Fuel Pump Relay 9434225 Examinations 1998 v70 non turbo

[MrAl]

Hello,

I just took out my relay and took the cover off and found that there is a whole electronic circuit in there with about 25 small parts. I'd like to test it but without a schematic it would be hard. I assumed at first it was just a relay, but it's not.

Anyone have any info on this relay?
All i know so far is that there is a chip in there a Motorola MC14538B which is a dual monostable multivibrator and there are various small resistor about 1/8 watt and also some surface mount resistors. Two electrolytic caps.

[scot850]

Try here Al:

viewtopic.php?t=9681

Neil.

[abscate]

It’s not just a relay, even though we call it that. It times out and shuts off the fuel pump if it doesn’t detect the motor running , this prevents it from pumping fuel to a fire after an accident.

Jump it with a wire to test it for funkiness. I probably have a spare to sell if needed

[MrAl]

Try here Al:

viewtopic.php?t=9681

Neil.

Wow that's a big thanks, that is a great explanation and also confirms my suspicion that either of the electrolytic caps are bad. I cant thank you enough.

I also forgot to mention that whatever Volvo engineer designed this circuit definitely got one thing wrong. You never use an electrolytic capacitor with a voltage rating that is too close to the operating voltage, unless you dont care that it fails prematurely. This is something that no good engineer would do unless they were pressed intensely on the production costs.
So i can say with absolute certainty that although the design may be great otherwise, the 16v cap is a very bad choice. The designer may have gotten confused about the voltage being 12v only, when it can actually go higher. Too high to trust a 16v cap. This in turn, and the 'buzzing' i read about and the years of electronic design and repair i have behind me, tells me that this must be the most common failure for these relays and i would bet most could be repaired like that in the link. In fact, it is probably the 16v rated cap, although electrolytics are not super reliable anyway so definitely change both.
It also confirms that an electrolytic cap works to replace that one too, because it looked sort of like a mylar cap so i wasnt sure if i should replace it or not. The ramifications of the wrong cap could be inaccurate timing, although i dont know how accurate it has to be without seeing the schematic which i wish we could get ahold of.

In any case, this helped a lot so thanks much!

[MrAl]

It’s not just a real even though we call it that. It times out and shuts off the fuel pump if it doesn’t detect the motor running , this prevents it from pumping fuel to a fire after an accident.

Jump it with a wire to test it for funkiness. I probably have a spare to sell if needed

Hi,

I was going to ask about those things too.

Is that all the relay does then is shut off if an emergency comes up?
Would that mean that you could jump it if it stalled out and you had to get it home?
If so, i could make up a jumper.

Have to remember to carry a torx T25 too, and i found i needed to use a stubby handle to get the screw closest to the drivers side side rear view mirror because the hood gets in the way of a long handle.

You know what else is interesting, i read about the buzzing it can make when it is failing and i remember hearing that a few times when starting the car, but just not this time. Last time was maybe a month ago. I was wondering what the heck that could be, but the car started normally so i forgot all about it. It happened one or two other times too in the more distant past.
So maybe it was telling me that it was going bad.

Thanks for the offer to sell me a relay, i wonder how much you would ask for it, and also are you sure you have an extra for yourself if you do sell it, i read that you should carry and extra with you.

[scot850]

If you become a junkyard regular, you usually end up with several of these. I recently used one to help a 'new' 850 owner with the poor running of their car. It would be good to have a 'proper' way of testing these off the car, and especially if we end up rebuilding them to know the work was successful!

Neil.

[Chuck W]

The capacitors I use when I repair mine are 25V.

Part numbers for the 22uF and a 100uF capacitor that usually require replacing are Digi-Key 565-1304-ND and UVY1E101MDD-ND, respectively.

I redid a bunch of the JY spares I had a while back.

[MrAl]

If you become a junkyard regular, you usually end up with several of these. I recently used one to help a 'new' 850 owner with the poor running of their car. It would be good to have a 'proper' way of testing these off the car, and especially if we end up rebuilding them to know the work was successful!

Neil.

Yes i was thinking that myself. A good test to determine if anything was wrong.
Unfortunately, the electrolytic caps are difficult if not impossible to test in-circuit, which means they would have to be removed to be tested properly. The usual problem is either the capacitance goes down or the ESR goes up, or both. The testing method isnt all that simple either we need a scope and waveform generator or else a capacitance meter that can test for ESR as well as capacitance. There may be some that can test in-circuit though but we'd have to buy that.
On the other hand, if we had a way to energize the circuit and provide it with the proper signals, we could do an overall test. I am not sure if this would work for every case though because an intermittent problem may not show up right away anyway.
Also, the contacts have to be tested with some current, so it would be difficult.
Still, maybe not impossible im going to be looking into this.

