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Another fuel pump question


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14 replies to this topic

#1 jeffroid

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Posted 22 November 2004 - 05:50 PM

Sorry for the long post, but I did my homework and searched the forum first and I still don't understand.

I've been posting about my '83 GL 4WD wagon. I got it all back together and have been driving it back and forth to work and it's been doing fine. This weekend I took it out on the highway for the first real time. After a while at 65-70 it would cut out and run crappy but not die. I'd exit and roll up to the stop sign or light or whatever and it would still idle, but when I'd go to take off driving again, it would die. As soon as I turned the key and restarted, it would be fine again, until I got back on the freeway and drove for a while at 65-70. After a while, I figured out that all whenever it started acting up all I had to do was turn the key off and back on again and it would "reset" and run fine for a while until the next period of high fuel demand at which point it would start all over again.

Like I said, I searched thoroughly and read all the posts about the Fuel Pump Control Unit. I figured it was bad and was making the fuel pump think the car wasn't running and shutting off the fuel pump for safety. I replaced the unit with the one from my parts wagon. It looked the same, but the part number was very slightly different, although both wagons have Hitachi carbs. Anyway, that didn't work - same problem so I switched the FPCUs back.

Also, I'm thinking, If it is that control module telling the fuel pump that my engine is not running and to go into "safe" mode, it's going to shut me down completely, not just make me run crappy, right? And how come it never showed up for weeks until I got on the highway and drove 65-70 MPH?

BUT if it's something else like filters or fuel pump or carb, how can the thing be instantly fixed just by turning the key off and back on again?

So I ended up patching into the hot (blue) wire right at the fuel pump, and spliced another wire to run right back to a dash mounted switch and then to a wire that is hot with the key on. That seems to fix the problem. But now, it appears that the pump won't run at all unless the hot wired switch is turned on. In other words, it's not doing what it did before - "fixing" itself by turning the key off and on again.

Again, sorry for the long posts, but this is really a rubix damned cube trying to figure out, and I was hoping that someone would have an idea as to what my problem is, or what that Fuel Pump Control Module is actually supposed to do (and how and why).

THANKS ! ! !

#2 Sweet82

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Posted 22 November 2004 - 06:29 PM

I think the first thing you need to do is eliminate the easy things.

Change both fuel filters and see if that was the problem. It could be something restricting fuel flow in your filters.

My guess would be that the FPCU is good and it's a filter or a pump issue?

When my pump went out it was an intermittant short and would do wierd things. It never did leave me high and dry as it would alway refire after a rest.

Give it a basic tune up.
Glenn
82 SubaruHummer
01 Forester

#3 jeffroid

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Posted 22 November 2004 - 07:24 PM

I think the first thing you need to do is eliminate the easy things.

Change both fuel filters and see if that was the problem. It could be something restricting fuel flow in your filters.

My guess would be that the FPCU is good and it's a filter or a pump issue?

When my pump went out it was an intermittant short and would do wierd things. It never did leave me high and dry as it would alway refire after a rest.

Give it a basic tune up.
Glenn
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01 Forester

Thanks for the reply - my post was getting long enough as it was to elaborate, but I have pretty much eliminated tuneup and and filter issues. Both filters are brand new, and I can watch them fill up easily when the pump is operating properly. Plus, like I said, when it starts running crappy all I have to do is turn the key off and back on again and it runs like a bat out of hell.

I'm with you on an erratic fuel pump being a possibility, but I'm not even sure when or when I am not getting voltage to the fuel pump. I have to do a better job of troubleshooting. I reckon I need to figure out a way to monitor the voltage to the fuel pump while I am driving down the road.

But are those fuel pumps inherently finicky by nature? I couldn't get the one out my parts car to work bench testing it with a battery charger, and it was working fine when I quit driving the car and parked it in my yard. I would have already replaced it, but they want like 50 - 60 bucks for one.

Anyway, thanks again for the reply and any for any help that anybody else can provide.

#4 chef_tim

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Posted 22 November 2004 - 09:08 PM

I had the exact same thing on my 86 wagon. It acted like there was alot of water in the fuel. Eventualy I can to the same conclusion that you did, turn off the key and it seemed to "reset" and it would be fine. I changed the carb and it has beeen fine ever since. Later, Tim

#5 jeffroid

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Posted 23 November 2004 - 12:12 AM

I had the exact same thing on my 86 wagon. It acted like there was alot of water in the fuel. Eventualy I can to the same conclusion that you did, turn off the key and it seemed to "reset" and it would be fine. I changed the carb and it has beeen fine ever since. Later, Tim

Interesting. That's kind of a curve ball. Thanks for the idea, Tim. Sounds like that's what your problem was, but I think I've got more troubleshooting to do before I decide to swap carbs.

For one, at least for now it appears that hot-wiring my fuel pump has eliminated the symptoms. I don't know if that points me to the carb or not. I need to check some voltages to the fuel pump under different conditions also.

