-18% Long Term Fuel Trims at idle.
-18% Long Term Fuel Trims at idle. I think writing this out will help in the diagnosis process, and I could use some other opinions as well.
The situation: 1950 Chevy truck with:
LQ9/4L80
LS6 cam and springs
Magnacharger MP112 with 1.9" pulley
Five-O injectors - higher flow rate for setup
Mail order tune from reputable tuner.
Engine and trans have been swapped in, and all power-adders have been added since swap. This is my first attempt to run the engine since adding the blower, cam, etc.
I've got a rich idle condition. Fuel trims go to about -18% once the system reaches open loop.
Brand new MAF. Reads about 10-12g/s at idle (idle speed is a little slow due to poor idle condition)
Retorqued header bolts, and no exhaust leaks found.
Injectors ohm'd within spec.
Compression is within range.
O2 sensors appear to be oscillating and heating as they should.
Coolant sensor appears to be operating as it should.
MAP reads approximately 40kpa at idle.
Vacuum is around 8lbs at idle. Haven't been able to detect any leaks.
It's hard to say, but I think the rich condition goes away at higher engine speed, but that needs better testing. Tomorrow I plan to better monitor the fuel trims at 1500 and 2500rpm.
I made an attempt to check for leaking injectors, but the magnacharger fuel rail doesn't clip the injectors in, so they pop out under pressure when removed from the manifold.
My next step is to pull the injector plugs individually while the motor is running and see how the fuel trims respond. Percentage changes in the fuel trims should indicate any leaky injectors.
Any other thoughts or advice would be appreciated.
The situation: 1950 Chevy truck with:
LQ9/4L80
LS6 cam and springs
Magnacharger MP112 with 1.9" pulley
Five-O injectors - higher flow rate for setup
Mail order tune from reputable tuner.
Engine and trans have been swapped in, and all power-adders have been added since swap. This is my first attempt to run the engine since adding the blower, cam, etc.
I've got a rich idle condition. Fuel trims go to about -18% once the system reaches open loop.
Brand new MAF. Reads about 10-12g/s at idle (idle speed is a little slow due to poor idle condition)
Retorqued header bolts, and no exhaust leaks found.
Injectors ohm'd within spec.
Compression is within range.
O2 sensors appear to be oscillating and heating as they should.
Coolant sensor appears to be operating as it should.
MAP reads approximately 40kpa at idle.
Vacuum is around 8lbs at idle. Haven't been able to detect any leaks.
It's hard to say, but I think the rich condition goes away at higher engine speed, but that needs better testing. Tomorrow I plan to better monitor the fuel trims at 1500 and 2500rpm.
I made an attempt to check for leaking injectors, but the magnacharger fuel rail doesn't clip the injectors in, so they pop out under pressure when removed from the manifold.
My next step is to pull the injector plugs individually while the motor is running and see how the fuel trims respond. Percentage changes in the fuel trims should indicate any leaky injectors.
Any other thoughts or advice would be appreciated.
Yeah, that's what I'm thinking at this point, too. I wouldn't have thought that with new injectors, though. We'll see.
I guess there could be a short somewhere telling the injector(s) to open when they shouldn't? I'd imagine I'd see a code for that, though.
I guess there could be a short somewhere telling the injector(s) to open when they shouldn't? I'd imagine I'd see a code for that, though.
Ed that's likely. I have seen a bunch of stuck injectors on junk yard engines that are all gummed up and either won't open or won't close. I find it best to soak any used injector before trying to use them. Plus it does not cost much to clean them.
Can you datalog the engine to verify all else is ok?
Can you datalog the engine to verify all else is ok?
An injector stuck open effects the side (bank ) it is on. An injector stuck open has a much larger effect than 18%. Every one I have seen maxes long & short trims on that side at 25%.
it is more likely that you need a better tune for your setup...
