Multiple Misfire and Transmission Slipping

[Tynan918]

Working on a family members '07 Tahoe LT he recently bought as a daily driver, and it has some issues.

I scanned it once before and the main focus is the multiple misfires and bad transmission slippage.

Misfires - We've checked the spark plugs and they looked okay. We checked resistance of the spark plug wires and they checked out good. We checked spark using a timing light gun and a couple weren't sparking or were weak, so we changed them out but it didn't fix the misfiring after clearing the codes.

How do I go about accurately troubleshooting and pinpointing the misfire causes.

Transmission Slipping - I haven't drove it on the highway/freeway, just on the main roads and nearby neighborhoods. From 1st to 2nd gear, RPMs can get as high as 5,000 if I keep my foot pressed on the gas pedal. 2nd to 3rd gear basically the same scenario. To avoid shifting at high RPM, I have to slightly take my foot off the gas pedal and it will shift where and when I want it to. We've changed the transmission filter and fluid but that didn't fix the issue. Fluid was brownish but not an excessive amount of shavings. Also, the shifter handle at the steering wheel will not go in 1 as if it doesn't exist, only goes in 2 a stops there. Maybe the shifter is misaligned and causing the slips ? Traction mode light is also stuck on and can't turn it off by pressing the button.

I'm told that the misfiring will cause the transmission to slip, but this bad ? Would the traction mode being stuck cause the slipping ?

Pretty sure this is a 5.3L and a 4L60E I'm referring to.

 

[Joseph Garcia]

Do you have, or have access to, a quality bi-directional scanner? If not, I recommend that you get yourself a quality bi-directional scanner to add to your tool box. Then, you will be able to read ALL trouble codes, along with a brief explanation/pointer to the source of your issue. You will also be able to reset/delete trouble codes, after taking corrective action. You will literally save thousands of dollars in diagnostic and repair costs over the life of your truck, and you will most likely recoup the cost of the scanner within 1 year.

 

[j91z28d1]

for the miss fire, there's tons of videos on youtube to help diagnostic. but basically tpi. need fuel/air/spark and compression.

most people do plugs and wires first, cause it properly needs them anyways, plugs and the wires are wear items as weird as that sounds. Just checking with a ohm meter doesn't tell you much really.

then try and check for fuel. there's a few different ways from looking for a wet plug, or spikes in the o2 sensor voltage, to just swapping a inkecor from a bad cyl to a good cyl and see if the miss follows it. same with a coil to test for weak spark. see if the miss fire follows the coil.

compression test. it can help incase you've got a afm or valve spring problem.


I'm no tranny guy, and you can test that it's in a gear and not half in half out by disconnecting the shifter cable at the tranny. but don't run yourself over doing it. generally if your tranny slips like that clutches don't last very long after.

 

[Doubeleive]

get the engine straightened out first, then go onto the transmission but essentially yes if the engine, misfires, maf, air flow ratio all that crapola is not right the transmission "can" be affected for sure. how bad? can't really say for sure I have had them buck like a bronco or not shift or shift incorrectly.
with that being said the maf can cause misfires and a whole host of other issue's seemingly unrelated entirely. misfire, lean codes, vacuum codes, transmission codes, you name it.
that doesn't mean go throw the parts cannon at it, you need a good scanner.
AND always start at the battery and grounds. KISS

 

[Fless]

As @Doubeleive stated, verify the basics. A dirty or defective MAF can cause lots of issues, and GM OE is the only way to go when replacing them.

Also, do a CASE relearn with a capable scanner to rule out any issues with the correlation between the crank and cam sensors.