7427 install, first impressions

[EagleMark]

Glad you got it tweaked!

The throttle kicker may be in Govenor TBI pictured earlier, maybe not? But there is another one that is a solinoid just like old days bolted onto TBI and kicks the throttle linkage. It's activated by another control box simalar to one that controls EGR. If the guy sends pictures I'll post them up.

One of these days since you worked out the issue with timing, you should turn it off again and see if it does do something else in PCM other than activate soliniod.

[gregs78cam]

I just got my truck up and running on a '7427 with a TH350 and thought I would add a tip, Pin B6 on this PCM is listed as "not used" but it is infact a 5V reference output. So don't mix it up with the CTS sensor input that goes in pin B8, it causes some issues.

[JeepsAndGuns]

Dont guess we need to ask you how you know this....

[EagleMark]

Dave W just found another pin mistake when using the 16197427 with the 700r4, so we are going to have to redo that write up properly...

[EagleMark]

I just got my truck up and running on a '7427 with a TH350 and thought I would add a tip, Pin B6 on this PCM is listed as "not used" but it is infact a 5V reference output. So don't mix it up with the CTS sensor input that goes in pin B8, it causes some issues.

I just looked at the 16197427 wiring diagram and it has nothing from B6... so the directions we have in the 7747 to 97427 are correct, right? You just misplaced a wire?


Just checking because Dave W is making the change he found in the write up.

[dave w]

Dave W just found another pin mistake when using the 16197427 with the 700r4, so we are going to have to redo that write up properly...

I've done 4 of the '427 PCM this year. Three were TH400, one was a 700R4. I'm having trouble with getting 700R4 TCC to work. The original write up from TGO is for a TBI F-Body. Subsequent posts after the original TGO post state PIN E11 is to be used for the 700R4 TCC control. I have not changed the wiring from E10 to E11 to acknowledge the wiring change will fix the TCC problem I am experiencing.

I added notes to show what differences I found on Full Size Pickups vs the F-Body car. The conversion works as written. I have not been able to find a published wiring schematic showing either a 1994 or 1995 application using PCM '427 PIN B6. I'm sure that a volt meter has confirmed that PCM '427 PIN B6 is a 5V reference, but I'd like to see an actual published wiring schematic showing B5 being wired as a 5V reference.

For TH400 applications that had 1228747 ECM's, I've installed 1973 ~ 1986 TH400 kick down switches on the accelerator pedal, that are wired to supply Ground to the kick down relay.

dave w

[gregs78cam]

Yea it was my mistake, I made a spreadsheet from the swap info in TGO, some time before the article was posted here, and I screwed it up. Small mistake. But yes with key on B6 shows 5.0 Volts.

[EagleMark]

Man you had me worried I had to go through this harness I already did, it's hanging on the wall with the PCM ready to put in my kids truck. Since it already ran on my bench and I watched data in TP while emulating I couldn't figure out how that wire for CTS was wrong... it's for a manual trans so I wouldn't have the issue Dave W found for 700r4. Don't understand the issue Jeeps andGuns is talking about because I got data... but his ALDL was from 7747. So I think he found P3 to P4 data (orange wire) is in a differant spot in ALDL port. I never looked and rewired from stock wiring schematic.

The harness I started with was from UnKnown? Plugs wouldn't fit 7747, 427 860... but it had heated O2 and wires for electronic tranny... and some other weird stuff I had never dealt with, I think it was out of a FWD car...

Anyway good work guys! We know our wiring conversion pin out is accurate!

Greg, is that spread sheet worth posting in the 7747 to 97427 thread?

[JeepsAndGuns]

Before I installed my ALDL plug, I removed all other wires from it other than the two datalog wires and the ground. One wire is white with a black stripe, the other is orange and I think it had a stripe too, but cant remember. Mabey the 7747 had a stripe, and the 7427 didnt. Its pouring down the rain right now or I would check. I just swapped the pins on the ecm connector and never touched the aldl plug.

[gregs78cam]

Greg, is that spread sheet worth posting in the 7747 to 97427 thread?

I'll PM you with it, and you can tell me.

