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Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 3681
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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200 chevy silverado po137 and po157 codes runs fine other than

Customer Question

200 chevy silverado po137 and po157 codes runs fine other than when hard accellerating bogs and loses rpm ,already replace both o2 sensors, did not correct the problem
Submitted: 4 years ago.
Category: Chevy
Expert:  Jerry Newton replied 4 years ago.
Low voltage on both O2 sensors accompanied by low power is going to be one of two things: either your fuel pump is dying, or you have a restricted exhaust. Catalytic converters and fuel pumps are both fairly common failure items.
Customer: replied 4 years ago.
the only time it has low power is under hard accel. if i drive it normal without trying to put it in passing gear it runs fine, but it only does it when under hard to moderate accel. if grandma drove it. she would prob not notice it , until she got creamed by an oncoming vehicle when she tried to pass. sorry best way to describe. it is aggrevating right now . , but you are saying possible fuel filter? fuel pump? or cats could be blocked? if i were to take the cats off and gut them? ( just hipothetically of course) would it affect the way the truck runs , if that is the issue? thanks for your help
Expert:  Jerry Newton replied 4 years ago.
Possible fuel filter, but not likely. Certainly, if you already have one, put it in and see how it does. Gutting the cats..... well, that's illegal for one, and will result in a constant check engine light for two. The way to pin this down is to put a fuel pressure gauge on the engine and drive it, and observe the fuel pressure when it acts up. If the fuel pressure is staying strong at 55-60 psi when it's bogging down, then it's not the fuel system. After confirming that, I'd be looking at converters.
Customer: replied 4 years ago.
how often have you seen this, people have said injectors, tps, o2 sensors, dealer said they would look at it for 98.00 and start there by replacing parts, i am old school and want to know that i am not just throwing parts at it, but new filter air and fuel is a good idea, ever heard of a k&n doing it by too much oil. covers the maf. replaced filter and cleaned maf just a few minutes ago. gonnna see what it does, then i will hook up gauges to fuel rail? to get reading. is that the proper place the valve on the fuel rail. if i am at a dead stop and mash the throttle it just bogs down and wont go. thanks for your help. sorry to be a pain. thought the cats would send a code. not like the earlier stuff i guess.
Expert:  Jerry Newton replied 4 years ago.
The K&N filters are a problem, because like you said, the oil gets on the MAF and contaminates it. GM has a bulletin about it. The by product of this is that the engine fuel trim gets skewed by the contaminated MAF, and that is what wrecks the catalytic converters. It's too late to clean the MAF and make the problem go away at this point, I suspect, because the damage is already done. But I would suggest getting rid of that air filter so you don't have a problem in the future, after you've made repairs to the exhaust system, if that's what it is. I would not put O2 sensors in it, they're reading accurately. I wouldn't put a TPS in it. I wouldn't replace any injectors. Put a fuel pressure gauge on it and drive it, and see what the pressure does when it acts up. If it's not fuel pressure, they do make an exhaust back pressure gauge, it screws into the O2 sensor hole and you can drive it with the gauge attached and see if the exhaust back pressure climbs when you accelerate. It should stay below 1-2 psi, plugged cats will force that gauge right up.
Customer: replied 4 years ago.
so your recomendation at this point is to replace the maf sensor? beacuse it prob can not be cleaned? it made no difference when i changed the filter and cleand the sensor, before codes were erased, i then erased the codes and they returned right away, then erased them again, and truck runs o.k for now,(except revs up and gains speed , but seems to not want to upshift)took it to a tranny shop before the motor was looked at and he said not a tranny prob. engine prob. but this is what it did before also and then back to the same thing. i have a fuel pressure gauge, but not long enough to see when driving also the service port i need an adapter, i prob lost it, thought it had ore than one when i bought it. you seem to be leaning toward the cats? again sorry to be such a pain, just tired of it.
Expert:  Jerry Newton replied 4 years ago.
The more you tell me about it, the more I'm convinced that you have a bad cat. It sort of mimics a tranny problem, I'm not surprised that you consulted a trans shop. MAF sensor should probably be replaced, but that's not going to solve your problem. My analysis is that you are going to get new cats, a new MAF sensor, and you're going to reinstall the factory air filter, and that's going to fix you up.
Customer: replied 4 years ago.
just to let you know. i changed the fuel filter, then drained it into a clear glass. black is all i see, can't even see through it. filter had a date code of 05 on it assumed it was replaced a while ago. milegae when bought 112000 (mileage now 144000) this truck has been mine for about 1 1/2 years now and always had this prob , but lately alot worse, the cats are expensive. 468.88 from napa. any ideas where else to get them. cheap!!! also my fuel pressure gauge does not have a hose long enough for me to see inside the vehicle and my wife is too big to ride in the engine compartment when the hood is closed. (just kidding) do they make a longer hose, with the adapter for the service port it is larger than the one i have. thought i had more adapters, but can't find them also where do i get the back pressure checker thingy you talked about and how much is it about. would rather spend a little to verify then fork out 468.88 and find out that wasn't it.
Expert:  Jerry Newton replied 4 years ago.
