kevgibbs Posted July 10, 2021 Share Posted July 10, 2021 Hello Gents, I have a 1997 CH with a E7-400 VMAC2. I have a Blixxton module on it. When I first installed the module the boost pressure would build up to 34psi. A little while ago I was taking off from an intersection and I had the truck at full throttle. I suddenly felt the engine go to about half throttle ( with the the pedal still all the way to the floor) and right to back to full throttle again except now it will not build over 28 psi of boost. My first thought was my Blixxton module went bad and caused something to go screwy. There was also absolutely no difference in performance between the 3 different settings on the module where as before there was a significant difference. With my Blixxton module still under warranty, I sent it in for a warranty claim. A few weeks later I received my original Blixxton module back with a test result showing that it was functioning as it it should. Now I'm beginning to wonder if there is now a mechanical issue with the fuel rack inside the pump or if there is an electronic issue somewhere. The truck is not showing any active codes. I was going to plug into it sometime soon and see if the throttle pedal position sensor is working properly. Does anyone else have any thoughts? Quote Link to comment https://www.bigmacktrucks.com/topic/67310-boost-pressure-lost-e7-400-vmac2/ Share on other sites More sharing options...
mrsmackpaul Posted July 10, 2021 Share Posted July 10, 2021 (edited) Sorry Im no help here, but that sounds like a sensible place to start, maybe it has come loose and shifted, I am assuming it's like a normal automotive type of sensor I have never worked on these really need to shut my trap, will observe from the side lines and learn something Paul Edited July 10, 2021 by mrsmackpaul Quote Link to comment https://www.bigmacktrucks.com/topic/67310-boost-pressure-lost-e7-400-vmac2/#findComment-476633 Share on other sites More sharing options...
Joey Mack Posted July 10, 2021 Share Posted July 10, 2021 34 is a bit high... anyway, do you simply have a boost leak.... gaskets, hoses, C.A.C. boots, top right corner of the C.A.C.?....... jojo 1 Quote Link to comment https://www.bigmacktrucks.com/topic/67310-boost-pressure-lost-e7-400-vmac2/#findComment-476634 Share on other sites More sharing options...
theakerstwo Posted July 11, 2021 Share Posted July 11, 2021 Like Joey said check for boost leaks and not just looking but with about 25 psi from the turbo hose up to the head.You can get that much pressure to the head if you turn the engine slow watching for peak pressure at the gauge. Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/67310-boost-pressure-lost-e7-400-vmac2/#findComment-476664 Share on other sites More sharing options...
fjh Posted July 12, 2021 Share Posted July 12, 2021 If you have a Mack 18 speed in plug the switch on on the cylinder on the back torque limit switch may have failed and caused a de rate Quote Link to comment https://www.bigmacktrucks.com/topic/67310-boost-pressure-lost-e7-400-vmac2/#findComment-476690 Share on other sites More sharing options...
kevgibbs Posted July 12, 2021 Author Share Posted July 12, 2021 21 hours ago, fjh said: If you have a Mack 18 speed in plug the switch on on the cylinder on the back torque limit switch may have failed and caused a de rate Where is the torque limit switch located? Quote Link to comment https://www.bigmacktrucks.com/topic/67310-boost-pressure-lost-e7-400-vmac2/#findComment-476733 Share on other sites More sharing options...
brettj3876 Posted July 14, 2021 Share Posted July 14, 2021 On 7/10/2021 at 6:20 PM, Joey Mack said: 34 is a bit high... anyway, do you simply have a boost leak.... gaskets, hoses, C.A.C. boots, top right corner of the C.A.C.?....... jojo That seems about right with the blixxton. 33 is what we were pushing with one Quote Link to comment https://www.bigmacktrucks.com/topic/67310-boost-pressure-lost-e7-400-vmac2/#findComment-476788 Share on other sites More sharing options...
kevgibbs Posted July 14, 2021 Author Share Posted July 14, 2021 Update on the situation: I re-installed my Blixxton and changed my fuel filters and I have absolutely no change in the situation. At maximum, my boost pressure is 29psi where as before it was pushing 33psi sometimes 34. The condition that I experienced at the intersection a while back doesn't support that it has a boost leak however I'm not ruling out that possibility, that's what I'm going to look for next actually. That day, I very clearly felt the throttle go to about half throttle and suddenly back to about 95% throttle without my foot ever coming off of the accelerator. This has me thinking it is a issue inside the electronic system of the fuel control. I did verify that my throttle pedal position sensor is working correctly. That's about all that my tooling will do unfortunately, I can't read any other ECM data regarding fuel control. I wish I had an actual VMAC2 reader to help the situation, my local mack dealer doesn't have one anymore Quote Link to comment https://www.bigmacktrucks.com/topic/67310-boost-pressure-lost-e7-400-vmac2/#findComment-476830 Share on other sites More sharing options...
Joey Mack Posted July 14, 2021 Share Posted July 14, 2021 I read some posts over again, so you have a gray plug at the injection pump??? ok, those can get, bad/loose connections. just a thought. if the pump is not delivering fuel correctly, then boost will be lost..??, just a thought, jojo 1 Quote Link to comment https://www.bigmacktrucks.com/topic/67310-boost-pressure-lost-e7-400-vmac2/#findComment-476832 Share on other sites More sharing options...
kevgibbs Posted July 14, 2021 Author Share Posted July 14, 2021 38 minutes ago, Joey Mack said: I read some posts over again, so you have a gray plug at the injection pump??? ok, those can get, bad/loose connections. just a thought. if the pump is not delivering fuel correctly, then boost will be lost..??, just a thought, jojo Yes it has a gray plug on the back of the pump. That very well could be a possibility Quote Link to comment https://www.bigmacktrucks.com/topic/67310-boost-pressure-lost-e7-400-vmac2/#findComment-476833 Share on other sites More sharing options...
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