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Big ignition problem on 93 non-turbo
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Posted by mac (more from mac) on Thu, 26 May 2005 18:57:11 Share Post by Email
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this is a 1993 2.1 liter non-turbo. I've had this thing in the shop for over a month now and they can't get it running right. It originally was idling at a stop light quite nicely, then it went onto one-two cylinders with a horrid mechanical noise. At first I thought the intake cam had broken and the noise was internal pieces destroying themselves. But it was an ignition problem.

The problem is that the dwell, and other scope-viewable characteristics run fine then they go screwy.

Like it'll idle nicely with a dwell of about 60 degrees at 800-900 rpm, then the dwell will jump to 85 and it'll go off song. Like the (I don't know the term) time during which the plug is firing/coil discharging varies from almost nothing to (what I'm told is) about 2X what it should be. Other things as well, things I don't understand well enough to relate them here.

How they've 'splained it to me: there's a good signal to the EZK from the crank sensor, a square wave that looks on scope like what it should. There's a good signal from the EZK, again a square wave that looks like it should, to the amplifier. But at the coil it's all messed up.

I'm not qualified to use a scope (I'm a wrench and bloody-knuckle weekend mechanic-type that tries to avoid this new high-tech stuff) but the firing trace I see on the scope is unevenly spaced horizontally (indicating, I think, considerable variation in the dwell/timing) as well as having an uneven duration (what I'm calling the horizontal distance for each cylinder's trace) which I think indicates that the plugs are not always firing at the proper time relative to the air/fuel charge in the cylinder so that the "explosion" doesn't last as long as it should in some cases and longer than it should in others (consistent with bad dwell control, I suspect), and the voltage peak per cylinder varies...again, I suspect this reflects the basic timing problem, it taking less ommph to fire when the cylinder pressure is lower, again a timing problem.

The shop is a Bosch Service Center, the tech is very experienced with Bosch systems. But now he's grasping at straws.

They've replaced the crank sensor (same result with old and with new replacement), the EZK or ignition "computer" (same result with a new, out of the box unit as with the original and with a used replacement), the ignition amplifier (same result with 2 different new ones as with the "old" one).

The cap/rotor are also new and look/test ok. Wires and plugs test ok. They've run the course on the diagnosis testing described in their ALLTRADE technical data bulletins for this engine. Everything _seems_ to check out ok. But she no run good.

There is a capacitor on the coil. Nothing in the specs talks about such a unit. They take it off, and the engine won't run. So, first question is "what is this thing? Is it an RF noise suppression thing or?" Their ALLTRADE data is silent on this. Anyone have any specs on this thing or is it an add on? (if add on for RF supression, why would it be needed for engine to run?)

They want to know if there is a resistor in the voltage supply to the + side of the coil ... their ALLTRADE data is silent on the matter. With the engine running, the voltage at the + terminal on the coil is about 13v, at the - terminal about 1.3 volts. (they tried feeding 12v to the coil, and are wondering if this might have caused some of what they are seeing, which might be the case if there is supposed to be about a 3v drop to the coil)

Could this be caused by an injection issue? They note that from the EZK unit (or was it the crank sensor?) there's a Y that feeds the ign AND the injection. They've disconnected the injectors cylinder-by-cylinder and the rpm drop is pretty much the same so there's nothing major wrong (?) with the FI.

Any learned suggestions would be appreciated!

Thanks

posted by 67.127.191...
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