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Throttle lagging and hesitation

Old 04-04-2019, 10:12 PM
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Throttle lagging and hesitation

Today I had a weird hiccup . After driving from job to job a few hours I kinda noticed something wasnít right with the throttle. It was kinda like I was only getting maybe 60-70% of the actual throttle I was pressing , Gears all shifted fine but slower than normal pick up . Got to where I was going and few hours later it started up and was fine the rest of the day . After my last job , t started doing it again . I changed the fuel and air filter tonight . I have a electronic fuel pressure gauge and itís around 12-16 psi . Anything else I can look into if it continues ?
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Old 04-04-2019, 10:30 PM
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Any codes? Maybe you drove through some gum......
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Old 04-04-2019, 10:45 PM
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Originally Posted by SIXSLUG View Post
Any codes? Maybe you drove through some gum......
I donít have reader , if I have time tomorrow Iíll swing by my friends shop. I have the fass ddrp , can they get weak? Or they either work or donít ?
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Old 04-04-2019, 10:56 PM
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I’ll also add , when I was in my driveway, idling and I quickly pressed the throttle , it had a air gasp or something before the engine started to rev. Reminded me of when an accerator pump on a old carb was worn out . When the truck started running back to normal, that disappeared also .
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Old 04-05-2019, 11:34 PM
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I think I have it figured out . The previous owner wired my fuel pump and trailer power to a. 3 prong solenoid on the fire wall . When I had the key on I couldnít hear the fuel pump running , I gave the solenoid a wack and it turned on my fuel pump , the truck came back to normal power .
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Old 04-06-2019, 04:52 AM
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Change that solenoid as soon as possible- unless you like spending a lot of money on an injection pump!
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Old 04-06-2019, 08:23 AM
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Originally Posted by AlpineRAM View Post
Change that solenoid as soon as possible- unless you like spending a lot of money on an injection pump!
i bought one on the way home and will be installed this morning . Any idea why he woulda did it this way ?
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Old 04-06-2019, 10:52 AM
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Sounds like a backyard mechanic...I CAN DO IT MYSELF!!! Those crimps and zip ties are a dead giveaway and a good set up for a short or fire. Hopefully your vp wasn't sucking fuel for too long. I'm still on my original and ran about 2 weeks on a dying in tank pump before the FASS....FASS says 50,000 hours of run time is attainable, my truck has around 6200 on the hour meter so I should be good for a while......
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Old 04-07-2019, 02:01 AM
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The basic idea for the relay is not bad- but in stock form the ECM powers the pump directly, and can adjust the power to reduce pressure while cranking.
But if you use a bigger pump it can damage the ECM, so you power the bigger pump through a relay.
Trailer power and lift pump on one circuit... cool, kill the injection pump if you have a short in the trailer wiring.

So,as Sixslug said, sort that wiring, remedy the fire hazard.
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Old 04-07-2019, 01:53 PM
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I’ll get it sorted for sure . Changed the solenoid and the fass is buzzing on key power
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Old 04-07-2019, 03:37 PM
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Well, the ECM does supply power to the lift pump for some time when the key is switched to on- but during engine start it commands only 50% duty cycle (therefore much less pressure) from the fuel pump. One of the problems with aftermarket lift pumps is that you need to get it sorted that the VP44 was developed for only 0.4 l per cylinder and for cost reasons was adapted to .95 l per cylinder - so during engine start you need just enough fuel to make the engine run, any more is detrimental, and while running at power the 5.9 Cummins is a lot more than what the VP44 was planned for.
So you need a working lift pump while driving, but low pressure while starting. Those old fashioned solenoids do not cut it, get a solid state relais instead, it will give you the desired fuel pressure at engine start, and while running.
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Old 04-08-2019, 06:27 AM
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Wink Throttle lagging and hesitation

Hello All,
In looking at the picture you can note that the solenoid and the automatic re-settable circuit breaker are both mounted to the firewall with Robertson screwdriver type screws like the kind used in the travel / motor home industry.
This could explain why the Trailer brakes and Lift Pump are wired this way.
Both that type of solenoid, circuit breaker, and screws were commonly used in the recreational vehicle industry back in the day. Now a days there are better solid state choices available as noted by AlpineRAM.
Could have been done at a or by a person that worked in that field.
Any way
happy Mopar
Arron

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