I have just purchased this 1994 940 Non Turbo a few months ago. The problem is it is hard to start when cold. Once started it is hard to keep idle but once it's warm runs great. It became even more difficult to start when cold once I installed a new fuel temperature sensor.

The previous owner told me within the last two years he replaced both the in tank fuel pump and in line fuel pump near the fuel filter.

More background;

I have replaced the following;
1) cap, rotor, wires, plugs
2) Air Mass Meter
3) Intake Manifold Gasket.
4) Seals on all the Injectors
5) Idle Air Control Valve
7) Crank Position Sensor
8) Fuel Filter, Fuel Lines and all vacuum lines.
9) Fuel Pressure Regulator
10) Cleaned Throttle Body and replaced the gasket.
11) Checked the timing belt and the timing marks line up.


The Fuel Pressure is 36PSI at idle. If I unplug the Fuel Pressure Regulator it jumps to 46PSI. After a few hours the fuel pressure goes to about 8PSI and appears to keep going down.

Does anyone know what the fuel pressure should be if left over night or for a few hours?

Really at a loss here. Please help!

 

your fuel pressure sounds fine to me. the spec is like 42-44 PSI above manifold... manifold is negative, like -7 or -9 PSI at idle. all numbers are approximate.

fuel pressure dropping after an hour isn't a problem. if it drops as soon as the pump is shut off, then you got a problem (there is a one way valve after the fuel pump). when you turn the ignition on, the pump runs 1-2 seconds to build fuel pressure.

wow, you replaced a lot of bits... were they really all bad, or were you just shotgunning stuff? I'm a firm believer in diagnosing the problem before blindly replacing parts and hoping they fix things. does the idle switch on the throttle work? does this car throw any OBD codes? (see Engine and OBD Diagnostic Codes you don't need any reader or whatever).

does this car have EGR ? (California cars usually do, others usually don't). is it a 'pulsair' ? (bunch of weird air plumbing from intake side to exhaust side) or is it a turbo (late 940s often were turbos without even saying so on the outside).

 

The Idle Air Control Valve, Fuel Pressure Regulator and Air Mass Meter just out of pure frustration. They were not too expensive but it's starting to add up. I did bring it to a non volvo specialist and received codes of 2-3-2 telling me too lean or too rich. The crank position sensor was another guess but and inexpensive one.

It does have an EGR Valve, pulsair I read is not relevant really. Are you referring to the throttle position sensor? If so, how do I check that?

 

well, a broken pulseair valve could do funky stuff. I've never worked on a car with pulseair so I dunno the test procedures offhand. its possible the valve could stick when the engine is cold and free up when its warm, I dunno.

ditto a stuck open EGR valve results in a really bad idle and stalling. if you have a mity-vac (a little handheld vacuum pump, useful for various things up to and including brake flushing), its fairly easy to test the EGR. disconnect the two vacuum lines at the EGR vacuum controller, and put the OBD thing in 'Diagnostic Test Mode 3' on the pin 6 (ignition) side, and it cycles the EGR actuator valve, so if you hook up a piece of clean vacuum hose to it and suck gently on it with your mouth, you'll feel the 'on/off' action of the test. if you do, then stop the diagnostic mode, and hook the mity-vac up to the hose that was attached to the bottom of the vacuum controller (this hose goes to the EGR valve itself under the intake manifold), start the car, and when you pump a mild vacuum, the car should stutter and almost stall, stopping as soon as you release that vacuum. if it does that, the EGR system is probably OK.


there is no 'throttle position sensor' in the normal sense, just a idle switch. its closed when the throttle is at idle, and clicks open as soon as its off idle. there might also be a full throttle switch but thats less important. first test is with the engine switched off, gently turn the throttle cable drum, and you should hear a distinct 'click' just as it comes off idle, and again when it returns to idle. 2nd test is to disconnect it, and use an ohm meter to confirm the switch opens/closes when you move the throttle on/off idle.

