Fuel pump troubles

[mike327]

I have went through 4 fuel pumps in about six months time. I am running a LT1 that has a carb intake with stock TBI throttle body, Howell harness, EBL PCM. This is in a 90 Jeep YJ that orginally had a 4 cyl fuel injected engine. I used the original oem fuel pump to start with. It is suppose to put out 42 PSI but the engine would starve for fuel at WOT. Replaced with another oem replacement Airtex pump and had the same problem. Changed to a Airtex for a 92 Camaro, can't remember the number. It lasted about a week, replaced with another Airtex pump. It lasted about two months and now it has went south. I am running 20 psi with a aeromotive regulator in the return line. Are these pumps that bad or what? I have checked voltage (12 vdc), ground is good, changed fuel filter. I have read on the nets about people using the oem Jeep pump with no problems but mine seems to be the exception. Are Delco pumps any better? Any thing I need to check that could be causing the problem with pumps.

[gregs78cam]

I have never heard anything good about Airtex pumps. I have a few stock 20+ year old GM pumps that are still going strong.

Make sure the tank is clean, and the filter sock on the bottom of the pump is attached and functioning.

[jameslleary]

TBI pressures are 9-13 psi, unless you are using a 454 throttle body from a 94-95 Truck. Too much PSI will cause problems.
Throttle bog issues have been mentioned with Carb intakes and TBI adaptors, due to the sudden open space under the spacer.

[phonedawgz]

Pumps will burn out if they are running on low voltage. This may be your problem, especially since you say multiple pumps went out. The problem with measuring the voltage at the pump is if there is no load at the time of the test (ie pump disconnected) the circuit isn't being taxed, and a high resistance connection in the wiring will not show a voltage drop.

http://www.youtube.com/watch?v=boAA6_saiSk

[EagleMark]

Throttle bog issues have been mentioned with Carb intakes and TBI adaptors, due to the sudden open space under the spacer.

Easy AE fix...

[mike327]

Pumps will burn out if they are running on low voltage. This may be your problem, especially since you say multiple pumps went out. The problem with measuring the voltage at the pump is if there is no load at the time of the test (ie pump disconnected) the circuit isn't being taxed, and a high resistance connection in the wiring will not show a voltage drop.

http://www.youtube.com/watch?v=boAA6_saiSk

Thanks thats not the way I checked the voltage. I will be replacing pump with a Delco pump and check voltage as in video and see what happens.

[mike327]

TBI pressures are 9-13 psi, unless you are using a 454 throttle body from a 94-95 Truck. Too much PSI will cause problems.
Throttle bog issues have been mentioned with Carb intakes and TBI adaptors, due to the sudden open space under the spacer.

I used the instructions in the EBL manuel to figure fuel pressure based on 290 to 300 hp. It seemed a little high to me but I am new to this. When i get the fuel pump issues resolved, i will revisit fuel pressure again.

[JP86SS]

I would look at how many amps its pulling.
If it is a high(er) volume pump, the line from the pump to the TB/regulator may be a restriction causing load that you cannot see.
ie; needing 25-35 psi getting to the TB or point of restriction, then it relieves down after the restriction to keep the reading there at 20 psi.
A pressure reading at the pump outlet would give you the actual pump load, (psi X GPM) * 0.000583 = electric motor HP to drive the pump.
you may find that having the pressure at 20 (at TB) is more than the motor on the pump can handle.
The amps may be higher than you expect and too small of a feed wire would result in a large voltage drop under load.
Anyway, over amps tells you to turn the load on the motor down.
Jp

[mike327]

Ok, installed the new fuel pump. Checked voltage drop as per video and had a .8 drop with key on engine off. Checked voltage with the engine running and had a 1.5 voltage drop. If I check voltage at the fuel pump, engine running using the Fluke with red on power feed and black to chassis ground I get 12.5 vdc. The power feed wire is 16 ga. which is OEM Jeep. I thought that was kinda small but the Howell relay is 16 ga. also. I have not checked pressure at the pump yet but plan on doing so.

[pmkls1]

To begin with 16ga is a little small for any fuel pump IMHO. Something in the 12-14ga range would be much better and I would lean toward the 12ga myself. Your reading of 12.5v with the engine running is WAY too low. The alternator should be pumping out between 13.0-14.6v at idle depending on circumstances, and the voltage at the fuel pump should be within ~.2v of the reading you get at the battery or alternator. I would strongly recommend replacing the ENTIRE wiring for the fuel pump from your voltage source all the way to the tank and also inside the tank and then to ground. Also, make sure you have a good chassis ground as that is just as common of a problem as the positive side of the system. What size is the fuel feed line on the Jeep ? For an application such as yours the feed line should be 3/8" minimum. Most FI applications I see use a 3/8" fuel feed line anyway, but it's worth checking. But, it sounds that the likely source of your problem is the power and ground to the pump. Other than old age and high mileage, wiring issues are the next most common cause of fuel pump failures and also repeat failures such as your experience. HTH,
Phil

[EagleMark]

For a comparison a stock LT1 fuel pump feed wire is 18 gauge and when upgrading the fuel pump it needs a 12 gauge wire. So a wire size increase should fix the voltage drop but if the Howell harness is only 16 gauge to feed fuel pump relay I'm not sure it will help having bigger from relay to pump. Longer the run of wire to pump would be where voltage is lost.

There's always a ground issue with fuel pumps. More pump and more fuel = more ground issues. Unless the engine is a stock low HP, when I do a conversion the fuel pump ground comes back to block. Issues are fuel pump ground to frame, is frame grounded to block? Or worse grounded to body? Corrosion?

