Rough running 7.4 Vortec

[TexasAggie]

I have a scanner with live data, but haven't played with it yet. What fuel trims should I be looking for while driving? What else should I be checking on this thing?

 

[stutaeng]

Both the short term fuel trims (STFT) and long term fuel trims (LTFT), on both banks...

When you add both STFT and LTFT they should be 0, or close. And the LTFT should be less than 10%.

 

[chevman_88]

I have a scanner with live data, but haven't played with it yet. What fuel trims should I be looking for while driving? What else should I be checking on this thing?

I would actually start at idle and watch long and short term trims on bank 1 and bank 2 once you get into closed loop. Typically you want to see 0 +/- 10% total trim (long term plus short term). If you are seeing higher total trim your PCM is adding fuel, negative trim is removing fuel, etc etc.

If you are within spec at idle, increase RPM to 1500, 2000, and 2500 (just need to see what trim is doing with higher speeds). If you remain in spec the whole time, chances are you don't have a fueling issue, but you can take a drive at that point to see if being under load changes that at all.

You can also watch misfire counts while you are doing this if you want. I know I have a slight miss at idle, however, my counts don't reflect this. I've read that the black box PCMs aren't as sensitive to this but 0411s are, but I can't confirm whether that's true or not.

 

[TexasAggie]

Great stuff! Now I just need to hook up the scanner and figure out how to monitor this stuff!!!

I got the blue driver pro on sale at Amazon. I'm hoping it is as easy to use and the reviews claim.

 

[Carlaisle]

You can pull the upper intake at a leisurely pace in about 30 minutes assuming the EGR fitting is in a cooperative mood. The tank is a bit of a pain to do from below, but not that difficult. If you have some stout friends or other way to lift from above, it's more pleasant to get to the pump by removing the bed. A new set of injectors will set you back around $500. You can also get a set of take outs for 20% of that. I'm running a set that has performed flawlessly for me for years, but used parts aren't everyone's thing. You need to be careful selecting injectors. Certain ones are plug and play replacements that require no tuning, but not all.

 

[TexasAggie]

Good to know about the upper intake. My engine bay is SUPER clean, so I assume all nuts/bolts will turn freely, but I've been burned by that before. I'm guessing some new gaskets are needed for putting it all back together?

I have a suburban, so dropping the tank is the only option.

As far as injectors, I've read a bit about them but not enough to not be ignorant. I have no issue with used parts, but how what exactly should I look for (new or used) when that day comes?

 

[TexasAggie]

Did some driveway testing and my fuel trims are all staying relatively low.... 5% plus or minus on both banks, term and short term. Adding them together rarely got above 7 or so. I'm going to do quite a bit more driving this weekend and will check the logs.

As far as misfires, I can't figure out how to get the scanner to read that info. When I go into mode 6 it doesn't list misfires as an option. Any ideas?

 

[TexasAggie]

No start condition returns! She started up just fine this morning when I moved it out of the driveway. Went back to get her and she won't start. Not sure where to go from here......

 

[stutaeng]

Check for fuel pressure and spark. Spark at any given spark plug, if not, then go to the coil.

 

[chevman_88]

Look at your distributor harness and coil harness/wire to distributor. Starting to sound like a loose connector or maybe bad wiring.