Why would my truck run well in OPEN loop and have bad power in CLOSED loop?

The only thing I change to make it run in OPEN loop is the
MIN TEMP to CLOSED LOOP in $8D.

What (besides the obvious fuel corrections) affect this poor driveability and power?

Is my timing different when in closed vs. open loop? If so, what table (name - using Tunepro) is this in?

I see the BLMs change in CLOSED Loop taking fuel out to get to 14.7. I have tried changing the AFR to make it 14.0:1 and the computer does this in CLOSED loop, but it still has bad power and bad driveability (coffing and sputtering on AE).

It idles fine at 126 BLMs. Cruising at 1200 - 28000 BLMS go from 120 -> 138, depending on the RPMs.

 

Is the O2 sensor known to be good?.

 

Thanks for the reply.

I see it swinging AFR and MV in both open and closed loop using moates software.... else I don't know what else would tell me it is bad or good.

This means it is good, correct?

 

What else should I be looking at? EA? EA TPS? EA MAP? :hail:

 

Could my O2 sensor be too far downstream in the exhaust?

It is at the header collector right now. It is a 4 wire (presuming) heated O2.

Anybody?

 

OK, So I tried taking timing out at my 1200 - 1800 rpms. I took out about 3 degrees.

I also took out some fuel from my MAP at the higher MAP delta in AE. I only dropped a 0.01 point from 50 and 40 (I think).

Apparently this made the pinging WORSE! In both OPEN and CLOSED loop.

According to my O2 the truck is STILL RUNNING RICH though.

It keeps taking fuel out, and that's when it shakes and shutters (almost gives a lean pop in the intake) when in closed loop.

What's wrong? What else to look at?

I am SOOOOOoo lost.

 

Should be OK, there.

 

OK. Thank you.

So even though the computer is taking out fuel, should I add AE MAP.

If so, shuold I add AE delta MAP fuel at the lower 10, 20, or higher delta MAP values (40 and 50) for my hesitation at 1400 - 1800 rpms?

Or should I be looking at a different table entirely?

The DELTA TPS seems to have helped me a LOT with the intial pump shot, but now the problem is after I give it part throttle.

 

Are you sure that the ECM is taking fuel? what are the BLM's
If there is a leak in the exhaust stream? it will seriously skew readings and add lots of fuel.

 

I am only sure in open loop, (MIN OPEN LOOP TEMP = 255) the AFR from the NB O2 shows 13.3 - 14.3 from the ALDL using Moates software.

Then in closed loop (MIN OPEN LOOP TEMP = 100) is tightens it up to 14.7 and it coughs and sputters when I am trying to accelerate like normal driving from a stop light. It stutters when I give it throttle from cruising too.

Basically it "feels" VERY lean. It feels like it will POP through the intake from being so lean.

As far as I can tell, the exhaust is not leaking, but I am not sure. I have a NICE set of Doug Thorley TRI-Y's with a VERY thick flange, and I don't hear any exhaust noises on acceleration.

A leak in the exhaust would be seen by the computer as a lean condition then, and the computer would ADD fuel, not take it away, right?

 

*sigh*

Could it be my code is FUBAR'd? Time to start over (again)???

Could it be, somehow, I have enabled VSS, when I don't have it on the car? Would this cause my problems in closed loop?

 

The AFR you are seeing on the scanner is commanded, not read. In open loop the commanded AFR generally changes according to load and temperature. In closed loop the commanded AFR is 14.7 to keep the cat-con happy.

If not running a cat leave the ECM in open loop.

While in closed loop there are O2 window values that are used in the feedback loop. The ECM changes the fueling (INT/BLM) in order to keep the O2 sensor toggling about this window.

It may be that the O2 sensor is silicon poisoned or the O2 window terms are too low. A silicon poisoned O2 sensor reports rich forcing closed loop fueling lean.

As you are using a '730 and $8D for a TBI unit there are other issues. The biggest being that the injectors do not fire often enough for consistent fueling.

