Which P4 PCM should I use

[CDeeZ]

I lowered those values to around 3K RPM and tested, they were in fact the cause. I've set them as high as they'll go now.

I still get code 24.....

I swapped gauges recently, from the "moonie" (88-90 C/K) style gauges to the later style cluster with needles (91-94 C/K). Everything works with the cluster, but at random intervals the speedo will jump up to some MPH much higher than actual speed the vechile is traveling. I wonder if this could be causing that error? All wires were soldered (like always) and everything else with the cluster works, but I wonder if its related to my code 24 issue?

What would be the benefit, if any, if I were to disable that error code in TunerPro so that it cannot be set by the PCM?

[CDeeZ]

What do you guys think I should do about the code 24? I thought about unchecking the box for that error code in the bin inTunerPro so that it cannot be set and stored as an error.

[gregs78cam]

I personally would try to figure out why the speedo is jumping, and remedy that, which will also eliminate the error code. It sounds like your twisted wire pair from the sensor are picking up a stray spike. Might check that the wires are twisted together along their entire length. When soldering those I usually go as far as to remove them from connector, solder, shrink, and re-twist them right up the connector.

[CDeeZ]

Thanks. I will check the twisted wires for the VSS, see if I find anything there. The older style gauges never had this speedo issue and the VSS and wiring for it have remained unchanged since. You think that it sounds like a spike being picked up by the VSS? It's been a few days since I swapped gauges, but IIRC, the DRAC itself has both VSS wires going into it (or out of it depending on how you look at it) and I know that when I installed the newer DRAC with the newer gauges, I didn't twist the VSS wires as they were coming out of the DRAC, didn't think I needed to. They should be twisted up everywhere else though. Maybe the VSS wires near the DRAC are picking up electromagnetic interference from something else in the dash.


I was looking at the only two known manual bins for '7427, BHDC and BMHK and BOTH of these bins have error 24 disabled! It appears as if code 24 – low transmission output speed is something that pertains to E-trannys, and not stick shifts.


On the 747 to 427 conversion thread it is said: “output speed not from DRAC set”. What exactly does this mean? I believe I've read that this PCM can take VSS signal with or without DRAC, so which one is better? Right now I've got a DRAC in the mix (obviously). What would be the point or advantage to bypassing the DRAC and feeding the VSS directly into the PCM? How is this done? I have a 40 PPR reluctor wheel in my transmission if that matters.

[EagleMark]

The manual bins are from $0E and a 4L80E trans with 2 speed sensors, not $0D for 4L60E. Only need DRAC for speedo, cruise and ABS

[CDeeZ]

Yes those bins use $0E mask, but I thought that BMHK and BHDC were for 5 speeds & not 4L80s, since it lists that in the full bin name in the fileman?

And by the way Mark, correct me if I'm wrong here, but didn't you guys end up running one of these binaries, either the BMHK or BHDC for your sons '427 $0E?

I'm going to try an experiment: copy all my changes so far from the bin I've been working with ($0D-BJLH.bin) fuel tables, injector constant, cylinder volume etc. etc. and give the $0E a whirl with either BMHK or BHDC. Maybe it will be better?

[EagleMark]

We did use an $0E maual bin and Code 24 is off.

[CDeeZ]

I gave a 454-5spd bin a try after copying my VE and spark tables, spark biases, injector flowrates etc. It didn't seem to run right so rather than mess with that I reverted back to the BJLH 5.7/60e bin. I also have turned off code 24, at least for the time being.

Today when I had some free time I took the dash apart and removed the gauges. I took the two wires for VSS, hi and low speed signals, and twisted them up from the DRAC all the way to the wiring harness as it disappears into the dash. I also checked the VSS wires under the vehicle and they seem to be sufficiently twisted to keep out unwanted electromagnetic exposure, RFI or whatever we should call it.

On a side note, while inspecting the VSS wires under the truck, I found what appears to be a broken transmission mount on my T56. Either that, or it has come unbolted somehow. I think this tranny mount has been rattling for some time. I don't know how I didn't discover it sooner than I did. Probably because it's been so hot for a while now that I don't wanna crawl on the scorching pavement under any vehicle.

It was 104* F in the SHADE today here in the OK

[EagleMark]

You really shouldn't be playing with Spark Bias from mask to mask or even bin to bin in same mask! For example using Spark Bias from $42 5.7L to $42 7.4L you are now off by 9.8 degrees in main table. Only another 100 possibilities to think of...

Just looked at $0E and compared 5.7L to 7.4L and same thing, 9.8 degrees off in main table, now how does that effect coolant temp spark, PE spark, Decel Spark, DFCO etc...? Way to much for me to rule out or attempt to work with...

Weather here today was 80's and thunder storms, feels like Louisiana or Florida (no big bugs yet, but first time I have ever seen slugs cover the sidewalks at night?). We never have thunder storms this time of year? Watch the news and or grain belt is in horrible drought? Ha! Our farms are still under water. Still cutting grass twice a week without watering.

[CDeeZ]

I thought if I copied the spark tables AND the biases it would be ok. I though the place one might get into trouble is if you copied the spark tables but not the biases! No matter, I went back to the 5.7/60e bin I've been working with and I'll probably continue to use that since I've had the best luck with it.

I wish it was 80's and stormy here. Yeah it is incredibly dry here, needing some rain pretty bad. It's been so hot and dry the grass hasn't been growing all that fast. I guess extreme heat and lack of water will do that.

[dave w]

I've adopted the practice of using a starter .bin that is close to the intended application as possible! I understand that is some applications the "close" starter .bin file is not going to be very close. Usually there are settings with Deceleration Fuel Cut Off (DFCO), injector voltage offsets, and choke settings that WILL cause some serious CHALLENGES if the starter .bin is not very close! For me the easy part is the spark and fuel tables, but figuring out how to set DFCO so a consistent exhaust backfire will not blow out a muffler is not an easy fix! To date, the most challenging "Tunes" I've done have been with SBC 383's!

dave w

[CDeeZ]

Yeah that makes perfect sense. I actually have a a backup copy of my base bin that I started with, saved as "starter.bin" so I know that's the bin to revert back to if I make some changes that don't pan out, plus that bin already has my basic settings adjusted : Initial Spark, Injector-LBS/HR, EGR-disabled, etc. etc.

It sounds like you might be speaking from experience on blowing out mufflers? Yikes! I can only begin to imagine how difficult it would be to tune a 383 SBC since the "closest" thing would be some kind of 350.bin
and even that I'd guess would be pretty far off due to the significant difference in engine displacement.

By the way dave, since you brought it up, what specifically are some of the challenges you have faced when tuning for a 383? Just wondering.

I've kicked around the idea of building up a 383TBI to replace my 350 TBI, but the 350 seems to have tons of life left in it (thankfully!) so even that wouldn't be any time soon likely.
As cool as a 383 would be, I think when the time comes for a replacement for the TBI-350 I should finally drop in my LQ4

[dave w]

By the way dave, since you brought it up, what specifically are some of the challenges you have faced when tuning for a 383? Just wondering.

The quick answer, EVERYTHING! Choke, DFCO, AE, PE, 4WD LO (when equipped) and Emissions (when required) are the real time consuming challenges.

dave w