top end power issues

[aschroeder78]

Hello, I just finished my build for my 97 TJ. used the 97 block, scat crank from clegg, 4.2 rods .040 4.0 pistons. also have the stage 1 cam from clegg (howards cam) flow daddy header and full magnaflow exhaust(hi flow cat and muffler) starts and runs good but seems to lack power on the top end. climbing small hills it wont go much over 60mph. compression test shows all 6 between 178-182 psi, fuel pressure is 58psi, vacuum is solid, plugs look pretty good but may be a touch on the lean side. im at a loss as to what is causing this. i will admit i dont know alot about fuel injection systems so that may be an issue. i dont think that the injectors are stock but i dont see ant numbers on them. any help is greatly appreciated.

[Randy Bobandi]

You haven't done any tuning? Are you running the stock throttle body? I wouldn't run that engine without a 255LPH fuel pump and 400+cc injectors. You can never have enough fuel pump/injector. Also, what transmission, tire size and gear ratio?

[Cummins90]

400+cc injectors. You can never have enough fuel pump/injector.

What? If you present the ECU a mechanical variable beyond its adjustment capability you will have running issues.

Lets get a picture of the fuel injectors try your best to get some sort of identification on them. Your rail pressure is higher than it should be. If you have a scanner with live data lets get the key on engine off sensor readings and then again with the engine running at idle.

[aschroeder78]

no tuning, stock ecm. running a 65mm BBK throttle body. new factory replacement fuel pump. i will take a pic of the injectors but am positive there are no numbers on them. it is a 1997 tj with a 5spd. 4in lift, 35's, 4:56 gears. just ordered a set of bosch 27lbhr 283cc injectors, hopefully those will be in on monday

[Russ Pottenger]

At 58psi I suspect the 27lb injectors will give you too much fuel

[Randy Bobandi]

400+cc injectors. You can never have enough fuel pump/injector.

If you present the ECU a mechanical variable beyond its adjustment capability you will have running issues.

Adjustment capability? You don't actually think that 400cc injectors would be too much for a 300 HP engine do you? lol. Fuel injectors under 1000cc have ZERO issues in the short pulse width range (Idle). Injectors of that size also prevent Non-linear pulse width and operation over 90% duty cycle.

it is a 1997 tj with a 5spd. 4in lift, 35's, 4:56 gears

You gotta address that fuel pump as well. Over 50 Psi, there's a problem with the regulator. You're gonna burn up the stock unit. Walbro offers plug N' play 255LPH and 350LPH pumps for all 4.0L Jeep models.

[aschroeder78]

i dont have an external regulator, how do you adjust pressure?

[Randy Bobandi]

The fuel pressure regulator is part of the pump assembly and they are replaceable. The regulators are available separately, though replacing them rarely fixes the problem. The problem is typically due to cheap aftermarket pump assemblies that are not built to spec in the first place. If it was my 97 TJ, I would order the DELPHI FG1353 for the 19 Gal tank or the DELPHI FG1355 for the 15 Gal tank. I would pull the pump out of that assembly and replace it with the Walbro GSS342 255LPH Fuel Pump.

[aschroeder78]

just installed some 27lb bosch injectors and it has made a huge difference, 80mph up hill no problem. going to look into getting my pcm re progrommed and see if i can get a little more out of it. thanks everyone for the info!

[aschroeder78]

Still running great, got a few hundred miles on it. will be getting the tuning done in the fall. terrible mileage, 9-10mpg... was getting a solid 15 with the stock 4.0. is this normal?

[aschroeder78]

Still running great, got a few hundred miles on it. will be getting the tuning done in the fall. terrible mileage, 9-10mpg... was getting a solid 15 with the stock 4.0. is this normal?

[Cheromaniac]

Sounds like the engine's running too rich.

[SkylinesSuck]

I see a lot of back and forth here resulting in confusion @ Randy B & Cummins90 You guys aren't comparing apples to apples. You can (and should) tune larger injectors for your build. In this case it's almost impossible to have too much injector. Many people on this board however just go with putting slightly bigger injectors in a build using the stock tune. With a mild build, this usually gets things in the ballpark at WOT and they let closed loop take care of everything else. While not optimal, this "works" most of the time. The car world I learned the most from engine wise would never consider major changes without tuning which is what Randy is assuming, hence the confusion here.