'93 Buick Century 3.3 - low fuel pressure?

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  #1  
Old 03-07-14, 12:07 PM
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'93 Buick Century 3.3 - low fuel pressure?

Anybody know what kind of fuel pressure I should be seeing on this car? The closest manual I have gets me to 1992, and it calls for 38-46 psi. At the fuel rail Schrader fitting, I get right about 38, so the pump seems weak by that set of numbers. But, looking on my parts store's website, replacement pumps for '93 are making between 50 and 90 psi, which tells me the existing pump is washed up. Car is slow to start but will idle okay once it does, but does NOT want to answer the accelerator pedal in any gear. Also, no Check Engine Light except at pre-start bulb check. If it were my car, or if I were going to work on a bunch of them for money, yes, I would invest in a manual. But since it's not, and I'm not planning to,... Anyone? Any help is greatly appreciated - Chris
 
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  #2  
Old 03-07-14, 05:49 PM
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key on engine off......41-47 psi.start engine fuel pressure should drop 3-10 psi.check fuel filter if restricted.do some snap throttles and see if pressure drops.
 
  #3  
Old 03-07-14, 05:50 PM
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If it is not responding to the throttle , I would check the Throttle position sensor ? Then go from there ?

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wyr
 
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Old 03-08-14, 05:11 AM
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I would change the fuel filter as joe mentioned before I went too much further. Even if it's not the cause of the low pressure, it's good preventive maintenance.
 
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Old 03-08-14, 06:30 AM
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+1 Another vote for fuel filter replacement.
 
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Old 03-08-14, 06:46 AM
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Problem is definitely with the fuel supply. While changing the filter, the brown stuff that dripped out of the old filter did not smell like gasoline. It looked far more suited to putting fires out than to supporting combustion. If that's what's in the filter, I can only imagine what's in the tank and has been running through the pump. While in neutral, I can "snap" the throttle and the gauge needle dips lower, maybe 2 psi. But, engine running or not, I never saw pressure break 40. And, wouldn't a TPS set a code and turn the light on? Also, if I should see 41-47 psi, will replacing the pump with one that fits and works but makes higher pressure overwork the pressure regulator? Just want to do this right, one time, and be out from under this car. Thanks for the help so far - Chris
 
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Old 03-08-14, 06:51 AM
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I'd be inclined to put in a bottle of fuel system cleaner and then pull the fuel filter in a week or so and inspect, maybe replace it.
 
  #8  
Old 03-08-14, 07:23 AM
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if fuel pressure is dropping under snap throttle fuel pump is not supplying necessary volume of fuel.check fuel pressure after replacing fuel filter.maybe the sock filter in tank is clogged.if getting low pressure after changing filter you probably need a pump.....the only thing that can also cause low fuel pressure is resistance either on the voltage side or the ground side of the pump circuit causing the pump to turn slower.....i use a low amp probe with a labscope and look at pump amps and can also calculate the pumps rpm.if you have a voltmeter you can check voltage drop at pump electrical connector.most of the time it is the pump.do you know how many miles on the pump?
 
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Old 03-08-14, 10:38 AM
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Thanks some more, posters. Didn't check pressure after changing the filter, but a test drive after the swap revealed the exact same behavior as before. Pump is almost certainly OE, puts about 175K on it. Then there's the fact that the car sat for an unknown period of time before the current owner took possession. Thinking to drop the tank to get all the crud out and go ahead and replace the pump. Still not sure which way to go with the multiple pressure ranges available on replacement pumps. Thanks, autojoe, for the pressure info you had - what was your source? If anybody has the figures from a Chilton's or such a manual, that would be awesome. Thanks again for all - Chris
 
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Old 03-08-14, 11:08 AM
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pressure info from alldata professional information system.
 
  #11  
Old 03-08-14, 12:12 PM
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So, pretty authoritative information, huh? Thanks autojoe. So it looks like the pump is indeed kaput. While I've got the tank out, I'll check voltage drop and resistance, for sure, though. No sense not checking everything possible while it's all uncovered. If it IS the pump, looks like I need to head for the ones in the lower range of output pressure, right?
 
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Old 03-08-14, 03:42 PM
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go to local parts store and give make/model/engine size and they should be able to match up the pump by specific vehicle information.stay away from airtex.....get delphi or ac delco.delphi have a lifetime warranty at autozone.....make sure to replace the strainer and flush tank if possible.
 
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Old 03-08-14, 07:56 PM
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Looks like autozone's got the pump in a delphi for reasonable. Used to shop them all the time - quit when they fired counter help for using his pistol to thwart a hold-up and possibly saving his manager's life. Maybe it's time to soften up a little... - Chris
 
  #14  
Old 03-09-14, 01:49 AM
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Go to O'Reilly Auto Parts .

