Slow Startin 350 Mack

[odiie]

My new pride and joy starts right away but only fires a few times then it cranks for quite a while. Where is the most likely place that I'm losing my prime. I assume thats what is happening. No obvious outside leaks. How do I diagnose this? Any help appreciated.

[Rob]

My new pride and joy starts right away but only fires a few times then it cranks for quite a while. Where is the most likely place that I'm losing my prime. I assume thats what is happening. No obvious outside leaks. How do I diagnose this? Any help appreciated.

First thing I would do is remove the fuel line that is from the tank to the inlet of the filter housing. Replace this with a temporary line into a supply of diesel fuel from a can on the floor. Get the engine started and running smooth, then shut it off. Let it set the amount of time that you had trouble with prime loss and see if your temp line solves the problem. If it does, replace your suction line. If it does not and you have an inline check valve, ensure it is good, or replace it for good measure.

If it is losing prime, it is most likely due to air getting into the system from a pinhole in a line, or a drainback from some type of check whether it be a valve, the transfer pump valves, or whatever else is in the low pressure side of the system. Chances are with the engine starting right off, running a short while then dying out, it is starting on the fuel gallery storage within the pump. It runs until this supply is exhausted. The transfer pump overpowers the drainback leakage to the line and eventually refills the pump gallery and the engine restarts as you grind on the starter. This assumption is that your primary, and secondary fuel filters are physically mounted lower than the injection pump, otherwise you would drain your filters down and need to refill them to restart the engine.

I have also seen plunger barrels so worn out the truck would be difficult to start, idle fine, but have limited power when asked to deliver fuel.

I'm assuming your truck runs well once started.

Rob

[odiie]

Thanks Rob, yes it does run fine once started. I'll try the temp line.

First thing I would do is remove the fuel line that is from the tank to the inlet of the filter housing. Replace this with a temporary line into a supply of diesel fuel from a can on the floor. Get the engine started and running smooth, then shut it off. Let it set the amount of time that you had trouble with prime loss and see if your temp line solves the problem. If it does, replace your suction line. If it does not and you have an inline check valve, ensure it is good, or replace it for good measure.

If it is losing prime, it is most likely due to air getting into the system from a pinhole in a line, or a drainback from some type of check whether it be a valve, the transfer pump valves, or whatever else is in the low pressure side of the system. Chances are with the engine starting right off, running a short while then dying out, it is starting on the fuel gallery storage within the pump. It runs until this supply is exhausted. The transfer pump overpowers the drainback leakage to the line and eventually refills the pump gallery and the engine restarts as you grind on the starter. This assumption is that your primary, and secondary fuel filters are physically mounted lower than the injection pump, otherwise you would drain your filters down and need to refill them to restart the engine.

I have also seen plunger barrels so worn out the truck would be difficult to start, idle fine, but have limited power when asked to deliver fuel.

I'm assuming your truck runs well once started.

Rob

[jzack]

Funny thing, I'm having almost the same problem with my 94 E-7 350 right now. Every morning my truck needs to be re-primed. Called the local Mack service manager and he said probably take 2-3hrs to diagnos....ouch @ $108 per hour. So before I bring it in to let a mechanic hook up a pressure guage and eat a sandwich while he watches for the needle to drop (at least thats what I picture him doing) thought I'd try for advice from the Mack savvy folks here on the forum.

Here are some clues-

1) Gradual Worsening: this problem would pop up once a month, then once a week, now every morning.

2) Manuel priming has limited results: first 2-3 pumps are air, then I can feel the fuel in the plunger, but I can never get it to feel rock hard no matter how long I pump it (I know that sounds bad). I've run this truck out of fuel before when I was younger and dumber and I remember it popping right off after pumping the primer until it hardened up. Now it can take 10 seconds of cranking to start even after the manuel priming.

3) No Visual Leaks: similar to the earlier fellows problem, I don't notice an outside leak or smell any fuel in the garage.

If anyone with knowledge and/or experience with the electronic Bosch V-mac I system, and recalls a common problem or two that fits the above symptons, I would greatly appreciate the advice.

