I have a 1994 Buick Century Wagon with a 3100 SFI V6 engine that I can’t get to fire at all. I have read many posts with the same problem but haven’t been able to find a follow up fix from them. My Buick just wouldn’t start one day after running fine before. I came to this sight and tryed some of the suggested troubleshooting and found, while testing for power to fuel pump, that if I jumped from the battery to the gray wire on the fuel pump relay the car would start and run fine. So that rules out any fuel pump problems or fuel filter problems. I then swapped fuel pump relay to a different similar relay on the car and still wouldn’t start. I have read on this sight about the oil pressure/ fuel pressure switch being a possible cause and I beleive I have found that switch. It is in the side of the block toward the front of car and has three wires, (orange, tan and gray) going into it. I was going to try to jumper the orange to gray but didn’t want to do the wrong jump in case of negatively effecting the EMC controller, usually green/white wire? I also heard of the crank shaft sensor located on the back side of block but am not sure of which of three sensors I’m seeing back there to test. I guess first I’m looking for help on proper jumping proceedure. I tryed jumping the gray to orange in the fuel pump relay but no good. I get 12 volts at that orange and for a couple of seconds 2 to 3 volts at the green/white wires at the fuel pump relay when ignition is turned on, so when I jump the orange to gray at the relay it should start as it does when I jumper from battery to gray. I had relay apart when I jumpered the orange to gray, do I have to jumper with relay together and use a pin/needle wire jumper so rest of relay wires are connected? The same would apply for jumper testing oil pressure switch and crank shaft sensor? If it’s not the switch or sensor then it looks to maybe be the EMC? Any help or tips would be appreciated Thanks
Was the relay you temporily used to replace the fuel pump relay the exact same part number? It could be that your original fuel pump relay is faulty, and the replacement you tried isn’t the same configuration, so that couldn’t possibly work. Even if the leads are the same, the fuel pump uses a lot of current, so you have to use the exact part to do this test in a meaningful way. I guess if I had this problem one of the first things I’d do is I’d get a wiring schematic. then trace it out and make sure the signal which turns on the fuel pump relay is getting to the relay.
A quick way to check for a faulty crank sensor is check for spark at one of the plug wires. If there’s spark the crank sensor isn’t the problem. If there is no spark the crank sensor could be the problem.
Power to fuel pump relay coil comes from the PCM on the grn/wht wire. I assume that wire should have 12 volts on it when the engine is running to power the relay or in the START mode possibly. While in the START mode it looks like the red wire on the relay should supply bypassed power to the pump. See if you have 12 volts on the red wire while in the START mode. If you don’t then apply power to that wire and see what happens. If the engine starts and runs then you need to see where power is supplied to the red wire at. It appears the fuel pump relay is bypassed when the oil pressure switch is turned on after the engine is running and then it supplies power to the pump. You would be wise in investing in a factory service manual for the wiring. Check Ebay for copies.
See if you can find and post a wiring diagram for you car. With a good schematic and a voltmeter this should be diagnosed in about 5 minutes.
The relay I swapped out to test the possible faulty fuel pump relay was the exact same Bosch part number but after making the switch still no start.
Going from the original statements you made about this issue and the test results you got it seems to me the trouble you are having is due to a power wire connection problem to the relay and not a problem with the relay itself. If you follow the testing informataion I gave in my previous post it should help lead you to the real trouble with the circuit.
Yes, you need a schematic and a DVOM or a red/green test light along with a crash course on DC circuits.
Some of the GMs of that period had a fuel pump circuit fuse hidden in the harness near the relay.
I don’t want to muddy the waters but are you sure you got the fuel pump relay? Its not the same as all the other relays in the relay center. I think it fits on the fire wall and has a slot in it to slip on a retainer. Looks like the same as what mine were and I had to buy one to test it. Also it supposedly has a fuel pump inertia switch that would shut power off if bad. Have no idea where it is, but its listed in the catalog.
Seconding @Bing, usually the fuel pump relay – since it handles so much current, and has other safety consideration in the design – is unique among the relay set used in the car. It’s surprising your car uses two identical relays like that, one for the fuel pump, and the other for something else. It’s possible your car uses two of them, but like Bing says above, good idea to double check, as you may not be looking at the relay that powers up the fuel pump. It’s also possible – if you car indeed uses two – that both have to be installed for the fuel pump to turn on. If you could post a link to the car’s fuel pump wiring schematic, I expect folks here will be happy to assist further.
I went according to a Haynes manual of this year and model car to find the fuel pump relay. It shows a bank of 5 relays and I have found the 15 Amp fuse on that bank for the fuel pump and it was OK. I can only hope that this manual is correct but when I unsnap that relay and hot wire from battery to its gray wire that is supposed to feed power to the fuel pump the car starts and runs just fine. So with that jump I beleive it answers some questions about a bad fuel pump, fuel filter, correct relay, even eliminating a bad crank sensor because of how good the engine runs when hot wired from battery. I need to check red wire yet for 12v as Cougar suggested and I also need the correct scematic, the Haynes manual has the wiring diagram for a 2.5L only and mine is a3.1L V6. I also beleive I have to check the ground coming from that relay, black wire I think, to make sure it’s got a good ground.
