Causes for ECM Code 21 Ignition Malfunction

Edge · 11-02-2008, 10:06 AM

The ECM threw code 21 for ignition system malfunction. There are no drivability problems except that fuel mileage looks like it may be lower. (I haven't calculated it yet, I am just going by the mileage and previous gauge position. ) The power transistor fails the continuity test. Power and ground look ok to the ignition module. The manual calls for a logic tester to test the ignition signal to the ECM which I don't have. Is this possible to have a bad ignition power transistor without any drivability problems or can there be another cause for the code 21?

speedshot · 11-06-2008, 06:03 PM

If yours is still running be glad! My '85 is giving me the same code but it won't start (no spark at all). I changed distributors, coil and the plugs and wires were fine. It all happened after I (on the advice of others!) changed the timing belt. It sounds like it is spinning over a little bit faster, but when I pulled it through by hand it felt like it had great compression. Can you mess up the ignition timing by mistiming the front cam? I can turn the distributor by hand (as per the Haynes) and it sounds like the injectors are firing (?). The voltages don't match the manual (never drops totally to zero) It's got about 180K on it and I want it to live! Any help would be seriously appreciated!

vernk · 11-06-2008, 06:33 PM

Quote:

Originally Posted by Edge

The ECM threw code 21 for ignition system malfunction. There are no drivability problems except that fuel mileage looks like it may be lower. (I haven't calculated it yet, I am just going by the mileage and previous gauge position. ) The power transistor fails the continuity test. Power and ground look ok to the ignition module. The manual calls for a logic tester to test the ignition signal to the ECM which I don't have. Is this possible to have a bad ignition power transistor without any drivability problems or can there be another cause for the code 21?

have you changed cap and rotor plugs and wires lately (not really sure if that would or not), other then that I would say replace anything that fails testing

Quote:

Originally Posted by speedshot

If yours is still running be glad! My '85 is giving me the same code but it won't start (no spark at all). I changed distributors, coil and the plugs and wires were fine. It all happened after I (on the advice of others!) changed the timing belt. It sounds like it is spinning over a little bit faster, but when I pulled it through by hand it felt like it had great compression. Can you mess up the ignition timing by mistiming the front cam? I can turn the distributor by hand (as per the Haynes) and it sounds like the injectors are firing (?). The voltages don't match the manual (never drops totally to zero) It's got about 180K on it and I want it to live! Any help would be seriously appreciated!

yes the distributor runs off the front cam, if you have no spark at all double check your wiring make sure connections are made and are clean. check and see if the coil is firing (pull the coil wire going to the cap) and see if that is firing if that is make sure all plug wires are on tight, and in the right order, if there is a chance your cam timing is off fix that first. I don't have my FSM on me right now but if you need me to look though it let me know.

speedshot · 11-06-2008, 06:55 PM

Thanks for the reply! I will re-check everything. I know I was getting 12 volts at the coil, but the wierd numbers when I was probing for voltage at the distributor harness had me curious. Is it supposed to drop completely to zero? If so, I might have a ground issue. When I did the belt I tried very hard to be sure it was all re-connected right ( I really didn't want to disassemble the front case again) but anything is possible. It's just going to be one of those hunt and search missions. I hate wiring problems! Thanks again!

Edge · 11-06-2008, 07:22 PM

Quote:

Originally Posted by speedshot

If yours is still running be glad! My '85 is giving me the same code but it won't start (no spark at all). I changed distributors, coil and the plugs and wires were fine. It all happened after I (on the advice of others!) changed the timing belt. It sounds like it is spinning over a little bit faster, but when I pulled it through by hand it felt like it had great compression. Can you mess up the ignition timing by mistiming the front cam? I can turn the distributor by hand (as per the Haynes) and it sounds like the injectors are firing (?). The voltages don't match the manual (never drops totally to zero) It's got about 180K on it and I want it to live! Any help would be seriously appreciated!