This in itself may be fooling the O2 sensor. I do know that cylinder to cylinder fuel distribution will be poor.

RBob.

 

Interesting, I didn't realize the O2 AFR is what the computer WANTS to see while it is in open loop. I thought that was what the computer SEES FROM the O2 sensor. Bummer, all this time, I thought I was doing good, especially, when I saw the AFR rich in open loop, and I leaned it, then the engine was "happier".

The problem with either my tuning, or running open loop, it is WAY too rich. I have blackened my oil, but not my spark plugs. I suspect my AFR is rich on cruise. Else, I am not sure what else the problem is so far.

My problem with going to 7747 is 1) wiring and 2) I have two 7730 computers just-in-case, one was to fail while I was on a trail.

Anyone want to trade a 7730 computer for a 7747 computer?

I haven't noticed a fueling problem with the 7730 computer in the last six years. I got this setup from Howell-efi. Two people I know just got the Howell-efi with TBI, and Howell is now shipping them with the 7747 computers.

I looked in TunerPro, I see I have VSS checked, but I did NOT have it checked in September.

Could this be my AE issues when in closed loop?

Thanks for the reply.

 

OK , now I'm confused unless I read wrong..
Are you lean or rich? first you are lean and last reply you said rich? What are your BLM's showing?
If you have a lean Pop though intake look at Lower RPM higher load areas before AE. Like if you get a pop off idle - look at VE areas from idle to say 1200 in the -70-80-90-100 KPA ranges
depending how much KPA you pull at idle. You want to be above that where you are at when you lose vacuum when go pedal is being kicked.

I would maybe first change O2 to be safe, then work from there.

 

KPA = 38 - 48 at idle.

Open Loop (this AFR info is from the '7730 ALDL
~14.5 AFR at idle
~13.8 in AE (rich correct?)
Not sure at cruise (I suspect very rich) I haven't logged it during cruise in open loop.

Closed Loop
14.7 at idle - BLMS are 126
I am presuming it goes lean on AE in closed loop, I get couphing and sputtering on acceleration. I see BLMS going from 120 - 140 depending on RPMs and how far I press the throttle.
PE is set for 70% I am not even going to try to tune PE as I don't have a wideband.

Anyone know which years and models have a 4 wire O2?

KNowing that RBOB saying is correct for open loop, "The AFR you are seeing on the scanner is commanded, not read." then I am going in the wrong direction when I am running OPEN LOOP.


This is hard for me to understand, as in OPEN loop, my AFRs where shown as 15.2 + (lean) when I hit AE, then I added more TPS DELTA increments (richen it up), and then I got MUCH better response and the AFRS in open loop started showing 14.0 and it is a much better feeling engine (more power) on AE.

Thanks for listening to my TBI on a '7730 woes.

BTW: What am I missing because these are not P&H injectors? Is it simply upper RPMS and WOT? Or does the '7730 us P&H on AE too?

 

Ok First, Rbob is correct but you are still not really seeing why..
The AFR that you are seeing displayed is what the ECM is trying to obtain and will not change. - its not by any means what the actual AFR is.


Ok , It very well may go lean during AE, but you also have to understand that during AE like off idle you are hitting area of the VE that are only touched on for a second.. So Richening some AE functions may very well get rid of you sputtering but may only mask the problem.. which is VE need scaled correctly in high Load/Low RPM ranges.
For instance if KPA is 42 at idle 800rpm , when you touch the gas, you will jump into the 60-70 KPA range of 800 RPM column, but only for a brief second and never get a BLM reading to tell you where you should be.. But if you idle Value (800RPM/42KPA) is just say 32% VE, then you know that every value in the 800 RPM column as KPA increases need to be higher numerically the the previous lower. look at the first, if they are not scaling up, then there is a big problem.
The reason you are probably only seeing this when closed loop may be that INJ. constants are wrong as to what is really being flowed. Or maybe because the open loop function to run richer - like the "Open loop F/A ratio % change vs. coolant and MAP tables" which richen mixture during open loop function..

