93' Cobra (CJ7) No Fuel pressure

Jeep2351

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Jun 3, 2021
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NEWBEE here so please be gentle. I've scored through posts and posts of fuel pressure issues on here and can't quite find my issue resolved. First off let me say it's a crate motor installed in a Jeep CJ7. I built it off a 93' cobra, injectors, intake, all that jazz. I don't have a thermactor, EGR or smog pump on it. the only codes that come up are emissions related. I had her running and rolling for a few weeks while I was getting the Gremlins out. Then it died in my driveway, felt like a fuel problem. So after lots of research and reading I changed the FP. (It was a GM version from Novak, doesn't work when 12volts is applied). K, bad pump. Bought a Walbro 255, changed pigtails and hooked it up to the sending unit.
KO, pump primes but no pressure. Since I had to fab my own lines there's no schrader valve. OK, Has BBK Fuel rail, bought a BBK FPR and installed gauge on FPR, now I can check for pressure. No pressure at the gauge, removed FPR rotated the Vacuum line towards passenger side. Cranking over had almost 10lbs bouncing and acting like air in the line, also leaking fuel at fitting. Guess I should include she runs great on Ether. Removed FPR (again) rotated Vac port towards driver side (not on purpose) tightened up fitting for gauge. No leaks, no pressure now. With key on it primes(no pressure) but sounds like fuel is going back into the tank from return line. I have spark, pulse and a rebuilt computer, Guy says it's power module was bad and sending distorted voltages out. Made sense, not enough voltage to run the pump, not enough fuel pressure. Getting ready to drop the tank(again) Inertia -Good, 12-volts at pump-Good Pressure at rail, no Bueno. Probably going to do a rig job from pump to pressure gauge to try and sort this out. Going to remove the line from the rail and pump and blow from motor back, mabye previous check valve is in there, I dunno, any sweet words of wisdom would be appreciated.
 

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Jeep2351

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Jun 3, 2021
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SOOOOOO, pulled the lines blew them out everything is clear, same with the fuel rails and return line. Ordered up a new o-ring for the sending unit seal. re-tested my voltage at sending unit, testing between ground pig and screw on top, I get 13 volts for 1- second, then goes to 7 w/key in run position, once cranking it rolls between 10,11 volts. Pump I had installed advertised as Walbro, but had a different stamp on it. New pump has Walbro stamp and looks to be legit. I'm concerned about my voltages going to the pump. Shouldn't I have a nice 12volts when cranking? Ordered up a new ignition switch because it's the original one from 1983(dirty contacts? 38 years old, $20, probably not the issue but $20, isn't going to hurt anything). Took the FPR and blew air through it holding finger on outlet set the pressure to 40psi. Waiting on seal to re-install everything. Thoughts? am I missing something simple here?
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Massachusetts
That’s a badass motor.

what ECU are you using to run it? What mass air meter? 24# injectors?
 

Jeep2351

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Jun 3, 2021
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Morrison, CO.
That’s a badass motor.

what ECU are you using to run it? What mass air meter? 24# injectors?
It's got the X3z, 24# injectors, I think my mass air flow meter is a 76MM, I'll have to check when I get home. It's been awhile since I messed with that part of it. It's only an x302 crate motor, but since it's in a CJ7, figured that was plenty for it. waiting on my switch to show, tomorrow is the day, see if I can crack the code.
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
36,444
12,352
224
Massachusetts
It's got the X3z, 24# injectors, I think my mass air flow meter is a 76MM, I'll have to check when I get home. It's been awhile since I messed with that part of it. It's only an x302 crate motor, but since it's in a CJ7, figured that was plenty for it. waiting on my switch to show, tomorrow is the day, see if I can crack the code.

The X3Z computer does require a specific MAF to function properly with the 24# injectors. That's why i asked. It's a package deal. X3Z, 24's and the F1SF-12B579-AA 70mm MAF.

That MAF is actually off a 91-94 Supercoupe, but it has a unique MAF transfer value that is specific to the X3Z ecu.

If you are running a 76mm aftermarket, you might have issues depending on what that MAF is. It's not a "calibrated" 24# injector MAF is it?

Depending on what parts you do have, it might be more beneficial to swap to an A9L vs get the right meter for the X3Z.
 

Jeep2351

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Jun 3, 2021
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Morrison, CO.
The X3Z computer does require a specific MAF to function properly with the 24# injectors. That's why i asked. It's a package deal. X3Z, 24's and the F1SF-12B579-AA 70mm MAF.

That MAF is actually off a 91-94 Supercoupe, but it has a unique MAF transfer value that is specific to the X3Z ecu.

If you are running a 76mm aftermarket, you might have issues depending on what that MAF is. It's not a "calibrated" 24# injector MAF is it?

