I have a feeling I am at maximum capability of my maf sensor. At 4200 RPMS, the voltage is 4.52 volts, and stays there as the RPM's increase to 5200.

Could someone confirm for me that the range of my MAF is what I think it to be .5V to 4.5V. I have an 86 corvette.

Thanks

 

I've seen stock Bosch MAF's report up to 254 gm/sec which corresponds to about 4.72 volts with the stock MAF table settings.

Individual MAFs do vary in their output, but I suspect that your airflow (rather than the MAF output) has peaked at roughly 226 gm/sec or 4.52 volts. The ecm can read up to 5.1 volts.

No real way to be sure unless you can provide additional airflow or try another sensor and see what happens. If you still have a tpi, I'd expect the flow to be limited.

 

The actual air flow numbers the ECM is seeing is around 245. What I do not understand is that the airflow increases then plateau's at anything about 4200 rpms. I have a modified TPI intake on a 383.

 

Have you already adjusted the max flow vs rpm table? This will limit the airflow according to the rpm. The values you've reported are similar to the table settings shown below:

Max. Air Flow Vs. RPM

RPM gm/sec
0 23
400 23
800 30
1200 48
1600 68
2000 89
2400 111
2800 141
3200 170
3600 200
4000 220
4400 236
4800 245
5200 247
5600 247
6000 247
6400 255

 

I will need to pull that table. I'm thinking that 255 is set at 3600 RPM's and up.

 

I'm just hitting the 255 gms at 4600 rpms with my setup. Stock MAF sensor, 52 mm TB, 383, AFR 195 streets, 230/236 cam, HSR intake, LT headers, much more. It is possible, but I doubt you are getting to 255 gms at 4200 with your setup. Seems more like the voltage is maxing out for some reason. How is it running? Is it going lean after 4200 or so rpms? If it is maxing out and going lean then congrats, that's what all we MAF guys shoot for! Just adjust the AFR% enrich vs rpm table to make it shoot for a higher and higher percentage of enrichment as the rpms go up. On mine I put too much enrichment percenatage in the AFR% enrich vs coolant temp, then have negatives in the AFR% enrich vs rpm table. Smaller and smaller negatives as the revs go up. Seems to keep a much more steady afr at wot that way for some reason than it did when I had the vs coolant temp table zeroed out and all the enrichment in the vs rpm table.

 

I have 5 different Maf's and on the same engine setup. The max Grams/sec vary from 187 to 255. Same engine, chip, rpm, ect..... the biggest headache is, because the air flow changes (volts out), each Maf requires a change to the injector constant to keep BLM's at 128.

Some Maf's are used, the lowest reading ones (187,200,205), the new one is 215, the rebuilt is 235, and the wells is 255.

That peak value doesn't change, it follows the specific sensor. I think as they get older the volts out drops.

The volts difference from 187 (4.21 VDC) to 255 (4.71 VDC) is only .5 volts.
The Injector constant changes (to keep 128 BLM) from 22# (187 maf) to 33# (255 maf), and that is a big difference.

 

It runs like crap!! I cannot explain it. Almost seems to run rich. After dealing with this thing for two years, I don't know. I can change the AFR anywhere between 10.5:1 up to 13.5:1 and not difference in how the damn thing runs. That is why I was wondering if the maf was pegged, perhaps there was something else I was missing.

 

If you're able to scan, what is the behavior of the narrow band O2 sensor above 4200 rpm? This will provide at least some indication if its going too rich, or lean. 880-900 mv are considered to be reasonable N/A values in the upper gears. Does it blubber or pop? How do the plugs look?

What about the injectors: size, type, fuel pressure, injector constants, low pulse width and battery offset values? All of these parameters have a big influence on fueling, just like the MAF voltage and MAF calibration.

Enrichening the target AFR via PE will quickly overflow the bpw calculation with elevated airflow values at modest rpms. This may explain why extra enrichment doesn't help. Could be that your bpw is already maxxed given the airflow and rpm, despite decreasing AFR's

 

One thing to be careful of on the MAF based TPI setups is the TPS voltage. If it goes too high the ECM will think that the reading is bad. This in turn causes the ECM to drop out of PE mode.

RBob.

