I know you tune to 900mv at WOT, 880 is pretty close. Base engine is pretty much the only thing left to check, everything else has been checked multiple times. The Vette is currently down due to a busted leg on my chip, I am awaiting fresh eproms from moates. I may be checking cam timing and lift while I wait. And compression for the hell of it. Keep in mind my ALDL sample rate. I don't know which way the gas pedal is going when it takes a sample. The TPS voltage gives me a good idea, but it could be as I am backing off between shifts, etc. so I will give the next sampling for ya all to ponder.....

34MPH
4275 RPM
4.04 v TPS
95.9 GPS Maf
8.75 ms PW
125 BLM
128 INT
910.2 mv o2
85 crosses
143 LV

4275 RPM is at the point where the car goes no faster. Everything here seems good except MAF flow. I am getting excited as I come closer to fixing this, looks like I am getting about half the airflow I need and the car runs pretty strong. I will post the results of my base engine check soon. Thanks!

 

Getting back to basics, have you swapped your ignition module and checked or replaced your coil? Obviously, plugs and wires have been done.

 

Plugs,wires, cap done at 0 miles, MSD coil and Jegs ICM last summer at 5k. Runs a little better, but no fix.

 

With those last results , I would say you are going in the right direction. You have never seen 100gps on MAF which means no airflow. With a proper base engine, it doesnt matter if you are lean or not, you should still be pumping air at RPM's. I sure would like to see vacuum results.That would confirm a proper MAF result.
Keep us informed.

Dave

 

Not really, stoich is stoich. When you are tuning to 12.6 you are tuning rich, not "just right". Rich is safe, with the archaic electronics we are using you have to tune rich to overcome deficiencies elsewhere(detonation,piston damage, etc.) It is also the best and easiest way to make power in our situation.
Now that wide bands are used with modern electronics we can get much closer to 14.7 and maintain it(and make power with it), but things have come along way in the past 15 to 25 years.
In the business I am in now we run wide bands from the manufacturer, and can take advantage of the increased flexibility of compression, boost , aggressive spark curves with out the threat of damage.
Without widebands and FAST(not the company,the speed) electronics we wouldnt have direct injection, because we couldnt run it reliably.
Very interesting conversation, I am enjoying it!! Hopefully we can all brainstorm and get this thing fixed!!

Dave

 

Yep.

 

I am loving this convo, too. It is hard to find tuning info in the archives, especially on the 870 ecm. Which brings up my next point, as to the lameness of the scans and the baud rate. The 2 snaps I have posted were the same scan, sample points that were next to each other. About a second apart, I assume. I got my blank chip from Moates today, I may get the vac test done and I will post results. I burned it a little less rich
(pw-load) and I will do a scan, also. Keep in mind that there is something wrong with my car (and I don't think it is my tune) so it could be affecting the scan.

 

Thats the problem !

as the ecm tried to compensate by widening the inj pulse to its maximun, the scan shows O2 too rich because of the wide inj pulse width...not because there is actually a rich condition...the ECM THINKS there is because it THINKS there are 22 lb inj running with the broad fuel pulse.....

bOTTON LINE, WHEN YOU STARVE IT FOR FUEL the scans will show it rich because the ECM is compensating its *** off and its not getting results, so it knows its sending too much fuel, so it shows as rich when its actually LEAN as it can get...The ECM reads the response of controls, like the fuel inj signal....not what is coming out of it. Thats gonna be lean as hell and confuse the O2 even more.

wrong theroy with the fuel inj......you can get bigger inj and dial down the pressure to have less, but you cannot buy small inj and run high pressure to get more. If its a 19 lb, that is ALL it can possible do.
Go find some 24lb/hr and run then at around 35-38lb/hr and it will run fine. Check the spark plug color after a run to confirm the color of the inner insulator. The open exhaust is begging for more fuel...not less. If there was ANY intake work done.....go up another step.

19lb ? seriously?

Problem solved.

 

I am not in the position to say if any of this is right or wrong, due to the fact A) my car is not running properly B) I am just a dude with a corvette trying to learn all this stuff. That said, I bought the injectors before I knew anything, or was a member of this forum. I had a TPIS Insider hints book, which said they were getting 350 HP+ on 19 lb injectors. I believed it at the time, and I was doing a stock rebuild, (and mine is pretty stock) so I scored them cheap on Ebay. So your saying the injectors are going static (max pulse width)? Does it show this on the scan? The flow of the injector is rated at a certain FP, so increasing the FP will not increase the flow of fuel? Also, I increased the injector pulse width in the chip to compensate....was this ineffective and still caused the problems you are describing? Are you also saying that the computer is telling the 02 sensor whether or not the exhaust gases are rich or lean? My last sample showed 910mv on the o2. maybe not rich enough, but certainly not lean. I have also ran Bins with both the 24# PW and 19# PW....had the same problem with both.

