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2002 Avalanche 5.3 O! M! G!

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09 Feb 2020 16:39 - 09 Feb 2020 17:28 #37329 by Potanist
2002 Avalanche 5.3 O! M! G! was created by Potanist
Hi, my name is Rich… and boy do I have a nightmare truck. First I had misfire problems P0300. I’ve replaced the fuel pump 3 times before I got one to run at the right pressures. You get what you pay for is all I’ll say on those pumps. I had to replace a few gas lines and changed the fuel filter while I was at it. On the 3/8″ line it kinked a little a 90 bend and hoped it wasn’t too bad of a restriction. I have good fuel pressure now, 50 psi idle 59 psi revving… had replaced the MAF and MAP sensors. Was getting misfires all over the place but mostly on the even number bank side. Replaced the fuel injectors with rebuilt upgrades. They have 4 holes instead of 2 and have less of an opening pressure (28 psi)… whereas the old injectors were like 50-55 psi range. Had also replaced all the coils, plugs and wires as a basic tune-up because my daughter just bought me this truck out of no where… but it had a lot of problems we weren’t aware of. The new injectors took care of 90% of the misfires.

Now I no longer get the P0300 but get P0174 and P0171(lean codes for both banks) now. Done smoke tests, nothing. Then I bought a used GM Tech 2 and saw my fuel trims were really out of range after watching your videos to learn how to use it. I thought it was a vacuum leak again being illiterate and tested again for a leak with the smoker, nothing again. I thought my MAF was bad. I had replaced it before but defective parts happen so I exchanged it for another new one.

The first day I drove it my LTFT was at 16 and 14 and my STFT were bouncing back and forth around 0 while driving. I thought it was running better and that maybe I just had a remaining vacuum leak.

Well in driving it the next day the fuel trims were back to their normal tricks: LTFT both sides pegged at 25 and the STFT jumping around between 10 to 16%. Driving it further fuel trims bank 1 was the same but bank 2 had a LTFT of 25 and a STFT of 54… Then I look again and both fuel trims on bank 2 went to 0 as well as O2S1 sensor was 0 and I did have a infrequent heater code for that O2 sensor. So I’m hoping that changing that O2 sensor will solve a lot of problems on bank 2. But I don’t think it will specifically will take care of the P0171 and P0174 (at idle 550 to 605 rpm) problems… or will it? Ordered the O2 sensor today.

Added info: I do have a frequent misfire on #6. Compression is 135 and changed the coil and plug again. I swapped the wire with the one next to it to see if it follows... it didn't. But, since changing the fuel injectors IF that engine is going to misfire, it does it mostly on #6. I also got a code P0151 at 1988 rpm, engine load 26%.

5.3’s are noted for intake leaks… I did the water test and the brake cleaner test but I think I looked at the scanner wrong after I did it. Only looked at the LT and not the ST. I didn’t have the scanner the first time I did the test. I was watching for the engine to run rough when I didn't have the scanner, but it really didn't run rough… and I’m still illiterate about all this. Lol, thanks again
Last edit: 09 Feb 2020 17:28 by Potanist.

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10 Feb 2020 15:17 #37362 by Donut
Replied by Donut on topic 2002 Avalanche 5.3 O! M! G!
What are the compression numbers for the rest of the cylinders? From what I can remember the rule of thumb is approx. 15% deviation in compression from lowest to highest cylinder readings before it will become an issue. Those '02s have displacement on demand? Could be possible one of those useless DOD lifters has decided it'd be better suited as a paperweight.

Another thing that also comes to mind is you may have to tune the ECM for the new injectors. What with both opening pressure and pintle number changing I'd wager that fuel map is all off in the rhubarb.

I'd tackle the cylinder 6 misfire first, though. That will definitely throw off your trims.

"Don't ever say 'easy' until the check clears."
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10 Feb 2020 18:16 #37364 by scannerjohn
Replied by scannerjohn on topic 2002 Avalanche 5.3 O! M! G!
I would start with, what "other problems" did this truck have prior to doing any work on it?

You threw a lot of parts at this truck so I would ask, why?

Three fuel pumps that did not work properly, are you buying junkyard parts? did you do any wiring testing?

All the codes you mention all have to do with a lean condition which is the lack of fuel, so the fuel pump, fuel lines, kinked fuel line and non OEM injectors are going to play greatly into your problem.

Old saying goes, "garbage in, garbage out". At this point trying to diagnose the problem with that much garbage in will only get a garbage out diagnosis.

Fuel pressure should be 55-62psi. I'd go back to the OEM fuel injectors and fix that kink. May have pressure but the kink can lower volume. That along with those "upgrades" are not helping.

