Strange Idle

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I've been noticing my truck's been idling strangely for about the past two days.
When i slow down coming to a stop light in gear, I'll engage the clutch before lugging, and the idle kicks up a little, i'll take it outta gear and it'll still be idling a little high... (my tach isnt acurate at idle, so i'll give ballpark estimates) around 900-1000 rpm, after a few seconds it'll slowly drop to 600-800 rpm(can't tell cuz the needle wont stay still) after this drop in revs, it begins pulsing about every other second... almost like it's miss-ing...
any ideas???????

joe

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1990 w-250 4x4 cummins 5. 9,NV4500,tweaked injection pump, 16cm2 housing, 3"
JRE exhaust, 4. 10 gears

 

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I am not an expert on the injection system yet, but I'd check to see if something isn't sticking in the pump maybe. Like that little pin that comes out and rides against the diaphram shaft? I don't know if that would cause this, but it's worth a shot! Maybe something in there needs a little gunk cleaned off it or a little lube.

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Mine: '93 250 LE 4x4 5spd 4:10 Pwr win/loc/mir,cruise,dual 5" chrome stacks,12cm2 turbo,pyro/boost,diamond plate tool box, CB, 16x10" AR rims, 285/75/16 Bf goodrich, US Gear E-Brake,Fuller Roadranger shifter, PW injectors, K&N. "wirenut_21529" on Yahoo Messenger
Moms:'96 Ford B-Series school bus (5. 9 Cummins!)I'm gonna Bomb it!
Dads:'94 GMC 2500 6. 5L Turbo
pictures.

 

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I had the same problem about a month ago and I checked every thing. A guy told me to just change the T. P. S.

 

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TPS???
throttle position sensor?

 

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Do NOT waste $$ on a TPS, unlike an EFI car, the TPS has nothing to do with the engine! It only gives info to the computer for the shift into O/D. I know there are problems in our VE pumps regarding a pin and there is a recall for it. Be sure there are no problems in the throttle linkage and there are no fuel delivery problems. What I would do next time it acts bad is to pull over and remove the fuel filter, if it's not filled to the top and or has bubbles/ foam in it, there is a bad transfer pump or porus suction lines.

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'92 W250,3. 54,auto,reg cab, raven hi top cap, tach,boost,transtemp,pyro. 16cm housing.

 

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Joe,
Sounds like the Fuel Injection Lift Pump may be going out. This is a small pump located on the lower left rear side of the engine, between the fuel tank and the fuel injection pump and it acts to supply fuel to the injection pump under constant pressure. Without the constant pressure, you get fuel starvation problems. It may very well be that at higher RPM, the lift pump is still able to supply the required pressure, but at lower RPM (idle), it starts to show failure.
I had mine replaced a few months back by Cummins here in Albuquerque. I think they charged $65 for the part + install, which you certainly can do yourself.
Just a thought.
Hope this helps,
Steffan Marley

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'93 W250 CC, 4X4, 3. 54 Gearing, NV4500 5sp,
16cm2 Turbo Housing, Pacbrake, Amsoil Bumper
To Bumper W/Bypass, Boost/Pyro/Oil Temp Gauges,
3. 5" Exhaust, HP Injectors, K&N Filter, Hella
Lights, Icom 2 Meter and Uniden CB Radios.

 

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I think im gonna let Cummins check it out at the Power Booster bar-b-Q in a week... havent been driving it... noticed steel showing on my back tires...


thanx,
joe

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1990 w-250 4x4 cummins 5. 9,NV4500,tweaked injection pump, 16cm2 housing, 3"
JRE exhaust, 4. 10 gears

 

[Archive]

I think it might be the lift pump
today i was at the tire shop, after they put my tires on, i started it, it idled for a second then died... it's never, ever died on me... i started it again, it didnt die but there was that weird pulsing/missing sound...
kinda embarassing as there were a couple PSD guys in the lot

joe

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1990 w-250 4x4 cummins 5. 9,NV4500,tweaked injection pump, 16cm2 housing, 3"
JRE exhaust, 4. 10 gears

 

[Archive]

I dunno what it was, but the pulsing/missing sound is gone. It's been almost a week(filled up at a different station that gets way more buisness) no Idle pulsing, It still takes a few seconds for the idle to drop though after runnin on the highway.
Tanks for your valuable posts
joe