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Go Back   Dodge Cummins Diesel Forum > 2nd Gen. Dodge Cummins 98.5-02 24V Forums > 98.5-02 Powertrain
98.5-02 Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission Ect..NO ADVERTISING .

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Old 07-06-2009, 03:03 PM   #1 (permalink)
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compression or blow by test

I'm trying to find out why my truck is a lack of power. Ive read on forums about blow by test and about compression test what one is more accurate to determine engine wear.
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Old 07-06-2009, 03:22 PM   #2 (permalink)
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Compression test...But low power problems are normally fuel related... But if the rings were bad you'd see alot of blow-by oil mist out of the crankcase vent...

Did you check for error codes?

What's you fuel pressure like?
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Old 07-07-2009, 11:55 PM   #3 (permalink)
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I dont now how to test fuel pressure but just put vp44 on 2 months ago. is it hard and exspensive to check fuel pressure or not important
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Old 07-08-2009, 12:04 AM   #4 (permalink)
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Quote:
Originally Posted by 1999mudder View Post
I dont now how to test fuel pressure but just put vp44 on 2 months ago. is it hard and exspensive to check fuel pressure or not important
Fuel ressure is critcal function to power and lifespan of the VP44... As for checking you need a gauge in the cab and check the pressure under load...

Gauges

Here is the fuel pressure specs...
Lift Pump Diagnostics
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Old 07-08-2009, 12:15 AM   #5 (permalink)
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Sorry thought you were talking about injector preesure when I did the vp44 I put new lift pump and low fuel pressure light. the light never comes on even under load.
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Old 07-08-2009, 12:20 AM   #6 (permalink)
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Fuel pressure is VERY important on these engines. Your VP44 gets ALL of its cooling and lubrication from the fuel provided by the lift pump. If the lift pump isn't giving you 10-20 psi at all times, your VP44 will soon fail. A failing lift pump could cause your lack of power, and might explain why your last VP44 went out.

You can test fuel pressure with an external test gauge, but your best bet is to get a fuel pressure gauge installed on your truck. You can get a Glowshift electric FP gauge for about $60, and a single gauge column mount for about $30-35. I'll post a picture of this setup below.

If you do find that your lift pump is out, you should really consider an upgrade. The stock replacements are barely adequate at best. An Airdog or FASS system would be a much better choice. Much better fuel flow and filtration with a lifetime warranty.


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Old 07-08-2009, 12:34 AM   #7 (permalink)
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I would hesitate to point the finger at the engine compression. Not likely. If the engine doesn't make adequate compression, it will have a tough time starting. Once running it should make power even if the rings are worn. If you have a bad valve, the engine will have a "miss" and cracking injector lines will determine which one it is.

But most likely it's either an air delivery issue, or fuel delivery issue. I'd check all the turbo boots, feel around the exhaust manifold for leaks, and if you haven't, scan for codes. Can't hurt to check fluid levels and conditions, either, especially the transmission.

If you have a boost leak, or preturbo exhaust leak, the boost sensor will prevent fueling, making your rig anemic until it revs up. Otherwise, +1 to above responses.
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Old 07-08-2009, 12:36 AM   #8 (permalink)
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Sorry Mike, I guess that I need to type faster. Your response wasn't up when I started typing that last one.
Quote:
Sorry thought you were talking about injector preesure when I did the vp44 I put new lift pump and low fuel pressure light. the light never comes on even under load.
Was the lift pump a factory one or an aftermarket? I believe that the warning lights don't come on until the fuel pressure drops below 5 Psi, much lower than you want it.
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Old 07-08-2009, 01:00 AM   #9 (permalink)
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Quote:
Originally Posted by Mopar1973Man View Post
Compression test...But low power problems are normally fuel related... But if the rings were bad you'd see alot of blow-by oil mist out of the crankcase vent...

Did you check for error codes?

What's you fuel pressure like?

Is this where the puke bottle normal is? Ive extended the hose down further, and when my engine is running there is mist out of the bottom. Does this mean my rings are bad?
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Old 07-08-2009, 01:26 AM   #10 (permalink)
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[QUOTE=GuN_Sm0k3;1775209]Is this where the puke bottle normal is? Ive extended the hose down further, and when my engine is running there is mist out of the bottom. Does this mean my rings are bad?[/QUOTE

Mist and vapour are normal, as there is nothing stopping the air from being pushed out of the engine thats in the crankcase, lots of smoke and heavy mist is a different story, that would be compression gasses leaking past the rings. usually if its that bad there are other issues that go with it like hard starting and heavy oil consumption.
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Old 07-08-2009, 10:24 AM   #11 (permalink)
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Quote:
Originally Posted by BuffaloLake View Post
Sorry Mike, I guess that I need to type faster. Your response wasn't up when I started typing that last one.

Was the lift pump a factory one or an aftermarket? I believe that the warning lights don't come on until the fuel pressure drops below 5 Psi, much lower than you want it.
Correct I've also got a warning light too... It a Cummins pressure switch set at 3 PSI... So like if I didn't have a gauge I got be starting/idling at way below 10 PSI and droping to 4-5 PSI and still never trip the light...

Low pressure light are fine to grab your attenetion but the DO NOT replace a fuel pressure gauge by no means. The lowest pressure the VP44 can handle is 10 PSI...



So back to my orignal question what you fuel pressure like on the highway at WOT?

YouTube - Stable fuel pressure - AirDog 150

Testing you fuel pressure is that easy... Get up to 55 MPH put you foot to the floor and see what it drops to if the needle falls below 10 PSI your in trouble.
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