Well, first thing is to put a test light on the prime terminal to determine if power is coming through. If not, I guess for $10 you could just replace the relay to be sure. However, the oil pressure sender has a by-pass for the fuel relay so that if the pressure is up, power will by pass the fuel relay and still power the pump. It would take a while cranking, but should still start with a bad relay after pressure is built up. The ECM is what commands the relay though to close so is it possible you have a bad ECM? My hope is that you have a bad relay but if you are correct and substituted the same relay, that doesn’t make sense. Might want to take a look at the pictures at Rockauto to make sure you have the right relay. Also that inertia switch would cause what you are experiencing. Relays usually don’t go bad and with the by-pass, unlikely that is your only problem. Check the trunk for the inertia switch. I always used to carry a spare relay and ECM just to rule everything out. But if it runs when you jumper it, that means your wiring and pump is ok atleast from the relay on.
I agree with the OPs last posting statements about things that would seem to be working okay when bypassing the FPR and the engine runs fine. The FPR uses both of the switched relay contacts to get power to the pump. One of the contacts ties to the red wire which I believe is tied to the trouble. I just don’t know where the red power wire ties to since the data I was looking at doesn’t show where it ties to. It most likely ties to a fuse in the fuse panel under the dash but it might go to the panel under the hood. I just assume it is tied to switched power coming from the ignition switch. Leave the relay in place and apply power to the red wire on the relay and if the engine starts up you have just proved the trouble is on the other end of the red wire.
I’m approaching my level of incompetence but the red wire should come directly from the fuse to the relay. Spliced into it along the way is the red wire going to the oil pressure sensor. The gray wire on the other side of the relay should go to the PCM. Spliced into the gray wire would be the other gray wire going to the other side of the oil pressure sensor. So if there is oil pressure, the relay is by-passed. If you have no power at the red wire at the relay, there would be no power to either the relay or the oil pressure switch. Then the problem has to be between the red wire at the relay and the fuse.
So just for kicks, replace the fuse or jumper directly over it. Maybe its bad but looks good. Jumper from the fuse then to the red/relay then if ok, there should be a problem with the wire itself. Wire connections, corrosion, I dunno. I quit.
I finally was able to get back to the Buick and I pulled the relay for the fuel pump and tested it by using the green/white pin and the black/white ground pin on the relay cap. I wired them to 6 volts and the relay itself clicked and I could feel and hear the click. This was done off of the car with a seperate 6V power source. So the relay I beleive to be working. I then tried again to get a volt reading on the red wire but got nothing. I then traced the red wire back from the relay about 8 inchs and found the end with an empty female connecter just hanging. I tried to find the male to connect this deadend red wire connector to but could see nothing at all. I then went to my now actual wiring scematic for this engine, 3.1L, and saw that the red wire is for the fuel pump primer conn. only. Not sure if that red wire would have 12V always but it has no power now and I don’t know if it ever did. I then made sure the relay was together and with a small portion of the orange wire that goes into the relay stripped back, I hot wired from there to the hot side of the battery and got the car to start and run just as it did when I hot wired battery to gray wire, but this time was going through the relay instead of by passing it. So that tells me somewhere my orange wire that is supposed to always be hot, according to the scematic, has a break or bad connection.
Now according to the scematic again the orange wire also goes to the oil pressure/fuel pressure switch, so I’m not sure if that could still be involved? I tried to find that switch and according to my Haynes book it’s on the side of the block toward the front of car next to the oil pressure guage. I found the location and the possible oil pressure/fuel pressure switch but what I think is that switch on my car has an orange, gray and tan wire going to it. On my scematic it shows it should have only an orange and a gray wire, no tan. So I’m a little confused about if I have the correct switch? However I did jumper the orange to gray on the plug off of the switch I think is my oil presssure/fuel pressure switch and with relay back together car still wouldn’t start.
When I test the orange wire with a meter I can only get 1 to 2 volts not 12V. I started to try and trace back from relay the orange wire but it’s like a rats nest and very difficult to find where it goes. All wires are tightly wrapped in and no room to work as is usually the case. I intend to try and start at one end or the other, whichever looks the easier, and take a length at a time where orange wire is accessable.
I could use any info on what or where to look on this 3.1L for the oil pressure/fuel pressure sensor. I’m still not sure if I’m checking the right switch or not?
Looking at some data it shows the orange wire is supplied power via a fusible link and a inline fuse after that. Check to see if you can see a rust colored fusible link tied to the starter solenoid wire from the battery connecting to the orange wire. There may be more than one fusible link. Check for the inline fuse near there also. Use your meter to check for power. The orange wire should have power at all times. Once you find that trouble you should be good to go.
Not much to it. Here is the schematic.
I did find the fuse for what I think is the fuel pump. It is a 15 AMP fuse and is located on the bracket of the bank of the 5 relays under the hood. Even though the fuse looks OK. I did replace it but car still didn’t start. I then went to the fuse block and replaced the ECM/PCM fuse, which also looked OK, but still no start. So those fuses are not the problem. I will look for the inline fuses/fuse links Cougar mentioned next.
Still not sure of location of oil pressure/fuel pressure sensor?
Along with making sure fuses are good you also need to verify power is getting to them. A good fuse with no power to it gets the same results as a bad fuse does having power to it.