1993 Corolla Dirty CMP signal

[Hildy]

Long time no talk! How have you all been, good i hope!

Anyways, here we go. We have a 1993 corolla in the shop with a 1.8 (7A-FE) motor, auto. Cust was complaining of intermittent no starts (very intermittent) usually after a short (5-10 min) stop after a long drive. We had it in the shop several time for days on end and couldnt get the thing to quit. Finally one day it quit in a parking lot near my shop so i loaded up my bag of goodies and went to check it out. No Spark!, Great, but before i could do any other tests she flashed right up, Damn!. Scanned once it got back to the shop, had code 12, NO CMP SIG. WHILE CRANKING. So i hooked up to both my CMP, and CKP signals (both in the distributor) and checked out my signals, the CKP was great, but the cmp was very dirty and glitchy. Couldnt get the thing to die, so we recommended a distributor to the customer, letting him know it was mostly an educated guess (yeah i know), as i have replaced many of these for this same code and problem. Got the new one in there, and waddya know, same glitchy signal. Now here are a couple things i never noticed before, that i somehow caught in my hours of headscratching after.

1. The glitch (by glitch i mean a single straight up and down line going to about +5/-5v at an idle) happens exactly 4 times per engine revolution, once riding on the cmp (1x) waveform, and 3 more times after

2. The cmp waveform is not coming all the way to ground (neither is the ckp but its waveform is beautiful)

3. KOEO, the cmp+ wire has .70v at all times

4. Have done voltage drops on all grounds at ecm, checked all grounds under hood, ran my own ground to distributor housing

5. Alternator diodes good

6. If the coil is disconnected at the distributor, the signal cleans up.

7. The coil signal at the IG- terminal in the dlc has a brutal voltage spike of over 100v, and again does not reach ground fully

I have some more info as well, it will come to me, but LOST is on right now as well, thanks in advance guys,

Jason

[crackerclicker]

hello hildy, could you post some screen shots? the spikes or glitches that you're talking about would be good to see. depending on your ground ref the g (cam) and ne (crank) signals may not sit on the ground line of the scope. the ig- terminal should have the 100v spike because you are measuring primary volts. that is the "primary inductive kick" you are seeing. when you say the g signal cleans up when you disconnect the coil makes me wonder if there is some secondary leakage, but you would see more than +/- 5 volts in that case. some screens of what you are seeing would be worth a thousand words in this case . also, if you have the time, scope igt and igf with a secondary or injector trigger and post what you find.

[Hildy]

Hey man, thanks for the reply, the top one is the cmp signal, and this one is at the IG- in the dlc. We had a new distributor coming as the original new one that we put in showed signs of previous install, with the 2nd new distributor the glitches are about half as bad, but still there as you see in the first pic. The car seems to actually be running fine, and the no start issue seems to be gone completely, but this pattern still bothers me, and i would love to put this one at rest. We put new wires and plugs in as well, as i found some pretty decent carbon tracking on the plugs. This took care of the ever so slight stumble it had. Hope these pics are visible, first time i have ever saved anything off of the modis, kind of a pain to get it onto the usb drive, has a hard time recognizing it, anyways guys, thanks in advance!

[crackerclicker]

yeah, i know what you mean about saving imagaes with the modis. i had difficulties with the usb, so i just got a cf card for it. much easier with the cf. the cam signal looks ok to me. those small bumps are most likely noise, and nothing to worry about. the ig- wave doesn't look right, but that may just be because of the 200ms timebase (20ms/div). if this car gives you any more trouble, scope the igt and igf with a secondary and injector on the other two channels.

[greasybob]

I'm not to familiar with the Corolla but I noticed a simular ignition pattern on a Subaru I was recently working on. I included what I caught on the scope below along with my explanation for what I saw, though I'm not sure if it is correct. It would be interesting if you could current ramp the coil at the same time. I figured the ignitor to be at fault for not holding the voltage down during coil saturation. As for what you see on the cam signal I'm pretty sure it's voltage from the coil leaking onto the signal as it shows up 4 times every cycle. Is this an aftermarket distributor? Where is the ignitor located on the Corolla? I also included what I consider a normal ignition pattern which I took from a Neon.

[Hildy]

Hey guys!, the car is gone, and hopefully trouble free, kept it for 3 days, test drove whenever i had a spare minute, all seemed good. As far as those glitches, they weren't that small until the 2nd distributor was put in, and yes it was an aftermarket one. Initially those glitches were so bad at idle i couldn't get my trigger to catch anything but the glitch, it was peaking to the same voltages as the signal (at idle), when i would rev the engine, the signal became stronger, and the glitch stayed the same as at idle, so i could then see the the cmp waveform. If it does come back i will grab some screens of the igt, and igf, but for now it is gone. Also i cant imagine that those glitches would cause a complete no start with a code 12 "No CMP Sig While cranking". I could see a hard start/stumble/misfire. The crappy thing was this car would never die on us at the shop, and the customer was pushing for a fix, which is understandable. Anyhow, Thanks to you all so much for the help and tips/suggestions, every job I do, and all this community help sure goes a long way to help you make a good, CONFIDENT, diagnosis. I remembered the day when i was scared to condemn a regular old TPS! Now I'm pretty much the only tech in the shop for electronic diagnosis, but Im still under experienced, (Mechanic for 10 years, a tech for maybe the last 4 or 5 HA), so what i'm trying to say is that your guys' help goes a long way here on the west coast, have a good weekend all!

[Hildy]

I'm not to familiar with the Corolla but I noticed a simular ignition pattern on a Subaru I was recently working on. I included what I caught on the scope below along with my explanation for what I saw, though I'm not sure if it is correct. It would be interesting if you could current ramp the coil at the same time. I figured the ignitor to be at fault for not holding the voltage down during coil saturation. As for what you see on the cam signal I'm pretty sure it's voltage from the coil leaking onto the signal as it shows up 4 times every cycle. Is this an aftermarket distributor? Where is the ignitor located on the Corolla? I also included what I consider a normal ignition pattern which I took from a Neon.

Sorry and to answer your questions it was aftermarket, and the ignitor is in the distributor assembly along with the coil, so they have both been replaced twice. For the coil pattern i originally thought bad ground as well, so i ran ground straight to the distributor base just in case ( in the diagrams available to me it looked like the ignitor grounded through the distributor), and that didn't change anything. Then i checked all ecm grounds, and all engine grounds, repairing a corroded ground just in case, but all were acceptable voltage drop. This one was a pickle froster for me for sure lol!

[crackerclicker]

hey hildy, if you're a sucker for scope diagnostics (me too!) try this forum: http://www.autonerdz.com/cgi/yabb2/YaBB.pl
it is set up by THE pico scope man here in the u.s., but all are welcome. there are some really good posts there. i've seen a lot of familiar faces (names) from this forum on there.

[Hildy]

hey hildy, if you're a sucker for scope diagnostics (me too!) try this forum: http://www.autonerdz.com/cgi/yabb2/YaBB.pl
it is set up by THE pico scope man here in the u.s., but all are welcome. there are some really good posts there. i've seen a lot of familiar faces (names) from this forum on there.

Thanks alot man, appreciate it!. I'm a sucker for sure, just not a very experienced one