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1996 Buick Century Fuel problem


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My old 96 Buick Century is driving me up a tree. The car only has 47,000 original miles. Seems to be a fuel problem. I've changed the fuel pump in the tank, checked the fuses, and swaped out the relays, but it still acts as though it is not getting fuel. It will start on a shot of starting fluid so the problem is not ignition. Where do I look next Buick gang??? I thought possibly a fuel pressure switch??? Or something else? Thoughts anyone before I shove it over a cliff and let it land up side down in a hog pen, and let the chickens roost on it. Oh yeah, it is a 3100 engine. Thanks, Dandy Dave!

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Ooohhhh JD, your guessin just like me. Any profit in the chicken and egg business??? I'll turn it into a chicken coupe and sell high class Buick eggs n Buick layers. Gotta be worth at least a dollar a dozen more. ;)

I guess what I'm asking is if anyone has a wiring diagram of the fuel system and location of possible faulty components. I was getting ready to pull out of a parking lot onto the highway when it just up and quit. Was running fine up until then. The fuses are also fine. The ones I could find at least. The panel is in the glove box and there are several more fuses up on the right hand side of the car by the radiator above the relays. Maybe I should unhook the battery and see if the computor will reset its self??? Modern Lectronic nightmare that it is. The good thing is that I have a parts car to pull pieces off of that still runs with 300,000 trouble free miles on it. Rust has taken the suspention, and body, to an unrebuildable point on the parts car. Dandy Dave!

Edited by Dandy Dave (see edit history)
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My brother in law had a '96 Regal that did the same thing. I never figured it out, but the shop did after 3 hours of fiddling. It had an internally corroded wire under the hood that (I believe) led to the underhood fuse box. It seems like it was for the ignition, but you may want to start in that area.

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You changed the fuel pump, but did you check the pressure? If the pressure relief has failed, the new pump will not build pressure.

Of course there are many other things it could be, sounds like you have just scratched the surface.

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How about a clogged filter somewhere in the fuel line? Clogged injectors? Can you hear the pump pumping when you turn the key on?

As the case with most fuel delivery issues, you need to start at the gas tank and work your way forward to the engine, or start at the engine and work your way towards the tank, checking for fuel along the way. You'll figure it out.

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Just a thought. What was the exact action you were taking when the car quit? Turning the wheel, stepping on the brake, etc. This may lead you to your electrical gremlin.

Sitting between a few cars waiting for the light to change. When the light changed the car quit before I could even give it fuel. Dandy Dave!

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You changed the fuel pump, but did you check the pressure? If the pressure relief has failed, the new pump will not build pressure.

Of course there are many other things it could be, sounds like you have just scratched the surface.

It sounds like the pump is not running in the tank. It could be the fuel pressure regulator, but it seems more like an electrical problem. The car was sitting and idleing fine, and then just like someone pulled the plug. Dandy Dave!

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The car idled fine, and ran on the road fine until it just quite. I took another look and the pump in the tank is not running. It runs with a bench test and, even with testing it inside of the tank by running jumper wires to the black and gray wires in the plug. I'm thinking the defect may be in whatever switch turns the pump on and off, where ever that may be? I may just have to bite the bullet and buy a wiring manual. Dandy Dave!

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Dave, I googled this and here is one answer I found:

Hello!

If you look under your hood, you will see a row of relays mounted to the core support near the radiator, on the passenger side of the enigne compartment.

The fuel pump relay is the one on the end closest to the center of the car.Steve765440175.9348326736

Read more: I have a 1996 buick century, which relay under the hood controls - JustAnswer http://www.justanswer.com/buick/2xot6-1996-buick-century-relay-hood-controls.html#ixzz1kbTchOVm

If this is like Dougs 89's there could be multiple relays in that spot, each sporting the same part number. Temporarilly hooking the fuel pump relay wire to another for test purposes should be okay

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Dave,

Have you checked for voltage at the connector? You may have pulled a wire part-way out of the socket, or not have the connector well enough together. If you changed the pump, did the old one work when jumpered? If you find the fuel relay, and it's good, then check under the fuse to make sure you are getting voltage past the fuse. Matt

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The oil pressure sending unit (a switch, usually) will determine whether the pump runs or not--period. From that signal, the relays and such will be energized by the computer. There is a start override, but once it's in "ON", the oil pump sender takes over. As your car probably as the warning light, the sender can probably be a two-connector sender, but it could be two separate senders . . . one for the light and one for the computer.

