I built up a 454 to replace my 350 in a GMC Suburban

I built up a 454 to replace my 350 in a GMC Suburban 4WD and was told that re-programming the ECM was a simple thing 5 years later I'm still having issues with the system despite sending it out to several tuners. It runs too rich at low power settings 13.8 and too lean at high power settings 16.0 or there about till RPMs catch up. Seems to throw the Code 13 when the mixture at low power ticks 14.0 or lower. It runs fine but the check engine light will fail my emissions. I monitor with the Wide Band Innovate system. I monitor fuel pressure and its rock steady. I have the larger TBI and new injectors. The gear ratio is 488, I pull a big boat up long high passes. The O2 sensor seems to work, monitor with a meter it swings high with a rich mixture .900VDC and Low with a Lean mixture .400VDC. Any ideas? My last tuner was at a loss but doesn't specialize in OBD1 systems. It's mostly stock 1987 vintage 9.1 compression, 500CID RV cam, Edelbrock TBI Alum, manifold no EGR, Headders, High Flow Cat, Heated 02 Sensor. How touchy are the OBD1 systems?

:welcome:

The 1993 - 1995 Second Generation TBI computer has more tuning parameters than the 1987 - 1992 First Generation TBI computer. The second Generation TBI computer is about 50 times faster, 8192 Baud rate vs. the First Generation running at 160 Baud rate. Memory size of the Second Generation TBI is 64K vs. the First Generation 4K.

The Second Generation TBI can be wired so the WBO2 data will show up in the TunerPro RT data log.

What is your computer part number?

dave w

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How touchy are the OBD1 systems?

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Welcome to the forum.
"Touchy" isn't a word I would use to describe the early systems. Tuning early TBI could be likened to crop dusting. You try to get everything covered but at the end of the day it seems there are some areas that still need attention.

Tuning without a tool to monitor and record data for later review is an extrmely challenging task and requires a large investment in time and patience. Tunerpro RT is a one of several good tools to monitor and record how the engine is running. Data from Tunerpro can be input into a special tool that will help generate corrections for you or your tuner to apply to the chip to help adjust the calibration values.

In order to tune the calibration completely the vehicle needs to be operated under conditions similar to thiose in which you are experiencing problems. If you're seeing lean or rich operation with the vehicle loaded and climbing hills it may be tough for a tuner stationed in a shop in town to realize what the problem is.

Can I ask how your tuner(s) have asked you to collect data so they could see what changes could be made?

The CPU Part number is a 777747. The CALPAK is from a 350 CDI but from what I understand shouldn't affect anything, it runs in limp home ok. I don't have any software and wondering whether of not to invest in the whole shebang or bail and order the Holley System. I have 2 CPUs one with the standard 26 pin EProm and one with the 28 pin Flash. I purchased a performance 454 26 pin chip from Summit but it runs terribly with that setup (very lean). I had a tuner with a dyno set up the 28 pin flash chip and as far as drivability goes it runs great, my Check Engine light comes on after the truck runs 10 minutes or so in a light cruise. I haven't actually checked the emissions, I might mod the light and just see. Is it worth the time involved with the OBD1 system to get it right?

Thanks

The Tuner drove it around some and pulled data from his equipment to look at. I don't have anything. But might consider ordering equipment if the OBD1 can be made to work.

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Is it worth the time involved with the OBD1 system to get it right?

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I would think it will take less time to make these corrections than to start from the beginning with the Holley system. Have you spoken with the tuner who used the dyno about making small corrections to fix the c/e light? That should require a minimum investment in time, money, and hardware. Tunerpro is $30 and you can buy a cable for around $10-$15.

I'm not sure if the 1227747 TunerPro RT screen shots below will be confusing or helpful.

I posted the TunerPro RT screen shots to show the "tuner" data available with TunerPro RT.

