Intending to do fuel only TBI on 4 cyl aircraft engine

[lgrant]

2Many, you, and your associates, are terrific resources - again this is great information. The SDS MPFI system I referred to above had a cockpit adjustable system (a readout gauge and dial) to allow the pilot to tinker with the AFR and that must be using a potentionmeter. I find that far more desirable than using a ECM lean cruise mode. So let's all of us eliminate the lean cruise requirement when considering an ECM.

Configuring and programming the ECM is my weakest area but I'm eager to learn. Regarding 8 cyl vs 4 cyl, if one does not need the ignition, it seems like the most critical setup feature would be to be able to specify the presences of just one injector - the 1 bbl on the 4 cyl vs the 2 bbl on the larger engines. Does the 7427 lend itself to such a specification?

Initial Summary:
1227427: fastest and probably most popular; probably most info available
1227730: has 4 cyl program and may be desirable for both migrating to marine ECM and also adding ignition later on.

Let's consider adding to this list and listing features I haven't thought of.

QUESTION: the intake manifold on a 4 cyl Lycoming is integrated into the oil sump/pan (and then tubular runners go from the oil pan to the cyl head/intake ports) and there isn't much opportunity to install sensors, etc. In order to install a GM single bbl TBI, I will probably have to devise a 1" to 1.5" extension from the existing carb flange to the TBI mounting flange. Can a MAP sensor be installed in this extension area which will be very close to the throttle body? or does it need some distance from the throttle body?

Thanks,
Larry

[dave w]

Initial Summary:
1227427: fastest and probably most popular; probably most info available
1227730: has 4 cyl program and may be desirable for both migrating to marine ECM and also adding ignition later on.
Thanks,
Larry

The correct part number for the '7427 PCM is 16197427.
The 1227730 and 1227727 have identical electronics and can use the same binary codes and memcals. The 1227730 is common to "under dash" installations or inside the car. The 1227727 is designed for "under hood' use for weather resistant applications.

The '7427 has two spark tables and two fuel tables Near Idle / Off Idle. The parameters to switch between Near Idle / Off Idle tables are TPS and MPH.

GM ECM's / PCM will need a Distributor Reference Pulse (DRP) telling the ECM / PCM what the engine RPM's are. The ignition module will convert the AC sine wave coming from the distributor pick up coil into a square wave signal for the ECM / PCM.

dave w

[lgrant]

Thanks Dave for the clarifications. I think one of the electronically identical installations is the way to go for me.

All,
I took a day off to clear my head. But now am planning a trip to P-N-P to see what parts can be gathered from a 1227727 doner car (a 4 cyl GM 90-92 W body platform - Lumina, Regal, G.P. or Cutlass Supreme). Probably an unnecessary question but where should I look for the ECM number? Any advice on what not to overlook?

Additional thought: Most all aircraft have a master switch that kills power to everything at the end of the day. Will that be problematic - will the ECM lose it's custom settings and default to something that looks for a lot of stuff I won't have? If necessary, a special circuit could be rigged to keep the ECM powered - would prefer not to have to do that.

Question: is there a practical limit to how long a runner can be in a TBI setup? I may have one approaching 24". That's from carb mount flange (soon to be a single bbl TBI mount flange), going through the oil pan and then coming out and up to the intake port. The good news is that the tubular runner is perfectly round and with nice smooth curves. The air should be flowing pretty well. I guess the end result is not likely to be worse than the carb installation.

Please send your suggestions for the scavenger hunt. I'll be off the air for a few days trying to process all this.
Thanks,
Larry

[steveo]

Additional thought: Most all aircraft have a master switch that kills power to everything at the end of the day. Will that be problematic - will the ECM lose it's custom settings and default to something that looks for a lot of stuff I won't have? If necessary, a special circuit could be rigged to keep the ECM powered - would prefer not to have to do that.

absolutely not, in any sane ECM, the calibration is flashed or written onto a prom and is not lost when power is cut

some values (long term trims for closed loop, iac position stuff, maybe a few other details) are stored in ram and will be reset to a default value, also specified in the calibration

it would be a good idea to tune those defaults to be appropriate, though... for example i found my car likes an inital IAC opening of about 45 steps, but the default keep-alive was a little bit low. once i bumped it up, it was a lot happier if i disconnected power to the battery (since it has to 'learn' idle operation a bit)

that kind of stuff shouldn't bother you, you probably dont want an IAC at all, do you

[dave w]

Thanks Dave for the clarifications. I think one of the electronically identical installations is the way to go for me.

All,
I took a day off to clear my head. But now am planning a trip to P-N-P to see what parts can be gathered from a 1227727 doner car (a 4 cyl GM 90-92 W body platform - Lumina, Regal, G.P. or Cutlass Supreme). Probably an unnecessary question but where should I look for the ECM number? Any advice on what not to overlook?

Additional thought: Most all aircraft have a master switch that kills power to everything at the end of the day. Will that be problematic - will the ECM lose it's custom settings and default to something that looks for a lot of stuff I won't have? If necessary, a special circuit could be rigged to keep the ECM powered - would prefer not to have to do that.

Question: is there a practical limit to how long a runner can be in a TBI setup? I may have one approaching 24". That's from carb mount flange (soon to be a single bbl TBI mount flange), going through the oil pan and then coming out and up to the intake port. The good news is that the tubular runner is perfectly round and with nice smooth curves. The air should be flowing pretty well. I guess the end result is not likely to be worse than the carb installation.

Please send your suggestions for the scavenger hunt. I'll be off the air for a few days trying to process all this.
Thanks,
Larry

There are advantages / disadvantages to intake runner length. Ideally equal length runners for all cylinders would be preferred. Some of the newest engines have long runner / short runner designed into the intake manifold. I don't remember which is best for high RPM, I'm thinking short runners. TBI is wet flow, so keeping the fuel air mixture moving at a high velocity is mandatory!

dave w