Depending on what parts you do have, it might be more beneficial to swap to an A9L vs get the right meter for the X3Z.
I'll check out the part Number later, but very much appreciate the INFO. Plan on diving back in on her Tomorrow. She was running before I burned up the fuel pump, now can't get it to run on anything but ether.
 

Jeep2351

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Jun 3, 2021
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I'll check out the part Number later, but very much appreciate the INFO. Plan on diving back in on her Tomorrow. She was running before I burned up the fuel pump, now can't get it to run on anything but ether.
So, I got home last night and checked the MAF #F1ZF-12B579-AA, AFH55-03B. Do you think the A9L is worth the $400.00, or just swap out the MAF for a 70MM? What's the long term best result, as far a conversions go, I've read the X3Z isn't the ideal ECM, but like I said I got a great price on it. 40k miles $150.00. Going to reclean the tank tonight, as the old sock disintegrated and chunks are floating in there. The opening is only 3 inches or so, figured I'd try to get a wand in there and stir up what I can, then bake it tomorrow in the sun. Again, thanks for the info.
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
36,444
12,352
224
Massachusetts
So there still remains a few unanswered questions. That is the electronics for a stock 91-93 mustang with 55mm MAF. However there are certain aftermarket MAFs designed to use the stock electronics but resize the inlet to the electronics to trick the meter. Since you said you had a 75mm maf, no idea of this is the case or what that meter is “calibrated” to. So I can’t answer yet which is the best course of action until we fully id that MAF.

cheapest, easiest solution is to track down the 93 cobra MAF, which also came in supercoupes.

the part number is F1SF-12B579-AA with AFH70-02 underneath. AFH70 means it works with fords 70mm MAF housing, which was in a few cars. Thunderbirds and cougars had them, as well as a flanged version in the sn95. It needs to be paired with the f1sf electronics to work with the x3z and 24s
 

Jeep2351

New Member
Jun 3, 2021
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Morrison, CO.
So there still remains a few unanswered questions. That is the electronics for a stock 91-93 mustang with 55mm MAF. However there are certain aftermarket MAFs designed to use the stock electronics but resize the inlet to the electronics to trick the meter. Since you said you had a 75mm maf, no idea of this is the case or what that meter is “calibrated” to. So I can’t answer yet which is the best course of action until we fully id that MAF.

cheapest, easiest solution is to track down the 93 cobra MAF, which also came in supercoupes.

the part number is F1SF-12B579-AA with AFH70-02 underneath. AFH70 means it works with fords 70mm MAF housing, which was in a few cars. Thunderbirds and cougars had them, as well as a flanged version in the sn95. It needs to be paired with the f1sf electronics to work with the x3z and 24s
I checked the ID of the inlet side of the meter and it's roughly 3.25" which converts over to 82.55 mm's. Guessing it's an 80mm? I'm assuming it's been recalibrated, (Bought it off EBAY Years ago) but sounds like the right maf is in my future. The Harness is Ford Racing M-12071-A50.
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
36,444
12,352
224
Massachusetts
I agree. Getting the correctly matched parts makes sense here.

Will it solve your issue? Unknown. It's certainly not helping
 

Jeep2351

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Jun 3, 2021
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Morrison, CO.
I agree. Getting the correctly matched parts makes sense here.

Will it solve your issue? Unknown. It's certainly not helping
Had a fairly decent weekend on her, made some good progress, New pump installed, changed the ignition switch. I'm still not getting pressure on the BBK FPR pressure gauge, But She's firing for a few seconds , runs and dies (without ether)with the maf unplugged. Gave up on finding the F1SF MAF, Ordered a Walker aftermarket one. New MAF comes in Thursday.
 

Jeep2351

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Jun 3, 2021
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Ugh, still fighting her, slowly, I definitely have a fuel delivery problem. Pulled the regulator off the rail as I’m getting fuel to the regulator, but stops there. Can’t get fuel through the bbk fpr Bought the 26$ stock version, still no fuel. Smelled gas on old one and chucked it. Bought bbk cause of the rail, and could use gauge Could I really purchase this many bad new parts. When blowing air through the fpr I can get my gauge to move holding my finger on the outlet. What gets me is the new pump won’t push it through on it’s own disconnected from rail. I looked at the bbk rebuild kit and parts look different, diaphragm looks same, just a little ridge on the metal piece. Is this my problem? Anyone else had issues with bbk 1706? She still runs on ether, needs fuel dang it!!!
 

Jeep2351

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Jun 3, 2021
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Why can I not get fuel through the fpr to the rail? Fpr is hooked to inlet hose hanging loose and apparently it’s stopped right there. Prime it watch the hose blow up like a water balloon and no gas coming out. Wtf am I missing? Rebuilt the bbk 1706(probably didn’t need too) pressure reads when blown through the outlet (wrong direction) can’t get fuel or air through the little hole on my stock or bbk fpr. Ideas?