Date: Mon, 05 Sep 2005 10:53:57 -0400 From: ma_twain <ma_twainnospamo.com> Subject: Re: SAAB Quality Since GM?
Johannes wrote: > > Pooh Bear wrote: > >>Johannes wrote: >> >> >>>Pooh Bear wrote: >>> >>>>mattleibovitchnospaml.com wrote: >>>> >>>> >>>>>I agree. The DIC shouldn't even be a replacement item. GM's various >>>>>distributorless ignition setups (since 1984) have proven to be pretty >>>>>much trouble free and will last "forever" much like any other >>>>>solid-state electronics. Why is Saab's version so very different? >>>>> >>>>Because the're too much clever electronics is in that DI cassette ? >>>> >>>>As an electronics designer, I'd like to know what the typical failure >>>>mode(s) is (are). I'll bet there's something(s) straighforward that's >>>>fixable by design. >>>> >>>>Graham >>>> >>>The failure is related to the heat and lack of cooling possibilities when >>>mounted on top of the engine. I took mine apart, the insulation in one of >>>the coils had burned through, I guess it short circuited. >>> >>>It also help if you diagnose any overheating problem immediately, i.e. >>>don't drive round with the temperature gauge at 3/4 mark. It must always >>>be at a healthy 1/2 mark. >>> >>You reckon it's just heat ? Obviously that came to mind. Electronics can take >>some pretty serious heat as long as it's actually purpose designed to do so. >>Silicon semiconductors have a top limit on operating temp of 200 C. >>Integrated circuits rather less. Varies with complexity but up to 125C. >> >>Graham >> > > It's the copper windings in the coils, not the Silicon. I don't think there > are any semiconductors in the DI itself, all the electronics is done before > the DI and it's supplied with 400 Volts at the plug end. This reduces the > size of coils necessary so that they will fit into the confined space. But > extra heat combined with the vibrations will rub on the insulation material > in the long run and may short circuit a coil. Once short circuited, the > increased current will burn the coils. To prevent this, keep the engine cool. > If the engine temperature rises above normal while driving on a hot day in > city, then switch off the ACC and bear the heat. > Actually, I found the reverse with the AC. When you turn on the AC, the axuillary electric cooling fans come on. This helps cool the engine. Try this and see if it is true in your Saab. The best for the engine would be to rig a separate switch so you can turn on just the electric cooling fans without running the AC compressor.
 |
 |
 |
 |
 |
