M90 rebuild (rudy)

[4pointslow]

In open loop the PCM commands a slightly richer than stoichiometric mixture.
Closed loop the pcm tries to adjust the A/F based off of the O2 sensor readings.
Keep in mind that OBD1 is slightly stupid, it can not detect misfires like OBD2 can.(OBD2 looks at fluctuations in the crankshaft speed).
When there is a misfire lots of oxygen ends up in the exhaust making it look lean when it may not be, so the pcm would add fuel when it is not needed.
OBD2 can tell if there is a misfire and go into open loop so it doesn't adjust to the bogus O2 readings.
That is just one of the weird scenarios that can happen.

An A/F mixture of 10:1 could foul the spark plugs in minutes, check the plugs.

 

[jd4242]

I would stop driving it until your tuner gets that adjusted tune for you.
Without seeing any data I may not be of much help.
Pull the plugs, see if they are black(fouled) or clean.
Weird things can happen when the mixture is not correct.
Pull the dipstick too, smell the oil on the dipstick.
If it smells like fuel change the oil.

Driving a vehicle with the A/F way off can lead to engine damage.
An overly rich mixture can cause lots of fuel in the oil from normal crankcase blowby entering the crankcase.
Fuel in the oil can thin it out and ruin bearings.

To check fuel pressure you could hook up a gauge and watch the pressure.
Make sure there are no exhaust leaks, if there are in front of the O2 sensor it can wreak havock with the A/F mixture.

Thing is i dont think its a tune issue. .something is causing it to flop back and forth..

I know rich or lean can cause damage and i havent been driving it far or running it long..i maybe have 30 mins on motor total and that 4 or 5 different short trips..

Oil and water look good,no smells or signs of anything. .plugs look like what af gauge reads depending on when i pull them,ive pulled them 3 times just to make sure gauge wasnt off..

Yea first step is gonna be read what bs codes it will give me..2nd is check fuel pressure and 3rd is going to be the O2 that i couldnt get out so i pulled the exhaust, i may have damaged it trying to get it loose..

If all that checks then tps,iat and coolant sensors. .

If all that checks then i guess all thats left is the tune but i need to make sure all thats good before i keep hassling my tuner..before it was just running lean which is understandable considering this motor draws twice the air,but now its going back and forth and sometime running fine so im lost

 

[jd4242]

In open loop the PCM commands a slightly richer than stoichiometric mixture.
Closed loop the pcm tries to adjust the A/F based off of the O2 sensor readings.
Keep in mind that OBD1 is slightly stupid, it can not detect misfires like OBD2 can.(OBD2 looks at fluctuations in the crankshaft speed).
When there is a misfire lots of oxygen ends up in the exhaust making it look lean when it may not be, so the pcm would add fuel when it is not needed.
OBD2 can tell if there is a misfire and go into open loop so it doesn't adjust to the bogus O2 readings.
That is just one of the weird scenarios that can happen.

An A/F mixture of 10:1 could foul the spark plugs in minutes, check the plugs.

What does it start in??open loop?? Because when it first starts and runs for about 3 mins it runs PERFECT. .perfect af and smooth as baby..then it flops to being super lean..and bounces back and forth from 16-17 and will slowly work its way to about 14-15..then depending on its mood it will run either really lean wile cursing or really rich..last 2 trips it did both 4 times before just picking one to stick with,either so lean wont run or so rich it wont run..

Im about to unplug a O2 and see what it runs like in open loop all the time,least that would tell me its a sensor right?

 

[vroomzoomboom]

was going to say crapped out FPR?

 

[jd4242]

was going to say crapped out FPR?

I have 2..the stock one on the rail and one after that which runs my nitrous. .i doubt both are bad but definitely a bad pump is in my mind..

I know i need to do more test but figured id get some suggestions and knowledge/direction from yall first..lol

 

[vroomzoomboom]

or could it be a bad vacuum line going to the FPR causing it to jump around? it is boost referenced after all

 

[jd4242]

or could it be a bad vacuum line going to the FPR causing it to jump around? it is boost referenced after all

Guess should explain little better..i have 2 fpr..the stock one on rail which is vacuum reference and has a one way valve in line to protect from boost..the 2nd is in the return line currently mounted where the ac was,it is boost reference. ..i did have 2 gauges..one is electronic and screws in at Schrader valve..and 2nd is in the 2nd fpr..the electronic one is broken and the 2nd on i took off and screwed a line into the hole to feed my nitrous. .but before both guages went bad i had them both set to same psi at idle and both adjusted fuel preasure to same level, for most part the boost reference one adjusted slightly more because boost would continue to increase where vacuum stops..

Ive checked all the lines and wires to where im seeing double,they all seem fine and when i runs good i pull good vacuum and have no misses or stumbles. .it literally runs soo smooth..then goes to **** and cant make its mind up

 

[gmanpaint]

Temp sensor? It does take part in AF mixture. Just a guess, since you haven't mentioned it yet.

 

[4pointslow]

Vehicles always start in open loop.
Unplugging the O2 sensor is a good way to force it to stay in open loop.
That will keep A/F at a slightly richer than stoich when all is working correctly and tuned etc.

The coolant sensor causes weird things as well so that too is a good place to check so that is good advice.

Get one of those gauges hooked up to fuel pressure and see if that is steady like it used to be.
Can you read the fuel pressure while driving or only at idle?