Thanks, Jeff

[Rob]

The hand primer pump that you mention is the actual pump that "lifts" fuel from the storage tank. When you operate the "hand primer" you are actually actuating the valve mechanically and bypassing the internal lobe on the camshaft the actuates these same valves. If you look at a schematic of the pump, it is clear how it works and the valves and seats internal to this pump do fail. When they do get weak the symptoms are as you describe. A rebuild kit for the type on an E6 engine is only about $40.00 and well worth the expenditure as part of a yearly service. Like differential, or transmission fluid in your car, it is seldom thought of for maintenance but I've rebuilt probably a dozen of those little pumps, (takes all of 15 minutes) and it has cured problems as you mention, along with low fuel delivery, (such as plugged fuel filters).

On the older engines, these are the only check type valves in the low pressure side of the fuel system.

Rob

[jzack]

Thanks much Rob. You may have just saved me a good chunk of change. I'll ask my dealer about a rebuild kit for my E-7.

[jzack]

Well I've replaced the hand-pump and it still leaks down. Then I noticed when I prime with the hand pump I can hear fuel splashing back into the fuel tank. So I replaced the check-valve in the return line, but I am still getting leak down over a weekend. So Rob, now I'm thinking the next step would be the supply pump which I believe is what you were referring to in your last post, correct? If so, my dealer here told me there isn't a rebuild kit for my E-7 and a new one is about $200-300. Oh well....

Thanks, Jeff

[HK Trucking]

Well I've replaced the hand-pump and it still leaks down. Then I noticed when I prime with the hand pump I can hear fuel splashing back into the fuel tank.

That's normal. When you operate the hand pump, you are pumping fuel from the tank, thru the filters, then thru the inj. pump, and then thru the return line back to the tank.

That splashing noise you're hearing in the tank is the fuel pouring from the return line into the tank.

So I replaced the check-valve in the return line, but I am still getting leak down over a weekend. So Rob, now I'm thinking the next step would be the supply pump which I believe is what you were referring to in your last post, correct? If so, my dealer here told me there isn't a rebuild kit for my E-7 and a new one is about $200-300. Oh well....

Thanks, Jeff

Check all the lines on the suction side of the system for chafed or rubbed thru spots or loose connections. Also check that the primary filter is tight.

Air is getting in somewhere and causing the fuel to drain back while shut off.

_____________________________________

(From your previous post)

1) Gradual Worsening: this problem would pop up once a month, then once a week, now every morning.

That suggests to me that there is a suction line which is getting a progressively more severe leak, such as a rubbed thru spot. Sooner or later the leak will get to the point where the pump won't pick up any fuel, and it will just suck in air. At that point the engine will not run at all.

[jzack]

Thanks for your input HK. I'll check all my lines and filters to make sure they are tight this afternoon. The reason I've been focused on internal parts (check valve, seals) is because I've yet to see any wetness on lines or fittings. I figured if air is getting in that fuel would make its way out, but this is just my backyard mechanic logic. I've never worked on trucks for a living.

Curiously, after replacing the plunger and check valve the problem did get better. Back to happening once a week rather than every day. So after replacing a part I would think its fixed until the next Monday morning rolls around and no fuel....argghhh!! I'm starting to think I should have just taken it to Mack in the first place rather than trouble shoot it on my own.....we'll see.

Jeff

[theakerstwo]

Remenber this about any fuel system and that is when it is not running any fuel line or filter or fitting that is above the fuel tank level that cane leak in air will let the system loose its prime. The fuel will run down to it own level due to the weight of it. So a rusted filter can can do this or some of the old fuel lines can do it. Look for a stained or oil looking spot on any of the lines. Some times you will have to make a sight glass or hose out of clear plactic line and put in the system along the way eleminating some of the stem to find the air sucting into the sytem.On the making of a clear line for test reasons make sure yo have no l;eks in it or you will be like a dod who chases his tail all day and never can find it.I have seen that happen.

[David]

I should have just taken it to Mack in the first place rather than trouble shoot it on my own.....we'll see.

Jeff

Why pay $100 per hour for someone to keep changing parts until they finally find the problem. You would end up with a $1000 bill for a $30 part and someone else education.

[David]

There may be a check valve at the transfer pump. It's on the end of the hose from the primary filter. You can remove it, stand it up, put a spoon full of fuel in it, and see if it drains down.

