I just completed a complete engine swap to a 1988 TBI-7.4L from a TBI-5.7L in my 1989 K1500 truck. The computer (ECU-1227747), sensors and the 7.4L TBI were also swapped. I did leave off the smog pump for now. My question is the engine seems to be running great except at idle. The A/F mixer gauge show the engine is running rich only while idling. I also noticed after starting the engine (operating @ 185’f) the idle is fine 750-RPM but after driving around for a while the idle RPM is sticking around 950 RPM while in park and still running rich. Then I shut-off the engine, restart, wait for the rpm to stabilize the RPM goes back to 750-RPM and is still running rich.
I have a digital Air/Fuel gauge (electrically buffered) to the ECU-O2 Sensor output. So I'm reading what the ECU is seeing, rich! Can the ECU be operating in “Open Loop Mode for some reason at idle? I have no exhaust leak to fool the O2 sensor. Remember my gauge is displaying what the ECU is seeing. I do have a lap top computer with WinALDL but not sure what I'm looking for. I need your help!


Thanks
Byron T.

 

Check for vac leaks.

Do you have the CTS hooked up?

 

CTS Coolant Temp Sensor yes I do.
Thanks

 

Byron

That may be a source of problems. You must make sure that O2 ground reference pin D6 is connected to Air-Fuel gauge ground reference.

In WindALDL O2 voltages should transit from about 50 mv to about 850 mV when in closed loop. In open loop your NBO voltage will be near constant value. When Rich it will be above 450 mV and lean below. One of the reason for open loop is a faulty CTS - verify in WinALDL that CTS reads back realistic temperature. ECM uses CTS and run time before it enters close loop operation.

//RF

 

Thanks Rf for the reply. I'm going to ask some dumb questions.

RF writes...
In WinALDL O2 voltages should transit from about 50 mv to about 850 mV when in closed loop.

Question: Afterward with all condition are meet (ECT/time etc.) then the ECU will start adjusting the fuel/air to trying to get the O2 sensor moving across the 0.45 volt rich/lean switch point for optimum fuel efficiency and emissions. I'm I correct?

What the heck is NBO stand for. I don't see this anywere in WinALDL. I believe it's something about the O2 sensor output or is this output parameter. Please help me here...


As for grounding... Very good point.
Thanks for the tip.
Byron

 

Narrow Band Oxygen sensor....

 

Byron

Welcome to TGO

Yes, when ECM operates in closed loop it varies injected PW while observing NBO readings. So basicly it is constantly adjusts fuel mixture back and forth between rich and lean. Typical C3 ECM ('7747) takes about 1 second to complete the rich lean cycle.
In open loop ECM uses a fixed PW base line and NBO readings will be more less constant.

//RF

 

Thanks again for the reply RF.
I've been driving the truck to work and I love the extra power, the down side is I'm now a OPEC member, 10 Mile per gallon. The reason for the engine swap is for towing my toy trailer. Yes, if I had a bunch of money I would just go out and spend 60K on a new diesel truck, but I'm also a gear head. I bet after I check out some of the recommendations from the group I'm going to get into the tuning phase to correct this rich idle problem. I have about 8 months before I go in front of the smog policy. I start doing my home work searching the archive in how to start in a logical order or method in tuning so I'm not running (tuning) in circles. Maybe the group knows of some good reading material (links) for beginners. Thanks again. Stay tuning for more posting.
Byron

 

Top of the page:

https://www.thirdgen.org/forums/tbi/...free-tune.html

 

Just a FYI, some TBI calibrations called for open loop at idle. Which might be what you are seeing on your guage. Also don't take much stock in the guage, it's simply stating that you are richer or leaner than 14.7....it won't tell you how far off you are even though there are several LED's to either side of stoic.

Best bet is to get into tuning, it'll really unlock a LOT of the mystery behind FI.

