Great Alternative for Dizzy/Air Solenoid Valve

scmguru · 09:24 PM

I needed a new solenoid valve (item 37 in diagram- part #911 618 123 00) and wasn't able to find the part I needed. So I did some digging around and found the following alternatives:

1. Check out eb*y or your other favorite part source and look for mercedes changeover EGR solenoid valve.

I was able to score the identical solenoid for less than $10 shipped and it looked identical and worked perfectly (no need to change existing wiring harness). (See picture below)

Another alternative would be to support our fine hosts and use the updated Part 996-605-123-01 and get a NEW part.

If you use the newer part you'll have to change your conector plug from the old type Mercedes connector to a Bosch type Fuel Injector Harness Connector.

And it looks like it mounts a bit differently (clip vs metal bolt in housing).

JFairman · 09-14-2009, 07:08 AM

Good tips!

911st · 09-14-2009, 07:26 AM

I am not strong on the ignition side.

What is that vavles purpose?

Dose it advance the ignition at curse or pull back ignition under boost?

JFairman · 07:46 AM

The origonally blue cloth wrapped vacuum retard line goes through it before going to the retard pot on the distributor.
For the first 45-60 seconds after a cold start the K-jetronic ECU under the driver seat closes this solenoid valve blocking the intake manifold vacuum retard signal from reaching the distributor. The result is timing is not retarded at idle while the valve is closed so it is advances a few degrees which raises and strengthens idle speed about 300 rpms.

I've never held a stopwatch to it but somewhere around 45 seconds after a cold start the ECU opens that solenoid valve and intake manifold vacuum reaches the retard pot on the distributor, timing retards a few degrees and the idle speed abruptly drops about 300rpms.
The aux. air slide valve opens and is bypassing some air around the throttle body to raise idles speed at the same time during a cold start but it closes up gradually.

That is the right hand valve in the picture above.
The one on the left operates the air pump diverter valves.

911st · 09-14-2009, 08:16 AM

JF,

Thx.

So one of the valves blocks the vac advance function on the distributor except during start up?

Is there an opportunity here?

Would eliminating the valve's blocking of vac advance help with throttle response off idle or from cruse?

I have always wondered if there was opportunity that most 930's are leaving on the table on the ignition side.

JFairman · 09-14-2009, 08:32 AM

No, the right hand valve in that picture blocks vacuum retard to the vacuum retard side of the diaphram pot on the distributer. There are no electrical solenoid valves in the vac advance line.
There is a little mechanical thermal valve in the vacuum advance line on the late eightee's USA cars. It's mounted back on the breather cover with red cloth covered hoses going to it.
It blocks vacuum advance for a while until engine heat opens it after a cold start to lower emissions while the catalytic converter is heating up.
I'm sure they all work perfectly after 25 years... right.

This has been discussed in other threads before.

911st · 09-14-2009, 01:02 PM

J,

I have been reading posts and trying to better understand how a 930 ignition system works.

I was thinking of opening a new thread on this but hoped you could help.

I am leaving out or not interested the little extra valves for now that modify the vac/boost signals to the Dist.

Can you help me with the following:

What is the mechanical advance delta. Or, if a US dist is set at -25 deg w/o any vac lines, what would we expect to see the timing be w/o the vac/boost lines hooked up at idle?

What is the delta or total additional amount the Vac Advance that the vac-can, can add to timming? That is, if we ran the car above 4000rpm at cruse and were timed at 25 deg base, how much addational advance could we potentaly see?

Can you confirm that the can on the side of the 930 truly only advances timing. It can not retard it. That the only retarding it dose it pull back the vac advance that was added by it?

Do you know why the 3.0 turbos only had a vac/boost line to one side of the advance can and why they changed to a vac/boost line to each side of the can with the 3.3?

I assume the vac line on the outside of the vac advance can is a normal intake manifold signal from after the throttle body. Is that right?

Where dose the other come from and what type of signal is it?

Thanks for your help in the past and here if you can help me again.

I just love trying to better understand these cars.

The best,

Keith

911st · 09-14-2009, 01:03 PM

JF,

Sorry, I thought sent this as a PM not an addation to the post. Please feel free to PM me or post here.

911st · 06:03 PM

Ok, I am going to through this out there.

It looks like vac/boost circuit that runs the back of the Dist. can looks like is is all about smog compliance at idle.

It is looking like there might be an opportunity to just disconnect it totally and plug it anywhere back to the source at the manifold.

The purpose of that back part of the advance can seems to be to cancel out the vac advance at idle.

This "retard" side I believe is more like a "advance calculation" side and keeps the vac from advancing timing at idle like the euro and 3.0 Turbos are allowed to do.

The advantage of keeping it would be meeting smog at idle.

This should improve throttle response of idle.

Could this be correct?

911st · 09-14-2009, 07:07 PM

OK, been talking to Chris (356-930) and it seems the "can" only retards timing if I understand.

One side retards timing with vac. Thus with loss of vac the retard is taken away which effectively advances timing. The other side retards timing with boost.

It seems the loss of vac advances timing about 10 deg, the mechanical advance adds about 18 deg. After about 5 lbs of boost timing is pulled back a total of about 8 deg.

Thus, if we set the timing at 26 deg, at cruse after about 3000-4000rpm we would pull 34-36 deg of advance. Idle timing would I guess be about 0 and quickly advance to about -10 with loss of vac.

It looks like there is some solid potential for playing with the pre boost ignition curve on a 930.

