exister99 Posted January 16, 2006 Share Posted January 16, 2006 Hello Fellow Soobsters! This past Saturday I had a fuel delivery failure due to trouble with my Fuel Pump Control Unit. I took it apart and this is what I found inside http://www.andrewhstone.com/images/Auto/DCP_0088.JPG The little black box with a "150" printed on it is a relay. Since it is the only component with moving parts on this circuit I surmised it's solder joints are the most likely to fail so I unsoldered it, opened it up, tested it, closed it and soldered it back on. The car started up just find. There is still a possibility that I encountered an intermittent failure in one of the other joints and I am ready to address this if it comes up. I also built some jumper wires that would allow me to hotwire the fuel pump to keep from getting stranded in the event the FPCU fails again. Looking at the circuit in the picure it became apparent that it is all fairly common components: resistors, relay, transistors, a power inverter, etc.. My question is, has anyone ever tried building this circuit from components rather than paying $300 for a new one? I have seen the solutions that bybass the FPCU and use the signal from the oil pump or fan to drive the replacement relay, and my hat goes off to the ingenuity of those who came up with them. However, I would think that most of us would rather keep our rides as stock as possible, especially with regards to critical components like fuel delivery. Does anyone have any ideas about where we might possibly get a hold of the original schematics for these FPCUs? It would be possible but tedious to reverse engineer it. I am thinking that it would be cool to buy the components and solder up a replacement FPCU. It seesm most of ours are starting to fail at around 20+ years so I think this would be a popular item. my guess is the parts would come in under $50 and when it is finished you would have an up to spec FPCU with all new components and solder joints that ought to get your Soob through the next 20 years (assuming you don't roll it first :-p.) So, what do you all think, any suggestions or input? Link to comment Share on other sites More sharing options...
Cougar Posted January 17, 2006 Share Posted January 17, 2006 The item that is most likely to fail is the relay. The rest of the parts usually don't have trouble. A transistor may fail but you can usually use a generic one to replace it. I repaired the ECU in my '88 GL-10. A transistor had failed in the fuel pump driver circuit after I replaced the alternator. Link to comment Share on other sites More sharing options...
exister99 Posted January 17, 2006 Author Share Posted January 17, 2006 Notes on Subaru Fuel Pump Problems. The car has refused to start on 3 separate nonconsecutive cold mornings. On Saturday, 14 January, 2006 it would not start and I decided to begin diagnosing. The float bowl on the carb was empty, and no fuel came out of the fuel lines while cranking the engine. There was no voltage at the fuel pump while cranking. There was no clicking noise when the ignition was turned to ON or when the engine was turned over. Once I hot-wired the fuel pump it began to pump and the engine started and ran once the bowl in the carburetor filled up. I removed the FPCU. I opened and inspected the FPCU. I unsoldered and opened the relay on the FPCU. I connected the relay coil to the battery and the switch clicked just fine. I resoldered the relay to the FPCU and reinstalled the FPCU. The car started fine and ran for two days. This morning was chilly and the car wouldn’t start. Plan of Action. Pull the FPCU and inspect all solder joints. Put the FPCU in the freezer for an hour and see if that makes the relay switch stop working. Possibly find a new relay at Fry’s and install it. If that fails look into testing and replacing the transistors on the FPCU. The fact that the fuel pump was getting no voltage when I tested it indicates that the problem is almost certainly not in the fuel pump. What else besides the FPCU could cause a lack of voltage to the fuel pump when it is cold outside (30-45 degrees F)? Link to comment Share on other sites More sharing options...
Subarian Posted January 17, 2006 Share Posted January 17, 2006 I circumvented the problem on mine by running a wire from the + terminal on the coil to the fuel pump. Now the pump is energized whenever the ignition is in the run position. Link to comment Share on other sites More sharing options...
exister99 Posted January 17, 2006 Author Share Posted January 17, 2006 I circumvented the problem on mine by running a wire from the + terminal on the coil to the fuel pump. Now the pump is energized whenever the ignition is in the run position. Yeah, I can start her up just fine if by installing a jumper to hot wire the fuel pump. I may seem stubborn, but I am pretty dead set on doing everything I can to resurrect the FPCU. Looking at the schematics it seems that on this year the FPCU and the ECM operate pretty much independent of each other so I doubt there is anything wrong in the ECM. If my efforts fail I may end up resorting to the relay and oil pressure sensor set up described in other posts. Link to comment Share on other sites More sharing options...
Subarian Posted January 17, 2006 Share Posted January 17, 2006 Good luck. I understand completely the desire to make it work, just because you know you can. Link to comment Share on other sites More sharing options...
Cougar Posted January 17, 2006 Share Posted January 17, 2006 The relay contacts internally are most likely dirty and intermittent. A common problem. Replacing the relay on the board should fix you up. The other parts on the board are very reliable. Link to comment Share on other sites More sharing options...
exister99 Posted January 17, 2006 Author Share Posted January 17, 2006 The relay contacts internally are most likely dirty and intermittent. A common problem. Replacing the relay on the board should fix you up. The other parts on the board are very reliable. Yeah, the impression I have gotten from my research is that all of the other components would be more likely to die and stay dead, and that the intermittent, cold induced nature of the failure points pretty strongly to the relay. Fortunately I found a 12V relay at Radio Shack that looks like it has the exact same pins and dimensions as the one on the FPCU. I plan on soldering it on tonight. If that turns out to be the fix it will be great news for those of us who have suffered FPCU failures. I noticed on the relay packaging that it is rated for like 100,000 switchings or some such, so it definitely has a finite life. I will keep you posted on my progress and report the Radio Shack part # if it works out. If all goes well someone will have to show me how to post an article on the Ultimate Subaru Repair Manual. Link to comment Share on other sites More sharing options...
exister99 Posted January 19, 2006 Author Share Posted January 19, 2006 Just a quick update. Radio Shack part number 275-248 is an exact replacement for the relay in the FPCU. All you need to do is clip off the NC pin and it will be a perfect fit on the circuit board. I bought one and installed it two days ago and have not had a no start condition since. The car does have to turn over a few times before it starts first thing in the morning, but has not yet failed to start. I am going to wait for it to make it through a few more freezing mornings before calling it a fix. Link to comment Share on other sites More sharing options...
Sweet82 Posted January 19, 2006 Share Posted January 19, 2006 What's wrong with a Junkyard part for $5-10? I had the same issues and looked at a new one but that just didn't make sence. I also wired my pump to the coil until I could locate a Junkyard FPCU. Seems to me a JY is a quick, cheap, real fix? Glenn, 82 SubaruHummer 84 GL Mad Max 01 Forester Link to comment Share on other sites More sharing options...
exister99 Posted January 19, 2006 Author Share Posted January 19, 2006 What's wrong with a Junkyard part for $5-10? I had the same issues and looked at a new one but that just didn't make sence. I also wired my pump to the coil until I could locate a Junkyard FPCU. Seems to me a JY is a quick, cheap, real fix? Glenn, 82 SubaruHummer 84 GL Mad Max 01 Forester Since these relays have a finite service life one pulled from the junkyard is likely to fail soon anyway. Soldering in a brand new relay is IMO the best fix for a faulty relay, especially if you can find one that is an exact replacement like I did. Also, junkyard Soobs are hard to come by in Central Texas. You can bet that the next time I come across a junkyard Soob I am pulling the FPCU, mostly so I can use it as a prototype to build my own from discrete components. All part of my ongoing effort to take the Soob to the 500,000 mile mark. Link to comment Share on other sites More sharing options...
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