Idle RPM hunting, fluctuating
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    Default Idle RPM hunting, fluctuating

    Drove from Northern New Mexico to Los Angeles today in the 4BT Scout, for work.

    Pulled over for fuel in Flagstaff. At the bottom of the off-ramp, when engine came down to idle, RPM was bouncing up and down between 700 and 900, on about a 2-second cycle. At the bottom end (700) the whole engine was shaking pretty badly.

    Stopped at Home Depot in Barstow and rigged up something to keep idle at about 975-1000. There is no RPM hunting at that high idle, so it's an OK workaround for now, I guess.

    Did some poking around over on DieselTruckRegister.com and people over there suggest that it's the governor spring. Sound logical? I had the pump rebuilt only 3750 miles ago by Tennessee Diesel Care and Performance.

    If it's the governor spring, is there somewhere I can pick one up in LA?

    Any ideas are welcome. I am here in LA for a while and would like to get it sorted out, as I will be using the hell out of the Scout.

    Thanks, as always,
    Christian

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    first question is, why would you let TN diesel care touch anything? look around on the web, they are known for junk.
    88 Chevy Airforce crewcab. 6bt NV4500 valair clutch, modified 4k GSK
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    Remove your fuel filter and dump it into clear plastic jar. Let it set for about 20 minutes and see if there was any water in your fuel. Replace the filter with a new one. Dirty water contaminated fuel can cause this. This swells the filter element and restricts flow which in turn slows down the engine. The engine senses the low idle speed and compensates by adding more fuel which in turn starts the cycling effect.

    If that has no effect recheck all of the hose clamps on your fuel lines and check the fuel tank cap for venting and the pick up tube in the tank for a restriction.

    If that has no effect then check your lift pump pressure. A marginal lift pump has also been know to give the same effect. Did you replace the lift pump before you did your conversion? That's always cheap insurance especially if you plan to take long trips from home.
    BobS

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    OK.. Didn't know TN diesel care was known to be sub-par.

    I've got the piston lift pump from CrewCab59, with about 5000 miles on it. I hope that's not bad yet. Also, fuel pressure gauge reads consistent between 13 and 15 psi. It does not fluctuate between these pressures along with the RPM.

    I guess I will check for water in the fuel when I can.

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    Question: Does the good fuel pressure reading suggest that it is NOT a water-in-fuel / plugged-filter issue?

    Also, I did ask TN Diesel Care to install a 3200 RPM gov spring while they had the pump open, but from my tachometer I can tell they did not. Yesterday, i had the engine pegged at about 2600 RPM for a while, before the problem started. Is it possible that I stretched the gov spring? Does that make sense?

    I could just install the 3200 spring, because i want one anyway, and see if that fixes the problem.

    Christian

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    I was under the impression that the p-pumped engines had idle hunting issues due to the gov spring. I did not know that the VE pumpes could do the same thing.
    1994 Dodge Dakota Ext Cab 4x4. 4BTA 375hp and 720ft/lbs torque, 12.9 at 103mph 1/4.
    There are no stupid questions, but there are a LOT of inquisitive idiots

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    Quote Originally Posted by khaoskustoms View Post
    I did not know that the VE pumpes could do the same thing.
    My VE equipped 4BT is proof that it can happen. My little engine has got it bad.

    Anyone know the easiest way to get my hands on a 3200 gov spring? Seems like it's worth a try.....

    Thanks,
    Christian

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    1. Did you check what BobS said? Just because you have fuel pressure still doesn't mean you don't have water in your fuel .
    2. Fuel pressure ,the pump is working fine.

    The Ve gov isn't going to stretched by driving , during the install yes but it would had done that from the start not 3k down the road.

    Scott

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    Quote Originally Posted by khaoskustoms View Post
    I was under the impression that the p-pumped engines had idle hunting issues due to the gov spring. I did not know that the VE pumpes could do the same thing.
    This is becuase the tension is tighter than the other.

    Scott

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    OK, got my clear plastic jar, and fresh fuel filter. Will try BobS's suggestion after work.

    One other weird symptom.... you know how some people rev their engine IMMEDIATELY when they start their car.. like they have their foot on the gas as they turn the key? My 4BT is doing exactly that all by itself now. It starts at a high RPM and then immediately goes down to about 1000 (which is where I have it set now).

    C

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    Could your fuel screw moved a bit during your drive? Mine did that starting thing when I had my fuel screw turned in to far. It never surged like you are describing though. I backed the screw out and made sure the locknut was tight. No problems since.
    1994 Dodge Dakota Ext Cab 4x4. 4BTA 375hp and 720ft/lbs torque, 12.9 at 103mph 1/4.
    There are no stupid questions, but there are a LOT of inquisitive idiots

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    the part # for the 3200 spring is Bosch p/n 1-464-650-366. it should have 366 printed on it in blue. lets hope they put it in and you're just having other issues. the spring is not real expensive.
    88 Chevy Airforce crewcab. 6bt NV4500 valair clutch, modified 4k GSK
    http://67-72chevytrucks.com/vboard/s...d.php?t=522535
    72 Scout d60/14blt, 4bta
    http://www.4btswaps.com/forum/showth...72-Scout-Build

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    Fuel screw hasn't moved... in fact the little crimped-on protective "hat" is still there.

    Followed BobS's suggestions, to no avail. (No water in fuel, and new filter produced no change.) Fuel line is clear all the way to the tank and looks good, as do all the clamps. No air in fuel... at least not before the lift pump.

    Messed around with the idle some more, and got it to idle as low as 875 without hunting, which sounds almost normal. Any lower than 875 and it starts cycling. It used to idle right at 800 all the time.

    Any other ideas?
    Who do I call to get that Bosch spring?

    Thanks,
    Christian

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