TunerPro RT is a very good "Scan Tool" also.

dave w

All this comes through the OBD1 connector? I'm in the process of specifying a laptop, I assume that the interface is through a USB? Is the software compatible with Windows 10?
The screenshots were helpful, thanks, but I will need to get up to speed on exactly how to read the data.
I see the values go from 15.2 to 18 then catch up and go back to 15.2 during WOT excursions.
Then go rich for awhile 10.0 when the throttle is rapidly closed. The value will eventually settle on a leaner 13.0 then back to 15.2 at the new cruise setting.
If I'm going down a hill the mixture goes ultra lean 28.0 looks like fuel is cut off till a load is reapplied. I'll assume that's computer lag? Does this look generally normal for this? The Narrow Band O2 sensor seems to cycle between .900VDC down to .400VDC does that look generally normal?
I realize these are just ballpark figures, but does the operation look "relatively" normal?
I fly aircraft so my mixture settings are not nearly that dynamic, or precise.

The tuner that I've been using got me this close, but his workload is such that he doesn't have time to do much more.
I plan to fake the Check Engine light circuit then run it through emissions and see what happens, it's passed emissions before with a standard CAT but I replaced it with a High Flow CAT, that's when the Check Engine light started coming on. I've been told that was a Coincidence?

Thanks Dave

Yes, TunerPro RT works with Windows 10. ALDL cables are USB connections to the Laptop. http://aldlcable.com/products/aldlobd1u.asp ALDL cables require a software "Driver" to be installed to work.

The 1227747 corrects fuel mixtures (rich / lean) using Block Learn Multiplier (BLM) and Integrator (Int). Possibly a Google Homework assignment (Search) would be helpful to learn more about BLM's & Int's?

BLM - long term fuel correction.

Int - short term fuel correction.

In a perfect world, BLM's (fuel mixtures from the injectors) will be 128. BLM's averaging from 123 - 133 are often considered acceptable.

BLM's above 128 means the fuel mixture is lean. BLM of 143 is leaner than a BLM of 133.

BLM's below 128 means the fuel mixture is rich. BLM of 113 is richer than a BLM of 123.

For the Do-It-Yourself "tuner", adjusting the 1227747 BLM's is usually accomplished using TunerPro RT data logs to determine where the BLM's are Rich / Lean. The BLM correction factor is Old BLM / 128.

Example Old BLM is 143 so ... 143 divided by 128 = 1.12 correction factor. The correction factor math means add 12% more fuel to achieve a BLM of 128.

It would interesting to know what your 454 BLM's are averaging! Agreed, OBD1 can be touchy to adjust BLM's.

dave w

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I see the values go from 15.2 to 18 then catch up and go back to 15.2 during WOT excursions.

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not normal. anything into WOT or power enrichment should almost immediately drop below 14:1. ideally below 13:1. you need more fuel and maybe a bit of fuel for tip-in too (there's acceleration enrichment parameters to replace 'pump shot' on a carb for that kind of stuff)

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Then go rich for awhile 10.0 when the throttle is rapidly closed. The value will eventually settle on a leaner 13.0 then back to 15.2 at the new cruise setting.

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when you drop off the throttle hard, you're going from no vacuum to extreme vacuum for a second, so odd fueling for a very short time is normal, also o2 measurements in this kind of situation can be whacked right out. you need to be more specific when you say 'eventually'. is eventually two records? twenty? one second? one tenth of a second?

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If I'm going down a hill the mixture goes ultra lean 28.0 looks like fuel is cut off till a load is reapplied. I'll assume that's computer lag

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yeah that's a good thing, it's DFCO (decelleration fuel cutoff). it's a mode that increases engine braking and fuel economy during engine braking that's hard enough. one thing sometimes you have to play with are the parameters related to transition between DFCO and normal running (if it 'jumps' or 'hesitates' when entering or leaving this mode). there's a lot of math and tuning done in the computer so it'll happen without the driver noticing

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Does this look generally normal for this? The Narrow Band O2 sensor seems to cycle between .900VDC down to .400VDC does that look generally normal?

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it should cycle between approx 900mv to approx 100mv. if it's not going lower than 400mv when cruising, something is wrong.

where are you measuring it from?

I realize these are just ballpark figures, but does the operation look "relatively" normal?
I fly aircraft so my mixture settings are not nearly that dynamic, or precise.

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The tuner that I've been using got me this close, but his workload is such that he doesn't have time to do much more.
I plan to fake the Check Engine light circuit then run it through emissions and see what happens, it's passed emissions before with a standard CAT but I replaced it with a High Flow CAT, that's when the Check Engine light started coming on. I've been told that was a Coincidence?