I am just trying to help you understand alot of this, if you increased AE and problem got better, than you are right that you were going lean.. But it may be because VE table is not scaled correctly.. Like when you touch the gas and hit these High kpa Low RPM areas, you may be lean because VE Table value is to low not allowing enough fuel but can be masked by added xtra AE to compensate.
You may try holding foot on brake and toughing gas to raise KPA with out raising RPM much and see what BLMS look like after a few seconds in those areas.

Not off hand - Do a quick search.

 

Thank you for your reply. I really do appreciate it.

I did quite a bit of VE table changes in closed loop when I first got the BBC in there.

My low RPM (<2500) VE tables seem to be pretty good (BLM 128 +/- 6), but I have NOT tried changing the upper KPA on these. Basically, I followed (or at least I thought I did) the stickies above to get my BLMs in line. When I got these lower RPM VEs, and KPAs, basically I scaled them to follow the curve of the upper VEs.

In other words, I took quite a bit of points out of the lower RPM VEs and as such, I took out an equally PERCENTAGE of points out of the VEs of the upper RPMs and KPAs to have a similiarly smooth curve(s) in the upper VEs as it had before.

Basically, the VE curves all got scaled down about 15 or 20% from a stock AXCN bin.

I have been moving away from my Howell Bin (was for a 383) and started modifying an AXCN bin.

Questions
So if the computer is trying to command a 14.7 AFR, but it doesn't really know if the O2 is getting 14.7 AFR why am I pursuing VE tables at all?

 

Because the VE is the first thing that the ECM uses as fuel measurement device and makes changes/corrections from there to try and maintain what it thinks is 14.7:1 - and you are right, if you 02 is indeed bad that you are just chasing you tail. But I am guessing that its not.
Also, If upper KPA is not correct as I assume they are not, the ecm never really gets a chance to make a correction to those areas.. because you hit them so quickly and are already out of those areas before the 02 ever forms an opinion on them.

Understand now? When you hit the gas, the first thing you ECM does is reference the higher load areas along with AE. then correction starts after ECM has established a BL for that cell.

Is there a healthy cam in this 402?
If so your Upper kpa ranges are probably way off.
also I see you are using a throttlebody on a victor EFI type intake? From what I hear these take alot of AE to be happy.

 

OK, thanks again.

I understand WHY the VEs should be there, and how they effect other settings. I also understand what you mean about the upper KPAs for my VE and how

I guess, what I did't understand before, was the reading in MOATES software shows 14.7 AFR. I thought this was coming FROM the computer in closed loop because that is what the computer is creating (adding or removing BLMs), not commanding. If this is the case, why would the comptuer COMMAND 14.0 AFR in open loop? even though the BLMs don't change?
I read 14.0 AFR on AE in open loop and it doesn't make sense. It still seems to me, the AFR is not being commanded, it is what the computer is interpreting from the O2 swings in OPEN LOOP.

I have a Crane 266 cam (it's .210/.210). I have an Edelbrock intake dual-plane. The engine is smooth, powerful and driveable above 2500 rpms, but below 2500 rpms it sputters and coughs. Every once-in a while, not sure if't at a certain temp or what, but I have GOBS of torque and driveability down low, I would be happy if I could get 75% of that power consistently in the under 2500 rpm ranges most of the time.

1) What all this boils down to is, I need to redo my VEs - correct?
2) I should re-do VEs in CLOSED LOOP, and I use the BLMs on the readings of the ECM - correct?
3) I need to artificially induce upper KPAs with the brake - correct?
3 - a) Shall I do this in different gears? Will it matter?

Thanks again.

nhromyak@comcast.net might be easier if you're willing.
Heck, I will call you if you're willing, PM me your number. I'll buy you a paypal beer!

Should I post my BIN?

:hail: