Re: Trunk Fuel Resistor
 

Hi,

I got a chance to pull the trim and check the resistor.

I get 1.3 Ohms, with the leads providing about 0.3Ohms of that.

So, seem like it's a 1 Ohm resistor.

Hope that helps!
Ian.

Re: Trunk Fuel Resistor
 

Special thanks Ian, removing the trim must have taken some time.

The reported problem:-

(1) “When I got the engine running normal, I would unplug the fuel control module from under the deck lid, yet the car would continue to run normally.”

(2) “Yet when I unplug it (The resistor), the car starts. When its plugged in it does not.”

Ian, unfortunate that I have to call on you again but only then can we move forwards as the situation is completely confusing.

I must ask you to please confirm that the resistor was disconnected when it was measured.

Again thanks, Trevor.
.

Re: Trunk Fuel Resistor
 

Hi Trevor,

the resistor was unplugged when I took the measurement.

Cheers,
Ian.

Re: Trunk Fuel Resistor
 

Thanks Ian this has been a tedious process as you will understand.


(1) “When I got the engine running normal, I would unplug the fuel control module from under the deck lid, yet the car would continue to run normally.”

Therefore the resistor is completing the pump ground circuit.

(2) “Yet when I unplug it (The resistor), the car starts. When its plugged in it does not.”

Therefore when the only the modulator is in circuit and the pump is running at a controlled speed and pressure the car starts, but when the resistor is connected in parallel with the modulator it does not start, possibly due to high pump speed and abnormal fuel pressure.

The final power transistor in the modulator is NPN and is switching on when the driver PNP is switched on via the ECU at c14. The ECU ground switching circuit must be OK as the pump relay is operating OK.

Conclusion:-

A short to ground within the resistor housing would result in the pump always running at full speed and this would account for the strange situation as per (1), the failure to start as per (2) and also other erratic engine behaviour. Furthermore the pump must draw a lot more current than one would expect.

Alternatively, both resistors measured are faulty and have reduced in value, which would be extremely unusual and unlikely but not impossible. Unfortunately the correct specifications can not be located.

Check the resistor for an internal short to ground.

Re: Trunk Fuel Resistor
 

Wow, I did not check quickly enough to see all the posts that I have missed.

Ian - Thank you very much for this tedious check. It is not lost on me how much effort is involved and once again I want to thank you.

Trevor - I am extremely fortunate to have such a methodical and detailed member assisting with this trace-down.

If I am following you correctly, because the reading of Ian's resistor off the car measures in-line with what I observed, you believe it to be an internal grounding issue within the resistor. I also agree that it would be very unlikely that both are faulty - but as these similarly aged cars are compared it could happen.

I messaged Huskymaniac regarding a thread he created in 2017 about a dropping fuel resistor and his homemade fix. I was looking for updates and feedback regarding his fix and if he noticed any non-reported side effects. I am between replacing my resistor with another used one or build my own as Huskymaniac presented but would love to hear any feedback from the forum.

Re: Trunk Fuel Resistor
 

You wisely and rightly say, "but as these similarly aged cars are compared it could happen." If my one and only old eye is seeing right, Tony used a 20 ohm resistor which is exactly what I would have expected to be the value involved as per my previous comments. One ohm makes no sense at all.

Quite a long time ago I corresponded with Tony by email and have his email address. He is a good guy and knows what he is about. I will shoot off man email and hope that it will reach him.

Meantime we must now ask Ian as to whether he is experiencing any problems with his car. The plot thickens, is becoming extremely interesting and has many ramifications.

Cheers guys, looks like a merry Christmas.

P.S. Unfortunately my email to Tony has bounced due to the address I have no longer operating. I have sent a personal message and hope for a reply as it would be very sad to have lost touch.

P.P.S. It is clear from the photo that Tony used a 20 ohm resistor as it is definitely marked 20R and this value could be made up from four common 5 ohm wire wound 10 watt or even 5 watt resistors, connected in series and these could be temporarily installed using screw connectors and checked for heat prior to making up a permanent set up. Tony knows what he is about and he must have researched the correct value.

Re: Trunk Fuel Resistor
 

Hello. old timer(s). Well, for some reason I stumbled upon this thread, & as I had no idea what a trunk fuel resister was, I vaguely followed along. I have neither the talent, or ability to deal with such a problem, so I'd no doubt dump the issue upon my "Do-it-all" local mechanic, & say "fix it" - "here's my blank check". But, so far, my '92 with 166k has never experienced said nightmare. So, the question is.........how common is this problem, & am I whistling in an approaching graveyard? Thanks to all....especially the old kiwi fart. ;)

Ron.