It sounds like something happened with the connections after the timing belt as stated in the above post, so it's good advice to check all the connectors . Look closely at the coil wire, that has a cover over it and may not look like it is disconnect. You might also check the power transistor. Check/clean the ground points on the wiring harness around the front cylinder bank and also near the coil and power transistor. See link for additional info http://www.autocarepronews.com/defau...=art&id=83958&

speedshot · 11-07-2008, 04:27 PM

Thanks Edge,

I'll re-check all the connections. On that link it seemed to indicate that the voltage should drop to zero (which it does not) it just fluctuates a bit. The possibility of a bad ground sounds dead on (no pun...). Did I mention I hate wiring issues?

Spedshot

*CapedCadaver* · 11-07-2008, 08:27 PM

code 21 is the primary ignition circuit. ie, the power transistor, resistor/condensor pack, and ecu-PTransistor wiring. the secondary ignition is the coil output, plug wires, distributor cap, rotor, and spark plugs. basically pre- or post- voltage increase.

changing plugs, wires, and all that crap WILL NOT fix a code 21. we had a code 21 on my friend's 89 (3rd gen, but still an EFI VG30E) and it ended up being, of all things, a loose ECU harness.

speedshot · 11-09-2008, 03:08 PM

here are the voltage numbers I got after testing:

at the harness entering the distributor black and white wire 11 volts
green and white wire 5 volts
green wire 4.97 volts
black wire .03 volts

harness entering the power transistor small blue wire .08 volts
big blue wire .03-.04
lack and white wire 11.78
black wire .01

at the harness entering coil black and white wire 11.81
pair of blue wires .03

when I checked the distibutor by hand spinning (by the Haynes and the link previously provided) I got:
green wire 2.61-4.95
red wire 11.00
black wire .00
black and white wire .00

The testing was done after the battery had been used for a while (might be why I'm getting under 12 volts in part of test). Also, as I was spinning the distributor the fuel pump was cycling on and off which also drew down the battery. The self diagnostic is still indicating code 21 and now 13 (chts). I know this is a lot of numbers, but it might give you an indication of where I'm at. The distributor I used was the original from the car. I have a second one in the car now and, as best I recall, I was getting similar numbers from it. I hope you can noodle something out from this. My wife wants to throw this one away, too!

Thanks
Speedshot

speedshot · 11-12-2008, 04:30 PM

It would appear that when I was testing the distributor, and apparently letting the injectors fire away, I might have a hydrostatic lock situation.
I'm going to have to pull a wheel to get to the damper bolt and turn it over by hand. Rapture and joy! If it's not one thing, it's three.

speedshot · 11-20-2008, 06:56 PM

vernk, quick note if your availaible. can I check fro spark with the second distributor (just attached to the harness?) to see if the connections are working? with the voltages I got, I'm hoping the wiring is good but somewhere the timing is off.

vernk · 11-20-2008, 07:13 PM

u might be able to do that your injectors will still fire unless you pull the fuse for the fuel pump and you would have to spin the distributor by hand and be careful you don't get shocked. If I get what you mean is you want to hook up a distributor thats not bolted into the block and spin it to see if the coil is doing it's job? be sure that the ground wire is grounded.

or what I do is pull the wire of the distributor that comes from the coil and set it on top of the intake so that you can see it from the drivers seat (if you have no one to help) by looking just under the hood and turn the engine over best if done at night

speedshot · 11-20-2008, 07:52 PM

Thank you very much! That's what I'm trying to do (once I get it defrosted) There are a couple of other things I have to check, but this will get me closer. I'm fairly certain the valve timing is on, but not as sure about the ignition. Thanks again!

vernk · 11-21-2008, 01:06 PM

you should be able to somewhat check the valve timing by pulling the valve cover and the spark plug and turn the engine over by hand till it's at TDC and watch the the lobe on the cam

Edge · 02-02-2009, 10:18 AM

Quote:

Originally Posted by speedshot

Thank you very much! That's what I'm trying to do (once I get it defrosted) There are a couple of other things I have to check, but this will get me closer. I'm fairly certain the valve timing is on, but not as sure about the ignition. Thanks again!

How are you doing? Did you ever get the code 21 fixed and the car running? I still have a code 21.