I also replaced the crank sensor,both fuel pumps(although one is very noisy),filters,etc.

 

which pump is noisy, the one under the car, or the one in the tank?

there was a rash of aftermarket in-tank pumps which were wired backwards such that they were sucking rather than pushing the gas out, this would cause the main pump under the car to be quite noisy AND have trouble delivering sufficient fuel. Sounds like its time to do a fuel pressure test, AND a fuel flow rate test. randomly replacing parts gets expensive fast, much better to diagnose the actual problem and deal with it directly.

 

Not sure what brand main pump you used as a replacement but it has been my experience that the replacement Bosch main pumps aren't as quiet as the originals were.

Pierce is correct about the in-tank pump wiring. I replaced my tank sending unit with an aftermarket and I checked the wiring ahead of time (comparing it with my old unit) and found both the connector and the internal wiring was incorrect. This site documents it well: In the Tank - 240 Volvo Tank Pump and Sender

 

Some diagnosis would help you out a lot here. As you have found, you can throw a shedload of parts at a fault and still not fix it.

The fault you describe can be either fuel or ignition. Its intermittent and quickly resolves - thats hard to trace. You are going to need some diagnostic equipment and the skill to use it.

Having said all that, it seems like you have replaced pretty much every likely component so far except the igniter module. By the sound of your fault, I'd be going to that next... If you want to know why I think this, look here. Hope it helps!

 

Thanks, I did replace the ignitor module-is it the one that screws into the inner left front fender? So, I should change the radio suppressor? Where do i get one? thanks.

 

the 'radio suppression relay' is just a on/off relay that powers the fuel injectors, its called 'radio suppression' because when they moved all the relays under the center console, the injector power spikes caused radio interference, so they took the injectors off the main fuel relay, and moved them out to a new relay under the hood. you can get them from anywhere that sells volvo parts, www.fcpeuro.com or www.ipdusa.com are my favorite choices. but radio suppression relay failures are usually complete dead engines.

 

what test equipment do you have or have access to?

 

A Fluke meter.

 

I replaced the coil today, as I suspected, no difference. I'm gathering quite the stash of spare parts!
Further info: It never seems to occur under throttle and I can apply full throttle and there is no hesitation, stumbling or power loss.
When I ease off the gas, it will stutter or stumble. When this occurs, I looked at the tach to see if it would go to zero. It did not, although it did correspond to the stumble. The car never dies. It does stumble while sitting at a red light-usually once during the light phase. Heat and AC seem to make it worse. It will do it about every 20 seconds when its at it's worst.
The car always starts easily, hot or cold.

 

OK, if the tacho doesn't drop to zero you can rule out the entire ignition system primary side and the suppressor relay.

If it doesn't stumble under acceleration, you can PROBABLY rule out high voltage side of the ignition.

This is good - it leave fuel as the obvious cause.

 

The under car is noisy. I replaced it in one of my first attempts to solve the problem. The old pump wasn't noisy. I read that maybe the primary pump was OK and the problem was a failed secondary pump. I also replaced it with no effect. I did not, however, test for flow direction. After realizing that the problem was still there, I pulled the cover in the rear and verified that the secondary pump was working-it was, although unknown if flowing in the correct direction. I thought if the secondary pump was not working that there would be a number of issues-hard start, loss of power,etc. Doesn't really seem to match my symptoms, does it?

 

Its unlikely to be fuel pump flow. If it was, it would stumble under acceleration when maximum flow is required.

I'd be putting a fuel pressure gauge on the fuel rail and see what is going on - it could be that the pressure regulator is on the fritz

Good reference material

http://www.volvowiringdiagrams.com/v...%20Tracing.pdf

 

fwiw, if everything else is good, a dead in-tank pump will mostly result in issues when you're below 1/3rd tank of gas, the car will run fine if your tank is full. the main pump /will/ be somewhat noisy all the time, more so when the gas gets lower.

 

That is great stuff! Where do I get a diagnostic tester to retrieve codes? Thanks.

 

on the LH2.4 cars, 1989+, no tester is needed, its a LED + pushbutton + jumper wire under a plastic cap on the left fender. See https://www.volvoclub.org.uk/faq/EngineOBDCodes.html you want to perform 'DTM 1' on both pins 2 (fuel injection) and 6 (ignition)

 

Near as I can tell I retrieved the following codes 322, 311, 322. Then a bunch of 111s as I tried to check the systems individually. Then 334 141

 

thats a fairly random bunch of codes. 322 suggests there's an issue with the MAF (aka AMM) or its wiring to the ECU. 311 is something I've never seen. 334 is a REX1 only code, impossible if you have Bosch ignition/injection, and 141 isn't even a valid code.

 

Latest update. I've driven the 940 another 5K with the annoying stumble. Recently(for the first time) it began to throw a CEL upon start up. It goes away after a minute or two of driving. Checked codes again and I think it was a 3-2-1.

 

3-2-1 is 'cold start injector missing' which is fairly improbable. not even sure a 940 has a cold start injector (they used them on early cars, then got rid of them on later ones)

 

Oops. It was 322. Should I replace the MAF?