intake backfire,loss of acceleration, lurching

**monette** · 06-05-2009, 10:16 AM

Hey everyone. I spent the better part of last night on your site to try to find an answer to my problem. I found several ones that are close, so I decided to register and post my specific issue.
I have an 07 Yukon XL 55K that I run on E-85 almost exclusively.

2 weeks ago on our way out to town, the XL started to loose acceleration power. It was backfiring through the intake. It was lurching. Applying the accelerator made it lurch more and backfire more but gave no more acceleration. It was at a quarter of a tank.

A few days later it happened again, this time on a tank of regualar unleaded gas (rules out the ethanol as a problem I think). Again, same sympton, on a quarter of a tank of gas.

Yesterday, it happened again this time at a little less than half a tank of gas (unpredictible). I am finding that when this happens if I continue to run the car less than about 35 mph then i don't get as much backfire or lurching.

Oh yeah, two preceeding events. The day before this all started we had it in the shop to replace the tires 275/55/20 and while they had it up the battery died (strange) so they replaced it. The next day all of the problems started. I keep wondering what they could have accidently touched or bumped that would send my system over the edge. Could it be a new battery did something?

My mechanic (local gas station owner) has worked diligently on it (tested fuel, run diagnostic, drained tank, looked at fuel line & pump. Currently he is looking at the vent screen and the spark plugs because I found those solutions on your website. What else could this be?????

**werty** · 06-05-2009, 11:39 AM

MAYBE the fuel guage is off and youre runnin outa gas /?

**monette** · 06-05-2009, 11:58 AM

Thanks for your response. When this happend the first times (first day of Memorial Day weekend) we took samples of the fuel (e-85) and then the second time (day after Memorial day)we drained the fuel tank. Both times showed plenty of fuel. Can you think of anything else?

**ct9a** · 06-05-2009, 01:26 PM

If it is a fuel shortage issue, it could be the pick up unit. Sorry, don't know too much about the newer motors. Good luck.

**werty** · 06-05-2009, 01:31 PM

COMPUTER throwing no codes ????/////

**monette** · 06-05-2009, 01:46 PM

It is not the fuel level, samples were taken all three times (although this last time it only had about 5-6 gallons when they drained the tank which seems kind a low for having a quarter of a tank).

The computer codes varied. Running lean (okay E-85), fuel tab or trim tab, but that was rectified, and the one he pulled off today was mass airflow sensor.

He checked my vent screen (called a different name) to see if it was clogged and it was very clean.

My mechanic thinks I need to take it to a dealer and have them reflash the computer. When we had the battery replaced he is thinking it might have wiped out the memory.

Odd thing is, the dealer has had two of these recently and my mechanic has another vehicle (09 silverado) in the shop now for the same symptons. Any thoughts

**Dr_Zero** · 06-05-2009, 02:23 PM

I would lean towards the fuel I know you said you got some unleaded and some e-85 but depending on where you live if there is a high moisture content you can get water in your tank or in the tank at the station.

On powerblock this weekend they were talking about e85 and how it absorbs water and not to use it in a vehicle that is not going to use the fuel up rather quickly due to the water issue. Well I have a 40+ gallon tank and I dont like running around with 1/4 of a tank so I can keep the water out.

Your fuel can look normal but be watered dow or not mixed right at the blender if you can find some real unleaded I would try some of that again and stay away from the alcohol except in the margaritas.

**monette** · 06-05-2009, 05:39 PM

Sounds possible. We are going to run reg in it for the next 4 or 5 tank fulls. We are suspecting a computer issue that stems from pulling out the battery???? Maybe it lost its memory and some of the upgrades? I do live in a humid environment, right along the Mississippi river, but I have been running E-85 for over a year now and never a problem. We did check for water in the first two incidents, one was E-85 and we found no water (but it would be hard to find because the alcohol mixes/absorbs the water) and the second batch was regular with no gas in it and that should have been easy to find. The regular gas was bought in Ohio when we were on a trip. Nonetheless, we will be putting in reg for the next 4 or 5 tank fulls and that will hopefully resolve the problem.

I have heard that problem with E-85 and boats, with the boats being on the water and having the fuel sit there for long periods of time. Luckily we have not had that problem with our boat, apparently only our Yukon XL. Thanks for your suggestion. I will keep you posted.

**monette** · 06-21-2009, 02:40 PM

Okay, just got my Yukon XL back from the shop on Friday, it was in for a week. DTC codes were showing mass air flow, lean left bank, and something else. So he unplugged the battery overnight and then plugged it in and reprogrammed it. Yeah, it seems to have worked. It appears that changing a battery is no simple task anymore. They are guessing that I lost some of my parameters and updates that are in stored in the computer when the battery was changed. However, now we have a different problem.

When you start the truck, it will sometimes continue to turn over even though the engine has all ready started, or it will start real rough. Weird stuff. It is not the starter or the igniton switch. Husband though maybe the cylinoid (SP?) but apparently not. It is not throwing any codes anymore but continues to do this. My friend has a newer burb (08) and it is doing the same thing. I told her to get hers in and find out what is wrong (she is still under warranty) and let me know.

Dealership says they suspect fuel injector(s). But will have to perform a couple of different tests to make the costly determination. They are thinking it is a mechanical and not electrical (because it is not throwing any codes). Any other guesses?