Engine/Transmission (1998.5 - 2002) symptoms of a bad lift pump

[ESwartzer]

under hard tow on the grapevine in So Cal. Istarted hearing a small rapping sound under the hood. it since has also developed a light miss that keeps time with the noise. Fuel mileage is also down nearly twenty five percent since then. My question is does this sound like simptoms of a bad lift pump, or should I look elsewhere for the problem. DODGE has been of no help to me ; I drive a 98. 5 ISB

 

[KWIKKURT]

I would check all your Exhaust manifold bolts first. The Back one especially like to loosen up and fall out. Feel free to call me for more help. Kurt Yardley 505-534-0434

 

[JyRO]

As strange as this may sound...

Eswartzer - you may have a couple things going on. I'm going to leave the LP out of this to start with. The small rapping sound under the hood sounds earily similar to something I have had, as well as a handfull of others.



Mine happened while pulling a steep grade in the meat of the powerband in 4th pulling my 9,500 lb. 5'er. Mine sounded like a light thump, thump,thump,thump,thump. It sounded just like a tire going flat slowly. But I couldn't feel any shake in the body or pedals or steering wheel. And it went away immediately upon releasing the throttle. It came back on the same grade when I picked back up the throttle. It only happened at hard loading and in 4th gear.



Turns out in my case (and the handfull of others) that the noise is coming from cavitation in the coolant system. If I remember correctly, the water pump is cavitating. But this is easily remedied by a cheap change of thermostat (which I assume changes the head loss of the coolant system). It is a certain thermostat from D/C. I don't know the p/n off hand. Others do. If this sounds like your problem (with the noise), I'd post a question asking about that p/n. I was skeptical that this was the problem. But, other guys who pull more regularly than me say they've changed the problem and it cleared it right up. Like I said, mine did sound like a thump, and I can image a hose full of coolant (possibly being thrown around), could make this sound if the water pump was cavitating.



Otherwise, if its a bad LP, check out the topic I started, "Its got to be the LP," and other LP topics. Plenty of info here to help you diagnose the LP, if that's what the problem is.



Good Luck!



- JyRO

 

[ESwartzer]

Thanks for your reply JyRO I, will look into the water pump scenario but I;m pretty sure that water pump cavitation would not reduce fuel mileage by twenty five percent. The sound that I,m experiencing is more like a bad lifter, not a whumping sound. Ive had a blowby test done on it and there is virtually no leakage. Another shop I took it to said it sounded like a bad injector, so I replaced stock injectors with bosch 275,s. The engine pulls better and somewhat smoother, but the noise remains, and fuel mileage is still lousy. Also the miss feels like a missfiring spark plug in a gas rig. It is more noticeable under any load ,than when unloaded. So again I will ask,would someone give me a list of symptoms for a bad lift pump,also symptoms for a bad injection pump. Im open to any kind of help or advice you can give me: Im located in Tracy Ca. in the central valley.

 

[Lsfarm]

Symptoms

ESwartzer, usually you will get a stumble or miss in the whole engine if it is starving for fuel. A knocking noise with a miss sounds more like an injection pump if it isn't the injectors themselves.



With the history of lift pumps, I would get a fuel pressure guage on that truck as soon as possible! You should see around 12-15PSI at idle, and no less than 8 psi at wide open throttle.



Some engines don't show ANY symptoms with a dead lift pump, so there is no hard and fast answer to your question.



Briar at BlackMountain diesel sells a test fuel pressure guage, or install a perminant one so you can always keep an eye on the health of the lift pump.



Greg L. The Noise Nazi

 

[Ron Bissett]

If you want help , help the helpers with information on your truck you state 98. 5ISB any transmission ? mods? exhaust brake , or other stuff Use the button and add signature to your post. Ron in Louisville KY. Oo. Oo. Oo.