Backwards Behavior from WRD

[ctaylor738]

Hello again, all -

Last August I bought a 1966 230SL with a dead engine.  It is now back together with with a 1 mm over rebuilt short block, new valve seals, and a spiffed-up engine compartment.

I blogged about all the fun I had on mercedesshop:

http://www.mercedesshop.com/shopforum/showthread.php?t=233372

I don't have any history on the car, but the IP was very clean, and has a "Rebuilt by Mercedes Benz" stamp.

The car is running quite well, except that the WRD is behaving exactly backwards.  The car idles reasonably smoothly around 800 RPM when cold, and increases to 1500 when completely warmed up.  The WRD appears to be working - lots of air when cold, shuts off completely when warm.  Starting is immediate, but the engine likes to die for the first 30 seconds or so.   No power at all when cold - lots of sputtering and backfiring until at least a minute of warm-up.

So there is obviously a cold enrichment problem.  But what I can't get my head around is why the idle would increase with the auxiliary air shut off.   

Appreciate any ideas,

[al_lieffring]

this is just a guess. but it sounds like the main rack mixtrue adjustment is too rich, and when the cold start enrichment is added it goes from too rich to way too rich, and the additional air from the thermostat slide isn't enough too keep the idle from choking down.

Of course the first place to start is with the linkage tour, then work with the idle and main fuel adjustments. Most peiole on this forum reccomend changing the overall pump adjustment adding or subtracting shims from under the air slide assy. But I usually give the main rack adjustment screw inside the pump a click or two at a time then test drive to check the results.

Al

[ja17]

Hello,

If it is caughing back through the intake when cold, this is usually caused by a lean running condition. Too high an idle warm ....... can be a linkage issue, to much air and fuel, incorrect timing or a combination of these things.

If it is backfiring through the exhaust it can be rich running issue or timeing issue.

Make sure the linkage is correct first, all other adjustments are a waste of time unless the linkage is set properly. Next try the "linkage CO test" to determine exactly what the mixture siituation is.

Keep us up to date.

[merrill]

you can "turn off" the wrd.

there is a small bolt head just forward the base of the assembly.

I think if it is on there is an "0" stamp facing up.
to turn if off you turn the "0" down.

be careful because some of these have a lock pin.

the easiest way would be to remove the assy from the pump, then you can view how yours is set up then turn it off and re assemble.

be sure to replace any shims etc the are there when you pull it off.

Of course, try  Joe's recommendations first.

[ctaylor738]

Thanks, guys.

It is definitely running lean when cold, the spitting is back through the intake.  I will check the linkage adjustment.

But I am still mystified why the idle would be lower with auxiliary air being pulled through the WRD. 

[ja17]

Hello,

Al is correct, in that the fuel mixture is incorrect at certain temperatures making the idle change incorrectly.

Thanks, guys.

It is definitely running lean when cold, the spitting is back through the intake.  I will check the linkage adjustment.

But I am still mystified why the idle would be lower with auxiliary air being pulled through the WRD. 

[ctaylor738]

Over the weekend, I took the linkage tour, as well as checked dwell and timing (both fine).

I verified that the air throttle plate is closing completely.  It is.  In fact, it isn't even touching the adjustment screw.  There is about a .5mm gap, which I elected to leave alone because the nut is a non-metric size and whole thing is completely unmovable. 

#1

I started the car and let it warm up.  There was a lot of dying initially (it was cold on Saturday), and the idle started out at 650 and came up to 1150 when warm.  I took a CO reading and it was 1.2%.  So I reduced the idle air and was able to drop the idle to around 950, which raised the CO to a little over 4%.  Then I gradually reduced the idle air.  As the idle approached 850 it would suddenly drop to 650 and the CO would go to the 9% range.  I tried to lean the idle mix.  When I pushed the adjusting knob in, I could it engage in the slot, but there was no turning it in either direction.  There was certainly no click.  Picture of knob attached.  So I went back to a 950 idle and took a short test drive (good) and checked a plug which looked perfect.



