cant figure out random missfire

[Mike Daley]

so i have a 96 2.3 2wd 5 speed. i bought it with a random missfire an the CEL on. i replaced the plugs, wires, and coils. i checked for vac leaks, i checked for intake manifold leaks, i unplugged the AIT, MAF, and TCV and it ran worse when either one was unplugged. i scanned for codes and came up with:

P0133
P0300
P0171

i cleared them and dove for about 20 miles and the CEL has not come back on yet. but it still doesn't run right. still a random missfire. can a bad o2 sensor be causing this issue? what are your ideas? thanks in advance guys!

 

[Mark_88]

Howdy and welcome to TRS~!

It looks like you have read the codes and got their basic level information, but you can get it here if you need to clarify...

http://www.therangerstation.com/tech_library/OBD-II_codes.shtml

133 for the 02 sensor and 171 for the lean bank (like my account too!) and 300 for random misfire.

Lean bank and 02 sensor could indicate either a vac leak or the MAF is not reading right and not seeing true air flow.

You've changed your coils so that would rule them out pretty much completely...

I would check for vac leaks again...did you spray the brake fluid or something around the engine bay to check for idle change?

Another source for all this could be the heater/ac control panel vacuum...I accidentally did not connect mine properly and right away I was getting rough idle, misfire and stutter...Once I reconnected that vac module it smoothed right out and ran like a...truck!

So, if you've done any other things recently try to backtrack...like adding a new sound system or something that involved working around that area...and just reconnect the hoses and check that check valve (round ball) thing under the hood...that is also vacuum...as well as the EGR sensor that should be mounted on the passenger side of the engine...but some have it on the wheel well covered by wires and such...

 

[Mike Daley]

Howdy and welcome to TRS~!

It looks like you have read the codes and got their basic level information, but you can get it here if you need to clarify...

http://www.therangerstation.com/tech_library/OBD-II_codes.shtml

133 for the 02 sensor and 171 for the lean bank (like my account too!) and 300 for random misfire.

Lean bank and 02 sensor could indicate either a vac leak or the MAF is not reading right and not seeing true air flow.

You've changed your coils so that would rule them out pretty much completely...

I would check for vac leaks again...did you spray the brake fluid or something around the engine bay to check for idle change?

Another source for all this could be the heater/ac control panel vacuum...I accidentally did not connect mine properly and right away I was getting rough idle, misfire and stutter...Once I reconnected that vac module it smoothed right out and ran like a...truck!

So, if you've done any other things recently try to backtrack...like adding a new sound system or something that involved working around that area...and just reconnect the hoses and check that check valve (round ball) thing under the hood...that is also vacuum...as well as the EGR sensor that should be mounted on the passenger side of the engine...but some have it on the wheel well covered by wires and such...

thanks for the reply! so as you asked, yes i did spray the engine compartment down with starting fluid and didn't see an idle change at all. i made sure to spray the vac lines and intake really good too. i have cleaned the MAF, maybe about 1,200 miles ago and it didn't change a thing (that was my first step that i took to trying to fix the issue) the only recent work that i did was add a RPM gauge. i just had take the gauge cluster out and move the radio a little bit and the truck ran like crap before, and after. so i don't think that my recent work caused any problems. the plugs looked a little white like they were burning lean so im kind of leading towards replacing the bank 1 o2 sensor next. but i hate throwing parts at something and just hoping that it will fix the issue!

 

[Mark_88]

OK, and I would not replace the 02 sensor outright...it may need to be replaced but testing is better than replacing parts.

I had to search the forum for a recent post I read by RonD (the old Beach Boys song "Help me RonD yeah...)...anyway...

Read the second post down and fill in the missing gaps with what you've done so far and what has not been done...testing the injectors, fuel pressure, fuel pressure under load...unplug ICM to see if the engine stalls...etc...

http://www.therangerstation.com/forums/showthread.php?t=160582&highlight=lean+condition+rough+idle

If that doesn't help get to the bottom of it then maybe the O2 sensor is wonky...

 

[tomw]

Don't forget that misfire can cause 'lean' condition reported by the O2 sensor. Misfire leaves some O2 molecules in the exhaust stream, which the O2 detects. It then reports a lean condition assuming that the engine fired properly, which SHOULD have consumed the O2's. It didn't and they weren't.

You have to get rid of the misfire before assuming the sensor is bad.