But like JP mentioned the fuel feed line from pump to TBI unit... it has to be 3/8ths or bigger for TBI and TPI which is the pump you have. Smaller would put a big strain on pumps output = load straining pump. Since your voltage drop is double when running? Did you use the Jeep 4 cylinder fuel feed line? What size? Although pressure was MPFI 43 for the 4 cylinder jeep the volume was much less needed.

I'm down to 2 pumps, GM or Carter. Carter is vane drive and noisier but a better pump. Even if airtex pumps are not the best I doubt you could go through 4? You've got wiring or fuel feed issues causing a load on pump.

[pmkls1]

For a comparison a stock LT1 fuel pump feed wire is 18 gauge and when upgrading the fuel pump it needs a 12 gauge wire. So a wire size increase should fix the voltage drop but if the Howell harness is only 16 gauge to feed fuel pump relay I'm not sure it will help having bigger from relay to pump. Longer the run of wire to pump would be where voltage is lost.

There's always a ground issue with fuel pumps. More pump and more fuel = more ground issues. Unless the engine is a stock low HP, when I do a conversion the fuel pump ground comes back to block. Issues are fuel pump ground to frame, is frame grounded to block? Or worse grounded to body? Corrosion?

But like JP mentioned the fuel feed line from pump to TBI unit... it has to be 3/8ths or bigger for TBI and TPI which is the pump you have. Smaller would put a big strain on pumps output = load straining pump. Since your voltage drop is double when running? Did you use the Jeep 4 cylinder fuel feed line? What size? Although pressure was MPFI 43 for the 4 cylinder jeep the volume was much less needed.

I'm down to 2 pumps, GM or Carter. Carter is vane drive and noisier but a better pump. Even if airtex pumps are not the best I doubt you could go through 4? You've got wiring or fuel feed issues causing a load on pump.

I thought that most GM vehicles used larger wire than 18ga for the fuel pump Mark ? Regardless, with that kind of voltage drop there is definitely a wiring issue. I'm not familiar with howell products I believe. I prefer a heavy duty relay like the GM oval relays used for many applications like fuel pumps, cooling fans, high speed blower relay, etc..... Those relay terminals will accept up to a 10ga wire with no problem. As far as grounds are concerned, there is a recommended setup for full-framed applications. From the battery there should be a large lead going to both the engine block and to the frame. The engine block should have another ground strap going to the body in a separate location. Then a ground strap from body to frame. The ground straps should be a quality heavier braided exposed type strap and are usually easy to locate. What this does is tie the entire vehicle together so that all electrical components can ground to the nearest location and still have a good reliable ground source nearby and regardless of location voltage readings will remain consistent. Unibody vehicles are obviously a little easier because you combine the body and frame thus eliminating a ground strap. My point is, with this setup you can ground something like the fuel pump to the frame and have no issues as long as the physical connection is clean. Just about any electrical device that I know of is recommended to have as short of a ground path as possible to eliminate resistance issues, electrical noise, and other issues. Having too many components ground to the same location also causes other issues on more sophisticated vehicles with numerous modules connected on a data network. I hope all that makes sense as not only is this something that was stressed to me during an advanced electronics training session from GM, but this is actually how late-model C/K pickups are wired. As far as your comment on fuel pump brands Mark, I'm in agreement on the GM pumps but I'm not familiar with Carter units. Carter has been around for a very long time though and I'd say that their products are pretty good. Another brand that hasn't been mentioned and is a personal favorite is Walbro. Walbro has quite a reputation for making good pumps and has powered a couple of my vehicles now for a combined total of well over 200k miles without so much as a hiccup. I believe their pumps are a gerotor design and they do have a reputation for being noisey compared to an OEM pump, but they are dependable. Something that I liked about Walbro was that you can find them easily and they are reasonably priced.

[EagleMark]

Not sure what gauge GM used as standard or if they are all differant but the stock LT1 is 18 gauge so the HotWire kit says and it goes to 12 gauge... I'm all for overwiring when it comes to high demand and long distence...

Reason I usually ground fuel pump back to block is who knows whats grounded on a conversion vehicle? Older rigs and hot rods sometimes have none? His is a newer Jeep with EFI from factory so should be grounded properly like you discribed, if none were removed or broke or corroded?

Yeah the Walbro also has a good reputation.

[mike327]

I did check the ground and it had a 0.3 voltage drop. The pump is grounded to the body. I have the battery to block, block to frame and body to block grounded with short battery cable. Now fuel line is small, it is going to be 1/4 to 5/16 (guessing). Fuel line being to small would cause my starvation/psi drop at wot with the OEM Jeep 4 cyl pumps. Thats the reason I went to the TPI pumps. I will change the fuel line and do the voltage test again. Now to figure out what fuel line to use.

[mike327]

After taking a look this morning the fuel line is 5/16 from the tank to firewall. I adapted to 3/8 to the tb and back to the return at the firewall which goes back to 5/16 to the tank. Ughhh! I have not found a smoking gun yet, just a few could b's. The fuel pump outlet is 5/16 at the pump so I would not benefit from running 3/8 fuel line, i don't think. My understanding is the smallest point/orifice will be what regulates flow/volume.

Tell me about TBI fuel pressure. OEM TBI fuel pressure is 13 psi. I read the internets and everybody says that 13 psi is barely enough for oem with no performance upgrades. I am running 21.5 on the return side. I used EBL flash instructions to come up with this number with orange and black injectors. I guess my question is am I running to much fuel pressure causing me pump problems? I will be checking psi at the pump today.