 

I took it out and scanned the car. Just at a quick glance AFR was between 12.25 and 12.5 on the wideband, and narrow band was high 800 to about 940 mV. I am going to disect it a bit more. Right now I have to work on the babies room!!

I did see the maf hit a ceiling though. Car still runs like crap. What is the difference between a blubber or pop?? I have either one i'm sure.

Thanks

 

Something I noticed. The TPS voltage was only 4.35 or so. I thought my TPS may have been out of calibration. TB closed TPS voltage was .57. Push pedal, it jumps to 4.39. Well, I played around with the foot pedal a bit, and really jammed it to the floor and it jumped to 4.55. So I wasn't mashing the pedal hard enough.

I will take it out later and see if I can increase that TPS voltage to 4.5 or more during WOT driving.

 

The spark advance table I have only goes to 208 load and 4800 RPM's. What happens for loads greater than 208 or rpm's over 4800, or both? Is the last number in the dataset used?

Thanks

 

An intake pop is lean and an exhaust pop is rich.

What do the plugs look like?

Any carpet pad's under the pedal will cause a lower WOT TPS. Also move the top of the TPS sensor for WOT and the bottom for idle.

Try manually opening the TB with key on and engine off to see what the highest volts are.

Yes it just uses the last value, the high load and high rpm use the same values. It is old school that at WOT all the SA is in by 3000 rpm or in that range.

 

I have popping out the exhaust. The AFR is in the low to mid 12's.

In order to check the plugs, would I need to do a WOT run, then pull immediately? By driving any distance would corrupt how the plugs look?

I know when I setup timing on my old birds, I set all the timing at 3k, so I am familiar with that idea.

 

I was just curious what the plugs looked like. Just pull some and look. General tendency was what I was thinking, White or black or something in between.

"It runs like crap!! I cannot explain it. Almost seems to run rich. After dealing with this thing for two years, I don't know. I can change the AFR anywhere between 10.5:1 up to 13.5:1 and not difference in how the damn thing runs. That is why I was wondering if the maf was pegged, perhaps there was something else I was missing."

I would check the plugs, when in the "runs like crap" area.

It would help if the affected area's where more defined. There are many similar issues that have same/different causes.

 

I just recently changed the plugs. They all looked okay, had a tan color and seemed to be uniform.

It starts running poorly at the higher RPM's. When I say that I mean over 5k. Not exactly 5k but there abouts. It looses power, and the motor flutters, with occasional backfire out the exhaust.

AFR seems to be about right in the low to mid 12's. I was going to play with that a bit, and get it closer to 13, because it is my feeling that it is rich. I'm not getting any spark knock approaching the higher RPM's. My tune called for 32 degrees of timing at max load and RPM's. I was going to add a few degrees of timing as well.

I thought I was missing something because I think the MAF does quit reading about about 4.5 volts. How would I test that? Could I put it on the bench apply power and ground, and put a leaf blower in front of it and check the output voltage?

 

Added 4 degrees of timing. Seemed a little better. Hard to tell though. I did manually shift the car, and the car ran fine up to 4700 rpm's. So my issue is occurring higher than that. Car shifts at 5140. So somewhere between 4700 and 5100.

 

Yes, any high speed air flow, vacuum or maybe a window fan or furnace blower funneled down to 4" could be used to max the maf and check max volts. It would be easier to test a max then a measured flow.

That value is good to know because any higher amounts would need more PE. The Mafs flow more air then they can read.

 

That is what has me puzzled. It seems my AFR is decent enough not to have any issues. I suppose every setup is a little different. I am going to shoot for the high 12's and see if the car runs any better.

 

Have you checked the table that Tequilaboy mentioned? I had to change that table, mine was going into MAF default mode at a higher rpm part throttle and going dead lean. Raising the values in the table solved my problem.

Sounds like you are very close to getting your problem solved if it is running good up to 4700 rpms.

IMO, your AFR of low to mid 12's is a little rich but not too bad, as long as your timing is not way too low and your plugs are not too cold to burn up all the fuel. I would think you should have stock-ish heat range plugs, depending on the rest of your setup.

Are you seeing mid 12's AFR at part throttle or just at WOT? If at part throttle then that is too rich and needs adjusted.

