TimberJack Posted October 11, 2016 Share Posted October 11, 2016 I've heard from a few folks that you can shim the plunger to create more fuel pressure. Does anyone know if this will work? I just replaced mine on a 2004 AC 427 and the pressure is still low. Quote Link to comment https://www.bigmacktrucks.com/topic/47228-ac-fuel-pump/ Share on other sites More sharing options...
Mackpro Posted October 11, 2016 Share Posted October 11, 2016 How low is low? 59 psi is where the overflow valve opens at. Any thing above 59 psi is good. I think the overflow valves are staked where you cant shim them. However , anything is possible I assume. Quote Link to comment https://www.bigmacktrucks.com/topic/47228-ac-fuel-pump/#findComment-348423 Share on other sites More sharing options...
TimberJack Posted October 11, 2016 Author Share Posted October 11, 2016 At 1250 rpm it's showing 68 and it calls for 50-80 psi. Truck has gotten weak over the last couple of months. It's got new turbo, intercooler, injectors and Mack has checked the Egr valve and said it's work fine. I'm clueless and tired of throwing money at it. Quote Link to comment https://www.bigmacktrucks.com/topic/47228-ac-fuel-pump/#findComment-348434 Share on other sites More sharing options...
Mackpro Posted October 11, 2016 Share Posted October 11, 2016 Hopefully you have a Boost /manifold pressure guage in the upper LH side of guage cluster. A good running ASET AC engine will have 33 psi of boost under a load. Quote Link to comment https://www.bigmacktrucks.com/topic/47228-ac-fuel-pump/#findComment-348442 Share on other sites More sharing options...
TimberJack Posted October 11, 2016 Author Share Posted October 11, 2016 Nope sure don't, we plugged in computer at dealership and it was showing 32 psi under load but not sure how accurate that is. Quote Link to comment https://www.bigmacktrucks.com/topic/47228-ac-fuel-pump/#findComment-348449 Share on other sites More sharing options...
TimberJack Posted October 11, 2016 Author Share Posted October 11, 2016 It's like something is smothering it. When you leave a ref light it takes for ever to get up to speed, and if you ever let up on throttle it want recover you best off drop a gear Quote Link to comment https://www.bigmacktrucks.com/topic/47228-ac-fuel-pump/#findComment-348450 Share on other sites More sharing options...
Mackpro Posted October 11, 2016 Share Posted October 11, 2016 If the laptop says 32 psi thats good. All AC engines have a boost pressure sensor even if they dont have a guage in the dash. The laptop was reading off that sensor. Single or dual exhaust? We had several trucks here with single exhaust and the baffle would break inside the muffler and get side ways blocking off the exhaust flow. Quote Link to comment https://www.bigmacktrucks.com/topic/47228-ac-fuel-pump/#findComment-348453 Share on other sites More sharing options...
TimberJack Posted October 11, 2016 Author Share Posted October 11, 2016 Dual exhaust, I will check them just to make sure. I've even changed the ecm. First I put a 380 hp still the same, 427 hp same and the 460 hp same. I couldn't tell any difference from the 380 to the 460. Quote Link to comment https://www.bigmacktrucks.com/topic/47228-ac-fuel-pump/#findComment-348458 Share on other sites More sharing options...
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