I have read all I can on what affects WOT actual AFR . I have made a lot of changes in table 1 and AFR vs RPM in PE but am still having a problem with very rich condition between 1500 and 3500rpm. One of the tests I do for WOT is to start in 1st gear @1500 rpm and then go to WOT up to 5,000 rpm. (my engine is gettin tired of this)
But the graph shows when I hit the throttle @1500rpm, there is a very brief spike up to about 16AFR, then a steep drop to 10.6 AFR
which climbs to 12.5AFR at about 3500rpm and stays pretty steady to 5,000 rpm. So I am runing very rich from 1500 to 3500 rpm in this test.

I reduced my AE vs TPS thinking maybe I was getting too much pump shot but even taking out drastic amounts doesn't seem to help.
The acceleration feels smooth but I wonder if running this rich from 1500 to 3500
isnt hurting performance.

If I start at 2500rpm in 2nd the AFR stays consistent in the 12.5 range to 5,000rpm.

If I start at 3000 rpm in 3rd the AFR stays consistent in the 13.0 range to 5000rpm

My questions are:

How should I be testing actuall AFR at WOT? Based on the above
it changes depending on where I run WOT.

In the 1500 to 5000rpm test, what tables do I need to be looking at to get rid of the rich condition between 1500 and 3500 RPM?

I am embarrassed to tell you guys how many chips I have burned trying to get consistent 12.5 actual AFR's at WOT under various WOT conditions.

Hope this makes sense. I would be glad to send a graph if someone would care to take a look..
thanks very much for any help.................... Totally stumped bob

 

Are you using the LM1 to data log? I ask because the 8746 ALDL is too slow for this.

Check the WOT AFR vs RPM table. Many of the '8746 bins have the commanded AFR very rich. This is done to douse the cat and prevent it from melting. If a cat isn't a problem then change that table to something reasonable (12.5:1). Then try again.

With the WOT AFR table at 12.5 I would then make changes to the VE table in order to get that AFR.

RBob.

 

What's the stop watch say?.
The Buttometer is a poor timer. Unless your actually measuring performance you might be going the wrong way. That's what happpens when you worry about tuning to a number rather then tuning for performance without using any indicators.

I'll bet your not even close to how many I've done.

If you'd started with an ecm bench you'd probably progressed further faster, with less wear and tear on the car thou.

 

I am using the LM1 to data log . I started with 12.5 in the AFR vs RPM table and made various methodical changes taking out fuel at 80, 90, and 100 kpa in table one.

Do I need to look lower KPA's to solve this problem?


I also noted that changing commanded AFR and leaving the tables alone had little effect on actual AFR! I could go as high as 14.0 with it and see little change in the graphs . maybe I needed to go higher to see an impact????

I haven't used the g-tech to test performance yet cause I thought I should save that till I get the numbers consistently into the 12.5 range and then start fine tuning with performance runs to see if it liked 12.0 or 12.7afr etc the best. Time for a g-tech run.

Your thoughts are appreciated................bob

 

rsilver: i am new at this but doing a similar program. can you explain your comment "taking out out fuel 80/90/100 kpa". it was expalined to me to leave those values alone. we only hit them in PE. i was suggesting disable PE and datalog the higher KPA values 70-100 and also 2800-3200 rpms to optimize my fuel tables to allow the PE "adder" to be accurrate. this is when it was said dont do it leave alone? i understand there was potential to do damage to engine? too lean? anyway i ran on dyno and it showed 12.1/1 in PE or WOT without touching those higher map values. my WOT PE ratio was set in prom at 12/1. i have since set it at 12.5. my struggle is the pumpshot tables as i have a (cold weather) stumble. GTECH is coming. WB02 in going in 4/04. comments anyone ???

 

OK on the LM1 to data log. At your altitude what is baro? (key on, engine off, MAP value). Then subtract 3-5 KPa from that for the drop across the TBI. That is about what I'd expect for min KPA at WOT.