Clear all codes and erase the memory to clear block fuel memory and get fresh data. STFT, LTFT and 02 voltage activity, ECT and MAF data at idle and any codes.

keep us posted on your results...


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11 Feb 2020 08:37 - 11 Feb 2020 08:39 #37372 by Potanist
Replied by Potanist on topic 2002 Avalanche 5.3 O! M! G!
@ Donut

Before I changed the injectors I was getting a lot of misfires all the time on 80% of the cylinders. After I changed the injectors it pretty much dropped to 10% being that #6 cylinder. Like when I can get it to misfire now is to punch the gas from idle and back to idle again. On a misfire graph I have other cylinders that misfire also but #6 always is in the lead. I didn't check the compression on the other cylinders. At the time I was working was a mechanic via the internet and he asked what the compression was on that cylinder. BUT and I say but the place I got those injectors from said that nothing else needs to be done other than to put them in. It's some GM upgrade to the fuel pressure problems this circle of GM vehicles have with fuel pressure. Thanks for your input...
Last edit: 11 Feb 2020 08:39 by Potanist.

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11 Feb 2020 09:26 #37373 by Potanist
Replied by Potanist on topic 2002 Avalanche 5.3 O! M! G!
@ scannerjohn

On this stupid truck... I've never seen a vehicle with soooo many problems. The person who owned it before me absolutely didn't have a clue. I had to replace all of the steering components. The rear brakes didn't work at all. I couldn't even bleed the rear brakes. Had to replace the ABS solenoid body. Then found the brake hose for the rear cross threaded and leaking.

Then on to the codes... The truck ran like total shit on and off. Being that I already found the truck a mess with the brakes and steering I figured the motor is a mess too. So, I thought an oil change and a tune up was in order. Changed the plugs, wires, coil packs and all four O2 sensors. I found where one of the O2 sensor's wires had been worn through riding on the driveshaft. I really thought it was going to run right after all that and it didn't. I put my cheap scanner on it and I was getting only a P0300, random misfires, and no other codes.

I was like WTF? I had no clue at that point on what else to do. So I contacted the help of an online mechanic. He told me to check the fuel pressure... found it to be 48 psi. So he said to change it but warned me that these fuel pumps for these trucks either work or don't work. He also said that once he changed the fuel pump up to 5 times before he got one to maintain working pressure.

I first tried an ebay cheap Chinese fuel pump because I've had luck with them in the past. Not this time. Replaced it with a Carter fuel pump... another fail. Replace the Carter with a Delphi and got usable pressure 50psi at idle and 59psi at WOT. The online mechanic said that this is good since it's able to hit 59psi. In changing these fuel pumps I had to replace some fuel lines to boot and I changed the fuel filter while I was at it.

The truck still ran like shit. The machanic said he couldn't help me any further unless I got a good scanner and recommended a GM Tech 2. Found a used one. Dropped the mechanic support after I got my scanner cause the pretty much broke me buying that. Lol, I saw all the misfires with the scanner and changed all the fuel injectors. 80% of the cylinders were misfiring. That dropped to 10% after changing them.

Trying to pass inspection but codes p0174 and p0171, lean banks, keep me from doing so. Going to YouTube for help I stumbled onto reading fuel trims... and that's where I'm at today. That's my story and I'm sticking to it.

Was told by scannerdan and another scanner dude that it sounds like my MAF sensor. Changed it again. Oops forgot to mentioned I changed the MAF and MAP sensor. So I changed the MAF again and it did seem to run better the first day... I guess it was in learning mode because the second day it was back to running high trim numbers. Can't remember now but one of the scanner dudes mentioned a restricted fuel line and that damn kink line popped up out of my memory.

I don't have a blacktop driveway nor do I have a garage. So, I work on my vehicles when the weather is bearable or if I have to... which sucks.

Thanks for your help

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11 Feb 2020 09:30 - 11 Feb 2020 12:26 #37374 by Potanist
Replied by Potanist on topic 2002 Avalanche 5.3 O! M! G!
@ scannerjohn, those injectors are OEM. They were calling them an upgrade which I took that as their answer to their fuel pressure problems.
Last edit: 11 Feb 2020 12:26 by Potanist.

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11 Feb 2020 09:49 #37375 by Potanist
Replied by Potanist on topic 2002 Avalanche 5.3 O! M! G!
I also checked the back pressure of the cat only bank one over last summer and it was good. I'll check the other bank 2 cat when I get under there to replace the B2S1 O2 sensor.

