M20 - New Head, Low Power

[AWDBOB]

Have you tried a new set of plugs? Most fuel wet plugs are fouled.

Lorin- this is a fresh set in a fresh build that I'm trying to diagnose a low power issue on!

[digger]

is that oil on #1 and #5?

[TobyB]

...and it sure looks like it was running rich before it was shut down. When an M20
is running right, the plugs always
look to be right on the edge of lean to me, and yours are quite fat.

fwiw.

t

[LJ851]

Lorin- this is a fresh set in a fresh build that I'm trying to diagnose a low power issue on!

Yes, and fouled plugs will reduce power output quite a bit. Plugs are cheap and easy to replace.

As others have already mentioned, also verify cam timing and dyno test it to prove the power level is low. I have seen cam timing a tooth off on other engines affect the fuel mixture quite a bit.

[AWDBOB]

is that oil on #1 and #5?

Yes it is wet with oil. Some of them only on one side of the tip of the plug.

I rechecked compression again last night just for good measure, both 1 and 5 were even, right at 150psi.

...and it sure looks like it was running rich before it was shut down. When an M20
is running right, the plugs always
look to be right on the edge of lean to me, and yours are quite fat.

fwiw.

t

Yes, and fouled plugs will reduce power output quite a bit. Plugs are cheap and easy to replace.

As others have already mentioned, also verify cam timing and dyno test it to prove the power level is low. I have seen cam timing a tooth off on other engines affect the fuel mixture quite a bit.

Thank you for the plug info! I should've been more clear in my initial response regarding the plugs! The head has been low on power since I installed it with new plugs. Pulled the plugs after a few hundred miles and they looked like that.

BUT I am installing new plugs today because I obviously will not reuse them. Also am going to verify cam timing again today (last time I checked was March of 2015 when I last had the car in my possession).

I am thinking of throwing in the stock injectors and chip because it really appears as if the car is running rich, and I had those few issues with the chip from the get go.

[TobyB]

^ good idea.

Plugs that look like that will clean right up if put into an engine that's running right...

t

[squidmaster]

Hey there, I've seen issues similar to this with bad injectors. Either one/some injectors are firing at such a different rate that fuel compensation sends the other's out of consistency to even out the AFR (assuming you have an o2 sensor plugged in and installed).

Did you get the chip from BH? I believe most of what they carry is for the M50 injectors, which run less than 17.5lb on the M20 FPR, and the chip is intended to match that.

One way to get a little bit of an idea (though not definitive) is to take an IR thermostat to each of the header primaries to check for EGTs. While all we get is the temperature conducted by the exhaust manifold, any large differences would point toward a difference in combustion mixture. Not definitive, but it might give you a spot to start checking.

Running the stock injectors (14.5) on a tune for the M50 injectors (~16.3 @ 3bar), the ECU can correct fueling enough through fuel trims, as long as you have the o2 feedback. Could be another path of troubleshooting.

If the injectors are bad and you go for a new set with different flow ratings, give me a shout for a reflash will definitely make sure you're setup right

However the oil on the plugs could mean a bad gasket or seal. Oil in the combustion chamber can raise CR as well, as it fills in the gaps that caused any loss. I'd try new plugs first. Cheap and easy (like me)

[squidmaster]

But yes, the 280/274 cam will take a little low-end away, and give it to the top-end. Better for track, but for daily driving it's more Italian style power.

[AWDBOB]

Hey there, I've seen issues similar to this with bad injectors. Either one/some injectors are firing at such a different rate that fuel compensation sends the other's out of consistency to even out the AFR (assuming you have an o2 sensor plugged in and installed).

Did you get the chip from BH? I believe most of what they carry is for the M50 injectors, which run less than 17.5lb on the M20 FPR, and the chip is intended to match that.

One way to get a little bit of an idea (though not definitive) is to take an IR thermostat to each of the header primaries to check for EGTs. While all we get is the temperature conducted by the exhaust manifold, any large differences would point toward a difference in combustion mixture. Not definitive, but it might give you a spot to start checking.

Running the stock injectors (14.5) on a tune for the M50 injectors (~16.3 @ 3bar), the ECU can correct fueling enough through fuel trims, as long as you have the o2 feedback. Could be another path of troubleshooting.

If the injectors are bad and you go for a new set with different flow ratings, give me a shout for a reflash will definitely make sure you're setup right

However the oil on the plugs could mean a bad gasket or seal. Oil in the combustion chamber can raise CR as well, as it fills in the gaps that caused any loss. I'd try new plugs first. Cheap and easy (like me)

But yes, the 280/274 cam will take a little low-end away, and give it to the top-end. Better for track, but for daily driving it's more Italian style power.

Thank you Jesse!

Cam timing was on- I am really leaning towards injectors at this point. I have a spare set of green tops that I'm going to send out for a rebuild and then swap in (as I sold all of my stock injectors a while back).

The plugs weren't soaked by any means, but plugs 1 and 5 were definitely wet when the other ones were all light brown (which is still on the rich side, I believe).

Thank you for the response, and I will PM you in regards to the chip.