85 GN Will not set DTC's but flashes code 12

[deus402]

like the title says, i have an 85 Grand National, it idles around 2000 RPM, and the engine bogs down under acceleration. I jumpered pins A and B on the ALDL, it flashes code 12, but no other DTC's were set. I have a mastach ALDL cable, so i decided to fire up WINALDL, so i could at least see what was going on where, but WINALDL doesn't recieve anything off of pin E of the ALDL connector.

at this point i kinda figured the ecm is smoked, but it does flash code 12 when the aldl jumpered, and when you unplug various sensors/engine controls it affects how the car idles... also, if you enter the service mode, it does switch from the fast flash to the slow flash like it's supposed to... but even when i unplug stuff that i know should set a DTC, it will not.the car will only flash dtc 12.

does all this mean that my ecm is smoked? if so can i just get another ecm and put my chip in it? if so is there a list somewhere of witch ecm's will work with my car? any other ideas what is going on here?

[Keller]

First, WINALDL is somewhat of an odd piece of software. More importantly, the 84/85 ECM is an even odder piece of equipment.

There are many reasons a TR might bog: fuel delivery, ignition issues, etc. Anything from a clogged fuel filter, to a weak fuel pump, to a messed up ignition system, to a failing alternator...any of these might cause the issues you describe and never set a trouble code.

Now, the data you collect might tell a story, and help you determine the cause of the issue. Do the WOT MAF numbers look low? Do the O2 numbers at WOT numbers look low? Lots of knock retard?

The ECM can fail on these cars, but not often. I'd want to take a look at the hard data and not the codes (or lack thereof) before calling the ECM bad.

[deus402]

Originally Posted by Keller

I'd want to take a look at the hard data and not the codes (or lack thereof) before calling the ECM bad.

I concur, but there is no data stream coming off the aldl either, so there is nothing to look at.


also, when i unplug stuff that i KNOW should set a code, it doesn't.

[Keller]

That seems very suspect. What items are you unplugging? Are you doing it with the WINALDL connected or not?

[deus402]

winaldl doesn't show any data at all, so i disconnected it. with nothing jumpered/plugged in to the ALDL (i.e. just how you would normally drive it) if i unplug the MAF sensor, the SES light does not come on, and after shutting off the car and jumpering the ALDL it still only displays code 12, when it should be throwing code 34 as well... ( MASS AIR FLOW (MAF) CIRCUIT (LOW / NO SIGNAL) )

i almost wish it wasn't throwing code 12 so i would know for sure that it was the ecm or at least the aldl wiring harness...

but like i said, when i unplug the MAF the idle changes...

also, if i enter the "Field Service Mode" (see attached pic) it _will_ start flashing once per second, which allegedly confirms closed loop operation...

[deus402]

I am almost sure it's the ECM now, i'm going to pull it out and see if there is anything obviously wrong... seems like the "loss of trouble code" symptom is especially relevant...

again, anyone know what vehicles i can pull an ecm out of that will work with my EEPROM?