'02 5.3ltr problems under load misfiring

[Crazywelder72]

i have a 2002 Tahoe 5.3 and let me start by saying that even tho i am mechanically inclined, i am not a mechanic.

The problem is intermittent, the truck will start and run normally and even revving the engine it dosnt start the problem. while driving and accelerating all of the sudden you have a tremendous loss of power and bogging, sputtering exhaust sound changes and hard to make 30mph holding the foot to the floor. the Service Engine Soon lamp starts flashing but not storing any codes. Sometimes it will finally stayed lit and held a few codes:
misc cyl misfire PO300
Bank 1 too lean PO171
Cat sys to low Bank 1 PO420
Cat sys to low Bank 2 PO430
O2 Sensor vtg low bank 1 sens 1 PO 131
this vehicle has always had excessive oil consumption but has never smoked (consumes a quart every 2k miles) but always had a issues with a 02 sensor sens 2 (i just forget which bank)


i changed the fuel filter and all 8 sparkplugs today but the problem remains.
(the plugs were interesting and i will post pics later but all on drivers side were carbon covered and passengers side were lean looking. all the electrodes had similar wear.

after another test ride i got it to run like like crap again and while it was running like crap i got a vac gauge on it to the port on the intake. the needle was steady at -16. I sprayed all around the vac lines and everywhere with starting fluid and had NO change in the needle or idle. When i revved the motor the vac would climb to 0 and back to -16 when i let off.

i am thinking about the fuel pressure regulator first thing tomorrow but NAPA has a few listed for my truck 50psi, 56.56psi, and 62psi. and the prices range from $50 up to $115.

How do i know which is the correct one????

After that i am STUMPED and need help!!!!

 

[Crazywelder72]

small update, as it turns out i needed the 62psi fuel pressure regulator ($115) and it didnt fix the problem. so now i am stuck and need help.

 

[samotahoe]

Maf sensor and/or you might have the cat clogging the exhaust

 

[Crazywelder72]

A few weeks back, I did a water pump and when I was doing it I cleaned the MAF and the butterfly at the intake. All was running well after that.

After finding a TSB saying to use Iridum plugs gaped at .040 not the original .060 I had to redo them today. That didnt fix the problem either. Actually got a cylinder 1 misfire code once today as soon as I put it I reverse. After clearing the code and going around the block, it was the same as described earlier.

How do you check for a clogged cat?

 

[samotahoe]

I never use the cleaner to just clean the maf. if the maf is bad then it will run better for a lil while then go back to crap. the only way to fix the maf issue it to replace it. for the cat you might need to unbolt and look ta

 

[fubared79]

I had random missfires and worse under load but otherwise intermittent. My distributor was a tooth off. I spent about a grand doing a lot of pointless repairs before taking it to Firestone and let them chase the problem.

 

[needhelp02tahoe]

I would say cat is plugged up this very thing happened to me on my hoe and I did just about everything you did and same thing there are a few ways to check this I used both you can wait till the sun goes down and drive it around ur Neighborhood for 15-20 mins and then look under the truck and see if they are glowing red if clogged they will be. Or you can unbolt the exhaust from the Manifold and drive it very briefly to see if the problem stops if it drives fine that's ur problem

 

[Crazywelder72]

over the weekend i ran 1/3 of a can off seafoam thru the vacuum intake port. that seamed to go well and after all the white smoke was done i was getting a lot of black smoke that i assume was carbon burning off but the problem remained. I pulled the fuel rails and while on the bench i cleaned and verified that all 8 injectors were working and spraying nice. i inspected the o-rings a greased them with Vaseline, the problem remains. on Monday the last thing i did was replace the bank 1 sens 1 o2 sensor. it was reading 0.00 volts. put the new one in and no change... since i dont really have a way to know if the MAF is working properly i disconnected it and it instantly ran worse, plugged it back in and the idle came back up. (it is doing something but who knows if its in spec) I swapped the MAF with the one in my 99 5.3 silverado and it ran horrible so i swapped it back. the next day i dropped it off at my mechanic as i was out of diagnostic options. no luck there, he says i have a vac leak and wants me to install new o-rings on the injectors but i dont think that's it.. but i started thinking .. my mechanical gauge was reading at -16MAP but my obd2 meter was reading -10.5MAP so i started to think if the MAP sensor was not reading properly and throwing everything off. Tonight i replaced it and cleaned the Idle Air Control, anyhow the mechanical gauge reads -20MAP and that's a huge improvement but the meter still reads -10ish to -11. this is a video i took of both gauges doing a snap throttle test in the manual. and the mech gauge reads and responds exactly as described. http://youtu.be/Qd-6IRmMKoA

i took it for a ride and it was the first noticeable improvement. as long as you were light on the peddle it drove normal. if you tried to kick it down a gear with a heavier foot you could tell it was about to run all screwed up again. as soon as you would feel it starting to run ruff i would back out of it and it was ok.

im not ignoring the previous comments about the MAF or the clogged cat, just not quite there yet.