Let the car cool for a few hours and retried.  Temp gauge was at 40 or so.  Idle was lower, CO was at 7.7% at temp of 40.  It warmed up and stabilized as before.   Conclusion, pump is providing enrichment?


#2

On Sunday, I measured the IP rod and found it to be 237 mm.  Adjusted it to 233 and tried a cold start.  Much dying and a then a rather severe rising/falling idle.  Went back to 237, and rise/fall greatly improved.  Tried again to get idle around 850 and CO adjusted. Had brief confusion over what end of the pump determines "clockwise" and determined that it's from the FRONT of pump.  Still having issues moving the adjustment, but must have done something because now have idle at 900 and CO at around 8%.  Started to snow, so ended efforts for the day.

[ja17]

Hello Chuck,

The linkage arm on the injection pump must be on its stop at idle.  Just changing the rod length will alter something else. Try disconnecting the IP rod with the car running. let the pump linkage lever rest on its stop. Your linkage rod if adjusted correctly should be aligned to the lever.

By shortening the rod you actually made the engine run leaner.  You will need to get the idle mixture thumb screw working correctly before you can completely sort things out. 

Do you know how to do the split linkage CO test with the engine running?  This is probably something I should demonstrate at PUB with the cameras running.

[ctaylor738]

Thanks, Joe.

Even with the rod at 233 mm, the IP lever was against the stop.  I didn't see much else change, so maybe I have a bunch of slop in the linkage.  I will try to get a more experienced hand to feel the idle adjustment on the pump.

And I will take a look for the split linkage CO test, try it, and report back.

I also need to figure out how to determine that the air and pump actuating levers are coming off there stops simultaneously, since I can only look at one at a time!

[ctaylor738]

Well, some more fumbling and bumbling tonight, along with a positive result.

Started the car, air temp at 40 degrees or so, needed to be kept at 1500-2000 rpm for maybe 15 seconds before it would idle.

Time from
Start            RPM     Temp    CO%

2                  675      0         8.9
5                  600     40        7.9
9                  630     80        7.8

I then raised the idle to approx 960 RPM with the adjusting screw and got a CO reading of 6.7%.   This is where it is stable.  Dicked with the idle mixture and figured out that the thumbwheel has three positions: 

1. Out, freewheeling
2. In a ways, turns with slight resistance, no discernible click
3. All the way in, turn until feel in slot, not able to turn once in slot.

I am not making this up.

So I made small adjustments in posiition two, keeping the idle around 960.   This brought the CO to 6.3 and then 4.4.

Took a short drive to clear things out after all the idling, car ran great.  Rechecked CO at 4.4, Pulled #1 plug, burn looked perfect.

Looked again at the linkage movement.  At idle, both air plate and IP are against the stops.  When linkage is moved, IP lever is open maybe 1 mm before air plate moves.

So now I need to get idle down to 850 and reduce CO proportionately.   

[ctaylor738]

The last couple of posts seem to have been trashed, so here is the latest.

Following Joe's advice, I was able to free the idle adjuster by grabbing the adjustment wheel with a small pair of vise grips, pressing it in, engaging the slot and turning it CCW.  Gernold told me that jamming at full rich is common, and occurs when someone attempts to adjust the idle mix with the engine running.  I backed it off two clicks, and now have CO of roughly 4% at idle.

An ongoing problem is that the idle is stable at 950 RPM.  When I try to go lower, say to 900, it will suddenly drop to 600-ish and go lumpy.  Then, sort of randomly, it will speed up to 900 or so.

[Tonys113]

Rotation CCW?
Please help me get this straight.
CCW to Lean the mixture
CW to Richen the mixture

Would this be from Looking Forward at the rear of the IP
Or Looking from the front of the car toward the rear.

I am having similar troubles.
I have stabilized the surging with the correct timing
Have been through the Linkage Tour and have everything as indicated
About to Take of the WRD and remove shims in an attempt to lean out a rich at all rpm problem


Thanks

Tony

[Naj ✝︎]

Looking Forward at the rear of the IP

[ctaylor738]

Update.

