I was just finished replacing an O2 sensor that had 225,000 miles on it, and the original ignition coil, and I was under the hood marveling at how smooth my engine was running. Then all of a sudden the electric fan kicked on, and the engine surged and threatened to die. It leveled off again a few seconds later and seemed to run fine.

This isn't a big deal, but I would like to know what might be causing this, so if anyone has any ideas how to fix this problem I would be very grateful for your advice. It charges fine according to my DV/OM, and I'm not really sure what else might be causing the issue. This poor car seems to have a lot of electrical gremlins, I have replaced almost all of the engine mounted sensors, as well as a number of other electrical components. So most everything electrical is new... or new to the car anyway. But I figure at some point I'm going to end up replacing everything and it will basically be a new car... hahaha.

 

What year and model?

Do you see the battery voltage drop at the coil when it kicks on?

 

Oh right, sorry. Its a 1993 940 Turbo Sedan. 250,000 miles. I haven't checked whether or not the voltage drops at the coil when it kicks on, lets assume it does drop, because as far as I can figure, it must be a drop in available power causing the engine to surge when the fan kicks on. So, assuming that it does drop, what is your diagnosis?

 

I would start by cleaning both ends of your battery cables.

 

Both the cables and the battery were recently replaced. as well as the plugs, plug wires, distributor, coil and o2 sensor.

 

It's a trap, RUN!

 

You say "surged" but I think you mean the opposite since it almost died... Anyway, I'd say this is normal to a point... That fan draws a lot of current and this affects the RPM momentarily until the computer kicks the idle back up.

 

Its not a trap, its a Volvo. An old *** Volvo. One that has served me well for a long time and has sentimental value.

 

Yes, I meant that it shudders, not surges. I was thinking that it was probably worn components in the fan that were drawing more current than normal as the fan turns on.

 

Quick question, does anyone know what type/brand/viscosity of fluid to put in my differential?

 

75w90

 

Thanks for the info.

Honestly, I don't think the car is trying to lure me in so that it can kill me with the fan or anything. Its just misunderstood. But next time it does some **** like that me and the car are going straight to the field be3hind my house and I'm putting a bullet right between its eyes. Once a Volvo gets a taste of human blood, its best to just put it down.