Tweecer question?

[Axianator]

On my '97 I have to set the 1-2 shift point at 38 mph which is .5 mph above the stock setting. At this setting and with stock line pressures on the 1-2 shift the actual shift happens at 50 mph. The mph setting is the only reliable way to get the car to shift at the speed I want as the rpm parameters have little effect.

I can safely say that I have never seen a vehicle that shifted 12 MPH over the commanded value.

Is this behavior unique to your SHO, or have you observed it with other Gen 3 SHOs?

As I was told this is because things are happening too fast for the processor to get the info and do anything about it in time based on rpm data.

This problem used to be an issue with some early 12 MHz and 15 MHz EEC-IV units. In fact, V6 MTX cars could effectively raise their "hard", PIP-based rev limiter by several hundred RPMs simply by fitting their SHO with a lightweight flywheel.

However, the excuse that "things are happening too fast for the processor [to sample]" has not been applicable to any Ford since the advent of 18 MHz (and faster) computers. With regards to SHOs, this fact has held true since the adoption of the H3Zx and D4U1 computers on the '93-'95 ATX SHO, all of which used 18 MHz processors and can reliably sample sensor data up to 7,000 RPMs.

 

[SHOZ123]

This is with all the V8s I have tuned. Perhaps the shift strategy look up logic has changed?

The other WOT shift parameter of rpm I have never got to work correctly. It would always overshoot. I will say that I have been advised by the mainly SCT Mustang tuners to change the N/V ratio when I had the different FD gears and this did nothing too. Might be unique to the V8 programs?

With the different FD gear the shift points for the 1-2 shift I set to 37 mph.

Stock the 1-2 mph shift point is 37.5 mph. Clock speed on the first generation of G3 PCMs is 21 MHz. On the second generation it is 24 MHz. The 2nd generation PCMs have the stock 1-2 shift points at 37.5 mph.

I do have the shift happen at around 7050 rpm for the 1-2 shift too. Lower rpms for the other gears.

This is with the same gear ratios as the G2 ATX SHO. The tire size is 225/55/55 stock.

 

[Axianator]

This is with all the V8s I have tuned. Perhaps the shift strategy look up logic has changed?

It's very possible. Quite honestly, I think your "delayed shifting" phenomena has more to do with calibration quirkiness (and, in the case of your specific vehicle, your final drive ratio changes) than it does with processor clock speed.

The other WOT shift parameter of rpm I have never got to work correctly. It would always overshoot.

That's a better result than the WOT shift point scalars in our D4U1 calibration. Our parameters don't have any affect on WOT shifting!

I will say that I have been advised by the mainly SCT Mustang tuners to change the N/V ratio when I had the different FD gears and this did nothing too. Might be unique to the V8 programs?

Given what I have seen and heard of SCT's mapping for the V8 calibrations, it would not surprise me if they had incorrectly mapped the location for the master N/V ratio scalar.

With the different FD gear the shift points for the 1-2 shift I set to 37 mph.

What was the average variance in actual vs. commanded shift speeds with your stock gearing?

 

[SHOZ123]

I am currently using stock gearing so 38 mph commanded and actual 50 mph at 7050 rpm.

With the 3.98 gears it was 37 commanded mph and 44 mph at 7000 rpm. But I don't know how accurate the speedo was. The speed readings are what is being reported to the PCM and then logged. IIRC the speedo was off by about .05 miles per mile judging from the odometer reading and the measured mile.

And I really don't know if the rpm settings ever did anything. At least they did not before hitting the rev limiter.

 

[Sho Amo]

is there anything besides the knock sensor that would pull timing? sometimes my car doesnt feel like it pulls very well. sometimes the tach goes to 7k nice and smooth and other times it looks like it stumbles a bit on its way up.

would i be able to tell through datalogging with the tweecer if i have the timing belt off by 1 tooth? i used the mtx tensioner and the mtx timing belt marks but ive always felt like the car doesnt have as much power as it should.

 

[SHOZ123]

IIRC the mtx PCMs only pull 1 degree timing from the KS tables.

There are other sources that the timing can be pulled from depending on the data from the ACT, ECT, and the MAF sensors.

 

[Sho Amo]

this is a 91 w/ x2j btw.

act? ECT is engine coolant temp? and i have cleaned the maf a number of times. guess ill try putting in a new one.

anyone got anything for my other questions?

 

[SHOZ123]

Yes if they are reading low or high they may be parameters in a table somewhere.

You can rig up a back probed set of wires that you can run to the interior then connect a digital volt meter to. That way you can compare your real time data with a know value.

The sensor may be bad but not far enough out to the range to set a code. Or better to log, if you can, the PCM inputs for the sensors. Then you see what the PCM sees.

I should say on thing I have see when trouble shooting through data logging is that the info all looks good but there is a definite problem you can hear and feel in the car. Usually this is a hardware problem that has nothing to do with a PCM input or output.

I had a guy who's car I tuned and it would run great. Until it was warmed up good and out on the highway. If you floored it above 50 or so then it would stumble and miss. Let off and it ran great. 1st & 2nd at WOT great, only in 3rd and at WOT.

The fuel pressure would be low at WOT in the lower gears (above 30 lbs) but the aerodynamic load put an added strain and the fuel pressure would drop to 20 lbs. For what ever the reason it could not flow enough at the highest loads. Data logs looked great but you are only seeing the commanded outputs.

 

[rubydist]

IIRC the mtx PCMs only pull 1 degree timing from the KS tables.

There are other sources that the timing can be pulled from depending on the data from the ACT, ECT, and the MAF sensors.

While I haven't played w/ the SHO pcm's yet, all the Ford obd2 pcms that I have played with would pull 1 degree per event (per knocking cylinder) up to a limit of 10 degrees in their stock form. I'd be surprized if the SHO pcm only allows the knock sensor to pull 1 degree total - can someone confirm that?

 

[SHOZ123]

Yes you are right it is as you say. Here is the retard table and the max allowed is -8 degrees.



What I have seen when logging is you will never make the timing back if you start getting the KS going off. Even if you past the point of the pinging.

 

[rubydist]

That matches my experience too - the pcm will pull timing speedy quick if it actually sees knock - it can pull all 8 or 10 degrees of timing in 2 or 3 revolutions of the engine. Then, it adds it back in at a rate of 1/4 degree per second, so it takes 40 seconds to put those 10 degrees back in!

When I tuned the Ranger, I set it up so it pulls timing out at 1/2 degree per event, and puts it back at 4 degrees per second, so that it actually puts the timing back in after it stops seeing knock. As long as the timing gets pulled 2x as fast as it gets put back in, you will be okay, imho. btw, the 2x factor is typical GM programming...

 

[SHOZ123]

I will set the retard to -15 and then slowly add timing back to log and find where the pinging was.

Always seemed to be at peak torque.

 

[Sho Amo]

that fuel pressure issue sounded interesting. ill try getting a fuel pressure gauge rigged up.