Guys I am getting my *** kicked by this issue, and I desperately need help from the obvious experts on this forum. Before I begin, I am not a mechanic ,however I do work on electronics. Please excuse my Ignorance

Brief history, When the car was working I would regularly have to disconnect the Mass Airflow Sensor During Cold Start (Morning/After sitting at work 7 hours) this would allow me to crank the vehicle and reconnect the MAS once started. Car would run, and drive Great once cranked (Worked For Over a year)

Major Issue Start, My family was on our way to Orlando FL when the vehicle suddenly died right in the middle of Atlanta Rush hour traffic . The car was not registering overheating, However we had easily been driving for 3+ hours at this point and it was a hot day. We wait maybe 8 mins, and thank god it cranked back over and we where on our way! Stopped at the nearest exit, and check all fluids,belts,the basics. Car was idling kinda strange at this point, but after resting 1 hour it was back running normal. Made it the FL no issues, even after 1 week in FL Heat, no sudden death symptoms. However something strange started happening with my lights. every time I would turn on my head lights it would "kill the Blinkers" Once headlights where off, it was fine. Make it all the way back from FL no noticeable issues with the vehicle running.

Present day, The car has stopped starting even with the MAS cable disconnected. It will crank over, and once in a very (Random/Rare) Blue moon, it will start, if I slowly apply pressure to the throttle- it will rev up, and if I keep it above 2,000 RPM's it will stay alive. If however by gods grace it does idle, it goes down in the 500 range and starts falling on it's face, til it dies and no longer wants to start after (Still cranks however). If I apply a decent amount of gas, it dies and fails to restart.

We know we are getting spark to the plugs (Looks yellow even coming out of coil) We are getting fuel to the rail and pressure (Sorry don't know the PSI Yet) When fuel is placed directly in, it sputters just like normal and sounds kinda like it wants to crank for maybe 0.001 MS lol but overall no change. The tachometer Jumps when attempting to start, and I can hear the inline pump kicking on during ignition.

What me and my father-in-law Have attempted to do:
1)Replaced every single relay behind the ash tray. For the ignition control relay I have tried 2 sets (One that I keep on spare, and the other brand new) No change.
2)Replaced both (2) radio compression relays with 4 different sets of used Variants, No Change.
3)Replaced ballast resistor with a spare used one, No Change
4) Replaced power stage (Only able to locate One) Used spare. No change.
5) Replaced ignition coil with 3 different variants of Used ones, out of other Volvo's. No Change
6) Replaced in tank pump, with used pump from (740 1990 turbo) No change.
7) Replaced RPM Sensor with Known good used one, No change. It looks like this http://www.volvoclub.org.uk/faq/Imag.../RPMSensor.gif
8) Tried using The ECU off the Volvo 740 (Both bosch) No change.
9) Cleaned all contacts, and checked all available grounds (I could find) No Change.
10) Replaced Fuel Pressure Regulator With used one. No Change
11) Replaced whatever is hooked up right before the turbo hits the exhaust connected with a vacuum line, with spring and black rubber on the inside. No change.




Please help

Volvo 940 (turbo 4 door Sedan) 1991 No start


Ps. Also changed MAS with used one, No change.



140k Miles

1) Forgot to mention, No errors

 

Whats the mileage on your 940?

Some things you should check:

1. Run your cars ECU and lets us know if any errors are being stored, you do not need any special tools for this, at least I dont think.

2. Check your battery, you might have a low battery or an alternator going out.

3. Since you've replaced your fuel relay then I'd inspect your fuel hoses for any leaks or clogs. Running a Volvo with a failing MAS or with it unplugged will cause excess fuel to flow at all times

4. Your MAS is dead, plugging it back in with the car going will fry it quickly. These commonly fail so the odds are your used ones dead too.

I wish you the best of luck with your 940, let us know when you get it sorted out.

 

140k Miles

1) Forgot to mention, No errors (If you are referring to the probe type testing driver side under hood?)

