*$#@&# 91 z34 code 12

[Jim_Shorts]

Hey guys, my lumina won't start without starting fluid and then will idle rough for a couple of minutes - maybe. I get 40lbs fuel pressure on the rail and i'm showing spark on every wire when i clamp a timing light to them. An online manual i use (alldata.com) says that when i do a scan that I should get a code 12 when the check engine light is on ( I don't get a code 12 after scan using autoxray 6000 ) and that if i get a code 12 after connecting 2 of the termanals together (I do) that its either the ecm or prom chip. ++Does this sound right?? ++ I am getting all the sensor readings, and a couple of codes when its running rough ( usually mat & map ). I dont want to waste more money on a prom for nothing. Thanks

new parts :
ecm
wires
plugs
ignition module
oxegen sensor
crank sensor (not installed - cant reach it heh)

[Schurkey]

Do you have fuel pressure with the key on, engine off?

Seems unreasonable that you need starting fluid to fire the engine if you have fuel pressure, and the engine will continue to run without starting fluid. If it runs without starting fluid, the injectors are obviously firing and you must have fuel pressure. So either you have no fuel pressure KOEO, or the injectors aren't firing when you crank the engine. Very odd.

First guess: No fuel pressure KOEO because of an electrical fault. Perhaps the fuel pump isn't running until you build oil pressure?

[Jim_Shorts]

Hey Schurkey & all
When i turn the key on there is a 3 second hum of the fuel pump every time & there is 40lb's pressure on the rail. When i was able to get engine to run, i checked and there was 38lb's constant fuel pressure. I pulled the upper intake manifold & raised the fuel rail a couple of inches and had sumone crank the engine - I couldnt see any of the injectors spraying. Operational data from a scan says 49.00 ms injector pulse and changes if I get the thing running. One strange reading is catalitic temp = 572 degrees ( i just replaced the oxegen sensor).

P.S.
Should i get a code 12 when scanning this car ? Or just when i ground that diagnostic terminal ?

[Schurkey]

First guess: Your scan tool IS receiving a code 12, which it is interpreting as "no codes found" or whatever it says.

[Jim_Shorts]

Thanks Schurkey,

Common sense goes a long way, I do get a "No Codes Found". I didn't equate that with code 12, saves me $ if i don't need a prom.
Now i just have to figure out why the injectors aren't getting the command or a consistant command to spray. Guess I'll start by trying to make my arm 2" wide an replace that crank sensor.

[richtazz]

Check your ECM and do a "tap test". If your original ECM has GM service # 1227727, the ECM may be the problem. With the car running, gently tap the ECM. If the engine stumbles or dies as you tap the ECM, you found your problem. That particular ECM mentioned above has a MUCH higher failure rate than most GM ECM's, partly due to it being mounted under the hood, and partly due to it's design. Normally, symptoms include random loss of injector pulse, spark and crazy engine temp (-40 deg), etc... Just for reference, when doing the jumper wire test, a code 12 indicates no distributor/spark reference. Since you're doing a key on/engine off test, this has been universally interpreted as a start of the code sequence, but technically, it's telling you there is no spark signal which is normal since the engine isn't running. It doesn't show up on a scanner test, because the scanner knows the engine is off and automatically omits this code to eliminate confusion.

[Jim_Shorts]

Thanks for the info Richtazz

I was getting that wierd -40 degree manifold reading but if your air cleaner sensor isn't connected (which mine wasn't) it also gives that reading. I just replaced the ecm but i did the tap test just to make sure i didn't get a bad one.
What i did figure out is that i can get the engine to run once, when its cold and the battery charger is on high/start. As soon as i turn the battery charger off, the engine quits and wont run again on its own again. The battery is 2 weeks old and the cables look good. I tried starting the car last nite and the battery hardly had a charge. (Also when its running if I try to give it any gas it will stall).

I'm worried that theres a short sumwhere.

[richtazz]

Charge the battery, check the voltage and then leave it unhooked for a time and check the voltage again. IF the voltage drops below 12.8 volts, teh battery is junk. If it passes this test, hook the battery up and let it set the same length of time, and re-check voltage again. If it loses any charge, you have a parasitic draw. You can then unhook the negative cable, put a test light between it and the battery, and if you have a draw, it should dimly illuminate. Start removing fuses one at a time. Any that cause the light to flicker or get dimmer as they are removed is the circuit where the draw is.

[Jim_Shorts]

Thanks richtazz, your worth your weight in gold.

I hooked a test light on the negative side of the battery and it lit up, started pulling fuses and it went out when i pulled the horn fuse. The engine started with help from the charger and then ran on its own for about 4 minutes.
I hooked up a little voltage tester to the battery again and it still showed a draw of about 50 ma (if i'm reading it right) or the same as a 9 volt transister radio battery.
Pulling every fuse and connector i could find didn't stop the current draw. If i pull any more parts off this car to inspect wiring, I may as well do a ground up restoration.

[richtazz]

I will find out for you what an acceptable draw is (I believe it's 5ma, but don't quote me yet). Remember, your ECM and radio both draw a small amount of current even when the vehicle is off for memory purposes.

[richtazz]

acceptable current draw with everything off is less than 25ma. A formula given to me by one of my Grand Prix forum buddies (bnaylor) is to divide the battery's reserve capacity by 4, ex. A 100min reserve capacity battery could hold a maximum 25ma draw without going dead quickly. My original guess at 5ma being normal is close to correct, as the ECM and radio memory draw 3ma and 2ma respectively. I hope this helps you out.