8VBB V8 Injection pump:

[Rob]

I'm thinking I have a bad transfer pump again on the R795. This thing runs very well but at times while idling, it just shuts off. The primary fuel filter is full, the secondary is dry, or very low. If the secondary filter is filled the truck starts and stumbles till fuel delivery stabilizes then runs well again. All the rubber fuel lines are new as are the filters. Usually this truck starts right up and is smooth running and ready to go.

Tonight after filling the secondary filter for the second time due to engine starve out, I noticed after starting the engine no return fuel flow to the tank. After the engine was running about 30 seconds, I noticed the return start and run full stream about 20 seconds then stop again. About a minute later, the engine starved out again. This is at idle speed with me standing beside the truck. Once again I filled the secondary filter, started the engine and after a couple minutes, it smoothed out again, and this is where I'm at now. While I had it running I removed the return line to tank and no fuel flow there. I then held the rpm at 1500 for about 15 seconds and it never did flow any fuel.

I'm thinking the transfer pump hasn't enough suction to pull the full all the way from the tank without great effort. I'm wanting to get this pump and nozzles into the fuel shop anyway for recalibration to get away from the "Maxidyne" tuning. I am going to install the Mack 10 speed into this truck.

Any thoughts or ideas?

Rob

[ducky698]

Hi, dont you love those fuel issues try ddealing with it 500miles from hom with 2 trailers on.

on the correct drivers side of the pump at the back there is a valve that has a spring and a needle in it, there about 800bucks from mack, pop this out and give it a clean. its the fuel pressure reg, mine was rusty and causing it problems, its next to the rack at the back with allen key hole in center. drop the hole thing out.

the little valves in the transfer pump are easy to change to, there only like 5 bucks each, those valves are in the top when you pop the fittings out the pump.

Grant

[Rob]

Hi Grant, glad to see you post again with us. I have to start my reply but before thanking you for your advice I must correct you as to the "proper" driver's side as we both know it is on the left as you sit in the driver's seat. Now with that correction in place: It is supposed to be nice tomorrow and I will check into what you mention.

You ever gonna get back up to the Naperville area?

Thanks,

Rob

[ducky698]

Hi, no sorry, your wrong, no wonder you have so many accidents over there, the steering wheel is on the wrong side of the car! remember thsat saying from a famous film???

I had a look at my pump today, it has an allen head center and 2 slits on outer for a fairly wide mack tool. you should be able to get the whole thing out with out a problem.

I will be back in Naperville as soon as I can, next time I am over there I wont be coming back here.

Grant

[theakerstwo]

Rob i would before i did any thing make you a tee to go in line of the supply line frome filter to injection pump and connect a 50 psi gauge to it. I have one i built almost 46 years ago and you have to have one to trouble shoot a mack fuel system. connect to a gauge and long hose and tie it to wiper arm and test prssure at full load. My tee was a # 6 swivel brased to a male brss # 6 fitting and a # 4 taped into the side for the hose.Sounds to me your sucking air. And you need a clear plactic line to go inline to or after trhe transfere pump to check for bubbles.The checking of fuel pressure will show you a few things but if you dont have enough pressure setting in the shop running then with visegrips pinch the return line to the tank and if the pressure comes up the the fuel over flow or regulator valve is not holding the pressure up. But if the pressure does not come up after pinching the return then look for air or a restriction like a flapper in the hose. If non found then work on the transfere pump.

[theakerstwo]

Your on the right track about getting away from the maxidyn tuning .It is a mess to drive a maxidyne with a 10 speed.

[Rob]

Hi, no sorry, your wrong, no wonder you have so many accidents over there, the steering wheel is on the wrong side of the car! remember thsat saying from a famous film???

I had a look at my pump today, it has an allen head center and 2 slits on outer for a fairly wide mack tool. you should be able to get the whole thing out with out a problem.

I will be back in Naperville as soon as I can, next time I am over there I wont be coming back here.

Grant

HI Grant, most guys can learn under classroom environment, but you have to move across the world to learn the proper side of the road to drive on???? And then you want to move to the seemingly "traffic collision capitol" of Illinois???? Sometimes I think you "aussies" are as thick as me.

I was in Naperville last week and on rt. 59 there was two traffic accidents both involving tractor trailers, and cars. The light at Aurora Rd. had a new Freightliner with a Chevrolet Equinox flipped over, and the next light at 104th street had a Lexus hit by an International. You know how busy traffic is a 8:30am in that area and it took nearly 45 minutes to get past.

Be sure to call when you get over here.

Rob

[Rob]

Rob i would before i did any thing make you a tee to go in line of the supply line frome filter to injection pump and connect a 50 psi gauge to it. I have one i built almost 46 years ago and you have to have one to trouble shoot a mack fuel system. connect to a gauge and long hose and tie it to wiper arm and test prssure at full load. My tee was a # 6 swivel brased to a male brss # 6 fitting and a # 4 taped into the side for the hose.Sounds to me your sucking air. And you need a clear plactic line to go inline to or after trhe transfere pump to check for bubbles.The checking of fuel pressure will show you a few things but if you dont have enough pressure setting in the shop running then with visegrips pinch the return line to the tank and if the pressure comes up the the fuel over flow or regulator valve is not holding the pressure up. But if the pressure does not come up after pinching the return then look for air or a restriction like a flapper in the hose. If non found then work on the transfere pump.

