Throttle Position Sensor ( TPS ) causing misfires???

[hymnforthewretched]

So the X is back up and running after doing the head gasket!

Only issue now is im throwing a Multiple cylinder misfire code ( P0300 ) associated with a knock sensor code.

this all happened after i changed the spark plugs and fiddled with the TPS ( casue my friend took it out for some reason so i tried to re adjust it ). I adjusted to my best abilities. while adjusting TPS the first codes came up. After resetting, if i fiddled with the TPS again, the code woulds come up again. So i reset it, and it stayed off for a couple days only to return again. now the engine light flashes every time i idle. after i start driving for 15 seconds or so the light goes out. so it seems it's misfiring at idle.

Ive read some places the TPS cannot cause a misfire, but ive read other places it can. I'd to get Xterra folks who may have had simlar issue or head of this happening. the only symptom i can see is after the truck warms up at idle, theres a vibration.. not sure if this vibration is from the misfire. any help would be appreciated.

 

[AZhiAZiAM]

when my TPS went bad or unset. it was actually a throttle and rev problem. Also from what i learned is the TPS has to be set with a voltmeter not by hand. i had it fairly close but after taking it to my mechanic he showed me how it had to be set with one, sorry but i don't remember the correct voltage. So if you are trying to set it correctly i'd look into that too.

 

[hymnforthewretched]

when my TPS went bad or unset. it was actually a throttle and rev problem. Also from what i learned is the TPS has to be set with a voltmeter not by hand. i had it fairly close but after taking it to my mechanic he showed me how it had to be set with one, sorry but i don't remember the correct voltage. So if you are trying to set it correctly i'd look into that too.

Ya I found that out after i adjusted. Either way I made it better than it was but now not seems it trips the engine light and the miltiple misfire code. Can a faulty or out of adjustment TPS cause misfires?

 

[AZhiAZiAM]

to be honest i'm not sure. sorry was just sharing what my tps did encase it helped at all :/

 

[Cyclemut]

No, an out of adjustment TPS won't cause a misfire.

I'd look at your distributor real good, make sure the connector is solidly connected.

Since it's night, now is the perfect time to do this... Start the engine and let it idle. With a spray bottle of water, spritz the engine with water. Not a stream, but spray. Look all around and see if you can locate any errant sparks. Could be that didn't get a couple of plug wires on good. And listen real good for the crack of that spark. Spray around distributor too, may have cracked the cap.

Do you smell any fuel? Have all the vacuum lines connected? A vacuum leak can cause a P0300 too.

 

[hymnforthewretched]

No, an out of adjustment TPS won't cause a misfire.

I'd look at your distributor real good, make sure the connector is solidly connected.

Since it's night, now is the perfect time to do this... Start the engine and let it idle. With a spray bottle of water, spritz the engine with water. Not a stream, but spray. Look all around and see if you can locate any errant sparks. Could be that didn't get a couple of plug wires on good. And listen real good for the crack of that spark. Spray around distributor too, may have cracked the cap.

Do you smell any fuel? Have all the vacuum lines connected? A vacuum leak can cause a P0300 too.

Ill give this a try. do i want sparks? what does this test prove in the end?

I just switched to new plug wires, and in the process made sure there all connected good. Didn't solve the problem. I have a new cap and rotor to install in the morning, but the exisiting ones dont seem to be broken or not functioning properly. In the end ill have new plugs, wires, cap and rotor. Easy things first.

No fuel smell. Before this problem occurred I did have a engine light come on with a fuel system running lean in bank 1. At this time i also had poor gas milage and a hesitation where suddenly the power would kick in. this made the old plugs black in that bank. found out I didnt put the right o2 sensor connecters to the proper connections, so i had them reversed. I also had a loose clamp on the air intake, that seemed to fix that problem. The adjusting of the TPS seemed to fix the hesitation. there doesnt seem to be any air leaks. i believe i fixed them all. its new gaskets on the intake manifold and such so everything should be sealed up.

