95 Mustang 5.0 Fuel/tuning Issue

[71_maverick]

Hi all, I think I got a decent problem and could use some ideas. The car is 95 5.0 stock short block, stock cam, Typhoon intake, TFS 170 heads, 1.6 rockers, tnw nitrous plate, 255lb fuel pump, BBK fuel reg. and shorty headers, NO egr, cruise, PS, AC.

I bought the following parts from a road track sn95 part out, bbk fuel reg, t4m0 computer, 30lb injectors, and c&l 76mm maf. I ran the computer and fuel reg last summer on my stock 5.0 no problems. yesterday I wanted to bump my fuel pressure for the new mods. Come to see its set at 70psi! So I change it to 40psi, short test drive I get popping out the exhaust, no acceleration, severe bogging barely able to run under any load. so I change it back to 70psi. Acceleration is decent no bogging no exhaust popping cruises ok but acts like it could use a tune(expected).

the computer is untuned per previous owner. The only idea I have left is the computer has to be tuned. I tried the 30lb and c&l with correct sample tube but couldn't get it to idle(before I I changed to fuel pressure). I'm thinking the next step would be to set the fuel pressure to 38psi and swap back to the 30lb and c&l. Just to throw some more on it I cant pull codes because it wont connect but that's a problem for another day. Any thoughts??

 

[General karthief]

The computer may be the problem, got another one you can test?
I had to jackup my fp and found it was the computer.

 

[jozsefsz]

It's possible to make your injectors behave like the next larger size up by increasing the fuel pressure. It's likely that the MAF was calibrated to 42lb. injectors. 30lb. injectors being run at 70psi (instead of 39.5) will make them act like 40lb injectors - though probably a little lean but within the limits that the computer can adjust for. This can be done without tuning. Sounds like they may have been looking to push everything they could through that nitrous plate, which is understandable. Always get the bigger injectors when in question.

https://www.rceng.com/technical.aspx

Now why the C&L didn't respond properly to your bringing it back down to 39.5 with sampling tube adjustment I don't know, other than the fact that C&L's aren't all that reliable. You sure they're 30's? You used the purple sample tube (think that's right for 30's on a 76mm). FYI flow ratings for aftermarket injectors are typically at 43.5 and not at 39.5 so adjust to 43.5psi fuel pressure as your baseline (with the vacuum line disconnected).

The injectors might have also been run so long at 70 that they no longer respond well at low pulsewidths at a lower pressure (poor idle).

How to address this depends on your goals for the car. If you want a reliable daily driver and aren't going to be putting all kinds of fog through it, then ditch the C&L, get some 24's and a matched MAF or Cobra computer (or the factory 19's and stock MAF). Or go back to what it was running before for the short-term.

Checking if it was 'tuned' is pretty easy - passenger kick-panel and check if there's a piggy-back chip on the computer's J3 service port. That's the only way to tune these guys, there's no flashing the ROM or anything like that.

 

[71_maverick]

I have a automatic computer I could switch to for testing. There is nothing on the outside of the ecm so ill pop the cover and check it out. Its interesting what you said about the 42lb injectors. I bought the C&L tube with injectors, he said they were 42lbs but I looked the part number up they are bosch 30lb type 3 ev1 all brown bodies. the sample tube was red, I tried to start it originally with the red tube and injectors couldn't get it to run, sputter then die. so I bought from mac the 30lb tube and it would run but not idle without opening the throttle a little. I think the cobra computer is going to be the best choice. Should have just slapped a carb on it lol.