If the crank sensor is worn or damaged from the previous balancer episode, it MUST be replaced (maybe you have a spare?). A damaged crank pickup sends bad signals to the ICM. The signal from the crank sensor is used by the icm to determine when to trigger the next ignition coil. The cam signal (ecm pin A11, icm pin J) (25` after piston #1/4 reaches top dead center) starts the firing sequence on the #3/6 coil (as well as times the sfi on this motor). The icm processes the crank signal into the reference signals at pin B5 and B3 on the ecm. At ~400rpm the ecm applies 5 volts to circuit 424 (ecm pin D5, icm pin B) to switch the spark timing control from the icm to the ecm. An open or grounded by-pass circuit will set code 42 and the engine will run on icm timing.
EST circuit 423 (ecm pin B4, icm pin A) open or grounded will also set code 42.
If you are getting an intermittant code 42, based on what the flow chart says in my CSM you have an intermittant open ckt 424. That is pin B at the ICM and pin D5 at the ECM. The wire may be broke, but it's more likely that the connector is a piece of crap on the ICM side (it may have oxydation deposites or have a bad sping inside on the wire-side contact). With a tiny screwdriver the connector can be disassembled, cleaned and re-sprung, this will usually fix connector issues (use di-electric grease to prevent future oxydation). An open ckt 424
shouldn't effect startup quality, but will adversely effect performance and economy.
Now for the crank sensor, it's a hall effect switch. Damage to the sensor or interupts could cause early or late switching. It's normal for the gap on the inside of the vane to be narrower at the top and bottom, and the gap on the outside of the vane to be narrow in the middle section, as long as the sensor does not contact the interupts. At least the one on this motor is like this because the curve of the vanes doesn't exactly match the curve on the sensor pickups.
(cue the crappy not to scale exaggerated graphic to illustrate the previous statement)
|.---|.\\...|----|
|----|...\\.|----|
|~---|...||.|----|
|----|...//.|----|
|.---|.//...|----|
If it's not the crank sensor........ :(
I had a similar hard starting condition that was caused by the timing chain having jumped. The original '86 vin 3 has a nylon camshaft sprocket and I believe (I'm not 100% sure because I've seen both nylon and metal sprockets in the junkyards on them) the nylon was used in '87 as well. It had begun taking progressively longer and longer for our car to start over a few months, during which time the computer threw code 41 (related to loss of cam signal) and occationally code 42, so we had replaced the computer, ICM, and a few other ignition parts only to see the problems get worse or alleviate for a few starts. The car ran rough and also had problems dying at stop lights and when starting from stops, when cruising and suddenly taking your foot off the gas, completely randomly, etc..
If you have over 100k miles and never changed the timing chain check to see if it jumped. If it has a nylon cam sprocket then the teeth tend to break off over time and fall into the oil pan... The last time I replaced a timing chain on my '86 I got the timing set for $26 and the gaskets set for $45.
One faster way to tell if you have the nylon sprocket problem (although you can't check the alignment) is to drop the oil pan and check for nylon rubble in the pan or the pump strainer, and shine a light up the timing chain cover and see if the sprocket at the top has broken teeth AND check to see if there is any play/slippage between the crank and cam sprockets AND make sure the timing chain damper isn't broken (the chain should be pretty tight without much play)... I know it's a tight fit and difficult to see without pulling the timing cover but it can be done. The downside to checking this way is that even if nothing is wrong you'll still have to change your oil and put a new gasket on the pan if it doesn't have a re-usable one.
If you do still have the original nylon cam sprocket and over 100k miles you are saving yourself a future headache by replacing it now because if enough of the teeth break off on the nylon sprocket the valve train will crash into the pistons, pretty much junking the motor unless you get lucky like I did where it jumped 1 tooth. Normal metal sprockets won't have that problem unless the chain stretches enough and the damper breaks. In both cases, a broken damper can cause the chain to jump.
I have the chassis service manual for the '86 vin 3 in case you wondered how I knew all the technical stuff
). I do not remember which lead is which, but one is ground, another is the supply and the third is the feedback to the ECM. You want to read between the feedback and the ground when checking the voltages and have the key in the run position.
