I'm running a 670 TB with 80#/hr injectors on a 355" engine (heads and cam). My problem relates to getting my motor dialed in at WOT. I burn my own chips using TC.

When spinning more than 3600rpm I get really good performance in PE mode at 80-85% TPS, however any more throttle and the engine lays over. I have moved my WOT AFR values up and down and maximized spark advance (32* + 4*PE adder at 90-100kPa). Data during this transition shows O2 counts stabile at lower throttle angle (approx 930) when I mat the pedal O2 starts to oscillate (800-950).

Has anyone experienced a similar effect and how did you deal with it?

 

O2 counts OR O2 Voltage? Cross-counts are the number of times the O2 sensor oscillates through stoichiometry and cannot be as high as you sate, maybe 50 or less. IF your numbers a Volts (millivolts), you are running rich and need to lean out SLOWLY over a few chips until you see some lower voltage numbers. Unless you have a pretty modded 350, you will not need 80lb injectors, or the 2" TBI,m for that matter.

Tell us/me whatcha running and we'll go from there.

 

Not to be curt, but I didn't ask what you thought of my motor and parts choices. All my parts are just fine running together.

Yes I am referring to O2 mV as is indicated by the values given. Counts is a generic term for any sensor data type. No my motor is not running rich. For a cam profile like I am running, +900 mV is necessary for maximum power at WOT.

I am very interested in any feedback regarding someone who has actually experienced a similar problem.

 

[QUOTE]Originally posted by Ramsey:
[B]I'm running a 670 TB with 80#/hr injectors on a 355" engine (heads and cam). My problem relates to getting my motor dialed in at WOT. I burn my own chips using TC.

When spinning more than 3600rpm I get really good performance in PE mode at 80-85% TPS, however any more throttle and the engine lays over. I have moved my WOT AFR values up and down and maximized spark advance (32* + 4*PE adder at 90-100kPa). Data during this transition shows O2 counts stabile at lower throttle angle (approx 930) when I mat the pedal O2 starts to oscillate (800-950).

Has anyone experienced a similar effect and how did you deal with it?

Sounds like you way too rich, IMO
with the vette AL heads I ran 28-30d total advance. This was with a 747 ecm though, dunno how different yours is. Some one over mentioned there is a subroute that does something weird if the EST test fails as you go WOT. Is your EST working?

 

Ramsey, I'm helping a friend tune his truck and we're encountering a similar situation. His setup is a 350, iron heads (ported, extrude honed, 2.02/1.60 valves), 9.5:1 compression, mild cam, dual-plane intake, and a Holley 670 TBI unit (with Holley injectors).

The problem he's having is that the engine lays over at about 4800rpm. Above that RPM, te O2 sensor's output begins to drop (like 600mV). (Note: I HATE using a stock O2 sensor as a WOT tuning tool, cause it just wasn't made to work like that.)

He keeps insisting that the engine is leaning out and can't get enough fuel. In an effort to fix that, I made a patch to the '747 code to extend the WOT A/F ratio table all the way to 6400rpm. We then richened the mixture above 4800rpm significantly. Result: no change.

Personally, I think that the engine is too RICH up top, causing the exhaust gasses to cool, which in turn cools the O2 sensor (giving the low readings). Of course, he won't try leaning it out, cause it just HAS to be lean right now. Argh!!!!!

IMO, your symptoms also indicate that your setup is too rich up top.

Nick

 

Incidentally I'm running a 16197427 and it is on a truck with a motor very much like Nick's friend. In case you are unfamiliar, the code in this box goes to 6400rpm.

Being rich is what I initially felt was the problem also (similar effect on my jetski at on point). I have tried setting the afr higher in the WOT afr table, but started to chicken out when I was going over 13.1:1 (from 12.5:1) without any significant improvement.

Grumpy: before I started dealing with this part of my tuning my timing at high load at those rpm's was set to 28* total advance. I'll dial it back based on your experience, no need to ride the ragged edge anyway. I have no codes set regarding EST and I do experience knock retard. Anything else I should test for regarding the EST function?

NickG: Please let me know if you convince your friend to try going leaner, especially if it works. I suppose I will go back that direction myself.

Thanks for the advice.

