HallenTi
Well-known member
I have had several problems with my 1990 coupe over the years, and am wondering if replacing the MEMCAL might be the answer.
The one problem that I am sure could be corrected by the replacement is the knock sensor. The Helm Chevrolet repair manual I have points to the MEMCAL as the culprit when I do the diagnostics for it. I have the proper voltage at the wire at the knock sensor, and the proper resistance range when checking the knock sensor itself. The diagnostic says if this is the case I have a faulty MEMCAL. I would like the knock sensor system to work properly, so I may set the timing properly and have the system function as designed. I have also done the diagnositc where you rap on the engine while it runs and watch the timing, and there is no change in the timing.
Another problem I have is cold-drivability. It "hesitates" somewhat when cold, requiring some "babying" until warm. I have tested the MAP sensor voltage at ambient and under vacuum, TPS voltage at closed (.54v) and WOT positions (5v), both the MAT and the coolant temp at 32 degrees and 212 degrees, and all appear to be withing the specs. When warm, this hesitation doesn't exist. I have also replaced the O2 sensor, however, I know that when runing cold, the ECM does not take the O2 reading into account, but it had many miles on it and was an inexpensive change. Are there other sensors I have missed that are used during cold operation?
The wires, cap and rotor are new, and the wires properly routed and clean. The plugs are also new (Bosch platinum) and gapped to specs. I have used techron fuel injector cleaner recently as well - double dose. I can't find anything (at least on my own given my limited diagnostic capabilities), and not certain that with the ODB I system the 1990 has, whether a shop can "read" the various sensors with any more success than I can with a DVM as they more eaily could on an OBD II system in later years). Those that have had similar problems, or that have had success or failure from either the Chevrolet dealer or independant shops with "diagnostioc testing" I'd like to hear from you. I wouldn't mind spending some money for a thorough diagnosis if available. Thanks in advance, Tim
The one problem that I am sure could be corrected by the replacement is the knock sensor. The Helm Chevrolet repair manual I have points to the MEMCAL as the culprit when I do the diagnostics for it. I have the proper voltage at the wire at the knock sensor, and the proper resistance range when checking the knock sensor itself. The diagnostic says if this is the case I have a faulty MEMCAL. I would like the knock sensor system to work properly, so I may set the timing properly and have the system function as designed. I have also done the diagnositc where you rap on the engine while it runs and watch the timing, and there is no change in the timing.
Another problem I have is cold-drivability. It "hesitates" somewhat when cold, requiring some "babying" until warm. I have tested the MAP sensor voltage at ambient and under vacuum, TPS voltage at closed (.54v) and WOT positions (5v), both the MAT and the coolant temp at 32 degrees and 212 degrees, and all appear to be withing the specs. When warm, this hesitation doesn't exist. I have also replaced the O2 sensor, however, I know that when runing cold, the ECM does not take the O2 reading into account, but it had many miles on it and was an inexpensive change. Are there other sensors I have missed that are used during cold operation?
The wires, cap and rotor are new, and the wires properly routed and clean. The plugs are also new (Bosch platinum) and gapped to specs. I have used techron fuel injector cleaner recently as well - double dose. I can't find anything (at least on my own given my limited diagnostic capabilities), and not certain that with the ODB I system the 1990 has, whether a shop can "read" the various sensors with any more success than I can with a DVM as they more eaily could on an OBD II system in later years). Those that have had similar problems, or that have had success or failure from either the Chevrolet dealer or independant shops with "diagnostioc testing" I'd like to hear from you. I wouldn't mind spending some money for a thorough diagnosis if available. Thanks in advance, Tim