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11 Feb 2020 18:26 - 11 Feb 2020 18:50 #37381 by scannerjohn
Replied by scannerjohn on topic 2002 Avalanche 5.3 O! M! G!
so at this point you have P0171/174 (lean on banks 1 and 2) misfires on all cylinders especially #6. Positive LTFT's of 25 on both banks and a P0151. You have changed all four 02's and B2S1 which has had previous wiring damage is acting up giving you a P0151 and you have ordered a new 02. If you put on the new 02 what was the result.

post the following info... short and long term fuel trims for bank 1 and 2 at idle, Idle RPM, idle condition (high, low and or rough) MAF g/s and engine coolant temp. 02 voltages for B1S1 and B2S1 and loop status.

increase RPM steadily to 2500 and note trims. Do the values increase or decrease. Note 02 voltage readings. Do they oscillate are they fixed high or low.

even though you cannot find a vacuum leak (external) you may have an internal one, but lets not get to far ahead at this point.

forgot to mention, check the 02 heater fuses... #31 and #32. If the 02 circuit shorted, it may have blown the fuse.


Last edit: 11 Feb 2020 18:50 by scannerjohn. Reason: Added more info

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12 Feb 2020 08:21 #37413 by Potanist
Replied by Potanist on topic 2002 Avalanche 5.3 O! M! G!
Thanks ScannerJohn… I will do those things within the next couple of days. I appreciate it!

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19 Feb 2020 17:04 - 19 Feb 2020 17:05 #37651 by Potanist
Replied by Potanist on topic 2002 Avalanche 5.3 O! M! G!
Well, I finally got to the truck again. Weather here has been sucky at best. I got the O2 sensor in B2 in it's S1 place. Warming the truck up to go into close loop never happens. WTF now? And I also noticed that now my b1s1 O2 isn't fluctuating like the other 3. I'm starting to think the computer is bad or possibly both S1 O2 sensors were bad. One being stuck high and the other was to zero. Tried to get the info you requested after forcing the loop to close. I may not be specifically what you asked for but it's some info.

Keep in mind that B1S1 is stuck at like 472 and did throw a code P0134 for Insufficient Activity on B1S1.

At Idle: B1ST 50%, B2ST 2%, B1LT 25%, B2LT 25%
At 1500 rpm: B1ST 23%, B2ST -3%, B1LT 25%, B2LT 21%
At 2500 rpm: B1ST 52%, B2ST 1%, B1LT 11%, B2LT 21%
At 3500 rpm: B1ST 52%, B2ST 5%, B1LT 0%, B2LT 23%

Guess I'll get back to you when I get the other S1 sensor in... SMH

Thanks again
Last edit: 19 Feb 2020 17:05 by Potanist.

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19 Feb 2020 17:38 #37654 by Potanist
Replied by Potanist on topic 2002 Avalanche 5.3 O! M! G!
Oh, my main question now is why does this cursed truck not go into close loop?

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19 Feb 2020 17:48 #37655 by Potanist
Replied by Potanist on topic 2002 Avalanche 5.3 O! M! G!
I heard the same rumor of those DOD. To be honest I don't know if it has those or not.

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19 Feb 2020 17:48 #37656 by scannerjohn
Replied by scannerjohn on topic 2002 Avalanche 5.3 O! M! G!
did you check fuses #31 & 32? they are the heater fuses for the 02's. If not going into closed loop, heaters are not working. if not the fuses, must have a wiring problem.

do you have the tools to do voltage checks?


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19 Feb 2020 17:50 - 19 Feb 2020 18:06 #37657 by Potanist
Replied by Potanist on topic 2002 Avalanche 5.3 O! M! G!
Forgot to mention that the fuses were good, sorry. And Yes I have a voltage meter. I just don't get why it was working all this time before and today it's not... Unless changing the one on the other side screwed it up?
Last edit: 19 Feb 2020 18:06 by Potanist.

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19 Feb 2020 17:54 - 19 Feb 2020 17:59 #37658 by Potanist
Replied by Potanist on topic 2002 Avalanche 5.3 O! M! G!
Starting to think that's why they sold the truck. Never thought something couldn't be fixed... but man this truck sure does come close. I was also wondering about the wiring when I pulled the lower cover off below the steering column and saw a lot of wires with electric tape around them. I was praying to God that they didn't screw something up electrically. The wires had cut in the insulation like test points with a shitty tape job over the top of each one.
Last edit: 19 Feb 2020 17:59 by Potanist.

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19 Feb 2020 22:00 #37664 by Jasondo
Replied by Jasondo on topic 2002 Avalanche 5.3 O! M! G!
This truck is a flex fuel truck you might check the alcohol content on your scan tool also while watching your scan tool unplug each O2 sensor to see if they're plugged in the right spot.

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19 Feb 2020 22:41 #37666 by scannerjohn
Replied by scannerjohn on topic 2002 Avalanche 5.3 O! M! G!
verify you have 12v going out of the fuses... go to the connectors at the 02's and check for 12v then check for a ground.


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