dies when pressure goes to zero on the gauge so it appears to be telling the truth. I would try using just the mechanical pump with no pressure regulator which would eliminate and faulty regulator the voltage drop problem that may be occurring with the electric pump. Running just the mechanical hi-po Holley mechanical pump you should be able to supply fuel to +10 w/ engines like yours at idle. If pressure then still falls, you have eliminated the pump as the problem. If that does isolate the problem as electrical, you have a severe voltage drop in your harness. My Willys did sort of the same thing - 100 amp alternator wouldn't keep up w/ electric fan and AC until I discovered I had hooked the alternator voltage sensing wire incorrectly. I had hooked it to the battery cable so the alternator thought voltage was fine. I should have hooked it to the fuse block main where the voltage drop was occurring @ high load so the alternator would up the output to keep up with high demand.
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Old 03-29-2005, 10:39 AM
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In one of the later posts it reads as though the engine doesn't spit or sputter anymore now that is has the electric pump on, just that the pressure fluctuates.

Since the problem has occured with, and without an electric fuel pump, it is most likely not an electrical problem. Since it also occurs with the cap off, it is most likely not a venting problem. It could be a heat soak, or vapor situation. Try insulating the fuel lines, and possibly running a fan over everything when tuning to see if that makes a difference.
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Old 03-29-2005, 04:09 PM
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Eliminate the Power

Doc here,

One way to eliminate the Power, Is put a meter where you can monitor it, on the battery, should read 13.2 to 14.4 static....(not running)

Then, REMOVE the alternator belt, Run the engine (carefully monitoring the TEMP, Don't overheat it!) and watch the volt meter, and pressure regulator...When it comes up to temp and the fan cuts in look at the battery voltage, and regulator, do they both still drop?

If not, you have the fan circuit Taxing the system , imposing almost a "Rotor Lock " condition on the alternator....causing RPM drop, hence low pressure...

Next reinstall the belt, and pull the fan relay, or disable it...run the test again...

If it still drops, most likely it's mechanical...look elsewhere.

I had to go back and re~read the thread, (unless I missed it, which is highly possible) you didn't say when this pressure drop occurs, did the RPM's drop...Like the Choke coming off the detent...(or possibly in this case, more drag on the engine from the alternator)

Doc
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Old 03-29-2005, 04:46 PM
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There is no way the RPM level is dropping enough to make a mechanical pump lose pressure. Even an A/C compressor doesn't drag the RPM down enough the lose fuel pressure. We are all taking educated guesses because we can't see/hear/feel the problem. In a situation like this we need ALL the details possible. What has been tried, etc...

The problem is getting compounded by adding pumps, changing pumps, etc.. and not going back to the baseline. If you change something and it doesn't fix the problem you need to return back to where you started, that way you don't introduce "new" problems to the situation. Troubleshooting really isn't hard (I have done it for a living my whole life).

You should not "need" both a mechanical and electric fuel pump, pick one and stick with it. The mechanical pump should be more than enough on it's own as well. Running the mechanial pump, the fuel pressure drop shouldn't happen at all as long as the engine was still running (I don't care how low the RPMs drop).

Now by adding the electric pump, I can see how it would "restrict" flow if the power level drops (ie... from the fans), this could "possibly" limit the fuel pressure the mechanical pump could provide.

If it was my car I would, eliminate one pump or the other. Monitor the voltage and fuel pressure to see if the drop is related. You can buy a inexpensive volt meter and mechanical fuel gauge, wire and plumb them, tape them to the windshield and cruise around your neighborhood. this will give you a much better idea of what's going on. If you go with the mechanical pump there is no way the fans coming on is causing you pressure drop.

When you say the pressure drops how low is it dropping? Does it continue to drop slowly until it bottoms out? Does it drop instanly to a certain point and sit there? You need to eliminate the digital gauges for trouble shooting, the problem could very well be the gauge/s or sender.