 

I'm running a 670 TB with 80#/hr injectors on a 355" engine (heads and cam). My problem relates to getting my motor dialed in at WOT. I burn my own chips using TC.
When spinning more than 3600rpm I get really good performance in PE mode at 80-85% TPS, however any more throttle and the engine lays over. I have moved my WOT AFR values up and down and maximized spark advance (32* + 4*PE adder at 90-100kPa). Data during this transition shows O2 counts stabile at lower throttle angle (approx 930) when I mat the pedal O2 starts to oscillate (800-950).
Has anyone experienced a similar effect and how did you deal with it?

Once you start letting an engine breath that parts must match, 670 TB on a stock manifold just lets you hit the max amount the manifold will flow at lower rpm. Real easy to have a mismatch of parts.
On my cross fire project was just a matter of changing the runer lenghts, and building plenum spacer.
Also, the exhuast can become a limit.
You should from the sound of things have the TB and injectors to run decent.
Maybe running out of fuel pump?.

 

Grumpy: I'm flowing from the 670cfm TB through a 1.5" spacer/adapter combo to an Ed. Perf. that I port matched to my ported/polished, modified chamber Torquers with 2.02/1.6 valves and 56cc chambers (stat comp is around 9.7:1). The bottom end is a .030" over 5.7L block filled with hyper. pistons on older model (stoughter) rods hung on a .010 under 350 crank and an Ultradyne cam (@ .050: 211/221, total: 266/276 duration and .473 lift, installed straight up). The exhaust ports run to Thorly tri-y's (1 5/8" primaries) that are collected by a full 3" Borla exhaust. Fuel pump is the bigger pump spec'd by Turbo City (25-30 psi at a healthy flowrate) that pushes a regulated 15psi to my 80#/hr injectors that have been tested and flow-matched. Spark is by an MSD 6 box and coil with big Accel wires. Drivetrain is a 4L60E with TransGo shift kit that spins a 3.90:1 rear-end with 30" o.d. tires. All this stuff is bolted to a '94 Chevy C1500 ext cab. I hope no one mines me utilizing this f-body site, but I check in due to the occasionally useful discussion of TBI and its related programming.

I feel fairly confident that mechanically my setup is sound and well-matched flow-wise. I leaned out my afr yesterday with the result of the same full throttle decline in power and an overall loss in power from a lack of fuel. On the off chance that it might help I dialed in my TPS to avoid pegging the potientiometer before the throttle blades are fully open-no help though.

Could my problem extend from main fuel table settings. Are they used to calculate p.w. in combination with the WOT afr table? My v.e. settings are at 100% from 80kPa and up when over 3200rpm.

Sorry for the long post, but while I have your attention... I am also having a very difficult time getting my startup routine dialed in. The engine starts up okay, but until it is warm (>100*F at CTS) the thing will stall out if you give it any more than the faintest bit of throttle. I have decreased the afr in open loop at the higher load areas of the table, unsuccessfuly. However, the problem emulates the effect of an overly small (or non-existent) pump shot. Any suggestions for this issue would also be greatly appreciated.

[This message has been edited by Ramsey (edited November 05, 2000).]

[This message has been edited by Ramsey (edited November 05, 2000).]

 

I stopped using the stock 02 for anything other than it was originally intended months and months ago, its useless, especially with the symptoms you described which is the o2 oscillating between what are supposed to be "decent" values. Put down the scan tool, and just do some plug cuts. I would have never gotten mine running past 4000 rpm if i woulda kept looking at the stock 02 sensor. I had the same problem as you, and I thought it was leaning out. The first thing i did that was a step in the right direction was swap to some smaller injectors that I knew worked. I had previously been trying to richen everything up which of course did nothing but make it worse. Instantly, with the new injectors, though it wasnt perfect by any means, the car pulled very strongly in spurts in the rpm range that had given me so much grief. I cant tell you whether it was because the injectors were smaller or because the old ones were defective (i raised the pressure on the smaller ones to where they 'should have' flowed about the same as the larger ones as it turned out it was a bit less)
Regardless, that o2 behavior is very familiar to me and my suggestion to you is to just stop paying attention to it, find a long empty road ,bring a leather glove and a spark plug socket and ratchet and just start pulling plugs (make sure they are relatively new plugs and not 'stained')
I would also bring the ve values to just under 100% seeing as how the ecm will clip them down to 100 anyways, who knows what wackyness is going on in that box when the ecm sees that everything is up at 100%. I personally would just emulate the values that are looked up where it runs good at 85% tps (im guessing a little bit of vacuum) and go from there. BTW im running a 305, ported h.o. heads, 214/224, torker II, holley 2" and am using the stock 305 tbi injectors at 19 psi. So I think you are rich.


