zuperair Posted August 1, 2009 Share Posted August 1, 2009 I haven't had any luck searching this topic, any help would be appreciated. I swapped my fuely head on my L28 ('77) for an e31 head and set it up with triple webers. I removed all the associated fuely harnesses and the computer as well the dropping resisters. Before doing so, I tested the connections at the stock fuel pump, and found that power to the pump is initiated only after turning the key to "start". The relay then must keep the pump powered after the engine is running I'm guessing. When I attempted to start the engine after the swap, I found that I no longer had any power to the pump, and have traced that to the removal of the fuely computer. I bypassed the stock wiring with a makeshift harness to the battery, and got the engine running (wicked cool) so I know everything will work. How do I wire my relay/pump so that I can use the stock wiring? Is there an easy way to power the relay off the ignition circuit? Thanks in advance for any help/suggestions! Quote Link to comment Share on other sites More sharing options...
WildBill Posted August 2, 2009 Share Posted August 2, 2009 Not sure what fuel pressure on the injection system is, but typically would be quite a bit higher than you need for carbs, so might check on that first. As far as the relay, they are very simple, just need key on power to activate relay. Relays are very basic, just need a ground, power in, activation, power out when activated. If you can't figure it out with the stock relay, just go to the parts store and ask for a 30 amp 4 pin relay (can have 5, you just don't use the fifth terminal) and hook it up. The relays actually have a wiring diagram on them, or I'm sure you could find a schematic online or in an electrical book (check repair manual, or local library) Good luck! Quote Link to comment Share on other sites More sharing options...
zuperair Posted August 2, 2009 Author Share Posted August 2, 2009 Thanks for the reply. After going over the wiring diagram I'm now thinking that there is no pump relay. I mistook the "fuel injection relay" for the pump relay the first time through it. It appears the the power from the pump comes from the fuel injection computer which is powered by one of the fusible links. Now guessing that the FI computer also acts as a relay for the fuel pump. I'll find the correct wire from that remaining harness, and put a relay on it. Should have it sorted out today if I can make the time. On the fuel pressure issue, you are correct on the lower pressure required for the carbs. I already swapped out the stocker for a carter. 3-4 psi is all that's required for the DCOE webers. Volume is what they really like...Hi volume, and low pressure. Sounds like a great sales job when I think of it that way Quote Link to comment Share on other sites More sharing options...
theghosttanker Posted August 2, 2009 Share Posted August 2, 2009 If you have an e-31 head on there now just use a stock mechanical fuel pump with it and eliminate the electric one altogether. Quote Link to comment Share on other sites More sharing options...
thrustnut Posted August 2, 2009 Share Posted August 2, 2009 There was a relay in the system. There is a plug on the drivers side underneath by the steering column where one of the FI harness plugs was attached. When I did the carb swap on my '77 I Jumpered switched power to the power circuit to the pump at that plug for a while before I made my own circuit. I am running an independent relay for my pump now on a circuit I made, much easer then tracking down the stock wiring which I think you got rid of in the first place. Wild Bill was right...what pump do you have? If it's the FI pump I wouldn't start your car again till you swap it for a carbureted pump. Carter makes a pretty cheep electric with an in-line filter attached. Quote Link to comment Share on other sites More sharing options...
zuperair Posted August 3, 2009 Author Share Posted August 3, 2009 If you have an e-31 head on there now just use a stock mechanical fuel pump with it and eliminate the electric one altogether. I do have the e31, but I can't run the stock mechanical since it wont have the right fuel pressure for the triple webers. They're kind of touchy on the fuel pressure. There was a relay in the system. There is a plug on the drivers side underneath by the steering column where one of the FI harness plugs was attached. When I did the carb swap on my '77 I Jumpered switched power to the power circuit to the pump at that plug for a while before I made my own circuit. I am running an independent relay for my pump now on a circuit I made, much easer then tracking down the stock wiring which I think you got rid of in the first place. Wild Bill was right...what pump do you have? If it's the FI pump I wouldn't start your car again till you swap it for a carbureted pump. Carter makes a pretty cheep electric with an in-line filter attached. Interesting! I know the plugs intimately at this point. I have found the stock wire that leads to the pump, and have jumped that for a test. It worked, but I didn't think of jumping it from one of the other plugs that connected to the FI relay. I'll look at that today. I did buy a generic relay for the system yesterday. But, If I've got switched power in that FI harness somewhere, that would be an easy job. Mount the relay in place of the FI relay, and the wiring would be like a 9" harness tops. Oh, and the pump I'm using is a Carter matched for this Weber system. It works great. A little loud in the "Whirrrrrrrr" dept. but then again, I've got the car completely stripped down, no interior, carpeting, tail light assemblies. So, I'd guess with the car bare, it's louder than it will be when the car is re-assembled. I just got the exhaust system in it on Thursday. 6 into 2 Hooker Super Comp header (ceramic coated) into twin 2 1/4" pipes to twin glasspacks, piped to twin Ansa Turbo Tips. Just in the pre-tune stages now, but this thing howls!!!! I'll bleed out the new wilwood system this week so I can tune it for the road instead of the driveway. Up till now, I've just been using the custom emergency brake kit to stop the car here around the house. Thanks for the replies!!! Quote Link to comment Share on other sites More sharing options...
