Hi guys,

Mods are. RMW tune, headers, cam, injectors, one ball and 17% pulley. Also meth.

I have has since installing the cam and tune. A slight stumble at idle every few seconds. Very slight but noticeable like a miss.

Also on my obd reader my long term fuel trims are minus 10% on throttle and minus 14% at idle. Does this mean the car is trying to lean itself out? Worried of blowing something up at high rpm running lean!!!

I have been through everything. Correctly timed via timing case off method. New coils. New plugs. New wires. Vacuum leak found and fixed via pressurising system. Fuel pump primes on start up. Brand new oxygen sensor pre cat correct ntk one. Full compression test with 150 Accross the board. Leak down test too with 17% across all cylinders give or take four percent.

It happens without meth running too.

I'm stumped.

Any ideas? And will I be ok with those fuel trims taking it on the track??

 

I don't know much about fuel trims but how do your spark plugs look? that's the most sure fire way I know to evaluate how rich/lean a motor is running.

 

Running minus trims on longterm trims makes sense with meth....
You are pumping meth for fuel...
So the fact long-term fuel trims...what the computer is fueling +/- from the ECU make makes sense...the ECU just adjusts the fuel based on info from the first o2 sensor data....
Sometimes a little bit of data is dangerous..... If you have a miss, look at the mechanics of what's going on....

 

Only real thought....when was the last one you had the valve cover off?
Shot in the dark...maybe a bad valve spring or lifter? Cam with?
Change the knock sensor?

 

The plugs when I took them out looked fairly lean to be. A bit white etc. same with the oxygen sensors they seemed fairly white too.

The leak down test was fairly solid, was using that to weed out the possibility of a burnt valve or dropped valve, of I had a weak spring wouldn't it show up there?

I have had the meth turned off for a half a tank of gas now and no change to the fuel trims.

This may also help, this is the tune with the lamba graph. It was tuned with a slipping belt and I hadn't found that vaccum leak at the green supercharger inlet crush gasket yet so don't know if it will affect it. The lamba indicates rich, so I wonder if the factory Ecu is compensating for this?

Really loving your help guys and girls, please keep helping and nutting it out with me

 

Fuel trims are for closed loop compensation to maintain stoic fuel/air (lambda = 1). Bigger injectors are causing the trims to adjust negative to do this.

The new cam probably has more valve overlap, which increases "internal EGR" and degrades combustion stability at low loads. The later intake valve closing point reduces the effective compression ratio, further degrading combustion stability at low loads. That can explain the idle miss.

I was finally able to read your graphs and the lambda readings look perfectly normal for a power run with your mods. (Starting at 3000 rpm) it's a bit leaner than the OE calibration above 4500 rpm, but that's how Jan cal's them with those mods., as the pre-cat delete and exhaust mods lower EGT's

 

Thanks so much for your informative reply! I'll stop looking for issues that don't exist now. Very expensive especially when you have a obd reader. If I didn't have one I probably wouldn't have noticed hahaha