Hey guys need a little advice. I don't know what to set my base fuel pressure to. Some guys say 40 psi base with vacuum off and plugged, some guys say 55 to 60psi base. Just bought the car and put new fuel rails and FPR on it. I have the base set at 42psi drops to 39 with vacuum on. Car does run rich at this setting. Here is what I'm working with: 1995 gt 331 stroker. All emissions delete EGR delete etc. Trick flow track heat upper and lower intake. TFS stage 1 cam. Twisted wedge heads 1.6 rocker arms. Trick flow fuel rails, unknown aftermarket FPR with guage. Accell 30 lbs injectors. 70 mm accufab throttle body, 75 mm mass air sensor, custom cold air intake. 190 liter fuel pump. 5 speed manual. Any help would be great, I'm so new to EFI and have little knowledge on these things as my previous mustangs were carbed from the 70s. Car is running rich, but runs good. Just want to make sure I'm in the ballpark of correct FP. I've read anywhere from 40psi to some guys saying 55 to 60. This is a NA engine, no boost. Thanks everyone!
Fuel pressure help
- Thread starter clayton seiders
- Start date
89ripper
Founding Member
How do you know it is running rich? Smell? 55 to 60 seems way high to me. Have you run codes? Also your eyes arent burning are they?
Thats when you know its really running rich
Thats when you know its really running richShe's running rich buddy. Exhaust smells very rich, tips of exhaust are black, when you punch on the throttle she is a bit doggy and then picks up and flies. You can most def smell it when you get on the throttle and even at idle. When you shut it off and start it back up, it loads up and doesn't want to run, idles very low and wants to stall unless you give it throttle to burn up the fuel. A lot of forums I'm reading, most the guys say set base pressure at around 40 which I'm only a little higher than that. But a few guys say with my application, I should be above 50. Wouldn't that make it more rich??? Which is the opposite of what I need. Maybe these 30lbs injectors are too big and I should go even lower on FP? Like I said I'm new to the EFI world completely and learning as I go....
89ripper
Founding Member
Are you on a stock tune? 30lbs might be a bit much with no power adder but your ecu detetmines a lot of how your fuel is burned, so im curious have you pulled any codes? I had an o2 sensor wiring problem and it made my eyes burn with how rich I was running
I have 42 lb/hr injectors on my NA 331 with zero issues. It’s all in the tune.
Typically base pressure with the vacuum disconnected is 39 psi on a stock car. If the car has been tuned (chip on the service port of the ECU) or has an aftermarket system on it then who knows what it was set at. Can you contact who you bought it from and ask if it’s tuned and if they know what the fuel pressure is supposed to be set at?
Typically base pressure with the vacuum disconnected is 39 psi on a stock car. If the car has been tuned (chip on the service port of the ECU) or has an aftermarket system on it then who knows what it was set at. Can you contact who you bought it from and ask if it’s tuned and if they know what the fuel pressure is supposed to be set at?
The car has never been tuned before since the engine build so I'd imagine it is stock tuned? I had no idea you have to tune the computer system. Don't even know where or how you go about doing that...lol.
Well I did contact previous owner he said to set it at 55psi. I think he is off his rocker because it seems to have plenty enough fuel at the base 40 psi that I have it set at. And also no, it has never been tuned. I guess I take it to a professional tuner to have that done? Doesn't sound like a task a normal service garage handles...
89ripper
Founding Member
Clayton consider this. You have a stock ecu with stock parameters ( redundant maybe) and you start putting on a bunch of parts. Now the ecu is trying to work with the values that came from the factory and as such will cause driveability issues. This is what Aero and I are referring to by "tuning".
Myself I have never had a tune for my car, however it does have its issues. Ive learned from on here about workarounds and what not, keep in mind stock 302 block heads/fcam/intake.
We need to see why the computer is deciding to throw a bunch of fuel making it smell rich. Aero has confirmed your injector size is fine, he is at 42lbs.
In my case I had bad o2 sensor wiring, pulled codes, engine bank lean, so guess what? Ecu starts dumping a bunch of fuel to compensate making the car run rich. Remember when I said my eyes were burning? Yeah it was that bad...
In short for my long answer, find out if the ecu is stock or has any tune/modification done to it...
Okay thankyou for the explanation. It may sound like a simple thing to explain but when the most tuning I have ever had to do was adjust air/ fuel mixture screws and floats on a 750 holley carb, I'm in the dark when it comes to these computer systems and EFI. I will see if I can take a look at the ECU, see if it looks stock ( which I'm pretty sure it is) and then go from there.
89ripper
Founding Member
Totally get it. Ive owned my mustang for over 28 years now and i still learn something new everyday. Within last 6 years ive replaced my ecu and its run better than ever
So you have basically thrown the kitchen sink at the stock ECU and it cannot “adjust” for all of it. Biggest problem is 331 vs 302. Way more air demand than a 302 this it needs more fuel. Do you know if the Accufab mass air meter (MAF) is calibrated for the 30 lb/hr injectors? If not then that is causing more problems. The ECU has tables in it that are set up for a 58mm MAF with a stock element and 19 lb/hr injectors.
You can hurt the motor is you continue to run it this way. You need to stop and get a Diablo or SCT chip and have the car dyno tuned.
You can hurt the motor is you continue to run it this way. You need to stop and get a Diablo or SCT chip and have the car dyno tuned.
Ahhhh, Newbees and a used hotrod! 
Get the 'magic book' a ford assembly manual. Worth the bucks even if it's got some 'modifications ' take notes of what you find, like codes, you'll know what the factory set stuff at, just because you got a bigger this you may not need a bigger that, or that that is not big enough,
Remember fiddlin with those bleeders, power valves and idle screws? You listened and felt the engine to adjust the carb, the computer does the same through the sensors and does the adjusting, we have to make sure the info is accurate or within tolerance.
I went through this carb to EFI transition
Get the 'magic book' a ford assembly manual. Worth the bucks even if it's got some 'modifications ' take notes of what you find, like codes, you'll know what the factory set stuff at, just because you got a bigger this you may not need a bigger that, or that that is not big enough,
Remember fiddlin with those bleeders, power valves and idle screws? You listened and felt the engine to adjust the carb, the computer does the same through the sensors and does the adjusting, we have to make sure the info is accurate or within tolerance.
I went through this carb to EFI transition
Thanks man. Yes im that EFI newb that bought an already built project haha. I considered just swapping all the fuel injection stuff out for my edelbrock rpm performer Intake and holley double pumper, and ofcourse would have to just get a throttle cable figured out and have a much simpler set up. But then again I would have to bypass the computer in which I don't know about doing that either. Plus I already dropped about 450 bucks into parts putting on the trick flow rails and aftermarket FPR, along with the various fuel line fittings to make the set up work. So I mise well keep the set up and try to find a local tuner to get it running the way she should. The engines built and balanced wonderful, even with just a mild TFS stage 1 cam it revvs quick and is thirsty for high RPMs ( she sings to 6500 quick and smooth). Pulls great especially hitting 3k rpm + and the 410 gears get it there quick. Fun car, just a new game to me. Before I was running a 347 stroker with ford's F cam and the old school card set up in a 70 stang with 355 gears and 3200 stall. That too was a fun car, ran a little quicker than this one but I think a lot of that has to do with the lack of tuning issues. Thanks for all the advice guys!
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