 

[jd4242]

Vehicles always start in open loop.
Unplugging the O2 sensor is a good way to force it to stay in open loop.
That will keep A/F at a slightly richer than stoich when all is working correctly and tuned etc.

The coolant sensor causes weird things as well so that too is a good place to check so that is good advice.

Get one of those gauges hooked up to fuel pressure and see if that is steady like it used to be.
Can you read the fuel pressure while driving or only at idle?

Yes the digital one in cab normally works but the sensor stopped working about a year ago and just never got around to replacing it..

I guess good thing is there isnt alot of sensors to check but again catch 22,if i had more sensors they probably would be telling me what's going on and i would be able to read them through a handheld. .

Im definitely leaning towards fuel psi or O2


O also i am still running the same tune that the motor ran on previously. .unless this motor is moving drastically more air at idle and cruise it should be able to adjust or in the range of my current tune...wot maybe a whole different story once boost is introduced..but idle and cruise should be close

 

[jd4242]

Ok couple things..fuel psi was way off,was ready 80psi..adjusted it back down to about 43psi..

Reset and took for drive..still no change runs super lean at idle and cruise. .then sometimes it flops to running good af like 14-15 for a couple mins then flops back to super lean..its not doing the super rich thing anymore but no matter if it lean or good cruise, acceleration is and has always been right at 11-12,this is the only consistent thing..

Sooo i unplugged my temp sensor and no change,CEL comes on but motor still flops back and forth every couple mins with lean being the more common scenario...

First start runs perfect every time for about a min or two before jumping to LEAN..after that it jumps back and forth about every 5 mins from running good to leannnn..

Fuel psi looks good no matter how the motor is running,no change

 

[jd4242]

With the coolant sensor unplugged and a plug where to foul how I would read. Rich correct since the oxygen sensors wouldn't be adjusting??

Also same scenario sensor unplugged and say a injector stopped working, how would I read??

Way i see it in open loop i eliminate the sensors and its still flopping back and forth..to me that leads to plugs,fuel psi, a injector or even a coil..i did switch back to my accel coil pack,i was running a stock coil before..

 

[jd4242]

Also sold my Hoosier 295 slicks and bought a set of 315s..sold and paid same price $100..lol

 

[4pointslow]

What ever you changed like the coil pack, change it back and see if something like that is the cause.
Check that O2 sensor to see if it is working.

I don't know why you are unplugging the coolant temp sensor.
If you want to check the coolant temp sensor then measure the resistance of it.
Some read like 30,000 to 50,000 ohms at room temperature, I am not sure what your exact spec would be.
OL would mean the sensor is open and needs replacing. (provided you have the meter set to the right settings)

 

[4pointslow]

If an injector stopped working you would have a misfire.
If a plug fouled you would have a misfire.
Misfire means nothing burned, fuel and air would enter the exhaust. The O2 sensor only senses oxygen (not fuel).
So the pcm would think it was running lean.
The pcm would add fuel to compensate if it was in closed loop.
It would not add fuel if in open loop.

You have true dual exhaust right?
How many factory O2 sensors does it have? one or two?
Where is your wideband?
If the wideband is installed on the side that has the misfire it would read lean (above 14.1 to 14.7 at idle)

If there is only one factory O2 sensor and it is on the side with the misfire, it would make the pcm add fuel.
If the wideband was on the other side it would see a rich mixture from the pcm adding fuel.
If the wideband was on the side with the misfire it would read lean.

 

[jd4242]

If an injector stopped working you would have a misfire.
If a plug fouled you would have a misfire.
Misfire means nothing burned, fuel and air would enter the exhaust. The O2 sensor only senses oxygen (not fuel).
So the pcm would think it was running lean.
The pcm would add fuel to compensate if it was in closed loop.
It would not add fuel if in open loop.

You have true dual exhaust right?
How many factory O2 sensors does it have? one or two?
Where is your wideband?
If the wideband is installed on the side that has the misfire it would read lean (above 14.1 to 14.7 at idle)

If there is only one factory O2 sensor and it is on the side with the misfire, it would make the pcm add fuel.
If the wideband was on the other side it would see a rich mixture from the pcm adding fuel.
If the wideband was on the side with the misfire it would read lean.

I thought unplugging the temp sensor would force it into open loop??

Yes i do have dual.yes there is a O2 in both and the wideband is only in the driverside..

Its not running like there is a miss though, just running like the af is off..

 

[4pointslow]

Was working double shift today.
Unplugging coolant temp sensor puts it into open loop but makes pcm think it is negative 40 degrees F.
Unplugging O2 sensor just puts it into open loop.

 

[jd4242]

IT WAS THE DRIVERSIDE O2...WWWWWOOOOOOHHHHOOOOOOO THANK GOD!!!

Shes running good now!! Time to break this bad girl in and get on the dyno!!!

 

[4pointslow]

Good Job finding that problem!
Cant wait to hear the updates on how fast it is now!

 

[jd4242]

Good Job finding that problem!
Cant wait to hear the updates on how fast it is now!

Yes thank you and everyone else for their input. ..definitely helps when you got friends trying to figure it out also..

I can tell you i beat a charger tonight and i never went past half throttle...lol i did see 6psi tho...yeaa yeaa i know i need to let the clutch break in but killn v8s is just too fun!!! Lol