Fuel Spits sputter pops and bangs under load. Help wanted

Hello i have a 89 fox 5.0 that i bought non running. I brought home and managed to get it running only to find out the block was cracked and mixing coolant and oil. Long story short i got a junkyard 5.0 out of a 2000 mountaineer took the heads off sent to the machine shop had them resurfaced and valve job as well as added better valve springs for cam swap. The old engine already had it so i just swapped. Put the engine back together with the gt40p intake new ford 24lb injectors new accel distributer upgraded altenator deleted egr system new 24lb calibrated maf. The car was an auto and i went ahead and did the manual swap also. So got the car timing set at 14degress and everything was fine. I started taking it out for test drives and it ran extremely well. It ran great for 2 days then after stopping for fuel the car started to spit sputter pop and bang under heavy load free idle it seemed fine. I got her back home and figured it was fuel related since it happened to occur after pumping gas so i decide to drop the tank and take a look the baffle was broke but the pump assembly seemed fine. I decided to go ahead and replace the tank as well as the pump thinking this was my problem. Also replaced my fuel filter put everything together and still the exact same issue. I replaced my plugs and checked gap. Still the same. Oh and i replaced my wires when i put the engine together so those are fine. I have a fuel pressure gauge so i decided to see what was happening without the vacuum line it would hold 40 and with it connected it dropped around 37. So then i started accelerating and noticed that under acceleration it would drop about 10psi to about 27 28psi. So i unhooked the vacuum line and capped it and checked fuel pressure again. This time it seemed to hold 40psi so i took it for a drive with the vacuum line to the regulator off amd capped and it ran alot better but would still have the same issues this time higher up in the rpm band. So i ordered a new fuel pressure regulator adjusted the pressure at 45 without vacuum 40 with but it still drops while accelerating no load. I havent test driven it yet but am sure its still the same. Im at my wits end with this thing i dont know what else to look for or check. Any help or guidance would be greatly appreciated.

AeroCoupe said:

You know you are not getting enough fuel up to the motor. Back the fuel pressure back down to 39 PSO with the vacuum disconnected. The ECU is expecting this pressure so when you turn it up it cannot compensate for the additional fuel. This will play into things when the lack of fuel pressure under load is solved.

Coupe of questions:
1) Have you pulled codes? Regardless of the CEL flashing or not you need to pull them.
2) Have you changed the fuel filter?
3) Have you followed the fuel lines from the pump hanger to the injector rails and made sure there are no linked or collapsed lines?

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Yes the fuel filter was replaced when i changed the pump and tank. I will re adjust the fuel pressure to the oem specs and see what happens. Lastly i havent checked the lines to and from the tank so i will check those today also and provide an update.

AeroCoupe said:

You know you are not getting enough fuel up to the motor. Back the fuel pressure back down to 39 PSO with the vacuum disconnected. The ECU is expecting this pressure so when you turn it up it cannot compensate for the additional fuel. This will play into things when the lack of fuel pressure under load is solved.

Coupe of questions:
1) Have you pulled codes? Regardless of the CEL flashing or not you need to pull them.
2) Have you changed the fuel filter?
3) Have you followed the fuel lines from the pump hanger to the injector rails and made sure there are no linked or collapsed lines?

Click to expand...

Forgot to mention the only codes present were egr and evap codes presumably due to them being deleted.

Well i readjusted the fuel pressure as well as removed the lines and blew air threw them as well as visually inspected and all is well there. I started it up and took it out for a drive and well everything is the same still sputters pops and bangs under acceleration. I again unpluged the vacuum and it ran alot better but starts breaking up at around 4k rpm. With the vacuum line on the fuel pressure is around 40 and about 36 with it on. Again when free reving with the vacuum line on the pressure drops to 30. With the vacuum line removed and plugged its stays constant at 40 reving or idle. Any guesses?

Well i hooked up a vacuum gauge to the fuel pressure regulator source and at idle it reads around 10 to 12 psi and when i rev it goes up to about 17. Dont know what that means especially since its supposed to probably be the other way around. I dont know how it could of ran great for a few days then after filling up i could end up with some sort of mechanical issue such as valves or blowby issue. Im guessing a leakdown test will give me an answer.

Also fuel vent is good

Update i re ran the vacuum tests and previously i would slowly open the idle and got the previous reading. I redid the test except it was around 12 at idle and when i punched the throttle it would go to 0 then after letting go it would increase momentarily to about 18 then drop back down to around 10-12

General karthief said:

You have a vacuum leak

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What exactly makes you believe there is a vacuum leak? The lower vacuum at idle?

General karthief said:

Yes

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I believe i mentioned in my initial post the car has a cam which i believe explains the low vacuum. From what ive read 10 to 12 is normal is this not correct?

General karthief said:

That's the issues with mystery cams, unknown overlap so vacuum could be lower.

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Cam is edelbrock 3722
282 Dur
498 lift.

In any case i dont believe i have a vacuum leak since i have also already sprayed about 2 cans of brake clean around any possible intake leak with no change in idle. I think im just going to save some money and get a terminator x at least to eliminate the salt and pepper shakers and or wiring and ecu as the culprit. At this point everything else is new.