I've seen some TPI cars wanting timing up into the 39 or 40 degree range at WOT, depending on the heads, cam, compression, etc. Mine liked that until the heads/cam/intake swap, now it likes 35 degrees total. Before leaning out the fuel at WOT I'd try advancing the timing more and more until you pick up a little spark knock. Then back it down 2 degrees. If you can get away with more timing it should lean it out a little without making any fueling adjustments at WOT. You can always add 1 or 2 degrees at a time into the PE mode spark advance table to save you from changing your entire part throttle timing table.

One last thing, how new is your dist. cap and coil and such? Is it possible that your spark is getting weak or breaking up or getting weak in the higher rpms causing the mixture to not be completely burnt up? Doubtful but thought I'd ask.

Keep us posted.

 

What do you mean about maf default mode? I have not heard that before.

I don't believe I am going lean. The wideband confirms this, and the narrow band further points to that. I agree, low 12's is probably a little rich. So what I have done is zero out the PE vs. coolant temp table. Then I am adjusting the %PE vs RPM table. I am able to see differences. The last thing I did was increase timing from what was 32 degrees for rpm's above 4800 and load var above 208. It seemed a little better.

I would like to add more timing and see where I get. If I can get results adding timing, should I try leaning the mixture out any?

Also, I suspected my ignition early on, so about two years ago or so I put an msd 6al on the car. It did make a difference in throttle response.

Part throttle driving AFR looks okay.

Once again thanks for all the help and responses to this.

To add to my frustration, I took the car down to the local meat store to get some fresh hamburger to grill. Driving back, the rain was coming up quick, so I was driving fairly aggressive. I stomped it from about 25 mph, and the back end came loose, and the car pulled hard and shifted without any issues at all. Damn, I didn't have any of my tuning stuff connected.

I am going to evaluate my last tune. In my logs, as soon as I get on the car, knock retard pulls 6 degrees of timing, and as the rpm's increase to redline, the knock retard slowly decreases. This is something I have never been able to understand. I could post the graph from datamaster if anyone is interested.

Thanks,
Craig

 

The table is called "MAF Max Air Flow vs RPM", this sets the upper limit to air flow and will lean the tune because less air measured means less fuel.

IMHO this table is there to limit the big rush of air when you tromp the peddle, you can use this to do some AE tuning. Raise the values to richen and lower to lean, I run mine 10% to 15% over the normal wot air flow.

The default table is used when the MAF is dead or missing, they are two separate tables and are used to do two separate things.

If you are getting knock retard then the spark needs to be lowered at that rpm and load. I'm at 20 degrees at wot and still need to remove more timing (6 degrees), 10:1 and 87 gas aluminum heads and 70 cc chambers.

I lowered "Load Variable for Scaling LV8 Scale Factors" at LC5B0 (Arap 6E) from 80 to 70 decimal counts. This is a global drop in the load. At wot just after a shift, the load goes to 245 just under the limit. This affects your timing mostly, it keeps it (lv8 numbers) from maxing at high load.

The calulation is cal = argument X 64

80 = 1.25 scale factor
70 = 1.09 scale factor

I have never read about anybody adjusting this value, it is suppose to be about cylinder filling (calculated vacuum ??).

I have often wondered if a stock 305 would max the lv8.

 

In reading all this something else just came to mind. There is a setting (in Tunerpro for the 6E anyway, you likely have it too) for ALDL spark advance (again at my work computer here and can't remember the exact name for sure). I once had the problem that the car ran great but not so good when hooked up to the computer for datalogging. This ALDL spark advance setting was set to 6. It was advancing the timing 6 degrees when I was hooked up to the ALDL for datalogging. If yours is set higher than 0, it is adding timing which could cause all your problems. Could cause the knock counts to be up at WOT and could cause the upper rpm problem you are having too. This all came to mind when you said the car ran great when you didn't have the datalogging stuff hooked up. Check it out.

Pandin, I'm going to look into the last thing you mentioned myself. One thing I noticed is that when I'm at cruise rpms, in overdrive, and completely off the gas, my LV8 is still usually in the 60's and 70's. Any amount of throttle at all, no matter how light, and it is into the 80's and even low 90's. Ive never seen any LV8 in any datalog lower than high 50's. I always thought maybe they were running too high. My ARAP 6E already has been hacked and I have that command so I'll try lowering it and see what happens.

