Super rich running Motec

[dsfnctn]

It seems like my Motec powered 3.4 was running just fine when I parked it over a year ago. When I started it up it is now running super rich. Even doing a compression test I could see fuel comming out into gauge. I know the first thing someone will ask is what is the fuel pressure. There are less and less people now working on these old air cooled motors which is why I figure ill have to learn the system and fix it with some outside help. I am now sourcing the specialized threaded adapter to read the pressure at the rail. I was told that the Motec was set and forget. Problem at my age I am behind in the computer assisted world and it is not easy to find at every street corner someone that can just simply plug the laptop in and have a look without having to sell me a set of close ratio gears and new upgraded brakes. Also the M4 is a bit outdated.
Any help would be appreciated. The compression is great and the motor wants to have a run.

[jpnovak]

Usually a suddenly rich is due to a failing sensor. This would be for all EFI types. Here are the most common.

Check the MAP sensor lines to make sure the are not cracked or pinched. This will tell the engine it is running WOT all the time.

Check the Temperature sensors (you might have two). Failed open (high resistance) typically means the engine is cold and enrich the mixture

Check for reference voltage at the TPS. No reference voltage usually means the TPS thinks it is WOT and will enrich to compensate.

Do you have a PC interface? This is the fastest way to look at these values.

BTW, any Motec tuner/operator should be able to plug in and diagnose very quickly.

[jpnovak]

BTW,

You can download the latest M4 release tuning software here:

https://www.motec.com.au/software/latestreleases/

[dsfnctn]

Hi Jamie
Thank you for taking the time to reply
You have inspired me to try to understand the system.
Thanks for explaining

[spuggy]

You don't say how long ago the conversion was done, and how many miles you drove it/variety of conditions? I'm wondering if the warmup cycle was actually "perfect" before - and if ambient temps are exactly the same now?

It could be as simple that the warmup cycle (which takes time/iterations to tune, and you only get one decent shot per day) isn't quite right - either for the conditions, what you're doing now (starting but not driving), or you're simply noticing now that it needs adjustment.

In addition to checking the output of the temperature sensor(s), you may want to look at where they're located, and any tables that control the warmup cycle (usually modifies fuel trim, maybe timing too).

My M800 conversion originally used a temp sensor in the chaincase; With a lot of oil volume and a big FMOC, it was pretty futile to try to get sensible warmup with that sensor alone - it lagged head temperatures by too much - 10 minutes or more.

Fudging it with a "time-after-start" enrichment table wasn't satisfactory either. Especially on hot re-starts - with no meaningful temperature input, you'd always get excessive enrichment...

Once I fitted a 3.2-style cylinder head temperature sensor, it was pretty obvious that an air-cooled motor doesn't need enrichment once CHT is at 60C, and mine hits that a minute or so after start, even on very cold days. But if the ECU has no way to "know" that, the motor can run pig-rich until it does...

[icarp]

Is the system really a Motec ? or the original Bosch Motronic . If it is Motec who did the conversion ?
They would be able to offer some guidance . Keep at it , sounds like you have the sprit to learn and become one with your 911. Post a pic of your injection and engine , that might help.
Ian

[safe]

Originally Posted by jpnovak

Usually a suddenly rich is due to a failing sensor. This would be for all EFI types. Here are the most common.

Check the MAP sensor lines to make sure the are not cracked or pinched. This will tell the engine it is running WOT all the time.

Check the Temperature sensors (you might have two). Failed open (high resistance) typically means the engine is cold and enrich the mixture

Check for reference voltage at the TPS. No reference voltage usually means the TPS thinks it is WOT and will enrich to compensate.

Do you have a PC interface? This is the fastest way to look at these values.

BTW, any Motec tuner/operator should be able to plug in and diagnose very quickly.

+1 on a failed sensor.
I had a "coolant" sensor that failed and that screwed around with me for long time until I found it.

Any tuner should be able to help, most can move between different systems.