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Location: dfw tx
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Question trigger contact dwell on djetronic

i'm about to check my trigger contacts, and i haven't seen it mentioned if there is a "dwell" they should stay open or closed when checking. since there's no way to adjust other than bend the tab, what should i be trying to achieve if i do this?

thanks in advance for your advice.

PD
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Old 09-27-2002, 08:28 AM
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The "dwell" is about one-half of a distributor rotation.

Not much to adjust, they aren't very sensitive to exactly how long they're open and closed like the ignition points are. If they lose tension, or if the cam is worn down, you can re-bend the arms a bit.

--DD
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Old 09-27-2002, 08:44 AM
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Cool

Thanks DD upon closer inspection i see that it's not like a cam lobe but a long ridge then a long valley, lasting about 1/2 a rotation.
I was having the 1 & 4 cylinders drop out at idle. I bent the point tab to make more gap and it seems to have fixed it.

PD
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Old 09-27-2002, 11:04 AM
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The two points control a flip-flop in the ECU. The ECU derives a LOT of information from these pulses - initiation of the circuit that sets the injection pulse width, selection of the injection bank to fire, and derivation the engine speed from the spacing of pulses.

Ideally, they're alternately on/off for exactly 180 degrees. Biggest problem with them is contact "bounce", which causes extra injection pulses and all kinds of bad drivability problems.

If your points are shot to the point where you're having to tweek them, I'd suggest replacing them. You'll probably find that a lot of drivability problems will go away. Check my website for oscilloscope photos of contact trigger point operation.
Old 09-27-2002, 01:30 PM
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I have 5 distributors with the points in them, i'll look for the best set and put them in. i suspect they are too wide right now, but at least it brought #1 and #4 back at idle.

i also found out my mps is bad (leaking vacuum) and replaced it with a spare early 1.7 that i had. I was able to turn the small inner screw out to get good mixture, then adjust the idle on the ecu and it seems good on both counts. Do you think this will suffice till i find the proper mps?

I"m looking to get an exhaust analyzer to check on the settings, but is the o2 sensor trick the best way to get the full load set right

Thanks for your reply and also your website, I"ve spent many hours studying it already.

PD
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Old 09-28-2002, 05:20 PM
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Quote:
Originally posted by hardflex
I have 5 distributors with the points in them, i'll look for the best set and put them in. i suspect they are too wide right now, but at least it brought #1 and #4 back at idle.

i also found out my mps is bad (leaking vacuum) and replaced it with a spare early 1.7 that i had. I was able to turn the small inner screw out to get good mixture, then adjust the idle on the ecu and it seems good on both counts. Do you think this will suffice till i find the proper mps?

I"m looking to get an exhaust analyzer to check on the settings, but is the o2 sensor trick the best way to get the full load set right

Thanks for your reply and also your website, I"ve spent many hours studying it already.

PD
The trigger contact points are identical for all 4-cyl (and some other) D-Jet applications. You can take any of the points you have and use them. Later points incoporate a "splash shield" that shields the points from any points lube being thrown against the contact areas during operation.

I'm guessing you have a 2.0L from the way your worded your use of a 1.7L MPS. The only difference between the 1.7 and 2.0L MPS's is the setting of the full load enrichment. The adjustment you made to the inner screw affects the overall mixture, and any adjustment to this screw without proper calibration tools usually results in problems. Also, if you didn't do the adjustment while a vacuum was pulled on the MPS, it's likely that you changed the setting of the outer adjuster, as it usually is what turns when you do the adjustment on a MPS w/o vacuum on it. This changes the slope of the part to full load transition and results in a different full load setting. Lastly, unless you drilled the full load screw (the big slotted screw in the MPS housing), you likely affected the full load setting, as this screw has to be very carefully set to achieve proper mixture.

I'd suggest that if you want to keep your car and want to have things right for a long time, and keep your injection, that you purchase a new MPS for your car from Pelican. Yes, I know they're insanely expensive, but the rebuilts are not properly calibrated and have drivability issues, and used units are often buggered with or are already leaking or worn nearly to failure.
Old 09-28-2002, 07:38 PM
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I did adjust the unit with the engine running, so i'm hoping I didn't mess it up. It's a 76 2.0L

A new mps unit will have to be for later. I've been bringing back to life 2 914's and a spare 2.0 engine for my other car, a 72 1.7 with 1.8 jugs. and my credit cards are taking a beating :=< the 76 car is due to be garaged for paint in the coming weeks, so i'll wait until it's ready for the road again and evaluate it then.

PD
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Old 09-28-2002, 09:51 PM
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