I have often wondered if switching back to the 24 pounders would be the fix. I have a set on the shelf. But I have yet to be convinced. Edit: There are lots of people running 19 # injectors in 350's on ThirdGen...the Ford Yellowtops are rated 19# at 39 psi (22# at 43.5) I am pretty sure they will run a 350 over 4300 rpms.

 

Alright Dave....I did the vac test. I looked funny driving down the road with a FP gauge and vac gauge taped to my windshield. WOT 4000rpm vac gauge near zero and no budging upward. 16 inches at idle. No bouncy needle. This seems ok to me. Cruise 16-20. FP held rock steady at 43.5 pounds at max RPM (FPR
vac blocked) I also hooked a DVM to the signal wire on the MAF. Most I got out of it was 3 volts. I think it is reading correctly....just no air to read.

 

Vacuum looks ok at idle, and cruise, BUT, your vacuum at wide open throttle should go to 0 then start to build again, if you have no vacuum build at WOT you have a problem. If you think about it, you need to start building otherwise you have effectively ha no air going thru the engine. Do a google search for vacuum gauge readings, and you will see what you should have.

You said you have no RPM rise after about 4300 RPMS. is this only under load? In every gear? Go out and run again WOT at 4k rpms, and see if you can get the vacuum gauge to climb up at all. You will not get idle vacuum but you should get something.
Another thing you may want to do is a plug check,what does it look like.

Dave

 

Let it be known, I am NOT a programmer, but I have worked with fuel injection since 1988. I am a driveability tech by trade, and have built SEVERAL high power SEFI powered vehicles for GM and Ford.I have worked hand in hand with several dyno tuners to crunch data and make decisions on tunes.Back in the day with EEC 4 powered fords I personally ran several SB ford with supercharging with 19lb injectors to 350 HP on a wheel Dyno, we did this by jacking up fuel pressure upwards of 80 to 100 PSI. Not recommended, but then that was the norm then. I agree with everybody else that the injectors are a little on the small side, BUT they should work with increased fuel pressure. You are not showing lean at full throttle, you are not as rich as some people would like to see, but you are NOT showing lean. People are getting very confused as to what happens at part throttle and full throttle. In closed loop part throttle the processor is not looking at voltage per se. THe processor is looking at the number of switches over and under 500 mv for a given amount of time. It then adjusts fuel pulse width to keep the vehicle at a given switch rate.
At wide open throttle around 3.75 volts(ish) tp the processor starts going after a table, it does not care where the O2 is . And it does not adjust on the fly within reason. When you are looking at the O2 , you are just looking at the voltage it is making, That reading is not manipulted by the PCM, it is an input to the PCM.
Your biggest problem, and what everybody keeps looking past is the MAF gps. It is also an input to the processor, and it is telling the processor I AM NOT FLOWING MUCH AIR. The processor is going to tailor fuel rate to that.
Are you leaning out , possibly, is that the reason you are not getting RPM, probably not.

Again, make sure your base engine is correct, or you will chase your tail.

 

I am pretty sure that the vac gauge needle is stuck near zero when the thing runs out of air at RPM. I have lengthened the hose to the cockpit so I can keep a better eye on it. I pulled a plug and it looks fine, but it has been in there for awhile. I am going to burn a chip with a global 10 percent change in the PW vs. Load table. It was too fat at 16 percent, to the point it was affecting my gas mileage. The chip I burned at a 5% PW increase last night made the car run much better all the way around, except at WOT. My FP is set so the injectors are at 22#. You are right about the MAF flow, even as a noob looking at the scan, this was a red flag to me. Chasing this tune around is a waste of time IMO until I find out what is really wrong. Though it is fun to chase, and I am learning a lot, I want to get to the bottom of this. I am pretty sure my motor is not being damaged by lack of fuel at this point. I have a new cam, intake, runners and FI waiting to be put on, but if I do that and still have the same problem, I will not be a happy camper. I may have to do that, but only after I have ruled out everything else beforehand. Switching crosses have been mentioned many times. I see the o2 is switching, does that number represent the number of crosses since the last sampling? Do mine look normal?

