Hello,

My 1994 940 was fine a week ago driving on the highway. Recently, took a day trip and after about going 50 miles or so, experienced acceleration problems and the rpms were fluctuating wildly.

Got off highway and let it cool for awhile(30 min) and tried running it again, it did same thing and stalled out repeatedly. Let it cool for an hour and then it ran decently and was able to get back home.

First assessent, figured it was either the fuel pump relay or the AMM. Replaced the AMM and it is running ok for now. Just did it yesterday, so I'm still assessing.

Dear stallison,

Hope you're well. If your car has Bosch ignition/fuel management (cylindrical coil mounted on the passenger-side strut tower brace), a more likely source of the intermittant function is the ignition power stage (IPS).

The IPS is mounted (on non-turbo cars) on the driver's side inner fender wall, next to the air box. The air box cover must be removed, to access the T-20 screws, that secure the IPS - black, with a gray cap - to its aluminum base. The IPS has a single connector, removed by pressing down on a wiring connector release "bail".

The resumption of smooth-running after a cooling-off is what suggests that the IPS has failed. The aluminum base is a heat-sink. The factory-installed heat sink "paste" - originally a gel that transfers heat from the IPU to the aluminum base - likely has dried-out. The heat build-up is what drives the intermittant operation, when an IPS is at the end of its service life.

In any event, you likely should carry a spare IPS.

Another potential source of failure is the Crank Position Sensor (CPS). This is mounted atop the transmission bell housing. The sensor's insulation sheath deteriorates with time and exposure to heat. When water gets into the wires, that carry the CPS' signal to the engine control module, the fuel pump shuts down. This is a safety measure: if an engine bay is torn-apart by a collision - and the engine stops turning - the fuel pump shut-down keeps fuel from being pumped towards a badly-damaged engine. That limits fire risk. See this site's FAQs for instructions on changing the CPS.

Hope this helps.

Yours faithfully,

Spook

Thanks spook,

I will look into those two things, the IPS and the CPS.

Another thing that is happening now is there is a clicking sound from the fuel pressure gauge when the car is idling.

Dear stallison,

Hope you're well. Most Volvo 940s do not have a fuel pressure gauge. Do you perhaps refer to the fuel pump relay? On '94 940s, that's a bright blue cube, mounted on the central relay block, in the first row of relays, i.e., that closest to the car's front seats.

Or, do you refer to a part that is in the engine bay?

I await further.

Yours faithfully,

Spook

Sorry Spook,

Your right, its not the fuel pressure gauge, its the line/fuel pressure regulator in the engine compartment. My actual engine is not the original and I believe the replacement is a really close to a 240 engine. THat's why I know its a fuel pressure regulator.

It is not terrible of a sound and only makes it when it is idling.


THanks,
Stallison

Dear Stallison,

Hope you're well. The fuel pressure regulator (FPR) should not make any noise. When the engine is off, remove the black vacuum line, that attaches to the front of the FPR. If there's gasoline in that vacuum hose, then the FRP has failed and should be replaced.

The B230 engine was used in 240s, 740, and 940s. However, the FPR format was changed. If memory serves, an FPR for a 240 has a threaded connection, where it joins the fuel rail. An FPR for a 940 is secured to the fuel rail with a hose clamp.

I mention this, because if the engine indeed is from a 240 car, then you need to get a replacement FPR that will fit a 240, rather than a 940.

Hope this helps.

Yours faithfully,

Spook