My 2003 986 S had its M96.24 engine replaced by a 2008 M97/21. It is using the original (986) exhaust, clutch, manual gearbox, and ECU. The flywheel and intake/throttle assembly came with the new engine.

The intake was modified with a cold air box and the new engine's 3.5 inch tube was used with the new engine's MAF.

The car seems to be running perfectly well at idle, the variocam-plus kicks in at 3050 rpm (increasing intake valve lift), and performance is noticeably better than the original 3.2 engine. It sounds and pulls OK.

However, I have a durametric which is giving me the following errors (the shop that did the engine swap assures me they will take care of these, but I thought I would share my theories on them and ask for your opinion):

• P1101 - Porsche fault code 594 - Input variables charge - measurement
• P1126 - Porsche fault code 356 - Oxygen sending adaptation - lower load range bank 1
• P1133 - Porsche fault code 358 - Oxygen sending adaptation - lower load range bank 2

From what I understand, these indicate that the car is running lean. Assuming there are no air leaks (from e.g., a faulty Air-Oil Separator) these are my theories on possible causes:

• The 986 MAF reaches a limit and it cannot enrich the mixture further, even though it senses the high airflow corresponding to the M97.21's increased capacity and larger intake (this would require a change in the injection timing map?)
• The 987 MAF cannot be used with the old Motronic 7.8/20 ECU because, even though it corresponds to the intake's diameter, the voltage values it sends are for the newer 7.8/40 ECU.
• The old Motronic 7.8/20 ECU gets confused while the variocam plus is operating in low RPM mode, since the ECU has no concept of such a mode. So, while the intake valve lift is low, the ECU mistakenly interprets data from the exhaust oxygen sensors as a lean condition.

I realize it must be unorthodox to use the old ECU with the new engine but, assuming it is not an option to change it, what are your comments on the situation?

Many thanks for your valuable input,
Costas

PS: I also get a "check battery/generator" warning on the dashboard sometimes on startup, which I presume to be due to the M97/21's higher wattage generator (2100 vs 1680)? Charging voltage was measured at 13+ and the battery stays good.

 

Swapping in a much newer engine can be a problem. Generally, either the Ecu from the car with the donor engine wants to be used or a new Ecu for that MY car bought and used in the car receiving the engine or the existing Ecu in the car receiving the engine needs a reflash to accomodate the differences between the original and new engine.

Unless the original engine and the replacement engine have identical features (like VarioCam Plus) the original Ecu can have difficulty with the new engine.

Is the new engine larger in displacement? While the stock Ecu has a great deal of adjustment: +/- 25%; it might not have that much to accomodate a much larger engine. If the adjustment gets to +/- 10% an error code can be set. What are the long term fuel trims when the check engine light comes on and the P11XX error codes are present?

Research the Ecu replacement or reflash but before you spend any money be darn sure you have eliminated more basic things. These include no intake air leaks - always suspect when any intake system touched -- and that the fuel delivery system is 100% ok. Fuel pressure, fuel flow are on the money.

Also, ensure the exhaust system has no leaks. Any leak can let in outside air which can affect one or more oxygen sensors which can affect engine fueling.

Not sure what to make of the alternator issue. A larger alternator with more output could account for the warning light, I suppose. But before I sourced an orignal alternator to see if that eliminated the problem I'd first eliminate more basic things. And that includes making sure the battery's in as good a condition as it can be.

Sincerely,

Macster.

 

Thanks for all your suggestions! I do understand that the new ECU is the right way to go but, for now, I will have to try updating the old one if necessary. They are reasonably close (Motronic 7.8/40 vs 7.8/20), though the new one does have a faster processor. The two engines are also close: the M97/21 is a 3.4L derivation of my original M96/24 3.2L. The M97/21 was used in later Boxsters (and in the Cayman).

There is no check engine light. I found out about these errors only because I have the durametric cable to check for them. The "check battery/generator" warning however is visible to the driver (it could very well be that the battery is on its way out - it is about two years old).

I will see if I can gather some real-time data through durametric to answer your question on fuel trims. I didn't know of the 25% ECU adjustment range you mention. That is valuable information, thanks. The engine capacity difference is about 6-7% (3.4L vs 3.2L). However, the 987's intake is larger also (3.5 inch diameter vs 3 inches in the 986). So, it could be that the 10% threshold you mention is reached. It would be good to know if the ECU does have a greater range to compensate for the increased airflow, despite the error codes. At least then the engine would not be running lean.

The 35 extra hp that the new engine is supposed to produce (albeit on a 987 with the proper ECU and exhaust) does seem to be present on my car as well. It is noticeably quicker. The old engine was also very well maintained so it is reasonable to assume that it was putting out around 260hp (and therefore I am comparing correctly).

One thing I noticed about this new engine is that at around 5200 rpm it begins to pull more strongly - although it is no slouch from 3500rpm either (when the variocam plus switching provides a "kick"). This is not visible in the engine's power/torque diagram, though the change in torque at 3500rpm does show:

 

Well, I'm a firmware engineer -- though I do not write engine controller firmware (but I do write automotive test equipment firmware) -- and I would not assume the two firmwares are the same.

I've never used the Durametric software package so maybe it has something that detects the Ecu firmware version number and deals with the variations appropriately?

If not then even the error codes may not be valid and reliable. You need to be sure your data is valid before you can hope to trouble shoot what's going on.

Also, if the old engine controller microprocessor is slower than the new one -- which is clearly an indication the two Ecus and firmware images are not the same, they differ considerably would be my WAG -- the old engine controller microprocessor may not have the cpu cycles or processor bandwidth or the hardware clocks to accomodate the needs of the newer engine and its faster processing demands.

I'm thinking you need to find someone who's successfully grafted the engine you have into the MY car you have and pick his brain as to what's going on.

Could a new firmware flash or custom firmware flash will do it. But it could require something more.

Sincerely,

Macster.

 

Yes, I know what you mean. There is no question, the firmware is different. I am hoping that the engines are similar enough for the old ECU to be able to operate the new engine. So far, there seems to be a decent chance of this as the car is running great (with the exception of those three fault codes which don't however cause a check engine light).

If the fault codes are because the engine is in fact running lean, due to ECU mismanagement, then I am hoping that someone reading can point me to the correct map :-)

Durametric is a diagnostic software with a cable, able to read and clear fault codes for different ECUs depending on the Porsche model you specify. As for the data being valid, there are no vacuum leaks I think. One question is how the new engine's MAF voltage values are interpreted by the older ECU. I am also hoping that someone reading can confirm that the MAF output voltage range is the same. It seems fair to assume that it is, since the 987 S was using my older engine variant and ECU (M96 and 7.8/2) until MY07.

Thanks again for looking into this!