The relays on the holder on the cowl are what I call "Universal Bosch Relays". Three relays for different functions, but they're all the same part number relay. That's why you can swap them around and not cause problems.

The IAC might be a long shot, as when they start having issues, the idle quality and speed can be noticeably different than they normally are. Same if the air passage in the throttle body which the IAC controls is clogged with deposits. If it's bad or not functioning correctlly, I believe THAT should set a code.

As you didn't mention the Check Engine light doing anything durring all of these times, that would mean that all of the main systems are probably not where the fault is. If the fuel pump's supply system stops due to the oil pressure sending unit being flaky, the computer would probably consider it "doing its job", rather than providing "out of range" readings. Or that somebody switched the engine off.

"Extended crank time" would be a result of a restricted fuel filter or a whacky pressure regulator, even with a new pump. As you didn't mention that problem, that might be ruled out.

Which brings up the question . . . Once the car dies, how long before it will crank over and restart??? Do you turn the key to "OFF" and start over or just turn it from "ON" to "START"??? After the engine dies, what about the memory in the radio's station settings and clock??? Before the car dies, do the instruments/warning lights in the instrument cluster do anything unusual, like several flash on once before the engine stops???

Changing the fuel pump was a good first move, even with the lower mileage, now you know that it's supposed to be a good one.

In order to troubleshoot this deal, I recommend a digital voltmeter and a test light. With the engine stopped, after it stops AND you're in a safe place, check the voltage between the battery and any ground surface, plus at the end of the battery cables, too. Then, once the car will restart, with it running, check voltages at the same locations. IF you see any differences (as to voltage loss), especially in the cables, this might help you determine what might be going on . . . provided the oil pressure sender is not causing the issue.

Just some thoughts,

NTX5467

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Dave, I googled this and here is one answer I found:

Hello!

If you look under your hood, you will see a row of relays mounted to the core support near the radiator, on the passenger side of the enigne compartment.

The fuel pump relay is the one on the end closest to the center of the car.Steve765440175.9348326736

Read more: I have a 1996 buick century, which relay under the hood controls - JustAnswer I have a 1996 buick century, which relay under the hood controls - JustAnswer

If this is like Dougs 89's there could be multiple relays in that spot, each sporting the same part number. Temporarilly hooking the fuel pump relay wire to another for test purposes should be okay

Thanks, but I've already done this JD.

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Dave,

Have you checked for voltage at the connector? You may have pulled a wire part-way out of the socket, or not have the connector well enough together. If you changed the pump, did the old one work when jumpered? If you find the fuel relay, and it's good, then check under the fuse to make sure you are getting voltage past the fuse. Matt

I did not have my muti meter with me when we changed the pump the other day as I did the pump change in a friends shop on his lift. I have checked the fuses with a test light and all are fine. My buddy with the lift has limited tools. Yes, the old pump worked when jumped. Dandy Dave!

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Dave, the crank sensor is a common problem on 3100's. If the PCM does not get a signal from the sensor (telling the PCM that the engine is turning over), the fuel pump will not get voltage. Check it out.

Will check this out and change it. Could very well be the problem. Thanks, Dave!

Edited by Dandy Dave (see edit history)
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The oil pressure sending unit (a switch, usually) will determine whether the pump runs or not--period. From that signal, the relays and such will be energized by the computer. There is a start override, but once it's in "ON", the oil pump sender takes over. As your car probably as the warning light, the sender can probably be a two-connector sender, but it could be two separate senders . . . one for the light and one for the computer.

The relays on the holder on the cowl are what I call "Universal Bosch Relays". Three relays for different functions, but they're all the same part number relay. That's why you can swap them around and not cause problems.

The IAC might be a long shot, as when they start having issues, the idle quality and speed can be noticeably different than they normally are. Same if the air passage in the throttle body which the IAC controls is clogged with deposits. If it's bad or not functioning correctlly, I believe THAT should set a code.

As you didn't mention the Check Engine light doing anything durring all of these times, that would mean that all of the main systems are probably not where the fault is. If the fuel pump's supply system stops due to the oil pressure sending unit being flaky, the computer would probably consider it "doing its job", rather than providing "out of range" readings. Or that somebody switched the engine off.

"Extended crank time" would be a result of a restricted fuel filter or a whacky pressure regulator, even with a new pump. As you didn't mention that problem, that might be ruled out.

