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Discussion Starter #1
Been a while since i have posted but i am truly stumped. About 2 months ago i passed ca emissions just fine. Told i could of tripled my pollution and still passed. But for the past 2 yrs i get the stumble issue. I have done all the classic suggestions. Cap, rotor, coil, wires, FPR, Pump, Filter, timing. But its driving me nuts at this point. Also have replaced CTS, ACS,Thermostat,IAC, and TPS. Checked the timing and it was at 6* put it back at 10. Helped some with stumbling but it came back. Pulled codes KOEO 11,10,33,96. KOER 8,10,44,33,77,74,65. Considering a bottle of 0w synthetic(No thermal breakdown while im being [email protected]%*) and a trip to Ford with it.
 

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That 96 could have something to do with it, that's the fuel pump circuit. I'd get a fuel gauge on it and see what the pressures are.
 

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Discussion Starter #3
That 96 could have something to do with it, that's the fuel pump circuit. I'd get a fuel gauge on it and see what the pressures are.
tested fuel pressure holds steady at 29 psi. revving the motor brought it up to 32 then it went back down to 29 to hold the pressure. released the fuel pressure with the valve on the gauge while holding the relief it only dropped to 25 psi. after turning off the motor and checking the gauge the pressure rose to 32 and is holding there.
 

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tested fuel pressure holds steady at 29 psi. revving the motor brought it up to 32 then it went back down to 29 to hold the pressure. released the fuel pressure with the valve on the gauge while holding the relief it only dropped to 25 psi. after turning off the motor and checking the gauge the pressure rose to 32 and is holding there.
29 is too low. Should be at 32 min then rises when reved.

You say with the engine off you're at 32? Is that with cycling the key a few times? You should be around 40 psi KOEO.
 

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Discussion Starter #5
29 is too low. Should be at 32 min then rises when reved.

You say with the engine off you're at 32? Is that with cycling the key a few times? You should be around 40 psi KOEO.
Yes engine off is 32, pulled vac to FPR and held strong at 38, 40 with revving up to 4k
 

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Discussion Starter #6
so is it possible that the new Fuel pressure regulator is bad and wont let the pressure run above 30 psi since with no vac the pressure raises up to 40 psi?

ANYONE?
 

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I "rented" a fuel pressure gauge from AutoZone, and suspected its accuracy, so if you are using a borrowed gauge, it could be off 2 PSI. (reading 30# when it should be 32#) I bought a gauge and confirmed that my fuel pump was slow starting up, and then could not keep up with engine demands. After a few minutes the pump would get up to speed, it had the correct pressure and volume.
It's your truck, but IMHO, you have plenty of pressure to make the truck run fine as long as it doesn't drop below about 30# when you rev the engine.
 

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tested fuel pressure holds steady at 29 psi. revving the motor brought it up to 32 then it went back down to 29 to hold the pressure. released the fuel pressure with the valve on the gauge while holding the relief it only dropped to 25 psi. after turning off the motor and checking the gauge the pressure rose to 32 and is holding there.
When I Rev the truck it drops to 26 psi.
When you rev the truck, the pressure should RISE.
Do you have two pumps on your 1990? You said in your first post that you changed the fuel pump a while ago.
The FPR seems to be working correctly, as you said that you pulled the vacuum line and the pressure went up (which it should).
When you rev the engine, two things happen, the vacuum drops which should increase the fuel pressure (the FPRs job), and the engine needs more fuel, which is the fuel pumps job.
It appears that the fuel pump can't keep up, so either the fuel pump(s) are failing, or the fuel filter is restricting the amount of fuel the engine wants (which would cause the fuel pressure to drop when revving the engine).
Try changing the filter again, maybe you picked up some crap.
 

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He should have enough pressure to run smooth. Not ideal, but sitting still with no load, it shouldnt stumble at those pressures.

You've replaced about everything that could electrically go wrong, but dont forget injectors have a mechanical aspect to them also. You could have one injector with a sticky plunger, or a fouled tip that isnt spraying right and causing a stumble. I believe some injectors have a small filter screen on the fuel rail side as a last ditch attempt to catch debris that made it past the main filters. Possibly got some gummy fuel, or shelac from sitting or reacting with these suck ass alcohol fuels.
 

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He should have enough pressure to run smooth. Not ideal, but sitting still with no load, it shouldnt stumble at those pressures.
Totally disagree.

If the pressure drops when the engine is reved, he's not getting enough fuel.
 

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Discussion Starter #12
ok so i disconnected the vac from the FPR and took it for a drive still stumbled. so i started following my fuel lines and found this. its the point where the fuel lines cross over the front driveshaft and begin to follow the trans bell up into the engine. Does this look normal? shouldnt there be hose clamps? Could it cause the bucking if air is getting in the fuel line? sorry for the image size just scroll down and you will see the bracket and fuel line.
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Is the fuel line leaking? If you have only one fuel pump, the pressure would be about 40 PSI and the fuel would be squirting dangerously all over the bottom of your truck.
If you have two pumps, the pump in the tank also pressurizes the fuel line, albeit at a lower pressure, and the second pump on the rail boosts the fuel pressure to 40 PSI.
So, unless you have an engine mounted mechanical pump, the fuel lines are under pressure.
 

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If you pulled vacuum off the regulator and plugged it and had 38-40 psi, that is normal. You check the pressure with vacuum off. The regulator regulates how much fuel GOES BACK to the tank.. If the regulator were busted, most of the fuel would run straight back to the tank and not much into the engine, and you'd lose fuel pressure. You can normally diagnose a busted regulator by pulling the vacuum line and smelling inside it, if it smells like gas, it's suspect. You may have a fault in your fuel circuit I suspect.
 

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The bulk of your fuel lines are steel, with some flexible braided sections. Uses those o-ring seal A/C style connections. There will be some rubber protective sleeves over certain areas of fuel line, and this might be what your looking at (hard to tell on my screen). If there are hose clamps, then someone has modified the fuel system.

Have you monitored your fuel pressure while actually driving? The most demand on your fuel rail is when the engine is loaded down good pulling a hill. If you can maintain decent pressure, and it still stumbles, then its not fuel pressure. Still havnt ruled out a flaky fuel injector.
 

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Discussion Starter #16
OK so after thinking about it I pulled a plug. And checked the gap was at .053, so I regapped the plugs to .044. In the process I found the plug 4 wire had a hole right where the boot for the plug was. Got new wires and took it for a drive. No stumbling, miss. Idle rock solid, more power... so far. Keeping my fingers crossed. Oh and the pressure gage was rented so maybe it's readings are off? Thanks for your help guys. Have been a big help. Now just needs a wash so the ford gods can smile on me again. Lol
 
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