 

'vette, how are you reading the output voltage from the MAF? Has the data stream been patches, DVM on the wire, or is it being derived from the MAF table gms/sec value?

RBob.

 

What I was running into was at wot (with a 383) the LV8 was maxing at 255. The number is a multiplier (1.25 scale factor), so this setting is increasing the load number by 25%. Since I have way too much spark advanced for my setup, I was using this to lower the spark advance globally.

I am going to guess that this LV8 is a simulated vacuum reading and that pegging it (high load/low vacuum) is not really an issue.

My thinking, right or wrong, is small motor/big load and big motor/small load.

 

What should knock retard look like on a graph? What I am seeing isn't what I imagine. As soon as I go WOT, no matter the RPM's, spark knock jumps to 6 degrees retard.

So if I am cruising at 1400 RPM's and jump on it, the knock retard jumps to 6 degrees, than as the RPM's increase to redline the knock retard decreases and by the time I am at redline it may be 1 degree or 0.8. So i'm not sure. I even disconnected the knock sensor and this still happens. At least I think I did. I will have to double check that tonight when I get home.

 

I may be mis-understanding. The bin I am working from was done by someone else. I paid for it, and I am doing the mofidying from that. The car never ran right.

So in that table 255 g/s is set for values greater than 3600. So if I were to lower the 255, to say 230, this would lean my mixture? I could almost see how that would work. The engine is requireing 255, but 230 is the max, so less fuel, because I have limited the max amount of air. Is that correct?

 

I am using an LM1 to monitor the output voltage of the maf. Right off the maf output wire.

 

You have to look at your maf sensor raw number at say 3600, mine is pulling 191 grs/sec of air at 3600 wot. My max table is is set at 231 grs/sec at 3600. So I am not even close to the max limit. The max setting is 20% higher then the "normal" wot air flow, if the max table is above raw maf sensor reading, then the max table is not used at all. It doesn't matter if the max table is 195 or 255, if the measured air flow is less it makes no difference.

If I lowered my max air flow setting to less then 191 grs/sec at 3600 rpm, then it would start to lean out the fuel.


If you were adjusting the default table, when the maf is unplugged, it would make a big difference rich and lean. But only when the maf is not used, hook the maf up and all is well, you would not be able to tell.

 

With spark knock, shouldn't I see it increase with RPM's. It does the opposite.

 

If you are getting spark knock retard, then at that rpm, load, and temperature, you have too much spark advance. You can run that way but are at risk for detonation (major engine damage) if your knock sensor fails. The method I use is any place there is spark retard, I lower the spark table just prior to that place. Knock takes time to build so you want to work down the spark advance, at just lower rpm and load area's. Remember that more then one table can affect the final spark advance number.

I would save the knock sensor for bad gas ect...

Look at your PE spark advance and lower that first, also raise the knock test temp to 304 to disable it (LC237 arap). The knock test is used to force a knock retard at first wot then holds that value till key off.

The PE spark adds 9 degrees SA at peak torque to force a knock test retard. It has been my experience that staying out of spark retard, gives a better tune, then having the knock sensor removing too much spark advance for too long of time.

For a street engine 2-5 degrees under spark retard is a good place to be.

If you faith in knock sensors, just set all the spark tables to 50 degrees and let the sensor sort it out. A rattling exhaust or any banging noise, can also remove spark advance.

One test of a knock sensor is scan tool attached, key on, motor off, and monitor the spark retard. Then hit passenger side exhaust manifold with a rod and hammer, each easy whack should show up as one spark knock count. Mine passed this test but the sensor was still bad.

 

I did run several scans where I unplugged the knock sensor, and the graph looks identical to with the knock sensor plugged in. I think it is something in the tune. Maybe I'm wrong.

 

I removed 4 degrees from the areas that I was getting knock retard. Scanning the car again didn't really yield different results. Can I do any damage by retarding timing to much? I'm only gonna move about 4 degrees every time until it disappears.

 

I would zero out the PE spark advance and see if there is any change. One person reported that he was getting 8 degrees retard from the 9 degrees of PE spark advance.

