Avalanche 5.3 Start/Stall Noise While Accelerating No Power
Guys forgive me as this is my first post and I am having some trouble getting through this. I want to share a case study with you. I am not sure how the pictures and such will upload and hope it all comes out right.
So, the owner attempted to go to work one morning and after driving about 10 blocks the truck began to hesitate and stall. He said it restarted and would not accelerate. He hard, what he described as engine noise, and the truck basically fell on its face or stalled under load. At this point it stalled and would no longer restart.
It was towed to a local shop where it has spent most of the last month outside. The tech there told him the engine is faulty and parked it. So with that said, a customer of mine, recommended us for a second opinion. The owner did not believe the engine was at fault.
It was towed to me and I began with the basics. Went out to verify complaint. The truck had other ideas and started right up. Engine sounded to be in very good health. Check engine light was on. I scan tested the vehicle and had multiple codes. However, with what I was told of history of recent repair attempts, I was unsure what codes may have been set and what might be a problem. I decided to write them down and clear them.
Mind you I had codes for lean on both banks in history. Data stream is where I went next and saw that my STFT were near 0 while LTFT were hovering around 10%. Raised RPM up and saw the trims climb a bit to around 12%, a clue? Ok, now I picked some other things to watch so I could test drive and record some data, although I had zero confidence because this truck was showing no symptoms that the customer stated. I picked my upstream O2 sensors (which are brand new from the a different repair shop), MAF, Fuel trims, Injector Pulse Width, Throttle position, Coolant temp, and Engine RPM. Off I went and made it about 40 yards. Sudden, and violent detonation followed by stalling. Ouch. So, what just happened? Looking back on my data, I saw my fuel trims peg to about 50%, o2 sensors drop to 0v, Aiflow reflecting what would be demand for open throttle, throttle position 45%(correct), injector pulse width through the roof. Attempt to restart, and it fires right up and idles fine. Fuel trims now show a bit higher than before on live data. O2 sensors switching. Blip the throttle and o2 both drop to 0v and lean pop . Ok, now we are getting somewhere.
I limp back into the shop and install my Mityvac 5545 fuel gauge. This gauge, like the SUR&R discontinued model does both pressure and volume which can be of use in many instances. I have my partner cycle the key to check for any leaks at the connection points, and see the site glass begin to fill with "fuel".... What the heck did I just see? It appeared more like 2-stroke oil filling the glass than gasoline. I opened the bypass on the gauge to catch a sample of the fuel in a clean container.
Ok, Houston, we have a problem comes to mind. I poured some of this mess into a glass jar and capped it... At this point, I sent the pictures of this along side a mug with known good 93 octane fuel for comparison to a bunch of friends, some of whom belong to this group. I got basically the same replay for all. "Yuck"! About sums it up. I did a burn test and yes, it does ignite and burn, but something is in there that should not be. At this point I call the customer to touch base on where I am.
Mind you I have about 10-15 minutes into the vehicle at this point. Now I get some more tidbits of information. The day this started his wife was leaving for work and found that she had two sidewalls slashed on her vehicle. Then he gets into this truck for work and the thing starts acting up. Hmm.... I explain that we will need to remove the tank with the roughly 20 gallons of whatever this is and replace the pump, the fuel and possibly the injectors. He says to hold. Ok, so as my partner is fixing things, I ask if he needs me. I get the nope, all good here go test all the other stuff you want to test on that truck. I smile and take out the PICO. I use my low current clamp on the fuel pump to see if it tells my anything more. The truck is running well now and accelerating fine. Nice! I figure if I can get a good waveform now and then again while it is broke, we might see something interesting. So, the pictures I am including are what I got.
Now, the waveform for the pump does not look very good, but that is not the only thing we were looking at here. When it was running well, we had around 11 amps and a bit over 7200 RPM. This was with the engine at 2000rpm.
Ok, so now we have to wait till it acts up again. I finally get it to do it after another attempt to drive it. I recapture the waveform as well as the data pids in the video at the same time. This time my amperage is around 5 amps and the pump rpm is over 9600rpms. Nice thing with the PICO is that when you add the cursors to the waveform, it does the math for RPM for you. Lower amperage, higher rpm indicates the pump is not working as hard as it was before, which indicates cavitation.
Whatever is in the fuel system is being pulled into the sock on the pickup and causing this thing to suck air. Of course to prove this we have to remove the tank. I am currently awaiting the OK from the customer, and honestly am not sure he will go ahead with it. I know this is a basic diag, but am interested to get feedback from those of you that are here. I am only learning compared to most of you, and hope to continue doing so.
Givien the slashed tires My guess would be a couple of liters of dark soda in his fuel tank ,
Joe, great stuff! Can you explain the significance of the frequency/amperage? My assumption is, there may be a few that do not realize the power of this technique
The amperage is reflecting the work being done by the pump, so if the amperage is higher the pump is pushing fluid, as the amperage drops and rpm increases it is indicating that is performing less work, as there is no fluid to move. I think.
AWESOME! Thanks for taking the time, Brother
Thanks for teaching me
Thanks for sharing, I once had a 02 impala taxi , 0-25 ps compression, valves would not seal, contaminated fuel.. could not get deposits off valves via chemicals , head / valve job.. fuel pump and filter / flush lines... went to fill up at gas station and "Click Click" back to shop and found a snickers bar in the filler neck LOL...
Thanks you for reading through it. Are you serious? A candy bar?
LOL yes, when I used air gun to blow out the filler tube another tech said my car took a ____ and it has peanuts in it ...
WOW!!!!!!!!! That is unreal man. And a chocolate bar did all that damage?
Nice write up. Keep us posted on what you find in the tank. The last one I had similar to this was I found about 50 cigarette butts and lbs of sugar. Let's just say the recently single owner knew you did it. Great use of the equipment Joe. It put you on point for sure.
Thanks so much Mike!
Nice write up. Thanks for sharing and hope you get the job to fix it.
Joe, Awesome write up and I definitely enjoyed it. Great example of narrowing down the problem with the scan tool, and then following the diagnostic path where it needed to go. Following the data and clues, and finally confirming suspicion of fuel pump with the scope. I'll be taking some lessons from this one. On an unrelated note, that fuel sample is making me re think my morning can of Coke...
If he has insurance on the truck it should be covered under vandalism. I've repaired many with insurance coverage.