Idle Fuel Adjuster

[jcochran@cox.net]

Hi,
 Does anyone know if the idle fuel adjuster located on the rear of the injection pump has a "stop" or "default point"? Does it continuously rotate past 360° or is there a stopping point that can be used as an adjustment reference. If it has a stopping point is there a standard tuning starting point such as "five clicks clockwise" or "six clicks counterclockwise" from that point?

Thanks,
Jim Cochran

[ja17]

Hello Jim,

The knurled adjuster engages as hex shaped, slotted screw inside the injection pump. Only try adjusting it when the engine is not running. It is a typical machine screw that screws in and out. If you screw it in, it will eventually get tight and no longer move. If you keep screwing it outward it will eventually move so far back that the screw head will stay engaged with the knurled thumbscrew. Before this happens the "clicks" felt for adjustment will become less apparent or may go away all together.

There is no home or default position, but it is meant to be positioned so that you have adjustment available to you in both directions. We can write a small book here at this point on the subject, but it has all been covered in detail already on this site. Try to search up the "injection pump tour" to start with. Also you will find that the "split linkage test" will be very helpful for finding out if your injection mixture is rich or lean. Another subject which must be dealt with is checking the critical engine linkage. Go through the "Linkage Tour".

We will help you along, keep asking questions.

[jeffc280sl]

Hi Jim,

Joe has tremendous experience and I would not second guess anything he says.  You should take time to read the information he has suggested. 

The knurled nut on the rear of the pump is not used to set idle on our cars.  The fuel injection system is extremely complicated and a step by step approach must be used to diagnose problems even as seemingly simple as adjusting the idle.  BTW, fine tuning of the idle is set using the air screw near the hose coming from the air cleaner.  The screw is part of a Y fitting that goers into the intake manifold.

I suggest that you read, read and then read some more.  Take Joe's advice and take the linkage tour.  Its a great place to start.  Replace all loosened ball joints on the linkage and follow the instructions to the letter.  Its a great place to start and will not cost you big money.

Following that look into obtaining a gas analyzer.  You want to measure the air fuel ratio at idle.  Read about air fuel ratios and gas analyzers.  That reading can be adjusted using the idle screw mentioned above.  You want the mixture and engine rpm to be correct.  If you still have issues you can read about the cold start valve (CSV).  Make sure that is working properly.  Then read up about the barometric compensator.  Very interesting device.  Make sure it works.  Make sure you have the correct fuel pressure and fuel flow.  Read, read.  Check the ignition system.  Make sure it is correct.  Renew the distributor if need be. 

Only after the linkage tour, CSV or warm running device, barometric compensator, fuel flow and ignition are correct then you can think about the knurled nut and its function.  I recommend leaving it be.  Don't touch it until everything else is right.  Then come back and start asking questions about the knurled nut.  By all means please ask questions about the steps in between.  Some may be answered by reading the advice of others who have been there.  I'd say it took me 2 years to get the fuel injection pump running perfectly.  For me it ended up with adjustments to the fuel injector pump using a MAP sensor, air fuel meter and lap top computer.

Best regards,

Jeff 

[wwheeler]

I second what Jeff and Joe say. They know what they are doing! Owning my car since 2007, only now have I got all of the fuel injection issues close to being worked out. It takes time and patience. My advice is to learn what each device related to the injection system does before you even think about changing any adjustments. The Technical Manual is a great place to start. Frequently your problems are related to not one, but several issues.

My car had everything incorrectly adjusted when I bought it. Amazing that it ran as well as it did.

[Cees Klumper]

So ... I am going on a limb here by saying I always thought the knurled screw was, besides to help set the idle air/fuel mixture, in fact also used to adjust idle RPM. By adjusting both the screw and the air valve on the intake manifold you either provide more or less fuel/air at idle, which raises or lowers the RPM. It's been a while since I read the linkage tour, and I may not have gotten it correct, or forgotten what I once knew, just thought I should mention this. Somebody set me straight (even if it is telling me I should go back and read the tour again)!

[ctaylor738]

Well, I will saw the limb off, by saying that I have not found the pump adjustment to make much difference in idle rpm.  If the mixture is really rich or really lean, an adjustment may add a few RPM, but the idle speed is really controlled by the amount of air from the idle air valve.  The pump adjustment will definitely make the idle smoother as you get the CO percent closer to spec.

Cheers,

CT

[Cees Klumper]

Thanks Chuck, that is actually what I meant; in order to adjust the idle level, you must adjust both the air valve as well as the FI pump knurled nut to maintain the right CO level. If that's not correct, someone step in now before urban myth is born.

[stickandrudderman]

Air: screw, knob: fuel.
I'm sure there's a joke in there somewhere........

[Cees Klumper]

While somebody works on that, my question still stands.

[garymand]

Cees, Good catch.  You are correct and your limb intact.  the FIB is used to set the RPM, by setting the amount of fuel.  Yes, the air screw on the intake manifold allows the appropriate amount of air at idle.  (it e buttler fly (thottle) valve is supposed to be closed at idle, therefore NOT letting air into the manifold during idle.  The butterfly valve is set to BITE the bore without binding at idle.) 

"The knurled nut on the rear of the pump is not used to set idle on our cars."  is absolutely wrong.  That knob is all that sets (or meters) the amoung of fuel allowed to enter the injectors at Idle.  The manifold screw meters the idle air,m and should be the only air source.  Only those two should be used to set the idle RPM and A/F mixture.I


This can be very confusing and I resisted getting into it, but the statement is inaccurate.  The problem maybe in how we think about the process.  Since we can't turn the FIP screw with the motor running, then we adjust the air as the final adjustment.  If the CO is in spec but the RPM is too low or high, then you adjust the gas with the knob and re-adjust the air until the RPM and CO are acceptable.  But this should be a very clear point that the FIP adjustments determine the FUEL in the F/A ratio even at idle.

