Testing Trigger Points

[Schroeter]

Starting a new thread, and quoting part of another one:

From Schroeter:
I've got good spark. Seems to want to start for 1 second, then no kicking. Then flooding. Bosch D-Jetronic system. W114 model. 1969 250ce.

I pulled 2 injectors out to watch the pulse, and it starts nice and short pulse, then about 1 second later, long/heavy pulse.

There was fuel in the throttle position sensor area, could this have damaged that sensor?

I was also wondering if the injector trigger contacts in the distributor may be mucked up from flooding?

Just looking for suggestions.

Best Regards,
Michael Schroeter.


From Graham:
"I doubt you could damage the TPS - It is on outside of throttle housing.

Trigger points are a possibility. I had this happening on my SL. The fiber cam followers had worn down and the points were staying closed for almost a full revolution. As a result, the injectors were firing at the wrong time and for too long. If you open the distributor up and look at the trigger cams, you can see how they work.

When I had a similar problem, I took the distributor out and tested it on the bench. If you connect an ohmmeter from the center contact to each of the others in turn, and rotate the distributor, each set of points should stay closed for about 110 deg or so. Or at least thats how my good points are. I wish I had had an oscilloscope or a scopemeter, but the ohmmeter did work.

If they don't test out, you may need a new set of trigger points. But they are VERY expensive. Used sets may be as bad as the problem ones unless they come out of a known to be good running car!

I have an idea on how we could adjust the trigger points. If you are interested, it might spur me to do it and take some pictures!"

From SChroeter:
"Hi Graham,
I'll start taking my distributor appart. I'll take pictures also.

I'm very interested in you idea on "adjusting trigger points".

I'm a bit new to this forum, but I'll try to start a new thread here in a moment.

Cheers,
Michael Schroeter "

[Graham]

We have a cold spell coming up so may I will make up the jig and tool I have in mind for adjusting trigger points.

Simple idea really. Remove one half of the point sets (they can be removed by removing the circlip and sliding them out of their mounts.

Make up a plate that will slip over the spindles the points rotate on. Scribe a line on the plate exactly on the centerline of the spindles. Scribe two additional lines parallel with this centerline such that they are the distance we would like the points to be apart. This can be determined from the cam min diameter plus a small amount (to be determined)

Make up a lever tool with a slit at the end that will fit over the fixed part of the points. Slip it on, then bend the point plate so that the fiber slider will line up with the scribed marks. Do same for all 4 points.

Put points back together and recheck opening angle for each set using ohmmeter.

I am pretty sure this can be done. Just need to do it and work out the details!

Once done, points should be good for another 100k miles

[bwostosh]

How about a junk distributor body cut open so that a feeler gauge can be inserted between points (like Ign points) while the rubbing blocks are on their respective cams.
Those trigger points are expensive and I do have a few distributor bodies.

[Schroeter]

My test with ohmmeter was successfull. Here's what I did:

Background: W114 Benz with D-Jetronic fuel injection (1969). This system has "trigger points" in the distributor. There is a convenient little "drawer" on the side of the distributor where these points slide out.



You could test the resistance by connecting the ohmmeter to the 3 pin electrical connector and rotating the distributor, but I chose to remove the distributor and pull out the trigger points (3 screws total). Here are the steps:

1- Remove vacuum hose from distributor
2- Remove dist. cap
3- disconnect the Green wire from coil or ignition switch box (depending on your setup)
4- Remove the 10mm/ Flat head bolt (I removed the battery first to gain better access to this bolt with a long wrench to avoid stripping).



Now you can remove the trigger points from the distributor. Pic above shows distributor with trigger points removed already.

5- Remove the 2 flathead screws from the side of the distributor
6- Slide out the trigger points (pull gently on the black electrical connector).




Now you can test the points with an ohmmeter.