With your combo and the 65# injectors they may be running static. I'm not sure which heads the Edel 6085's are, do you estimate the HP level should be 340-350 or so?

If so, should be running ca. 24psi fuel pressure. If running static that would explain the fuel curve and lack of response to VE table changes. Can get the injector PW via the ALDL by patching it into the ALDL stream via the PROMID field.

IIRC, the '8746 does a lot with the baro term. May want to see what changes the ECM makes regarding baro.

RBob.

 

Ronny, I already had my ve table set up for non-pe or non-wot mode. My thoughts were since the WBO2 data log was showing me rich at 1500 to 3500 rpm at WOT, I should take out fuel at the higher kpa values ie WOT. I started taking out fuel at 100 kpa and that solved my rich WOT problem above 3500 but didn't impact the rich problem below 3500. So I started taking out fuel at 90 and also 80 kpa to see if that would help rich conditon at lower rpm. ( mods at appropriate RPM) Today I went furthur and subracted fuel clear down to 60 kpa. NO DIFFERENCE on the graph. Anyway that was my though process on subtracting fuel in pe mode for WOT rich conditions.

Rbob, good point on the min kpa for wot at my altitude. Denver is over 5000 but my testing has been at 7,000+ feet so maybe I hit wot at a really low KPA. As I mentioned above I took out fuel today clear down to 60 kpa with no change in the graph but maybe I gotta go lower. My laptop is broken so will have to wait on map value/baro.

The 6085 heads are the egr aluminum heads with 165cc intake volume, 2.02 valves and as I recall they flowed in the area of the GM vortec heads, probably a little lower I don't remember. As for hp, I hope its around 300 at this altitude but I don't think it is that high.

I don't know what running static means??I am using a bpw "constant" of 135. Can someone help me out on this?
Do I need to change the BPW? I calculated it to be around 127 via a formula I read but I never changed it cause I didn't have a WB02 to tell me I was rich at WOT and when I did datalogging I was able to adjust for all cells without modifying BPW.
Sounds like I gotta explore this cause Ve table mods are having little effect which is consistent with Rbob saying I am running static

Could you guys help me with this a little?I will do a search on getting PW via aldl and jpatching in to aldl stream but I don't know how to do that yet. Will also check out what running static means.

As usual, all thoughts appreciated....humm, running static, no response to ve table changes, guess I will be staying up late and reading some more tonight...........................old carb guy bob

 

Wouldn't running the injectors static at WOT make for a lean condition under most circumstances? Or is it depenant on fuel pressure.

Steve

 

Ok, its late but I followed a thread between Rbob and bmmonteSS
and the indepth discussion of BPW. That was awesome!!!I have a clue now but I agree with the above post that if the injectors were static I would be lean on my WBO2 Wot runs. Right?? The opposit was tru at higher rpms, I was rich.
The car was losing power after 5000 , breaking up a little and I could never get it tuned to eliminate that. But when I got the WBO2 it showd I was rich in the 10.0 afr range with some areas richer than that. I got it to 12.5 actual over 3500 buy going to 13.5 commanded AFR and taking 5 to 7% fuel out at 100 kpa from 1200 rpm to 3200 rpm. The car pulls better in that range but is still anemic after 5000rpm which I attribute to the TBI intake and
limitations of flow in the TBI unit. I DON"T KNOW anymore though, maybe its because I really am short of fuel at that rpm. Seems based on the math on BPW that I should be static at 5000 but that should show up in a lean AFR reading.

Well, I am gonna sleep on it and read it again and hope you guys can stay with me a while on this.

Meantime, even though it is rich at the lower RPM's it runs great ther. Very strong. I will g-tech it against my original chip without these changes.

Thanks Rbob for your thoughts. i hope you hang in there with me a little on this........bob

 

rsilver, what is the fuel pressure that you are running? I noticed you mentioned being as rich as 10.0 according to the WB. That is right where the sensor limit is. So the engine may even be richer then that. This would explain why removing fuel has no apparent affect on the WB reading.

