i'm at a loss...misfire continues

[BrianSD_42]

The thing about this thread that irks me is that you say you have all these issues but no CEL from the issues.

How are you having a misfire without a CEL ?

Can someone who has serious experience with Toyota engines please comment on this? I am quite curious.


:hiding:

 

[bama16]

The thing about this thread that irks me is that you say you have all these issues but no CEL from the issues.

How are you having a misfire without a CEL ?

Can someone who has serious experience with Toyota engines please comment on this? I am quite curious.


:hiding:

I wish I knew, it would make this process a whole lot easier. The light came on when Iunplugged the TPS, so i know it works, but it goes away once it's plugged back in.

I will see if i can find the specs for the TPS and test it.

Is it possible that either the crank or cam position sensor could cause these issues?

 

[bama16]

I have found that at idle at a light.. If I mash the gas to the floor it will spit and sputter until exactly 2k rims and then I clears up. I have also found a hiccup at 3k rims. Does this narrow it down to anything specific

 

[zacattack20]

Go back to what [MENTION=76419]Doc2012[/MENTION] said first. You're saying it is misfiring but what you think in your head is a misfire might be transmission related. If you were having a misfire that bad then your Check Engine Light would come on and would leave a code for you to check.

I've been having misfire issues for quite a while now but mine is the exact opposite of yours. My truck runs fine and I don't feel any misfire but it keeps throwing the codes and lighting up my Check Engine Light. So it makes me believe that it is ever so slight of a misfire that I don't feel it, which would make me think that if you are having a misfire as bad you say, then the Check Engine Light would most definitely light up.

 

[bama16]

It does it in Park when revving.... If I brake stand it will do it too... Occasionally I will get a pop out of the intake on acceleration... So I know the motor isn't running like it should. I'm certain it's not tranny slip

 

[Mellemel]

For what it's worth, my intermittent annoying misfire was cured by replacing the downstream O2 sensor.

 

[ukrunner]

Vacuum leak? Too rich at cold to go lean enough for you to notice. I'd grab myself a couple of cans of starter fluid and spray it at all the vacuum hoses and couplings. If the engine changes how its running, you have a leak.

 

[angus]

Vacuum leak? Too rich at cold to go lean enough for you to notice. I'd grab myself a couple of cans of starter fluid and spray it at all the vacuum hoses and couplings. If the engine changes how its running, you have a leak.

Beware that this can work but you are spraying a fuel all over a running engine - BE CAREFUL.

 

[csp]

Mine is doing the same thing. I wouldn't call it a misfire necessarily. I call it a stumble.

This one is also fine cold, but stumbles from a stop if I don't ease into it once the engine is at operating temp. Mine threw a check engine light for the air/fuel sensor (CA emissions) and the right bank rich.

Replaced the sensor and cleaned the MAF with MAF safe cleaner. Reset the check engine light and still stumbling, but the check engine light hasn't come back on (has been over a week since the light reset). I haven't had any time to get into troubleshooting but hopefully will be able to this weekend. I have printed out the FSM pages already.

I've been leaning towards a dead spot in the TPS in my head and temp could absolutely have something to do with that. Mine stinks like something is burning as well at times and it's coming from the right bank of the engine. I need to shoot components with an IR temp gun next time I notice it.

 

[Rock_Rat]

He should have a 0420 code if sensor

For what it's worth, my intermittent annoying misfire was cured by replacing the downstream O2 sensor.

Definitely, if the O2 sensor is bad then the computer has to guess what the AFR should be creating either a too rich or too lean condition but the OP should have a 0420 code. I'm not sure what the delay in the ECM is for the code. I'm sure it's quite a bit (>10sec) so as to not trigger a nuisance CEL/fault. It could be on it's way out but the ECM sees it as a spurious indication and won't latch the code until it becomes a "hard" fault. Does anyone have any digital software vendor logic for the codes? (Not the logic the consumer sees - (I'm talking "and" gate "or" gate logic) As someone on this thread has already mentioned, best bet is a scan gauge/data reader to check TPS and AFR. Could be an intermittent coil pack. From the video clip it seemed like the timing was advancing but he really needs a data reader.

It's $100 bucks to put it on the scope at the stealership. They'll give you the printouts and set you up with tech support. It's hard to troubleshoot without raw data. Do the easy stuff first. Try and isolate it to one "path of influence". For the most part, it's either: Mechanical, Electrical or Fuel (too lean, too rich) (hole in the exhaust can cause this too) related.

