Fuel Pressure Drop

Magnum PD · Oct 5, 2015

I'm being serious. A Ford tech can be useful.

IHPowerstroke7.3 · Oct 7, 2015

Well thank you. I have to say there are a lot of people on this site with more knowledge than I have when it comes to modified stuff. Have learned a lot over the years.

Love your 96 by the way, super clean!

mandkole · Oct 7, 2015

IH, Ive read this thread a few times now and noted a few info gaps that I wanted to confirm on the supply line that you swapped back to stock.

I don't doubt that it could be the brand new pump that does not perform, however, please re-hook back up the 5/8" line and recheck supply again. You could be facing an in tank issue with the stock pickup. The pump could be pulling through an obstruction. hate to see you get another pump and have same issue.

Magnum PD · Oct 7, 2015

IHPowerstroke7.3 said:
Well thank you. I have to say there are a lot of people on this site with more knowledge than I have when it comes to modified stuff. Have learned a lot over the years.

Love your 96 by the way, super clean!

Not if you see it in person. Needs a paint job

IHPowerstroke7.3 · Oct 7, 2015

mandkole said:
IH, Ive read this thread a few times now and noted a few info gaps that I wanted to confirm on the supply line that you swapped back to stock.

I don't doubt that it could be the brand new pump that does not perform, however, please re-hook back up the 5/8" line and recheck supply again. You could be facing an in tank issue with the stock pickup. The pump could be pulling through an obstruction. hate to see you get another pump and have same issue.

You are correct, however I didn't post all of my steps correctly. I first replaced the pump, keeping the 5/8 line connected, and then restested. Then I switched back to the factory sized line. Dennis believed that it was possible having the 5/8 line before the single stock pump was too much for the auction side.

When it gets switched to dual pumps, it will be going back to the 5/8 pickup.

IHPowerstroke7.3 · Oct 7, 2015

Needing a paint job on a near 20 year old truck isn't so bad. Should see trucks up here, rusting and only 5 years old!

dsberman94 · Oct 7, 2015

IHPowerstroke7.3 said:
You are correct, however I didn't post all of my steps correctly. I first replaced the pump, keeping the 5/8 line connected, and then restested. Then I switched back to the factory sized line. Dennis believed that it was possible having the 5/8 line before the single stock pump was too much for the auction side.

When it gets switched to dual pumps, it will be going back to the 5/8 pickup.

Still might need to do in tank mods. Those screens in the tank get very clogged up and it won't be able to pull enough fuel through to maintain enough pressure.

IHPowerstroke7.3 · Oct 7, 2015

I know it's an issue with even stock trucks. But it won't be an issue going back to the 5/8 draw straw. What other in tank mods would be needed?

dsberman94 · Oct 7, 2015

As long as the screens are gone there wouldn't be any to gain for flow.

The other easy to do one is to cut the fill and vent pipes on the inside of the tank as close to the outside of the tank as possible. Just allows the last few gallons to go into the tank faster.

bruce · Oct 8, 2015

The truck didn't even have in tank mods? Well thats where I would have started. Fuel pressure shouldn't drop with 160's with stock nozzles,EVER!

mandkole · Oct 8, 2015

IHPowerstroke7.3 said:
Spent some time with the truck today, talked with Dennis from Strictly and discussed my findings with him. Think we figured it out.

Injectors are a Full Force stage 1, 160cc stock nozzle as per customer. Stock pump should not have a problem supplying them. Dennis had me verify some things. Checked power to the pump, its within 300 millivolts of battery voltage. Also asked me to check how much fuel the pump would push out the fuel drain on a couple key cycles. Compared to my stock 7.3, customers truck would flow almost a whole quart more than my truck would (my original 120k mile pump) on 2 key cycles.

Logged data, In the tune he brought it to me with (say its a hot tune) WOT in 3rd, 3200 rpm, mass fuel desired was 100mg, pulse width was 4.6-4.8 ms, ICP would hold between 2800-3300, IPR duty cycle was 44% from what I remember. Fuel pressure would drop from 60 to 40 psi.

Went to his tow tune, WOT in 3rd 3200 rpm, mass fuel desired was only 76-80mg, pulse width max I saw was 3.6 ms, ICP and IPR was the same. Fuel Pressure drop was 5-6 Psi max.

So just as I figured from the get go, too much fuel in that tune for the pump to handle. Asked the customer if he switched tunes, says it was the same in all tunes. Should have checked for myself, but didn't have time to go play around last week.

Going to go to dual sd pumps and re evaluate.

Thank you to everyone for the help.

There are still inconsistencies in this for it to make sense that this truck needs dual pumps.

What we know;
--there are hundreds of trucks running a stock pump (some old, some new) and stg 1s with no issues.
--With the key on bucket test, this truck has a very strong running single pump against another benchmark pump. (likely there are no in tank issues with that much flow)
--At 4.8ms, the injectors could only get most of their fuel out at the lower rpm (partially explains why the pressure came back as the engine rpm increased)

Suspected;
--There is obstruction somewhere in the system that limits fuel when fuel demand is high. (filter, line screens, hose collapse, etc)

Id suggest continued troubleshooting before spending lots of money on adding a second pump.