After all that ( the very same day ) is when the misfire code started, and basically hasn't stopped since. Always comes on during idle. Then go away on your driving, sometimes will eventually just stay on no matter what till you clear it. while driving everything feels normal, no misfires that i can tell, but there is a shake at idle.

I have a feeling my mechanic friend ( domestic guy ) who i had do my ignition timing, may have done it incorrectly. I believe he set the timing light for top dead center and not 15 degrees BTDC. Could this possibly cause misfires?

Thanks for all the help

 

[hymnforthewretched]

So now the sparks, wires, cap, and rotor are all replaced

Checked all plugs for tightness and confirmed all wires are seated. Also the plugs are firing good by the looks of it. No lean conditions.

Checked all vacuum hose for clamp tightness and any deterioration, all checks out. Did find a tiny air line not hooked up ( the one that connects to the upper air box) this didnt seem to fix anything. Plus it's before the meter so it wouldn't qualify as unmetered air.

Only thing left that i touched was the tps. And possibly the ignition timing being out 15 degrees.

 

[Cyclemut]

Timing could be messing with you, for sure!

The sparks would indicate errant firing, the spark would mean it's not getting to the spark plug, bad. Not seeing sparks is what you want.

I'd still spray around the intake, all the gasket areas, with some brake cleaner at idle and see if it changes anything. If it does, vacuum leak. If not, then it's all sealed up.

Fix your timing! That's hard on the engine.

 

[hymnforthewretched]

Timing could be messing with you, for sure!

The sparks would indicate errant firing, the spark would mean it's not getting to the spark plug, bad. Not seeing sparks is what you want.

I'd still spray around the intake, all the gasket areas, with some brake cleaner at idle and see if it changes anything. If it does, vacuum leak. If not, then it's all sealed up.

Fix your timing! That's hard on the engine.

Alright, so i fixed the timing. It was out about 7-8 degrees. I sprayed brake clean on all the vacuum lines and gasket areas and it didn't do anything. also sparyed water on the engine, again nothing happened, no sparks visible or audible.

Engine light still comes on with those codes.

Im starting to think maybe something to do with the fuel system.

 

[Cyclemut]

Do a search on the fuel pump connector on top of the sending unit, under your passenger's side rear seat.

 

[hymnforthewretched]

Do a search on the fuel pump connector on top of the sending unit, under your passenger's side rear seat.

I know this item is a recall, i checked this part when i started having these issues. In not sure if its been replaced by the previous owner, but i checked it out myself and i cant see corrosion or any sign that connectors are cracked or not working properly.

The info below is from the FSM and basically describes exactly whats happening. In my case, the blinking MIL happens at idle, then turns off after about 7-12 seconds while driving. Once i idle again, lets say a stop light, the MIL blinks again. this cycle goes on for a while until eventually just like the FSM states, the light while driving stays on, and then blinks at idle.

So basically im pretty sure the misfires are happening at idle. why im not sure. because there at idle and not driving rpms, im leading to believe its fuel related because once throttle is applied the fuel parameters go up dramatically, and correct the misfiring.

Now the FSM says a front heated O2 sensor can casue misfires.. but i dont understand how thats possible. Since i had a head gasket leak, and left the truck sitting for 6 months before i got it back up and running the cats probably had coolant, water, etc in them. the burning of these could have fouled the O2 sensors. Like i said earlier i had a code before the misfore codes come up that bank 1 was running lean, the plugs matched that. but after i switched plugs and switched the O2 connectors around, the plugs have stayed normal, and the lean code never came back.


The misfire detection logic consists of the following two conditions.
1. One Trip Detection Logic (Three Way Catalyst Damage)
On the first trip that a misfire condition occurs that can damage the three way catalyst (TWC) due to overheating, the MIL
will blink. When a misfire condition occurs, the ECM monitors
the CKP sensor signal every 200 engine revolutions for achange. When the misfire condition decreases to a level that
will not damage the TWC, the MIL will turn off. If another mis-
fire condition occurs that can damage the TWC on a second trip, the MIL will blink. When the misfire condition decreases to
a level that will not damage the TWC, the MIL will remain on.
If another misfire condition occurs that can damage the TWC, the MIL will begin to blink again.

