Power Loss

Leon Owner/Technician Arkansas Posted   Latest   Edited  
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Driveability
2005 Chevrolet Silverado 1500 4.3L (X LU3) 4-spd (4L60-E) — 1GCEC14X95Z187512
P0300 — Random/Multiple Cylinder Misfire Detected
P0101 — Mass or Volume Air Flow Sensor "A" Circuit Range/Performance
Lack of Power

Hello, customer brought the truck to us due to power loss on a hill. this truck will run fine here at the shop and on the road except when you climb a big hill, about a 1/2 mile into the climb you start to feel it shaking/losing power and gets worse as you climb. once you get to the top it will kind of blow itself out and it runs fine again till the next hill. while it is doing this it will show misfires on Cyl. #3 & #4 on the misfire counters on my scan tool, (Verus Edge) I scoped the ignition system and the pattern looked good but I did pull #3 plug out just to look at it and the porcelain part of the plug was cracked. so we replaced Plugs and wires with no change. Fuel pressure is 60psi, we did replace the fuel pump because initially the pressure reading was around 52psi, but I later found out my pressure gauge was junk, either way that did not fix the problem. I attached some screenshots and also the data file I'm not sure if the data file will work but the screenshots have the same info on it, where I circled the MAF pid is where the problem is occurring, we did replace the MAF sensor just in case this was causing the problem-no change. The CAM retard was at -7 degrees so we replaced the distributor (comes with cap n rotor) and the CAM retard is now 1-2 degrees, this did not fix the problem either. I also did an upper intake cleaning with BG solvent and Equipment and a transmission flush, neither of these fixed the issue. Thanks in advance

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Gary Owner/Technician
Michigan
Gary Default
 

I've had this with partially plugged converters. Can you do a VE test on it?

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Dave Mobile Technician
Ohio
Dave Default
   

It does not look like a fueling problem. Considering what you have replaced, I would be looking at exhaust back pressure.

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Dan Owner/Technician
Texas
Dan Default
   

…Leon...be aware that MFI (with relocated injectors,which this IS,most likely) ...MIGHT not LIKE solvents/cleaners in the upper plenium area...the HIGH PRESSURE TUBES that go TO the injectors could become soft/swollen from the treatment and BLOW OFF the injectors...just so you (and others) know...I have seen it on one 4.3...and it hydro locked on raw gas...looking in thru the throttle bore…

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Randy Diagnostician
California
Randy Default
 

Check vacuum reading when this happens

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Tim Curriculum Developer
California
Tim Default
 

Assuming that the MAF hash starts about the same time as the misfire, my initial thought was a clogged Bank 1 cat because B1 STFT initially drops while B2 STFT rises. This is typical of a clogged exhaust on the negative-trending bank. However, you say you have misfiring on 3 & 4, which are the middle 2 on each bank, and MAP doesn't drop (it would with a clogged cat). So while I wouldn't rule…

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Christopher Diagnostician
Michigan
Christopher Default
 

Leon Have you checked exhaust back pressure? Maf is bouncing which I have found to be indicative of a restriction. Does it begin to spark knock while acting up if you w.o.t? I couldn't open first file so maybe my questions are answered in that data?

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Laird Owner/Technician
Nova Scotia
Laird Default
 

Did you check the fuel pressure under load driving down the road when it starts to misfire or was that with no load?

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Dan Owner/Technician
Texas
Dan Default
 

...Leon...(Per your edit)...That is about TWICE what I consider OK for exhaust BP...Dan H. ...again...

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Geoff Diagnostician
Hawaii
Geoff Default
 

weird, I cannot see any "edit" with any BP readings Hobbs,

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Dan Owner/Technician
Texas
Dan Default
 

...Geoff...I know I didn't imagine it...I think he said 3.5 to 4 IIRC...Dan H...aka...Hobbs...South Texas...

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Dan Owner/Technician
Texas
Dan Default
 

...Geoff....you are right...I can't find it either...that IS weird...I know I saw an edit about his BP...???...kinda make me doubt my sanity...Dan H.

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Dan Owner/Technician
Texas
Dan Default
 

...Geoff...see his reply to me below...there WAS an edit...it went POOF (???)...Hobbs.