Home Page | O'Reilly Auto Parts

Or if you have time to order the part , rock auto.com .

God bless
Wyr
 
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Old 03-15-14, 05:11 PM
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thanks autojoe and wyrtwister. Took the pump and car info to my local o'Reilly. They came up with one matching pump. So I replaced pump and sock, started the car hoping for the best, and the stumble is still there. I thought to disconnect the injectors one at a time, and each one caused some degree of stumble. My diagnostic computer doesn't have the cable to fit this setup, so I thought, "What else other than fuel is not reported to the PCM?" Ignition was the only other thing that came to mind. I started removing plugs to check condition, and was excited when I thought I had found a bad plug wire. Turned out not to be the case; timing light shows all 6 cylinders firing. Finally, disconnecting the TPS caused a bad stumble and set a light which went away when re-connected. Same with the MAF sensor. And, as I probably did not report originally, the idle is not as smooth as I had thought, and out of gear the stumble gets really bad around 1400 RPM. In gear, the car will barely power itself up the slightest hill. I also have a simple code reader (A-B jumper type), but it showed only a 12 for diagnostic mode. I want to check the pressure again to confirm the performance of the new pump, but other than that I'm back to square one. Help, anyone? Chris
 
  #16  
Old 03-16-14, 01:08 AM
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How many miles on this car ? Have the plugs been replaced ?

Check all the vacuum lines , hoses , devices ?

Does it have crankshaft or camshaft sensors ?

Probably has a coil pack instead of a distributor ?

Coolant temperature and oil pressure OK ?

You are getting good air flow through the air filter ? No debris blocking air flow into the air filter ?

Is the transmission shifting properly ?

What would it cost to buy a cable for your diagnostic computer to fit this car ?

God bless
Wyr
 
  #17  
Old 03-16-14, 08:01 AM
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Thanks wyrTwister. About 175k miles. Plugs are NOT OE, at least - they're Champions, so they've been changed at least once. Did have to replace a couple vacuum hoses before getting this deep in the car, but the rest look good and I can't hear any leaks. It's got to have one or both cam and/or crank sensor, right? But I had a '89 Olds with the 3.8 and it gave a light and code when the cam sensor quit. Has coil pack ignition but all 3 packs are hitting, verified with timing light on all 6 plug wires. Coolant temp sender turns cooling fan on and off properly, oil warning light goes out after start. Air filter looks pretty fresh and no debris blocking flow. Car won't really get moving fast enough to even tell it's shifting, so tranny is unknown. Could be vacuum modulator, I guess - it DOES have a hose/line to it and I wouldn't be able to hear a leak there... Next steps, I figure, are: check manifold vacuum, make jumpers to allow reading resistance through TPS (signal to power or signal to ground?), change spark plugs to AC (I've seen Champions and others quit working for no apparent reason, may or may not show good with timing light...?), confirm pressure with the new pump, and invest in the cable for my Genisys. Am I missing anything? Thanks for all so far - Chris
 
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Old 03-16-14, 09:18 AM
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I had the same engine in a 92 Cutlass Ciera and endured a stretch where it behaved a lot like yours. While I never checked the fuel pressure, the garage I took it to resolved the issue by cleaning out the throttle body - said it was very dirty. I'm assuming they knew what they were doing because the acceleration was back afterward.
 
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Old 03-16-14, 10:19 AM
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Thanks for the input, mitch17. Might give that a try too. This is so weird, because the owner says the car was running good until it started running like crap. No gradual decline, just POOF and it's bad. Makes me suspect one or more bad spark plugs(going to ground ahead of the gap?) or an undetected vacuum leak before anything else. I even checked to make sure the spark plug wires were on the coil packs in the proper combination as to firing order (3 with 6 on top pack, 2 with 5 in the middle, 1 with 4 on bottom). Pretty sure after all the head-against-the-wall time , the solution is going to provide a palm-to-the-forehead moment or two. Adding cleaning TB to the list - gasket/s shouldn't be too spendy. Will post results as they come in. Thanks again to all; keep it coming! Chris
 
  #20  
Old 03-16-14, 10:46 AM
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Eh, all of the sudden going to crap makes me think something failed more than accumulation of dirt.
 
  #21  
Old 03-16-14, 11:27 AM
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Yeah, that's kinda where my head is too. The only vacuum devices I can't see that might have started leaking suddenly are the climate control door motor selector and the transmission modulator. And I've already stated how I feel about the plugs that are in the engine now. One of the spark plugs was loose in the head - at work, just recently, this same kind of behavior was exhibited by an vehicle with one loose spark plug on a Chevrolet 427 with HEI distributor ignition rather than waste-spark coil packs. The center electrode on the offending plug was EATEN AWAY! But it was also loose enough that it was losing compression on that cylinder. These cursed machines we have created and depend on are so picky! Okay, that's enough rambling from me for now. Again, thanks to all - keep the good stuff coming... Chris
 
  #22  
Old 03-18-14, 06:24 AM
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This is a stab in the dark , but please bare with me .