Have you done a compression test? It seems that all the sparking and fueling components are working {fuel pressure & volume tested?} so that leaves 'mechanical' pieces that are not in good shape.
tom

 

[Mike Daley]

i have no tested the fuel pressure yet. it would be low, but it seems that a rough idle, and smooth rpm's above 1,500 rpm's wouldn't be low fuel pressure because it would be breaking up at higher rpm's when the engine wants more fuel. not at idle. get what i am saying? i will test it anyways. what should the pressure be at during idle, and under load?

 

[Mark_88]

I see what you're saying...and it doesn't seem right...and may not be the problem. Something...MAF letting in too much air that the computer is reading through the O2 sensor as lean...as Tom said above or RonD in his post...where the MAF is letting more air than it is telling the computer (not actually letting more in, but you know how it works) so the computer doesn't throw more fuel at it but the sensor sees more O2...and on and on...

Unfortunately, these can be either really simple or convoluted and drive you crazy. One guy did the parts swap not too long ago and got nowhere...but found the air box or the connecting hose had a hole under neath and this was just past the MAF so he was getting way more air than the computer expected...

When you disconnected the MAF, did the engine idle drop and/or stall or did it keep running as if there was no difference? That was a sign of a vacuum leak that would not otherwise be noticeable...

 

[Mazda]

Hello Mike and welcome to TRS

Let me ask you some questions.

1. Are you getting the misfire all the time or only when you start up the truck.?

2. Not trying to be a ass but are you a big guy and hit or rub against the steering wheel when you get in or turn the wheel at all when you start up the truck. I'm a borderline fat ass and do this all the time.

3. Does the truck stumble/misfire when it's started up . Like it isn't getting enough fuel.

If Yes to some or all I believe I know what your problem is....

 

[Mike Daley]

well i inspected the intake boot and there seems to be no damage. i also unplugged the maf and it would idle up and idle high and then slowly drop back to a rough idle like normal.

Mazda, im 185lbs and near 6 feet tall so i guess i could say that i am pretty thin haha. and no i dont rub the wheel when i get in. the only time i turn the wheel when i go to start the truck is if i am just holding it to unlock the steering wheel and ignition. when the truck is first started, it idles up kinda high, like 1,200 rpm's and then drops down to about 800 and the misfire begins. it does away at like 1,300 rpm's and shows back up only around 2,500 rpm's.. so to make it easy to understand, it has a miss at idle and around 2,500 rpm's

 

[Mazda]

well i inspected the intake boot and there seems to be no damage. i also unplugged the maf and it would idle up and idle high and then slowly drop back to a rough idle like normal.

Mazda, im 185lbs and near 6 feet tall so i guess i could say that i am pretty thin haha. and no i dont rub the wheel when i get in. the only time i turn the wheel when i go to start the truck is if i am just holding it to unlock the steering wheel and ignition. when the truck is first started, it idles up kinda high, like 1,200 rpm's and then drops down to about 800 and the misfire begins. it does away at like 1,300 rpm's and shows back up only around 2,500 rpm's.. so to make it easy to understand, it has a miss at idle and around 2,500 rpm's

Mike,

Lol , Your symptoms are similar and well not similar to the Power Steering Sensor failing.

What it does is compensate for the low power our 2.3L have when the truck is started and then immediately driven (turning the wheel to leave) or someone turns or moves the wheel during startup. I had very similar symptoms with my B2300 a few years ago. It is supposed to stop giving a reading after a while I believe after you get above 2000 RPM but mine would not and I think would give a random misfire every so often. Especially after stopping at a light.

Did you turn the wheel when you were doing the KOER test when scanning for codes. It should have picked it up but again mine did not.

P0550 Power Steering Pressure Sensor Circuit Malfunction
P0551 Power Steering Pressure Sensor Circuit Range/Performance
P0552 Power Steering Pressure Sensor Circuit Low Input
P0553 Power Steering Pressure Sensor Circuit High Input
P0554 Power Steering Pressure Sensor Circuit Intermittent


Anyway long post but might be your problem as it was mine. I usually don't like throwing parts at problems is only 20.00 usually. And can be changed without losing to much Power Steering Fluid. (Trans Fluid)

http://www.rockauto.com/catalog/moreinfo.php?pk=42684&cc=1138081&jnid=519&jpid=3

Bryan

 

[Mark_88]

Well, Mazda, that could be what is causing Mike's rough idle...always good to check the coeds...and something I will have to keep in mind because I just removed the power steering from my 96 and swapped in a manual gear box.

I'm hoping mine doesn't throw a fit on me...the CEL was on before I tore it down and the previous owner didn't bother to scan it...he just wanted to part it out so he could park his new F-150 in the spot...