1993 960 Really poor fuel economy

[Kappy5003]

Recently I started using my 960 even though it needs a replacement rear main seal.

I live in regional Western Australia and many months ago while working in the city I noticed my fuel economy was a tad poor, twice I had the check engine light come when the fuel was low.

When I checked the codes what popped up was front o2 sensor, I cleared the codes and the same code has not returned, however the fuel economy has plummeted eg.worse than 13mpg. Also tail pipe is very black.

I also notice slight miss at idle and sometimes I can feel it in normal driving.

My question is can the O2 sensor be faulty and not throw up codes, I guess a faulty O2 sensor could affect economy.

Or what other sensor can be faulty that doesn't throw code and can affect economy and is there a way of testing sensors.

Cheers
in advance.

[93Regina]

My question is can the O2 sensor be faulty and not throw up codes

Yes...with two O2 sensors, there will be a code on newer vehicles.

When parts like spark plugs, wires, O2 sensor, etc., have not been replaced in a long time, replace them.

Fuel Injectors - Around here, it cost from $10.00 to $15.00 (US) (each) to have injectors inspected/clean; with older vehicles, they should be pulled and tested.

Compression Test - If all cylinders are similar, then your issues are related to above, most likely.

[Kappy5003]

Thanks,
My 960 has a OBD1 system, is it possible to have had a O2 sensor code that was cleared and still have a faulty O2 sensor even though I now get no code?

Injectors were only done about 40 K ago.

Cheers

[precopster]

No need for spark plug wires on these are they're a coil on plug setup.

Anything is possible however from my experience owning a 1993 960 the fuel pump under the passenger seat can begin to fail thereby dropping fuel pressures and forcing you to floor the pedal to add more fuel causing high fuel consumption due to poor atomisation at the injectors.

Check fuel pressure before replacing any other parts.

[93Regina]

O2 sensor code

O2 sensors can last upto 100,000 miles (US) if no containment(s) act on them. Anti-Freeze, some chemical additives, oil, leaded fuel, etc will destroy an O2 sensor.

Kappy5003 has a good suggestion, check rail pressure; of course, if fuel filter has not been changed in past year or two, then change it outl

Remove it, and examine it.

[Kappy5003]

Thanks Mike
Oops don't know how I got this wrong, mine is actually an Oct 94 build.

Couldn't find fuel pump under passenger seat doesn't even seem enough room for one.

Doesn't seems as if extra pedal is needed.

What do I need to test fuel pressure,can I do it my self ? I live about 250 km from anyone that cares about volvo's.

So having had a look at some testing of O2 sensors an O2 fault code may not be a faulty sensor only a reaction by the sensor yes??

[93Regina]

What do I need to test fuel pressure

A cold engine, and maybe a tire pressure gauge might work for a quick/dirty check. Use cloth to shield spray.

Volvo 960 basic testing

Volvo Maintenance FAQ for 7xx/9xx/90 Cars

Something like this might work: Actron CP7818 Fuel Pressure Tester Kit

On 240/940 engines, a Ford pressure tester should work.

Ford 90' Fuel Inj Adapter

When was last time timing belt was changed?

2.9L 6-CYL 1994 Volvo 960

O2 sensor

If your tailpipe has a blackish carbon look, so does your O2 sensor...

Check your rail pressure, pull the O2 sensor....

[Kappy5003]

When was last time timing belt was changed?

Timing belt done about 40k kilometres ago,idlers,tensioners everything.

I see a valve nipple at the firewall end of the fuel rail is that where I test fuel rain pressure??

[93Regina]

I see a valve nipple at the firewall end of the fuel rail

I assume so, unscrew and test when cold; if a tyre gauge works, throw it away when done.

One would prime the system; on 240/940 of that vintage, you just turn the key to on position, and fuel pump(s) should prime the fuel rail.

As noted, a Ford pressure tester might work.

[93Regina]

valve nipple

Should be around 43 psi with engine off.