1991 Volvo 240 stalling. About six months ago when I would drive for ~30 minutes and then sit at a stop light or stop sign. The car would stall out as I was pulling away. Occasionally I could force it to keep going by putting it in neutral or flooring it. I can almost always restart it but keeping it running is impossible. If I wait 15-20 min the problem fixes and I am usually able to make it to destination.
I was having a similar problem a year or 2 ago that was fixed by replacing the fuel pumps and filter, fuel pressure regulator, catalytic converter and finally the fix was the mass air flow sensor.
Now I am having the same problem only after a longer period of time. I have replaced the fuel filter, and the fuel pump relay(one side is still getting hot). Tested the fuel pump which when the car stalls drives the pressure from spec(35-38) to 48-50 psi. Additionally the pump is not hot at all during a stall, and the voltage is present all through.
The O2 sensor when removed was not generating any voltage when heated by a propane torch, using a method described in another thread that I can't seem to find. This resulted in a slightly longer run time. I have had the catalytic converter checked by removal and visual inspection. After this it was stalling even sooner, but that also was the hottest part of the day.
I then ran the codes on the OBD I port and found O2 sensor codes from when I ran it home without an O2 sensor mounted in the catalytic converter. And a code for the RPM sensor missing or intermittent. When the MAF is disconnected while cool it runs worse than when it is connected. I have not had the opportunity to try to restart after a stall without the MAF connected. The MAF as far as I can tell when checking it matches spec, but a clear diagnostic routine would be appreciated. Putting it in diagnostic mode 2 I can hear it activate all of the sensors without codes. I was able to get it to give me sensor reports OK for everything (the fast blinking mode) that was described in a combination of running and off. I checked for intake leaks yesterday evening by spraying with carb clearer around all of the connections. Finally I have also pulled and scrubbed and replaced all fuses related to the engine.
My question is where do I go from here? How do I test/clean the RPM sensor and where exactly is it located? I've tried almost everything I have been able to find on the web... And I don't know where to go from here.

 

phew, you need to use paragraph breaks and organize your writing a little better, thats hard to read.

if the CPS ('rpm sensor') has thrown faults, then check the CPS (Crank Position Sensor) and its wiring, if that fails, the car will NOT run, and the wiring back there behind the head is notorious for causing problems.

its a magnetic inductive sensor, so its signal is small and hard to read externally. the usual way to test is to verify you're getting ignition pulses when cranking (your tach should bounce). if no tach bounce, then thats definitely suspect, especially if you get any sorts of codes from the OBD position 2 (ignition), even 1-1-1... Reading any code on #2 indicates the ICU is 'alive'.

 

When following the diagnosis steps defined from Brickboard for OBD1. And cranking the sensor checked good. Also I do not have a tach in this one.
Do you have a good method to test the AMM? I am beginning to be suspicious of the ECU.
Ps. Sorry about the rambling nature and poor spacing I'm using a mobile device.

 

about the only 'test' I know of for the AMM (aka MAF) is to unplug it and see if the car starts. if it starts, it WILL run poorly without the AMM as its in a serious limp mode, but the fact that it starts at all, and doesn't start when the AMM is plugged in usually means its a bad AMM.

if the ECU is displaying ANY blink codes, including 1-1-1, that generally means its AOK, although its very remotely possible the injector output is fried, its pretty rare. However, pink label -561 ECU's are known problematic and probably should be replaced with compatible newer ones. The ECU is just forward of the passenger door hinge, behind the plastic interior panel to the right of the passenger footwell. See Engine ECU for the various ECU versions and what works with what. You can use a compatible ECU from a 940 as long as its an appropriate version per that chart.

if you're getting OBD codes from the ECU indicating missing crank position sensor, well, thats a giant flag that there's a problem with the CPS.

 

It will start with or without the amm plugged in. It's the running that is difficult.
I have just been out on a short drive and when it started stalling I pulled over and disconnected the AMM. I restarted the car and with my foot on brake and revving the gas the second or third time it stalled out. As it did on the street and other places.
Update now it can't even keep it running long enoguht I get up and down the driveway with out the amm plugged in. Where do I do next.
Update 2: no codes other than AMM

 

is the ignition system in good shape? (plugs, wires (bougicord!), cap, rotor) and you're getting a strong fat spark? weak ignition can cause all kinda uglies.

is the temp sensor within reasonable resistance range?

test: remove the passenger side kick panel, and the right side footwell cover (forward of the door). the ECU is in there. with the car fully warmed up (and shut off!), disconnect the ECU, and use an ohm meter to measure the resistance from pin 13 to pin 17 of the connector plug to the wiring harness. if you use a small bright flashlight and maybe a magnifying glass, you can read the pin numbers inside the connector. see Engine Sensors for a table of values.... when the engine is *hot* it should be just a couple 100 ohms, and when the engine is cold, its like 2300 ohms at 68F(20C), or 2000 ohms at 80F(27C). The temp sensors rarely fail, but wiring issues can cause problems, and its on the side of the engine under the intake manifold where it can't easily be seen (there's 3 or so sensors along there)

while you're in there, see what version ECU you have. there's a early LH2.4 one with a pink label thats notorious for going bad. you can replace those with much newer ones from later years of LH2.4 940's
See http://www.volvoclub.org.uk/faq/Engi...ReferenceChart

oh yeah... when the AMM isn't plugged in, then engine might start and idle, but its not at all drivable, thats just a test. if it won't start when the AMM is plugged in, and will start without it, thats a sign the AMM is bad.

you need to clear OBD errors after doing the AMM unplugged test.

