E7 400 low power

[Anonymous]

Hello everyone.  Have 1990 ch613 with a 9 speed and an E7 400 all mechanical motor that is very sluggish. This is my fist Mack bought to pull equipment and haul grain. Truck was bought as a project with a blown engine. My dad and overhauled the motor and had the pump and injectors sent off and checked. Pump shop put new delivery valves in and set it to 10% over factory specs. We set the timing to 21 degrees. Pulled my first load with it last night. It was a light load and then truck is just slow to rev under load and has a shutter/serge. Checked fuel pressure at pump and have 20 psi at idle but have no clue if that’s in spec or not. Anyone know what the fuel pressure spec is? Only builds 20psi of boost. So I will be checking for boost leaks.  Did find the air line to the afc was cracked and replaced it thinking I found the problem but made little to no difference in power. For reference I feel like my old ford with an L10 has the same amount of power as this truck. Any help is appreciated. 

[fjh]

31 minutes ago, Anonymous said:

Hello everyone.  Have 1990 ch613 with a 9 speed and an E7 400 all mechanical motor that is very sluggish. This is my fist Mack bought to pull equipment and haul grain. Truck was bought as a project with a blown engine. My dad and overhauled the motor and had the pump and injectors sent off and checked. Pump shop put new delivery valves in and set it to 10% over factory specs. We set the timing to 21 degrees. Pulled my first load with it last night. It was a light load and then truck is just slow to rev under load and has a shutter/serge. Checked fuel pressure at pump and have 20 psi at idle but have no clue if that’s in spec or not. Anyone know what the fuel pressure spec is? Only builds 20psi of boost. So I will be checking for boost leaks.  Did find the air line to the afc was cracked and replaced it thinking I found the problem but made little to no difference in power. For reference I feel like my old ford with an L10 has the same amount of power as this truck. Any help is appreciated. 

Temove the line to the afc and suck on it if you can suck or blow thru it the diaphragm may have a hole in it! Also check your linkage and stop for going full on full off!

[JoeH]

Charge air coolers like to crack. You should see 35 psi of boost.

Get a couple 4 inch PVC pipe end caps, put an tire valve stem in one, and clamp one end cap into each rubber hose on the charge air cooler. Hook up your tire chuck to the valve stem on the one cap and listen for leaks.  My '95 E7-350 had a nice big crack down the front right side of the charge air cooler.  Went from 1100+ degrees on the pyrometer at 22psi boost to -900 degrees and 35psi boost.

[JoeH]

In the event you don't have a crack, figure the charge air cooler system is good for 35 psi.  Don't leave it on for too long if it's not leaking.

[Mackpro]

I pulled up the 1990 Mack tune up manual. A E7 400 specs are 21-37 psi fuel pressure. Pump timing at 19 degrees and boost pressure under a load should be between 20 and 28 psi . . 

[Anonymous]

Checked operation of linkage tonight they are both correct. Need to double check afc. Checked the charged air cooler while waiting on parts and it was split on both sides and replaced it with one from Mack. I need to double check for boost leaks. I guess need to also check fuel pressure under load.  I was just watching it at idle. I did notice the gage was bouncing at 20psi and thought that was odd for an oil filled gage. It built up to 22psi at say half throttle. 

[Mackpro]

Also on those engines, the air compressor gets it fresh air from piping that goes around the back of the engine to the back of the intake manifold.  This is all on the turbo boost pressure side. So any leaks in that part equals lower boost pressure. The original intake manifold gasket were standard gasket material and were prone to blow out. The newest gaskets are steel core and more durable. Once you get the after cooler on, hook up the drivers side piping and on the passenger side install a test plug where you can pressure check the after cooler and intake manifold and air compressor intake piping . While there will be air passing through the valves and out the exhausts you can still build enough pressure to check with soapy water on all hoses and gaskets and fittings. My homemade pressure tester .

[Anonymous]

4 hours ago, Mackpro said:

Also on those engines, the air compressor gets it fresh air from piping that goes around the back of the engine to the back of the intake manifold.  This is all on the turbo boost pressure side. So any leaks in that part equals lower boost pressure. The original intake manifold gasket were standard gasket material and were prone to blow out. The newest gaskets are steel core and more durable. Once you get the after cooler on, hook up the drivers side piping and on the passenger side install a test plug where you can pressure check the after cooler and intake manifold and air compressor intake piping . While there will be air passing through the valves and out the exhausts you can still build enough pressure to check with soapy water on all hoses and gaskets and fittings. My homemade pressure tester .

I will try that this evening. Checked fuel pressure under a load this morning and it was agin 20psi at idle but under a load it was dropping down to 10 then cruising would come up to around 18psi. I think fuel pressure maybe my biggest power thief now. I'm going to check all the lines agin make sure I don't have one that's pinched or collapsed also will be checking the draw straw from the tank too. I forgot all about the air compressor inlet line too. will check that out for sure. 