Re: Trunk Fuel Resistor
 

Merry Christmas Ronald.

Yes you old fartng wino, you do have talent and ability and are not as dumb as some may paint oldies you and me. You have wisely smelled a possible sleeping secret demon lurking amongst the stars.

The thread hints at a very real hidden virus and it will be interesting to hear from Ian. "Meantime we must now ask Ian as to whether he is experiencing any problems with his car. The plot thickens, is becoming extremely interesting and has many ramifications."

Ron you old bugger, from the moment we communicated so very long ago I have loved you so there it is. The place needs a bit of laughter going into a new year, so let's light up the fartable gas and drain a box 'o wine. LOL To hell with poverty, give the cat the canary. ;-)

Old fart Trevor.

Re: Trunk Fuel Resistor
 

Hey guys, just got an email from John about this.

The resistor I replaced was the transmission dropping resistor. As far as I know, it is still working well. But this sounds like a different resistor. Luckily, I believe these resistors come in a range of values, including 1 Ohm. You should be able to find them, and heatsinks, on Digikey, Mouser or Newark.

Trevor, I will email you. Not sure what is going on with the email.

Re: Trunk Fuel Resistor
 

Problem as it stands is the replacement part is no longer available. Looking for an alternative will be required.

That is unfortunate. The resistor looks very similar to the fuel one being discussed in this thread. I guess the hope will be a similar fix would also address this issue.

I spent some time this morning looking at fuel resistors used in other Subaru's hoping to find something that could be used. It seems many models have a similar fuel resistor and could be a cheap alternative to building our own.

Re: Trunk Fuel Resistor
 

Quote:

Originally Posted by Trevor (Post 749820) Ron you old bugger, from the moment we communicated so very long ago I have loved you so there it is. The place needs a bit of laughter going into a new year, so let's light up the fartable gas and drain a box 'o wine. LOL To hell with poverty, give the cat the canary. ;-) Old fart Trevor.

And a merry festivus to you, Trevor.

These cars are just like our failing bodies. we can keep building replacement parts, but in the end..............Uh, NO RUSH! However, when the world has gone "self-driving", you & I will mercifully be drainin' heavenly wine from the cloud. Cheers, & more cheers 'til then - Ron. :D

Re: Trunk Fuel Resistor
 

Attention "theflystyle",

Unfortunately we have become side tracked and must get back on the main line and wait until the resistor in your car is checked for for an internal short to ground. Only at that point can other possibilities be considered.

By the way a Christian name would assist towards personalising this discussion. As you can see we are all friends here. LOL

Re: Trunk Fuel Resistor
 

More info on the car I tested the resistor on.

It's a project car, has never been my daily driver (I sold my daily driver SVX). It does have only 47K miles on it, California car, and not a lot of abuse. But, I can't vouch for reliability at this time.

I might be able to get access to my previous daily drive SVX. I'll update this thread if I do.

Thanks,
Ian.

Re: Trunk Fuel Resistor
 

Can someone post a picture of this resistor?

Re: Trunk Fuel Resistor
 

Also, I need to ask exactly what gets unplugged and what gets plugged when the engine is able to start. Does the engine start when the control module is unplugged and the resistor is plugged? Or, does the engine start when the resistor is unplugged and the control module is plugged? Or, does the engine start in either case? If the engine starts with either one unplugged is it true that when both are plugged then it does not start?

I am going to assume, for the time being, that the engine starts when the control module is unplugged and the resistor is plugged. I am assuming that there was a mistake at some point when it was said that the engine will start when the control module is plugged and the resistor is unplugged. Given that assumption, I would say that the resistor is probably fine and that the measurement of one ohm is probably correct. In fact, one ohm makes a lot of sense. That resistor forms a voltage divider with the pump when the pump is running. Electric motors tend to have a low resistance so the series resistor would have to be low as well. Therefore, I would conclude that the problem is the control module and not the resistor. Most likely, the final transistor in the circuit is blown (base and collector are shorted) and the control module is supplying 12 volts-ish, through the internal resistor, to the pump when it is plugged in. If that is true, the external resistor is probably getting very hot and the internal resistor in the control module is probably getting very hot.

Fly, can you either measure the voltage across the external resistor or, with a clamp-style current meter, measure the current through it? I would be curious to know how the voltage and/or current changes when the control module is plugged versus unplugged.