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Kent Owner/Technician
Tennessee
Kent Default
 

Leon, from my experience with this type of symptom I would be suspicious of exhaust valve sticking in the valve guides. This is due to a reduced clearance of valve stem to valve guide caused by carbon buildup. During a long hill climb, the heated exhaust valve stem diameter increases causing the valve to stick just long enough for the hydraulic lifter to pump up which causes the exhaust…

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Scott Owner
California
Scott Default
 

Hi Kent, You must have posted this right when I started to type. I got called away so I put up a duplicate post. I agree with what you had posted.

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Kent Owner/Technician
Tennessee
Kent Default
 

I have been through this very type problem many times with not only Chevys but the early Saturns of the 90s.

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Scott Owner
California
Scott Default
 

Hi Leon, Another thought would be sticking exhaust valves. I used to see these on the 5.0L and 5.7L, but I guess it could happen on the 4.3L's as well. On the V8's the fault usually would occur on the center cylinders - 4 and 6, 3 and 5. This happened because of the valve layout and having two exhaust ports next to each other. This raised the temperatures on the center cylinders, along with…

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Freddie Diagnostician
Arkansas
Freddie Default
 

Leon, where is your foot at in throttle when this happens ? A tps reading would help tremendously. With a 20+ fuel trim & front o2’s NOT flat line high & you R at wot then u COULD have a fuel problem. If these readings r not wot, please take some & post

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Geoff Diagnostician
Hawaii
Geoff Default
 

That crazy hash on the MAF makes me think the air filter is ripped, or is too small for the air box or something. If you rev this to 5000 rpm the MAF should be above 165 g/s also.

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Stuart Mobile Technician
Illinois
Stuart Default
 

I have a buddy that had the same vehicle and it had the same symtoms when it was brand new but only when he traveled through the mountains​.​Then it couldn't get out of it's own way​.​When he got it back home and I took a look at it he has replaced the air filter with a K&S​.​What was happening is the air filter was collapsing and when he put it back to…

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Niall Owner/Technician
United Kingdom
Niall Default
 

There is a lot of activity on Bank 1 Sensor 2

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Dan Owner/Technician
Texas
Dan Default
 

...Leon...DID you do an EDIT of THIS post mentioning exhaust BP NUMBERS ???...I know I saw one...but DID I REALLY ???...Dan H. ...South Texas...

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Leon Owner/Technician
Arkansas
Leon Default
 

Dan.. yes I did post BP numbers but they aren't there anymore, I tried to post them again and it just disappears. 3.5-4lbs while the problem is occurring, on bank 2. I forgot to check the other bank while the problem is occurring but here at the shop I had 1-2 lbs both banks throttle snap.

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Dan Owner/Technician
Texas
Dan Default
 

...Leon...Tanks for the verification...I thought I was going senile or flipping my lid there for a second...I knew I saw that edit from you (thought I did,anyway)...I really wonder what happened to it (???)...Dan H.

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Geoff Diagnostician
Hawaii
Geoff Default
 

Bang on the converter on that side and see if it rattles. Broken pieces can act like check valves and cause intermittent issues.

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Dan Owner/Technician
Texas
Dan Default
 

...Geoff...you are right about that for sure...Dan H...aka...Hobbs. ...South Texas...

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Shane Technician
Massachusetts
Shane Default
 

I know you said you had the fuel pump out, did you check the fuel. Could the be water in the tank and when going up hill it sucks up mostly water and your problem happens.

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Robert Diagnostician
Florida
Robert Default
 

looks like MAF is under reporting at higher rpm to me. The MAF should be in the 125-140 range and you maxed out at 118 the fuel trims support the under reporting air as well on acceleration. My experience with clogged exhaust is fuel trends closer to normal with both sides clogged or one side going positive and one side negative with only one bank clogged. The fuel trims in your captured data…

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Albin Diagnostician
Washington
Albin Default
 

Nice data captures. The scan data shows a restricted exhaust. In the MAF data & load data, you see all the scribble marks, this is from the air flow pulsing in and out through the MAf sensor. This is caused by the exhaust pressure way too high. The fuel trim numbers also support a plugged up cat. Last week I had a Jeep Wrangler with about the same data you have captured. The front cat on the…

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Robert Diagnostician
Florida
Robert Default
 

