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Discussion Starter #1
I decided to remove my ecu and check the mosfets as described in BillJ's webpage.

I got some odd results, middle pin (to the metal part of the fet) on each resistor read 0ohms the right hand pin approx 8-9M ohms.
The left pin, infinity on the right hand fet, and 8-9Mohms on the other 2.

So, should i replace them all?

Mosfet MTP3055V is mentioned.. Is this the original item? What properties of the FET is important to match?

Chris
 

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Personally I read across the transistor (measuring between the two outer pins) getting a short circuit (0.0 Ohms) on one where it should have been open circuit.
The lowest reading I gained on what I consisdered to be a good transistor was around 0.1 MOhm (100k Ohm and plenty high enough to act as a switch still) I guess this was due to the surrounding circuitry allowing a certain amount of leakage, the other one was in the MOhm range.
Why measure in this way? Well the outer pins are the input and output of the transistor and the centre pin turns the transistor on and off. If the transistor is allowing current to flow when it ought to be off the APC valve will have a constant current to one of its' coils which will blow it in a short time (each APC coil is around 2.5 to 3 Ohms, at 12 volts this will give a 4 amp current, and the fine wire that forms the coil doesn't like that sort of current for long).
I replaced the one faulty transistor I found by this method and all has been fine since.


Have you got a problem with your APC solenoid?

Nick.
 

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Discussion Starter #3
HI, thanks for the info.

Ive got a problem with inconsistent boost, and also a misfire. I thought it would be worth looking at while i had the ecu out. Ive no previous experience of testing ecu components, and ust followed the proceedure i read.
 

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Ahh, Well I'd measure the resistance your APC coils (one each side of the centre pin of the APC solenoid connector, as mentioned abover they ought to be 2.5 to 3 Ohms each). If this is correct, you have voltage at the APC solenoid (centre connection at 12v with ignition on), and with the car moving along you get more than base boost then there is nothing electrically wrong with the APC system. However you might have an issue with the internals of the APC solenoid 'gumming' up causing fluctuating boost levels.

Since you mention missfire as well, I'd go for checking it out with a new/proven DI before going any further.
 

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Discussion Starter #7
Yes, correct plugs at 1.1mm.

Misfire intermittent, happens 85% of time. At all throttle positions, full throttle, part, cruising and occasionally overrun. will also do it on cruise control.

Ok, ive done some more measurements on the mosfets...
Taking resistance measurements between pin give similar results for the following combination.

the 3rd fet from the front, when measureing beteen the 2 outside pins were 7.08Mohms, and the other 2 fets gave 0.1Mohms exactly, could that be a problem?
 

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0.1MOhm is 100,000 Ohms, quite enough to act as a block to the current path, and also the same as I found on one of my FET's (I believe this figure is measured because of components that surround the FET and if taken off of the circuit board it would measure M Ohms by itself). My duff one was quite obviously faulty at 0.2 Ohm or thereabouts. I really don't believe your FETs are faulty. All this would lead to is an incorrect boost pressure anyway.
I think the fact that you have a bad missfire points at the DI / plugs still. Try another set of plugs and a known, good DI if at all possible.
 

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Discussion Starter #9
Im not sure where ill be able to get another di to check it with, how possible is it that i happen to get another DI with the exact same fault?
Would a faulty Di also cause the car to boost to 1.4-1.5 bar one day then underboost the next? i can understand how a faulty di or plugs could trick the ecu into thinking its knocking and thus reduce boost, but im not sure how it could Up the boost?
 

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Hi sorry to bump this post .. but is okay to test ecu pins also ? my dmm in 2K ohm selection I get .. from ecu pin 2 to 25 , 442 ohms aswell on Pin 25 and 26 431ohms .. I dont get any other numbers on any higher ohm selection on my dmm. working mosfets numbers should be atleast in Mohms ? I guess I have burnt mosfets ?
 
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