A number of froggers have mentioned driveability problems on the odd occasion. I was having a troll around and found a site with some interesting injection Q&A. One that I found particularly interesting, though, was this. I assume it could apply to any car with hydraulic lifters, so I thought I'd post it as a warning about using the incorrect oil viscosity...



Had some doozey problems recently that involved Magna TS, Subaru Liberty, Mazda MX6, VW Transporter. The complaints centred on driveability problems - unstable low engine rpm, stalling, rough idle, no initial power, hard starting. In all cases the systems were thoroughly tested for correct input signals, fuel pressure & delivery checked, etc. No codes were recorded so that meant no short cuts. Eventually in each case it was a matter of sitting down and looking at the facts. Determine first what actually was causing the instability - it could only be fuel, spark or mechanical. The ignition pattern was perfect, timing spot on, plugs good - they were nice and clean (that indicated they were burning and on the lean side). The injector "on" time did not alter, making richer/leaner had no affect on the stumble. Therefore it was not an engine management problem. It had to be mechanical and yet the engines all performed well under aggressive driving. It had to be a burn problem - suck, puff, bang or blow. The gas analyser kept indicating that these engines were all carrying too much oxygen in the exhaust, yet they were not excessively lean - as revs came up the oxygen dropped. We had to have a problem with valves/timing. Further investigation revealed the lifters/lash adjusters were pumping up under these conditions. A leisurely engine flush and change onto the CORRECT grade of oil, in all these cases fixed the problem. Be aware of oils - many manufacturers specify 10w/30w oils not 20/50. Be aware of service interval history. The moment these things slip past their scheduled service period - it's only a few thousand overdue - the more the contaminated and thickened oil is going to cause lifter type problems especially at low engine rpm.