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yeah, probably, what's the error code that's causing the check engine light?

Hi Dave: Thanks for taking this time, sounds like there is hope for the OBD-1 system so I'll stick to this.

On the O2 sense voltage: the actual swings are more like 1.2VDC to 0.400VDC but with the new information I'll attempt to get a more accurate reading on the low side, I'll also get a better meter. Any chances that my chassis ground is floating somewhat due to possible oxidation? I don't have a good bonding measurement meter. The measurement is at the ECU connector.

The WOT figures have always been very lean almost like a delivery issue but I've verified this is not the problem. The Lean run must be programming, it's more pronounced during cold days. I'll get more exact figures.

I will get a better Closed Throttle enrichment timing numbers but from memory it was close to 5 seconds before it leveled out to leaner figures.

The Error code is (13) O2 Sensor missing or shorted. This has been a gradual process that began a year ago. Started as a once in awhile thing to now its every time I drive it.

Again thanks for your time

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Originally Posted by steveo

not normal. anything into WOT or power enrichment should almost immediately drop below 14:1. ideally below 13:1. you need more fuel and maybe a bit of fuel for tip-in too (there's acceleration enrichment parameters to replace 'pump shot' on a carb for that kind of stuff)



when you drop off the throttle hard, you're going from no vacuum to extreme vacuum for a second, so odd fueling for a very short time is normal, also o2 measurements in this kind of situation can be whacked right out. you need to be more specific when you say 'eventually'. is eventually two records? twenty? one second? one tenth of a second?



yeah that's a good thing, it's DFCO (decelleration fuel cutoff). it's a mode that increases engine braking and fuel economy during engine braking that's hard enough. one thing sometimes you have to play with are the parameters related to transition between DFCO and normal running (if it 'jumps' or 'hesitates' when entering or leaving this mode). there's a lot of math and tuning done in the computer so it'll happen without the driver noticing



it should cycle between approx 900mv to approx 100mv. if it's not going lower than 400mv when cruising, something is wrong.

where are you measuring it from?

I realize these are just ballpark figures, but does the operation look "relatively" normal?
I fly aircraft so my mixture settings are not nearly that dynamic, or precise.



yeah, probably, what's the error code that's causing the check engine light?

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The heavier GVW trucks with 350s and 454s have very prolonged power enrichment delays and very high throttle percentage required to enter PE. I have seen some as long as 60 seconds if the RPM does not ever reach the RPM threshold to bypass the delay. One of the motorhomes I tuned from GM had settings that required 99.5% TPS to enter PE and 60 seconds delay unless the engine was over 5,000 rpm. The rev limit fuel shut-off in that calibration was 4,600 rpm!

Good afternoon:

With some help in the right seat I came up with the following scenario:
Minimum voltage at the 02 Sensor measured at the ECU was 0.250VDC AFR 13.4 (This took a few minutes after initial start) where it initially settled at 0.500VDC before warming up and dropping to 0.250VDC.
Maximum voltage at the 02 Sensor measured at the ECU was 1.20VDC AFR 15.2
If I read you right this 0.250 VDC threshold is too high, possibly triggering the CEL?
(This looks abnormal)

Just off idle cruise 18.5 AFR (This may be normal)
Light cruise 13.8 AFR (This may be Abby normal) Looks a little rich
Med cruise 15.8 AFR (This may be normal)
High cruise 13.8 AFR (This may be normal)

WOT from standing stop normal transmission shift 13.8 AFR almost immediately. (I do have low gears and the acceleration is brisk)
(This may be normal)

WOT from cruise transmission shift down from 13.8 AFR to an initial 18.0 AFR then to 13.8 AFR was around 3 seconds. (This may be normal)

WOT from cruise lugging no downshift from 18.0 AFR to 13.8 AFR was around 6 seconds. (This may be normal)

Cruise to rapid Closed Throttle from 15.8 AFR to 10.0 AFR immediately, after 3 seconds it goes to 28.0 AFR.
(This may be normal)

Did I get the general idea correct?

Thanks

Here's what a generic AFR table looks like, to give you a rough idea of what AFR to aim for at various KPA and RPM points.

Thanks Kitch