High LTFT's, Can not resolve, need help!

**jfl330** · 07-01-2011, 04:23 AM

My Predator still shows very high LTFT's (~ 20) using factory tune loaded. I have pulled the intake and put it back with new gaskets/seals, redone the complete pcv system, repaired the brake booster hose, and pretty confident that I do not have any vacuum leaks.

What else can cause the high LTFT's? Could a bad O2 sensor or cat casue this? Could the PCM itself have an issue?

Get a random P0174, P0101, and some Cat code, but infrequently.

Car has SLP lid, BBK 80mm TB, BBK SSI intake, and flowmaster welded into to stock SLP SS exhaust. Other than that, stock. Air systme removed, but did this before that was done.

This is getting frustrating.

Jon

**pajeff02** · 07-01-2011, 04:27 AM

Those mods would absolutely result in a higher than stock airflow through the engine. On a factory tune the PCM has to add fuel to maintain the correct air-fuel ratio. You probably just need a tune.

Assuming you have eliminated other potential issues, a MAF that is mis-reporting airflow could also add to the problem.

**Firebirdjones** · 07-01-2011, 08:11 AM

I'm with Jeff, you've changed the entire intake setup including an aftermarket BBK intake manifold.

You really should get the car somewhere and have a tune done.

Little things like a lid or a muffler you can get by with,,,but changing that intake manifold is pretty major. If your 02's are old (50,000 miles or more) I'd swap them out anyway before a tune.

**Frost** · 07-06-2011, 07:01 PM

+20 is a lot though generally speaking, even with the mods.

Try this:
Unplug the MAF. Clear the LTFTs wither with your tuner (if it will do it) or unhook the battery for about 15 seconds. Start the car up and drive it and see what the LTFTs do. If they are significantly lower, your MAF may be on the way out. When they go, they don't quit, they report low.

**jfl330** · 07-07-2011, 09:44 AM

Originally Posted by Frost

+20 is a lot though generally speaking, even with the mods.

Try this:
Unplug the MAF. Clear the LTFTs wither with your tuner (if it will do it) or unhook the battery for about 15 seconds. Start the car up and drive it and see what the LTFTs do. If they are significantly lower, your MAF may be on the way out. When they go, they don't quit, they report low.

I am putting in two new 02 sensors Sat and will see what difference if any that makes. But I know one went bad yesterday as it was stuck on 920mV all the time. They've got 113K on them so seemed like a good idea.

Will try the MAF thing after I see what the sensors do. I also have a Granatelli MAF I can throw in to see what changes that yields.

Thanks!
Jon

**Frost** · 07-07-2011, 02:02 PM

If you are throwing the GMAF, throw it in the woods.

**jfl330** · 07-07-2011, 05:05 PM

Originally Posted by Frost

If you are throwing the GMAF, throw it in the woods.

That's why it's not in now, picked up a used OEM of unknown status. We'll find out Saturday.
Thanks!

Jon

**mike171562** · 08-11-2011, 06:47 AM

was it the MAF?

**jfl330** · 08-11-2011, 11:16 AM

Well, finally got around to trying this MAF disconnect, and the difference was dramatic. Bank 1 LTFT's stayed very close to zero all the time. Always low single digits if not. Bank 2 was another story. The STFT's hit +50 and LTFT's hit +25 at one point. The the LTFT's settled in around +11. Then close to coming home (about 20 miles later), the Bank 2 LTFT's were low single digits to zero.

I have had a fairly frequent (not every engine cycle, perhaps every 4th) P0174 code which is related to Bank 2. As I mentioned in earlier in this thread, I do have a GMAF I may put in just to see if it behaves better than this OEM one.

Should I be looking for a NEW OEM MAF now? Should I get an LS6 version?

Thanks,
Jon

**Frost** · 08-11-2011, 09:48 PM

It took you a MONTH to try unplugging the MAF for SD? You need to not drive the car with this issue. If things are so far off that you have +30 trims, every single throttle transition will be lean and will want to knock at tip in.

So you sound to have a dead misfire or more than one on bank2 or a leak in the exhaust big enough to pollute the sensor's reading at low airflow such as idle. You really don't want to be driving the car with it flooding one side like this.

**jfl330** · 08-12-2011, 05:12 AM

Originally Posted by Frost

It took you a MONTH to try unplugging the MAF for SD? You need to not drive the car with this issue. If things are so far off that you have +30 trims, every single throttle transition will be lean and will want to knock at tip in.

So you sound to have a dead misfire or more than one on bank2 or a leak in the exhaust big enough to pollute the sensor's reading at low airflow such as idle. You really don't want to be driving the car with it flooding one side like this.

It's a third car that I use only occasionally. I may have started it twice in that month. What about the much better readings on bank 1 with the MAF unplugged? I have had the bank 2 problem once in a rare while with the MAF connected. An exhaust leak would not come and go. Would it? This is the second time the really high readings on bank 2 occurred since I got the car in Feb. The car still runs the same when this happens, could my Predator be mis-reporting? It is old and very first gen of the SLP Predators, firmware is 2.0. If there is a dead mis-fire, would it run badly, set another SES/DTC code? I am taking it in to Chevy Monday to have the cats checked as they are under warranty until next month.

Thanks for your support!
Jon

**mike171562** · 08-12-2011, 05:50 AM

Check your Fuel Pressure, my LT's were at 25% and it was because the hose on my Walbro FP had popped off.

**jfl330** · 08-12-2011, 06:10 AM

Originally Posted by mike171562

Check your Fuel Pressure, my LT's were at 25% and it was because the hose on my Walbro FP had popped off.

With the MAF unplugged, the LTFT's were perfect on bank 1, bank 2 acted strange, but came around. If it were a fuel pressure problem, it would show on both banks, wouldn't it? The MAF be unplugged would not affect the fuel pressure.

Jon

**mike171562** · 08-12-2011, 07:47 AM

Originally Posted by jfl330

With the MAF unplugged, the LTFT's were perfect on bank 1, bank 2 acted strange, but came around. If it were a fuel pressure problem, it would show on both banks, wouldn't it? The MAF be unplugged would not affect the fuel pressure.

Jon

Not sure, When I was trying to track down my problem, my LTFT's would be almost normal at part throttle, I would check just to be sure, I just went to Autozone and borrowed their FP pressure guage and checked it in the parking lot.