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How to Set Points - Electronic Control Unit

Started by brettj, 20 August 2010, 09:43 PM

koan

Won't be the ignition control module, all that is working.

Don't know what idle assistance your engine has, often there's some sort of vacuum operated anti-stall setup on the throttle, maybe that needs looking at.

Are you supposed to set idle RPM in D or P?

Just sounds like the idle RPM needs to be increased a bit.

koan
Boogity, Boogity, Boogity, Amen!

brettj

The only part linked to the throttle that I can think of is the throttle switch. Perhaps that should be adjusted?

I believe you set the RPM in P.

Just thought of another possibility in regard to the stalling issue, perhaps the timing isn't set right. Could incorrect timing cause stalling when shifting between gears?

koan

Quote from: brettj on 28 August 2010, 11:55 AM
The only part linked to the throttle that I can think of is the throttle switch. Perhaps that should be adjusted?

Not unless you have logically deduced that the throttle switch is the problem (I doubt it is). All you are doing by playing with it stabbing in the dark which is not the sensible way to go about fixing the problem.

The timing should be adjusted to whatever the book says, there is (or should be) a sticker on the radiator support giving the conditions for timing setting, the RPM A/C on or off and any special needs like removing vacuum hoses.

Just sounds like the idle RPM needs to be increased a bit.

koan
Boogity, Boogity, Boogity, Amen!

oscar

Quote from: brettj on 27 August 2010, 09:25 PM
The bad news is, now the car will sometimes stall when put in drive and  off and on the rpm's drop from 750 to 500, the battery light comes on on the dash and then the rpm's suddenly shoot back up to the normal range of 750 and the motor either stalls or returns to normal operating condition.  I can't figure this problem out. Could it be the electronic control unit? How does that unit actually work? Never really understood its purpose.

Quote from: koan on 28 August 2010, 01:24 PM
Just sounds like the idle RPM needs to be increased a bit.

I'd agree Brett. Needs a tad more air and I doubt the TPS is an issue too.  Although, I'm not sure of an anti-stall measure on these things as such, the TPS does have a fuel cut off switch which operates on a closing throttle.  So as revs drop there's no injector activity until the revs reach a point and the injectors kick in. I've no idea what that preset is or how it's determined.  It makes you wonder if the fuel cut off switch can get stuck or if it's over ridden.  To my mind it gets over ridden once a minimum RPM is reached, but either way to rule out the TPS as a problem I'd simply disconnect it and see if the car stalls under the same conditions, ie, same engine temp when attempting previous start when it stalled. 

Which brings me to ask if this stall happens only when you've attempted cold restarts and/or does the same thing happen when the engine is fully warmed up?

When you mention electronic control unit, I assume too you're referring to the ICM, ignition control module.  From what others say they tend to quit working without warning rather than degrade in performance so the one you've got has got to be ok.

Quote from: brettj on 28 August 2010, 11:55 AM
Could incorrect timing cause stalling when shifting between gears?
Yep.  If it's too retarded then it'll stall when under load.  More likely too whilst the engine is cold.  Koan's right, there's supposed to be a timing decal on the cross member in front of the radiator on a US d-jet with timing details.  If it's missing, manual says 7deg BTDC vacuum disconnected.  IMO that's conservative.  With vac connected and revs at 1500 it should rise to 10-14deg BTDC.  It's a balancing act but try to match the manual's figures and give a bit extra advance by a couple of degrees if need be.  You'll need to set the idle screw as well.  Although it's only supposed to be adjusted once the engine's fully warmed up, I'd wind it out a little if you can't maintain an idle whilst the engine's warming up.  Once again, it comes back to the suggestion that the idle RPM needs an increase.

Good to hear your dwell's set.  FWIW, I read the black and white striped points superceeded the solid black wire type.  Couldn't find it in the manuals and it wasn't something someone else typed, it might have been written in a parts catalogue.
1973 350SE, my first & fave

brettj

OK - Yesterday, I drove my car  about 30 miles. Got home, parked the car for about a half hour, restarted, and the motor started to rev up and down uncontrollably all over again. It had not done this at all during the day.  I figured that the motor needed more air so I adjusted the idle screw. Nothing seemed to be happening so I turned the screw as far as it would go to see what would happen. The motor was also shaking as I adjusted the idle screw. The motor shaking stopped with the screw fully, opened but naturally the rpm's went way up. I've now adjusted the idle screw to the point where the motor does not shake and the engine does not want to stall between shifting gears. The only problem now is that in P the idle is very high, around 1600 but the timing seems to be set right with the idle in D at about 800. Is it safe to allow the engine in P to idle so high?  What is the normal setting in P for the 450SE?

koan

Quote from: brettj on 29 August 2010, 01:01 PM
OK - Yesterday, I drove my car  about 30 miles. Got home, parked the car for about a half hour, restarted, and the motor started to rev up and down uncontrollably all over again

Think that's a classic D-Jet problem, maybe one of the D-Jet folks can help you.

