Bad ground wire on Crankshaft position sensor causing misfires under acceleration?

[mopardude87]

Alright so i recently got this little 2000 Corolla and while it can run nice when cold it starts to misfire at operation temperatures especially under hard acceleration. Had a misfire on cylinder #4 so replaced coil and plug with factory oem specced ones.Car runs better now but still got those misfires. Cleaned PCV valve and throttlebody so i cleared most of the typical stuff. Even replaced the throttle body position sensor as well. Stuff was cheap enough so why not on a motor with 210k miles and a questionable repair history.

Decided to inspect the crankshaft harness as i hear these can go bad and i found a exposed what i assume is the ground wire showing. Insulation more or less has fell apart and off quite some time ago minus a bit that came off with a slight touch of course completely covered in oil dirt and grim. I figured today maybe i could clean it and rensulate it and attempting to remove the harness gently resulted in the ground more or less falling out of the main harness.

I assume if this ground was on the harness it must have been on by a hair giving just the slightest amount of ground. The wire is tough so i got is perhaps something in the undercarriage just gave this thing a good tug some time ago and me just fiddling with it just up and destroyed it.

So what do you guys think? Yeah i am replacing it but what are the odds its been causing this misfire?

 

[pcgeek11]

What you say is possible. Are you sure it is a ground or a shield wire that is exposed?

There are usually three wires involved for the crank position sensor on a Toyota.

Two go to the ECU ( Engine Control Unit ).

NE - : Green Wire on my Tacoma, goes to ECU.
NE + : Red Wire on my Tacoma, goes to ECU.
Shield : Brown Wire on my Tacoma, goes to ground.

* The shield wire acts as a noise filter for the wire harness and is tied to ground.

 

[mopardude87]

What you say is possible. Are you sure it is a ground or a shield wire that is exposed?

There are usually three wires involved for the crank position sensor on a Toyota.

Two go to the ECU ( Engine Control Unit ).

NE - : Green Wire on my Tacoma, goes to ECU.
NE + : Red Wire on my Tacoma, goes to ECU.
Shield : Brown Wire on my Tacoma, goes to ground.

* The shield wire acts as a noise filter for the wire harness and is tied to ground.

Pretty sure its a shield the main 2 went directly into the main harness and into the sensor itself while this one had a ground connector that relied on the bolt holding the sensor in place to hold this in place as well. Might have been brown or black? Had a bunch of gunk on what little was left of its insulation which fell right off.

All i did was remove the bolt then gently attempt to remove the harness when this wire ripped right out of the main harness. Its braided so not exactly a easy feat to accomplish. Maybe was a good thing it fell apart in my driveway and not on the road? Rest of the wiring looks old and tired too so this deal looks VERY old or perhaps original?

The misfiring issue has been driving me up the wall given i get no check engine lights and it happens at operating temperature. Obviously replacing the sensor but was more curious if a nearly busted shield to ground wire could cause all this non sense?

 

[pcgeek11]

In my opinion I do not think that a crappy shield would cause an intermittent misfire.

If it was a braided wire it is the shield.

I pretty sure if you had an issue with the crank sensor you would most likely have a code.

Do you have an Idle Air Control Valve?

 

[mopardude87]

In my opinion I do not think that a crappy shield would cause an intermittent misfire.

If it was a braided wire it is the shield.

I pretty sure if you had an issue with the crank sensor you would most likely have a code.

Do you have an Idle Air Control Valve?

My car does yes, well i did clean the throttlebody and it was VERY dirty. I might clean that just cause now.

Its not having no issues with idle at all or stalling though. Just bogging down and misfiring mainly under considerable or hard acceleration. The more gas i give it the more likely its gonna do it. Steep hills it would go crazy like the little engine that could but still it won't stall or die it would have its little fit then idle fine again once parked moments later.

Check engine light did come on some time ago when i first got this car with a intermittent misfire on cylinder 4. I replaced coil and plug reset the computer and since then no check engine light. The light only came on under harsh acceleration up a steep hill and it was sorta intermittently flashing with the severity of the misfiring or bogging as it seemed then just stayed on even on a cold start the next morning. Reset it went off after the coil and plug swap. Typical city driving it won't come on now just very harsh driving conditions that require prolonged hard acceleration like highways for example will turn on that light. Keep in mind during city driving it misfires and bogs just the same.

I am also suspecting the fuel injectors. Luckily those are cheap enough at $31 for oem ones rebuilt of course but a reputable site. Only cause when i pulled them i found hairline cracks in the plastic housing on 2 of them and one the fourth cylinder the crack is very noticeable but i can't find any leaks? I did read somewhere about a possible heat soak situation with cracked fuel injectors? The cracks also sometimes mean nothing then other times people highly suggest replacing them. Given how caked up they were with stuff its possible they could be clogged too as the car looks like its gotten very little done to it over time besides a new o2/sensor.

Not exactly wanting to toss money into parts that may or may need replacing. All i got honestly is possible fuel injector issues and that crankshaft sensor. Most other things just appear to cause idle dying and stalling issues which i am not having any issues with. The crankshaft position sensor is going to be replaced obviously still but where to go from there i am a bit lost.

 

[deadlyapp]

Can you recreate it while in neutral and revving the engine?

Any possibility it's a sticky valve in cylinder 4, only shows up at higher revolutions? Might be worth running some cleaner through everything like seafoam etc and doing a pressure test of each cylinder.

 

[mopardude87]

Can you recreate it while in neutral and revving the engine?

Any possibility it's a sticky valve in cylinder 4, only shows up at higher revolutions? Might be worth running some cleaner through everything like seafoam etc and doing a pressure test of each cylinder.

Revving the engine in park or neutral results in a motor that purrs like a kitten. Its just when its under considerable load at operating temperature that i run into my issues. I can mimic the misfire in my driveway holding down the brake in gear.

 

[deadlyapp]

How strange. Sounds like the car is pulling timing or fuel under hard acceleration, which could be all sorts of things. Have you been able to see what the CEL is for each time?

 

[mopardude87]

How strange. Sounds like the car is pulling timing or fuel under hard acceleration, which could be all sorts of things. Have you been able to see what the CEL is for each time?

First few times it was a misfire on cylinder 4. It hasn't came on in a while actually but did some cleaning of this checking of that and thats when i found the crankshaft wire was all busted up. From what i read in various places the crankshaft does deal with fuel injection and various timing settings in some situations so i thought i was heading in the right place. For all i know that is it and since it needs to be replaced i guess i will find out sooner rather then later.

Plugs do appear to show signs of a lean burn and they all show this. A few of them had thunk white crud on them and they were the autolite xp 3429 i believe. I cleaned off the crud and will prob replace the other 3 as they got some autolite xp 3429 plugs i believe and factory prefers NGK.

I suspected the fuel injectors cause the fourth one especially has a brown coating like light carbon where the fuel comes out. Attempting to clean them with throttlebody cleaner made little difference. The brown residue or whatever it is happens to be there still. I assume they could be potentially clogged. Before i got the car it did sit for about 3 months with next to no gas in it so i think JUST maybe one or maybe a few of those fuel injectors got clogged.

 

[mopardude87]

Between the new crankshaft position sensor, new injectors and plugs now its running like a dream. Does seem to start a bit better and there is essentially zero shake in the motor at idle in park. Also needed some hose clamps cause i found a vacuum line from the throttlebody to the intake valve cover that was lazily replaced without them.

Got lucky with the Catalytic Converter after all that misfiring. California has deemed it road worthy and it passed smog with zero pending codes or any codes for that matter.