Fuel Pump Relay 9434225 Examinations 1998 v70 non turbo

[850oldschool]

You think a lot of people would be interested in this kind of thing?

Lots of people will be interested, and 99% of them will then buy a new one from FCP with a lifetime warranty.



It's a great academic exercise, but not one that would be financially viable.

I wonder how long it will be before FCP excludes electrical parts from the "lifetime" warranty.

[MrAl]

You think a lot of people would be interested in this kind of thing?

Lots of people will be interested, and 99% of them will then buy a new one from FCP with a lifetime warranty.



It's a great academic exercise, but not one that would be financially viable.

Hi,

Yes i think that's right. Sometimes i dont look for profit though as long as it can help others a bit and maybe pay for the parts.
But yes probably most will just buy a new one. I didnt realize they had a lifetime warrantee i must have missed that.

[JimBee]

abscate: Thanks for dredging up this investigation.
That capacitor could be a gremlin in a former experience I've had. While this discussion doesn't directly answer my question (might that 40 hz safety shut off the signal to the pump while the engine is running—but then somehow reset to keep the engine running steadily after a rest?) it definitely sheds light on potential issues that could have that effect, even intermittently.

[RedBrickCollector]

I've been researching the Fuel Pump "Relay" and wondering why it is officially caleld a controller, and MrAl definitely has left a gold mine here.

Just to check my comprehension, the main purpose for the circuit is for two functions that won't be fulfilled by a simple relay?
One is to automatically shut the pump off when priming, and one is to shut the pump off if there is an accident?
To do this, the relay is energized when the unit recieves power from key pos II but as there's no ECU signal it shuts off after some amount of time, a few seconds?
Then after starting, once it has an ECU signal, it stays on until it loses power or ECU Signal?

Is my understanding correct?

I love the idea of a new upgraded board to achieve this in a single part, I'd buy it if it's still on the table, but also I wonder if this can be achieved with a combination of existing off the shelf universal relays or similar components.

[MrAl]

abscate: Thanks for dredging up this investigation.
That capacitor could be a gremlin in a former experience I've had. While this discussion doesn't directly answer my question (might that 40 hz safety shut off the signal to the pump while the engine is running—but then somehow reset to keep the engine running steadily after a rest?) it definitely sheds light on potential issues that could have that effect, even intermittently.

Hi,

My only guess right now is that it could be that the capacitor heats up a little and then malfunctions because it is on the verge of malfunction already. When the heat hits it or the current causes it to heat a little, that takes it over the edge and so it no longer works properly. When everything cools down, it begins working again and thus the fuel pump relay works again as a whole.
This is just a guess because I have never tested for this. I do know that once the capacitors are changed out, this never happens again, or at least never happened again on my car.

There is a way to tell but you have to monitor both the pump relay itself AND the signal from the ECU to make sure it is not the ECU that is turning it off. You can monitor both from the fuel pump relay socket, but may have to use a socket adapter or solder wires to some terminals. When I did my testing I had wires soldered to the INSIDE of the fuel pump relay housing and run outside the housing and folded up toward the top. That was so I could connect alligator clips to each wire (stripped the ends of each wire and formed small loop to grab with the alligator clips). That would allow test leads to be used for a meter to measure what kind of signal was there or if the relay was closed or open.

[abscate]

If only fuel pump relays lasted as long as this thoroughly deep dive into a car part!

Well done , Mr Al

Next up, wiper blades!

[MrAl]

I've been researching the Fuel Pump "Relay" and wondering why it is officially caleld a controller, and MrAl definitely has left a gold mine here.

Just to check my comprehension, the main purpose for the circuit is for two functions that won't be fulfilled by a simple relay?
One is to automatically shut the pump off when priming, and one is to shut the pump off if there is an accident?
To do this, the relay is energized when the unit recieves power from key pos II but as there's no ECU signal it shuts off after some amount of time, a few seconds?
Then after starting, once it has an ECU signal, it stays on until it loses power or ECU Signal?

Is my understanding correct?

I love the idea of a new upgraded board to achieve this in a single part, I'd buy it if it's still on the table, but also I wonder if this can be achieved with a combination of existing off the shelf universal relays or similar components.

Hi,

If by a simple relay you mean a regular relay with no additional electronics, that would allow the fuel pump to turn on, but it would not be able to turn it off if there was a problem that the ECU though should be a reason to turn it off. That is a safety feature for what it's worth.

