Fuel Pump Relay 9434225 Examinations 1998 v70 non turbo

[MrAl]

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.

The component on the far right is the relay. That would be the 'universal' relay in your idea. That is the component just to the right of Q1.
The 'discrete universal component' would be the rest of the circuit.
The delay comes from the 100uf cap and associated resistor R1, the base resistor of Q1. When the signal cuts out, the transistor stays on for a certain time. After that time, the relay opens up. The diode with the 100uf cap prevents discharging the cap through that part of the circuit, while the discharge comes from R1 and Q1 base emitter only. The time constant is roughly R1*C2, but the total time delay would be longer than that by some amount. C1 allows the first transistor to turn on only if there is an AC signal present. A DC only signal will not be able to turn the transistor on which will not allow C2 to charge which will not turn on Q1 which will not turn on the relay. The relay turns the pump on when the contacts close. It can be a regular old run of the mill relay, as long as the contacts can handle the full current of the pump motor, and probably we need another diode across the coil, or a snubber.
Q2 buffers the input signal, Q1 buffers the relay so we can get a much longer time delay without having to use a really high value cap for C2.

I don't remember what the function of position II on the ignition switch does.

Here is a more detailed drawing...

[MrAl]

Hello again,

I just wanted to add, if that circuit were to be used it would have to be fully and carefully tested because it involves an important safety feature of the car. That means that the circuit should probably be taken as an example of what could have been used, but because it has not yet been tested or even built for that matter, the original part should be kept as is at least for now. Take it as a sort of academic thing for now.

[jreed]

My 11 year old fuel pump relay just failed... took it out and inspected it: many of the solder joints have cracks. The biggest cracks are on the pins to the relay frame (first picture below at lower mag, pictures two and three are close-ups of each pin on the relay frame). One of the diodes and several of the through hole components such as the resistors also have cracks (fourth picture). I took some photos using a microscope:

Fuel pump relay cracks

Just wanted to document and share to add to the knowledge base here.

[abscate]

Awesome pictures. A reflow should fix that

[MrAl]

My 11 year old fuel pump relay just failed... took it out and inspected it: many of the solder joints have cracks. The biggest cracks are on the pins to the relay frame (first picture below at lower mag, pictures two and three are close-ups of each pin on the relay frame). One of the diodes and several of the through hole components such as the resistors also have cracks (fourth picture). I took some photos using a microscope:

crack1.jpg
crack2.jpg
cracks3.jpg
crack4.jpg
Just wanted to document and share to add to the knowledge base here.

Hi there,

This looks like an easy fix, but maybe you should change out the capacitors too. They have been known to go bad in these cars.
Steve has capacitors and he is very generous with them.

So anyway, just go over the solder joints with an iron and some 63/37 rosin core solder or at least 60/40 rosin core. I would not use lead free solder though that stuff can be a pain to get to flow right. 60/40 has been used since the beginning of time, and 63/37 just flows at lower temperature.
The coil terminals may require a little more heat than the other terminals.

I am not sure if you meant you found a cracked resistor. If the resistor itself is cracked you will need to replace that as well. If you do not know the value I can look it up in my extensive notes on this troublesome little relay. I went through the whole circuit back when I had a problem with mine and I can identify most of the components on the board.

I am almost sure you will get this to work again.

[abscate]

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

Did you have to get out and move it on each tire rotation ?

Sorry, Sunday humor…