 

I do know about the problem with tuning with NBO. Reading a NBO you are not really sure were the engine is running, way rich to maybe way too lean or somewhere between. I been looking at the LM-1: Digital Air/Fuel Ratio Meter kits to help me in getting the job right and making my tuning experience more of a pleasure. Reading about the LM-1 product make you think this is the way to go. Any comments?
Byron

 

I personally like the zietronix setup, but the LM1 is also a very good system. You really don't "need" a digital display, as you log the WB data thorugh your laptop to view later. Trying to pay attention to a guage while you drive is pretty much useless and dangerous at that. Plus a lot of what you are trying to see happens so fast you can't even see it on a guage, you need to look back over the data after you've made a run.

A WB is the second tool you should buy after you get your tuning equipment.

 

I'm wondering if there is way to program or switch the ECM to Close Loop mode at idle if the ECM is now is operating in Open Loop mode at idle as other have replied?

Also, I'm wondering if the ECM will work with a WB sensor? Or do I need to have two O2 sensors. One NBO for the ECM and WBO for logging?

I haven't had the time but I'm wondering if I put back in my old 5.7L 747-ECM which did operated in Close Loop at idle would be the better ECM for tuning?

comments?

 

Not for sure about the 88 models, but I do know the 90 model 454 with the '8747 ecm does idle open loop.

If you get into burning your own chips for it, you can idle open loop, and all will be well.

Even after I swapped to the EBL (which is something else you may look at), I still have mine idling open loop. With the cam I have, it just does not like idling that lean (14.7), and would tend to jump around. Best idle is around 12.8-13.2 or so, depending on temp.

With the EBL Flash, that would be all you would need to buy, as you already have a laptop. Otherwise your looking at a programmer, UV eraser, or adapters, So...

 

Do not even bother with programmer, UV eraser, and adapters. I went through that stuff (did learn a lot) but after looking at EBL flash and now using it since August I would never even consider discrete solution (programmer, Flash chips, emulator, etc). What really made a believer is the ability of EBL system to log enormous amount of data real time with lap top for later analysis. An EBL data log gets a complete set of engine operating parameters approximately 15 to 20 times per second. You are lucky to get 1 set (incomplete mind you) from a stock 7747 per second thorough 160 baud ALDL.
The heads up display program gives you real time (useful) operating parameters. For bin file modification TunerPro xdf is provided. I am still learning what all of the additional parameters do! Also, EBL conversion comes with analog inputs which can take WBO output and mesh it into data log or use it for VE learns.
EBL is not cheap, but the ease, convenience and simplicity makes it by far superior solution. Now, I know I am going to get kicked for say so by the folks that use later PCMs. Since I have never used PCM (P4) they may have a better position to an opinion which is ultimetly better of the two.

//RF

 

Hi Byron.
My 7.5L went in my truck about 10 years ago, along with a 7747 ECM, so I got an idea where you're coming from. Yours is a 7.4, so there will be much more info and experience available to you than there was for me.
Yeah, mine idled so rich that small children and animals expired on the sidewalk. Yeah, the 7747 I started with was programmed for open loop idle below about 800 RPM, if memory serves, and absurdly rich for the big block. ( as was most of the fuel map )
Changed that to 400 ( truck idles about 550 ) which put it in a closed loop idle, so that even with the O2 cooling off at idle, it was so much better you could actually breath within 50 feet, and it stopped dripping raw gas out the tail pipe. Originally, it ran with the chip from the 5.7L, but at about 6 MPG and performed poorly. Now, the MPG is on-par with the old 5.7 in the low teens, and I'm not done. ( I am a little slow ) For performance, there is no comparison.
When I started this project, there was no info available on rolling your own. Now, there is considerable info, and experience, and nowhere is there more than here on ThirdGen in the DIY-PROM forum.
There isn't supposed to be ads for product, but if the moderator lets this by I can't recommend the EBL-Flash highly enough !! In my opinion, it's under-priced pretty severely.
Yeah, I got a stock of chips, two burners, and engineered an EEPROM replacement for the 2732 that the 7747 uses. Since I've been there, done that, let me advise you to not bother, except for possibly as an academic excercise. Just buy an EBL-Flash, and don't look back.
You'll still need to do your own programming, but it's the easiest way to a really good system that I know about, and trust me, I searched long and hard.
Just my 2 cents.
Oh, and the stock narrow band showing "rich" just means 14.6 or richer. It doesn't necessarily mean "rich" in itself. They are useless for anything but showing 14.64 and richer as "rich" or 14.71 and leaner as "lean." Between 14.65 aqnd 14.7 they're not terrible, but you almost never run there.

