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I have a 1998 Chevrolet silverado 4x4 with the 5.7 v8, the problem that I have is that when you start it for about five minutes it runs perfectly however when you start to drive and come up to a light or stop and leave it in gear it developes a shimmy and the entire cab starts to shake some times it will throw some codes for bank 2 O2 sensors and engine running lean. But normally the check engine lite stays off. what I have done so far Complete tune up (cap, roter, plugs and wires) also replace EGR valve gasket. Also have replaced the sending unit in the tank because the Fuel pressure was at 55 PSI vise the specified 60-66 PSI when the ignition was on but the engine was not running. I am at my witts end because my gas milage has suffered because of this as this is my daily driver.

Submitted: 63 days and 6 hours ago.
Category: Chevy
Value: $15
Status: AWAITING EXPERT REPLY
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Optional Information

Year : 1998
Make : Chevrolet
Model : Z71 k1500
Engine : 5.7

Already Tried:
Replaced Cap, roter, plugs, wires. fuel filter
Replaced EGR valve gasket
Replaced sending unit with in the tank and fuel filter again also cleaned out the tank with solvent and carb and choke cleaner

Posted by BRENT T. 63 days and 5 hours ago.

Answer

we need to do a simple fuel psi test......I would like you to attach your fuel gauge to the test port and cycle the key on then to off ( do not start the engine ) log down the starting psi come back in 10 minuits and recheck the PSI if there is more than a 5 - 8 psi drop you may be looking at a leaking fuel PSI Regulator or a leaking fuel pop-up or more....If so there is a real nice fuel injector replacement with true injectors and new meter body including the regulator......

63 days and 5 hours ago.

Reply

I am waiting the ten min then I will check the PSI

63 days and 5 hours ago.

Reply

I have the results after 10 minutes the PSI droped from 55 PSI to about 48 PSI.

Posted by BRENT T. 63 days and 3 hours ago.

Answer

ok what was the final say after 15 - 20 min did it stay at the 48psi or continue to drop?

 

63 days and 3 hours ago.

Reply

It continued to drop and now it is at 40 PSI

Posted by BRENT T. 63 days and 3 hours ago.

Answer

I believe we may have found your concern....now the hard part to final confirm that the fuel system is at fault you will need to block off the return fule line the best point is at the rear of the intake, you will need to remove the return line and install a block off on the intake side. then retest as before I believe you will find the same concern ( the loss of fuel PSI ) , if so replace the fuel injector spider in the upper intake manifold, This will be an up-dated unit with up-dated electronic fuel injectors, new PSI Valve and Fuel meter Body.......

63 days and 3 hours ago.

Reply

I will try this tomarrow but just to let you know I have gotten closer to the problem with you than I have with any of my know it all friends and one of them is a machinest who works at a popular machine shop in town. I would like to keep conversing with you will tomarrow evening be alright?

Posted by BRENT T. 63 days and 3 hours ago.

Answer

Well thanks, most of the technicians on this site are very accurate in their diagnostic procedures and have been in the industry many years, Myself I have been a GM Master Tech for over 10 years. get back with me anytime.....Brent

Accepted Answer

Paying the Deposit does not pay me. Please ACCEPT my answer when you are satisfied. Bonuses and positive feedback are appreciated! PLEASE ASK IF YOU NEED MORE HELP Thanks Again Brent T.

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Expert: BRENT T.
Pos. Feedback: 100.0 %
Accepts: 
Answered: 9/21/2009

Chevy Technician

GENERAL MOTORS MASTER TECHNICIAN, ASE CERTIFIED, 15 YEARS IN THE AUTOMOTIVE INDUSTRY

56 days and 14 hours ago.

Reply

Brent, I finally fixed the problem went through the entire fuel system and everything checked out took it to the chevrolet Dealership and they told me that it was the spark plugs because the passenger side plugs were all fouled. My plugs weren't bad just fouled, So I cleaned them and I remembered that this truck has four O2 sensors two per bank. So what I did was unplug the upstream O2 sensor on the passenger side (bank 2) and the engine steadied up almost immediately then plugged it back in and my problem returned. One other symptem that was happening that I did not know was a symptem at the time was that there was a faint hint of black smoke comming out of the exhaust when the O2 sensor was plugged in and cleared up when the sensor was unplugged. So the remeady for this problem was a bad up stream O2 sensor on bank 2 (passanger side). Thank you for all of your help

 

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