 

Final update for the night. Ran until stalling disconnected the AMM with no improvement in running. Could not inspite of 10 min of stalling run get the RPM sensor error back. Also still don't have a clear idea of location or description.
After further reading are the radio suppression relays a possibility, which would explain the increase in fuel pressure while stalling since the injectors aren't getting the signal to open?

 

240's don't have a radio suppression relay, thats a 740/940 thing only.

let me explain.

On the 240, the fuel injection+pump relay is behind the glove box. on the 740, they centralized all the relays behind the ashtray, at the bottom of the center console. this was directly under the radio. the fuel injectors all fire at once, and draw a couple amps total which was coming through that fuel injection relay... the big fat electrical spike this made gets into the AM reception and sounds like a buzz at RPM speed. the 240 doesn't have this problem because the relay and its wiring is far enough away from the radio.

so, the 2nd or 3rd year of 740, they added another relay under the hood to power the fuel injectors directly off the battery, and called this the Radio Suppression Relay. this relay is turned on by the main ECU relay which in turn is turned on by the ignition switch in II (run) or III (start), this moved the noise away from the radio and stopped the buzz.

 

...continuing. you said...

no.

If the fuel pressure regulator is doing its job, the fuel pressure should be 42-44 PSI relative to the intake manifold vacuum, constant regardless of fuel usage. at a high vacuum of -10 PSI, that could drop to 32 PSI, but I'd expect around 35-38 PSI at idle.

if you're seeing 50 PSI, then the fuel pressure regulator is NOT working right, or the return line is constricted?

was this a Volvo fuel pressure reguator, or something else? Uro and so forth chinese stuff is *JUNK*

 

No when I replaced it 2010 I replaced it with Bosch. I can now suck on the vacuum side without getting any fuel pulled through. Could the high pressure be related to low vacuum pressure from the intake manifold, cleaned circa 2012 to pass emissions. Involving a complete throttle body dissemble and cleaning and replacement of the gasket.

 

I've often wondered if the return line could be at fault for a lot if this which started after a long trip wherein I ran the car down to fumes on a 300 mile continuous run. While I filled up I left car running at a gas station I later found out was almost out of fuel. I then had to replace the fuel pump, filter, pressure regulator.

 

Replaced all wires, rotor, and plugs on last tune up ~10 months ago. Number one on the test list for tomorrow afternoon.

#2 on the test list

Yeah it's one of the unlucky ones. Do you think this is more likely since it ran worse after getting it back from the muffler shop? A bad problem made worse. A semi random side note I am having a problem with the rear lights, either one side or the other brake light will not fire but both parking lights will fire. Also while driving the back up lights will turn on but only while in D. Possible floating ground issue? Also the check seat belt light is randomly coming on and I can turn it off by hitting the large red light check relay senosor thing below the steering column.(not sure if at all related but possibly relevant)

 

even if the vacuum is 0, you shouldn't see more than 42-43PSI. only a turbocharger will have negative vacuum, aka positive manifold pressure.... (and yes, those hit 48-50PSI under full boost)

 

muffler shop?

hmm, they could have welded on the car .... yeah, that could have pushed it over the edge.




btw, running out of gas shouldn't kill the fuel pumps unless you left it on too long with them dry. these cars will run sorta OK with a bad in-tank pump, but they will not run well, bogging down under heavy sustained acceleration, especially if they have less than half a tank of gas. also the main pump will be working too hard, and noisy, this isn't good for it at all.

 

But isn't the vacuum what causes the diaphragm to open allowing the fuel pressure to decrease by returning to the tank via the return line? The lower the vacuum, the less the diaphragm is open the higher the potential fuel pressure, as the pump is going going full bore.
All of this aside does this lead to something other than the plan to check on tomorrow?

 

Does it matter that I was measuring at the fuel filter and not the rail as the kit I had did not have the adapters to match the rail connector?

 

Both current pumps are 3 years old, runs cool and quietly compared to the old one(I can hear when idling while out of the car with the radio off). I checked the in tank by removing the fuel line to the main disconnecting the power to the main jacking at the rear drivers door, and putting the key in position II. Loads of fuel came out quickly. Also took the opportunity to replace the failing fuel line with new ethanol resistant non in tank hose, made in the US. It's cloth covered and not cracking.

 

it shouldn't matter where you measure it, the laws of hydrodynamics say its all the same pressure.

if the fuel line return is completely blocked, the pressure will get up over 60PSI, I dunno how high. the pressure regulator releases this, so any fuel pressure above 42-44PSI is bled back into the gas tank. the vacuum line offsets this pressure, lowers it.

 

To confirm I've got this right, the vacuum line should be strongest on the fuel pressure regulator when the system is stalling(which would open the diaphragm all the way to relieve the pressure)?
Do you think a spring clip would help?
Seafoam poured directly in the return line?
Edit: formatting for clarity

 

Ok checked spark plugs. Look good worn according to chiltons manual. Good spark to fender. I could see it on video mid day.
I've seen good results with the voltage meter on the ECU connector for the coolant sensor. Although I am going to repeat when I can get it to stall. Also resistance is in range is within spec.