I swapped out the malfunctioning 8746 ecm in my 89 firebird formula (TBI on late '90's vortec 350 long block and TH700R4 trans)for a 7427 pcm last week finally and have run into a few situations that I wanted to comment on and/or ask questions about. First, I wanted to say that the actual swapping of the pins over to the new connectors was far easier than I expected. It did take a while, but I took my time and this was after putting in about 12 hours at work. I did want to note that I wired one circuit differently than how it was shown on the pin conversion chart. Instead of just moving pin C16 from the old ecm over to pin E13 on the 427, I took the brake switch input going to the TCC on the trans and routed it to pin E13 on the 427 pcm as it would normally be wired. I then simply ran an ignition hot wire to the TCC circuit on the trans connector. Since the TCC is unlocked by the ecm whenever you lift off of the throttle, this really isn't necessary. I had to wire-up the trans after I bought the car as it was originally a manual and was converted to an auto by someone that either didn't know how to or care to wire the trans so that the TCC would operate. I left the trans wiring fairly easily accessible so making the changes weren't difficult.
My first impressions were that the 427 conversion was definitely worth the time and relatively low cost. All driveability aspects are significantly better than the old 746 ecm could deliver. The amount of information available in the datastream makes tuning and monitoring much easier not to mention the datastream is so much faster. The amount of information regarding tuning and the amount of parameters that you can modify also make tuning much easier. I am still having a time finding the "sweet spot" regarding the ignition timing tables, but this morning I loaded the timing map from fast355's bjyl 350 tbi 700r4 bin and it appeared to be pretty good all the way around.
Before I ask a question I will describe my problem and then attempt a solution for the drive home and post the results. I installed the correct 4k knock sensor for the application. I went by the gm parts catalog for a 95 c/k 1500 5.7 vin k with auto trans and used a brand new delco sensor. My problem is that I am getting tons of bogus knock counts beginning right when I crank the engine. I bypassed the esc module by butting the black and white wires together near the module. I have used 2 different pcms and memcals with absolutely no difference. It will register between 200-500 knock counts while cranking to start. From there it will randomly register 25,50,100, or more counts at a time. I know the counts are bogus most of the time because of the counts it registers during startup and it will also register counts while idling. One possible cause I am considering and am going to eliminate is that the sensor wiring runs through the harness across the rear of the engine very close to the distributor and plug wires. I am using universal cut to fit accel spiral core wires and believe that I have some arcing at the cap due to the stainless conductor being pulled through the boots during assembly. My theory is that the wiring is picking up rfi and the pcm is interpreting that as a knock signal. I have a spare set of terminals and boots that I am going to install along with a new cap and rotor, but not tonight as I don't have time. But, I am going to fix the sensor wiring so that it runs straight through the main harness to the pcm and eliminating the loop that passes by the distributor. I was planning on doing that anyway, but was in a hurry to get the car running when I did the swap.
Gotta run for now, but more to come..........
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Originally Posted by dave w
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