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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15201
Experience:  GM Grand Master Technician 2007. 14 years experience.
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Chevrolet Tahoe 4x4: Ok...when we were in caldwell out of

Customer Question

Ok...when we were in caldwell out of nowhere when we would start car it would make this very loud knocking sound under passenger side. Once you drove it would go away and car idled and ran fine. Sunday we go to leave and it's still just making noise when start then goes away. Had cruise control on and it started clanging and loosing accerlating power and check engine came on. Drove it Tuesday light went off and after parking for a bit light came on and completely lost accelerating power from 70 mph to 25. Check engine was blinking. Now on start it is really rough and can't get power. Codes have been maf sensor and something on cylinder 8 and then goes away and just shows random misfire . We have replaced all spark plugs and wires and maf sensor . Checked rocker arms and coils. The computer is now showing maf sensor again even though it's brand new
Submitted: 2 years ago.
Category: Chevy
Expert:  Gary replied 2 years ago.
Welcome! My name is ***** ***** I will do my best to assist you with this problem.Ask me about added features such as phone contact anytime if you wish !
I am sorry for the long wait
can you tell me which MAF code was setting ?
this noise concerns me was the noise a loud noise from inside the engine ?
Customer: replied 2 years ago.
The noise sounded like it was under passenger seat but at one point one of the codes was on cylinder 8 which is close to passenger. I have a mechanic coming for the 3rd time today and I will get codes uploaded on here for you. First codes I got were 4×4 because that is out as well...been out for 2 years. And it here code was p0171and p0101. Since then we had 19 codes last time mechanic was here and one bring maf sensor after we put new one in. I will update codes here in a bit. We are at a total loss with this thing and so is our mechanic
Expert:  Gary replied 2 years ago.
ok let me know which code numbers are setting
the 171 is a lean running bank of cylinders and of course the 101 is a MAF code
so right now if you start the truck up and drive it the truck has no power and just bogs down when you try to accelerate ?
Customer: replied 2 years ago.
Yes that is what's happening and check engine light illuminates . It also has rough idle. When trying to accelerate more once it bogs at 30 mph it will start making a small crackling knocking sound.
Expert:  Gary replied 2 years ago.
ok we need the codes set first
then if it has the 101 code with the key ON unplug the MAF and see if the pink wire terminal in the connector you unplugged shows 12 volts at it and see if the black/white wire terminal shows a good ground ?
if those check out and nothing is restricting the MAF and the air cleaner is not restricted they need to connect a fuel pressure gauge to the test port on the fuel rail and i need to know what the fuel pressure is reading key ON engine OFF and also note if the pressure holds on the gauge or drops to 0 very fast
Customer: replied 2 years ago.
Ok I will get back to you asap...thank you
Expert:  Gary replied 2 years ago.
let me know we will figure this out for you
Customer: replied 2 years ago.
Hi sorry it took so long to get back to you...fuel pressure is 62 on and when off its 52. The only code showing now is p0101 random misfire.
Customer: replied 2 years ago.
Sorry not p0101 it's a p0300
Expert:  Gary replied 2 years ago.
that fuel pressure is good
with it at idle is the engine skipping or misfiring ?
Customer: replied 2 years ago.
At idle it is shaking . ..????
Expert:  Gary replied 2 years ago.
ok at idle when its shaking if you unplug one ignition coil at a time do any you unplug make NO difference in the idle ?
Customer: replied 2 years ago.
No backfire...and no its make no difference we went through coils
Customer: replied 2 years ago.
Who will be answering me now