Running Lean

So I took my Riv in to get new O2 sensors and fix my fuel gage and found out that my Riv is running a little lean. Turns out I didn't need new 02 sensors and my fuel gage is fine. but he said around 4500 RPM's it ran lean for about 100 seconds. He thought I might need bigger injectors, but I wanted to get your guy's opinion before I actually do anything.

Right now I have a 3.4" pulley, SLP Headers, Intense S1X cam, 105 valve springs, and a custom PCM from intense. SES light was on, but turned off on the way out there.

That SES should still leave a DTC in the PCM. Find out what set it off.

I don't put much stock in "custom" PCMs unless I tune it myself. If anything at all is different with the car (or fuel, or weather, etc.) since you had the custom PCM written, it could need a new program. Imo, PCM tunes are not a set-it and forget it kind of thing. They should be adjusted as variables change.

has the pcm had time to relearn everything?
i also agree with the DIY tune vs "custom". you may need to pick up a PT.
on the plus side i really dont think you are in need of bigger injectors with the 3.4 and cam.

Definitely don't need injectors yet.

With the cam and pulley you could be borderline near injectors. Need to see IPW from a WOT scan to be sure. But even if you needed injectors that wouldn't cause you to run lean except at WOT. It does take time for the engine to learn fuel trims. How did they determine it is running lean?

I can't remember what he said set it off, but they still have it, so I can ask when I go to pick it up on Monday or Tuesday. I may buy a PowerTuner because I eventually want to drop to a 3.2" pulley. I think he had it on a scanner or something, like I said I can ask. I should also probably mention that I don't have an L67. I have an L32, Gen V blower. I haven't gone WOT since I've had it back, kinda taking it easy for awhile.

custom tune or not..its a factory ecu..it should still adjust for different things to an extent....but being able to read AFR's and other sensor values will be the key to learning why its got a lean spot!

I have a very mild suspicious that I might have a vacuum leak and it may be causing my lean condition. ..? The thing is, I cant find any good info on what vacuum #s to expect with an XP cam.

I am currently seeing  7-8PSI or ~15-16in/hg vacuum at idle  and around 19-19.5PSI or ~38.7in/hg vacuum at cruise speed.

I am going to load stock MAF table and reset fuel trims tomorrow JUST to count whatever previous MAF tune out. WHat else could it be, tho? O2 sensor seems to be working fine. I do not have yet have wideband hooked up. Hopefully this weekend.

http://www.aa1car.com/library/what_is_fuel_trim.htm
If the numbers are +10 or higher for STFT and LTFT, your engine is running LEAN. Rev the engine to 1500 to 2000 RPM and hold it steady for half a minute or so. If the fuel trim numbers drops back down to a more normal reading, it confirms the engine has a vacuum leak at idle. This is because vacuum leaks have less of a leaning effect on the fuel mixture as engine speed and load increase.
I have a feeling that this is the case. I am hitting like +12 LTFT when coasting and +16 LTFT idling. As soon as I give it fuel it comes down to a lower + #.

I will spray and check for vac leaks this weekend.. WTf...

Quote :

I am currently seeing  7-8PSI or ~15-16in/hg vacuum at idle  and around 19-19.5PSI or ~38.7in/hg vacuum at cruise speed.

That can't be right. The lowest possible pressure (perfect vacuum) on Earth is 29.92 in/Hg. 21 in/Hg is about the max you'll see in a car. Maybe your vac reading is actually 19.5 in/Hg, or you're reading MAP, in which case you'll need to subtract atmospheric pressure (~29.92 or current baro). Example: 38.7-29.92 = 8.78, in which case you would have a problem.

getting -7.54PSI vaccuum at idle. I converted that to in/Hg and got 15.270188in/Hg

Yeah, but using the same gauge you're seeing -19 PSI at cruise, so something's not right.

What do your units say in vacuum? Most gauges report PSI when in boost (+), then switch to in/Hg when in vac (-), so that could be it. You're probably seeing 7.54 in/Hg.

I am going off my boost gauge. I get -7.54PSI boost at vaccum
http://www.convertunits.com/from/in+Hg/to/psi


Convert to in/Hg and you get ~15 in/Hg

What do you guys see in in/Hg or PSI for vacuum at idle?

Before anything what are you using to log vacuum? If you're just reading a mechanical gauge load up HPT and see what it says. I see around -9psi at idle and at most -12psi while cruising (going off of DHP scan). I think AA is right about how most gauges do in/hg under vacuum and psi under boost.

If you're reading off of a mechanical gauge like this, the numbers on the left are in units of "inHg".



I assume you are using a digital display since you're numbers are decimals. I dont think any gauge you can buy reads in "negative PSI", though. Maybe if there is a negative, it is just to indicate that it is reading vacuum.