You never said (or at least I didn't see) if you have relays running both the pump and the electric fans. If you don't the the fuel pressure drop is the least of your worries (fire being a bigger worry). Also neither eletric motor is getting full battery voltage if a relay is not used (and wired correctly).

Where are you taking the fuel pressure reading from? (regulator, carb, inline, etc..)

Royce
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Old 03-29-2005, 09:39 PM
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Hello everyone. Thanks for responding. Hey Tech, I was wondering if the gauge was faulty. I do have another pressure gauge that is not liquid filled so maybe I'll try it. I agree with camaroman, I shouldn't need two fuel pumps, but I was told before that adding an electrical fuel pump would eliminate my vapor lock problem. If I were to by-pass the mechanical pump for test purposes, would I mess it up if I left it installed on my motor? As for having relays, yes I do have both the fan and electric fuel pump on relays.

As for it spitting and sputtering, it hasn't done that since June 2004. I haven't driven it since then so I don't know how far down it will actually go. As for now it will drop down to around 2-4 psi at idle after the engine temp reaches 200 degrees. I have a liquid filled pressure gauge mounted in-line between my regulator and fuel filter.

When the engine is warming up the pressure gauge reads 7 psi. Once the engine reaches 180 degrees and the electric fan comes on, the pressure gauge slowly starts to drop down to 2 psi. At this point the operating temperature shows 190 to 200 degrees. I have a liquid filled temperature gauge mounted in my intake. I must admit that I know nothing about electrical stuff. I had wired the entire truck with the E-Z wire harness. Everything was labeled so I wired it according to the instructions. I Think?

If I didn't mention this before, the truck used to run just fine. One day I was driving it when it started spitting and sputtering. I looked at my clear fuel filter and it was nearly empty at idle. after sitting for a while it started up but as soon as it warmed up again it would sputter and die. At that time it just had the mechanical pump and a smaller electric fan.

Now I have a bigger fan (3300 CFM) and electric pump and it still does it. i am about to lose my mind here.
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  #26 (permalink)  
Old 03-29-2005, 10:03 PM
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From what you are describing, it is most certainly at least partially voltage related. You need to monitor that and tell us what it shows.

Royce, I am having a hard time with the relay statement. While running, system voltage should be constant unless there is a strange wiring situation where an overamperage is occuring.

Chris
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Old 03-29-2005, 10:13 PM
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Hey turbo explain to me why you think it's partially a voltage problem?
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Old 03-30-2005, 06:28 AM
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The fact that the pump is petering out as soon as the fans come on is a dead give away. That likely means that the fans are lowering voltage when they come on due to the increased amp draw. You need to measure voltage at the pump when the problem occurs. Untill you do that there is no more need to discuss anything really.

Chris
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  #29 (permalink)  
Old 03-30-2005, 06:42 AM
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Just for HA HA's, take a set of jumper cables or wires and ground the firewall/chassis to the engine block and see if the problem changes. If the low pressure problem was present with the mechanical pump as well, I would have to lean towards a heat related problem (vapor lock etc.). Then again, this might be one of those "you had to be there" kinda things.

Maybe Doc can post a little tutorial with pics/figures on how to do a voltage drop test and resistance test. Very simple to perform with a common DMM/VOM. Or you could give the ground thing a shot for the heck of it. HTH
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Old 03-30-2005, 07:25 AM
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Lots of good theories so far but one very small but very, very significant one hasn't been mentioned.

The voltage sensing wire on the alternator. If it's connection is too close to the alternator the alternator may not increase output sufficiently to maintain voltage when the fan comes on. That would cause the pressure drop you're describing.

Do an amperage/voltage test to see if the alternator is bumping output to compensate for the increased load. If it isn't, the voltage sensing wire may be too short for the alternator to accurately determine the neccessary output and adjust accordingly, the diodes may be bad too. Install a longer wire to make the connection as far away from the alternator as possible.

A 100amp alternator should have no problem maintaining power. If you have a one wire alternator, you have an entirely different situation .

Larry
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