Car is running reasonably well.  When cold, it starts quickly, runs for 5 seconds and dies.  Then restarts easily and is OK.  Idle starts at about 750 and comes up to 950 fully warm.  While warming up, the idle has a gentle surge that gradually diminishes and stops when the temp gauge hits 80.  Driving while warming up is OK if the RPMs are kept above 2500 under load.

Gernold had me check the CO at 3000 RPM, and said that it was critical that it be around 4%.  Mine was 5.6% and I'm not sure if I'm brave enough to adjust it. 

[Tonys113]

ctaylor 738, I feel your pain.
My 69 280 runs excellent once warm but will not run worth a ^&*^% at cold idle. I have been through the linkage tour, I have Crane electronic ignition, timing is right on at idle and 30 degrees BTDC at 3000rpm.
My car continues to run extremely rich at idle and just a bit rich at 3000rpm. I have removed the smallest shim in the collar under the BC (Barometric Compensator) which has made a significant improvement while driving but has dome nothing for the idle quality.
I can hear air rushing into the WRD at cold idle. Today I removed the Air Filter from the WRD once the car reached 180 (Thermostat Open and plenty warm BC), there is still a measurable amount of air coming into the WRD Filter. Enough to hold my finger firmly. This leads me to believe that there must be fuel enrichment as well.
Can someone tell me, once warm does the BC retract the pin thus removing it's force on the IP rack to lean out the engine?  Thus as it wears it does not retract enough?

Worst of all, it seams that every time I start this car it runs differently. I have gone from a stable idle of 800rpm warm to today it is 600 and seams to be on the verge of stalling. It will not idle above 800 when cold and coughs through the exhaust.

Any help will be greatly appreciated.

Tony

[awolff280sl]

Hi Tony,
It is my understanding that the BC is not affected by temperature. If it is functional, at higher altitudes the pin in the BC protrudes further which leans the mixture for rarefied air.

[Tonys113]

Well them possibly I misspoke regarding the BC.
What Effect does the operation of the THERMOSTAT enclosed in the WRD have on the Fuel Mixture? At Cold Idle v. Warm Idle v. Warm Running

Thanks

Tony

[awolff280sl]

When the engine is cold, the pin in the thermostat of the WRD is fully retracted. This allows more fuel and air to pass at cold idle. As the engine heats, the pin pushes out which reduces the fuel and air. At fully warm idle and running, there should be no significant fuel and air contribution by the WRD. 

[Tonys113]

Thanks Andy,

So it is natural to have pressure on WRD as you are removing the screws, almost to the full extent of the threads.
furthermore, Removing shims under the WRD will allow the pin to exert more rotational pressure on the IP rack and leaning out the fuel mixture.

So I believe that my thermostat is stuck, new one on the way. Finally PROGRESS.

Cheers

Tony

[Tonys113]

One more consideration on that note.
The screw on the back of the IP> Standing at the back of the car or basically at the driver door and reaching in to adjust will it be clockwise to LEAN the mixture?


Tony

[66andBlue]

Tony,
it is the opposite: clockwise -> richer, counterclockwise -> leaner.
But remember, shut the engine off before turning the screw and only one or two "click" each time.

[awolff280sl]

Tony, although your thermostat may inded not be working, it may not be its fault. The thermostat's pin pushes down on a cylinder that must slide easily up and down in the chamber against the resistance of a spring. You should check that it does. When I replaced my thermostat, I used brake cleaner on the cylinder and chamber, and even some very fine emory cloth on the cylinder. I lubed the cylinder with a small amount of lithium grease prior to reassembling the whole WRD. The improvement was remarkable: the car idles a about 1100 when cold and GRADUALLY the idle lowers to 800 as the engine warms. It even works in reverse: if the car is left to cool a bit ( but not go to cold) the idle will be somewhat higher than normal until the engine is fully warmed.

[Tonys113]

Thanks again for the insight Andy,
I will be removing the WRD tonight and will keep everyone posted on the progress.

I really appreciate it.

Tony