I don't have a decent manual yet (FSM scored and on it's way in the mail), but the wiring diagram in my Haynes and some of the other posts indicate that the FPCU talks to the choke.

Does anybody know why in the hell it needs to talk to the choke? Is there something to do with the fuel pumping or not pumping depending on the choke postition or vice versa? Or does that little box (FPCU) just happen to control the fuel pump and choke independent of each other?

#6 Sweet82

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Posted 23 November 2004 - 11:09 AM

It's the FPCU that does the talking, I just threw away my hand made wiring diagram yesterday---It may still be outside in the can?

What happens is the FPCU determines if the car has reached operating temp or if it is still cold. The choke is adjusted accordingly by the FPCU. It won't run worth crap (when it's cold) unless you have this working properly. I've been down that road...

In your case, I don't think it's the FPCU, you have swapped it out, without results.

When my Fuel pump went out back in the 80's the Subaru Dealer hooked a light up to the FP and put it on the rack...sure enough eventually the light went out and the car stopped. Intermittant short. You may want to rig up something like that? You could trace it to the wiring or the pump using that method.

A ground problem would make some sence.
Glenn,
82 SubaruHummer
01 Forester

#7 Sweet82

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Posted 23 November 2004 - 11:15 AM

It's the FPCU that does the talking, I just threw away my hand made wiring diagram yesterday---It may still be outside in the can?

What happens is the FPCU determines if the car has reached operating temp or if it is still cold. The choke is adjusted accordingly by the FPCU. It won't run worth crap (when it's cold) unless you have this working properly. I've been down that road...

In your case, I don't think it's the FPCU, you have swapped it out, without results.

When my Fuel pump went out back in the 80's the Subaru Dealer hooked a light up to the FP and put it on the rack...sure enough eventually the light went out and the car stopped. Intermittant short. You may want to rig up something like that? You could trace it to the wiring or the pump using that method.

A ground problem would make some sence.
Glenn,
82 SubaruHummer
01 Forester

#8 jeffroid

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Posted 23 November 2004 - 11:42 AM

It's the FPCU that does the talking, I just threw away my hand made wiring diagram yesterday---It may still be outside in the can?

What happens is the FPCU determines if the car has reached operating temp or if it is still cold. The choke is adjusted accordingly by the FPCU. It won't run worth crap (when it's cold) unless you have this working properly. I've been down that road...

In your case, I don't think it's the FPCU, you have swapped it out, without results.

When my Fuel pump went out back in the 80's the Subaru Dealer hooked a light up to the FP and put it on the rack...sure enough eventually the light went out and the car stopped. Intermittant short. You may want to rig up something like that? You could trace it to the wiring or the pump using that method.

A ground problem would make some sence.
Glenn,
82 SubaruHummer
01 Forester


Thanks - So you are saying that the FPCU senses temp and controls the choke. Where does it get the temp from? As I recall, the wiring diagram shoes it going to the choke, but I didn't notice the FPCU connected to any sensor. The fuel pump doesn't care what the temperature is, does it? In other words, the FPCU doesn't change the voltage to the fuel pump depending on temperature, does it?

In any regard, my choke seems to be working fine. I like the idea of the light. I was thinking about trying to figure out a way to hook up my multimeter so I could monitor voltage to the pump while I was driving down the road. A light might be a lot easier, and I am trying to avoid concluding it is the fuel pump until I am sure I am getting the proper voltage to the pump when I am supposed to, especially when for now the pump appears to be working fine "hot wired".

Anyway, thanks for the help.

#9 naru

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Posted 23 November 2004 - 02:33 PM

As well as a tired pump,I`ve seen your original symptoms from carb icing(it melts quick-heat pipe hooked up?)and a bad filter sock in the tank(non-sube).
However,since it works well hot wired,that seems to rule those out unless your weather has changed(icing).

Could be the FPCU can`t handle the higher current draw demanded by the pump at high flow.
Engine won`t die immediately when the pump is unpowered,but will run incresingly badly until fuel level in the carb is too low.
FPCU doesn`t sense temp,it merely supplies power to the choke heater and pump when it sees ignition pulses at the coil.Only reason I can see for powering the choke this way is to prevent the choke from opening w/the key on and engine off.

Unless you disconnected the FPCU from the pump before hotwiring,it may have been (furthur?)damaged.Could be that is why it doesn`t reset any more.
Wiring between the pump and FPCU is also suspect.
Hooking a voltmeter to the pump under running conditions is a great idea.
You may want to consider the filter screen inside the carb as well.
Good luck.

#10 jeffroid

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Posted 23 November 2004 - 04:45 PM

As well as a tired pump,I`ve seen your original symptoms from carb icing(it melts quick-heat pipe hooked up?)and a bad filter sock in the tank(non-sube).
However,since it works well hot wired,that seems to rule those out unless your weather has changed(icing).