[JeepsAndGuns]

Thought I would add this nice little tidbit of info I have found out while tuning.
As we all know I am running this pcm with a manual trans. Earlyer were were talking about this "throttle kicker" and when I have it disabled, I would have trouble pulling out. I would have to rev up more than I should and feather the throttle as I was letting out on the clutch. Turn it on and it would work a lot better.
But I have always had this slight drop in rpm's as I was pulling out. It was like the engine was straining to pull out. It never did this with the old 7747. I did some tweeking and changing of my idle spark table and it improved it a good bit, but it was still there.
To try and keep the story short I tried a couple diffrent bins a couple weekends ago. They both did a lot worse in other areas and all around, but one thing that was better, it didnt have the drop in rpm's when pulling out. So I started searching for the reason why. I simply copied over my fuel and timing tables, so it shouldnt be them.
I stumble across this scaler close to the bottom of the scalers. Its in the section labeled "IAC AE, PE, DFCO paramiters" In that section there are two scalers called lower and upper threshold for IAC AE.
The bin I am using (BMHK) was set as 3.1% for the lower, and 10.2% as the upper. The other bin had it set as 2.0% for the lower and 2.3% for the upper. So I figured it was worth a try, thinking that as I was pulling out, the IAC was opening and this might give it more fuel when doing so, thinking it might just need a extra shot of fuel when pulling out.
Burnt a chip and gave it a try. BLAMMO, it now pulls out smooth and no more drop in rpm, it now just pulls and goes! Watching the datalog dash as I pull out I can see the AE become active for a split second as I am letting out on the clutch. So its simply giveing my engine what it wanted, witch was just a little extra shot of fuel when pulling out.

Mabey this might help someone in the future.

[EagleMark]

That's exactly what it did! AE (Accelerator Enrichment) is your accelerator pump like on a carb! You gave it more AE, I'll bet the manual bin has more AE range in IAC then Auto bin?

[gregs78cam]

I don't have TP in front of me right now, but I thought there was a bunch of stall saver stuff in the '7427. You might look into those as well. I know that in my '98 Grand Am with the 5 speed it is not easy to stall the engine because the IAC, and fueling helps to prevent it, i.e stall saver. You should be able to ease out of the clutch with out giving it any go pedal without stalling. If it was happening when you add pedal, then yes the AE was needing some tweaking.

[JeepsAndGuns]

Yea the stall saver is working as far as I know. If I put it in first (this is a wide raito trans, aka granny gear 1st) I can let out on the clutch without touching the gas. But first is not normally used in normal driving, you pull out in 2nd. But in first the iac will open so as to keep the rpms up/keep it from stalling. In 2nd it would do that too, but it just always had that dip in rpm's. It just needed a little extra shot of fuel. I have noticed the 7427 pcm has way better iac logic than the old 7747. The iac even seems to work faster.
I dont think I have ever actually looked at any of the stall saver paramiters. I may check them out next time I have the laptop on.

[EagleMark]

It has more IAC logic and ever thing else because it has a bigger chip. The IAC is faster because 7747 is 160 Baud rate and 7427 is 8192 Baud rate. 160 Baud is like ever 1.2 seconds and 8192 Baud is so many times a second I forget?

Stall saver on 7747 I had to turn off for a an Off Roaders who wanted complete control of low RPM driving during rock crawling, they would lug and engine and it would rev up because stall saver kicked in, same guy new engine with 8192 baud system on new engine in same rock crawler said he wanted it turned off and I said to try it first, I had already drove it, lugged engine trying to stall with no rev up issue... no need to turn off it works so much faster he can not notice it working. Actually he said is was much easier to crawl because the engine had a rock solid steady RPM at idle and very low RPM he had to do less to operate engine driving and spends more time looking at and planning obsticles driving... although the engine needed a tune do to non stock engine build like cam headers etc... all I did was fuel and spark... there is so much that does not need to be touched on the newer 8192 baud TBI systems.

Next time I work on his truck I am going to look at the AE difference you found that fixed your issue, seems to be something that would improve this type of driving...