7- Set your multi meter to resistance (omega symbol). Connect one test pin to the center (of 3) terminals on the points electrical connector, and the other test pin to one of the end terminals. You should see 1. for open points and 0.00 for closed points (or vice versa - I can't remember/tired/car still not running frustration!).
8- Repeat for other side by keeping one test pin on the center terminal and the other moved to the other side.
9- (important) Repeat this test with the trigger points back in your distributor (so you know if the cam is working properly with the points).


Pic above doesn't show the points contacts but rather the contact point that moves against the cam.

Mine tested fine. If they don't test fine for you, make sure the points close properly, make sure they are clean. If still no luck, keep an eye on this thread, there may be some more suggestions for repairing points. Apparently they are expensive to replace.

Cheers

[Graham]

Originally Posted by Schroeter

My test with ohmmeter was successfull. Here's what I did:


9- (important) Repeat this test with the trigger points back in your distributor (so you know if the cam is working properly with the points).

Mine tested fine. If they don't test fine for you, make sure the points close properly, make sure they are clean.

When you say they tested fine - Did you measure over what angle each set stayed open/closed? As those fiber cam followers wear, the angle they stay closed gets bigger and bigger. At a certain point, the ECU gets confused

My car is a V-8, so we have two sets of those points. Upper and lower, but otherwise they are similar. Your points should not be AS expensive.

By the way - Nice cutaway drawing!

[Graham]

Originally Posted by bwostosh

How about a junk distributor body cut open so that a feeler gauge can be inserted between points (like Ign points) while the rubbing blocks are on their respective cams.
Those trigger points are expensive and I do have a few distributor bodies.

Some mechanics told me that they used a cutaway distributor. But I don't have one I want to destroy - It's my spare

I think it can be done with a jig - may be easier than trying to work through a hole?

But what it comes down to, is that the points can be adjusted by bending the tabs in the picture below along the yellow line. But just how much and how to get them even from side to side is what I have been thinking about.

It seems to me that the only way to test if they are right, is to measure the angle that each set closes for - should be in 100 deg range, I would think.

I seem to recall reading somewhere that some of the old D-Jet testers may have had this test function built in. Sort of like a dwell meter.

[Schroeter]

I finally tested the degree of opening for each set (2) points. Both are staying open for 150-160 degrees.

I measured this by printing off a picture of a protractor, then taping it to the black intermediate dizzy cap, so I could rotate the dizzy, and watch the rotor move around my paper protractor, with ohmmeter attached to the electrical terminal watching the resistance change from infinity to 1.

This is higher than your suggested specification Graham, so this could be the problem. I wonder if there is a proper specification, if someone has it, let me know. Perhaps they are different for different engine types.

My current troubleshooting seems to lead to injectors either firing at full pulse time, or not at all.

[Schroeter]

Embarrassing Update - the "no fuel" scenario was due to "no fuel in tank". This happens quickly when injectors are firing long pulses.

Back to flooding. This leads me to think the TPS or MAP sensors are failing. I will search the forum for testing methods.

[Graham]

Originally Posted by Schroeter

I finally tested the degree of opening for each set (2) points. Both are staying open for 150-160 degrees.

I measured this by printing off a picture of a protractor, then taping it to the black intermediate dizzy cap, so I could rotate the dizzy, and watch the rotor move around my paper protractor, with ohmmeter attached to the electrical terminal watching the resistance change from infinity to 1.

This is higher than your suggested specification Graham, so this could be the problem. I wonder if there is a proper specification, if someone has it, let me know. Perhaps they are different for different engine types.

My current troubleshooting seems to lead to injectors either firing at full pulse time, or not at all.

I have never seen a spec, but did see a write up by Bosch that mentions this angle as something to check.

The other way to check if your trigger angles are acceptable, is to remove the injectors/rails and have them discharge into a trough or series of bottles while turning the engine over. The shop manual outlines such a method.

Those angles do show that your trigger point cam followers are worn.

[bwostosh]

I have "loaner" parts for the substitution method of troubleshooting.

