I have a 1980 Chevy Malibu with the 229 V6. This is a predecessor to the 4.3 V6, but it's an odd-fire motor. It was recently rebuilt, but the carburetor is about dead, and I'd like to move up to EFI. I have a 7730 and a donor harness on hand.

I've successfully converted a couple of cars to EFI, but it was just sensors and wiring; someone else took care of tuning. I can learn that, but I wanted to find out if there might be an insurmountable problem before jumping in.

Can a P4 handle an odd-fire motor in software? If not, would it work with, say, an even-fire crank trigger to fake the RPM signal?

If I have to I can leave the original distributor in place and try a fuel-only if I have to, but I'd like to have the spark control features if possible.

 

This would also require an even fire style crank signal to the ECM, otherwise the RPM would fluctuate.

So it would be a fuel only set up.

Or, can an even fire crank & cam be used?

RBob.

 

No, there was no even-fire variant of the 229. It might be possible to cobble something up, but swapping in a 4.3 would be cheaper. Since the 229 is only about 9,000 miles since rebuild, I'd like to leave it in there.

I can add an even-fire crank trigger and move the pickup coil from the distributor to the front of the motor, but the GM system figures the timing offset from each distributor pulse, so that wouldn't do me any good, right?

Would it start without the distributor hooked up, or would this involve a bunch of reprogramming to get it going to start with?

 

The issue is that the ECM uses the previous cylinders reference pulse to fire the current cylinder. Which is why the ECM based spark won't work on an odd fire. I even thought that maybe a custom trigger wheel and DIS would work (waste spark). But that is a real can of worms.

The ECM requires a distributor reference pulse to fire the injectors. So something is required. That same signal is used to calculate the engine RPM, which is used in many places of the ECM.

RBob.

 

Well, rats. Solving that one is well beyond the skill level of a beginner like me.

I think I'll slope off to one of the Ford forums and see if there's any trickery that can be done with one of the EDIS coil-pack systems. If I understand how they work, the coil pack is "smart" and has separate advance and trigger wires. Of course, the Ford stuff is way more complicated and expensive than the GM bits. <sigh>

 

RBob,

What did GM use on the early CCC Q-Jet fed Turbo 3.8 engines in say a 1981 Turbo 3.8 Monte Carlo. Weren't those old Buick engines odd fire as well?? Also worth noting a 3.8 Chevrolet V6 was CCC Dualjet fed as well with EST controlled timing. I don't know if it was a distributor modification, a module or even something in the ECM coding.

 

No, all the turbo Buicks were even fire. Hmm, an online source says some of the later 229s had the electronic carb and CCC.

<much searching of parts-store listings and web pages> Best as I can tell the CCC 229s used the same 7-pin module as anything else.

The magic must have been in the computer.

Okay, if the base timing on an ordinary TBI is zero, how do you get any advance? The ECM can't fire the coil before it gets a pulse, so it's calculating a delay off the previous pulse, right?

But how would the CCC box manage that? Or am I completely wrong on how advance works in the TBI?

 

CCC is computer controlled carburetor. I don't know of any odd fire engines with ECM controlled timing.

The distributor in an odd fire engine has offset trigger points. This sets up the proper firing point on a per cylinder basis. Which also means that the distributor phasing to the crankshaft is important.

With the regular run-of-the-mill TBI engines, they are all even fire. So the distributor trigger points are evenly spaced. This allows the previous trigger point to be used for the current cylinder being fired.

RBob.

 

Duh, right. I was thinking "ESC", not "CCC". I'm not showing any listings for the odd-fire V6 with ESC, though the even-fire Buick and the 4.3 Chevy used it.

 

ESC (electronic spark control) is the knock detection & reporting system

EST (electronic spark timing) is the ECMs control of the spark advance and dwell. Although, not all EST systems control dwell, in many DIS systems the dwell is controlled by the ICM.

RBob.

 

I just educated myself on the 231 with some reading and the older engines were odd-fire, but the stuff from 1977 and newer are even fire.

The 229 definately had a CCC Carb and EST 7-pin distributor with the flat 4 wire connector.

I thought the timing control on the EST was just an offset amount via Pulsewidth modulation, rather than an actual reference pulse. Its been a few years since I have looked at the EST module operation in my GM manuals so forgive me if I am wrong.

