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1998 Chevy C1500 4.3L 200K miles Running Rough
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Bobertsr
New User
Apr 13, 2009, 5:44 AM
Post #1 of 6
(5555 views)
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1998 Chevy C1500 4.3L 200K miles Running Rough
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I'm working on the above vehicle and have a problem that I'm not sure about. The engine starts and idles smoothly and has plenty of power when accelerating BUT, between idle and heavy acceleration, in the "cruise zone", it has a lot of random misfires, bucking, surging, etc. The only OBDII code I'm getting is P0300-Random/Multiple misfires. I have changed: spark plugs, air filter, fuel filter, pcv valve, both upstream oxygen sensors and throttle position sensor. I have blocked out the EGR (for troubleshooting purposes). These have made no differences in the way the engine runs. I have checked compression (all cylinders within 10% of each other). Distributer and rotor look good. Ignition module checks good. Now, the suspected culpret...fuel pressure. It has the Central Sequential Post Injection (CSI) injection system. With the fuel return line blocked the pump pressure reads 70 psi and holds (fuel pump good, reconnected return line). With the pump running, engine off, pressure = 60 psi. When the pump shuts off after 2 seconds pressure = 55 psi and holds. When engine is cold started and idling, pressure rapidily fluctuates between 48 and 55 psi. When throttle is opened slightly, pressure = 52 psi. When throttle is rapidly blipped open, pressure = 60 psi. When engine is returned to idle after all this, pressure = 52 psi. To me the fuel pressure regulator may be bad but I'm confused about why it runs good while under heavy load? Does this sound like something the fuel pressure regulator may be causing?
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Loren Champlain Sr
Veteran
/ Moderator
Apr 13, 2009, 1:50 PM
Post #2 of 6
(5547 views)
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Re: 1998 Chevy C1500 4.3L 200K miles Running Rough
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Bobert; The fuel pressure spec for this vehicle is 60-66psi. Sounds like you are on the right track. Don't forget to check available firing voltage. Unlikely, but worth checking.
Loren
SW Washington
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Bobertsr
New User
Apr 14, 2009, 4:27 AM
Post #3 of 6
(5544 views)
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Re: 1998 Chevy C1500 4.3L 200K miles Running Rough
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"available firing voltage"?? Spark? Injector?
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Loren Champlain Sr
Veteran
/ Moderator
Apr 14, 2009, 3:19 PM
Post #4 of 6
(5533 views)
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Re: 1998 Chevy C1500 4.3L 200K miles Running Rough
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Bobertsr; I was referring to coil output; Available kV.
Loren
SW Washington
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kcauto
New User
May 9, 2011, 2:26 PM
Post #5 of 6
(4966 views)
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Re: 1998 Chevy C1500 4.3L 200K miles Running Rough
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Did you ever determine the cause or repair this issue?
I am working on one with the exact same issue... so exact, I'm wondering if this is the same vehicle!
thanks,
Cory
Edmonton,Alberta
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Hammer Time
Ultimate Carjunky
/ Moderator
May 9, 2011, 2:28 PM
Post #6 of 6
(4961 views)
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Re: 1998 Chevy C1500 4.3L 200K miles Running Rough
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This question is over a year old. Please start a new question if you would like some help.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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