Thread: LTFT spikes to +16/other times perfectly fine

I have been going in circles with this issue of my LTFT hitting +16 at times. Other times it is perfectly fine. I have sprayed brake clean and poured water on every vacuum line, gasket or rtv seal and trims will not change (usually -3-10 ltft at idle) Yes its rich but whatever. I even replaced my #1 o2 sensor with a genuine GM part. I have also replaced my BBV due to the findings of the orange diaphragm having a minor tear with no change. I have never kept an eye on my trims this much since my IC install at the beginning of this month. I want to say that I have watched my wideband dip into the 11's/12s (cruise/part throttle/idle) before my IC install so I believe this is an issue that has been on going. The car has no real issues with pulls. It does pull decent for what it is with no hesitation ever. At idle my fuel pressure is 45psi. At 2500 rpm it is at 44. When I got wot it will hit 62. Prime is 54 and will drop to 40 and rise back to 48. I have not tested fuel pressure when my issue happens due to the fact it is sporadic.

Some screen shots but the actual logs are linked here to the hpt forum.

http://www.hptuners.com/forum/showth...568#post383568

Today I removed the band clamp around my crossover and found a very minor leak (minor soot buildup) So I rtved the entire area where the pipe slips into and re installed the clamp. As well as rtving my map sensor just incase it was cracked and acted up due to heat. Nope.....nothing changed.

I am at a loss to an extent. I am thinking there must be some table I don't know of that is making me lean. It will happen around 4000-5000hz at light throttle in cruise for the most part. But...not all the time. I even added 1% of fuel to 3500-5000hz and it didn't change.


I am stock fuel pump. Maybe 100K on it? I am not sure as it was a used drop in. Maybe its getting hot and weak at cruise?? But it has no issue pumping out at WOT. When I first got the car 2 years ago it had an ebay 255 walboro and every now and then after driving and coming to a stop the car would die but would start right back up like nothing happened. Ended up being a bad pump so I ditched it for a stocker at the time.

I did remember that the stochio was set to 14.1 by the pervious owner. I switched it back to 14.7 and no change.

We need two threads for this?

Originally Posted by BillBoost37

We need two threads for this?

Separate Issue it turns out now. That is why the new thread.

Might have found something

http://www.hptuners.com/forum/showth...568#post383568

Well unfortunately the IFR change did not help. The car decided to act up the other day and today. What am I missing? Could the maf be at fault? Or fuel pump? I did hear a noticeable tick from the engine area today only when standing in front of the car. The crossover pipe has been re sealed with rtv and band clamped weeks ago. I did not see any soot anywhere. It might just be the nature of the headers though. It does seem like the 02 got lazy or it saw something?

welcome to the evap/purge emissions function.

when the fuel vapor in the charcoal cannister is used up the purge is essentially a vac leak and trims go positive and the pcm can diagnose evap/purge and system integrity.

99/00+ guys are ****ed with the more invasive tests of the eobd2. 04+ go full retard on the various tests and how many times its tested per drive cycle.

block the purge line or unplug the purge valve. disabling the vent is harder

Originally Posted by Turbocharged400sbc

welcome to the evap/purge emissions function.

when the fuel vapor in the charcoal cannister is used up the purge is essentially a vac leak and trims go positive and the pcm can diagnose evap/purge and system integrity.

99/00+ guys are ****ed with the more invasive tests of the eobd2. 04+ go full retard on the various tests and how many times its tested per drive cycle.

block the purge line or unplug the purge valve. disabling the vent is harder

I have no evap on my car that's the issue on why I can't figure out why it does this. Where the purge line would go I have that capped off with a brand new plug.

Your car is doing the cat diagnostic test. You need tiny tuner to shut it off.

the rear o2 can be turned off and kill the cat test with tiny tuner and a dhp only. or hack the vin in a bin and use old hpt to open the bin and save as a .hpt. this needs to be done if you dont have a cat, or run a hi flow cat on 01-03 cars.

Originally Posted by GTPpower

Your car is doing the cat diagnostic test. You need tiny tuner to shut it off.

Is it still possible to download this? Using windows 10 now a days. Also unsure on how to go about deleting this diag test. Would I just bring in an hpt file or something?

Originally Posted by wstefan20

I fought this exact same issue for a few months. It ended up being a combo between the rear o2 sensor, and a tiny vacuum leak on the throttle body. I've got a great post on a diy smoke machine leak detector that works wonders. The rear o2 on 20+ cars can't 100% be tuned out. I had mine tuned out with hp tuners but left the rear o2 in place fully hooked up. That's enough to trick the test.

I have brake cleaned the entire engine bay. Trims would not budge meaning no leaks. I have yet to smoke it. But with it doing this +16ltft years a go I am sure it has noting to do with a vac leak as the IC has been off 4-5x. As I have had this happen on the highway a few times but more so in traffic at low speeds to the point that the car will stall out.....when its hot it will do it way more. I did some googling and people had the 02 simulator in and it still acted up. Hence there is noting for it to respond back to the pcm to say hey I see the fuel. I remember 1 particular day years ago. I was sitting at a light ready to go up a slight incline to my apartment and the car hated life. This might of been back when I just got the wideband hooked up to actually see that the car was in trouble. Now for my car as mentioned I did swap the #1 02 to where my wideband is (where the #2) should be and the wideband to where the #1 is. The car obviously still acted up. IT was just a test to see if it saw it on both banks just not one. Now lucky for me I can leave my wideband alone as I mentioned I moved the #1 02 sensor right under the throttle body so I have a 3rd hookup area in the location zzp made in their headers by the trans dipstick tube. I can re wire my #2 02 up as I had to cut the harness I had to make for the sensor swap and place my #2 02 in that spot so it can read. But even so the car will add fuel right? But maybe not as long? Just a split second thing that the car comes right out of it?

I found this thread as well .

Help with tuning a series 2 L67

Originally Posted by PWNED

Is it still possible to download this? Using windows 10 now a days. Also unsure on how to go about deleting this diag test. Would I just bring in an hpt file or something?

I think it can still be downloaded. I'm not sure if it works with windows 10 though.

You need a bin file. Hpt does you no good. You need dhp to read the pcm as a bin file, then open the file with tiny tuner.

Thank you.....I have added the #2 02 sensor back and after a few weeks the car has not acted up!! As this was a daily thing basically.