Re-built FI Pump back on; now BIG idle...challenge

[jameshoward]

Frequent readers may recall that I had sent my R11 FI pump on holiday to Holland for some adjustment required because the oil resvoir was taking on additional oil from...somewhere. The gentleman who 'fixed' it did so by drilling 2 holes. I have found what they do: they allow the excess oil that the pump takes on to drain back through the drive back into the sump. (I found this out when I filled the pump's resevoir and tipped it foward to install it; much of the oil ended up on my shoes). The FI pump has been on a few days and, after a mare getting the car started, it now runs. I don't know what's going on with the FI pump oil situation right now - I haven't got that far yet, but I have driven the car for about 20 miles and it runs very well indeed.

The problem is now with the idle. Before the pump went off the car would not idle until warm without gentle pressure on the accelerator. When warm, it sat very happily at about 650-700. Very happily indeed.

Now, it starts very well and idles very well from cold. As it warms up, however, the idle starts to hunt. It seems to range from about 790 - 860 (using a digital tach) up and down. It will eventually stall.

I have read about every thread on the site to do with idle and have found and corrected some problems along the way. (Thank heavens for the search function).

I have done the following to my 1966 230SL, manual, w/power steering, no a/c:

 - Set dwell to 40 degrees
 - Set timing to 30 degrees at 3000rpm, no vacuum.
 - I have checked the CSV, which leaked a little when removing the 7mm screw.
 - I have removed, cleaned, reinstalled the CSV, and the leak is no more. (Great advice on this on the side, Ja17, Benz Dr and others - thank you). Checked the solonoid at the back of CSV and it works.
 - I have checked that the WRD (not checked by the guy who did the FI pump) on the FI pump draws air when started, and slowly reduces air flow as the car warms up. (It seems that this is proportional to the increase in idle hunting; i.e. as the air flow thru the FI pump air filter drops off, the idle starts to fluctuate).
 - The linkage is 233mm. I have done the rich/lean test whereby I disconnected the rod to the linkage. When opening the venturi, the car promptly stalls. The FI pump lever sits at the stop when at idle.
 - If I turn the air screw for idle at the manifold fully clockwise, the hunting is dramatically reduced, but does not disappear. If I turn the screw anticlockwise so I can hear a lot of hissing, the idle fluctation becomes very bad and the car will eventually stall.
 - With these settings, I have in exasperation gone to the back of the FI pump and enrichened the mix using the idle screw at the back by up to 14 clicks. It does seem to run better, but has not cured the hunting and the car smells like it's really running rich. It still stalls, but as I said, it is better or takes longer to stall.
 - I have then put the pump back where it was and gone lean 5 clicks; it runs worse and stalls more quickly.
 - I have a good flow of fuel (checked the flow and it gushes out easily meeting the 1L in 15 secs as per the BBB).
 - Plugs are newish (a few hundred miles on them); points are newish; I've stripped down and rebuilt the distributor and it seems fine.
 - Dashpot is fine.
 - Venturi flap opens fully, and rests closed binding nicely at idle.

I know I am missing something - obviously, since the car won't idle when warm - but I am now out of ideas. Perhaps I have a vacuum leak somewhere else but haven't a clue what else to check or how.

Any ideas would be VERY welcome indeed as I am royally stumped!

And I'd like to drive the car.

Thanks,

James

[Benz Dr.]

Adjujust the fuel mixture at the back of the pump. It's probably too lean.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[jameshoward]

Dan,

Thanks. I've tried that, up to about 15 clicks clockwise and it still idles badly.

I know it's a long post, but I've read about as much stuff on this site as I can find, including lots of your input and that of Joe, but I can't get the idle to settle and the car to run for more than a minute or 2 when warm without stalling.

JH

[hands_aus]

In the rich/lean test, what happens when you move the Injection pump lever thereby increasing the fuel supply? As you know if the rpms increase more than 100 then the engine is running too lean.

I read on here someone had to turn the Inj pump knob 18 clicks before the fuel supply mixture was acceptable.

Another thing... the hot idle air supply comes only through the idle air screw.
Are you sure the venturi is not leaking air? Have you cleaned it?

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[jameshoward]

Hi Bob,

Thanks for pitching in - I've read a number of posts on this kind of issue so I know you're no stranger to it.

When I conduct the JA test and advance the fuel lever, it makes little difference. When I open the venturi, the car falters and abruptly stalls.

From what I can see, this is about right.

I changed the points today, and by fiddlig with the idle stop screw and the air idle screw things are a bit better, but she still idle very roughly and as a result I've had to being the idle up to 1000 to avoid stall.

Any ideas?

JH

[Benz Dr.]

Well, lets go radical here. Is the pump installed properly? 20 degrees ATDC on number one piston both cam lobes pointing up? I had one set at 20 degrees BTDC and it would still run but talk about rich, WOW!

It's ether that or something is wrong with your pump. Send it back if you have to...

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[Benz Dr.]

What ignition distributor do you have? You should be setting your advance with the vacuum connected so that you get 30 degrees at or before 3,000 RPM. Some distributors will give you more than 30 degrees but you want at least 30 before you get to 3,000 RPM. That limit is the minimum you want and it should be there at or before 3,000 and not after.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[jameshoward]

Dan,

Mine distributor is a Bosch 051.

With the advance disconnected, I have set the timing to hit 30 deg at 3000 rpm. (I can't advance things much more as the distributor hits the locking nut at the collar).