The way I understand it , in very broad / general terms . The fule pump delivers fule to the engine fule system . Is there a pressure regulator ? I am pretty sure excess / not used fuel is returned to the tank ?

Would that be a direction worth looking into ?

God bless
Wyr
 
  #23  
Old 03-18-14, 07:43 AM
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if fuel pressure is low after replacing pump.......have a dc meter check for close to battery voltage on gray wire there should be a connector back at tank but if cant get to they make piercing probes for meters make single hole can put liquid electrical tape on later or backprobe connector.....should not drop more than 1/2 volt on power side with pump running.....i always run a jumper to negative battery terminal for meter ground connection best ground on car.....next probe the black ground pump wire with positive meter probe and negative meter hooked to battery negative terminal.....this is a ground to ground voltage drop test......meter should not read more than .10 mv......if pump is getting proper power and ground and fuel pressure is low.....fuel pressure regulator may be stuck open.note key on engine off fuel pressure then start car......fuel pressure should be 3-10 psi lower.take vacuum hose off regulator and should go high to koeo.check your fuel pressure key on engine off see if pressure drops.....should not drop 5 psi in 20 minutes.
 
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Old 03-18-14, 09:43 AM
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Thanks again for input, 'joe and 'Twister. as I understand it, yes, the regulator keeps pressure constant (within range) by bleeding off to the tank when demand is lower (high engine vacuum - idle or steady throttle opening). Which brings me to the next update...
I'm getting ready to go to work, but decided just for grins to hook the vacuum gauge to the car. Idle gives no better than about 15" steady. My old Chilton's troubleshooting guide says low vacuum like that points to late ignition timing, late valve timing and/or uniformly low compression. Since ignition runs off the crank position signal and there is no cam position sensor, I'm thinking it's jumped a tooth on the timing gears. Front cover and water pump look like they're OE, so timing set probably is too. Late timing is the only way I can see for it to jump. It would also account for the SUDDEN drop in performance and the low vacuum. Am I off base here? Still want to confirm fuel pressure and rule in/out the regulator. Thanks again - Chris
 
  #25  
Old 03-18-14, 06:56 PM
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timing computer controlled.....how many miles on car?worn out engine will cause low vacuum....low compression......vacuum leak......you have hard starting and low power?you have 15 inches of vacuum at idle......what do you get at 1000 and 2000 rpm?cranking and running compression checks would tell you alot.
 
  #26  
Old 03-19-14, 03:18 AM
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Un-plug crank shaft position sensor and see how that changes it ?

May not even start . That would indicate it was working ?

God bless
Wyr
 
  #27  
Old 03-19-14, 04:30 PM
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check if vacuum drops under load........sign of plugged restricted exhaust would cause hard start low power.also check the fuel pressure.
 
  #28  
Old 03-20-14, 05:16 AM
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First day off this week. Finally! Hope to be able to spend the day with this car - first go is to check fuel pressure to confirm pump working better and regulator function. Then going after the vacuum issue - plan to disconnect everything not necessary to engine operation, all at once, plug its vacuum port and take a reading. If vacuum still low, it's either late valve timing or an intake gasket leak, right? Pretty sure I'd rather do an intake gasket than a timing set. Will post what I find. Thanks again - Chris
 
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Old 03-20-14, 09:26 AM
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Just a quick update - unplugged all vacuum accessories except PCV and read vacuum. still no better than 16". Engine will rev smoothly to the moon with transmission in neutral and fuel pressure regulator unplugged. Seemed to idle better this way, too. Still won't get out of its own way in gear, though - stumble and low power still show up in gear. Plug the regulator back in, though, and the poor idle, low power and stumble are back, in neutral and in gear. That seems to tell me that the regulator is functioning, at least marginally, yes? Still need to borrow my O'Reilly's fuel pressure gauge and check all that stuff out, but for now,... Oh - also sprayed around intake runners while it was running - no effect at all. Thinking I'm looking for the cause of the low vacuum at this point. Might be just the fact it's got 170K on the odometer and 21 years under its belt, and the engine wear that go along with it, but my '89 Olds 88 did over 225K without acting this way. So for now, the mystery continues... Chris
 
  #30  
Old 03-21-14, 02:38 AM
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Our 96 Chevy Lumina 3.1 L has over 150,000 and , knock on wood , the engine is running good . I had to replace the in tank fuel pump a year or 2 ago . Would not start .

