Fuel Pump Relay 9434225 Examinations 1998 v70 non turbo

[MrAl]

I’m a student of the 1970s and have published many circuits in Horowitz and Hill. Mine have the dark light bulb on them.

Oh i never knew that. What kinds of circuits?

I have some interesting test data now on the 100uf cap that was in my board. I'll post the waveforms.

The first #1 is a typical cap with a small value ESR. You can see the ESR by the slope circled in red. The current and the change in voltage determine the ESR value. That one is small. The capacitance can be calculated by the part circled in green.
The second #2 is a cap that is pretty good there is very little ESR.
The third #3 has some significant ESR which may not work very well in some circuits that need very low ESR.
The fourth #4 is the kicker. That is what the cap i pulled out of the board looks like. That cap has a very large value ESR which means it cant be very effective at filtering the Vdd supply line which would lead to intermittent operation exactly what i am seeing. The capacitance can be calculated from the falling slope as before but that surprised me the capacitance looks ok right around 100uf. The ESR though means the cap should be replaced, which i will do.
Not shown is another 100uf cap that is brand new and the fast falling part circled in red in the other pic is much less so the ESR is much less than the old cap, so i will replace that one for sure.
The other pic VolvoRelay_100uf-Cap is an actual scope picture of the measurement of the ESR and capacitance. As shown before the ESR is very high but surprisingly the capacitance is just about right.

Im going to post the text part of this and then come back and attach the five pics in a minute or two.

[850oldschool]

ESR stands for "equivalent series resistance":

https://en.wikipedia.org/wiki/Equivalen ... resistance

[MrAl]

ESR stands for "equivalent series resistance":

https://en.wikipedia.org/wiki/Equivalen ... resistance

Yes it is like a resistance in series with the cap. When a current flows into the cap it has to go through that resistance and that means that the voltage at the terminals of the actual physical capacitor goes up or down quickly which is not how an ideal cap works. That means it can not act as a filter as well as if it had no ESR. This means the ESR is a very important specification because if the ESR is too high it can not act as an effective filter especially for power supply rails. The 100uf cap is used in that way for the relay board. It is supposed to filter the Vdd line which is the positive voltage for the IC chip and timing resistors. When a cap develops higher than normal ESR in a switching power supply the power supply will often turn off at unexpected intervals meaning of course the power supply becomes unusable. Once the caps are replaced with good ones, the power supply runs fine again. For the relay board it's almost the same thing. The operation can become very erratic because the Vdd line is not stable anymore. This circuit is especially vulnerable because the source of the current for the cap comes from the top side of the relay coil, which is kind of strange. That means when the coil deenergizes and the voltage rises, it tries to charge the 100uf cap even higher which is a source of noise on the Vdd line. Luckily there is a zener to tone that down a bit but the internal impedance of a zener is not zero so there will still be some Vdd modulation as the coil shuts off. That could cause all kinds of intermittent problems.
Needless to say, i will replace this cap and next i'll check the 22uf cap, but i'll be replacing that too.
Unfortunately the 100uf cap i got from the part number i got from the other thread isnt all that perfect either. It's got about 1 Ohm ESR. I would have preferred 0.1 Ohm for a power supply. It's still a lot better than the old one that was in there though so it should still work better.
This should clear up the intermittent problem once and for all

I went through all this because i wanted to be at least reasonable sure there was actually something wrong with the relay. If it was any more complicated though it may not have been possible but the complexity was not entirely out of range so it was doable.

I hope all this helps you with yours too.

[MrAl]

Some more very interesting news that could make the test of this relay even simpler.

If you read this thread out you would have read that i quoted a test where you connect +12 and ground to the relay and then tap the ECU line to the ground line several times and see that the relay contacts close, or just listen for the distinct 'click' as it closes.
Well, that was BEFORE i replaced the 22uf and the 100uf caps.
NOW all i have to do is touch the ECU line to ground ONE TIME and the relay turns on!
That change in behavior is very very significant as it says that the relay wasnt working right to start with when it had the old caps in there. The new caps make it easier for the ECU to keep the relay on and thus the fuel pump running.

Pretty amazing what two caps can do. I have a strong feeling it was mostly the 100uf cap though as that was the one we all suspected at first because the voltage rating was too low, and having the cap age for several years just compounds the problem. It also tested for very high ESR so maybe no surprises there. Since it is being used to filter the main power supply line to the circuit that's bad.

