Mod memcal jumper DRP 2 to DRP 4 on 16197427 ECU

**rsicard** · 02-01-2015

Gentlemen:

Performed jumper mod per HP tuners article jumpering Pin 56 for going from DRP 2 to DRP 4. After mod was done, plugged in 16197427 ECU into 1994 Big Block Suburban and it ran rough as though in limp home mode? Removed jumper from Pin 56, plugged ECU back in, started Suburban and it ran smooth. Pin 56 is the sixth terminal over from the left per the picture from HP tuners article. Wondering what went wrong. Maybe someone here can shed some light on the situation.

**1project2many** · 02-01-2015

I had to look at your other posts to figure out what you're doing. Have you made the software changes to select the correct fueling mode? Hardware change alone is not sufficient.

If you've been tuning the PFI intake in TBI mode then you might not be delivering enough fuel if you cut the injection pulses in half.

**rsicard** · 02-01-2015

Originally Posted by 1project2many

I had to look at your other posts to figure out what you're doing. Have you made the software changes to select the correct fueling mode? Hardware change alone is not sufficient.

If you've been tuning the PFI intake in TBI mode then you might not be delivering enough fuel if you cut the injection pulses in half.

Thanks VERY much for the reply. Have started with BJKW binary and have smoothed binary same per directions on this site. Also jumpered current sense resistors and inserted jumper per instructions in HP tuners picture on this site. With the jumper installed, the engine ran rough. Did not monitor the exhaust with a Wide Band EGO. Should have and then I would know that it was trying to run on too lean a mixture. This is an Edelbrock TBI to MPFI conversion. Edelbrock (502 cu in 29 Lb/Hr kit) did not specify to modify the ECU hardware. They only supplied a supplied chip to be installed. The 454 was bored out .030" and stroked to 4.25" for 489 cu in. This was done some 8 years previous and at the time bought Craig Moates APU1 stuff to tune it not knowing what the hell I was doing. Today it has become much clearer through folks like yourself what SHOULD be done to tune older GM EFI. Would VERY MUCH appreciate your thoughts on this matter.

**rsicard** · 02-01-2015

Originally Posted by 1project2many

I had to look at your other posts to figure out what you're doing. Have you made the software changes to select the correct fueling mode? Hardware change alone is not sufficient.

If you've been tuning the PFI intake in TBI mode then you might not be delivering enough fuel if you cut the injection pulses in half.

What you have said is what I have surmised. Did not adequately answer your post. No, software changes not made to correct fueling mode. Only found a binary that yielded something closer to a smoother and cleaner/leaner running engine. Understand that doubling the time between injector pulses will yield a leaner mixture. Now, if successfully getting it to run on the 4 DRP versus the 2nd DRP, by what approximate percentage should the on-idle and off-idle tables be enrichened to start with? Just a good guess will do. Then can go back, install the memcal jumper, correct the BJKW binary on and off-idle tables by some percentage and then start retuning from that point.

**1project2many** · 02-01-2015

Now, if successfully getting it to run on the 4 DRP versus the 2nd DRP, by what approximate percentage should the on-idle and off-idle tables be enrichened to start with?

That's a great question. If the code is operating in PFI mode (this is selectable in software) it will adjust synchronous pulsewidth to deliver the correct amount of fuel for synchronous delivery based on the number of injection events. But whether or not you need to make additional changes depends on how you've adjusted / affected asynchronous fueling. Fuel delivered asynchronously is independent of DRP's. It is event triggered and is based on table values and clock "ticks." With asynchronous fuel delivery in mind the answer, of course, is "Enough."

BTW, in synchronous TBI mode the injectors do not fire every second DRP. There are two injector drivers, each one alternates firing on every second pulse, which causes one injection event with each DRP. If Edelbrock has utilized both injector drivers then (presumably) half of the injectors are firing with each DRP.

This page describes fueling modes and selection on the hardware / memcal side and presents the only source of reference information we have for fueling modes. The information appears to have been scanned from GM documentation and does have some errors but this is what we've been working with.
https://web.archive.org/web/20030204...ECM/inj_op.htm

**rsicard** · 02-03-2015

Originally Posted by 1project2many

That's a great question. If the code is operating in PFI mode (this is selectable in software) it will adjust synchronous pulsewidth to deliver the correct amount of fuel for synchronous delivery based on the number of injection events. But whether or not you need to make additional changes depends on how you've adjusted / affected asynchronous fueling. Fuel delivered asynchronously is independent of DRP's. It is event triggered and is based on table values and clock "ticks." With asynchronous fuel delivery in mind the answer, of course, is "Enough."

BTW, in synchronous TBI mode the injectors do not fire every second DRP. There are two injector drivers, each one alternates firing on every second pulse, which causes one injection event with each DRP. If Edelbrock has utilized both injector drivers then (presumably) half of the injectors are firing with each DRP.

This page describes fueling modes and selection on the hardware / memcal side and presents the only source of reference information we have for fueling modes. The information appears to have been scanned from GM documentation and does have some errors but this is what we've been working with.
https://web.archive.org/web/20030204...ECM/inj_op.htm

Thanks very much for the info. How does the ECU determine asynchronous versus synchronous? Is the mode set via a hardware jumper, or is it set in the ECU binary file via Moates APU1 Autoprom and TunerPro RT software? I will go back and further review TunerPro RT software. You are a great resource on this subject.

**1project2many** · 02-03-2015

Ugh...
Software can select
Hardware can select

Software when program working
Hardware in backup mode

Asynchronous is primarily for transitions such as AE, stall saver. It's a means to deliver event based fuel when needed.
Synch for all else.
Some calibrations (4.3 V6 tbi) set for asynch all the time. They don't run well.

**1BadAction** · 02-03-2015

Originally Posted by 1project2many

This page describes fueling modes and selection on the hardware / memcal side and presents the only source of reference information we have for fueling modes. The information appears to have been scanned from GM documentation and does have some errors but this is what we've been working with.
https://web.archive.org/web/20030204...ECM/inj_op.htm

^ Someone needs to save that HTML file to the server here. I'll probably post it on my boat forum under the tow pig section also... That type of info is GOLD.