dat240zg Posted March 30, 2008 Share Posted March 30, 2008 I'm still having the issue of the fuel pump not turning back on after priming. In previous posts, people have stated that the problem was that the harness had been changed so that the wire from the oil pressure sending unit was being used for a oil pressure gauge rather than to the PCM. (If I hardwire the pump, it turns on and the car will run). I checked the harness diagram and the tan wire from the sending unit actually goes directly to the oil pressure gauge (stock) and not to the pcm. Is there something that I'm missing? I sent the pcm back to Speartech get a few mods done and they believe that the oil pressure sending unit at the back of the intake manifold doesn't need to be connected to the PCM inorder for the fuel circuit to be complete. If it does need to be connected, which pin on the PCM does it go to? It wasn't originally wired to it (that I can tell) - or - was there a wire from the gauge back to the PCM to complete the circuit? Here are pics of the instrument panel connector and pin description: The oil pressure sending unit is the tan wire: The harness as it goes in to the passenger compartment (number C220) Thanks for helping me understand. Bryan Dat240zg Quote Link to comment Share on other sites More sharing options...
deja Posted March 30, 2008 Share Posted March 30, 2008 I'm using the stock Z28 harness and the tan wire from the sending unit at the back of the block definitely goes to the gauge. I had issues with my oil pressure gauge and totally checked this out so I know that is correct. There is also the oil level connection to the gauge cluster (BRN pin D12 on a Camaro & A15 on a Firebird) , no clue if that can cause your problem: I looked that the PCM connections and could not find any oil pressure inputs to the PCM. But A7 (dk grn/wht) is the "fuel pump relay control" that goes to the fuel pump relay. Are you sure your VATS has been removed from your PCM? There is a signal that comes out of the VATS that controls the fuel pump relay. So even if you can start the car by bypassing the key resistor VATS will shut off the fuel pump. I'm still having the issue of the fuel pump not turning back on after priming. In previous posts, people have stated that the problem was that the harness had been changed so that the wire from the oil pressure sending unit was being used for a oil pressure gauge rather than to the PCM. (If I hardwire the pump, it turns on and the car will run). I checked the harness diagram and the tan wire from the sending unit actually goes directly to the oil pressure gauge (stock) and not to the pcm. Is there something that I'm missing? I sent the pcm back to Speartech get a few mods done and they believe that the oil pressure sending unit at the back of the intake manifold doesn't need to be connected to the PCM inorder for the fuel circuit to be complete. If it does need to be connected, which pin on the PCM does it go to? It wasn't originally wired to it (that I can tell) - or - was there a wire from the gauge back to the PCM to complete the circuit? Here are pics of the instrument panel connector and pin description: The oil pressure sending unit is the tan wire: The harness as it goes in to the passenger compartment (number C220) Thanks for helping me understand. Bryan Dat240zg Quote Link to comment Share on other sites More sharing options...
mark Posted March 30, 2008 Share Posted March 30, 2008 On my 93 lt-1 car I do not use the oil level sender or the tan wire for oil pressure. You can rule those out as the cause of your problem. My money is on VATS. JTR book give details about how to get around this if you do not have editing software. Quote Link to comment Share on other sites More sharing options...
deja Posted March 30, 2008 Share Posted March 30, 2008 I agree. I kept the VATS in mine adding a removeable resistor in place of the GM resistor key. Just a litle more theft protection. On my 93 lt-1 car I do not use the oil level sender or the tan wire for oil pressure. You can rule those out as the cause of your problem. My money is on VATS. JTR book give details about how to get around this if you do not have editing software. Quote Link to comment Share on other sites More sharing options...
dat240zg Posted March 30, 2008 Author Share Posted March 30, 2008 VATS was removed on mine, so no dice on that front. I guess that next I'll go back and re-recheck the ignition switch wiring. Thanks for the input. BTW, Dale, I've got to apologize on the time it's taken me to get that opti back to you - it'll be out this week. Bryan Quote Link to comment Share on other sites More sharing options...
deja Posted March 30, 2008 Share Posted March 30, 2008 Take a look at that "fuel pump relay control" that goes to the fuel pump relay (pin A7 (dk grn/wht) on the PCM and see what that is doing when the fuel pump shuts off. I've heard rumors that sometimes removing VATS setting from the PCM really doesn't work. LOL, no problem Bryan, its not like I'm going to use or sell it. VATS was removed on mine, so no dice on that front. I guess that next I'll go back and re-recheck the ignition switch wiring. Thanks for the input. BTW, Dale, I've got to apologize on the time it's taken me to get that opti back to you - it'll be out this week. Bryan Quote Link to comment Share on other sites More sharing options...