Another thing about WB's is that if the engine is misfiring at all the reading is not real. IOW, the WB will not report the correct AFR. I've seen an engine in lean misfire where the WB was bouncing off the rails (rich/lean) while the NB reported 850mV or more. Going even leaner and then the WB was reporting richer then stoich.

What I see as a possibility is that at lower RPMs the PW is just too high and the engine is just too rich. Then as the RPMs climb the injectors start going static. This may be causing the misfire at 5,000 RPM you posted.

Tonight I'll run some numbers with a BPC of 135 and various VE values and post the PW's that result.

RBob.

 

rbob, I don't have a fp guage so I don't know the FP. I modified the stock TB so I could adjust the FP and it is set about in the middle of the adjustment. Thats not much help, I know. FWIW, I did upgrade my fuel pump to a higher flow walbro so i have the capacity to increase the pressure quite a bit.

I would like nothing better than to determine I am going static and could benefit from larger injectors or higher fp's.
For the *** of it , I am going to reduce my bpw constant to 130 and see what happens at low rpm at wot.

I really appreciate your help. i hope I can understand the numbers if you have time to run them................bob

 

somewhere on the crossfire forum was a calculator to determine the max HP an injector can handle. was not a formula just plug in the numbers(cid/fp/duty cycle/ size inj) and see the result. i recall my 90 lbs at 9 lbs were good for 275 HP ??? which is where i am at per dyno. so a search and you may find it. was posted about 30 days ago ?

 

Really do need to get a fuel pressure gauge. I finally got to the point where I data log the fuel pressure.

Now, as promised, a little long. . .


According to Turbo's are your Friend by Hugh MacInnes:

6,000ft = 23.98 "Hg, 7,000ft = 23.09 "Hg

So average it:

avg = 23.54 "Hg, which is just about 11.5 psi (Machinery's handbook, 20th edition)

Convert to Kpa: kPa = psi x 6.895 (Machinery's handbook, 20th edition)

79.3Kpa

That would mean baro is about 80 Kpa at 6,500 feet and the maximum expected KPa reading at WOT.

According to this table (ANLU):

The BPC of 135 at a baro of 80 KPa will be corrected as such:

New BPC = (135 * 132) / 128 = 139

139 will be the BPC used at 6,500 ft altitude in standard air.

For those that have a puzzled look on your face. . .
The reason for this correction is that the exhaust system is more efficent with less backpressure. Thereby increasing the volumetric efficency of the system. The table above changes the BPC to increase the fuel delivery.

Now lets run a little program that will spit out the PW for a given set of inputs. The set inputs will be:

BPC = 139
AFR = 12.5
CTS = 90°C/194°F
BLM = 128 (neutral)
INT = 128
Injector bias of 375 usec.

The VE% and MAP will be changed.

Please note that the 90 & 100 KPa tables is shown for the benefit of our viewers residing at sea level.

As shown the PW can get quite high. Easily high enough to go static at upper RPMs and high enough to go nice and rich at lower RPMs.

One thing to remember is tha the injectors fire sync'd to the ignition. It can be difficult to comprehend the results of this. As the RPMs increase so does the frequency of fuel delivery.

So what happens is that the injector PW needs to follow the torque output of the engine. Highest PW will occur shortly after the peak torque (frictional losses and all that).

For a TBI system the time available to fire an injector can be calculated as such:

sec = 1 / (RPM / 30)

So at 6,000 RPM there is 5 msec between injector firings (this is the same injector). At 3,000 RPM there is twice as much time: 10 msec.

Now if we keep to 85% duty cycle (DC):

At 3,000 RPM: 1 / (3000 / 30) = 10 msec * 85% = 8.5 msec.
At 5,000 RPM: 1 / (5000 / 30) = 6 msec * 85% = 5.1 msec.
At 6,000 RPM: 5 msec * .85 = 4.25 msec.

