Engine management mods

[19bonestock88]

I’ve been gone a while and recently lost my work car and messed up my red Saturn. I’m wanting to modify the engine management to be tunable, instead of messing around with sensors. I’m aware that full standalone EMS are available that can do all I need and more, however there is a snag in the form of the cars body control module. As far as I’m aware it needs communication with the stock PCM in order for it to work the other parts of the car (fuel pump, lights, cluster and all). I had thought of doing a dual PCM setup using both the E16a PCM from my Ion and a P11 PCM from an 03-05 Cavalier, with the advantage that the P11 is supported by HPTuners while my E16a is not. Ideally I’d use the P11 to run the engine and the E16a to run the BCM and cluster, de-pinning all engine controls from the stock PCM connector and moving them over, with the E16a only seeing coolant temp, crank signal and speed signal. However I’d need to duplicate the same signals to feed to the P11. Any good ideas guys?

[Ecky]

What all is run by the body control module?

In most Hondas of slightly newer vintage than mine, there's the ECU, and then a multiplexer which is the hub for most of the chassis electronics. Generally speaking, aftermarket ECUs support communication with the Honda multiplexer. I'd be shocked if there weren't something similar or equivalent for General Motors.

That said, for simplicity, it's usually preferable to either flash the (Honda)'s stock ECU, or to use an ECU from a very similar vehicle. E.g. the ECU from an Acura RSX is typically used in Accords, Civics and other vehicles from the era, because it can handle all of the same sensor and chassis communications, and has the most tuning options available to it. This sounds like it could be similar to the Cavalier setup you've mentioned.

Sorry I can't be of any more specific help. I might suggest that, if you use Facebook, send a join request to the Guild of EFI Tuners. They're generally a pretty good lot, and very helpful.

[19bonestock88]

The body control module runs EPS, lights, power locks, and other various functions. Basically it controls the entire body of the car. Most people in the Ecotec community on FB tends to prefer to use a different PCM than the P11 (newer ones use faster processing and higher resolution in tables and such but they aren’t looking for the signals coming from a first gen L61, meaning I can’t use them for my engine). I did ask the guild if I could just stick two sets of wires on the needed sensors and didn’t get a straight answer.

[Ecky]

My experience with sensors has been that sometimes it works, and sometimes if the signal wires go to too many places, it doesn't work.

For example, my VSS goes from my transmission to under the dash, where it branches to the ECU, EPS computer and dashboard. In line to the dash I have a converter that drops the frequency. I also tapped on that branch, but before the converter, for my aftermarket cruise control.

Recently I added a separate converter for the cruise control, to drop its frequency to a different range, and I found my reverse lockout and other speed-dependent triggers stopped working. I still had speed on the dash and EPS worked properly, but the ECU started seeing 0mph, until I disconnected this most recent device from the tree.

[19bonestock88]

How does the PCM act with seeing no speed data? I wonder if I could tune the engine to run optimally without VSS data?

[Ecky]

Originally Posted by 19bonestock88

How does the PCM act with seeing no speed data? I wonder if I could tune the engine to run optimally without VSS data?

It might be fine, or it might be something you can tune around entirely. I wouldn't call it a deal breaker. You might even be able to convert some essential signals over to the different signaling - I've had to do that with several.

I imagine some "variable" components of the engine, such as VVT, might take it into account by default. It might also affect how the engine drops down to an idle, but if anything this might improve fuel economy - most vehicles idle higher when rolling in neutral vs stationary.

[toc]

coolant temp, crank signal and speed signal

- Coolant Temp is usually resistance based. So you'd need to measure it on the new ECM as a voltage, leaving it in place on the old, but... then you need to calibrate a range for the coolant temp on the new.. Another way would be to add a second thermistor to the coolant temp for the new.

- VSS and Crank Signals are usually a binary pulse signal - sharing this can be done much like the OBDuino / MPGuino, feed the resulting signal to the control unit (the usual method of operation is for an active voltage to be fed out to the sensor, and the pulses are generated by the sensor closing and opening the circuit, so don't provide the old ECM with two wires, just one, and make sure it's the one that is the 'input' to it, not the voltage feeding out).

Note, I said old ECM in the above, because it's more reliable for the new ECM to have correct sensor data, since it's controlling the engine, the old, only needs that information for the RPM display in the car.

Sharing the VSS though won't *really* be an issue for the new ECM - it's only making economy decisions with it, not critical engine running decisions.
The other ECM might be sharing VSS info with other systems, like the BCM for display data to the instrument panel, but also, ABS / SRS units.

[19bonestock88]

Yeah I was figuring to just add a second coolant temp sensor that way each PCM got solid data. Given that the crank signal and VSS are just a pulse, would it even matter that the signal was split between two PCMs?

[Piotrsko]

It would depend on the threshold voltage requirements of the sensor, digital is either on or off, go too low, and the device stops "seeing" a signal change

[19bonestock88]

I figure this is gonna be a case of trial and error. I wish a tuner could guide me toward what I’m after but most of them are biased against the P11 PCM for some reason, and that’s the only other PCM that natively runs the first gen L61 in the US. My next engine is still gonna be a first gen L61, but modified a bit for higher volumetric efficiency. I need a different PCM because the planned engine is going to require a higher rev limit to extract all of its power potential and with a tunable PCM I could manage stuff like lean burn as well as the other stuff needed to fully utilize the engine