1984 6.9l Rough Idle and Surging

Rix_IV

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Hey everyone. So I recently got my great grandfather's 84 F250 with a turbo'd 6.9 IDI running and its been idling and running really smooth. However, it has recently started to idle very rough where the whole truck is shaking. It has pretty excessive white smoke and has a strong smell of diesel from the exhaust. Once I start driving it smooths out, the smoke goes away and it has plenty of power. My guess is that I've got an injector stuck open and it's just dumping fuel when it's idling but if you guys have any ideas as to what it could be let me know!
 

chillman88

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First, I'd have it running at idle and loosen the injection lines at the injectors one by one, listen and see if the sound/roughness changes, then tighten it back up. If you have one particular injector that behaves a lot different compared to the others it's probably the culprit.

If you can't tell after that, run a bottle of this through the system and report back afterwards.

https://www.amazon.com/dp/B00IUGFZJW/ref=cm_sw_r_cp_awdb_imm_70T4XN24TXC1SYD419V7
Tractor supply sells it for like $15 and I'm sure other places do too. Be careful with it, one member got a mild chemical burn from it. It WORKS though.


Does it do it all the time or is it associated with low fuel or anything? It only acts up at idle?
 

Rix_IV

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First, I'd have it running at idle and loosen the injection lines at the injectors one by one, listen and see if the sound/roughness changes, then tighten it back up. If you have one particular injector that behaves a lot different compared to the others it's probably the culprit.

If you can't tell after that, run a bottle of this through the system and report back afterwards.

https://www.amazon.com/dp/B00IUGFZJW/ref=cm_sw_r_cp_awdb_imm_70T4XN24TXC1SYD419V7
Tractor supply sells it for like $15 and I'm sure other places do too. Be careful with it, one member got a mild chemical burn from it. It WORKS though.


Does it do it all the time or is it associated with low fuel or anything? It only acts up at idle?

I'll be sure to try that with the injectors. And it went from idling beautifully after I first got it running again to now running really rough. It's got a brand new fuel filter that I filled with diesel kleen. It should still have about half a tank of diesel in the tank (the gauge doesn't work so not completely sure) and yes it's only rough at idle, once I get moving it runs fine.
 

chillman88

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I specifically asked about fuel level because sometimes the pickup in the tank will fall off and cause issues under 1/2 tank. That wouldn't only be at idle though, it would be all over.
 

lotzagoodstuff

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How long did it sit and have you taken a look at the fuel? I’d pull the fuel line at the mechanical fuel pump and drain off a mason jar of fuel and take a close look at it.

The individual loosening of injector lines is a good tip as well.
 
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