[Anonymous]

Just finished up another round of testing. AFC is good, applied 20psi of shop air from the turbo on out and sprayed with soapy water. Only leak I found was on the compressor inlet line. Will be replacing that as soon as I get some new hose. I also checked all my fuel lines for blockage with shop air and rechecked fuel pressure and its still bellow spec. will be looking for a lift pump. Anyone have the part number for the lift pump? and what hose is suitable for the compressor inlet tube?

[fjh]

Fuel pressure is too low under load ! Check for a broken spring in the fuel return T or a restriction on the fuel lines or filters!Needs a minimum 20 to get full power!

[Anonymous]

On 8/2/2023 at 11:13 PM, fjh said:

Fuel pressure is too low under load ! Check for a broken spring in the fuel return T or a restriction on the fuel lines or filters!Needs a minimum 20 to get full power!

Checked return spring and the ball. They appeared fine. Replaced all fuel lines from filter housing to pump. and replaced lift pump with new pump from PAI. will now maintain 20Psi at idle and under load. Still feels really sluggish/bogged down and under powered. Hooked to my lowboy empty could only get 20psi boost giving it all it had up a slight hill. Going to shim the spring in the fuel return to try and get fuel pressure up a bit more. If that don't work Im draining the tank and checking the suction tube. Am I on the right track or am I missing something. 

[fjh]

14 hours ago, Anonymous said:

Checked return spring and the ball. They appeared fine. Replaced all fuel lines from filter housing to pump. and replaced lift pump with new pump from PAI. will now maintain 20Psi at idle and under load. Still feels really sluggish/bogged down and under powered. Hooked to my lowboy empty could only get 20psi boost giving it all it had up a slight hill. Going to shim the spring in the fuel return to try and get fuel pressure up a bit more. If that don't work Im draining the tank and checking the suction tube. Am I on the right track or am I missing something. 

Holding 20 under load is OK 15 and under is not good under load! shimming is worth a try ! did you check the afc  diaphragm for leaks for leaks?

[JoeH]

I'm stumped on what afc stands for; is this the puff limiter system? I was thinking maybe the puff limiter system was hooked up wrong

[fjh]

Yes it is puff limit on Rob Bosch  ! If the diaphragm has a hole on it you won’t likly see it ! Take hose off suck or blow on it if you can blow or suck on it continuously it’s got a hole on it it won’t ever get full fuel! It also may have a torque limit valve on it in the mix! 

[Anonymous]

I did check the afc for by sucking and blowing into it. I’m going to pull it off and check it out and make sure that it’s working properly. And not set for too high of boost to get full rack. If all that checks out I’m going to recheck timing. 

[fjh]

26 minutes ago, Anonymous said:

I did check the afc for by sucking and blowing into it. I’m going to pull it off and check it out and make sure that it’s working properly. And not set for too high of boost to get full rack. If all that checks out I’m going to recheck timing. 

Does it have the torque limit valve in the mix ! Minted to the rear of the engine or on the fire wall if so by pass it!

[Anonymous]

30 minutes ago, fjh said:

Does it have the torque limit valve in the mix ! Minted to the rear of the engine or on the fire wall if so by pass it!

No mine doesn’t have that. 

[fjh]

56 minutes ago, Anonymous said:

No mine doesn’t have that. 

K

[Anonymous]

Found this today hoping it’s going to fix it  

[fjh]

Yup kinda wondered ! how ever seen em alot worse !  May have to get from  a fuel shop someone who dabbles in cummins 5.9 ! Good luck getting that thru Mack!

Also did you pull the whole houseing? you might try spinning back the star wheel behind that a turn or two this will allow the boost to overcome it a tad faster and tweek the screw under the small cap a turn that moves the  fuel start point in which the boost begins! It will smoke some a tad of gray is good !  

[Anonymous]

I pulled the housing off. It moved freely with shop air but I just felt like something was still wrong so I pulled it all the way down. There’s actually two cuts in it. I think I can find one at my dads. I’ll let y’all know how it goes once I get it sorted. 

[Anonymous]

Got the afc rubber replaced, shimmed the fuel return spring, slid the fuel plate just a smidge (its maybe at the half way point, drained the fuel tank and found a washer in the tank, replaced fuel line from tank to filter housing and found that the air compressor intake line had a small leak and replaced it also. Now we have 30psi fuel pressure and no boost leaks. Moved my excavator this evening and the truck runs much better but still not where I believe it should be. Could only get maybe 20psi boost pulling a hill. Has no low end power. Will spool quickly if it at higher rpm tho. going to get a guy I know that is pretty good with the Bosch pumps to come look at it and make sure I'm not missing something or doing something wrong.  

[fjh]

When you had the load on were you trailing any smoke?

[Anonymous]

6 hours ago, fjh said:

When you had the load on were you trailing any smoke?

Not much. 

[fjh]

So try turning the screw in on the fac under the little cap that screw determines where the fuel starts coming on it! Turn it in half to one turn and try it! Max 20 pounds boost is off by at least 8  psi you should be making 28 to 30 !