 

hmm, another cause for 2-3-2 could be an air leak in the EXHAUST manifold, causing the system to suck in a little fresh air between exhaust pulses (venturi effect), this fooling the O2 sensor into thinking the engine is too lean, so it richens up.

 

I don't know what's a "fuel temperature sensor", but what u probably needed all along is the coolant temp sensor that goes in the head right under the #3 intake runner. Make sure that's working right since you have the symptoms of a failed one.

 

There are two temp sensors in this car. One is the fuel temp sensor (the choke like in the good old days) and the motor temp sensor going to the dash board to show the motor temp.Both are on the right side of the motor if you stand in front of it below intake #1 and #3 intake.

 

no, there's an engine COOLANT temp sensor (ECT) in the block for the ECU and ICU, then there's the temp sensor for the dash gauge. neither is a FUEL temp sensor, both are measuring the water temp inside the head.

and the ECT is NOT like a 'choke'. a choke on a carburetor restricted air to enrich the mixture. the ECT just provides a temperature reading to the ECU so it can manage the engine optimally... this INCLUDES enriching, but that's done by the ECU not by the sensor.

thats like saying the thermostat heats or cools your house when instead it controls the furnace or air conditioner that do the heating and cooling

 

Thanks, Pierce! Couldn't have said it better myself...

 

The Sensor is actually called a Fuel Injection Temperature Sensor, but yes mostly referred to as the ECT. I replaced most of the parts because they are maintenance items (mostly) many of them were in need of replacement. After all the car is a '94.

Remember, most often I received no error codes to follow because the check engine light was not coming on.

If I unplug the Air Mass Meter, the car will start up no problem. The interesting thing is I am now actually getting a "Check Engine" light now, where I wasn't before.

When plugged into Socket A The code reads 1-2-3 which refers to the Fuel Injection Temperature Sensor or ECT. The code error is "Wiring fault to or in ECT sensor;grounds corroded on intake manifold or engine."

I am beginning to wonder about the previous 2-3-2 I received from shop I brought it to? I didn't know how to receive the codes at the time, so I can't confirm that was accurate.

I traced the wiring for this. One wire the Red/Black wire goes to the module above the drivers side brake foot control (what is that? The Ignition Module?) and the other goes to the ECU on the Passenger Side "Kick Panel" to the right of the passengers feet.

The connector is good and I made sure I had continuity. The interesting thing is that I have about 5 ohms on what I think should just be a wire. So I'm wondering if there is corrosion giving me the extra ohms reading. (Interesting indeed.) Or perhaps the large connectors that plug into the ECU and the other module above the foot rest of the drivers side has some impedance that would raise the ohms reading. The only way to find out is to cut the wire. I may do that for my own knowledge. (Never a big fan of cutting wires but with some solder and heat shrink it's okay.)

I found that the ECU was replaced at some point based upon the writing in magic marker. See the attached photos.

So of course, with little background on this car, I'm guessing this has always been questionable.

Do these really even go bad that often? Why would anyone replace this?

I think I have to get to a mechanic or car like this to confirm, maybe the junk yard but these cars are getting difficult to find there.

Thanks for the responses.

 

I believe i pasted the link on reading hte codes before.

Engine and OBD Diagnostic Codes

some codes don't throw a check engine light, even when that says they do. the codes are remembered until you reset them per the procedure on that page (and verify that they are reset, took me 3 tries the first time to get the sequence right). unplugging the MAF and test-starting likely threw a code, so that should be read and reset.

now, the fact that it started with the disconnected MAF and doesn't start with it suggests there's something wrong with the MAF, maybe it has a heat soak problem.

Say, does this car have the heat riser tube (looks like a 3" foil pipe like a clothes dryer vent hose) that connects from the exhaust manifold to the bottom of the air cleaner box? IF it does, there's a flap in the bottom of the airbox that has a thermostat/spring to close it when its warm and open it when its cold out. I'd suggest using some bailing wire or whatever and wiring this tight closed, as they will tend to fail open, feeding the engine hot air, and causing the MAF to fail.