Mail order tunes without Data logs...are just best guesses no matter who it is from.
unless you get Datalogs and send it back and forth...its just a guess.
every car is different..and a mail order tune is just designed to get you going so you can get to a real tuner and get some real time data on your engine.
having fuel trims doesnt mean your car is not safe...it just means you need to get a better tune if you want those trims to be lower.
typically idle is controlled more in the VE table than the MAF table as MAF is only used at steady state...and idle is typically not steady state for more than a few moments at a time
it wont hurt anything to drive around and let the pcm correct by removing fuel ....its just not optimal.
if your o2 sensor has an issue, and the vehicle has to rely on open loop operation...its just going to be really rich at idle and probably have issues.
your slow idle speed is not related to fuel trims...the fuel trims are putting you around 14.7 AFR at idle
your poor idle quality is somewhere else in the tune... either Idle Airflow(most likely culprit) or a timing issue, or even just something as simple as the idle rpm is set too low.
dont be so quick to blame your injectors...it sounds to me like a tuning issue. (software issues...not hardware issues)
Mail order tunes without Data logs...are just best guesses no matter who it is from.
unless you get Datalogs and send it back and forth...its just a guess.
every car is different..and a mail order tune is just designed to get you going so you can get to a real tuner and get some real time data on your engine.
having fuel trims doesnt mean your car is not safe...it just means you need to get a better tune if you want those trims to be lower.
typically idle is controlled more in the VE table than the MAF table as MAF is only used at steady state...and idle is typically not steady state for more than a few moments at a time
it wont hurt anything to drive around and let the pcm correct by removing fuel ....its just not optimal.
if your o2 sensor has an issue, and the vehicle has to rely on open loop operation...its just going to be really rich at idle and probably have issues.
your slow idle speed is not related to fuel trims...the fuel trims are putting you around 14.7 AFR at idle
your poor idle quality is somewhere else in the tune... either Idle Airflow(most likely culprit) or a timing issue, or even just something as simple as the idle rpm is set too low.
dont be so quick to blame your injectors...it sounds to me like a tuning issue. (software issues...not hardware issues)
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It may be time for me to bite the bullet and buy HPTuners. Five hundred bones is just a lot to swallow when I've got two projects going at the same time. Not to mention, I'll have to put a new hard drive in a laptop as I don't currently have a Windows machine to run HPTuners on. I suppose it pays for itself eventually.
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With an LS6 cam and pretty much stock motor plus the blower it will actually be quite easy to tune. The big floppy 102 TB's and cams make it hard.
Just make sure you get the Pro verison with a WB so you can tune boost as well. The stock O2's are only going to help you at idle and cruising around. Someone was selling a WB and HPTuners Pro for a great price on here not too long ago. It was a vendor. Cannot remember who.
Just make sure you get the Pro verison with a WB so you can tune boost as well. The stock O2's are only going to help you at idle and cruising around. Someone was selling a WB and HPTuners Pro for a great price on here not too long ago. It was a vendor. Cannot remember who.
[QUOTE]typically idle is controlled more in the VE table than the MAF table as MAF is only used at steady state...and idle is typically not steady state for more than a few moments at a time. [QUOTE]
Easy to test that also: Try two cals by taking the one in the car now and pull 10% out of the VE table( multiply it by .9) and look at your fuel trims. Make yet another one by taking the one in the car now, and multiply the MAF table by .9, chech your fuel trims again.
Easy to test that also: Try two cals by taking the one in the car now and pull 10% out of the VE table( multiply it by .9) and look at your fuel trims. Make yet another one by taking the one in the car now, and multiply the MAF table by .9, chech your fuel trims again.
henceforth the reason I said you need a proper tune first...
it might be "expensive" in your mind to get tuned....
but you could find a local tuner who will deal with part throttle and spoend several hours on a tune for a couple of hundred bucks...and it will be worth it to know that everything is correct and working right
Yeah, I can't be sure of any of those things. Now I'm just trying to decide whether I want to tackle this myself or pay a local guy to take a look. It looks like the going price for a used HP Tuners Pro is about $500.
[QUOTE=Ed Wright;17955270][QUOTE]typically idle is controlled more in the VE table than the MAF table as MAF is only used at steady state...and idle is typically not steady state for more than a few moments at a time.
Easy to test that also: Try two cals by taking the one in the car now and pull 10% out of the VE table( multiply it by .9) and look at your fuel trims. Make yet another one by taking the one in the car now, and multiply the MAF table by .9, chech your fuel trims again. I use to ask this question a lot and tried to figure out some way to log how much is controlled by maf or by ve at a given time. Never accomplished that but have done what you described. Only thing is with my results a well tuned setup, most of the fueling came from the maf at idle.
Easy to test that also: Try two cals by taking the one in the car now and pull 10% out of the VE table( multiply it by .9) and look at your fuel trims. Make yet another one by taking the one in the car now, and multiply the MAF table by .9, chech your fuel trims again.
Digging this one back up. This thing has been kicking my ***.
