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PostPosted: Wed Aug 29, 2012 3:04 pm 
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Location: SoCal
This question pertains to my 1986 Isuzu Trooper turbo diesel. I just purchased it a few months ago, and the entire motor has had a "professional rebuild" from an unknown mechanic- I have no idea if it was rebuilt properly or who did the rebuild.

When I push in the clutch at high RPM, the motor remains at about whatever RPM it was running at and won't idle down. So I can get it to idle properly if I wait and push in the clutch once it drops to idle speed, but if I push it in at 2,500 rpm it will remain idling at 2,500rpm.

The throttle is not stuck open, it's returning fully. If I turn on the A/C for a second to add a load, it will suddenly drop to the correct idle speed and will remain idling correctly after the A/C is turned back off.

Any ideas? I suspect some adjustment(s) are off on this pump, but I'm not sure where to begin.

Google searches suggested that this can occur if the smoke screw is turned too high, but if anything I suspect it might be too low. There is no smoke visible in the mirrors, even at full throttle. Perhaps the smoke screw is too high, but the boost aneroid is set to limit peak fuel?

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'84 Volvo 760 Turbo Diesel D24T/M46


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PostPosted: Wed Aug 29, 2012 3:19 pm 
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Location: Germantown (next to Elvistown), TN
Tyler,

Welcome to the site. I appreciate the thoroughness of your question. Unfortunately, it's well over my head. :( However, while we wait for an expert to weigh in, let me encourage you to post an Intro (in the "My P'up" section), and update your Location and Signature. You should have received an email with instructions for all this. Let me know if I need to re-send.

I have other questions, but I'll wait for your Intro post.

Jack

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Original owner, '83 LS Diesel, 5-spd, 2wd, Long Bed (currently in "rehab") | '94 Amigo 2.6L, 5-speed, 2wd
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PostPosted: Wed Aug 29, 2012 3:30 pm 
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Thanks Jack! I updated my sig and location, but I'm gonna wait until later to post my introduction. I wanted to include some photos of the Trooper, but I need to wait until I get home from work to get them off my computer.

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'86 Isuzu Trooper Turbo Diesel 5speed/4x4
'84 Volvo 760 Turbo Diesel D24T/M46


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PostPosted: Wed Aug 29, 2012 4:20 pm 
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Tyler--

The most likely cause for failing to come back to idle (when the throttle is closed) is that the engine is running on its own lube oil. The oil can come from the positive crankcase ventilation, the turbo seals or the valve seals. I vote for the turbo seals. Perhaps the rebuilder did not rebuild the turbo.

Paul

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PostPosted: Wed Aug 29, 2012 4:24 pm 
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:lol: I was composing the following, but lost my network connection at the coffee shop...
JoeIsuzu wrote:
Great! I'm hoping Paul (from San Luis Obispo, by the way) will weigh in on this one.

Jack

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PostPosted: Wed Aug 29, 2012 4:36 pm 
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Paul wrote:
The most likely cause for failing to come back to idle (when the throttle is closed) is that the engine is running on its own lube oil. The oil can come from the positive crankcase ventilation, the turbo seals or the valve seals. I vote for the turbo seals. Perhaps the rebuilder did not rebuild the turbo.


Paul, thanks for your reply. Would this be possible without any visible smoking or high oil consumption? I haven't driven this vehicle a lot, maybe 1,000 miles- but didn't notice any significant oil consumption or visible tailpipe smoke during that time. The engine also has virtually no blowby visible if I remove the oil filler cap during idle.

Is there some way to test your idea without pulling the turbo off? Maybe I should pull the intake manifold hose, such that the intake is open air at idle, without the turbo pushing into it?

Also, it doesn't rev way up out of control like it's "running away", more like it's just idling real high. I don't think it will maintain rpms over 2,500 on it's own, if I were to push the clutch in at 3,000rpm it would drop to 2,000-2,500 rpm.

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'84 Volvo 760 Turbo Diesel D24T/M46


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PostPosted: Wed Aug 29, 2012 11:58 pm 
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Tyler--

Well, I am not certain whether you will have smoke or not but it does seem likely. If you were to pull the turbo connection to the inlet manifold you might over speed the turbo but I think not as the fuel setting cannot be very high with only 2500 rpm with no load. If the fuel is coming from the manifold the engine should slow down immediately.

But, back to your first description of the problem, perhaps the full load screw is set too high. I know that this will cause the idle to go up and it cannot be turned down with the idle screw. But, I don't know what the clutch can have to do with it. You can try to turn the full load screw out by about 1/4 turn to see if that cures the problem. You will want to remember where it was in case you want to set it back. Also, you may then need to set the idle screw up a bit to keep it idling.

Also, are you sure the throttle lever on the pump is hard on idle even with the clutch in/out?

Is there any chance that the pump has been run on gummy or gum producing fuel such as WVO? It is possible that the internal governor is gummed up which will prevent it from properly regulating the fuel vs speed/throttle requirement.

Finally, I have had one n/a pump which behaved somewhat like you describe and while this pump has not been rebuilt I did take it apart to see if I could identify what might be causing the problem. What I found was a combination of several marginal wear/setting discrepancies that may have caused the problem. This is quite iffy.

Try this stuff and see if you can generate more data. Try the full load screw first. If you decide to try disconnecting the turbo be careful.

Paul

PS-- Where in So Cal are you?

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PostPosted: Thu Aug 30, 2012 12:20 am 
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Oil from crankcase will cut visibility to about 6' and kill any skeeters within 100'. Burn 5 quarts oil in driving 17' into trailer. When those turbo seals go there's no question. Put into 3rd gear and dump clutch while standing on brake. Ask me how I know? Jerry

New batch of Crabapple Jelly Paul. Trade for nude pixs of your wifey. hehehehehe Just joking but it is that good.


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PostPosted: Thu Aug 30, 2012 12:55 am 
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Paul wrote:
Try this stuff and see if you can generate more data. Try the full load screw first. If you decide to try disconnecting the turbo be careful.


Paul, thanks- I'll try turning down the full load screw first. If that doesn't do it, I'll try taking the pump off and shipping it to a friend who rebuilds these, and he'll look inside for any damage/wear. I've never had one apart, and don't want to 'learn' on my only pump.

I'm in Riverside... it's too hot to work on cars here!

Tyler

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'86 Isuzu Trooper Turbo Diesel 5speed/4x4
'84 Volvo 760 Turbo Diesel D24T/M46


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PostPosted: Thu Aug 30, 2012 10:49 am 
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soot fart wrote:
Oil from crankcase will cut visibility to about 6' and kill any skeeters within 100'. Burn 5 quarts oil in driving 17' into trailer. When those turbo seals go there's no question. Put into 3rd gear and dump clutch while standing on brake. Ask me how I know? Jerry

New batch of Crabapple Jelly Paul. Trade for nude pixs of your wifey. hehehehehe Just joking but it is that good.


Tyler--

As you can see, this conversation is going downhill :) Anyway, if nothing you do works, try some of Jerry's crabapple jelly. It will work wonders. Thanks, Jerry.

Paul

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