I have a '69 Firebird and recently replace all of the wiring with AAW wire harnesses. I can't get the car to start. Several years ago I replaced the points with an electronic replacement module and when I ordered the engine harness AAW provided me with a pink pigtail to replace certain of the wires at the fuse block and the ignition switch. I get 12.5 volts at the coil when the key is in the "Run" position, but it drops to 9.5 when the starter is cranking. I tested another hot wire and got the same results during cranking. I'm at my wits end, so any ideas worth exploring are appreciated.
Are you sure your starter solenoid is good? I recall the 9.6 volts min at cranking as a magic number so to speak. Normal voltage during cranking should be over 10 volts. Again I'm going on memory here.
Read this from an article and copied for you.
With a properly charged battery. While cranking, check the voltage at the battery terminal of the solenoid switch; it should be at least 9.6V or to manufacturer’s specs. If it is not, check for a voltage drop between the battery and the starter solenoid battery terminal. Clean the battery posts or replace the battery cables. (It is not recommended to repair the battery cable ends; entire cables should be replaced.)
While cranking, check the voltage at the starter terminal. It should also have a minimum of 9.6V. If it does not, remove and clean the cable connections. If cleaning does not cure the problem, starter solenoid is defective…remove and replace. While cranking, perform a “Voltage Drop Test” with the positive probe of digital volt meter on the starter case and negative probe of digital volt meter on battery negative post. If reading exceeds .1 volt, clean or replace battery to engine cable or connection.
Several years ago I replaced the points with an electronic replacement module..... I get 12.5 volts at the coil when the key is in the "Run" position, but it drops to 9.5 when the starter is cranking.
You don't mention whether you've checked for spark or not. Do your plugs spark when cranking or not? If yes, back to basics because you're looking in the wrong place for your problem...this might be a fuel or compression or ignition timing issue. Sounds like your car has been sitting a little while? Is your fuel pump still pumping during cranking? If mechanical, it's common for diaphragms to rip when first cranked after a long sit...which shuts off all fuel flow.
Assume nothing and test everything...which of the 3 is missing: spark, fuel, or compression?
Regardless, you need to do a proper voltage drop test along various runs to see where you're losing it...probing at the coil and getting 12.5 pre-crank and 9.5 while cranking doesn't really tell you much of anything about what or where the problem is. You need to test positive and negative sides of various circuits for true voltage drops while cranking. Tests might reveal undersized cables? Corrosion? Dirty or missing grounds? You're on a resistance search, and it's resistance that ONLY appears during high draw of cranking amps...making ohm meter with weenie 9 volt battery of no value...gotta do your resistance tests with a volt meter instead...properly.
This is a fairly nice video from classroom on how to properly do voltage drop tests...most home mechanics and many techs do these tests entirely wrong...by putting the meter probes in wrong places. Or they interpret the results wrong. Ignore the random chick holding the camera who answers a few questions WRONG when she speaks but is not corrected...just listen to the instructor: http://www.youtube.com/watch?v=_qfaLy-DS3w
The last 60 seconds of this video are where he points out the most common shadetree mechanic error when doing voltage drop tests. The point to drive home here is that the proper way to test for voltage drop is to make darn sure your meter is reading ZERO at the beginning of the test. So if you're saying it's reading 12.5 v before your crank, it means you are simply doing the voltage test wrong because your leads are hooked up in the wrong places. If properly hooked up for a voltage drop test, the meter should be reading zero before you crank. ALWAYS. The amount of voltage drop across an electrical run should read substantially less than 0.5 volts in most places to be considered good, and if you have a resistance problem across a wire run it might read maybe 0.6 to 2.0 or something like that...and this is exactly where your high resistance problem lies during cranking.
I have a '69 Firebird and recently replace all of the wiring with AAW wire harnesses. I can't get the car to start. Several years ago I replaced the points with an electronic replacement module and when I ordered the engine harness AAW provided me with a pink pigtail to replace certain of the wires at the fuse block and the ignition switch. I get 12.5 volts at the coil when the key is in the "Run" position, but it drops to 9.5 when the starter is cranking. I tested another hot wire and got the same results during cranking. I'm at my wits end, so any ideas worth exploring are appreciated.
Do you have a wire from the solenoid to the coil? This is what I found on the net.
Quote:
The starter relay has four posts: * large post on the bottom for the heavy cable from the battery switch * large post at the top for the heavy cable to the starter * post labeled "S" on the left for wire to the ignition switch's "S" post * post on the right labeled "I"
Connect a 12 gauge marine wire from the "I" post on relay to the + post on the coil. That will deliver a full 12 volts to the coil while cranking. If you give Kurt a chance he is likely to post up a photo of the relay.
You really only need to do this if you have the points type distributor with the resistor. Although, even without the resistor, you'll get still more voltage at the coil since the new wire run is short compared to the wire from the ignition switch - less distance means less voltage drop. Using a voltage drop calculator, 10 amps @ 12 V dc, 20 foot #10 wire = 6.7% voltage drop = 11.2 volts at the coil; versus a 3 foot run loses 1% = 11.9 volts at the coil.
Assumption is correct. The starter seems to turn just fine, but I get no fire. Fuel pump is working, fuel is getting to carburetor. I even primed it before firing, but no luck.
Good point about checking for spark. I was testing the voltage at the pink wire to the coil and because of the drop I assumed (for no good reason) that the drop would mean no spark, but I know better. I will definitely do that. As I noted elsewhere the car ran before the harness replacement just a couple of months ago, and I know fuel is getting to the carburetor.
You've given me several additional ideas to consider and thanks for the video referral. I've seen others on the same topic, but this one seems pretty good.
Just remember when dealing with the whole S & I terminal thing at the solenoid, and the yellow wire delivering full voltage from solenoid to coil during cranking, etc...most likely much of that was bypassed/abandoned and/or possibly cut out and/or rewired somehow when your points were removed in favor of the new electronic ignition module. Because that whole system from the solenoid becomes largely unnecessary (but as stated, COULD still have value to get you more voltage during cranking...might want to re-attach it if it has been disconnected and capped). Now that your correct factory resistance wire likely has been replaced or bypassed...which is indicated by the fact that you're claiming 12.5 V at coil with ignition on and not cranking. This high of a reading would simply not happen if you still had ballast resistor wire in place. With factory points system this number should be somewhere in the 7 to 9 volt range (ign on, not cranking), and it should be nowhere near 12.5, which would destroy your points very quickly, but is OK for a Pertronix or similar module, which permits removal of ballast resistance wire.
Your car has clearly been rewired...twice. Once when your electronic module was installed, and again now that you've replaced this harness. So you have a one-off custom wiring system now...and conventional troubleshooting rules and wiring diagrams for 69 Firebird might no longer apply in certain areas.
Update for anyone interested. After everyone's great suggestions I started at the battery and worked my way back. I found the problem at the distributor. Apparently, the combination of my PerTronix Ignitor points replacement module and MSD Blaster II coil was incorrect and when I tried to start the car for the first time I fried the Ignitor. The coil is .8 ohm resistance but the Ignitor needs 1.5. I guess the combination of the coil and either a resistance wire in the old wiring harness or the jumbled tangle of wires the previous owner had cobbled together created enough resistance to work prior to my engine harness replacement. I replace the Ignitor with an Ignitor II and all is well.
Now on to the exhaust system replacement, disk brake conversion and front suspension upgrade, in that order.