". I am also having a very difficult time getting my startup
routine dialed in. The engine starts up okay, but until it is warm (>100*F at CTS) the thing will stall out if you give
it any more than the faintest bit of throttle. I have decreased the afr in open loop at the higher load areas of the
table, unsuccessfuly. However, the problem emulates the effect of an overly small (or non-existent) pump shot.
Any suggestions for this issue would also be greatly appreciated."

check out your plugs when it does it, the 7747 (dunno about yours ) has a table for map afr adder in open loop that might be of some use to you in this area. I wouldnt be surprised if it was infact too much pump shot drowning out your motor though, the plug will look wet if this is happening (which I think it is)


Pablo



[This message has been edited by Pablo (edited November 06, 2000).]

 

"Could my problem extend from main fuel table settings. Are they used to calculate p.w. in combination
with the WOT afr table? My v.e. settings are at 100% from 80kPa and up when over 3200rpm. "


yes they are, your WOT afr table is merely calculated AFR from your ve table #2 above 3200 which is always added to the last cell in the kpa column you would currently be in, so say you are at 4000 rpm and at 90 kpa, you would have 4000 rpm in ve#2 add to 90 kpa at 3200 rpm. The sum of both tables is what your WOT AFR is calculated from. The ecm assumes that that sum is 14.7:1 and adds fuel accordingly to end up with whatever fuel ratio youve chosen in your WOT AFR table.

Id say its highly likely that you are very rich. Both your WOT problem and your pump shot problem are the result of this


[This message has been edited by Pablo (edited November 06, 2000).]

 

Pablo: you're right, I have gotten to the point that plug cuts are necessary. I relied on the scan tool (with great success) so long to get all my part throttle stuff dialed in that it has not occurred to me to fall back on more traditional indicators of engine state to finish up my tuning.

I'm going to back off my ve for cells in the 100kPa range. It didn't occur to me that ve might peak at a given point and then decrease for my engine within the range of the main fuel table. I have always assumed that I would have no local max values that weren't at the periphery of my fuel table (concave up for the whole range). When I was running the 65#/hr injectors, they were operating so near their limit that I had to have even more of the upper cells loaded with 99.6% to get enough fuel.

Re startup: I'm running a later model box (7427/$0D) and I have two pump shot tables... diff map and diff tps. I am curious if they interact in the same manner during open loop as they do for closed? I have pulled some diff tps pump shot out to begin with.

 

from experience, ive noticed the hotter a motor is the more it can "mask" fuel problems, especially if its on the rich side. I have put way too much pump shot before on accident and I too could stall out the motor when it was cold but would run ok when hot.
Im not saying this is for sure the case with your engine, but , something to consider. You will see a real rich pump shot on the plug when it stalls EASY it will be soaked with fuel.

As for the max VE% figures, remember that your ve% is highest at peak torque, for example youll notice stock bins have the most fuel down low like around 2500 rpm which is where most of these motors experienced peak torque. Course as with all things there are no absolutes but in general.

Good luck, i know how you feel, ive been there

Pablo

 

Tell ya how accurate stock type O2 are.
Was able to make a good hard pass using data logging, and the O2 went to 0v, 0.
Granted this was on a turbo 6, but still the sensor was the right one, and less then a month old.

Yes, plug cuts.
Yes, some way of gauging performance is mandatory to tell if you going in the right direction. Got to be able to go back to back in testing.
Just because a table stops at 4800 doesn't mean that the engine forgets what to do it just maintains that AFR till usually 6,300 rpm.
With you combo, sounds like breathing shouldn't be an issue.
Don't be afraid of 80 in the 100 K/Pa areas. while 100s look good the engine might not actually like that much fuel.

 

Keep running 900mv O2 count and you'll be buying new rings in a year or two... adoy

 

Fastbroker: First, what's adoy?, second, I would be interested in the data you have that relates piston ring degradation and a WOT, O2 sensor reading of 900mV. If you are referring to the effect of a rich running condition that washes down the cylinder walls I agree if a motor ran rich all the time you would eventually see some premature ring wear. Fortunately, my engine typically runs just on the rich side of a stoichiometric mixture due to the accuracy of my part throttle settings in my main fuel table and the self-correcting features of the block learn system in my engine management software. From what I have seen personally, most ring wear is incurred through poor lubrication and lean running engine conditions.