Have you played with the throttle switch?

When you say "idle screw" you are referring to the air bypass screw and not the mixture adjustment?

koan
Boogity, Boogity, Boogity, Amen!

brettj

The air bypass screw.

More strange stuff today, I drove the car another 30 miles, again parked it for about half an hour and then restarted. At the restart the idle speed in P went down to 1000. I drove the car about half a mile and parked it. Went to get some stuff at the market and again about 20 minutes later restarted. This time the motor dieseled at bit at start up and the idle speed in P went back up to 1500. Could the probelm be the vacuum box attached to the distributor? What does that part actually do?

Also, in the distributor there is a plate in which the points sit. There are 3 screws in the distributor that seem to hold down that plate. Should the screws be screwed down tight to the plate or left loose? The arm of the distributor vac box is connected to this plate. Does the vac box arm move this plate for some reason? I have the plate screwed down tight. Perhaps that's the issue.

koan

Wait for D-Jet expert to clue you in on the idle problems.

The vacuum advance unit (vac box) rotates the plate in response to changes in vacuum from a port just below the throttle. You can test it by applying vacuum to the connection. In other words suck on it and the plate should rotate slightly.

The purpose of the advance unit is vary the amount of extra advance given under part throttle running but there should be no extra advance at idle with the throttle closed. Disconnect the line to the advance unit and block it with a finger, the ignition advance should not change with the throttle closed.

The screws have shoulders on them that allow the plate to rotate when they are screwed tight.

koan
Boogity, Boogity, Boogity, Amen!

oscar

That up and down idle is caused by the ECU sensing the rpm is running away or too high after considering the input of all the other sensors and components.  Classic case is 13B's video http://www.youtube.com/watch?v=9a4WiAk9Ass . It was diagnosed for me by a guy from the NSWMBC a few years back and only occurs at idle and usually disappears once the engine has fully warmed up but does depend on the AAV working.  Without getting too technical the ECU shuts down the injectors till the revs drop then brings them online again.  It's a direct result of too much air but you don't necessarily have to have the idle screw way open for it to occur nor does the AAV have to be stuck open or faulty.  I've had it happen when I've thought everything was in good order and working normally.  Like koan said it's a common d-jet thing and it's not something to get too worried about.  However, you can reduce the chance of it occurring by placing a restriction in the "Y" air tube that goes to the AAV.  I've done that a couple of times during winter months but it's been a couple of years since I last did the mod.  I'm usually off and driving before the problem manifests.

The shaking motor is a misfire.  Anytime mine does that it's usually a fouled plug or two and disappears after I've revved it a bit and warmed it up.  Prolonged idling and short drives will increase the chance of plugs fouling with crud.  This is where an occasional spirited drive is beneficial.  If your misfire disappears after you go for a drive I'd put it down to fouled plugs rather than querying other ignition parts or d-jet bits.

The three screws in the distributor are supposed to be tight.  They're attached to arms that clamp the advance plate down.  Not sure what the effect would be if they're loose but they should be tight.

I don't think any of your problems have to do with the vac advance unit.  It only affects initial advance during acceleration whilst the throttle begins to open.  Once the revs are up and the throttle is opened up more the mechanical advance takes over and vac advance has no affect.  An extreme example, there's no difference between a full throttle take off with and without vacuum. I replaced my faulty leaking advance unit and the perceived difference was minimal at normal take offs.
However, if you want to check the integrity of the advance diaphragm, check the following vid.  Push the advance plate with your finger to full advance then occlude the vac hose attachment nipple with another finger.  Let go of the plate which will snap back (there's not enough vacuum generated to hold it there), wait for a while then take your finger off the nipple.  You should hear a pffft as the air is sucked back in.   You can push the plate the other way and do the same for the retard side.
http://www.youtube.com/watch?v=_ClKtjqsqrI

 

1973 350SE, my first & fave

brettj

Thanks for the info. I'll do the test you suggested.