940 Help with yet another no start Volvo thread...

Evening fellas!

As I write this I'm about to start crying since I don't know how to proceed anymore...

A bit of background: owner of a 1995 (from Europe) Volvo 940 low pressure turbo B230FK. Currently running poorly on a PNP megasquirt (still a long way to go tuning it) but this shouldn't affect my issue since I plugged in ye good ol' ECU and obtained the same results. No codes on the ECU btw.

Now with the issue.

No start on the Volvo with no spark.
Car was running early December, left it in the garage and now in January it won't start. Battery is not the issue since I tried jumping it with another car after draining the battery when cranking.
Engine as stated turns over, I can hear the fuel pump and it stops after 2 seconds or so. Ignition relay was changed mid-2016, and I can hear 2 clicks.
Already tested the coil and it's working ok.
Unplugged a sparkplug wire and tested there was no spark.
Momentary power on terminals 1 & 15 at the coil when key on position II (then one right before it starts cranking).
Tested Power Management Module connector, got momentary current on pins 1 & 4.

When cranking the RPM needle didn't move (neither on the dash or on the lapotop) so I changed the RPM sensor. Thought this would be the issue but it wasn't.

On the relay I can see how the furthermost interruptor clicks 2 times, withe second one meaning it's not closing the circuit anymore.

I somehow can trick the relay, and after cranking for about 10 seconds, waiting and cranking again the engine starts up with a bang (I believe this must be the fuel injected previously) and even I give it gas it will eventually die after 10.20 seconds of running.

Bonus point: on the tunerstudio screen, the RPM signal icon stays in red while cranking, when I stop cranking turns briefly to green.

Please any help will be welcomed... and I don't wanna think that it's a grounding issue since the car was running before being parked, had never had this issue and now it doesn't start.

Step one: eliminate megajizz from the equation.

Then, on your car, I would probably look for codes in the OBD black box on the strut tower. Pin 6 is the EZK, pin 2 is LH. Is EZK alive or dead!? Tools required so far: eyes and hands.

ZVOLV said:

Step one: eliminate megajizz from the equation.

Then, on your car, I would probably look for codes in the OBD black box on the strut tower. Pin 6 is the EZK, pin 2 is LH. Is EZK alive or dead!? Tools required so far: eyes and hands.

Click to expand...

It should be the same if I check it on the armrest pseudo OBD-II connector, right? I don't recall any OBD box on the engine bay (not near the car right now).

Oh yeah, I forgot about late model euro cars have a cabin mounted OBD terminal. I also forget if a special tool is needed. Most likely. Without a special tool, you could manually go to the EZK box and check for power, ground, and ignition on signal.

Easier, would be to go to the MAF and check for power on the blue/ yellow wire. This will tell you if the EFI relay is powering up the computers/maf/etc.

A test light is a great tool. An LED test light to the powerstage input signal would tell you if the EZK is sending a 5v square wave to the powerstage.

Here is my EZK thread. I use an oscilloscope, but if you learn how, cheaper tools can also verify the same signals. Such as an incandescent test lamp to coil negative, crank sensor with a meter, etc.

http://www.forums.turbobricks.com/showthread.php?t=322395


Diagnosing a no spark should be pretty easy. These cars are pretty easy to work on compared to the modern stuff I deal with every day at the shop.

I would first confirm if the EZK is powered up or not and then go from there. Do you have injector pulse? A noid light works great. $15. Or you could take a test lamp to a positive source, then connect it to injector ground. Crank. Blink?

Do 900's have immobilizers? Is this irrelevant? (I don't have one or know how they work...)
Could that cause the no-spark? Or would that stop the starter from turning?

Yeah the 1995+ ones have immobilizers in europe.

ZVOLV said:

Oh yeah, I forgot about late model euro cars have a cabin mounted OBD terminal. I also forget if a special tool is needed. Most likely. Without a special tool, you could manually go to the EZK box and check for power, ground, and ignition on signal.

Easier, would be to go to the MAF and check for power on the blue/ yellow wire. This will tell you if the EFI relay is powering up the computers/maf/etc.

A test light is a great tool. An LED test light to the powerstage input signal would tell you if the EZK is sending a 5v square wave to the powerstage.