2. Two Trip Detection Logic (Exhaust quality deterioration)
For misfire conditions that will not damage the TWC (but will affect vehicle emission), the MIL will only light when the mis-
fire is detected on a second trip. During this condition, ECMmonitors the CKP sensor signal every 1000 revolutions. A mis-fire malfunction can be detected on any one cylinder or onmultiple cylinders.

 

[Cyclemut]

The misfire is happening at idle. The problem with giving it throttle and it going away is that when you give it throttle, vacuum leaks are also masked. But at idle, vacuum leaks are more critical.

Does your truck have an EGR valve? It it's sticking open, it will do exactly what you're describing too.

If the EGR isn't sticking open, then you need to double check for a vacuum leak. The EGR sticking open acts just like a vacuum leak.

 

[hymnforthewretched]

The misfire is happening at idle. The problem with giving it throttle and it going away is that when you give it throttle, vacuum leaks are also masked. But at idle, vacuum leaks are more critical.

Does your truck have an EGR valve? It it's sticking open, it will do exactly what you're describing too.

If the EGR isn't sticking open, then you need to double check for a vacuum leak. The EGR sticking open acts just like a vacuum leak.

I thought i had a EGR, but after looking at pictures of its location i dont see one. Its a 2000 X, is it possible they didnt come equipped with a EGR valve during a certain production date?

I got myself a scan tool, and have been reading more in depth in the FSM's. live data stream, with freeze frame data read outs combined with FSM knowledge i think ill narrow it down further. ill be able to gather fuel data and test the 02 sensors and such along with other data so at least i can start looking at the right area.

 

[Cyclemut]

After doing head gaskets, there's a bigger chance that something got missed or not connected than the computer not working right.

If you disconnect the MAF while it's running, does it change?

 

[hymnforthewretched]

After doing head gaskets, there's a bigger chance that something got missed or not connected than the computer not working right.

If you disconnect the MAF while it's running, does it change?

Oh for sure. i dont doubt that i have over looked something, but at the same time Ive looked over and over and cant seem to find anything.

I'll check on the MAF later today.

heres a few snap shots of the last freeze frame data that the PCM took at the last p0300 dtc. The short term and long term fuel trims between bank 1 and 2 are quite different, although i dont know exact what the numbers mean. The fuel sys. sta B1 and B2 both say CL,USING HO2S, that has something to do with the o2 sensors i believe but im not sure how it relates to anything. the data does also prove that it issue is happening at idle.

 

[Cyclemut]

CL = Closed Loop, using O2 sensors as feedback for the A/F ratio.

sta = status, showing that it's in CL vs. OL (open loop is when the system goes into known perameters, ignoring the O2 sensors).

What's curious is that your calculated load, at idle, is at 37%. Way too high.

Did you set your TPS correctly with the feeler gauge? At idle, you shouldn't be in closed loop anyway. Double check the TPS and make sure that the closed throttle switch is being activated so that the computer knows that your foot is off the throttle.

Also, check for air bubbles by shutting the engine off and taking the bleed screw out. Then squeeze the upper radiator hose and you should be getting coolant out of that bleed hole.

While you're checking things out, make sure that the wax pellet isn't keeping your throttle engaged (air bubbles will do this and the throttle won't go full closed). If you did adjust the TPS with the wax pellet engaged, then the TPS can't be set correctly. The truck has to be fully warmed up, wax pellet fully disengaged and no air bubbles. Then, and only then, can you correctly set the TPS. Then the system should go into OL and you'll see the A/F mixtures change.

This is something I haven't seen before, but in all actuality, it's looking like your TPS could be the cause of some, if not all, of these problems. But only because I don't think your wax pellet was disengaged during adjustment.

