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Old 09-23-2010, 12:15 AM   #1
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Default 91 Century - Extreme Power Loss

Hello all - My daily driver
is a 91 Buck Century with the 3300 in it. I was driving home last week, and as I was entering the freeway I was unable to get moving. Its bad enough that a Geo Metro was able to out accelerate. It takes over a mile to make it to 55 MPH. So here is what I have done for troubleshooting; Check spark with a spark with a spark tester at 20,000 volts, and it checked out, Ohm ed the wire, and they were good, changed the plugs, tested vacuum to verify no exhaust blockage, and that was steady, tested fuel pressure, and that was within spec. I have an AutoXray, and all of the sensors I can see look good. I had the thought that it might be bad gas so I put a bottle of Heet in it, and filled it up with premium from a reputable station. Oh, and I should add that it isn't pulling any codes. Any help would be much appreciated since I drive over 100 miles a day, and diesel is expensive at 17MPG.


Thanks,
Doug
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Old 09-23-2010, 09:23 AM   #2
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How old are the plug wires? I'm not a fan of ohm testing because it'* unfortunately not a good test of the wire carrying the high load of voltage. I'd probably replace them if they are old. If you aren't misfiring though, then why change them....right?

You only mention poor acceleration. Everything else seems fine.
How does testing vacuum test for exhaust blockage?

Kinda tough to diagnose this one from a distance if you don't mention anything being wrong except the acceleration. I'd probably think computer, but that'* a guess from the hip w/o anything to back it up.
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Old 09-23-2010, 12:53 PM   #3
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Quote:
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How old are the plug wires? I'm not a fan of ohm testing because it'* unfortunately not a good test of the wire carrying the high load of voltage. I'd probably replace them if they are old. If you aren't misfiring though, then why change them....right?

You only mention poor acceleration. Everything else seems fine.
How does testing vacuum test for exhaust blockage?


Kinda tough to diagnose this one from a distance if you don't mention anything being wrong except the acceleration. I'd probably think computer, but that'* a guess from the hip w/o anything to back it up.
The wires are fairly new, and are not rubbed through. Correct no missing.

Poor acceleration, and inability to maintain speed (55) up slight hills. GM Spec states that if Vacuum drops more than 3" between a steady 1,000 RPM, and 2,500 than check exhaust for blockage.

I do have a spare computer laying around, and I hooked that up, and had the same issues so the computer is out of the picture.
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Old 09-23-2010, 01:55 PM   #4
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When and how did you check the fuel pressure? Reason I ask is in the past, I've seen cars pass the FSM test of clicking the key off and on to achieve the highest reading. Yet if you have a good length of hose on the gauge and go for a ride, you find the pressure drops like a rock once it'* being used by the engine. And a failing pump will show more signs of issues when heated up.
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Old 09-23-2010, 02:59 PM   #5
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I tested the pressure while driving and it was steady from idle to WOT.
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Old 09-23-2010, 04:15 PM   #6
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Doug... help me out here, usually there'* an area or item that makes it easy to figure out. You tested it all and came back w/o codes and w/o anything showing up.

Pull the front O2 out of the manifold. Run any better? Only other thing I can think of is...cat might be plugged and the vac test might not be 100%
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Old 09-23-2010, 05:35 PM   #7
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Quote:
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Doug... help me out here, usually there'* an area or item that makes it easy to figure out. You tested it all and came back w/o codes and w/o anything showing up.

Pull the front O2 out of the manifold. Run any better? Only other thing I can think of is...cat might be plugged and the vac test might not be 100%
Easy would be nice, but it never seems to go that way with me. The not throwing codes boggles my mind, and nothing I have found looks apparent. I did replace the o2 sensor as part of a cheaper approach. The Exhaust test seems to be valid since I have read these procedures online at various sites including Alldata.

Right now I have two thoughts. Maybe its one of the first things I though (bad gas), but I did call the station, and they stated that there hasn't been any reports. The second would be maybe if the timing was off. I know that there isn't a way to time these motors, but my thought is maybe the timing chain may have skipped a tooth.
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Old 09-24-2010, 08:04 AM   #8
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The timing chains/gears on these motors is beefy. Beefy in a way like a SBC 350. With all the years of this forum, I don't believe there'* ever been a person with a tooth being off from a slipped chain. It'* that uncommon.

Humor me.. pull the O2 and go for a spin. Pretty please.
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Old 09-24-2010, 11:30 AM   #9
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I will try that tonight after work.I am also going to do a compression test tonight, and in theory this should tell me if the timing change jumped.
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Old 09-24-2010, 03:38 PM   #10
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When you do it ...please do it properly. All plugs out and the throttle blocked open.
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