356-930 · 356-930's Garage

Quote:

Originally Posted by 911st

OK, been talking to Chris (356-930) and it seems the "can" only retards timing if I understand.

One side retards timing with vac. Thus with loss of vac the retard is taken away which effectively advances timing. The other side retards timing with boost.

It seems the loss of vac advances timing about 10 deg, the mechanical advance adds about 18 deg. After about 5 lbs of boost timing is pulled back a total of about 8 deg.

Thus, if we set the timing at 26 deg, at cruse after about 3000-4000rpm we would pull 34-36 deg of advance. Idle timing would I guess be about 0 and quickly advance to about -10 with loss of vac.

It looks like there is some solid potential for playing with the pre boost ignition curve on a 930.

When I built the 356-930, I knew nothing about 930 engines. I was told I needed to attach a vacuum line to the boost retard port - so I did. The vac pot was left open to atmosphere. (Later learned that running the vac line to both ports was the right thing to do.) Since I didn’t have a timing light, I adjusted the timing by revving engine to 1500/2000, advanced timing until the engine misfired, backed it off till it was smooth, locked the distributor down. I drove the car thus timed for a few thousand street abuse miles.

I did get a timing light and checked it. 22 deg at idle, 40 deg at 3000 rpm. Off boost power was very good compared to off boost power once timing was set with a timing light to factory specs. (Timing was adjusted to factory when I changed the wastegate and upped boost to 1-bar, discovered WUR would not behave and everything I read on this forum convinced me I was a fool to run so much timing.)

My advice: Change ignition to MSD 6AL and its companion boost control retard module. MSD does make an ignition system that incorporates the boost retard control in the unit however, this unit does not allow one to set boost retard onset, only retard rate. The ability to add timing at low rpm/no and low boost will make a big difference in off boost performance. The ability to remove that extra timing will maintain on boost performance as well as prevent ring/piston damage/destruction due to detonation.
How much power the added timing at low rpm/no boost conditions provided I can’t say but my seat of the pants dyno says Yes to plenty more timing off boost.

911st · 09-15-2009, 10:02 AM

Chris,

Thanks.

Makes a lot of sense. At about 7/1 compression, combustion would probably be on the very slow side.

With your set up, when you settled on 20 deg advance, were you still pulling 40 deg at cruse?

I recall one built EFI motor that ran 42 at cruse but pulled it back quickly with acceleration. He said this helped spool to.

Your solution might be better than modifying the mechanical advance to limit the mechanical advance part from 18 deg total to about 14 deg. With that approach we could run -20 at idle, 36 at cruse, and 25 on boost and would not need the MSC. Might be worth checking the advance rate also so we have full mechanical advance by say 2500rpm (subject to verification).

For years I have suspected there was a some pretty good potential for improvement on the ignition side. I could not manipulate this on my C2 Turbo without a whole new ignition ECU.

The best.

mark houghton · 09-15-2009, 01:20 PM

I'm running about 36 degrees advanced at non-boosted cruise (as the combined result of the advance I've added at idle, loss of vacuum retard when the throttle valve opens off-idle, and the mechanical distributor advance....all added together). Using an MSD6AL and boost retard module set to retard 8 degrees when on full boost, my net advance on boost is probably around 20 degrees....or about what a stock motor will do with setting the idle at factory 0 degrees. It does wake up the bottom end considerably and has not resulted in detonation (to my knowledge) nor excessive engine temps. Been running that way all summer with no issues.

I would love to try even more advance pre-boost, but have run out of distributor rotation room.

356-930 · 356-930's Garage

911st: Yes, running 40 deg at cruise i.e. anytime engine not in boost and rpm high enough to have distributor mechanical full in. With boost above 5-psi, timing would be 32 deg, 3 degrees more than factory recommends.

Mark: More advance is but one tooth away!

mark houghton · 09-15-2009, 06:06 PM

Quote:

Originally Posted by 356-930

911st: Yes, running 40 deg at cruise i.e. anytime engine not in boost and rpm high enough to have distributor mechanical full in. With boost above 5-psi, timing would be 32 deg, 3 degrees more than factory recommends.

Mark: More advance is but one tooth away!

Yeah Chris, I just gotta get enthused to get in there and re-index the dizzy one tooth....or grind out a little more adjusment room in the slot. I think I want to target maybe 12 degrees at idle. And if I get really enthused this winter, I'll drop the engine and throw in the SC cams. At that point, I will be done (well....maybe swap out the 7006 for a 7200, and maybe slap on a set of headers). God, it just never ends.

JFairman · 09-15-2009, 07:46 PM

Mark, was it a really noticeable low rpm power improvement after modifying your advance curve with the MSD box?

mark houghton · 09-16-2009, 08:44 AM

Quote:

Originally Posted by JFairman

Mark, was it a really noticeable low rpm power improvement after modifying your advance curve with the MSD box?

I wouldn't say it was like "Holy $hit Batman, my tires are smoking" kinda thing, but it does result in quicker revs and more immediate throttle response, plus a little faster jturbo spoolup as a result. Most noticeable in the 2-4000 range. For the price of the module to go along with my MSD6AL ($125 used on evil-bay) I figured it was a relatively inexpensive add-on that just really complimented all the other modifications I've made. Very simple installation.

I guess a person could try out the concept of adding ignition advance without buying the module. Just dial in the extra advance, reset your idle and mixture, and see how you like it, but don't get on boost without being able to retard it back out!