jegster10 Posted March 31, 2018 Share Posted March 31, 2018 So I have a 1991 E7 400 vmac (Bosch pump) and the power has gone away after having some work done last fall. We had it in the shop and had a cracked head replaced and ever since then it won’t pull worth a darn. Used to pull loaded 80k up a large hill close to me and only drop from 70 to maybe 65, now it will drop back to 50. While hauling a load today I made sure to make some observations: Turbo builds boost well from 1400 up, gets to 25-27 psi. Pulls good in lower gears up until 10th (13 speed Mack trans) Pulls better in 12 than 10/11 Pyro quit working a couple days ago but EGT was around 800-850 on hard pull up to that point, though not sure how accurate it was. Any suggestions on where to look would be much appreciated. Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted April 1, 2018 Share Posted April 1, 2018 Stick a fuel psi gauge on it and see what you get under load. Quote Link to comment Share on other sites More sharing options...
jegster10 Posted April 2, 2018 Author Share Posted April 2, 2018 20 hours ago, Mack Technician said: Stick a fuel psi gauge on it and see what you get under load. We will work on doing this and update with results once we do. Thanks Quote Link to comment Share on other sites More sharing options...
jegster10 Posted April 6, 2018 Author Share Posted April 6, 2018 On 4/1/2018 at 12:06 PM, Mack Technician said: Stick a fuel psi gauge on it and see what you get under load. Ok, just got back from hauling a load of hay into a 20 mph wind, pressure was 32 psi at idle and never dropped below that while pulling except right after a shift it would drop to about 28 until boost started to build, boost was 27 while pulling. We thought about checking the valve adjustment, but I'm pretty well at a loss. Quote Link to comment Share on other sites More sharing options...
Timmyb Posted April 6, 2018 Share Posted April 6, 2018 I looked in to the boost specs for an e7 when ordering a new boost gauge for my dads truck. I’m pretty sure the boost shoud be over 30psi as I purchased a 35psi gauge. Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted April 6, 2018 Share Posted April 6, 2018 (edited) General tuneup for a v MAC 1 was check timing, pop injectors, check fuel pressure, check boost, pressurize charge air system, set overhead. We had occasions of timing slippage at slotted time gear. Remember Mack instructor telling us to slightly exceed the torque specs on timing gear retainer bolts. Edited April 7, 2018 by Mack Technician Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted April 6, 2018 Share Posted April 6, 2018 If you had a Kent Moore J-37077 you could check timing. Probably need a turn tool too. See one online sold for $210. Used 37077, eBay. Quote Link to comment Share on other sites More sharing options...
Mackpro Posted April 7, 2018 Share Posted April 7, 2018 As Mack Tech . Pump timing needs bumping up 1.5 degrees over what the valve cover says but not any more or it will over heat in the summer. Injectors need refreshing or replacing . Clogged muffler is a possibility. Pressure test the complete intake system. Blown intake manifold gaskets . The air compressor intake could be on the boost side of the turbo/intake , leaks there will hurt performance Quote Link to comment Share on other sites More sharing options...
jegster10 Posted April 7, 2018 Author Share Posted April 7, 2018 I know for a fact the muffler isn’t plugged ;). Compressor intake is on the intake side of turbo, all intake gaskets were replaced when they changed the head, and it ran fine up until that point which makes me think it’s not injectors either. We will start with checking the valves and timing and see what we come up with. I’ll update as when we get it done, but may be a little while as it’s work is kinda done at the moment and we are getting swamped with other stuff to do. 1 Quote Link to comment Share on other sites More sharing options...
jegster10 Posted May 30, 2018 Author Share Posted May 30, 2018 We finally got it in the shop and checked the valves, all except one were extremely tight. Will try to get it under a load later this week and see how it pulls, but the valves being that far off will probably make a big difference. Quote Link to comment Share on other sites More sharing options...
jegster10 Posted June 2, 2018 Author Share Posted June 2, 2018 Well we didn’t have a heavy load on it today, just around 20k plus cattle trailer into a wind, but it seems to be back to where it was before we had the work done, we still need to check the timing but it seems the valves were the main culprit. Thank you for all your help. Quote Link to comment Share on other sites More sharing options...
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