So far i found three design deficiencies (4 if you count the last one here) i was very surprised to find.
1. The 16v cap rating is too low should really be 20v or better.
2. There is no conformal coating on the circuit board.
3. At least on mine, there is very very little if not any contact wiping.
4. Again at least on mine, it looks like the 16v cap was subjected to either too much solvent for cleaning or the wrong type of solvent. This could affect the long term operation too.

For #1, the voltage rating should be higher for long life. Have to be a little careful though as the ESR can go up with voltage rating, although without a schematic it is hard to determine if a higher ESR would be a problem or not. it is not a problem in some applications but in others it is a very important design point.
For #2, a conformal coating is almost always included in military applications. It helps enormously to mitigate problems that are caused by moisture and 'whiskers' developing over time which can short some traces out.
For #3, i noticed that there is almost no contact wiping, and i actually can not detect ANY at all. That's a surprise, i have to wonder why that is. Contact wiping keeps the contacts clean. Each time the relay energizes and the contacts close, the contacts rub against each other a very small amount and that allows for better electrical contact. Virtually every relay has this except maybe for mercury wetted contacts, but these are not that. Could there be another type of contact coating that helps with this? It doesnt look like it but i cant be 100 percent certain of that yet.
What goes along with this though is that the reason for the no wiping issue is because the contacts touch at what looks like the VERY same point where the relay armature touches the top of the coil. That means there must be very little pressure between the contacts after the relay contacts close. This is very disturbing to say the least. I've never seen a relay that behaves like that, and so i have a hard time believing this is normal.
The problem this can cause is of course the relay contacts dont make good enough contact, and because of the materials used in the construction (metals, etc.) heat could cause a very very slight warping of some of the structure elements and that would mean that sometimes it works and sometimes it doesnt, and that's exactly what i am seeing with my car problem.
The way this is usually handled is a relay contact adjustment tool is used to bend the thin metal contact arm that is "supposed" to bend when the contacts close. This relay doesnt look like it should be adjusted like that though because the contact arm (very thin metal) is very very short, also unlike most other relays. However, it does look like the mechanical stop for the lower contact limit could be bent ever so slightly to get the contact wiping action to work properly and more contact pressure when closed, which should be a huge plus for this relay.
I am tempted to try just the contact adjustment idea just to see if it holds up over time, without changing the two caps. The only problem is though that if it does still fail because of the caps i have to get towed home, unless it is possible to jumper the relay contacts to keep the pump running. That means i would have to know if it is OK to let the pump run continuously in normal, no emergency situations. I dont know enough yet about the proper operation run time of the pump so i'd be afraid to jumper the contacts except for a quick test.

I think i may attempt to draw up a schematic for this thing. It's not easy to do with a double sided board and 25 or so parts, but it could be very interesting to find out why this dang thing is so complicated. I would also not be too surprised to find that there are other design issues also, which could be fixed as well and help get this fixed once and for all, and maybe this would help the general Volvo owner population as well.

I if i can find any more out about this and a drawing seems successful, i'll post more about this. In the mean time if anyone has or can find any more information about this relay please post so i can review.

Thanks very much to everyone.

[MrAl]

The capacitors I use when I repair mine are 25V.

Part numbers for the 22uF and a 100uF capacitor that usually require replacing are Digi-Key 565-1304-ND and UVY1E101MDD-ND, respectively.

I redid a bunch of the JY spares I had a while back.

Oh ok thanks i'll look them up.

Ok looked them up.
I see they are rated 1000 hours at 105 degrees C, but there are others that are rated at 2000 hours at 105 degrees C.
But now that i looked at the 16v cap better, it looks like a polymer type. That would be a little more expensive but only 1 unit would still be under a dollar USD.
If those electro's work though maybe i'll just go with those.

Thanks for the info and any other stuff you can find about this relay would be nice to hear about also.

I almost forgot to mention, since the board is double sided it would be better to mount the capacitor up about 1/4 inch off the board if the trace on the top of the board that connects to one or both terminals of the capacitor connects to anything else through a trace on top of the board. That allows us to solder the leads on both sides of the board. What happens a lot is when a part is removed you have to pull the lead out of the hole and that sometimes yanks out the plated through hole plating and that means that the top trace is no longer connected to the bottom trace unless you get lucky and the solder happens to flow down the lead to the other side of the board.
This is only if the top trace actually connects to anything else though. You can find that out easily when the cap is removed by examining the top side of the PC board. If it doesnt connect to anything but the cap then there's no worry soldering from the bottom only would be good enough. The via plating doesnt always come out, but it is a possibility.
I'd also be careful not to let the 16v cap can body touch or get too close to the copper braid on the relay in fear of a short or just interfering with the proper micro movements of the braid when the relay energizes or deenergizes.

[abscate]

I’m trying to remember if I have these in my “ send me a pm and I’ll mail them to you” box in my North office.

I think I do, I’ll check Tuesday