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Author Topic: Pump fuel screw......what setting is oem?  (Read 533 times)

September 19, 2018, 12:52:17 pm

Spokerider

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Pump fuel screw......what setting is oem?
« on: September 19, 2018, 12:52:17 pm »
I disassembled, cleaned and resealed an early aaz injection pump a while ago. When putting it all back together, I used the " count the threads" method of getting the adjustable setting screws back to their original settings. Thinking I got it pretty close, but.......maybe not quite bang on. Never did see / hear the engine run before I did this, so, I can only assume that the pump settings were correct.


 My question is.....what is the oem fuel screw setting at? Yes, I know it came with a tamper-proof cap..... How does the factory set this screw??
 Yes, even 1/8th of turn makes a diff, thus, my count the threads method may not be bang on as mentioned. I'm looking to get back to base-line and start tuning from there.

 Thanks.



Reply #1September 19, 2018, 06:31:22 pm

soma56

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Re: Pump fuel screw......what setting is oem?
« Reply #1 on: September 19, 2018, 06:31:22 pm »
Great question. Not sure myself but always thought/assumed wherever that tamper-proof cap is the default setting. Did you remove yours? My guess is VW calibrates it with a machine to ensure the perfect flow and amount in idle, idle to throttle arm opening up more fuel and with the throttle fully-open. And then some German teenager would affix the tab to that screw exactly where it's been set.

If you've got a sweet spot already just fine-tune it from there?

Playing with these settings - I always have a 13m wrench and flat head screwdriver ready when out and about to slightly tweak things on the side of the road to get things perfect, never-mind the potential of having a runaway diesel on your hands as well. If that happens, it's no big deal. Just shut her down and turn it down slightly (turn up the idle a little to compensate) - it means you're close  :)

Reply #2September 19, 2018, 08:58:18 pm

RunninWild

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Re: Pump fuel screw......what setting is oem?
« Reply #2 on: September 19, 2018, 08:58:18 pm »
when I had a cap on my golf I was still able to turn the screw in enough to cause an erratic idle, black smoke and a noticeable jump in power. I don't think the safety cap is necessarily the factory point or else I wouldn't have been able to turn mine any.


Why so obsessed with getting it to exactly factory spec? do you have an egt gauge? id just turn it to where you have a steady idle and no smoke if you arnt looking for a performance bump.

Reply #3September 19, 2018, 10:02:35 pm

sgnimj96

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Re: Pump fuel screw......what setting is oem?
« Reply #3 on: September 19, 2018, 10:02:35 pm »
diesel bench calibration machine is how it's officially done

The diy is to have the screw turned enough that it has full power,  any more than that will make excessive black smoke.   It can only burn so much.   So if you mess with it, do it in small increments and adjust the idle accordingly.     
if the fuel screw is in too much it will make the rpm's hang.  Not enough and the engine will be gutless.  It's pretty easy to find the sweet spot if the pump is working properly.
81 Scirocco 1.6D (conversion)               86 Gofl 1.6D                          1985 300TD

Reply #4September 20, 2018, 12:16:33 pm

Spokerider

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Re: Pump fuel screw......what setting is oem?
« Reply #4 on: September 20, 2018, 12:16:33 pm »
Thanks for the replies.
 I'm just trying to get a better understanding between the interplay of the adjustment screws.......cold idle, warm idle, residual fuel screw and max fuel screw.

 I have a newly rebuilt engine that I need to break in under load, and not in my driveway fooling with pump screws for an hour or longer. Want it running well enough to get the initial break in done.
 
 

 

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