2) Battery is 100% Good Very very high CCA (Known Good), But I will check alternator tomorrow. I am coming from a Mercedes 300D Turbo Diesel 83... when the alternator died completely on that car, it would still run/function perfectly.Would this cause a no start on the 940 really?

3)No fuel leaks, or clogs, I am getting an ample amount of fuel to the rail.. Defiantly no leaks. Need to check pressure at rail.

4) The MAS has been dead lol, Whole beginning issue. Don't think it should cause a no start however when it's disconnected. From my understanding air/fuel falls back on 32c mixture when ide, and 65c when drive. I know it can cause a no start when connected, however don't see how it could disconnected.

Thank you for the suggestions, Please advise. Thanks again!

 

if the engine runs with the MAF disconnected but doesn't when it is connected, you have a bad MAF. period.

you shoudl never hot plug the MAF, you could fry the MAF *or* the ECU.

 

Pierce 100% agreed, But what I need are the next steps to take (It no longer runs with the MAF disconnected or connected) Other then replacing the MAF with a new one (Which I plan on doing) What would you suggest to get it running again. I am not contesting the MAF being bad, Only curious if you think that's what preventing the no start when it's disconnected?

 

timing, spark, fuel, and compression. takes all of them

 

I'm not sure how a car can run without a MAF, as I've read all over the internets. The logic is sound, but I once left my MAF disconnected, and although it started, it would never idle unless my foot was on the gas. It would die immediately when I let off the gas.

Have you checked for vacuum leaks? A major vacuum leak can lead to a very rough idle and possibly even a no-start condition. Maybe take a look at your PCV system as well, although a clogged PCV wouldn't be the root cause of your no-start.

 

Sorry for being a noob, but how would I check the vacuum in the car? Is the PCV the connector built into the turbo intake hose? Can you actually remove that connector without breaking the hose? Thank you so much for attempting to lead me in the right direction!

Pierce, Dude you are like a god statues on the forums! I highly respect what you say, and appreciate it, However I am not mechanically inclined. I can figure out how to check time, However for spark,Fuel,Compression I am lost. I am getting spark (Yellow) to the plugs. Please leave a little bit more info such as instructions or actual steps. I know you know


Should the inline fuel pump always prime (whirl) during start, but stop after adequate pressure is built. I am noticing after I try to start a few times, it will not prime the pump without the key being removed, and restart starting sequence. Does that seem normal?

Thank you guys so much!

 

Guys I think I just a found a cause to the issue, When running ECU Diagnostic Test Mode 3: Injection System Component Activation Test, (hit button for 3 times no longer then 3 seconds on each press) I am unable to hear injectors turn on or off (Nothing). But I hear all other parts click after injector test. Need to know what the dependency of the injectors are so I can start replacing faulty component.|


Looking at this video at 7:15 I do not hear the injectors clicking at all
I hear the idle air valve working

 

the injectors get their power from the 'radio suppression relay' (mounted near left fender), this power goes to a resistor pack (also on left fender) then directly to the injectors. the injectors are switched on/off by the ECU directly (it 'grounds' the other wire to turn them on, and floats it to turn them off).

 

I think this car uses an injector ballast resistor pack (on the driver's side inner fender). If I remember correctly I think they should read about 6.8 ohms. A noid light can be used to check injector function. It's an led thing that plugs into the injector plug on the harness. You could make one with a 3.3k ohm resistor in series with an LED. I'm assuming the one you get has a forward current of 3mA. If none of that makes sense, just look for a noid light.

 

yes, the LH2.4 ECU requires load resistors for the high flow injectors used on the turbo

these resistors are very simple and robust, but the wiring can get mangled. the power comes from the 'radio interference suppression relay', goes to the common pin on the resistor module, then 4 wires go to the injectors. the other side of the 4 injectors are tied together and goes to the ECU pin 18, which is switched to ground to fire the injectors.