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  #31  
Old 03-21-14, 04:44 PM
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Still haven't been to O'Reilly to borrow their fuel pressure gauge, BUT -
with the oil filler cap off and watching for the one visible rocker arm to move, it seems like there's a lot of slack in the timing chain; rocking the crankshaft backwards and forwards, it takes a while for the cam to catch up with the change in direction. If the timing set weren't worn bad, there wouldn't hardly be any slop, right? I also want to check compression dry and wet, or do a cylinder leak test ( I actually have that piece of test equipment, of all things!), just to see if the years and miles have finished this engine. That's about all the news for now; more to come as it happens. Thanks to all - Chris
 
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Old 03-22-14, 03:24 PM
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So I started out intending to do a cylinder leakdown test, and started with the #5 cylinder because the front of the engine was easiest to get to. Got everything set up, #5 showed 20-25% leakage at TDC-compression. My tester calls that low leakage, though I'd like to see 15% or less. Moved to #3 cylinder, and the regulator on my test gauge literally flew apart! Hope my Matco guy will warranty it, but that's the end of next week. Still, while not conclusive, the results from cylinder #5 are at least encouraging. That's what I've got for now - more as it happens. Thanks all - Chris
 
  #33  
Old 03-23-14, 06:10 AM
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I bet it's the MAF. Get a descent scanner like a snap on to watch all the sensors live. I bet the MAF looks ok at idle but isn't responding to any change in air flow. That's why it's not setting the code.
 
  #34  
Old 03-23-14, 06:49 AM
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Thanks, tomf63. Should be able to pick up the correct cable for my Genisys scan tool on Wednesday when my Snap-on guy comes to the shop. Think a bad MAF sensor would better explain the sudden drop in performance than gradual wear in the timing set, although the late valve timing would account for the low vacuum... I hate chasing multiple issues, but it happens so often I should be used to it by now. 'K, that's all until Thursday. thanks again, all. 'Til next time, - Chris
 
  #35  
Old 03-24-14, 10:23 AM
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Please forgive me , I have kind of lost track of this thread . :-(

Do you have throttle body fuel injection ? If so , I am wondering is it is similar to our 91 Caprice ?

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Wyr
 
  #36  
Old 03-25-14, 08:09 AM
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it's multi-port injection. it does have a throttle body, of course, but it's just there to have a place to swing the blade from and mount the TPS to. Has individual batch-fire injectors in each runner.
 
  #37  
Old 03-26-14, 01:29 AM
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Sounds similar to out 96 Chevy Lumina V-6 3.1 L . It has multi-port FI .

Installed an in tank electric fuel pump and fuel filter on it . Can not think of any other fuel system work we have done on it ?

Think I mentioned I replaced the crank shaft sensor ? And spark plugs .

Best of luck . :-)

God bless
Wyr
 
  #38  
Old 03-27-14, 10:08 AM
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'Nother update - got a replacement regulator for my leak tester; now I have to get an adapter bushing to make it fit the tester. BUT - a coworker loaned me his iNNOVA scan tool, and while my much simpler code reader showed no current codes, the borrowed tool showed code history for throttle position low AND throttle position high. Checking resistance through the TPS gave me a consistent 4.7k ohms at idle and 1,7k at WOT, smooth transition all the way. I want to backprobe the MAF sensor once I finish the leakdown check on the rest of the engine, but with the engine not running and the plug disconnected, I got 11.5k ohms between the + pin and the unmarked pin (signal?), 4.8k between - and unmarked, and 7.4k between + and -. How does this look and what pins do I want to check while it's running? Thanks to everyone following this post for all the help so far - Chris
 
  #39  
Old 03-28-14, 02:39 AM
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Do not know about the MAF sensor ?

The Throttle Position Sensor should be fairly inexpensive if it needs replacing and fairly easy to get to ?

God bless
Wyr
 
  #40  
Old 03-28-14, 10:13 AM
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Thanks, 'Twister. Got my cylinder leakdown tester working and finished checking the front (odd-numbered) side of the engine. All cylinders show low leakage, but because of the late valve timing it's impossible to park a piston in place with the valves shut; it's already past TDC on the power stroke by the time the valves seat good. Cleaned the MAF sensor (it was kinda cruddy), put it all back together, and VOILA! - it's still running crappy. Back to square one. Again. Still think I'm going to go after the timing set, if I can get the owner to come up off that wallet. Autojoe, the fuel pressure figures you gave (41 - 47 psi), was that with engine running or just with key on? Boss just called; have to go to work on my day off, so I'm done for now. Thanks again to all Chris
 
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