 

WOW....!
I have performed some tuning years ago, and I do remember going though the process of Collecting Data/Modifying the Bin File/Removing the IC/Burning and re-inserting the IC, over and over again. This new tool will make it a pleasure in tuning compared to the way I been updating the IC-BIN file. I did read though all the information on their web site and have some questions. I know I’m getting off-topic here, but I didn’t fine any place on the ELB site to post them too. So here I go… I’m I correct in saying you can still use the stock O2-NBO but you can also add an O2-WBO to one of it input. How about using an O2-WBO be used in placement of the stock NBO O2-sensor, will this work? The “Malfunction Code” display has three green boxes for displaying malfunctions codes. My question is why are three green boxes? And here is the big one. The Volumetric Efficiency Lean Table, the information says: VE Learn Function will create a new BIN file ready to be used. My question is, don’t you need to use a program like TunerPro for modifying the BIN file? Am I missing something here? Live could not be that good.
Again thanks for this info.
Byron

 

Byron

1) EBL equipped ECM can use either WBO or NBO to run close loop. I run NBO during normal operation and use WBO for dialling in PE performance, throttle tip-in under various operating condition, WOT A/F and highway lean cruise mode.

2) Heads up display program collects enough BLM data and create an updated BIN file based on a test drive observed VE behaviour. The only parameters modified are VE tables. You can still modify this new file with TP, for example, to smooth out certain areas that were not observed during test drive. After initial fire up my BLM's were 116 to 118 range and after about 14 test drives observed BLM's are 128 +/- 3. I still have some area of knock which remains a bit of a research project for me. With lean cruise and TC disabled I was able to attain 13/18 MPG in 6500 GVWR '75 C20.

3) I am not sure about the green boxes - I have to take a look at it on my diagnostic lap-top.

//RF

 

bobr@dynamicefi.com should get all your questions answered.

Yes, or both at the same time. Choices are nice.

Geeze ! I'd have to look that one up, but it goes something like this.
Occured once, but went away. Coulda shoulda set an error, but didn't.
Occured, and stayed a while.
Actually set an error code. ( flash the SES light )

That's probably wrong, but it's along those lines.

Bob wrote into the program ( the laptop part, not the ECM ) (( he wrote both parts, but the ECM part doesn't do the Learn thing on its own. That's the laptop part )) a routine that will automagicly learn from what the old bin was, to what a new bin should be, either based on BLM or on ( preferred ) on your wide band, create and save a new bin file. Something like aldltobin.exe of old, but much, MUCH better !

Yes, you still need TunerPro ( EBL comes with an xdf file ) for changing anything other than VE tables, which it does NOT do automagicly.

There's a whole "Tuning with EBL" thread somewhere here on ThirdGen.
Go there for real world experiences with it.
Note that *I* think it's under-priced, but that's me.
It's also available with drivers to drive injectors for dual TBI, or TPI, stuff like that.

And a personal endorsement of the guy who makes 'em.
This guy goes WAY above and beyond. You won't get better support for anything anywhere.

 

I just want to drop you guys a note. Thanks for getting me up to speed with this effort and steering me in the correct direction. Much appreciated! You guys have been a great help and I can't say enough for your help. This is one of best group I have posted to compared to others. Thanks again and Happy Holidays.
Byron T.