Which brings up the question . . . Once the car dies, how long before it will crank over and restart??? Do you turn the key to "OFF" and start over or just turn it from "ON" to "START"??? After the engine dies, what about the memory in the radio's station settings and clock??? Before the car dies, do the instruments/warning lights in the instrument cluster do anything unusual, like several flash on once before the engine stops???

Changing the fuel pump was a good first move, even with the lower mileage, now you know that it's supposed to be a good one.

In order to troubleshoot this deal, I recommend a digital voltmeter and a test light. With the engine stopped, after it stops AND you're in a safe place, check the voltage between the battery and any ground surface, plus at the end of the battery cables, too. Then, once the car will restart, with it running, check voltages at the same locations. IF you see any differences (as to voltage loss), especially in the cables, this might help you determine what might be going on . . . provided the oil pressure sender is not causing the issue.

Just some thoughts,

NTX5467

NTX5467, This is the kind of info I was thinking about and searching for. Yes, now that you spell it out, it could most likely be the problem. No check engine light on. The car turns over, but has not started since D-day. I will change out the oil pressure switch and see what happens. Will also do some checks with my well worn Digital Multi Meter. I've used it so much though the years, the settings have worn off. But I know where they are. ;) Thanks, I'll be back. Dandy Dave!

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Another thought. If the Crank Positioning Sensor were bad, it would affect the spark? Yes or no? The engine has spark and will start quickly and run for a moment on either. I only did this once to verify that it was a fuel problem as too much either is not kind to an engine. Going to try the oil pressure switch first. Thanks again Buick Gang. Dandy Dave!

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Ever get to the point that you want to choke the living $#8% out of the engineer that created some stupid design.:mad: Little room for your fingers or hands, and sharp edges to get caught on everywhere. Someone grab and hold him so I can kick em where it counts! Now that I have that almost out of my system....

What is the correct size sensor socket wrench that fits the Oil Pressure Sensor??? Nothing I have in my box fits. Dandy Dave!

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Ever get to the point that you want to choke the living $#8% out of the engineer that created some stupid design.:mad: Little room for your fingers or hands, and sharp edges to get caught on everywhere. Someone grab and hold him so I can kick em where it counts! Now that I have that almost out of my system....

What is the correct size sensor socket wrench that fits the Oil Pressure Sensor??? Nothing I have in my box fits. Dandy Dave!

That's one of the reasons I got rid of the wife's Reatta. It took longer to change the thermostat on that thing than the water pump on my 55.

The parts store that sells the oil pressure sensor should have the special socket ($$$).

Willie

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For a quick check of the fuel pump, put a pressure gauge on the fuel rail port on the engine. Then go in and turn the key on. When going from off to turning the key on but not starting the engine and you should have a 3-5 second prime of the fuel system to get to operating pressure. If you do not hear the prime, then the relay, pump, on switch or something upstream is the problem. At the same time check for pressure and if it is less than about 45-50 lbs pressure, then the pump is suspect. That is where I would start without a Tech II scanner.

Edited by Larry Schramm (see edit history)
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I suspect the ECM "commands" the fuel pump to run. Which triggers the appropriate relay to send power to the pump . . . modulated by the oil pressure switch, but overriden in "Start" mode.

NOW, for something else . . . have you looked at the contacts for the resistor chip on your ignition key???? The VATS computer is another part of the circuit to run the pump, which is probably a final check before the pump is commanded to run. With use, the "ears" will wear down to where they're even with the plastic around them. So, you might need a new VATS "chip" ignition key. The dealer will need your old key to "decode" the chip (there are about 13 different ones!) to get the correct key blank . . . at this point in time, it will probably need to be ordered from GM, though.

On the backside of the VATS ignition cylinder are two orange wires with a common plug-in connector. Those two wires will go to the VATS computer under the instrument panel . . . separate from the other computer modules. The computer module is where the resistance in the chip key is verified (to match the computer) and complete the circuit to run the fuel pump.

Now, given the low miles of the car, it might be somewhat unlikely that the key is worn or the wires in the steering column have chafed enough to have an issue of shorting to ground.

What you might do is take the key to your local GM dealer's parts department and see if their key "reader" can decode your key. To see if it might be worn or if it reads it without any problems. While there, you might take the VIN to a service writer and see if he can still pull up your VIN to see if there's any record of the problem you have in the GM records. I'm not sure how far they'll now go back, though. IF the selling dealer is still in business, you might also consult them on the service records for the vehicle, too, to see if there's any history in their repair orders on a similar problem to what you're having.