You can buy a cheap mechanical gauge for like $15 and hook it up just to confirm what your actual vacuum is.

matt270avian wrote:

Before anything what are you using to log vacuum? If you're just reading a mechanical gauge load up HPT and see what it says. I see around -9psi at idle and at most -12psi while cruising (going off of DHP scan). I think AA is right about how most gauges do in/hg under vacuum and psi under boost.

I'm using HPT and Torque. I dont use in/Hg, it converts it to PSI for me. The formula is pretty dang simple to convert back and forth.

You are getting -9PSI at idle and I am seeing -7.5PSI. I just wonder how much the XP cam has an affect on this,

Like Codith said in my showroom thread, I am pegging 16.4 LTFT at idle and it may be a small vacuum leak.
Gonna find the little gremlin this weekend..

"-9 PSI" = 18.3 in/Hg vacuum.

Vacuum isn't measured in PSI in order to keep discussions like these from happening. That's why gauges typically look like this (note the vacuum units are roughly 2:1 to boost, same with th3fr4nchi5e's gauge on previous page):



Digital gauges are no different. On any scanner or gauge that reads "boost", it is calculating from MAP. It should calculate PSI in positive pressure, in/Hg in vacuum.

It's easy to figure this out. Just look at your MAP and do the calculation manually. Atmospheric pressure depends on barometer, which varies, but usually is ~14.7 PSI (29.92 in/Hg). If MAP is below this value, you are in vacuum. Above, in boost. Unlike boost and vacuum, MAP units are constant (PSI, in/Hg, kPa), which will be easier to figure.

If your scan is reading 9 in/Hg vac at idle, this could be correct with your cam. Maybe the cam has some valve overlap, causing loss of vacuum at low RPM.

Seeing ~15 in/Hg at idle. Not sure what it should be with XP cam. From what I am reading, stock L67 owners are seeing about 18-20 in/Hg at idle.
Hmmmm

How much vacuum at cruise?

About 13 in/Hg at cruise

You're absolutely going to have less vacuum at idle than a stock L67. You'd also have less vacuum at cruise.

Are you sure your fueling just isn't wrong and the car has to dump fuel to correct it? If you were pegged for too long at 16.4, it would toss a P0171....which would most likely indicate a vacuum leak. If you're only seeing this 16.4 at certain RPMS or throttle position, I'm betting that you need to adjust the MAF or PE table to fix it.

LTFT jumps to 16.4 when I stop and shoots up to high teens when i coast at highway speeds. Whenever im on the throttle, LTFT is as low as 0 and not so bad.

Whenever if im off the gas it just shoots right up, tho. I think this is a sign of a vac leak?

Run a log with MAF, FT, O2, and TP. Get a good look at the frequencies where the PCM starts dumping fuel. Remember, you physically changed the amount of air that enters the engine, even at idle. When you get a good baseline of the frequency range that needs fuel, try adding some MAF in those ranges and see if the FT's start to level out. If they do, you know you're chasing a ghost. It certainly can't hurt.

EDIT: Is this something you noticed after the Header install?

charlieRobinson wrote:

LTFT jumps to 16.4 when I stop and shoots up to high teens when i coast at highway speeds. Whenever im on the throttle, LTFT is as low as 0 and not so bad.

Whenever if im off the gas it just shoots right up, tho. I think this is a sign of a vac leak?

Under WOT you want the LTFT to be 0 or slightly negative, never positive. If it's positive it means the PCM is adding fuel because you're running lean. Any other time you want the LTFT to be between -3 and 0.

Yes, Matt. That's correct.

There's a few guys in this thread with what seems to be the same issue:
http://www.grandprixforums.net/threads/80405-P0171-Code-LTFT-Maxed-Idle

I have not seen the P0171 code yet, tho.

I am going to check this weekend for vac leaks.

Abaddon wrote:

Run a log with MAF, FT, O2, and TP. Get a good look at the frequencies where the PCM starts dumping fuel. Remember, you physically changed the amount of air that enters the engine, even at idle. When you get a good baseline of the frequency range that needs fuel, try adding some MAF in those ranges and see if the FT's start to level out. If they do, you know you're chasing a ghost. It certainly can't hurt.

EDIT: Is this something you noticed after the Header install?

I had the lean condition before header install but assumed it was being caused my the cracked plog/exhaust leak. Once we got the headers on and reset fuel trims and I was still getting uber lean 16.4 LTFT when I take my foot off the gas, I knew it had to be something else.

My MAF tune is fine. I either have a vacuum leak or something else. It's just like Codith said in the show room thread, it jumps right to 16.4 when I am idling or take my foot of the gas and coast.

charlieRobinson wrote:

My MAF tune is fine. I either have a vacuum leak or something else. It's just like Codith said in the show room thread, it jumps right to 16.4 when I am idling or take my foot of the gas and coast.

Then my responses are no longer needed. You have it figured out.