Could be the FPCU can`t handle the higher current draw demanded by the pump at high flow.
Engine won`t die immediately when the pump is unpowered,but will run incresingly badly until fuel level in the carb is too low.
FPCU doesn`t sense temp,it merely supplies power to the choke heater and pump when it sees ignition pulses at the coil.Only reason I can see for powering the choke this way is to prevent the choke from opening w/the key on and engine off.

Unless you disconnected the FPCU from the pump before hotwiring,it may have been (furthur?)damaged.Could be that is why it doesn`t reset any more.
Wiring between the pump and FPCU is also suspect.
Hooking a voltmeter to the pump under running conditions is a great idea.
You may want to consider the filter screen inside the carb as well.
Good luck.



Thanks - great ideas. I did not disconnect the FPCU and it did occur to me that I may have damaged it with the hotwire.

I'm going to play around with the voltmeter before I do much of anything else.

#11 jeffroid

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Posted 25 November 2004 - 12:10 PM

Sorry, but I need to bump this back up again because I had another incedent and have an entirely new question.


The '84 wagon started crapping out on me last night even with the fuel pump hotwired. I still haven't finished my troubleshooting with the voltmeter, but I picked up another pump last night so I could install it today (Turkey Day) if I needed to.

Problem? The Haynes manual I have says the fuel pump specs should be 1.35 to 2.06 PSI and 7.4 gallons/hour. The smallest pump I could find in any of the local parts stores last night was a Purolator PRO 06SV that puts out 4-7 PSI and 32 gallons/hour. I picked it up, but checked on the Purolator website when I got home, and they also make a PRO 04SV. They don't give the numbers on that one, but it's the one recommended for Subaru carb engines. It's the same price.

Question - Is using the higher flow pump going to "over power" my carb or whatever and put too much fuel in it? Or is the 06SV going to be OK to use? I guess my basic problem is that I don't understand exactly how things work. I think that the fuel pump fills the float bowl up and seats a needle which stops the flow when the level gets to the proper level. But is the extra few PSI going to over power the needle? Or is that even how it is supposed to work?

I would just go down and try and get the 04SV, but it's Turkey Day and everything is closed.

SAFE AND HAPPY THANKSGIVING EVERYBODY AND PLEASE HELP IF YOU CAN ! ! !

#12 Sooby Doo

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Posted 11 December 2004 - 12:15 PM

I have a related question, I was having similar problems and have not fixed it yet. I replaced the carb with a new weber and all of a sudden the fuel quite so I replaced the pump with a new one. Now I am not getting any power to my pump.

Here is my question, where is the FPCU located, and what does it look like? And the wiring diagram shows a fuse, where is that?

Thank you for any help.

#13 jeffroid

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Posted 11 December 2004 - 01:24 PM

I'm no expert but I saw this and your other post so I'll just tell what happened in my case:

I still haven't seen you share your make, model, and details on fuel system, but on my carbed '83 GL the FPCU is a little black box with a six wire connector. It's mounted down on the inside "kick panel" near the drivers side left foot. You will need to remove the panel under the dash, and the FPCU shares the same mounting screw as the hood release lever.

If you followed my earlier story, I was trying two different FPCU's that were behaving totally differently in terms of how many volts they were supplying to the pump and when. I got completely frustrated when it wouldn't even work hotwired, and out of desperation I started swapping parts from my parts car. Luckily, I started with the coil and noticed the little black wire that runs from coil positive through the little capacitor to ground was broken.

I fixed that and it eleviated the problem (more on the howire below). I'm still not sure how in the hell that worked, because I figured that little capacitor was only for radio noise suppression. Maybe I've got some kind of grounding problem somewhere else and that little coil wire is compensating or something.

In any regard, I still have the FPCU issues and am running the fuel pump off of a hotwire directly from a wire that is hot with the key on, to the fuel pump. It is switched at the dash and is spliced into and common to the positive wire from the FPCU so that I can trouble shoot by unhooking the wire from the switch and use that wire with a voltmeter to tell when and how many volts the FPCU is sending.

I've been daily driving that way ever since because I'm working in my yard, it's been raining a lot, gets dark at like 4pm up here, and I had other more urgent priorities.

I would try a hotwire. It would at least get you going so that you could troubleshoot. If I was doing mine again I might not splice the wire into the wire from the FPCU because that may have been what fried my FPCU.

Hope that helps.

#14 Sooby Doo

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Posted 11 December 2004 - 03:17 PM

Thanks for the input, I've been racking my brain trying to get this fixed. I failed to remove the majority of dash components before my parts car was crushed, so I do not have a spare FPCU. So now I'm considering doing a hotwire, it would take one less part out of the equation. Would I also need to hotwire my choke to a switch? I think I fried my FPCU when I wired my pump backwards, because thats when it stopped.

Thanks again
Oh sorry the car in question is my 82 GL

#15 Sooby Doo

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Posted 11 December 2004 - 04:37 PM

Well I just hotwired and it seems to be working. Thanks for the help




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