I understand. It's not uncommon to get that black junk out of the filter. And it may very well be that the filter is the problem, have you driven it after you put the filter in? I have seen filters do this, but it's unusual. The back pressure gauge is something that you may be able to borrow from Autozone, Advance, or somewhere like that. Otherwise, you'll be going to NAPA or somewhere like that to buy one. There isn't a cheap source for those cats, unfortunately, they are big money. But you've had this problem for a year and a half? I was under the impression that it just started acting up. Definitely go drive it and see if the fuel filter didn't fix your problem, and let me know.
Customer: replied 4 years ago.
will do gonna drive to see if i can get the back pressure thing and will be back shortly and will let you know.thanks
Customer: replied 4 years ago.
JUST GOT BACK RAN THE SAME. CHANGED THE MAF SENSOR AND DOES THE SAME. NO CDES YET, THEN ON THE WAY HOME NO CHECK ENGINE LIGHT, BUT GOT IT TO CODE, THERE IS A GUY THAT IS GOING TO CHECK THE FUEL PRESSURE TOMORROW, WHICH O2 SENSOR SHOULD I REMOVE TO CHECK THE CATS, THE FORE OR AFT ONE, OR DO I NEED TO CHECK BOTH SIDES AND WHAT AM I LOOKING FOR NO MORE THAN HOW MANY PSI. THE GAUGE GOES FROM 1 TO 8 , THANKS
Expert:  Jerry Newton replied 4 years ago.
You'll remove the pre cat 02 sensor and attach the gauge there. I believe spec is no more than 1psi of back pressure, if that needle starts to climb, then you've got a restricted exhaust problem.
Customer: replied 4 years ago.
THANKS WILL LET YOU KNOW WHAT HAPPENS AFTER THE GUY CHECKS THE FUEL PRESSURE. JUST WEIRD TO BE A CAT IN MY OPINION CAUSE I THOUGHT THEY WOULD AFFECT IT AT IDLE ALL THE WAY THROUGH THE OPERATING RANGE, NOT JUST UNDER A LOAD( HEAVY LOAD) FUEL MILAGE ON THIS TRUCK IS ONLY 15 HWY I THOUGHT IT WAS LOW, BUT IF THE CAT IS PLUGGED THAT WOULD MAKE FUEL MILAGE LOW. I GUESS
Expert:  Jerry Newton replied 4 years ago.
Cat problems usually only show up under heavy load. They started to melt, and partially block the exhaust. There's enough passage for the truck to idle and run normally, but as soon you put the wood to it and try to make it breathe, it chokes up. At this point, I'll be sort of surprised if it's not a cat.
Customer: replied 4 years ago.
ME TOO. I REALLY APPRECIATTE YOUR HELP ALL THE DEALER WANTED TO DO IS THROW PARTS AT IT. COULDNT STAND TO PAY THEM TO DO WHAT I COULD DO. I HAVE MOST OF THE TOOLS AND DIAG. BUT THEIRS IS A LITTLE BETTER, JUST A HOME MECHANIC HERE LIKE TO WORK ON THEM, BUT COMPUTER STUFF IS NOT MY BEST THING CONFUSING TO ME. I WILL DEFINATELY LET YOU KNOW WHAT WE FIND OUT . THANKS ART
Expert:  Jerry Newton replied 4 years ago.
You got it, Art. Let me know.
Customer: replied 4 years ago.
did the back pressure test removed one o2 sensor at a time and checked each side both at idle are below 1 psi and when reved way up only go to about 3 psi, conclusion they are good?! the catalitic convereters. also threw another code tonitepo171 system too lean bank 1 when you look at the freeze frame data it says dtc that caused freeze frame po171 throttle position 8.6% load value 7.4% air flow rate 19.56 gr/sec short term fuel trim1 42.9% long term fuel trim1 24.2% short term fuel trim2 42.1% long term fuel trim2 21.6%short term fuel trim3 69.5% longterm fuel trim3 -55.1% long term fuel trim4 -82.5% short term fuel trim4 60.1% fuel system 1 clsd fuel system2 clsd that is all my code scanner picked up. what do you think? thanks again also never told me how to give you a little extra for being so helpful
Expert:  Jerry Newton replied 4 years ago.
When you rev it way up, was it bogging down/cutting out, or was it just revving normally? Point is, you have to know what the measurement is when this thing is acting up. Based on what you've told me, I would say your exhaust backpressure is fine, but none of these tests mean anything unless you're getting the engine to act up when you take the reading. As far as the P0171, it looks like it's running out of gas, and I'm back to wanting to know what the fuel pressure is doing when this goes on. I know you mentioned that the gauge isn't long enough..... one thing you might try, if you're so inclined, is to simply remove the hood while you're testing. That way you can see the gauge on top of the engine when you're test driving it. Same with the back pressure gauge, you might have a long enough hose on that so you could see it with the hood removed. I know it sounds extreme, but it's only four bolts, and it goes right back on. It can make a lot of these tests easier. The fuel trim code is tricky, though: although it looks like it's running out of fuel, a plugged cat on that side will give the exact same symptom, because exhaust stops flowing and the sensors go lean. The computer only knows what the inputs tell it, and if it sees the O2 sensors drop to zero, it assumes that it's lean. The computer never assumes there is a restricted exhaust, you have to figure that out. Let me know if the exhaust readings were taken when the engine was acting up.
Customer: replied 4 years ago.
readings were taken in park . engine revs right up no problems in park or nuetral, only does it under a load i am getting the fuel pressure stuff checked tonite the guy couldnt do it last night.
Customer: replied 4 years ago.
got the fuel pressure readings today. 48 psi at idle full throttle still 48 psi when it is acting up 48 psi
Expert:  Jerry Newton replied 4 years ago.
48 psi is no good, this needs to run at 55-61. Put a pump in it, and rock on.
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 3681
Experience: ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
Jerry Newton and 7 other Chevy Specialists are ready to help you
Customer: replied 4 years ago.
thanks will let you know what happens
Customer: replied 4 years ago.
put a fuel pump in it and walla!!!!!!! never ran this goos , gobs of power like a new truck. thanks
Expert:  Jerry Newton replied 4 years ago.
awesome! i love it when a plan comes together. have fun with it, and request me any time.

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