The next table to look at is the "Spark Correction Coolant Temp vs LV8" (LC10F to 17A Arap).

Above 100* F in the last row (160 LV8), lower the numbers here till you dropped out the 20*Bias. If the bias (LC10A) has been changed then use that number, as it is subtracted from the correction table.

Main spark table (LC030-0FB), for wot, only the LV8 208 row should be lowered.

Changing these area's should have changed (lowered) the retard numbers at wot.

If not then something else is going on.

Where and how are you unplugging the knock sensor?
Are you powering down the ecm first and then removing the plug?
Have you disabled the knock test yet?

 

According to the graph the LV variable is dropping off when it should hold at 255. Something isn't right in what the ECM is doing.

You did mention that the tune is originally from someone else. It is always recommended that one starts with a stock GM BIN file. And make the changes from there. This way there is a known starting point.

Along the same lines, when the knock retard attacks in, do the counts also go up? Makes one wonder if the code hasn't been patched for some reason.

RBob.

 

I was able to eliminate the spark knock. I was mistaken, in the stock GM BIN ARAP vs. the one I have been modifying the car acts pretty much identical when spark knock is detecting. I was able to eliminate it by pretty much retarding the timing 10 or so degrees in the areas at and just before knock occurred. The only difference was the stock GM bin was pulling more timing because the max spark knock in PE mode was set to a higher value.

I need to go back and make sure that I actually unplugged the knock sensor correctly. I'm at a crossroads. My total timing now is about 21 degrees and the car does not pull timing. And I don't seem to have the higher rpm issue. Correct me if I am wrong, my AFR are in the low 12's. If I would lean that mixture to high 12's, could I add more timing back? I'm just trying to find a happy medium. The car feels sluggish now.

I probably need to start back at the stock GM bin. My LMA-2 took a crap yesterday, or so it seems. The only thing my LM-1 registers is AFR. I verified the voltages for the inputs right at the LMA-2 and they seem okay.

If I want a systematic approach, should I adjust the timing curve to reduce any spark knock, then work on WOT AFR? I don't see an additional 6 degrees of timing when my aldl connector is hooked up. Also I need to find out if LV8 is dropping with the stock GM bin. Perhaps there is some sort of patch in this code.

pandin, I have not removed knock test yet. Do you still recommend I do it, know that I know the spark knock must be a legit issue?

Thanks for all the help.

 

I would try it with and without, to see what changes and which is better for you.

 

RBob, are you sure there is something wrong with that? I know my LV8 drops from 255 to about 190 to 210 when my car shifts and fairly quickly recovers to 255. It's an auto (700R4) with 2800 stall, beefed up rebuild and snappy shift (accumulators blocked and such). By looking at his graph attached above I think the first drop in LV8 was because the spark retard pulled so much timing, and the second drop was from a shift. Wouldn't that be normal? I hope so, or I have a problem too!

 

vetteboy, I don't know your setup so I'm shooting from the hip here but on different setups I have done things to allow me more timing advance without making major changes with good results. You can try:

Run 92 or 93 octane gas.

Go a step or 2 colder on the spark plugs. Maybe you already are on the cold side but if not try going a little cooler. I actually just went 2 steps hotter on my plugs last weekend. Was staying cool for nitrous but I run the nitrous really rich so I figured I could go a little hotter on the plugs. Had to take my overall timing when not on the spray from 36 down to 34 because it picked up some knock. No knock at 35 so I set it at 34 to be safe.

Close up the plug gap to .035 if it is wider than that. Can even go to .028 but I don't like tightening it up that much. Some people run .060 but that just gives more of a chance for the air/fuel mix to begin to light up off of something else.

Cut back the ground strap on the spark plugs with a dremel after you gap them. Make them so the end of the ground strap is prettymuch lined up with the center of the electrode.

Make sure your cap and rotor are new or are in like new condition. The farther the spark has to jump to get from the rotor to the terminals in the cap the weaker it makes the ignition system. When the rotor starts getting rounded on the edge or the terminals in the cap start getting a groove or dish look to them they need replaced. I clean my terminals about twice a year with 400 grit sandpaper.