I will try it with the advance connected tomorrow.

Should I still set idle (which is about 4 - 8 deg) without advance?

One further question: when I was refurbing the distributor (with your advice on bushings) I was surprised by the amount of effort that the advance linkage took to move it when pushed with a screw driver. Does this sound about right to you? I assue the advance moves more easily when the thing is rotating at engine speed. Is there any way to check the advance is working correctly?

James

[Benz Dr.]

OK, you want to have the vacuum line connected so it will work as intended. The mechanical advance is 20 degrees on a 051 and the vacuum is only about 10 degrees. You can change that amount by moving the pull rod in or out on the vacuum box.
The mechanical part of the distributor should move freely. If it doesn't the cam is probably siezed on the main shaft. Don't feel too badly, in reality not that many people are sucessful at rebuilding their own distributors without a test machine if there are real problems to be solved.

Connect the vacuum line and re set the timming and leave it there. If the fly weights don't move freely or won't spring back to the same spot each time you will have to take it apart again and free it up.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[hands_aus]

Do you regularly (6 months or each service if sooner) add oil to the distributor shaft wick and the outside 'oil' point?

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[jameshoward]

Hi Bob,

As I said in the War and Peace-esque initial post, I've just stripped and re-done the dissy. As Dan notes, it's hard to tell if it works or not. I replaced the felt pads on the rotor arm and the felt between the bearings of the dissy so I'm confident that it doesn't lack lubrication.

I am also pretty sure the pump timing is correct.

When I had another attempt to get the idle to settle down with the new points, it was better. I suppose I could replace the plugs again...again! I seem to be moving between the idle stop screw and the air idle screw on the intake manifold - is this correct? Also, if I screw the screw on the intake manifold completely clockwise until it stops it runs better. If I go the other way, it idles more roughly.

?

[Benz Dr.]

Hummmmmmm......

Idle stop screw you say? Are you moving this thing around trying to find the sweet stop? It won't likey happen.
There are a number of posts that tell you how to do this but basically you have to turn the idle stop screw out until the throttle plate starts to grab a bit. Lock the stop screw in place and leave it alone. If you turn the idle air screw all the way in and it starts to run better it's way too lean at idle.
Adjust your throttle linkage to these new settings and try it. Idle speed is a combination of air, fuel and timming that you keep adjusting until it runs smoothly.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[jameshoward]

Dan,

Thanks - that gives me somewhere to go now. I am trying to find a sweet spot, hence the messing with the screws/stop.

I'll use linkage adjustment to attack it next.

Having the idle air screw fully in didn't seem right; I suppose it's meant to be out a little.

Does this mean I can move away from the 233mm linkage setting that is much discussed?

James

[Benz Dr.]

No. Stick to the proper 233mm or whatever is the right amount. What I mean is re adjust your throttle lever linkage so that it works right after you set the stop screw to the right amount.
When you move this screw you will have to shorten the linkage going from the cross shaft to the throttle lever. Adjust this linkage so that the IP lever and the throttle lever open at exactly the same time. You can do this by putting your finger on the pump lever and watching the throttle lever. You feel with one and see with the other - not possible to see both of them move at the same time.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[merrill]

james,
get a thin 19mm box wrench, remove the tuna can barometric pressure can that is on top of the inj pump.  there should be washers between the can and the pump.  do not drop them, they are an odd size.

according to hans at H&R there should typically should be 2mm thick washers there.  (typicaly,  this depends on the barometric pressure where you are)

once you know what is there let us know or call hans. he can guide you on the proper thicknesss needed based on the ATM Pressure where you live.

the washers affect the fuel flowing thru the inj pump, then the star knob on the rear of the pump is to fine tune the amount.

Matt
Austin Tx
66 230 sl - "white"
78 300 D - Blue
98 C230

[jameshoward]

With the help of Dan, Matt and others, I'm about as far as I can go without additional advice.

I have kept the linkage at 233, and done what Dan said: unscrewing up the changes I made to the idle stop screw etc thus it stops the venturi flap just binding at idle. It took 15 clicks clockwise to get the car to idle without stalling. It still runs better with the idle air screw closed though, and the idle still hunts up and down when warm between about 700-900. It just will not settle.

Remembering that I asked the pump guy to lean out the pump, the car seems to shudder a little between 2000-3000 rpm, as if it is faltering. It also needs to have higher revs to accelerate and drive smoothly, ie it would be happy at 35 mph in 4th, but now I need to drop it into 3rd otherwise it stumbles.

I've read the plugs and they're fine. I think the car is too lean throughout the whole range.

Question: to rectify this, do I go to one of the harder to reach screws on the FI pump, or what? I know you can lean it out my changing the shims on the WRD; is this easier? Would it be better to stick the car on a krypton tuner and see what it says and go from there?

I am definately making progress because I can now drive the car, but the hunting idle is really infuriating. Can I do much damage by running too lean?

JH

[merrill]

james,
do you have a place where you can get your exhaust co% read?

also, 15 clicks is a lot,  pull the tuna can and see if there are any spacers / washers down there.  mine has 1.9mm worth or washers.

also, you should be able to disconnect all linkages and get the car to idle.  the idle has a separate screw for the air, it is on the intake.  as the car leans out the screw has less and less affect on the idle rpms

once that is done then worry about the linkage.

Matt
Austin Tx
66 230 sl - "white"
78 300 D - Blue
98 C230