just wont run right!!!!! 2001 cylinder 4 misfire

[shorod]

What about the long term fuel trim numbers, are they really both the same (-19.53)? Also, please confirm the second -19.53 is LTFT rather than 'stf' that you have it labeled. If that's the case, this would suggest that long term the PCM has been trying to lean out the mixture on both banks quite significantly.

And you're correct, the purpose of the O2 sensor 2 is primarily to help the PCM determine the catalyst efficiency. Sensor 1 is one of the factors that will cause the PCM to alter air/fuel ratio. Unfortunately having a scan tool with datastream mode could really help you confirm if the oxygen sensors are doing what they should be doing.

It might be interesting as a short experiment to unplug the fuel injector for cylinder #4 and see if that makes the engine run noticeably worse and/or if it gets rid of the raw fuel smell in the exhaust.

-Rod

[bradw18]

every time i do something to it i clear the codes before i strart it back up. new cop on cyl 4 plug is new neither one of the 2 had rust or any kind of traces of water. iv been reading about the bank 1 and stft and stuff at a idle my car is

stft b1 10.9
ltft b1 -18.7
stft b2 15.6
ltft b2 -18.7

at 2500 rmps
stft b1 1.56
ltft b1 -12.5
stft b2 14.6
ltft b2 -12.5

come to find out that typo wasnt really a typo it was 14. so the whole motor isnt breathing right. its not just 4 like rod said. thats just the only one the computer is reading. what causes such a varity of reading in my 02s

[bradw18]

i have unplugged the cyl 4 injector and it didnt make any diffrence but i didnt put it on the scan tool though. sould i try doing that? i double checked all the numbers i wrote down at idle and 2500 and all those are right no typos there. and i did mean to put stft sorry bout that.

[bradw18]

i just thought of soemthing also each time i clear the codes its deleting the freeze frames along with the long LTFT thats why the numbers are coming out the same in the stft and the ltft

[danielsatur]

If cylinder 4 is a consistant misfire, the ECU will throw a DTC P0304.
By disconnecting the fuel injector, or COP on cylinder 4 , your engine would sound the same.

[bradw18]

but iv ruled out every cause i could think of in cyl 4 new injector plug and cop. the coil is firng fine. would just the cyl 4 cause the lean readings? im getting that code for cyl 4 misfire and im getting p0174 and p0172 which i could see from the stft and ltft. if sprayed the whole motor with carb clean thinkin it was a vacumm leak but the motor never reved up not even one bit. could egr or pcv valve cause this motor symptom? if so how would i go about checking them?

[bradw18]

like rod said maybe it isnt even a misfire after all...

[shorod]

Originally Posted by bradw18

i have unplugged the cyl 4 injector and it didnt make any diffrence but i didnt put it on the scan tool though. sould i try doing that?

Okay, so that indicates that there really IS a misfire on cylinder #4 and it's not a phantom code, ie: you are focusing on the correct cylinder. We're trying to take baby steps here. As Danielsatur mentioned, you will expect to have a misfire code since you definitely forced a misfire. Also since the engine sounded the same it would suggest that it's a pretty constant misfire, not just an intermittent misfire. Did you notice, with the injector unplugged, if your rich smelling exhaust was gone? You may want to connect the scan tool again and clear the codes one more time just to be sure you're back to your baseline with everything reconnected.

While clearing the codes will reset the STFT and LTFT numbers, what you're reporting is not that they are the same. The STFT numbers are positive values (suggesting the PCM is increasing the injector pulse width) and the LTFT numbers are negative numbers (PCM decreasing the IPW). A few years ago I read a good article on diagnosing with fuel trim numbers, I think it was something put on the Internet by MOTOR magazine. This is a auto tech trade magazine, not one of the car enthusiast mags. You might try searching the Internet for it if you have time today. I seem to recall that it mentioned the critical part is the mathematical difference between the STFT and LTFT per bank. It also suggested typical manufacturer limits and I think your LTFT numbers are approaching those (between 15 and 25 typically). What's very intriguing to me is the B1 STFT at 2500 rpms. This would nearly suggest the misfire is not present, or not being registered by the O2 sensors, at 2500 rpms. How smooth was the engine at 2500 rpms? You don't want to get much higher in engine speed while in Park or Neutral though as the rev limiter will kick in and feel like a horrible misfire.

-Rod

[danielsatur]

If you miss one of the 4 strokes on cylinder 4, it will cause a misfire.
Intake, compression, combustion (power), and exhaust.

Test's:
Air Intake - Smoke test for unmetered air leaks
Compression - ok
Ignition - Fire ok
Exhaust - back pressure test on catalytic converter.

If the catalytic converter was plugged, fuel problems,MAF sensor, or unmetered air leaks on your intake, would cause random misfires on both banks.

How many miles are on your upstream O2 sensors?
Force a misfire, and a DTC!

[bradw18]

how do i do a back presser test on the cat? and what is a smoke test. im thinkin the 02s are factory. they say ford on them. anything after 1800 to 2000 rpms the miss is gone. dont hesitate dont loss power runs great its just between idle and 1800 or so. i read that if you stft is low or high and you take it to 2500 and they almost return to normal chances are you have a vacumm leak. were else could there be a vacum leak whats the eblow under the intake that brakes or cracks called?

[danielsatur]

Smoke Test video, see www.youtube.com/watch?v=FfiQ7qWiG-M
Catalytic converter test, www.youtube.com/watch?v=IzyvL5tQLzU , any local muffler shop will check for free.

If the miss is during idle only, check the PCV/ Air supply line, and port on the valve cover, it gets plugged with PCV gunk.
The air tube on the bank 1 valve cover going to the throttle body, it supplys air for the engine during the closed throttle body condition (Idle).

Because of Age/mileage consider getting two H02 sensors for the upstream cat's only.

[bradw18]

just put two new upstream o2s on it just to make sure it wasnt them and it wasnt. still missing. but i can mark off bad o2s as a problem now. the driver side cat looks as if its been replaced.... it looks newer then the one on the passenger side. would this make a diffrence?

[bradw18]

on the v8 models were is the pcv valve? is it the same place as the v6 models? if so is it easy to check? im just waiting to put a new part on clear the codes and start the car and it idle perfect... is there a such thing a perfect on a ls hahahaha

[danielsatur]

Keep the old HO2 sensors for spare down stream replacements.

Have a back pressure test done free @ the local muffler shop, so we can rule that out too!

Also find a shop, that can perform a smoke test only.

[shorod]

There is a separate converter for each bank, so once plugged converter would not cause a misfire on both banks. It might cause a lack of power, but wouldn't explain a misfire that remains on a single cylinder or explain why forcing a misfire on #4 would not make a difference in the way the engine idled. Restrictions in the exhaust would typically be more apparent under higher load and not so much at lower rpm, opposite of what you're experiencing.

The V8 does not have a PCV valve or the PCV elbow that is a common issue on the V6, so don't waste time looking for that.

The EGR valve should be closed at idle and begin to open as the engine goes off idle. If it's not completely closing at idle that would be a vacuum leak, but again that would not explain the cylinder #4 misfire or results when forcing the misfire.

-Rod