Thanks Glenn and I certainly agree with you. I have replaced all the rubbing supply lines on this truck chasing this problem for months and it's getting old. The middle of last week I hooked up to my drop deck with a couple thousand pounds on it and pulled it around my shop property. The truck did not miss a beat and pulled well. With the exception of being really soft ground not allowing a good shifting scenario all went well. After about a 1/2 hour or this, I parked on level ground to drop the trailer. While pulling the gladhands, the damned truck stalls and dies. This after several full throttle acceleration runs!! Talk about frustrating. I have plenty of fitting and #6 hose so I'll grab a gauge later today and get it plumbed in. I have a brand new pump, (not rebuilt) on my shelf calibrated for the ENDT866B setting +20% uprate but don't want to use it till I know this engine is sound.

To be clear you want me to "Tee" into the discharge of the transfer pump before the inlet to the secondary fuel filter, with the gauge, and use a clear plastic tube on the suction side of the transfer pump?

Rob

[Rob]

Just got all three flaps to my chin(s) washed up and freshly deodorized so I'm off to the shop to build the test gauge.

More later......

Rob

[Rob]

Glenn:

Thanks for the guidance. You were correct in the fuel system was sucking air. When I ran new fuel line along the inside of the fuel rail on the rt. side, (incorrect driver's side) I did not notice the rubber insulator on the "Adel" clamp deteriorated. It was no longer present and the clamp band actually rubbed a small hole into the fuel suction line. I actually found it by removing both ends , (tank, and primary filter housing) and applying 35psi air pressure while soaping the line. The bubbles went crazy! I just put new ends onto a new hose section and replaced everything including a new "Adel" clamp and all is fine. The fuel return to tank is now a strong stream like after fifteen beers.

Thanks again to everybody for the help.

Rob

[ducky698]

Hi, fixed it, great. now you can work out how to pop that steeing wheel on the proper side

yes the traffic there is busy that time in the morning. My coupe broke down there on the corner of 59th an 104th if I have them correct, just near the auto shop, it was peak hour 5pm ish, bonnet up un the middle of the road, not good.

Grant

[theakerstwo]

Thanks Glenn and I certainly agree with you. I have replaced all the rubbing supply lines on this truck chasing this problem for months and it's getting old. The middle of last week I hooked up to my drop deck with a couple thousand pounds on it and pulled it around my shop property. The truck did not miss a beat and pulled well. With the exception of being really soft ground not allowing a good shifting scenario all went well. After about a 1/2 hour or this, I parked on level ground to drop the trailer. While pulling the gladhands, the damned truck stalls and dies. This after several full throttle acceleration runs!! Talk about frustrating. I have plenty of fitting and #6 hose so I'll grab a gauge later today and get it plumbed in. I have a brand new pump, (not rebuilt) on my shelf calibrated for the ENDT866B setting +20% uprate but don't want to use it till I know this engine is sound.

To be clear you want me to "Tee" into the discharge of the transfer pump before the inlet to the secondary fuel filter, with the gauge, and use a clear plastic tube on the suction side of the transfer pump?

Rob

make you a tee from a swivel and put it inline of the supply line to the injection pump after the sec filter that was it will fee what presssure the galley of the injection pump sees.This will check for flow pass the two filters and supply pump. If the pressure ant there then the flow want be as well.Lowflow will be from air,a restriction, stopped filter and also bad supply pump. this is done also when the pressure there is not enough and use the visegrips on the return line and this will test your supply pump if the pressure is low in the begining. The supply pump when the return is pinched of can run up to 70 psi.But the regulator or over flow valve is set to maybe 32 psi for the galley pressure. A plactic line clamped to a couple of # 6 swivels works good inline to and after the supply pump to see if there is bubbles and were from. Also when you have a miss on mack engine it can be from a broken deleiver valve in the bonnets inside of the injection pump. This can let a injector line bleed down between strokes and is found with a loosing of the injector line with air bubbles in the return line to the tank be cause the injector does not 100 % check all compression from the cylinder from reintering the injection pump. glenn

[theakerstwo]

Rob

Glad you found it. I had a hose to break with me last week on the job. Load of agbase and going down in a hole were a new build is to be and two you spanich speack kids give me a tour thru the mud and then a hard left turn as my steer bogs down. They were told to make the drivers hurry and as is was trying to turn a power steering hose broke. #15 tires on front and loaded you ant going to turn in the mud. Thye was in a faint mode. then thejust routed the other trucks around thru another gate. Yes was wandering why i was routed thru the mud any way my sons job 20 sent a guy down and with only 1 hr of down time was back with it.