It may be able to be done with two relays, but there would also have to be a transistor driver.
The way this could work is you have one relay function like the physical relay inside as the fuel pump relay does now. The second relay would be driven by a transistor. The transistor would receive its drive from a capacitor and full wave rectifier. The full wave rectifier would be powered from the ECU signal, and ground. When the ECU signal is present, the rectifier rectifies that into a unipolar pulsating DC signal and that charges the capacitor. The base emitter of the transistor would be driven through a resistor from the cap, and also ground. When the cap gets charged to a decent level, the transistor turns on, hence the secondary relay turns on, and that turns on the primary relay which turns the pump on. If the ECU signal is lost, there is no longer any DC voltage to charge the cap so the cap voltage decreases. Once the voltage gets low enough the secondary relay turns off, which turns off the primary relay, which turns off the pump.
That actually would not be hard to build. Two relays, a transistor, a resistor, a full wave rectifier (or even maybe just one diode), a decent size capacitor (maybe 1000uf 25v which is still cheap). I think that's all.
What surprised me is that one of the caps was only rated for 16 volts. I would think they would have used at least a 20v cap or 25v cap even better. Since the battery charges up to 14v or so normally, with a 16 volt cap that's only 2v margin of safety or even less. That's not very good especially since they are low voltage caps to begin with, where a slightly higher voltage cap would not cost very much more.

I kind of like the idea of using a two-relay circuit. Maybe I'll draw up a schematic later today. It's a nice simple idea I don't know why I didn't think of it myself

It would be very easy to use a single relay but we would lose the safety feature. I don't think that's a good idea at all. I could picture a scenario where something goes wrong and there ends up being gas all over the road.

[MrAl]

If only fuel pump relays lasted as long as this thoroughly deep dive into a car part!

Well done , Mr Al

Next up, wiper blades!

Hi Steve,

Ha ha. Yes, if they used a 25v cap instead of a 16v cap we may have never had this discussion at all

Electrolytic caps are notorious for failing in power applications though so maybe that would not be quite enough. I've had to change them out in several products in the past, and know lots of other people did too from posts around the web.

As I said before I think in this thread, I have done this kind of thing since I was very young so it was nothing new for me really. I had to dig deep into various kinds of electronic products to find out what might be wrong. That sometimes takes some extra effort.
it's also partly a hobby for me now too since I do not do any of this professionally anymore, being retired. I also talk to other people who do this kind of thing as a hobby as well as professionally still. Some of those other people go to much greater lengths than this. Believe me, from what I have done in the past and what others have done in the past, by comparison this would have been considered a walk in the park on a sunny but cool day

I am going to try to draw up a schematic showing how two relays with some other small parts can be used to emulate the functionality of the existing fuel pump relay. That would also bring out the simplicity of the concept they used to create this unique item.
They probably used that one IC chip because it was considered fairly reliable, and it was manufactured by the millions back then I bet so the cost would have been very low. A second relay would introduce a little less reliability I bet simply because it would be electromechanical instead of just electrical.

[MrAl]

Hello again,

Well the entire circuit came out even simpler than I thought at first. I had "two relays" stuck in my head because I thought of just using two relays at first, but then using one transistor with just one relay works also.

This can be considered a preliminary circuit which would need to be examined carefully, and of course some of the values to be determined yet.

The main issues are driving the relay of course, and making sure the relay will turn off with loss of ECU signal, and making sure not to tax the ECU output pin. BTW the ECU signal is shown as "V1" in the schematic.

This was a quick off the top of my head drawing so some modifications may still be needed. Functionally it should be the same however as long as the values are chosen correctly. This also provides at least some idea what is involved using more discrete parts.

Disclaimer:
You do have to realize that if you build this circuit and install it in your car it may void the warrantee.

[RedBrickCollector]

The theory behind my suggestion is to say

take the broken fuel pump relay to make a simple harness with a universal relay, and another discrete universal component that would take the ECU signal and control the relay that way.

Would you know if the ECU ends a signal in Pos II to prime the engine? Mainly I want to determine if the priming delay and the crash safety cutoff are the same circuit, in which case some sort of timer/delay component would suffice, something that would cut power after 4 seconds for instance. Off the top of my head it would be along the same lines as interior light delayed shutoff circuits.