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Hammer Time
Ultimate Carjunky
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Jan 3, 2012, 7:00 PM
Post #26 of 35
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Re: Power problem
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That's why I suggested he still do a road test with the fuel gauge attached.
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Discretesignals
Ultimate Carjunky
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Jan 3, 2012, 7:06 PM
Post #27 of 35
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Re: Power problem
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Sorry, I just reread your one reply and saw that. 
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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b_oneself
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Jan 3, 2012, 7:33 PM
Post #28 of 35
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Re: Power problem
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Thanks again for your lightning-fast responses. I would like to restate that it was my mechanic friend, Bill's initial impulse, based on the low vacuum readings that there may be restricted exhaust, and that is why he asked to cut the pipe before and after the catalytic converters (2) in order to examine any restrictions. He now wonders if the new cats they put in are big enough. He concurs that the O2 sensor spot to test pressure is a good idea. He says he will lend me his scanner tool tomorrow and that it does have a capability to make a data snapshot as the problem is occurring. (I just have to figure out that function of the scan tool.) I'll clear the codes, (P0131 , P0151) and go for a test drive to observe fuel pressure during the malfunction, as well try and retrieve a data snapshot at the same time. By the way, Bill's impulse now is to just replace the crankshaft sensor since he says it is relatively cheap, eliminating every electronic component (replaced with new ones, at least) with the exception of the downstream 02 sensors and the computer. What I keep wondering is why does it do this only when it gets very warm, not just the usual warm up engine time.
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Hammer Time
Ultimate Carjunky
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Jan 3, 2012, 7:40 PM
Post #29 of 35
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Re: Power problem
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I'd be shocked if the Crank sensor was causing this, especially the lean codes ad the downstream sensor does nothing for engine performance. The testing you are planning will give us a lot of things to study.
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b_oneself
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Jan 4, 2012, 6:17 PM
Post #30 of 35
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Re: Power problem
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Okay,
I did get couple of new trouble codes when I did the latest test with pressure gauge attached. Of course, everything for the first hour or so was fine (55-57 psi with no fault codes) until it got plenty hot and started bogging down. The check engine light came on and OBDII codes P0171 and P0174 came. I ran the test 3 times, clearing the codes after each test run. Each time, same codes. Then on the triple check, I noticed the fuel pressure did seem to stumble, right around the time the power drops (55 psi down to 50psi). I was able to duplicate this condition with the engine parked and slowly raising the RPMs (so it wouldn't immediately bog down) and then consistently at a high RMP the pump would drop to around 50 psi, sometimes even lower. At this point I used my jumper wire to the fuel pump in order to insure that I was getting 13.5 volts at that location to eliminate a voltage factor. Regardless of the codes, I guess I'm looking at changing the fuel pump, right? Maybe the pump starts goofing up when it gets real hot -it sure screams loud. Remember the fuel pressure does still spike up when I dead head the pressure. Gas tank removal time? I found a Delphi brand fuel pump at the auto store. Is that the same as Delco? The clerk at the store says that is the original manufacturer and the part is made in the USA.
(This post was edited by b_oneself on Jan 4, 2012, 6:21 PM)
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Hammer Time
Ultimate Carjunky
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Jan 4, 2012, 6:25 PM
Post #31 of 35
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Re: Power problem
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It sounds like you have done a great job troubleshooting. I think you are right on target. The Delphi is an economy version of Delco. It should be fine.
Drop the tank, change the pump and the filter too if you haven't already done that. Be sure to inspect the inside of the tank to make sure it's not tank garbage plugging up the pump or a restricted baffle starving it. I assume you have had this problem at various fuel levels.
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b_oneself
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Jan 4, 2012, 7:05 PM
Post #32 of 35
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Re: Power problem
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Thanks again, Hammer Time
I just hate to throw $$$ in the wrong direction. I've already had this tank out before and bench tested the fuel pump. I just wasn't duplicating the same conditions when the pump would fail (getting hot). Maybe the voltage drop to the pump did contribute to its demise. I did replace this exact pump 2-3 years ago -well a lot of miles ago. I am not sure what make it is, I just know I bought it from the dealer who is now long gone. The power problem was occurring at various fuel tank levels. The inside of the tank is impeccably clean, and yes we already changed the filter. I don't know anything about a baffle. I did notice the last time we dropped the tank that the fuel evap hoses (going into the charcoal canister?) were full of a brown, almost oily substance but this line never enters the tank or the closed fuel loop. I will not neglect to report back on what I hope to be the final phase of this challenge.
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Hammer Time
Ultimate Carjunky
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Jan 4, 2012, 7:23 PM
Post #33 of 35
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Re: Power problem
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Baffles are the dividers and compartments inside the tank that keep the fuel from all sloshing to one side of the tank. They usually have small openings to them that slowly feeds fuel to keep them full but if the openings get restricted, the pump can suck a compartment dry while there is fuel in other parts of the tank.
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b_oneself
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Jan 6, 2012, 11:37 AM
Post #34 of 35
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Re: Power problem
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So I finished installing the new fuel pump and took the vehicle for a long (3 hour) punishing test drive, with the fuel pressure gauge and scanner tool attached. And...Bingo -you sure were right about the importance of maintaining a minimum 55 psi for this 5.7 vortex engine. The fuel pressure never dropped below 57 psi, and actually jumped to 66 psi when the engine was under the most demand (load). Boy, the difference between 52 psi and 55 psi ...dramatic! Unfortunately I still have a few remaining issues, namely the fact that the check engine light is back on with codes P0171 and P0174 consistently reappearing (something about lean fuel mixture). I have further inquiries re: the voltage drop problem, but I'll address those later. At least I got past the power problem, thanks to your excellent advice.
(This post was edited by b_oneself on Jan 6, 2012, 11:41 AM)
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Hammer Time
Ultimate Carjunky
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Jan 6, 2012, 12:39 PM
Post #35 of 35
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Re: Power problem
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Yep, those are lean codes. I would have expected them to go with the pump. You did clear them, right?
Look for vacuum leaks or any place the intake snorkel is sucking air between the MAF and the throttle body.
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