'85 240 woes...

I'm having issues with my Volvo, and I can't quite figure them out.
Maybe someone can help?

When I'm accellerating (or when I'm not), it feels as if something's
pulling back on the car, or like it's not getting fuel for just a
second. Almost like if you were running, but someone had a string
tied around your waist and jerked on it every so often, causing you to
slow down but not stop completely.

The impulse generator went bad, we replaced that. We changed out all
of the spark plugs and wires (it was time for a tune up), and the
battery connection is fine. I don't think it's electrical.

We went through the fuel system; we checked the line, the fuel
filters, the pumps, the fuel pump relay, and all the wiring - it's all
good. I can't really figure out what it might be.

Anyone got any ideas?

 

As weird as it sounds, have you checked the gas cap? If the vent
fails, the evaporative control system will pull a vacuum on the tank
which the pump has to work against. Easy check: when the car is
behaving this way, shut it off and open the gas cap. If you hear a
sudden in-rush of air, that's your problem.
I wouldn't rule out electrical though. Be sure to check ALL the ground
wires to the block, especially the braided wire from the last bolt on
the valve cover to the firewall, since a loose ground can cause a
voltage error across sensors or even cause the injectors not to open.
Also check the wiring harness at the firewall...sadly '85 is one of the
years with the infamous GM-sourced wiring harnesses that have a nasty
habit of crumbling when they get older.

Bill

 

It's almost always the wiring harness that causes this, usually the coolant
temp sensor or air mass meter wiring shorts to something else and the ECU
thinks the engine is either colder or hotter than it is, making the mixture
much richer or leaner than it should be but it's worth replacing the vacuum
lines too.