[Stefan96]

Hej!
Since my swedish isn't good enough to describe my problem just yet I'll do it in english. Feel free to reply in swedish though!

I recently bought a 1997 S70 with 106 kW (144 PS/142 hp), so it's the 10v with the Fenix 5.2 ECU (B5252FS/S).
The car starts up and runs just fine for about 15 seconds, then it shuts off. One can even drive it just fine in that time, it's basically as if one turns it off with the key .
Initially I thought it was the immobiliser, but since it's more than the typical 1 to 2 seconds I'm not so sure about that.
The previous owner already replaced the fuel pump, pump relay and also the key antenna ring.
I also noticed, that when the ignition is on, the fuel pump comes on every couple seconds for one second or so to reprime the system. It does this indefinitely. My first thought was that it's losing fuel pressure, but I didn't see a fuel pressure sensor in any of the diagrams, so maybe the repriming is just a feature? I will measure the fuel pressure next and get a new filter while I'm at it.
In the meantime: If anyone with an 850/V70/S70 with the same engine/ECU could tell me if theirs does it, that would be really helpful in further diagnosing the problem. If you open the hood and get a little closer to the distribution rail you can hear the fuel rushing through the pressure regulator into the return every time the pump comes on quite clearly.

On a slightly unrelated note: I hooked up the Biltema diagnostic tool (the Volvo specific one) and it fails to communicate with the ECU, immobiliser and a couple other systems. It communicates fine with the ABS, Airbags etc. Has anybody had the same issue with theirs? I don't think there are any errors though...

Thanks for your help in advance!
- Stefan

[Hasse53]

My guess is that the pump relay is faulty or is of the wrong type.

The Fenix 5.2 uses led flash codes for communication. Go to Matthews Volvo Forum for more info.
https://www.matthewsvolvosite.com/codes ... or-thingy/

/Hasse

[Stefan96]

Thanks! I found the flash codes as well, just need to get around to make the LED "reader"!

I suspect the relay as well.
I measured the fuel pressure and while it drops quite fast from ~40 psi to ~24 psi while the car isn't running, the pump also does NOT stay on when the car is running, so the pressure drops until the car shuts off. Sometimes the pump comes on again fast enough to give it another couple seconds.
I bridged the relay contacts (87 (37 on the front of the relay case) and 15 ) to keep the pump running non-stop and with that it runs fine of course.
The relay that's in it is the typical red 103 one (898797000). From what I know pretty much all variants of the 850, V70 & S70 used that relay, or am I missing something?

-Stefan

[Stefan96]

I checked the relay by putting it in my V70 and it works fine.

I also measured the voltage at the 31b terminal and the difference between ignition off and on is a mere 0.5 to 0.7 V, so I assume there must be a bad connection somewhere in the wiring. I will try to check the connectors on the ECU next, but first I need to get the tamper proof bolt off - apparently no-one has been in there since '97...

I also had the immediate shut off right after start earlier with the pump relay contacts bridged (the immobiliser type issue) and it happened twice. Pulling the key and putting it back in solved it, but that probably means I should also have a look at the antenna ring. There is most likely multiple things at play here, maybe because someone tried to fix it and broke something in the meantime. The question is what happened first...

-Stefan

[Stefan96]

Update: I pulled the ECU and cleaned the contacts, but that didn't make a difference.
I'll measure the resistance between the relay terminal and ECU next. If that's fine I'm out of ideas...
I ordered a new relay just in case, but since it worked fine in my V70 I don't see why that would solve it.

Update in the Update: Measured the resistance and it's fine (~0.6 Ohm, but that's beyond the meters capability anyway).
I'll wait for the relay, even though that seems to not be the issue...
So any more ideas are more than welcome!