Albin what you said about the bouncing back and forth in the MAF sensor waveform makes sense now. I bet in cylinder pressure transducer would show the culprit under load. this was an example of one under load someone posted here not long ago on 08 Silverado

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Leon Owner/Technician
Arkansas
Leon Update
 

Update: I checked the exhaust BP on bank 1 while the problem is occurring, BP went as high as 5.5-6lbs, and starts bouncing from 2 up to maybe 5.5-6lbs while the problem is occurring so I'm like that's where the problem is. So I get a new y-pipe assembly, installed it,and I STILL have the same problem. Is there something like too much condensation in the exhaust? It seems its got a lot, when I…

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Dan Owner/Technician
Texas
Dan Default
 

…Leon ...That is WAY big for BP readings...be aware that cloggage (that is MY word) can MIGRATE further DOWN the exhaust system to the muffler and possibly the pipes... also I have seen (long ago) a two foot piece of exhaust pipe that was cut from a vehicle that was driving me NUTS...about 6 inches from either end (when viewed in with a flashlight) looked like the Snap-On truck had run over…

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Anthony Technical Support Specialist
Pennsylvania
Anthony Default
 

Hi Leon: Along with what Dan wrote, I've seen more than one muffler that had more precious metals in it than the cat did. Drop the rest of the exhaust. Guido

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Scott Owner
California
Scott Default
   

Hi Leon, I've seen and diagnosed quite a few restricted exhausts and one thing I can say - your scan data, description, and misfires, don't line up with what I typically see due to an exhaust restriction. I typically will see a smooth power loss, all HO2S's pegged rich, low MAF...With that said - How are you checking backpressure? When I suspect a restriction I'll remove a pre-cat HO2S and…

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Niall Owner/Technician
United Kingdom
Niall Default
 

I am based in Scotland so please forgive the ignorance, are bank 1 and bank 2 cat's part of the Y-piece, if so are the downsteam O2's directly behind these or are there secondary cats, one of your original scan data posts showed a lot of activity on the bank 1 sensor 2, interested to know that if the cats have been replaced what is it doing now.

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Albin Diagnostician
Washington
Albin Default
 

That vehicle only has one cat per bank with an oxygen sensor in front of each cat, and an oxygen sensor behind each cat. There is no secondary cats

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Niall Owner/Technician
United Kingdom
Niall Default
   

Albin many thanks for that, had a look at the Walker USA site as well, I would still like to know what that Bank 1 sensor 2 was reading after the Y - Piece was replaced. The reason for asking about secondary cats was on a ML320 with the left bank rear cat melted but front cat perfect? I wonder if Leon tried running the engine with only the new cats fitted rear not attached

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Stephen Educator
Ohio
Stephen Default
 

I think the first thing you need to do is graft you front O2s, MAF, RPMs, Lt & St fuel trims and TPS. But before doing that I would look at Load or Calculated load, with RPMs and Lt fuel trims. Drive the truck, full throttle it and record your maximum RPM before shifting out of first gear into second. Record Load and Lt fuel trims at max RPM or when the vehicle acts up. If the Load reading…

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Leon Owner/Technician
Arkansas
Leon Update
 

So... I'm still working on this truck, i have attached several screenshots of injector voltage and amperage pattern on injector #2, all of the injector amperage patterns have these extra spikes in them. what are your thoughts on these patterns? bad ECM? bad Injectors? the 3rd and 4th patterns are just zoomed out

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Albin Diagnostician
Washington
Albin Default
 

What are the fuel trims doing when this event happens? Now that you have done exhaust repairs, capture the fuel trim oxygen sensor voltage and load at full throttle. I would like to see what the computer is doing to control fuel.

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Leon Owner/Technician
Arkansas
Leon Default
 

Where I have the cursor is where the problem is occurring.

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Albin Diagnostician
Washington
Albin Default
 

Can you put up the Snap on file, so I can put the whole thing on one screen?

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Scott Owner
California
Scott Default
 

Hi Leon, Where, and how are you pulling your captures from?

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Leon Owner/Technician
Arkansas
Leon Delay
 

Hello All, Thank You all for your help on this truck. As of now the truck is still not fixed, I think we did improve the issue when we put the catalytic converters in but definitely did not fix the issue. The customer had to have her truck for a few weeks and then she might bring it back. I don't know if she will or not. If we get it back and fix the truck I will be sure to let you all know…

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