M20B25 Running Lean ?!

Post Sun Oct 12, 2014 11:50 am

il cut to the chase

87 m20b25 the idle is a little iffy, but it pulls well and sounds and feels smooth through the revs. until you reach about 4500 and it just feels a little empty.
it is completley standard. ive had the injectors cleaned and rebuilt by injectortune,
now it was taken to a dyno test just so i could see how healthy it is and if it was reaching standard ponies, and its not, it made 132bhp and 165lbft torque. il put a copy of the test graph up later on.
ive since changed the fuel filter (the old one was a long cylinder, new one is a oem m20) and changed the plugs to bpr6es, the electrodes on the old plugs were white.
the engine is coming out this weekend due to a bump/pothole hit at 60mph (didnt see it due to fog!) collapsed my offside supension, broke clean in half my offside engine mount, which all caused the engine to move hitting the viscous against the radiator, (both fecked) and the sump to hit the ground and crack! oh the joys....so il be going over with a fine tooth comb and cleaning/replacing things to see if it will help with the running lean issue,
so is there anything specific i should be looking at, can somone diagnose me a reason why it would be running lean and il go through them all ! or should i be worried about a bigger issue of why im losing 38bhp !
many thanks for help in advance

Post Sun Oct 12, 2014 12:12 pm

First checks would be blue temperature sensor, and a compression check - each cylinder should read in the region of 160-180 psi.

http://www.e30zone.net/e30zonewiki/inde ... or#Testing

How many miles has it done, and has it always run like that while you've owned it?

Post Mon Oct 13, 2014 8:27 am

These engines should really sing at around 4000 rpm.
My first instinct is also to check the blue temp sensor, also check for any crack/splits/air leaks in the rubber boot connecting the air flow meter to the throttle body, also check valve clearances as they may be very sloppy.

Post Mon Oct 13, 2014 1:15 pm

the blue temp sensor and rubber intake boot are both brand new, theres no air leaks that i can find, im going to go over every pipe once the engines back out,
i did an engine swap from a m40b18 to m20, i was told it had done about 90 thousand miles, ive only had it running/ driving for about a month and its been like it that whole month, obviously changing somethings made it a bit better but that hesitance/ emptiness is still there.

do you know what the valve clearance discrepancy is ?

Post Mon Oct 13, 2014 1:28 pm

eric792 wrote:the blue temp sensor and rubber intake boot are both brand new

That doesn't mean that the sensor is working, or that the wiring to it hasn't been damaged in some way (especially corrosion at the C191 plug). Get access to your ECU and test the blue temp sensor from there. If you need help, it's all in the wiki.

Post Mon Oct 13, 2014 1:32 pm

Is the rubber cap intact and in place on the unused stub pipe under the throttle body, next to the TPS?
Check that the timing belt isn't one tooth out.

Post Mon Oct 13, 2014 1:56 pm

The valve clearance for a M20 is 0.25mm/ 0.010in. when cold. Obviously it is important that the clearances are correct but I doubt it is the main source of your lack of power. Just another thing to check.

Post Wed Oct 15, 2014 5:04 pm

Grrrmachine wrote:
eric792 wrote:the blue temp sensor and rubber intake boot are both brand new
That doesn't mean that the sensor is working, or that the wiring to it hasn't been damaged in some way (especially corrosion at the C191 plug). Get access to your ECU and test the blue temp sensor from there. If you need help, it's all in the wiki.

Good point, i think it was from euros ;) says it all really ! il get onto to checking that then ! thanks

Brianmoooore

PostPosted: Mon Oct 13, 2014 12:32 pm
Is the rubber cap intact and in place on the unused stub pipe under the throttle body, next to the TPS?
Check that the timing belt isn't one tooth out.

i havent checked that yet but i will do thanks for reminding thats there! what is that pipe for btw ? il will be changing the timing belt this weekend so il see if thats jumped or not too.

Carmo13

PostPosted: Mon Oct 13, 2014 12:56 pm
The valve clearance for a M20 is 0.25mm/ 0.010in. when cold. Obviously it is important that the clearances are correct but I doubt it is the main source of your lack of power. Just another thing to check.

cool thankyou, yeah i was thinking of checking them before anyway because i have no history on the engine, so i just like to know everything is tickerty!

cheers for your help guys, il get checking and testing !