 

[Crazywelder72]

So after driving it for a few hrs today it does seem to show any difference between the cats. I used my non contact laser thermometer. That being said I don't think a cat is clogged.
Today I gave it a new set of plug wires but that didnt help either. I also replaced the upper and lower injector o-rings today.

What I did notice since replacing the Map sensor is driving it under 1500 rpms it's doing great but the scanner still reads -10 for map. 1500-2000 she starts running rough but if you back out of it it smooths out again. 2000-3000 it's pinging and bogging and running like crap again.

 

[Crazywelder72]

Back at my mechanic this morning while using a professional scanner we saw that every cylinder on bank one has had hundreds of misfires and none on the passenger side. We're thinking intake manifold gasket. But more importantly we tested the fuel psi and it was at 40. It's supposed to be 65. That would explain why driving at low rpms driving is fine.

 

[Crazywelder72]

Fuel pump fixed and quite a improvement but still not right. I think it's back to the vacuum leak that my mechanic was talking about.
At 3/4 throttle or heavy acceleration over 25mph trying to kick it down a gear, she's still misfiring and pinging on the drivers side of the motor.

 

[fubared79]

I had the same problem random missfire on one side. U put it in low gear and it would backfire like crazy. Went through the whole vaccuum lead, fuel pump, distribitor cap, full tune up, o2 sensors, new cats and mufflers until I though I exhausted all options. It was my distributor off one tooth. They have a sensor that sets the timing by ecu so it needs to be put in a shop to check unless there is a trick I dont know.

 

[Crazywelder72]

It's going back to the mechanic tomorrow. Mine has "distrubuterless ignition" where each plug has its own coil. So I am not sure how it picks up the signal.

Today I did the intake manifold gasket and the valley pan gasket. The valley pan gasket was the cause of the oil consumption and vac leak as it was leaking and oil would get sucked into the heads. So I am happy I found that.

I got it all back together and everything was much smoother and a definite improvement however the knocking and misfiring when climbing little hills or medium acceleration is still present.

I'll post some pics

 

[Crazywelder72]

The plugs on top are the passenger side (Bank 2). The driver side plugs show what I think is oil from getting sucked in from the intake ports that was leaking past the valley pan gasket and the intake manifold gasket.

 

[Tex99Tahoe]

Doggone, that was a mess in there! Like the Triumph in the backround...

 

[Crazywelder72]

Thank you. I hand fabricated almost everything myself on it and built the motor myself.

 

[Tex99Tahoe]

Looks great. Quite a skillset you've got. Lots of custom/chop/bobber builds goin' on nowadays...

 

[Crazywelder72]

Except I built that in 1996

 

[Crazywelder72]

i think this is the last problem. tsb 02-06-04-023A knock sensor. even tho i did look and inspect them for corrosion and what not, they looked clean. so i reinstalled them. i should have replaced them because i was already in there. now i have to go back in and remove the intake.

 

[Crazywelder72]

YOU WILL NEVER BELIEVE THIS UPDATE!!! So after driving it for a while it definitely seemed better, but still knocking a lot and the "service engine soon" SES light would come on whenever I was at idle or at a red light. I could take it for a blast on the highway high rpm's driving it hard and the light would never come on but as soon as I got off the highway and I was at a standstill the light would come on and it would always give me the PO 420 and po430 codes that both cats were running below efficiency. After much research I found on the Internet and article about adding 1 gallon of deluded lacquer thinner to 5 gallons of gas mixture and taking it for a high-speed run on the highway to increase the exhaust temperatures to burn off deposits on the cats. I did that for a few times didn't seem to notice much of any difference but it was definitely worth a shot. So I decided to yank the intake again and replace the knock sensors. while I had the wiring harness for the knock sensors out I checked it for continuity in the harnesses and replaced the knock sensors. When I first remove the intake and I was inspecting the new intake manifold gaskets I noticed at the bottom of all eight ports on the gap the new gasket they all had an oil residue. I was kind of baffled because it shouldn't be any oil coming out of the intake manifold. So I inspected the intake manifold by standing it vertically on the throttle body, while I looked at the underside trying to see where it was coming from. About a year ago I had a PCV valve that was stuck shut and I replaced it I remember that that brings oil vapor and crankcase vapor up into the intake manifold. That had to be the source of where the oil was getting into the intake. When I went to tip the intake back down I had oil pouring out the butterfly valve of the throttlebody. There was so much oil that has condensed and collected inside the intake manifold that as a vehicle was running it would just be drawing in more oil vapor into the combustion process which would be then triggering the codes for the the O2 sensors. I held the butterfly valve open and used a can of brake clean and sprayed it up the throat and rinsed out as much of the oil as possible until it was running out clean. I also Sprayed it up the eight ports of the plenums and down the Pcv valve hose.

After I reinstalled it the vehicle was running much better and the SES light stayed out for 2 days. No doubt there is a bit more oil in the intake manifold still tripping the SES light but it's a massive improvement. And something I NEVER heard of before " to check the intake for excessive oil build up by standing it vertically".