veneno

I am lost here I have 1998 corvette, automatic and installed a 408 stroker,224/230xe cam, long tube , LS2 intake, LS2 throttle body, 85mm maf. I am using HPtuners and have a mail order tune. The car was running decent with the mail order tune but running extremely rich at wot after installing wide band it showed 10 afr
But besides running rich it pulled through all the gears. I take it in for a dyno tune the first two pulls are clean even though very disappointing #'s
Tuner does some adjustments with his laptop the next dyno pull engine shuts down in the upper rpm's and backfires. Does the same next pull tuner is scratching his head he don't know what happened he thinks the maf is maxed out but I don't think so. The tuner puts the original mail order tune back but it's still doing the shutdown.I take the car test it out on the street as soon as you go wot it shuts down as if you turned off the ignition. Could the pcm be damaged? I disconnected the maf (same results), I disconnected the front o2 sensors (same results) and even though it's running open loop still runs extremely rich no changes in the afr. It idles fine and drives fine just once you go wot it immediately shuts down. Any ideas on this? My next step is to swap out the pcm

veneno

also I am using 40lb accel fuel injectors rated at 43.5psi
should my psi at the rail be 43psi? Right now it's at 60

enoniam

I doubt that the PCM is fried as I don't think it would work very well at idle and normal driving and then have problems just at WOT.

Are your LTFTs disabled? If not were they reset to zero during any of this? Do you know the type of adjustments made by the tuner such as were they to the MAF calibration or the Power Enrichment area?

veneno

I was hoping to post a data log but for some reason the file won't open
I will have to do another scan. I don't know what adjustments the tuner made I lost all confidence in him and don't want to take the car back to him. I just don't understand it did not do any of this with the original mail order tune so I reloaded the mail order tune but it's still cutting off once I go wot

douniasg

Here is the scan log it is in post #3. I can't attach hpl files here. http://www.hptuners.com/forum/showth...lls-after-dyno
Here is the tune98 c5 408 (1) (1).hpt

DOUG @ ECS

Regardless of whether it's fried or not I would upgrade the PCM to a 99/04 computer for that combo.

It's not expensive and will yield a better tune over all.

.

tblu92

With an LS engine your 40 lb injectors should be scaled at 47 lbs That would make it very rich if you did not scale your ECM at 4 bar --Your injectors are rated at 3 bar or 43 psi---
However it is a common problem for 97-98 C5's when adding lots of HP-----The old 97-98 MAF's tops out at only 11250 HZ where the newer 4 MAF's go much higher---Typically the old 3.5" MAF top out at around 500 crank HP---Beyond that you either need to update your ECM and MAF to the newer style---OR tune in Speed Density--OR tune in Open Loop
Also simply unplugging your current MAF does NOT disable it---It takes more----You must disable it in your tune as well---and while it's disabled remember that the timing automatically goes into the LOW OCTANE table----so for a true test you must copy the High table into the Low---so the timing is the same---
My opinion---??? Injectors are scaled incorrectly---Your tuner may be also correct---you are at the end of your MAF table----Only data logging your MAF HZ's will tell the truth with it on---If over 11250-then go to an open loop tune----disable your LTFT's---set your WOT fueling by using the "commanded fuel in open loop normal" table
Check the results with a wideband-------

PS I have tuned 500-550 HP 97-98 LS's this way with great success

enoniam

Don't know how unplugging the MAF doesn't disable it. PCM isn't going to be getting MAF data if it's unplugged so it has to be disabled.

That's not to say there aren't other things to do in the tune to support full-time running MAF-less such as adjusting the Low Octane table as you noted. However unless the Low Octane table is really screwed up unplugging the MAF and seeing how she runs should be a good test of whether or not the MAF being maxxed out is the problem here - and it doesn't appear to be, unless the VE table is well matched to what the MAF was doing, but I would doubt that.

Agree that running injectors rated 40 pounds at 43 psi should be scaled to 47 pound injectors. Scaling factor is the square root of 60/43.

enoniam

I just looked at your tune and log. The folks on HPTuners' site are correct, you are maxxing out the MAF. At 1:25.4 in the log the MAF reading is 504.9. In the tune the MAF at 11.25 kHz is 504.91, so at that point the MAF is at 11.25 kHz.

Not sure why it started when it did. Maybe it's hitting the max now that the weather is cooler hence denser air. Maybe something else changed in the intake just enough to get it to hit the max?

veneno

Ok is there any possibility maybe the ECM is sending false info? I swear I am not imaging things once the tuner got on his laptop things went downhill. The first Dyno pull was clean no shutting down or backfire it's the 2nd, 3rd, etc when the problems happened once he got on his laptop. Ok if it's indeed the maf I did unplug it and had the same results do you think the car needed more run time to learn? What about this scenario it shuts down on me even when I get on it in 1st gear from a stop. Is there enough speed or air flow to peg the maf in 1st gear?

enoniam

Your airflow is going to be primarily driven by throttle position and rpm. Unless you've got a REALLY effective ram air setup there isn't going to much of a difference at speed and certainly there isn't going to be a vehicle speed dependent ram air effect on a stationary dyno.

I noticed in that log it looked like you had hit WOT shortly before you hit where it shut down. Your rpms weren't as high the first time and the MAF wasn't getting above 500 g/s there.

There isn't any learning that would cause the MAF to be maxxed.

While it isn't absolutely impossible that the PCM is sending bad data, I think it is extremely unlikely that it is sending anything other than what it is seeing, meaning that I don't think the PCM or tune is inducing the apparent MAF hitting its max frequency. I'm not sure why you saw it start to act up when you did. Prior to the dyno session how high in the rpm range had you run the car at WOT?

In any event I think the advice of going to a MAF/PCM setup that allows more airflow through the MAF or going to a speed density setup needs to be your next move.

veneno

"There isn't any learning that would cause the MAF to be maxxed"

I disconnected the maf and took it for a test drive but it still cut off on me at wot. What I meant was maybe I did not let the car run long enough with the maf disconnected for it to learn? Or I could be wrong thinking disconnecting the maf will make it run speed density?

So, next step is a speed density tune I will report back with what happens it will be awhile it's cold outside and need to find a
different tuner

btw, yeah I was able to go past 6k before the dyno tune. I would go full throttle from stop to 3rd gear full throttle blazing the tires, lol

enoniam

It's running in speed density with the MAF disconnected because it doesn't have anything else to go on. It will go into a bit of a limp mode however because as tblu92 noted it will run on the low octane table. I'm doing some speculating here, but besides running on the low octane table it may be doing some other limp mode things such as the cutting out you are getting.

Also doing some more speculating, some of PCM's "something's screwed up I better turn on the engine light and/or go into limp mode" calculations require seeing the same issue on consecutive startup cycles. Is it possible that the dyno session was the first time it had seen WOT high rpm on two or more consecutive engine starts?

veneno

"Is it possible that the dyno session was the first time it had seen WOT high rpm on two or more consecutive engine starts? "

Yes that's correct I have never gone wot after starting engine and it was my first time going to the dyno.

So bro whats that mean? I have not thought of that and nobody has mentioned that. Thanks

enoniam

Just means that it is possible that the MAF being maxxed out never caused it to cut out before because it's now cutting out after having seen the same issue on consecutive starts. If so you should probably be able to see something come up under HPTuners engine diagnostics regarding the MAF, clear the history, and then be able to run it without it cutting out whether or not you are using the MAF. If using the MAF the error will show up on the diagnostics but not trigger a limp mode unless you go WOT on the very next engine start.

veneno

that makes sense, Thanks man