Getting your WOT AFR to the upper 12's may not let you add back in any more timing but it should add some power even at 21 degrees. I don't know how rock steady your afr stays during a run but mine floats from extremes low of 12.3 to a high of 13.2, most of the pull it is between 12.5 and 13.0. I have yet to find a way to keep it rock steady.

Just a few things to try that might help it get back to being a little more snappy. Also, you might need your timing down to 21 to keep out of knock and knock retard at and around your peak torque, but you may be able to put some timing back in after that.

 

Yes & no, it may be that the data for the graph is not being updated at a high enough rate. I placed a vertical yellow line and posted the same graph here.

Note to the left of the yellow line that the LV is dropping. This is OK (which is the opposite of what I posted previously). As the RPM increases and the airflow remains the same, the load decreases. But the drop is rather quick.

Then, at the yellow line the RPM is still increasing and the airflow is flat lined. And the LV is quickly increasing. My thought is that it should continue to decrease. This is prior to the engine RPM dropping from the up shift.

To me it doesn't add up. The LV value is the ratio of airflow to RPM.

RBob.

 

To get my wot spark advance "correct" (no knock retard). I am running at 12 total. Base is at 6 with no PE spark added.

This thing really is starting to run a lot better.

 

WOW, 12 degrees total spark? I've never heard of anyone having to run that low. What is your spark advance total at the higher rpms, right before a shift? Have you ever tried any of the things I've mentioned above to maybe pick the spark advance back up some?

 

Re: 356 RWHP TPI 310 Build Quote:
Originally Posted by madmax
Exactly, the ideal timing depends entirely on the circumstances. Given how flat the torque curve is, he's got it pretty much perfect for his setup.

As for the numbers, eh. Even if they're a bit optimistic, he's still done a great job given the quality of the torque curve. He's clearly put a lot of time and effort into this tune.

Re: 356 RWHP TPI 310 Build Whats to fix?

I run 87 gas 10:1 CR and a "peanut" cam. The desk top dyno's predict 500 FWTQ and 400 FWHP.

I am following Grumpy's "give the engine what it wants" rule.

If you have a faster burning head then you don't need all that SA.

I had issues setting the base timing but after getting that figured out, two things are apparent, less timing is needed and the car is a lot quicker. Even runs smoother.

 

I am a huge fan of giving the engine what it wants, too. Was just surprised that the engine wants that low of a number on SA. I run mine at 32 at the top of the table, with 2 degrees in the PE SA table, for 34 total. I give it 4 degrees less in each of the next 2 cells down, so I'm giving it about 26 degrees at the lowest rpm that my car sees on a WOT pass. All seems fine at that. If I run the 34 overall everywhere, when it shifts and the rpms fall it cuts out from detonation. (knock retard is disabled due to false knock from variable duration lifters and such).

Another thing that speaks loads for less timing = same or more power is a good tight quench distance. Whatever GM designer put .051 thickness headgaskets on the 'vette engine (not sure about the camaro's), on a .025 deck height block, should be shot in the head!

 

I am also running flat top pistons and 70 cc chambers.

My retro roller cam and lifters don't seem to affect the knock sensor, which is a surprize because they sure do tap at hot low rpm's.

 

I always run premium gas. Octane rating is advertised at 93. I am running one heat range cooler on my spark plugs. My CR is approximately 10.5:1

 

I've looked at all the scans with that bin. They all seem to be the same. LV8 drops off. It drops off just before the AFGS starts falling even though RPM's are going up.

 

I did some poking around, and in 6E I did find a parameter that is ALDL spark adder. It was set to 8. So it would seem that when I plug the ALDL connector in 8 degrees of timing would be added across the entire table. I have not verified this, but this is a good point that was brought up.

What things can I check to toubleshoot the LV8 issue. If I see it in another bin, would this recommend an ECM issue.

 

Yes you need to set what 8 degrees to zero or remove the cable jumper after the ecm starts to communicate with your lap.

If you are getting a big spark retard at the point of load drop, they could be related. I know that mine has a big hesitation when lots of retard is added.

My MAf would show low grms/sec spikes at random during wot, I suspected intake pops were slowing down the air flow, but that is just a guess.

And I still get high fuel msec spikes when in open loop.

It is not a perfect world we deal with.