I am sure the magic is in the distributor itself. The pickup wheel probably runs in inverse to the cylinders being fired, in that its running the reference pulse, 1 cylinder ahead of the actual engine, so that when the next cylinder fires, its at the proper timing. Just my theory. I would have to look at the trigger/pickup coil to tell you for certain.

 

You know', thinking about this (what you posted), it may be that the distributor is phased to a cylinder in advance. This would put the DRP (distributor reference pulse) at the proper point for the upcoming cylinder to be fired.

Ack, I'd need to draw some diagrams or such to see if that would work. The whole kicker is that the ECM converts SA in angle (degrees) to a time base (usec). This is why having the "number of cylinders" parameter correct is so important.

The only other piece of the puzzle would be to average two (or three?) DRP intervals to get the true engine RPM. The TBI ECMs (and others) use the time between DRPs to calculate the engine RPM. With an odd fire these would vary as to which set of cylinders are being fired. So average it between two (or three?) for the proper RPM.

Or, maybe it didn't matter that much as they weren't firing injectors, but just doing a look up for SA.

RBob.

 

Personally I'd just add an even fire pickup to the distributor or crank and run a 730 or whatever in regular 6 cylinder mode for fuel only and do the ignition in traditional non computer controlled fashion.
If you could hack the ccc ecu for the 229 (ecu# 6024 or 775500 I think) then you could use it for spark control, but it may at that point be much simpler to just swap in a more modern 3800 (the most produced engine ever IIRC).

I edited out my previous post, I mis-read the beginning and thought you had a 231 buick. I never realized this early chevy 90* V6 was also odd-fire.

 

I can make an even-fire crank trigger to get an RPM signal. What will the ECM do when it tries to diddle the spark advance and nothing happens? Will it just set a code and keep going, or will it go into some kind of limp-home mode?

 

ECM won't care, just need to un-set the code 42 malfunction flag in the calibration.

Note that the EBL P4 on a 6-cylinder is going to be for a MPFI set up. If going 2-bbl TBI then the standard EBL Flash ECM needs to be used.

RBob.

 

I almost hate to say it, but for this application it looks like MegaSquirt might be the best candidate, since it supports odd fire engines. There seems to be some difference between how MS/1 Extra and MS2/Extra need to be triggered for spark control, but it's worth a look. I don't know if MS3 supports odd fire engines or not.

 

That's the ticket!


What's an EBL P4? If it's a "Lockers", why would I have to have it?

 

Yeah, there are fancier Megasquirt models that will do it, but they're a lot more expensive than the GM bits, particularly since I already have them.

 

Got me there With the "P4" in the title my brain read that as EBL P4, which is based on the '7730/'7749 ECM. They are both the GM P4 series ECMs.

Nope, no need to have to run an EmBedded Lockers system. There is also the '7060 PCM which is in the P4 family and runs a 4L80E along with a 2-bbl TBI.

RBob.

 

Isn't the 7427 in the P4 family as well? The 93-98 style TBI/4L60E ecm. 97-98 for Export only.

 

Yes, those are in the P4 family, but because they also have trans controls, the control structure (code) is different than the MPFI ECMs (I.E. '7730/'7749/etc).

 

They are a P6 PCM. I was wrong on the '7060, it too is a P6.

I did some research to find out what defines an ECM/PCM as a C3, P4 or P6. It is the processor that is used. The C3's use the GMCM (General Motors Custom Microprocessor). It is a variant of the Motorola 6801.

A P4 ECM uses a GMP-4 CPU in a 52 pin PLCC package. It is a variant of the 68HC11A1 processor.

A P6 PCM uses a GMP-6 CPU in a 68 pin PLCC package. It is a variant of the 68HC11F1 processor.

There were rumors of a P5, but that appears to have been caused by folks finding "P5" in the etch of the circuit boards.

There are also P66 PCMs such as the LT1 '8051. This PCM uses two of the GMP-6 processors.

RBob.

 

A1 is the basis for the P4? i've never been able to get a real defining answer on that one before.

AFAIK, there were really only 3 P66 units, 94-95 LT1/L99, 93-95 Northstar, 93-95 3100/3.4RWD. of course, there were slight revisions to all of them at one point or another, but same basic layout.

 

Interesting, I haven't heard of a "P6" ECM/PCM before.