kwack

Hi,

I have an MY99 which had teh Prodrive kit fitted. Niow I am tradign in the car and selling the Prodrive bits. I have taken off the "T Piece" and fitted the standard one back on.

I have taken off the ECU and fitted standard back on. The problem I have is that when I rev the car and then come to a standstill the revs drop below idle and then come back up again, with a bit of float on the idle, this didn't happen before.

Any ideas on this and do I need to reset the ECU or something?

Any help appreciated

Cheers
Kwack

jpmason33

Use the search function and look up ECU Reset. This will enebale you to check any error codes on the ECU. It does sound rather like when my MAF was knackered, the ecu codes confirmed mine.

PS What are you selling the PPP for? V. Interested

Eprom

Looks like the Maf to me also, sometimes it will not show up until the ECU is re-set, which you have basically done by putting in the original ECU, the select monitor may not also find this as an error code.
If you want to sell the T peice send me a PM, i have fitted a PPP to MY99, and didn't know the restrictor was changed as part of the upgrade.
Thought it was intercooler pipe work, ECU, and remove middle CAT.

Found my MAF was faulty when i went from AE801 to PPP same problem as you MAF fixed it.

Hope this helps.

kwack

I have already got someone lined up to take the ECU and "T Piece" so unfortunately already taken.

Just for background information - what is teh MAF sensor and where is it located and how much? I don't fancy changing it unless I really have to as it is going next Saturday. It is strange that it did not happen before and only when teh ECU was changed? Does that make sense?

Kwack

jpmason33

The MAF sensor on the MY99 is in the the small black plastic box connected to the Airbox on the left side of the engine bay. It is about £70-80 from subaru dealerships (just get the sensor not the whole box). Its reasonably easy to fit (10mins) but you will need some security Torx bits to undo it.

MAFs of MY99s are well known for being very fragile. Are you running a induction kit?

The old ECU would have compensated for the failing MAF and therefore it may not have been noticable on the original ECU. The new ECU has not compensated for it therefore the problems!

A word of warning, a failing MAF can cause the engine to run lean and then you run a higher risk of Detonation.


James

kwack

Thanks for the response

I am unclear why a Prodrive ECU would hide a failing MAF but when replacing back to original would show this. What is so different between the two that would make this occur?

If it did not occur on the Prodrive ECU but was failing then potentially I have been running the risk of det for some time. Eventually what would have happened if the car did nto give any warning signs?

Kwack

Luminous

iTrader: (3)

Modern ECUs are capable of learning what your engine likes. I cannot explain this in technical terms as I know little about engine management

But the way it works is that there is a computer program within the ECU. It looks at what is happening in your engine, and compares this to values that it has stored. If your engine is not behaving as it expects it to, it alters some settings in an attempt to make the engine behave. When one of the things it chanages makes the engine function properly, it remembers this setting.

This learning process depends on how well written the software is, and therefore varies from car to car. The more recent cars having more advanced management systems.

As an example, you had the Prodive ECU fitted when all was fine. Over time the MAF sensor may have started to fail. The sensor still gave readings, but there were not perfectly accurate. The engine management system will have learned from the incorrect running of the engine how to compensate for this over time.

Fitting the new ECU means that this learning process has to start again. It should be able to compensate, but it may take a few goes for it to get it right.

The problem is that ECUs can only compensate so much. They are not very bright, and can only do so much to compensate for things that are not working correctly. They are also limited by the sensors that are attached to them. For example the knock sensor detects det, but struggles to do this at high revs. If the MAF sensor has been failing, then it is possible that the ECU has not reliased that there was a problem at high revs, and has therefore left the engine running lean. This can result in considerable engine damage.

Its a common issue for the MY99 model, many people here change the MAF sensor more often than recommended to try and avoid this problem.

If the sensor fails completely, then it will realise and the engine check light will come on. If it fails gradually (as it appears to have), then if you keep running the car flat out the engine will basically destroy itself

Of course, our resident troll does not believe any of this. Pete is firmly in the camp that the ECU will know when the MAF is dying and will adjust itself accordingly. As you can see, this is not alwayst the case

kwack

Thanks Luminous for the reply. Well written and has answered my concerns.
Many Thank
Kwack

Luminous

iTrader: (3)

I'm just glad I had a coherent moment

(you are quite welcome)