Project sat for a little while. I got busy, needed funds etc. Been working on it steady for a couple of months now.
My issue now is completely opposite. I'm running very lean. Short Term Fuel trims in my most recent run were +50%. Since my last post in this thread the following things have changed:
- New harness from PSI
- Bought HPTuners and set up my injector table where my tuner failed to
- Checked, double checked, and triple checked for vacuum leaks
- Grounds gone through and improved (4 gauge from battery to both cyl heads, block, chassis, body)
- New O2s
I've attached a log I took this morning and the tune too. I noticed a couple of things (excuse any inaccuracies - I don't have a windows computer at home or at work, so I can only access my logs at the shop). It looks like the throttle never goes below 18% - It's DBW. Not sure what's causing that.
Also, last week after getting my PSI harness installed, I noticed that one of the ground points in their harness was reading 30ohm with the ignition on and 1ohm with it off. I contacted them and was assured that, given my extensive grounding of the vehicle, it's not a problem. I'm not so sure, and I wonder if it might be a symptom of something else. A bad PCM maybe?
Anyway, I know very little about HPTuners, tuning these vehicles, etc, and I could use any thoughts or advice you guys might have to offer.
Thanks
Project sat for a little while. I got busy, needed funds etc. Been working on it steady for a couple of months now.
My issue now is completely opposite. I'm running very lean. Short Term Fuel trims in my most recent run were +50%. Since my last post in this thread the following things have changed:
- New harness from PSI
- Bought HPTuners and set up my injector table where my tuner failed to
- Checked, double checked, and triple checked for vacuum leaks
- Grounds gone through and improved (4 gauge from battery to both cyl heads, block, chassis, body)
- New O2s
I've attached a log I took this morning and the tune too. I noticed a couple of things (excuse any inaccuracies - I don't have a windows computer at home or at work, so I can only access my logs at the shop). It looks like the throttle never goes below 18% - It's DBW. Not sure what's causing that.
Also, last week after getting my PSI harness installed, I noticed that one of the ground points in their harness was reading 30ohm with the ignition on and 1ohm with it off. I contacted them and was assured that, given my extensive grounding of the vehicle, it's not a problem. I'm not so sure, and I wonder if it might be a symptom of something else. A bad PCM maybe?
Anyway, I know very little about HPTuners, tuning these vehicles, etc, and I could use any thoughts or advice you guys might have to offer.
Thanks
TECH Addict
Joined: Aug 2005
Posts: 2,305
Likes: 126
From: Monroe,NY
Do you have a wideband hooked up? Going by your log you are running really rich. I don't know much about drive by wire but I don't think they go to 0%. Can you get it to idle without giving it gas? I would like to see an idle log with no throttle input.
What makes you think it's running rich? From what I can tell, the PCM is dumping fuel trying to correct a lean condition.
Unfortunately, the log I posted is an attempted idle with no throttle input at all. RPM changes are simply from the PCM trying to maintain idle.
If both banks trim similarly then look at things like the
injector minimum pulse width or minimum fuel milligrams.
Big injectors need much less pulse width at the low end.
Also is your fuel pressure manifold referenced, or stock
setup? A fuel pressure that tracks MAP can relieve the
low end problems with injector control at short pulses
(as well as helping the big end).
injector minimum pulse width or minimum fuel milligrams.
Big injectors need much less pulse width at the low end.
Also is your fuel pressure manifold referenced, or stock
setup? A fuel pressure that tracks MAP can relieve the
low end problems with injector control at short pulses
(as well as helping the big end).
If both banks trim similarly then look at things like the
injector minimum pulse width or minimum fuel milligrams.
Big injectors need much less pulse width at the low end.
Also is your fuel pressure manifold referenced, or stock
setup? A fuel pressure that tracks MAP can relieve the
low end problems with injector control at short pulses
(as well as helping the big end).
injector minimum pulse width or minimum fuel milligrams.
Big injectors need much less pulse width at the low end.
Also is your fuel pressure manifold referenced, or stock
setup? A fuel pressure that tracks MAP can relieve the
low end problems with injector control at short pulses
(as well as helping the big end).
The fuel pressure regulator is the one that came with the blower. It is boost/vacuum referenced. Should this affect my injector flow rate table? Right now it looks like this:
If the FPR is referenced, should this table be the same value across all MAP readings? I don't think that'd be the source of my idle issues, but it's just a thought I had.