 

[hymnforthewretched]

CL = Closed Loop, using O2 sensors as feedback for the A/F ratio.

sta = status, showing that it's in CL vs. OL (open loop is when the system goes into known perameters, ignoring the O2 sensors).

What's curious is that your calculated load, at idle, is at 37%. Way too high.

Did you set your TPS correctly with the feeler gauge? At idle, you shouldn't be in closed loop anyway. Double check the TPS and make sure that the closed throttle switch is being activated so that the computer knows that your foot is off the throttle.

Also, check for air bubbles by shutting the engine off and taking the bleed screw out. Then squeeze the upper radiator hose and you should be getting coolant out of that bleed hole.

While you're checking things out, make sure that the wax pellet isn't keeping your throttle engaged (air bubbles will do this and the throttle won't go full closed). If you did adjust the TPS with the wax pellet engaged, then the TPS can't be set correctly. The truck has to be fully warmed up, wax pellet fully disengaged and no air bubbles. Then, and only then, can you correctly set the TPS. Then the system should go into OL and you'll see the A/F mixtures change.

This is something I haven't seen before, but in all actuality, it's looking like your TPS could be the cause of some, if not all, of these problems. But only because I don't think your wax pellet was disengaged during adjustment.

when i first did the adjust, i didnt know what i saw doing. i knew the idle was too high at the time, and that the TPS had been removed and reinstalled without adjustment. becasue i has having hesitation at the time and other problems i decided to adjust it myself and see what happens. by adjustment i just started the truck, and moved it till idle went to normal range and tightened the screws. i knew this was wrong but it made alot of things better, but also the MIL started going at this time and misfire codes presented themselves.

I since then bought a new TPS ( that i havent installed ) and bought a feeler gauge. I read the instructions on how to adjust it in the haynes manual, but it really doesnt make sense to me.

they talk about a throttle stop screw. i see a screw near throttle drum, but even when the throttle is completely closed, there is a gap of about 1/16 which is huge. the thottle drum is backed up against another part and cannot go any further... am i looking at the right screw? it also talks about ohms and stuff, which makes the process sound confusing.

and whats this wax pellet? my friend whos buying an X just mentioned the dealership replacing this part and i had no idea what he was talking about.

I looked at the live data stream on my scanner, and it showed throttle position. it showed 0% with me not touching the throttle, but when i pressed the throttle all the way it only showed 88% which means im not getting full WOT either. so its for sure out of adjustment.

Do you have a link to a good set of instructions for the TPS adjustment or maybe you have your own method that will work will for me? i can get the feeler gauge measurments from the book but it would be nice to have a easier to comprehend method. worse case scenario i can brig it to nissan, but i'd rather do it myself.

 

[hymnforthewretched]

Ill also check out air in the coolant. this is very possible. coolant was fully drained and re filled. i never did bleed the system cause i didnt think it was necessary on this system. but it may explain why the temp gauge will move closer towards operation temp, then at idle fall back down about a 1/4 of the way. this happens until the coolant temp really warms up to operating temp for a good 5 mins or so. after it warms up really good it stays put. seems like there could be air in there.

the bleeder screw is on top of the intake correct? and check it at operating temp correct?

heres a pic of the throttle to better explain what i mean:

1. location of what i thought was the throttle stop screw. ( sits 1/16th away )
2. part of the throttle drum that rests and stops on that piece attached to big spring
3. location of another screw that seems to rest against a actuating piece into the intake.



edit: ok i now know that the wax pellet is at the location of #3. i understand what it does now. but i still need to know where to take the feeler guage measurement.

Edit: I opened the bleeder screw once the engine was warm and running. no bubbles, just coolant. i still feel theres air in there though. the wax peelet seems to be operating properly. but with it disengaged ( sticking out ) the throttle stop screw ( number 1 in pic i believe ) is maxed out on the stop. now if this screw is set by the factory and doesnt need adjustment, then how do i get the proper spacing between it?