The time to deliver fuel diminishes quickly.

Now look at the above charts of VE%, KPA and given PW.

If the PW is too high and needs to be reduced the fuel delivery per milli-second needs to be increased. This can be accomplished by either larger injectors or higher fuel pressure.

I should write a book.

RBob.

 

rbob, this is quiet a paper! Unfortunately, I have now read it carefully 4 times and dont' fully understand it as it relates to my situation.

You have shown me how PW can get high enough to go static at upper rpm's and still be rich at lower RPM's. Thats a revelation for sure. In an earlier comment you made you suspected that at lower rpm's the PW is too high, the engine too rich but as rpm's climb the injectors start going static. If so, then I should reduce my BPW constant, recalibrate my fuel table and most likely raise FP (or go to larger injectors) to obtain enough fuel at higher rpm/map. So......

For grins I changed my bpw today from 135 to 130 to see if I could reduce the rich condition at low rpm while expecting to be too lean at higher rpm. Several things happened:

1) I can now consistently break the tires loose in 1st gear rolling @1500 rpm and my butt tells me it was a big improvement down low. That implies that my rich condition at low rpm is negatively affecting performance.
2) To prove this I expected my WBO2 graph to show that I was now leaner at lower rpm, but no, of course it showed that I was still rich at 10.0 AFR!!! So, given the limits of the sensor, I must still be WAY rich base on your comments? Correct??
3 I did go leaner at higher rpm, from 12.5 to a little over 13.0.

Sooo, either I got a problem with my sensor or, as you mentioned, the engine is actually richer then the 10.0 and
the WB sensor limit of 10 wasn't reached.

All of this made some sense till I read your paper and saw the calculated bpw of 139. That seems to be counter to what
I experienced above and the concept of the 135 bpw being too high.

Bottom line at this point: I thought I needed to reduce BPW , increase fuel pressure(or get bigger injectors) and re-calibrate VE table to hopefully reduce rich condition at low rpm and have adequate PW at higher rpm. My test using lower BPW above seemed to bear this out (rich WBO2 reading notwithstanding)Is this correct??

The calculated BPW of 139 is throwing me .

Sorry this is so long, hope you got the patience to read it.

Ahhhh, welllll, what do I need to do???................bob

 

To relate the information to your situation, use your VE table and convert the VE% at any point to PW (from above data). From that you have a good idea of what your PW's are. Check them at the higher RPM's and see what the duty cycle is. This will help in knowing how much larger or smaller the injectors need to be.

Say you want to know the PW at 3400 RPM and 80 KPa, your VE table has 95% VE at that point. From the above data your PW will be about 6.0 msec. If at 5,000 RPM and 80 KPa with a VE% of 95% you will know that the injectors are static.

Your bottom line statement is dead on. Try to get a good estimate of how much HP the engine makes and what the maximum (going to use) RPM is. Then size the injectors/fuel-flow large enough to cover that. Adjust the BPC so that 75% to 80% VE at the maximum RPM will give a 85% DC.

Then adjust the VE table for the desired AFR. Once the AFR is roughed in you can get a solid idea of required injector sizing. Then performance testing can be used to optimize the SA and AFR together.

As for the calulated BPC getting higher don't worry about it. That is only due to altitude. If you drive down to the valley the ECM will lower the BPC to match.

RBob.

 

rbob, thanks for staying with me on this. I am still fuzzy on some of the relationships but I started understanding a little late last night. Finally had to give up and go to bed. I am going to spend some more time on it this weekend cause I want to understand it better. It would be easy to just up the fuel pressure and retune and see what happpens but now I am P***** cause i don't understand your "paper" fully. I started on this forum with a bone stock 305tbi and before that I had only worked on carbs, soooooooo I will keep trying.
Hope you check back on this cause I will post when I finally understand and try to do a specific example for my combination to see if it makes sense.
Thanks again................. bob