Bouncing speedo and weird oil pressure.

[BruceKoukalaka]

I just picked up a 1999 Explorer Sport for my wife and as I was driving it home the speedometer started bouncing from 80 to 110 KPH and the oil pressure dropped to below the low mark on the gauge. there were no oddball sounds coming from the engine but the whole scene was a bit nerve wracking to say the least. The truck has just over 164,000 Km or 100,000 miles and it sat for a few years according to the person I bought it from (it was an estate sale) So I'm wondering if the cluster might be going south or if there may be other things I should be looking at.

 

[koda2000]

The bouncing speedo might be a bad VSS (vehicle speed sensor) which I believe is located on top of the rear differential on a '99. Easy to replace, one bolt and wiggle it out.

As far as the oil pressure, these vehicles do not have a true oil pressure gauge/pressure sensor. Instead they have an oil pressure switch which will keep the needle of the gauge in the center as long as you have at least 5 PSI of oil pressure. It could be you have a bad switch or (as the vehicle sat for a long time) sludge blocking the oil pickup in the oil pan.

If you have the SOHC V6 engine, I suggest you remove the lower oil pan and see if it's full of sludge. If so clean it out and also remove and clean the oil pickup screen. If it's a SOHC V6 you may also find broken pieces of tan plastic in the oil pan. This would indicate broken timing chain guides.

 

[BruceKoukalaka]

Thanks for the reply,I'll be checking into the oil sending switch and the VSS as soon as I get it to work.