Additionally, AFAIK 900mV does not necessarily have a specific and repeatable relationship with a particular AFR (ergo the need for other performance indicators, like plug cuts and acceleration tests). It seems that 900mV on one engine is not necessarily the same thing on another engine with another sensor due to various differences between the individual sensors themselves and in sensor placement (and the resulting temperature variances of the device). I base this statement on available anecdotal evidence and documented unsuccessful attempts to calibrate stock-type O2 sensors to a standard wide-band O2 sensor that does demonstrate accuracy and repeatability.

And in agreement with Grumpy re stock O2 sensors: Personally I work as an engineer designing pressure transducers using silicon strain gauge and quartz resonance technology. Even with the best and most expensive of these sensors one must perform rigorous characterization processes to get any type of precision and stability; I assume the O2 sensor technology in our vehicles is substantially less reliable due to a lack of device specific characterization that accounts for differences in tc and other factors I am not aware of. The fact that most late model O2 sensors employ a heating circuit (much like the older quartz bourdon tube technology) in order to limit their temp range shows that they most likely display poor linearity and temperature hysteresis in their response to O2 concentration at anything other than their designed temp range. I think the point that NickG raised regarding going so rich that the unburned fuel actually cools the exhaust sufficiently to ruin the response of the O2 sensor is very telling regarding these sensor performance issues.

Apart from that, after working with Ed Wright on dialing in a previous .bin for my engine he clearly indicated to me that at WOT for best performance (on a TBI motor) one should see a range of O2 sensor output from 860-930mV (a broad range he attributed to sensor differences). Additionally, from a bit of testing at the dragstrip and seat of the pants (yikes!) judgement I will stick with my claim that for my engine, best performance at WOT typically shows O2 counts over 900.

Of course, this raises the issue that FastBroker mentions: is increasing the performance of my engine actually hurting it? I don't really think so, I have monitored a buddy's totally stock TBI motor and it tended towards 900 counts at WOT also. It is unlikely GM designed this durability limit into their system.

Oh, I am ratcheting down my ve in the low vacuum cells of my fuel table with some success. And Pablo, pump shot decrease has helped cold start throttle tip-in, thanks.

[This message has been edited by Ramsey (edited November 07, 2000).]

 

No fight intended, but I stay on the lighter side (860-900, the lower side of your stated range) unless dyno/track testing tells me otherwise, which it RARELY does. IT's all love, man. I was referring to cylinder wash. I have just seen people running PE mode at lower rpms and then putting O2 counts too high which is bad long-term, as I think you would agree. also, even new O2 sensors can be "off" by quite a bit (as I found out this weekend) and just push you to too rich a situation. But, on your side, they could also be lean, too.


If you/anyone keeps OEM PE range on the PROM and/or does not get into PE a lot, stoichiometry (closed-loop operation) most of the time would obviously make this a non-issue. Sorry for the angst. Have fun!

 

I just bought my second O2 in like 30 days, for this one experiment, I got going.
Both, absolutely take a total crap compared to the wide band, period end of conversation. They are just switches, the cross .44 as they go from rich to lean.
I've tried 1 wire 3 wire 4 wire, and all of them are just nonsense. While you might note where you get best performance at with your car to say that someone else should tune to a specific voltage is just wrong. Period. Ya I know folks try to and lots of folks blow head gaskets, and eat exhuast valves, and stuff.
I've seen data logging from the chevy race shop, and done my own research on this, I make no money from anything I say or do with EFI on any of the lists so there is no reason for me to lie about it.

 

Interesting stuff, testiness aside. So then, Grumpy, are you recommending the WOT/cut method that Pablo spoke of earlier?

In all the 1/4 mile carburated BB Chevy drag engines I've built I've always relied on clean cut to determine jetting along with track MPH readings.

I've been getting mixed recommendations on TPI setups though and have begun to worry because my 415 was only pulling 700mv WOT readings using Diacom.

I really appreciate this exchange although I didn't quite follow the O2 sensor info. Are you referring to heated O2 sensors vs unheated? It is my understanding that the heated sensors only allow the engine to achieve and maintain minimum activation temps sooner. BTW, I'd always read that 600 degrees F was the threshold, but I read recently that 400 F is the point.

I've been considering a wide band sensor for the 434 TPI I'm in the process of building for a friend (see http://www.CorvetteForum.com "434 CID Build Up" and "434 Build Up Part II"), but if you're saying they're junk buying one may not be worth the expense. Of course we'll be using a computer system that can use wide band info.

I'd like any further info you may have of that.

Thanks for the dialog.

Jake -Not to be confused with my namesake.