 

One thing stands out.........your 158 degree computer logged coolant temp.
I would change the coolant temp sender that sends coolant temp to the computer, then scan it again and see if the computer and the dash gauge match.
Another thing, the 1985 TPI is all by itself. The 85 has a MAF module. The maf module can possibly be modifying the MAF signal to the ECM, and tell it an eroneous air flow. THat can limit your fuel if the ECM thinks the MAF is flowing less than it really is.
Another thing, make sure the previous owner did not disconnect the knock sender and install a resistor to keep the ECM from seeing any knock counts. With 19 Lb injectors, I would expect a lean condition at WOT. With 19 Lb injectors, I would guess that you would see fuel normal until about 4000-4500 RPM, and then start leaning out as the injectors are maxed out as engine RPM increases...to a point where the engine is RPM limited based on fuel suply

 

Cross over count is the number of times the mixture has gone over and under 500mv in 1.25 seconds, the higher the number the better, yours is fine. THe count is a good indicator of o2 efficiency.
I believe the coolant temp that ecm sees is a different sensor than the coolant sensor for the dash, you are looking at 2 different readings, I can double check that.
The MAF module is a burn off module, it does not affect the readings to the ECM, I have a picture of the schematic for the module, and the signal goes directly from the MAF to the ECM, the module only is in control of burn off.
I have an idea, I am not sure if it will work. Try disconnecting the MAF entirely, and see if you can drive the car. You will be in FMEM, and will be running on set tables.(Limp) see if you can get more than 4k then. It may not even run well enough to do it, but it's worth a try.
With the way you have described your vacuum at WOT, I think you have the answer.

 

Thanks for the response, Coupeguy. Not only is the temp off, the vehicle speed is off, too. I scanned all the way to 85 MPH. The highest the scan read was 53 MPH.
I have not ruled out the MAF. I hooked a DVM to the sig wire, and could not get it over 3v driving the car to redline. It may be reading the air or malfunctioning. I suppose it should go to 5v? Any ideas on how to make sure my MAF is good? Maybe I can find a way to blow some air on the wire...hmmm. It worked great before the rebuild. It has been cleaned.
Funny you should mention the knock sensor. The wiring was bad and it did not work. Much pinging...I fixed it right away and have not heard a knock since. My ALDL does not show knock counts....could the ESC retard the timing enough to RPM limit the engine? Detonation mostly occurs at low rpm(low vacuum)/high load conditions. My car runs great under these conditions.
I am still seeing(hearing) it both ways on the 19# injector thing. I still do not understand how increasing the FP and upping the pulse width to a reasonable (or unreasonable) duty cycle cannot work properly on a 350 making 275 HP on its best day. It has not had its best day yet, I think it is making no more than 200 hp. I am going to try unhooking the MAF.

 

I have problems since changing the OEM injectors. I say the newer ones have a different flow rate, or pattern, or something that makes them different.

 

I did a little brain storming with a tuner today, first off the difference between coolant temp at ECM and gauge is pretty common, two different sensors, and the gauge will generally be higher, because of where the sender is located(tstat housing compared to cyl head).
He was telling me that the car should go into open loop at wot, he has seen this before and it is generally because the tp is not showing wot.
From the looks of your scan that is not the case,but he did say to keep a close eye on tp voltage, and make sure it is clean voltage, not jumping around, you may want to sweep it manually with a meter to make sure.
He also told me to make absolutely sure your lifters are adjusted correctly, and not pumping up from being over tightened(which will kill topend power).
Just passing this along, hope it helps.

 

Dave, I appreciate very much you going out of your way to help me. The temp thing makes perfect sense, water would be different temps in different parts of the cooling system. I have not heard anything to suggest 159 degrees input into the ECM would cause the symptoms I am describing.
The open loop in WOT thing is how I started this thread. My scans clearly show that the system is in closed loop at all times after initial warmup. Someone suggested this was correct. I need to confirm that the computer should acknowledge (on the scan), going open loop above a certain TPS voltage. I will play with the TPS and DVM right away.
As far as the valves being too tight....they have been set 2 different times. I set them a 1/2 turn past zero lash. I would love it if this was my problem. I may try 1/4.
Now the vac gauge thing......I did some studying up. I believe that the vac gauge is showing what the MAF is showing......that there is no air. The symptoms of no recovery after mashing the throttle open are symptoms of low compression. I will do a compression check ASAP (probably one of the first things I should have done). The needle was always rock steady, meaning this is a problem shared with all cylinders, so it is not a broken ring or a bad valve. It also seems to confirm that my cam timing is OK. My car uses no oil, the plugs look good, and it doesn't smoke.
Once again....thanks. And I would love for someone to chime in about the open loop thing.

 

You are just comepetly wrong. new flow = sqrt(new pressure/old pressure)X injector size