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I just purchased a 1987 Chevy p30, 6.2 diesel. Starts and runs, but at idle, the rpm go steady up and down. I’ve never owned a diesel before, what things can I check without specialty tools? Thank you!
 

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Welcome to DieselPlace
If you haven't done so, start by replacing your air and fuel filters
Install a piece of clear fuel line on the return side of the Injection pump to help locate any air in fuel issues
 

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Ok, I think that would be this? Looks like I need to change the big line that’s like an upside down horseshoe on the pump, and both of those lines to the right of the injector pump. They are old and cracked :/ After I do that, can you help me “bleed” or purge the fuel lines?
 

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Ok, I think that would be this? Looks like I need to change the big line that’s like an upside down horseshoe on the pump, and both of those lines to the right of the injector pump. They are old and cracked :/ After I do that, can you help me “bleed” or purge the fuel lines?
Yes, You can find clear fuel line at any auto parts store.
Also, replace those rotted rubber lines and any others you may see.
For info on bleeding your fuel system look at this thread: How to remove air from the fuel system and/or find an...
 

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Welcome! Lets try to not make a bunch of separate threads for the same thing. That is the connector for the vacuum valve that regulates vacuum down to the TH400 vacuum modulator.
 

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Discussion Starter #8
I put a clear line on top of the injection pump, no bubbles. I’ve replaced the filters air and fuel, and replaced any worn hoses. Here is a quick video of how it sounds. What else can I check to fix the rpm surging??
 

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I put a clear line on top of the injection pump, no bubbles. I’ve replaced the filters air and fuel, and replaced any worn hoses. Here is a quick video of how it sounds. What else can I check to fix the rpm surging??
No video, only a picture attached. The best way to post a video here is to first upload it to youtube and then copy the video link in the address bar and paste it here in the thread

No bubbles in the clear line is a good sign.
Surging can be low fuel pressure also. Do you have the mechanical fuel pump or is it upgraded to an electrical lift pump?
I would Tee in a fuel pressure gauge post fuel filter and see what your pressure is.
 

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Discussion Starter #10
Thank you so much for the fast reply! I believe it’s the mechanical fuel pump, When you say post filter, the best spot to t in a pressure gauge would be right on top of the injection pump, or one of those 2 lines behind my fuel filter(square box one :(
 

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Thank you so much for the fast reply! I believe it’s the mechanical fuel pump, When you say post filter, the best spot to t in a pressure gauge would be right on top of the injection pump, or one of those 2 lines behind my fuel filter(square box one :(
The mechanical fuel pump would be on the passenger side of the engine, attached to the block and look like this:
mechanical pump.jpg

Tee in a fuel gauge anywhere on the line from the Fuel Filter and the Injection pump.
You want to see the pressure going into the Injection pump
 

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I put a clear line on top of the injection pump, no bubbles. I’ve replaced the filters air and fuel, and replaced any worn hoses. Here is a quick video of how it sounds. What else can I check to fix the rpm surging??
In your pic, looks like the filter mounting has had some sensors removed.

If you plan on keep it I would put a good fuel filter setup on it.
Like a Racor, mentioned in this thread

 
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Discussion Starter #13
In your pic, looks like the filter mounting has had some sensors removed.

If you plan on keep it I would put a good fuel filter setup on it.
Like a Racor, mentioned in this thread
Thank you Legendman, I have the heater sensor on the way, I’ll switch over the filter system as soon as I can, or if it pops a leak somewhere.
 
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