Just some thoughts . . . the plot thickens . . .

NTX5467

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Since you have been concentrating on the fuel supply side of this with little luck I'll be bold and suggest going to the spark control module. In this era the outside of the control module appears to be the ground for the idle circuit. It is steel and the bracket is aluminum. A light scuffing with fine sandpaper fixed an incorrigible 1990 Olds Toronado with the 3800 engine.

Heres a picture of what I found on my former 95 Riviera after tackling that Olds problem for a few weeks.

PS: the bracket on the 3800 is a two piece bracket. I took it all apart, sanded and used oxyguard on it before reassembly.

post-31834-14313882318_thumb.jpg

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Since you have been concentrating on the fuel supply side of this with little luck I'll be bold and suggest going to the spark control module. In this era the outside of the control module appears to be the ground for the idle circuit. It is steel and the bracket is aluminum. A light scuffing with fine sandpaper fixed an incorrigible 1990 Olds Toronado with the 3800 engine.

Heres a picture of what I found on my former 95 Riviera after tackling that Olds problem for a few weeks.

PS: the bracket on the 3800 is a two piece bracket. I took it all apart, sanded and used oxyguard on it before reassembly.

Thanks for the tip JD. I'll take a look and see if the 3.1 is similar when we get a warm Day. Dandy Dave!

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The 3100 had a big problem with the fuel injectors having low resistance. The ground side of the injector is controlled by the ECM. Be sure they all have 12 volts provided by the pink wire. It is fused. If the resistance is low the quad driver circuit of the ECM acts like a circuit breaker and opens. This is designed to protect the ECM from shorts. I believe that there are two driver circuits controlling two groups of three injectors. If you have one or more injectors with low resistance the driver will not ground the injector. The result is no fuel provided by all of the injectors (good or bad) controlled by that quad driver. If you have one bad injector in each group both drivers will not work The 3800 has injectors controlled by individual quad drivers. When on injector fails on a 3800 the result is no fuel to only one injector causing a miss on that cylinder. The car will still run. This is another suggestion to consider. You really need a service manual to follow the proper diagnostic chart. Good luck.

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  • 1 month later...

I finally have a decent enough day to take another look at the 96 Buick and the problem may not be anything Buick, but this device that I think is an anti thieft device. Says "Hellfire" on it, and it is wired into the trunk release and was behind the glovebox where the ECM is located. I did not get any kind of remote for this thing when I got the car. I'm going to try and eliminate it. As it makes my trunk release pop when I hook up the battery in the car and sometimes when I hit a bump. May also be my wiper and door lock problem. No telling what else it does. Maybe this is what is screwing with my fuel pump? Could it be someone close to me had a cell phone or device that shut down my car with the same frequency??? Fallukein trashy things people add to their cars... :mad:

Any advice or thoughts gang??? Dandy Dave!

post-44142-143138880615_thumb.jpg

Edited by Dandy Dave (see edit history)
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Well I have successfully removed the added "Hell fire" box which was definetly added to the system. Connectors were not even used and the wires were just wrapped around wires that were stripped for a short section. A real Cob Job installation. Where I am at now is trying to find out where the wire that feeds the 15 amp fuse that powers the fuel pump relay comes from??? The out wire is orange, and the in wire is red. I bypassed it today, the fuel pump runs as it should and the car started and ran for about a half an hour although it was running ruff at times. Why me Lord, why do I always get the tough ones. :eek:....:(......;) Dandy Dave!

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Dandy Dave, I have exactly the same problem with a 1995 Buick Century Custom. Have replaced fuel pump and fuel pump relay. Have checked fuses. Confirmed no activity whatsoever from the fuel pump, and believe it is not getting electricity. Trip to store tomorrow for voltmeter is in order to help continue this.

I have not tried bypassing the ECM/fuel relay fuse, but will after reading your latest post. Haynes book has some schematics in the back but matching that to where wires are run in car is a challenge. Wire colors did help locate which relay was for fuel pump, though.

Did you ever try the oil pressure sending unit, or the crank position sensor? Just wondering if you tried them and it still did not work, or if you did not try them yet.

I, like you, will be working backwards through the wiring. Who wanted to watch the NCAA tournament, anyway?

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Oh, I believe that red "in" wire is a fusible link wire, so that may be the culprit. What a great engineer thought up those, instead of actual fuses! I am sure they have a reason, but I would have rather seen a fuse I could change out easily. :rolleyes:

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