Fuel Flow rate 6.9

When i bought my ambulance the mechanical fuel pump had been cut off and a fuel pump shoddily put in. Id like to clean up the mess they left. What is the fuel flow rate needed for these IDI engines. Here is the current fuel pump that im trying to figure out if I need to replace.

Those little guys don't flow enough for even a stock setup. If you search, wes put out required flow numbers for most normal injection pumps, I think it was something like 50 gph. Be aware that the flow ratings most e-pumps show are at 0 psi. The moral of the story is you want to maintain 5 psi throughout the load/rpm range in order for the pump's timing to remain consistent.

Some guys use facet pumps, some use holley pumps, and some use carter pumps. You can read all about the positives and negatives of each until your eyes go blind. Some pumps require a regulator as well to keep it in the 5psi window.

My bus has a mechanical pump, and a sealed fuel system, so it works well and I have no issues or complaints. I see no reason to switch from a mechanical pump, but if I were to switch, I'd use a carter 4070. That's because they're available at most parts stores, have an output curve that is close to what a stock idi requires, and are cheaper then any holley or facet. A lot of times you can get them with a lifetime warranty as well, in case it ever goes bad. If you're worried about it failing on the road, buy 2, mount one in an accessible area, and keep the spare and tools in the truck.

This is great information. I am thinking the Carter 4070 is for me as well. I will keep the old one in a bay for emergencies. Also gonna scoop a schrader pressure gauge see what both pumps run. should the fuel pump be installed before or after the water fuel seperator. Mines been disconnected thinking about getting a new one. Im also curious what issues other than reduced power would you expect to see with reduced fuel pressure

Most E pumps are pusher pumps not sucker pumps so usually right below the fuel tanks is good.

@Booyah45828 has it nailed.

One of the reasons the Facet caught on here so well is that it was designed for refer trucks and can pull fuel 10' vertically. So mounting in the engine bay was A-OK. But it craps out at 30gph free-flow and won't supply enough under WOT.
Speaking of, the mechanical does a good job of keeping up with WOT because it runs faster with more RPM. I'm enjoying mine now that I've switched back to it.
As for the pressure what changes most is your timing. The IP is calibrated for 5psi inlet at all RPM and will do funny things with the timing when it's significantly higher(10psi+) or even a little lower(2psi-).

So to test that the Carter is delivering the beans you need to hook that fuel pressure gauge up where you can see it while driving, especially WOT up a hill or towing. I've done that a few times for testing, running the hose under the hood seal and using rare earth magnets to attach it to my wiper arm. It worked great, is fast and nothing can go wrong and get fuel inside the cab.

The_Josh_Bear said:

@Booyah45828 has it nailed.

One of the reasons the Facet caught on here so well is that it was designed for refer trucks and can pull fuel 10' vertically. So mounting in the engine bay was A-OK. But it craps out at 30gph free-flow and won't supply enough under WOT.
Speaking of, the mechanical does a good job of keeping up with WOT because it runs faster with more RPM. I'm enjoying mine now that I've switched back to it.
As for the pressure what changes most is your timing. The IP is calibrated for 5psi inlet at all RPM and will do funny things with the timing when it's significantly higher(10psi+) or even a little lower(2psi-).

So to test that the Carter is delivering the beans you need to hook that fuel pressure gauge up where you can see it while driving, especially WOT up a hill or towing. I've done that a few times for testing, running the hose under the hood seal and using rare earth magnets to attach it to my wiper arm. It worked great, is fast and nothing can go wrong and get fuel inside the cab.

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Im gonna grab a gauge tomorrow see what I'm currently getting while I wait for a proper fuel pump. Do you see any immediate danger in running the much less powerful pump until the new one gets in. I guess I dont really understand the dangers of too low fuel pressure.

I'm a fan of the mechanical pump. I run waste oil as fuel and was considering a Holley red or black because it's said that they can pump oil, but the simplicity of the mechanical pump has won me over. Obviously mechanical pumps go bad and so do electric pumps. My final decision was based on: I'm not building a hot rod.

idiambulance said:

I guess I dont really understand the dangers of too low fuel pressure.

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Too low fuel pressure puts extra strain on the injection pump. I can't say exactly what the effect would be long term, but injection pumps are too expensive for me to want to take chances on.

I tried a Delphi knockoff of the carter pump and it wouldn't flow enough for me towing pulling hills. It would run fine until pulling hard and then the truck just ran out of power. I went back to the mechanical pump too.

idiambulance said:

Im gonna grab a gauge tomorrow see what I'm currently getting while I wait for a proper fuel pump. Do you see any immediate danger in running the much less powerful pump until the new one gets in. I guess I dont really understand the dangers of too low fuel pressure.

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Not much of a danger AFAIK. These IP's can pull their own fuel if the pump dies. Not saying it's a good idea, just that they can get you home if they fail while driving, lol. But not if you stop the engine I reckon.

Mostly it will act funny and be underpowered. Seems like worst case the engine dies. I had a little cube pump I was using inline with the mechanical years ago that came with a little pre-filter. Bad idea! That little filter clogged up and it took me 2 days to figure out WTH was wrong with my setup...I was so frustrated. But I forgot all about that filter or I would have fixed it right away. It would run, drive, clog, die. Wait a while and try again, same story! Anywho so I don't think anything gets damaged, just starves for fuel.
If it runs fine don't worry about it.

It’s not just fuel pressure but volume also. I believe you want 7lbs of pressure and 1/3 pint of fuel with 10 seconds cranking.

You'll notice low/no power without fuel pressure to the inlet. The injection pump has a transfer pump on it, but you don't want to rely upon that. Fuel not only lubricates, but cools the injection pump as well. These aren't vp44's off a cummins that are super sensitive to low/no fuel pressure, but the right thing to do is to fix this sooner rather then later.

I feel guys liked the facets because they could mount them in the engine bay, they had a pre-filter/water separator on them, and they didn't know that the pumps were underperforming. A lot of them loved it because e-pumps mask the air intrusion issues that they had as well.

The 4070 is a vane style pump. I'd mount it as low and close to the tank as possible. It can "work" as a puller, but it's much better as a pusher. In all honesty, most pumps operate that way.

The only way you'll know an e-pump is satisfactory is by watching a fuel pressure gauge running down the road.

The carter 4070 was a great, reliable "go to" universal pump for decades. No longer. The quality has taken such a turn for the worse, it's shocking. I have quite the fleet of equipment, and I now have 8 dead 4070's sitting in a pile that failed after minimal hours of operation. A few old ones still work as good as new, but the newer ones (china) are not the same. So, just a word of caution there.

Holley, faucet and Walbro all seem to have better reliability. Reliability is #1 for me, everything I have is stock and not pushing more fuel then normal.