-Stefan

[Erik Å]

The "antenna ring issue" is simply caused by corrosion on the the connector pins in the green connector next to the antenna ring. Tin-plated contacts are simply not good enough for milliampere signal lines, Volvo should know better..
Remove the covers around the sterering column (remove three torx screws on the underside and bend the two plastic covers apart. The upper one can hang there in the rubber section next to the instrument cluster, just lift it up..) Unplug the antenna ring connector, put some vaseline on the connector pins, plug in and out a few times to remove oxide and you're good to go
I think that a failing crankshaft position sensor might cause the ECU to believe that the engine is no longer rotating, but still not set any trouble codes. Seems to be quite common problem, I have not experienced it myself (yet)
But fuel pump relay or failing pump are probably the most common problems.

[Stefan96]

@Erik Å,
Thanks for the tip! Yeah, RF is black magic I'll give it some contact cleaner and see if the problem reoccurs, most of the time it's fine.

Failing crankshaft sensor with no errors would be an interesting one that I haven't heard before, thanks!
I'd assume the ECU would also cut the injection in that case, but feel free to correct me on that. Since it runs fine with the relay contacts bridged that would be unlikely in that case. My V70 is the 2.5T with the Motronic 4.4, so I can't just quickly switch the two to check unfortunately.
Maybe the ECU connector just doesn't make proper contact on that particular pin, but upon quick inspection it looked fine... I could pull the ECU box out of course and have a closer look...

-Stefan

[Erik Å]

@Erik Å,
.. RF is black magic

Sure I know.. EMC, Electromagnetic Compatibility used to be my profession. I actually have some voodoo books over here
I have the later Denso injection system in my car (last P80 build, V70 MY 2000), the fuel pump relay seems to have some kind of digital serial communication from the ECU. I don't understand the reason, maybe the idea was to make it more difficult to bypass the theft protection. Still you can always bridge the output contacts of the relay with a simple jumper ..
But anyway, it seems to be a good idea to check that the wiring between the ECU connector and the relay socket is intact.

And also check that the previous owner has replaced the fuel pump relay with the correct type. Maybe there are different versions for different generations of the engine control, I have no idea. I guess that if the relay doesn't get the signal it expects (which is obviously not just a "high" DC level but some kind of pulse train) it may drop the pump supply after awhile to keep suspected car thieves off the streets And if the replacement relay happens to come from a junkyard, it may theoretically have the same problem as the first one.. Or if the output driver of the ECU somehow got damaged by the first broken relay.. Far fetched, yes indeed.
It would be interesting to check what is actually sent over the control line using an oscilloscope

[Stefan96]

I have the later Denso injection system in my car (last P80 build, V70 MY 2000), the fuel pump relay seems to have some kind of digital serial communication from the ECU.
...
And also check that the previous owner has replaced the fuel pump relay with the correct type. Maybe there are different versions for different generations of the engine control, I have no idea. I guess that if the relay doesn't get the signal it expects (which is obviously not just a "high" DC level but some kind of pulse train) it may drop the pump supply after awhile to keep suspected car thieves off the streets And if the replacement relay happens to come from a junkyard, it may theoretically have the same problem as the first one..

I realised that when opening it up to check the solder joints and an IC stared me right in the face. Why one would do that is beyond me...
The one I have is NOT a genuine Volvo part, so it might very well be that it works fine with the Motronic, but not the Fenix.
I did order a second hand, genuine Volvo relay (because I couldn't find a one new in Sweden), which like you said might have the same problem. I guess we'll find out...
But of course I just bought the "normal" red one, since that's the one that was in it. I need to have a closer look what versions used the other type and if they're NOT pin compatible (since that would of course be the easiest way to figure out what's meant to go into the car and what isn't).

Or if the output driver of the ECU somehow got damaged by the first broken relay.. Far fetched, yes indeed.

That is my current fear... although used ECUs seem to not be too expensive.

It would be interesting to check what is actually sent over the control line using an oscilloscope

I already had the idea to hook up my logic analyser... Lets see if that's necessary and if I can find the time to do that

[Stefan96]

So I had a quick look and the only relay type I can find is the 9434225, which I have, just not a genuine one.
The only different one was supposedly used in some of the 850s in '95 & '96 (the yellow 9434013) and that got a secondary output (87a & 87b instead of just 87). I am also pretty sure that there was no secondary contact in my relay box, but I'll double check that tomorrow. Then again, there should be no reason why that would have been used in mine...