thrustnut Posted August 3, 2009 Share Posted August 3, 2009 There is switched +12V at that same plug if you look at a wiring diagram. That's the power I used. If you do it that way you shoulden't need a relay at all. I just did it because I don't like leaving things jumpered, just seems like it would be the weak link in the system which would be bad in the fuel department. If that Carter pump is the same one I have, the interior won't make it much quieter. I have a full interior and can hear it kick on before I start up. Kinda nice though, at least I know its working! Sounds like you got a good build going, keep it up! Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted August 4, 2009 Share Posted August 4, 2009 The air flow meter has a microswitch in some year 280z cars. (don't remember if 1977 has it). You can test for that by holding the flap of the airflow meter open while the key is turned and see if you have power to the pump. A jumper there will ensure fuel pump operation whenever the key is turned.....unless you are keen on removing the entire injection harness to clean up the bay which will require jumpering and splicing elsewhere. Quote Link to comment Share on other sites More sharing options...
theghosttanker Posted August 4, 2009 Share Posted August 4, 2009 I successfully ran triple webers on the stock mechanical fuel pump, but I had trouble with double Webers, which was easily fixed by using a cheapo Spectre fuel pressure regulator. All of this is a much easier fix than using the electrical stuff! Quote Link to comment Share on other sites More sharing options...
zuperair Posted August 4, 2009 Author Share Posted August 4, 2009 There is switched +12V at that same plug if you look at a wiring diagram. That's the power I used. If you do it that way you shoulden't need a relay at all. I just did it because I don't like leaving things jumpered, just seems like it would be the weak link in the system which would be bad in the fuel department. If that Carter pump is the same one I have, the interior won't make it much quieter. I have a full interior and can hear it kick on before I start up. Kinda nice though, at least I know its working! Sounds like you got a good build going, keep it up! I feel the same way about leaving something jumpered. I did set it up with a relay yesterday using the power source from the plug, the keyed "on" power from the ignition switch, and a local ground. I even went as far as using the stock fusible link that was in the FI loop. The air flow meter has a microswitch in some year 280z cars. (don't remember if 1977 has it). You can test for that by holding the flap of the airflow meter open while the key is turned and see if you have power to the pump. A jumper there will ensure fuel pump operation whenever the key is turned.....unless you are keen on removing the entire injection harness to clean up the bay which will require jumpering and splicing elsewhere. Yeah, I did remove all traces of the FI system. No harnesses, computer, relay or resistors. When I pull the engine and trans for paint prep, I'll even grind off the mount for the air flow meter and the mount for the air cleaner. Going to get it as simple looking as possible. I successfully ran triple webers on the stock mechanical fuel pump, but I had trouble with double Webers, which was easily fixed by using a cheapo Spectre fuel pressure regulator. All of this is a much easier fix than using the electrical stuff! Interesting! I ran the 32/36 dgv dual weber setup for about 15 years in my 260. Always off of the mechanical with no issues ever. Had talked with several guys that had pressure reg's on their fuel lines for that setup, but mine was a dream. This triple setup I bought came with the carter, so I just went with it. They said it wouldn't need a reg', and at least in the driveway they're right. We'll see once it hits the road and gets under a load Quote Link to comment Share on other sites More sharing options...
thrustnut Posted August 4, 2009 Share Posted August 4, 2009 I'm running a 625 CFM Carter carb with probable the same pump with no regulator. I have a narrow band O2 to help get me in the ball park tunning wise and under full throttle I never had a lean problem. I'm not sure of the diffrences between tripples and a big 4BBL, but I have never leaned out under full throttle. Quote Link to comment Share on other sites More sharing options...
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