Need help reading data log, truck horribly rich
Thread Starter
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Senior Member
Joined: Oct 2001
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Need help reading data log, truck horribly rich
Anybody who understands the parameter data, please take a look at this and tell me if you see anything out of whack.
My truck is running horribly rich, like so rich the exhaust smells like raw fuel. I doubt it's a plug or pack issue as it's just too rich for something like that, they'd all have to have gone bad all at once.
Click here for Excel file of data log
My truck is running horribly rich, like so rich the exhaust smells like raw fuel. I doubt it's a plug or pack issue as it's just too rich for something like that, they'd all have to have gone bad all at once.
Click here for Excel file of data log
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Joined: Mar 1998
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From: Virginia
Hi Crued,
Looks like mostly C/L (Closed Loop) data, so let's just talk about that for a second, since you do not seem to have wideband O2 data for O/L (Open Loop), at least from what I saw in just taking a very brief glance at some of the data................
In C/L, you add up both the short term fuel trim (for say, Bank 1) and then the long term fuel trim data for that same bank, to get the actual TOTAL amount of correction the PCM has to make in order to achieve stoich A/F (14.64:1) in closed loop on that particular engine bank. With proper functioning O2's & no exhaust leaks, both banks should be within just a coupla-few percent of each other (and I didn't spend any real time to see if they are in your data).
Obviously, your PCM is having to pull out fuel in order to hit stoich A/F in C/L, so what needs to be done is to adjust the MAF meter's transfer function to bring that back into line. This is easy to do for any competent tuner to redo the transfer function in the PCM program, & we can help you with that if need be.
To get the picture for Open Loop, you need to run it with a wide band O2 in place, logging all the various data so you can get a plot of A/F based on engine rpms, along with logging the MAF voltage (or A/D counts), etc., at the same time - then with that info, the proper adjustment can be made to the MAF transfer function so that in O/L, you actually get the A/F ratios that the tuner is commanding in the fuel table. The Closed Loop fuel trim data gives the info needed for correcting the MAF transfer function at lower MAF voltages in Closed Loop, but you need to do a test of A/F's in O/L with a wideband O2 so you can see how far off the actual A/F's are from what is being commanded in Open Loop (basically, at full-throttle), in order to know how much to adjust the MAF transfer function there, too - so it's adjusted correctly throughout the entire range of operation.
It's pretty normal in stock factory tunes & even some performance tunes to have the PCM pulling out fuel at idle & cruise (Closed Loop) to hit stoich A/F until you can log the data with the new tune and then make the adjustments based on that. Your fuel trims are too high, thus your tuning needs some work.
Just give us a call at our number listed below if you'd like a hand with this - we can go over all of this with you & tell you exactly what needs to be done, and can also take care of the tuning changes for you, if you like.
Whatever you do (just in case you might have been thinking along these lines), don't try lowering fuel pressure to make up for this, etc. - assuming you're running normal stock rail pressures and no other mechanical issues are contributing to this, the fuel trims need to be corrected via tuning, which is a matter of making a new transfer function for the MAF. Jut call us at our number listed below if you do not already have a tuner to take care of this properly for you.
Good luck!
Looks like mostly C/L (Closed Loop) data, so let's just talk about that for a second, since you do not seem to have wideband O2 data for O/L (Open Loop), at least from what I saw in just taking a very brief glance at some of the data................
In C/L, you add up both the short term fuel trim (for say, Bank 1) and then the long term fuel trim data for that same bank, to get the actual TOTAL amount of correction the PCM has to make in order to achieve stoich A/F (14.64:1) in closed loop on that particular engine bank. With proper functioning O2's & no exhaust leaks, both banks should be within just a coupla-few percent of each other (and I didn't spend any real time to see if they are in your data).
Obviously, your PCM is having to pull out fuel in order to hit stoich A/F in C/L, so what needs to be done is to adjust the MAF meter's transfer function to bring that back into line. This is easy to do for any competent tuner to redo the transfer function in the PCM program, & we can help you with that if need be.
To get the picture for Open Loop, you need to run it with a wide band O2 in place, logging all the various data so you can get a plot of A/F based on engine rpms, along with logging the MAF voltage (or A/D counts), etc., at the same time - then with that info, the proper adjustment can be made to the MAF transfer function so that in O/L, you actually get the A/F ratios that the tuner is commanding in the fuel table. The Closed Loop fuel trim data gives the info needed for correcting the MAF transfer function at lower MAF voltages in Closed Loop, but you need to do a test of A/F's in O/L with a wideband O2 so you can see how far off the actual A/F's are from what is being commanded in Open Loop (basically, at full-throttle), in order to know how much to adjust the MAF transfer function there, too - so it's adjusted correctly throughout the entire range of operation.
It's pretty normal in stock factory tunes & even some performance tunes to have the PCM pulling out fuel at idle & cruise (Closed Loop) to hit stoich A/F until you can log the data with the new tune and then make the adjustments based on that. Your fuel trims are too high, thus your tuning needs some work.
Just give us a call at our number listed below if you'd like a hand with this - we can go over all of this with you & tell you exactly what needs to be done, and can also take care of the tuning changes for you, if you like.
Whatever you do (just in case you might have been thinking along these lines), don't try lowering fuel pressure to make up for this, etc. - assuming you're running normal stock rail pressures and no other mechanical issues are contributing to this, the fuel trims need to be corrected via tuning, which is a matter of making a new transfer function for the MAF. Jut call us at our number listed below if you do not already have a tuner to take care of this properly for you.
Good luck!
Thread Starter
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Senior Member
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thank you for that very informative explanation of the limited information available to you.
the problem is that i've had my current chip for over a year now, without issues. in fact, i just dyno'd 400/500 a week ago. things ran fine up to that, and after that (for a week). now all the sudden without any changes to the truck, it's doing this. yesterday i took the chip out, and the i get the same ridiculously rich truck on the stock pcm.
i also hillbilly tested all the injectors (stuck my finger on them) and they're all ticking. i also unplugged each coil pack 1 by 1, and saw a degradation in idle with each disconnection.
do you know what issue i may have knowing this information?
the problem is that i've had my current chip for over a year now, without issues. in fact, i just dyno'd 400/500 a week ago. things ran fine up to that, and after that (for a week). now all the sudden without any changes to the truck, it's doing this. yesterday i took the chip out, and the i get the same ridiculously rich truck on the stock pcm.
i also hillbilly tested all the injectors (stuck my finger on them) and they're all ticking. i also unplugged each coil pack 1 by 1, and saw a degradation in idle with each disconnection.
do you know what issue i may have knowing this information?