[Gambi80]

Funny thing, I'm having almost the same problem with my 94 E-7 350 right now. Every morning my truck needs to be re-primed. Called the local Mack service manager and he said probably take 2-3hrs to diagnos....ouch @ $108 per hour. So before I bring it in to let a mechanic hook up a pressure guage and eat a sandwich while he watches for the needle to drop (at least thats what I picture him doing) thought I'd try for advice from the Mack savvy folks here on the forum.

Here are some clues-

1) Gradual Worsening: this problem would pop up once a month, then once a week, now every morning.

2) Manuel priming has limited results: first 2-3 pumps are air, then I can feel the fuel in the plunger, but I can never get it to feel rock hard no matter how long I pump it (I know that sounds bad). I've run this truck out of fuel before when I was younger and dumber and I remember it popping right off after pumping the primer until it hardened up. Now it can take 10 seconds of cranking to start even after the manuel priming.

3) No Visual Leaks: similar to the earlier fellows problem, I don't notice an outside leak or smell any fuel in the garage.

If anyone with knowledge and/or experience with the electronic Bosch V-mac I system, and recalls a common problem or two that fits the above symptons, I would greatly appreciate the advice.

Thanks, Jeff

I'm having the same problem w/my truck too...97 w/the electronic Bosch pump. It'll crank for 10 seconds then spit and sputter for another 15 seconds then take off. Before you'd have to just BARELY touch the starter and it's goin.

[fjh]

I'm having the same problem w/my truck too...97 w/the electronic Bosch pump. It'll crank for 10 seconds then spit and sputter for another 15 seconds then take off. Before you'd have to just BARELY touch the starter and it's goin.

IF any of you guys are running a primary filter with a plastic bowl or a drain on it by pass that filter temporarly and try again over nite!

I have seen many of these racor type filters cause problems and As Rob mentioned by pass everything on the suction side of the fuel pump to a pail of fuel sitting higher than

the pump and see what happens.

[Gambi80]

IF any of you guys are running a primary filter with a plastic bowl or a drain on it by pass that filter temporarly and try again over nite!

I have seen many of these racor type filters cause problems and As Rob mentioned by pass everything on the suction side of the fuel pump to a pail of fuel sitting higher than

the pump and see what happens.

I don't have any of that. Just like the other guy mentioned. I've tried pumping the primer and I'll get maybe 3 pumps of fuel, then 10 or so of air, then fuel and I'll pump it for a while and it still sputters. I don't get the 1000 rpm smoke show off the get-go that I used to either.

[Rob]

On those manual pumps don't pump like there is no tomorrow. Slow, steady, and deliberate strokes is what it takes to fill the cavities. I've seem people really go to town and what they are doing is "cavitating" the fuel due to the air in the line and this defeats the purpose you are trying to attain.

Rob

[jzack]

Well, I THINK I found my leak. I'll know for sure next time I let it sit for over 24hrs.

I pressure washed the motor the other day to start out fresh and the next day I noticed a tiny bit of wetness around a fitting at the front of the head behind the waterpump (tough bugger to spot). It was the 3/16" fuel return line from the injectors back to the pump. The line looked to be all dry-rotted and practically desintegrated when I removed it. Went to Mack and got a new line and clamps and all was dry today. Fingers are crossed............

[fjh]

Well, I THINK I found my leak. I'll know for sure next time I let it sit for over 24hrs.

I pressure washed the motor the other day to start out fresh and the next day I noticed a tiny bit of wetness around a fitting at the front of the head behind the waterpump (tough bugger to spot). It was the 3/16" fuel return line from the injectors back to the pump. The line looked to be all dry-rotted and practically desintegrated when I removed it. Went to Mack and got a new line and clamps and all was dry today. Fingers are crossed............

Let us know the out come!

[Rob]

Yes let us know how you fare but it seems that leak would have to much more than just seepage to slow your startability. That return is used to cool the injectors during operation by returning heated fuel to the tank. If the line bleeds off due to a leak, this "airspace" that is left in the line would need to be refilled by pressurized fuel from the injection pump via spill port operation of the injectors. This could take a little amount of time during engine cranking because as you know a liquid cannot be compressed, but air can be. Until liquid fuel purges the air from the lines, injection into the engine cannot take place as liquid fuel lifts the pintle, or needle from it's seat within the fuel injector allowing fuel spray into the combustion chamber.

Rob

[jzack]

Well she fired right up Sunday night so I'm fairly certain the new return line was the fix.

Thanks to all who contributed, it was greatly appreciated.

Jeff