The knob will give you enough gas per click to raise or lower the RPM by about 50 RPM/click, in my experience, and of course you adjust the air after the fuel is changed.

[ja17]

Hello Cees, hope all is well. I think everyone is on the right track here but the information is just fragmented. Hope this helps.......................

Adjusting the knurled knob on the injection pump will change the mixture at engine speeds below 1700 rpms. This includes the normal idle speed of around 750 rpms.  So unless your engine is incorrectly idling above 1700 rpms this injection pump thumb screw is one of the adjustments which is normally used to achieve a good idle. I can think of at least four adjustments required to achieve a good idle. Correct linkage adjustment, correct idle intake air screw adjustment, correct injection pump thumb screw adjustment and correct adjustment of any auxiliary idle control devices on the linkage (linkage dash pots and linkage solenoids). Once everything else is dialed-in, the intake air screw is most easily used to fine tweek the idle.

[jeffc280sl]

Thanks everyone.  I agree with Joe that information is fragmented.  Its that way because the FIP is so complicated.  As I said the air screw is used to fine tune the idle.  What I was trying to say is that if everything else is correct by all means use this screw to fine tune the idle.  A gas analyzer will tell you quickly if the fuel flow from the knurled nut is in range because fine tuning the air screw will make the final mixture richer or leaner to again fine tune the idle.

I was trying to make the point that I would start with simple and inexpensive tuning efforts and work up from there.  Try the air mixture screw first.  Its right there and easy to get to.  If that doesn't help I would look at other things before the FIP itself.  Air fuel ratio metter would help you understand and give you more data points.  I recommend Linkage, fuel flow )rate at the fip), the WRD/CSV, barometric compensator, ignition etc. should be checked before touching the FIP.  After I was confident with everything else I would look at adjusting the knurled nut.  Record data!  I suggest you look at photos of the FIP and see exactly what screw the knurled nut turns.  The clicks are somewhat subtile and must be felt.  I suggest you zero out the knurled nut and record the number of clicks it takes to bottom out going clockwise (I think).  In that way you can always get back to your starting point by going to zero and turning CCW 50 clicks or whatever to get you to the start point. 

All of these adjustments must be taken slowly and data must be accurate or you can get lost and turn the knurled nut out of its adjustment range and lose your way.  You will kick yourself hard if you allow this to happen.

Br,

Jeff

[jeffc280sl]

I've attached a copy of a photo of the rear of the pump so those who have not seen it can understand what I'm speaking about.  We have been talking in this thread about the screw that is labeled "external idle thumb screw adj".   It is a six sided screw that uses a flat screw driver or the other end of the knurled fitting or screw.  The thumb screw, second name, is spring loaded and must be pushed in to engage the adjuster.  Once seated you can turn the screw with your thumb and index finger from the exterior of the pump.  As you can see there are two metal tabs which ride on flat sides of the screw.  These are the clicks we are speaking about.  One full turn of the screw is equal to 6 clicks for each flat spot on the screw.  The screw can be loosened such that it is not deep enough in the shaft to engage the flat metal tabs.  Don't do this!

Hope this helps.

Br,

Jeff

[garymand]

Hi,
 Does anyone know if the idle fuel adjuster located on the rear of the injection pump has a "stop" or "default point"? Does it continuously rotate past 360° or is there a stopping point that can be used as an adjustment reference. If it has a stopping point is there a standard tuning starting point such as "five clicks clockwise" or "six clicks counterclockwise" from that point?

Thanks,
Jim Cochran

Great, you guys  with all those starshad me worried! 

Back to the original question: NO, there is no default position.  I do know a way to tell where the idle gas screw is set, but first we need to know what you've done and state the motor is in now.  1st, as everyone has said: tuned motor, adj'd linkage, correctly set WRD, motor warmed to 80C.  I'm going to explain how to us the rack to see if the idle fuel adjustment is on or how far off it is, (approximately if you don't have an A/F meter)  2nd use the split linkage trick to give it a little more gas and then a little more air to see if it is rich or lean. 

Then get back with questions and what yuou think you want to do.  My FIB was incredibly miss adjusted and it has taken me years of intemacy with it to get it near optimal for my flavor of driving.

[jeffc280sl]

Thanks Gary for bringing us back to the original question.  I don't know of any factory setting for this screw.

Here is a picture of a similar pump.  It shows the flat head thumb screw in the center.  It is currently 66 CCW clicks from the CW stop.  As you can see the 6 sided screw has risen above the metal tabs which provide the clicking feel on each the six faces of the screw head.  I would say the effective midpoint of this adjustment is 25 to 30 clicks from its CW stop.  If all is lost in this regards and you don't know where you are I would zero the adjuster by turning the screw CW and then go CCW 25 to 30 clicks.

All adjustments can be made from this starting point.  Just keep records.  If you are going the start changing this setting I suggest you document a start point by counting the CW clicks until you reach the stop point.  Then back out CCW to your original setting.  Make sure to never go past 50 or so CCW clicks from the stop.  Clearly MB did not want the FIP operating at an extreme range past this point.

Br,

Jeff

[ctaylor738]

Here is a link to a post that contains information (which I believe to be from Bosch) about installing an injection pump and adjusting the idle.

http://www.sl113.org/forums/index.php?topic=20151.0

It states in two places that the adjustment of idle speed is with the air screw.  IMO (and experience), the limb is still sawed off.

Cheers,

CT

[garymand]

You need to understand what you are reading.