CAT 3126 rough idles then dies

[jcross]

I have a 1998 Freightliner FL70 with a 3126 in it. The truck has ran great until recently. This problem has been intermittent......someitmes it starts right up then other times it will take a second (acts like it has air in it) rough idle then die. The only way it will start again is if I take the seconday filter off and fill it full of fuel (there is no primer pump on it).

I've recently replaced the fuel tanks, new suction side fuel lines, changed the oil, new fuel filters. I also replaced the fuel pump solenoid. It will run great one day then do this the next.

I cannot find a fitting that will fit into the port by the secondary fuel filter to take a pressure reading on the fuel pump.

Ideas or suggestions......my CAT certified guy is a ways away and I'm trying to avoid having it towed. I can change parts or take stabs at it here at home. My gut tells me the fuel pump but could it be some sort of sensor or HEUI pump?

Suggestions...?

 

[davekc]

Could be a injector or speed sensor. That engine has two of them (speed sensors). Either one could give you those symptoms if you have ruled out the fuel pump.

 

[jcross]

I've replaced both sensors (timing and speed) under the HEUI pump. Cranked it over, ran great, high idled for about 30 minutes.

The next morning, cranked it over ran about 30 seconds and died. Acts like it runs out fuel and when I check the secondary filter it is almost empty.

By the way, when I crank it my oil pressure gauge does move to where it normally does.

No codes of any sort on the dash.

Thanks,

 

[fortwayne]

Had roughly the same thing. If you r loosing power replace the injectors and caps. Its better and more cost efficient to just do them all at one time. Also what r your amps/voltage looking like.

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[davekc]

Based on the extra info, it sounds like the fuel pump, or the pump sensor. A bad pump won't throw a code. A bad sensor usually will.
If the filter is empty, the problem is ahead of the injectors.

 

[BillChaffey]

This short story may or may not be any help.
Last winter my John Deere back hoe would run fine then sputter and die. Wait an hour or more and run fine for awhile and sputter & quit again. Highway department mechanic Say's "your not getting the fuel, probably the Injector pump" Two other Diesel mechanics come by say it's a short or the injector pump. Salvaged pump 30 days warranty $550.00 mechanics $500.00. Problem never goes away. I break the line from the fuel tank. No diesel flowing to the fuel pump (it's gravity feed) blow in the line no obstruction to as far as going in. Finally pull the pet**** from the tank. A piece of plastic about the size on my little finger nail was in the pet****. When the fuel pump engaged it sucked it into the pet****. When the engine stopped it would float back up in the diesel.
Check the most obvious first, not last.

 

[bluejaybee]

Hey jcross,

don't go away without telling us what your problem was. That's like telling a joke up to the punch line, then walking off. We're a curious bunch. We have to know!

 

[Deville]

I'd like to know to. Please reply!

 

[jcross]

I had to be away for a few days (boat races) and will get back to troubleshooting tomorrow (Tuesday).

But, I did rig me a pressure gauge by the secondary fuel filter and the reading was 0. I'm going to double check that tomorrow when I have time. I will change out the primary filter and blow the lines out and see what it reads, then go from there.

 

[rfields200]

I had to be away for a few days (boat races) and will get back to troubleshooting tomorrow (Tuesday).

But, I did rig me a pressure gauge by the secondary fuel filter and the reading was 0. I'm going to double check that tomorrow when I have time. I will change out the primary filter and blow the lines out and see what it reads, then go from there.

I believe you will find that your problem is a cracked injector O-Ring. The engine is losing it's prime when you shut it off. It will gradually get worse to where you will be on a hook. I had this problem on a 3116 Cat. I was towed several times before Cat figured out what the problem was. A friend of mine with a 3126 just recently had the same problem as you. He went through all the things trying to fix it like you did. Finally he took it to a shop and they found it was a bad injector O-Ring and the fuel system was sucking air. Running great now.

 

[Bruno]

I've replaced both sensors (timing and speed) under the HEUI pump. Cranked it over, ran great, high idled for about 30 minutes.

The next morning, cranked it over ran about 30 seconds and died. Acts like it runs out fuel and when I check the secondary filter it is almost empty.

By the way, when I crank it my oil pressure gauge does move to where it normally does.

No codes of any sort on the dash.

Thanks,

We had a truck that did the same thing, Check your oil to see if your not low on oil.

 

[Bruno]

I've replaced both sensors (timing and speed) under the HEUI pump. Cranked it over, ran great, high idled for about 30 minutes.

The next morning, cranked it over ran about 30 seconds and died. Acts like it runs out fuel and when I check the secondary filter it is almost empty.

By the way, when I crank it my oil pressure gauge does move to where it normally does.

No codes of any sort on the dash.

Thanks,

We had a truck that did the same thing, Check your oil to see if your not low on oil.

 

[paullud]

We had a truck that did the same thing, Check your oil to see if your not low on oil.

Well that depends on the kind of luck he has. If he has my kind of luck checking the oil would only ensure it is a $3k problem elsewhere, but if he starts replacing things first he will spend $1500 then realize it was just low oil, that way you still get that life just stuck it to me feeling.

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