Here is my EZK thread. I use an oscilloscope, but if you learn how, cheaper tools can also verify the same signals. Such as an incandescent test lamp to coil negative, crank sensor with a meter, etc.

http://www.forums.turbobricks.com/showthread.php?t=322395


Diagnosing a no spark should be pretty easy. These cars are pretty easy to work on compared to the modern stuff I deal with every day at the shop.

I would first confirm if the EZK is powered up or not and then go from there. Do you have injector pulse? A noid light works great. $15. Or you could take a test lamp to a positive source, then connect it to injector ground. Crank. Blink?

Click to expand...

With a bit of delay, but just switched back to it's original ECU. Tested the blue and yellow wire to the MAF and it's getting 11.49 volts so I guess the EZK is working ok.

One thing I noticed when cranking it is that I couldn't hear the fuel pump turning on, I could force the swith on the ignition relay and it would turn on the fuel pump, but it wouldn't do it by it's own means.

After cranking the engine a few times I wasn't able to pull any codes from the ECU, everything was 1-1-1.

I plugged in again the Megasquirt ECU and the fuel pump relay started working again but the other "coil" from the relay would click on and off.

Do you have any idea as to how to get codes from the ECU? Lambda light stayed on all the time so I expected to get a code but had no luck with that. The fact that the fuel pump stopped working after plugging in the original ECU left me

1. Do you have spark?

2. Do you have fuel injector pulse?

3. Do you have a test light?

ZVOLV said:

1. Do you have spark?

2. Do you have fuel injector pulse?

3. Do you have a test light?

Click to expand...

Hi ZVOLV!

Finally got my hands on a noid light, and aside from the no spark issue, I don't have any injector pulse as well. Since I'm running out of ideas, I took off the power stage and noticed that it had some sort of themal paste behind it, but in a bad shape. Is that normal thermal paste as the one used in CPUs? Could this be the problem?

Here's a pic of the power stage:




Is there any way of testing the power stage with a multimeter?

Good call on the noid light. It better than a meter because adequate current is also needed to make a circuit operate. I have seen 12v on a wire, but there was poor current. Use that noid light anywhere you can plug it in.i use them to verify a circuit is good for water pumps, window motors, etc. Voltmeter stays on the shelf now for those tests! If the light doesn't fit, I use a test light. A very very basic pro tool.

If you have no spark AND no fuel injector pulse that means your computer's are likely not powered up, or there is no crank sensor signal.

I would next start with trying to pull codes from the OBD box. If they are both dead I would suspect the EFI relay. It's a dual relay, one circuit powers the fuel pump and the other circuit powers the computer.

Testing a power stage with a meter....im sure there is a way, but I can't tell you the specs. It receives a 5v square wave from the EZK computer and then puts out up to 400v for the ignition primary. Instead, you could use a test light. I have been meaning to do some LED test light experiments on the 5v side of the circuit. A bulb test light at the coil negative would tell you if the powerstage is operating, but go back to the no injector pulse/no spark issue in this case. If you Google Volvo 740 no start there is a pdf file a guy wrote that has multimeter tests he developed with specs. I'm not sure how a 5v square wave at a low pulse width would show up on meters. Find out and tell me.

Here is what the EZK ignition waveforms look like on a scope as a reference: https://forums.tbforums.com/showthread.php?t=322395

anotherusername said:

Is that normal thermal paste as the one used in CPUs?

Click to expand...

IDK if it is the same per se. But... that's what we've always replaced it with.

anotherusername said:

Could this be the problem?

Click to expand...

Thermal paste that has hardened and is no longer conductive most certainly leads to intermittent operation and untimely failure of the power stage.

Once the thermal paste has hardened, it is no longer adequately conducting heat from the power stage to the heat sink which it is mounted upon.

You could hang a powerstage from a string and it would still work.

ZVOLV said:

You could hang a known good powerstage from a string and it would still work.

Click to expand...

Yes, to get it started.

There's a reason for the heat sink and thermal paste

Edit:// related: ignition transistor on MS2.2 Board drives ignition just fine at idle (standing up vertically on the board) but blew at high RPM, long duration pull on xway. Heatsink fixed the problem. MS3 boards have that same transistor mounted to a common rail heatsink by default.