It's been a pretty long road for me with this relay, i think i was working on this on and off for about three weeks. The relay should be working fine now glad that's over with

I got a lot of help with this car from many members here, so this is my contribution and I hope other people find this information useful.

[850oldschool]

Thanks for contribution, Al! Is your DSO test rig a combination of a laptop and a Hantek interface? I'm right on the edge of buying an oscilloscope for troubleshooting cars and miscellaneous electronic items around the house.

[MrAl]

Thanks for contribution, Al! Is your DSO test rig a combination of a laptop and a Hantek interface? I'm right on the edge of buying an oscilloscope for troubleshooting cars and miscellaneous electronic items around the house.

Hi,

It's like that but it's name brand is Intrustar. It's a USB scope so you dont get any knobs or a screen or anything like that, just two scope probe inputs you plug the scope probes into. The knobs and other controls are in the software that comes with it.

I got that quite a while back i think it was $70 and the reason i got that one was because it allowed for lengthy data recording. I've recorded hours of data with that some time back when i first got it. The waveform recordings are all stored on the hard disk of the desktop or laptop computer. It does not work with Android or Apple phones, just PC's that have Windows op sys. There could be an app for it by now as this was maybe 10 years back now, but i didnt check.

If i was to get one now though, i would go for one of those less than $150 USD as they are complete scopes with a screen and all the knobs and everything. They are pretty nice. I think the bandwidth runs from about 40MHz to about 100Mhz on them, if you want higher you have to go higher in price usually. But the nice thing is you dont have to lug your laptop out there with the scope and probes and other equipment just grab the scope and probes and go.
The 300+ dollar ones are really nice but probably dont need one like that.

Just to note, i also got a cheap 1MSPS (1 megasample per second) scope that had a little screen on it about 3 inches wide, and that thing was well worth the $25 bucks. I had to make my own battery pack but that was just a battery holder stuffed with 8 x AA batteries.
To show how far these things have come in the past 20 years, i used that little thing to decode every IR remote control i had for all my devices and there was no hassle. It clearly shows the waveforms no problem although it was just single channel.
Even that scope as cheap as it was would work on the car, i should have gotten that one out instead of the USB scope.

The ECU frequency is only 40Hz and i dont know a scope that could not see that waveform with no trouble because it is so low in frequency. Now if it was 40MHz i'd say get a better scope. It really depends on what you want to spend i guess.

Hey if you get one maybe you can post some pics here.

What else is amazing is these scopes are all storage scopes, something that would cost a bundle back in the 1970's maybe even the 1980's. When i worked back then, i used a storage scope that was as big as a small refrigerator. It cost something like $3000 at the time too. I also used the typical 20MHz CRT scopes with no storage ability. They were ok but no storage.
I also have a really really old 10MHz CRT scope made by BK a long time ago but that's bigger than my computer ha ha.

One side note about the CRT scopes, because they use an electron beam you can illustrate the Lorentz Force due to a magnetic field using just a plain magnet and bringing it close to the scope side after you form a dot on the screen. You can see the dot move as the magnet comes closer, and that shows how the Lorentz Force works. It's amazing how many videos there are on the web, and most of them do not provide enough detail to let you know which way the defection should go. They use wires and big magnets and huge current levels to show the wire jump. If they had shown the direction of current and magnet polarity and all that it would be much more informative. But you can only do this with a CRT scope the digital ones today wont be able to because they dont have an actual electron beam. Funny. Most of us dont have to illustrate that though (ha ha).

[MrAl]

Hello again,

I just realized another reason why i dont like modern cars.
A 50 cent capacitor cost me $100 tow fee to get home. That's just ridiculous.

Anybody know of a cheaper tow service in the central NJ area?

[abscate]

I’ll guess there are 1000 parts under a dollar that make a car not driveable.

I’ve never had a fuel relay failure in my fleet of 1999-2012 model cars, numbering 9, totaling 1.3M miles driven

FCP has a good tow cancellation service for you, at $55.... it’s part 9434225

[Chuck W]

... it’s part 9434225

That, or you just grab a spare JY relay or two and replace the capacitors in them and keep as spares. I did about 6 a while back and keep an extra in both of the 850s.

[850oldschool]

I've driven home on the jumper test wire once.