I used to do a lot of acoustic work when I was in the Navy and these days when I'm doing manual camera repair, I use acoustic means to time shutters. A few years ago, I used a combination of acoustic recording and scan lines from a CRT to time a 4x5 focal plane shutter in a Speed Graphic camera. I got the speeds accurate to within 1/30 of a stop which is far more accurate than most mechanical cameras. And the camera body was produced in 1953, so age doesn't matter.

But I digress, my apologies.

Wouldn't it be a similar procedure to acoustically isolate the #1 injector line from the other lines by removing the clips that bind them together, then using a pickup, record or live-feed the acoustic signal of the #1 line and the injector popping to very accurately find out how the IP is timed? Of course there is the issue of "freezing" the motion of the crankshaft optically through use of a strobe like a gasser timing light. It can be done but I'm thinking it would take a bit of gear and a bunch of patience.

All that work-around seems easier to me using gear that I know well, vice the counting of drips. Maybe it's just me thinking around this in an odd way.

Through this last few months of owning my '78 300D I've wondered things like this and how I could get around not having spark plugs to measure signal off of. I'd just have to create my own signal somehow and I'm thinking that acoustically timing the IP would not only be extraordinarly accurate, it would be just plain neat. When I get to a place where I have a garage at my disposal (in a month or so) I'll give it a try and post the results here.

Phil Forrest

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1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson

We have done a variation of this approach using equipment designed to sense the pressure drop in the injection line when the injector releases. A small pickup is attached to the line and, using a strobe, the injection timing can be determined from the marks on the damper.

The correlation on the 617 between the method that uses the electronic A-B lights (617 is capable of this in '84 and '85) is as follows:

A-B light sets timing to 15 ATDC. This is the precise correlation for the engine when it is drip timed to 24 BTDC.

The pickup and stroboscopic unit is then checked. The engine shows just about 15 BTDC.

So, if you're going to acoustically measure the #1 line, you'd be looking for 15 BTDC as the setting.

Thanks, I was wondering what the variance would be since I'd be measuring from a different point in the fuel delivery chain.

Phil Forrest

__________________
1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson

just to confirm here. you mentioned atdc first, then btdc after... which is correct? oh, I think I see. the a-b light measures to the ATDC setting, which lines up perfectly with the pulse of BTDC... I get it.

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A-B lights use a reference point at 15 ATDC which corresponds to an actual start-of-delivery at 24 BTDC. Actual SOD at 24 BTDC will be reflected by an impulse indication occuring at 15 BTDC.

No, it doesn't. The light just flashes 39 degrees late.

Now - wow - er how?

I'm interested to hear if you've got a reference for the difference between the start of delivery and the point of delivery when the injector lets go; at engine revolutions below the interaction of the timing device.

I've been trying to find one for ages.

The FSM mentions that it is possible to do "dynamic" timing (using a sensor on cylinder #1 injector line with a bit of jiggery-pokery in the form of signal conditioning and connecting this to a strobe light) but so far I haven't found at which point BTDC this is meant to be set.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

You and I have spoken on this exact subject in the past and the information was provided to you at that time.

Either you have forgotten it or dismissed it..........

Well I must have forgotten - sorry about that - can you send a friendly reminder?

EDIT:-

You had me looking through my PM box Brian!

In a reply to a PM that I sent to you asking for information, you said that you'd compared the use of the A-B timing lights and then set up a system that used a sensor on an injector line etc and that the result of that system gave a result of 15 degrees BTDC.

I guess this is the information you mean? (This means I'm checking to see that there wasn't something else sent that I have missed)

I really do appreciate real world results - and I do value measurements more than theory most of the time!

But nevertheless I still am at a loss to understand why the FSM would talk about "dynamic timing" and even go so far as to include another section describing how to set up the position of the tachometer probe on the front of the OM617 so that that too can be used in the process of "dynamic timing"; and yet not supply the basic data that says it should happen at XX degrees BTDC at XXX rpm.

It has got to be written some where => that's what I want to find!

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

No, it doesn't. The one drop per second just occurs at 9 degrees early.

See, I can also confuse the forum and post irrelevant info for no good reason.

Not according to Bosch, it doesn't. Start-of-delivery and start-of-injection are not the same concept.


If you choose to use the term "timing," I would submit that you need to specifty the specific event being described. In the absence of any qualification, I suspect that the typical reader would infer that you are referencing start-of-delivery.

I only need to qualify it if you're choosing to parse definitions for no good reason. I'm really not interested in that.

For most on the forum, we're simply trying to compare three different techniques available for setting timing. The fact that one of them measures the start of delivery, one of them is just a comparable standard, and one of them is the actual injection event is not meaningful in the discussion..........but, you already knew that and decided to waste space on here.

The fact that both occur at 15 degrees from TDC (albeit on opposite sides) is pure coincidence. There is nothing "perfect" about it.

The "drip method" really is not as much about "counting drips" as it might seem. The point is to position the IP at the point just before "full flow" becomes "no flow." Much like turning a water faucet off, but not quite all the way off.