EDIT: When the misfire begins, try and hold your throttle in that position long enough to throw a code. It's tempting to back off I know.

 

[Rock_Rat]

Leaning towards a bad O2 sensor

it only happens now from a standstill, engine warm, and heavy gas pedal. if the engine is cold it does fine. If i ease onto the throttle i can avoid the misfire, and any downshifts while cruising are smooth.

You know without testing we're all only "guessing" right now. I'm leaning towards [MENTION=100539]Mellemel[/MENTION] and an O2 sensor on the way out or you're very carbon rich. With the engine cold, your catalyst hasn't reached the light off point condition yet allowing the O2 sensor to cycle. (the wave form on the graph would be high and low). Once the engine is warm, your convertor should reach optimal temperature of about >600°, thus allowing the catalyst to use the stored O2 to burn the rest of the engine of HC, H2O, CO2. Sensor will flatten out, if working correctly and continue to monitor the temperature. If there's too much carbon deposits in the exhaust it won't work as efficiently and may never reach light off point. You end up with an unmanaged rich fuel mixture, poor engine performance and poor gas mileage. You may want to try some Seafoam (small amount) through your PVC vacuum line and try and blow out the carbon in your exhaust system. DO NOT use too much. Perhaps a 1/4 cup. Just throwing options at you but you need to get it tested while cold and when it's warmed up.

 

[TheDurk]

Hmm. With a cold engine, you are running in open loop, where the ECM ignores whatever the O2 or A/F sensor has to say, so a bad one is irrelevant, and uses pre-loaded settings until temp sensors tell the ECM the engine is warm enough to rely on the exhaust sensor and so moves to closed loop. A warm engine stuck in open loop for whatever reason (usually temp sensor) will miss because the mix is way too rich as it was meant for a cold engine.

It is worth hooking up a live scanner to see if your problem is occurring in open or closed loop operation and what temp the ECM thinks it is running at. Torque will do this for you. In any case, good running when cold tends to indicate that both ignition and fuel supply are good, and should focus your attention on sensors/ECM/mix/timing issues.

 

[bama16]

You know without testing we're all only "guessing" right now. I'm leaning towards [MENTION=100539]Mellemel[/MENTION] and an O2 sensor on the way out or you're very carbon rich. With the engine cold, your catalyst hasn't reached the light off point condition yet allowing the O2 sensor to cycle. (the wave form on the graph would be high and low). Once the engine is warm, your convertor should reach optimal temperature of about >600°, thus allowing the catalyst to use the stored O2 to burn the rest of the engine of HC, H2O, CO2. Sensor will flatten out, if working correctly and continue to monitor the temperature. If there's too much carbon deposits in the exhaust it won't work as efficiently and may never reach light off point. You end up with an unmanaged rich fuel mixture, poor engine performance and poor gas mileage. You may want to try some Seafoam (small amount) through your PVC vacuum line and try and blow out the carbon in your exhaust system. DO NOT use too much. Perhaps a 1/4 cup. Just throwing options at you but you need to get it tested while cold and when it's warmed up.

i appreciate the guesses. I've run seafoam through it and no change. I have an AEM wideband fuel ratio gauge in my Z. I was going to weld a bung in the exhaust and hook it up to see what it says. Plugs looks normal, but this would tell me exactly where it's at.

Hmm. With a cold engine, you are running in open loop, where the ECM ignores whatever the O2 or A/F sensor has to say, so a bad one is irrelevant, and uses pre-loaded settings until temp sensors tell the ECM the engine is warm enough to rely on the exhaust sensor and so moves to closed loop. A warm engine stuck in open loop for whatever reason (usually temp sensor) will miss because the mix is way too rich as it was meant for a cold engine.

It is worth hooking up a live scanner to see if your problem is occurring in open or closed loop operation and what temp the ECM thinks it is running at. Torque will do this for you. In any case, good running when cold tends to indicate that both ignition and fuel supply are good, and should focus your attention on sensors/ECM/mix/timing issues.

I have the BAFX OBD bluetooth scan tool coming tomorrow, and the torque app on my phone. Hopefully it's here early tomorrow and it'll tell me something new.

Thank you all for the help and the ideas on what to be looking for.