[Raymond 77]

Does any one know what the dis should be on the1973 450sl trigger points
fibre, mayine are worn down ,thay could be call rubbing blocks, thanks

Raymond

[Raymond 77]

Originally Posted by Graham

Some mechanics told me that they used a cutaway distributor. But I don't have one I want to destroy - It's my spare

I think it can be done with a jig - may be easier than trying to work through a hole?

But what it comes down to, is that the points can be adjusted by bending the tabs in the picture below along the yellow line. But just how much and how to get them even from side to side is what I have been thinking about.

It seems to me that the only way to test if they are right, is to measure the angle that each set closes for - should be in 100 deg range, I would think.

I seem to recall reading somewhere that some of the old D-Jet testers may have had this test function built in. Sort of like a dwell meter.

Hi I have a 1972 450sl and my trigger point rubbing blocks are worn,I adjusted the trigger points and gave them and extra .010 ?do you think is ok,thanks Raymond

[Raymond 77]

Originally Posted by Schroeter

My test with ohmmeter was successfull. Here's what I did:

Background: W114 Benz with D-Jetronic fuel injection (1969). This system has "trigger points" in the distributor. There is a convenient little "drawer" on the side of the distributor where these points slide out.



You could test the resistance by connecting the ohmmeter to the 3 pin electrical connector and rotating the distributor, but I chose to remove the distributor and pull out the trigger points (3 screws total). Here are the steps:

1- Remove vacuum hose from distributor
2- Remove dist. cap
3- disconnect the Green wire from coil or ignition switch box (depending on your setup)
4- Remove the 10mm/ Flat head bolt (I removed the battery first to gain better access to this bolt with a long wrench to avoid stripping).



Now you can remove the trigger points from the distributor. Pic above shows distributor with trigger points removed already.

5- Remove the 2 flathead screws from the side of the distributor
6- Slide out the trigger points (pull gently on the black electrical connector).




Now you can test the points with an ohmmeter.

7- Set your multi meter to resistance (omega symbol). Connect one test pin to the center (of 3) terminals on the points electrical connector, and the other test pin to one of the end terminals. You should see 1. for open points and 0.00 for closed points (or vice versa - I can't remember/tired/car still not running frustration!).
8- Repeat for other side by keeping one test pin on the center terminal and the other moved to the other side.
9- (important) Repeat this test with the trigger points back in your distributor (so you know if the cam is working properly with the points).


Pic above doesn't show the points contacts but rather the contact point that moves against the cam.

Mine tested fine. If they don't test fine for you, make sure the points close properly, make sure they are clean. If still no luck, keep an eye on this thread, there may be some more suggestions for repairing points. Apparently they are expensive to replace.

Cheers

Nice Job, I have trigger points reading
115 is that to much,and how far apart is your rubbing blocks,from the cam,thanks
Raymond

[Tony H]

The time the trigger points are closed has nothing to do with the pulse length-the ECU calculates that. The trigger point closing triggers the injection event. Also the particular time during the revolution the injector is fired is not critical-as engine speed increases it becomes less and less relevant. What is important is that the ECU gets a strong, clean signal from the trigger points.

[Raymond 77]

Originally Posted by Graham

We have a cold spell coming up so may I will make up the jig and tool I have in mind for adjusting trigger points.

Simple idea really. Remove one half of the point sets (they can be removed by removing the circlip and sliding them out of their mounts.

Make up a plate that will slip over the spindles the points rotate on. Scribe a line on the plate exactly on the centerline of the spindles. Scribe two additional lines parallel with this centerline such that they are the distance we would like the points to be apart. This can be determined from the cam min diameter plus a small amount (to be determined)

Make up a lever tool with a slit at the end that will fit over the fixed part of the points. Slip it on, then bend the point plate so that the fiber slider will line up with the scribed marks. Do same for all 4 points.

Put points back together and recheck opening angle for each set using ohmmeter.

I am pretty sure this can be done. Just need to do it and work out the details!

Once done, points should be good for another 100k miles

Hi I have my trigger points set up at 115 do you think thats ok

Raymond from saint john nb