80LS1T Posted March 30, 2008 Share Posted March 30, 2008 Who did the wiring for the harness? The PCM provides power to the fuel pump relay not ground. When I wired up my car this past winter I assumed that the PCM provided ground and wired it accordingly. This did not work as you could have guessed. Make sure you have power going to pin 85 while cranking and pin 86 should be ground all the time. It sounds like your pins 30 and 87 are good since it does prime up. My LT1 stock harness did not have the oil pressure switch hooked up to the fuel pump wiring and I did not do anything to the harness to bypass it. I am not using that sensor/switch and mine starts. Do you have any codes? I just had some issues with my LT1 not starting too. I thought it was an ignition control module but it turned out to be a bad connection at my opticrap. After reading some trouble shooting guides on "alldata" I found that if your throwing a code 16 your fuel pump and injectors will not work. My fuel pump did prime but I was not getting an RPM signal to my PCM so I had no spark. I ended up cleaning up my connection and packing it with dielectric grease and my problem was gone. While I was trying to get that connector off of the opticrap my fuel pump was turning on and off. Make sure your getting a RPM signal to your PCM or it wont turn the fuel pump on. One more thing, make sure you have the correct opticrap connector. There are 2 versions a long and a short one. If you have a 95' opticrap it should have the long one(about 4" long). Guy Quote Link to comment Share on other sites More sharing options...
dat240zg Posted March 30, 2008 Author Share Posted March 30, 2008 Guy: John at speartech did the harness. Harness has a seperate fuel pump relay wired in. I'm going to keep tinkering with it over the next few days. I have a few issues that I need to sort out (unrelated, but still an issue). Thanks for all of the input. Quote Link to comment Share on other sites More sharing options...
SSflyer Posted March 31, 2008 Share Posted March 31, 2008 Also, check to see that your fuel pump relay has a good ground. On my LS1 I had the same problem you're having, and it was just a bad ground. Have somebody put a fingertip on the relay while the key is being turned and see if you feel it click on... Quote Link to comment Share on other sites More sharing options...
Bartman Posted March 31, 2008 Share Posted March 31, 2008 ...The PCM provides power to the fuel pump relay not ground... I'm pretty sure that on my 94 LT1, the PCM is providing ground for my fuel pump relay. I had a problem with mine when I first installed it, and it turned out I was providing power for it with a source that didn't have power while the engine was cranking. Quote Link to comment Share on other sites More sharing options...
deja Posted March 31, 2008 Share Posted March 31, 2008 PCM provides power to the relay, ignition provides the power to the pump through the relay contacts. This is the print for the fuel pump control from the PCM: I'm pretty sure that on my 94 LT1, the PCM is providing ground for my fuel pump relay. I had a problem with mine when I first installed it, and it turned out I was providing power for it with a source that didn't have power while the engine was cranking. Quote Link to comment Share on other sites More sharing options...
Bartman Posted March 31, 2008 Share Posted March 31, 2008 PCM provides power to the relay, ignition provides the power to the pump through the relay contacts. I think this could vary between years and/or models. My PCM definitely provides ground to my relay and I add iginition hot from my Datsun harness to make it work. This thread talks about someone else that has a fuel pump relay that operates with positive signal from the PCM. It also has good information about how the system works that may help Bryan. Read post #9 from Ken (wheelman). http://forums.hybridz.org/showthread.php?t=116522 Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted March 31, 2008 Share Posted March 31, 2008 http://www.digitalcorvettes.com/forums/showthread.php?t=54543 bits of info that might prove worth reading thru in differant areas of this thread Quote Link to comment Share on other sites More sharing options...
deja Posted March 31, 2008 Share Posted March 31, 2008 You provide ignition hot to the relay coil or the contact? My print is from Shobox and is for a '95 Camaro or Firebird and my GM shop manual is for a 95 too. Our 94 Z28's might be different. I never really checked since I never had fuel pump problems...until the relay died. Your thread and Grumpy's both mention Corvette and that might be different than a Z28 as far as that oil pressure thing. Bryan is using an engine from a Firehawk so who knows what that things uses, but I wouldn't be surprised if it uses the oil pressure thing too. I think this could vary between years and/or models. My PCM definitely provides ground to my relay and I add iginition hot from my Datsun harness to make it work. This thread talks about someone else that has a fuel pump relay that operates with positive signal from the PCM. It also has good information about how the system works that may help Bryan. Read post #9 from Ken (wheelman). http://forums.hybridz.org/showthread.php?t=116522 Quote Link to comment Share on other sites More sharing options...
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