94 has a miss after reaching running temp, and shut off for a bit (1 Viewer)

[Reverend Ink]

My '94 has a random misfire that is driving me nuts. Starts and runs great when cold, but might have a misfire if I go to drive it and it is still around running temp.

For example...get in the car to drive home from work (about 20 minute drive) it runs beautifully. Wife calls and asks me to stop at the store on the way home and inside for around 20 minutes I come back out and start it up and it has the miss. If I let it sit a little longer to cool down the miss goes away.

Cap, rotor, wires, and plugs (all Toyota) replaced in February 2016

Firewall hoses (PHH inlcluded) and HCV all replaced in July 2016 due to coolant leak.

Bought a set of injectors from Gineric and sent them up to Mr. Injector. They were installed in March of this year along with a new fuel filter. Two days later...head gasket popped. March 2017

Head gasket, radiator, thermostat, water pump, fan clutch, radiator hoses, fan blade, ummm...a couple other things I don't remember all replaced April 2017. Water pump and fan clutch from Cruiser Outfitters (with outstanding service getting them to me in less than 48 hours!!!) but all the rest is Toyota. EGR may or may not have been jumpered at this point.

It is seriously driving me nuts. To the point that I've got to run an errand, and I know it is still warm...so I'm driving the minivan. Help!!! Please!!!

 

[elripster]

When you say misfire, does it happen at all speeds or does it just idle too low when restarted when warm?

 

[Reverend Ink]

Sorry, I totally meant to add this.

It is more noticeable down in the lower RPM and smooths out above 1800-2000 RPM (give or take). I noticed today that if I'm just cruising along it can be a bit smooth, but if I need to pass someone or something of that nature it gets quite rough.

Idle is at 650 without A/C and around 900 with A/C on no matter what.

Intake tube has been replaced with a welded metal tube. That I'll try to get a picture of. PCV was changed about 3 years ago (when VCG and grommets were changed).

First time it started was around June of 2016. I tried to find it, gave up, took it to dealership where tech found a corroded connection on #6 injector wire. Replaced and it ran okay for a while, then it started back up. Didn't bother taking it back to the dealership as they hadn't charged me for the previous diag as it went away and was way more randomly occurring compared to now.

 

[ZackR]

I'd look at the injector wiring harness where is passes the EGR. Thats where I found shorted wires which caused my intermittent misfire. You have to open up the loom and get all the way to the wires to see whats actually going on.

My misfire was most noticeable up to 1900 rpm and eventually smoothed out. It was also noticeable when trying to pass or accelerating but less so during a steady cruise.

 

[Reverend Ink]

My misfire was most noticeable up to 1900 rpm and eventually smoothed out. It was also noticeable when trying to pass or accelerating but less so during a steady cruise.

Yeah, that sounds pretty similar to what I'm dealing with.

 

[elripster]

That sounds a lot like lack of fuel when power is required. I second checking the harness.

Frank

 

[elripster]

One thing does get me thinking. When and engine is cold it is running open loop. As it warms up it goes closed loop and starts listening to its sensors. If you have warm operation issues, that often means a sensor is reading incorrectly but within range (no fault) or the ECU is too dumb to flag a fault (common with the 3FE but unsure of the 1FZ). It could be that one cylinder is leaning out and a slight compensation for the others is not enough and thus the miss. In open loop mode it might just over fuel enough to mask this. If the harness checks out I think you want to start measuring O2 voltages and the likes at the check connector.

Frank

 

[BILT4ME]

One thing does get me thinking. When and engine is cold it is running open loop. As it warms up it goes closed loop and starts listening to its sensors. If you have warm operation issues, that often means a sensor is reading incorrectly but within range (no fault) or the ECU is too dumb to flag a fault (common with the 3FE but unsure of the 1FZ). It could be that one cylinder is leaning out and a slight compensation for the others is not enough and thus the miss. In open loop mode it might just over fuel enough to mask this. If the harness checks out I think you want to start measuring O2 voltages and the likes at the check connector.

Frank

This is what I was thinking too. Also check temperature sensors (2) and knock sensors (2) for cracked/broken connectors or replacement of them.

 

[Reverend Ink]

It doesn't do it every time though. It's becoming more common though.

Thank you. I will take a look at the sensors as well.

 

[Rifleman]

This is what I was thinking too. Also check temperature sensors (2) and knock sensors (2) for cracked/broken connectors or replacement of them.

I 2nd on the temp sensor, in open loop (cold) it doesn't use the temp sensor, in close loop (hot) it does.

 

[elripster]

Here is a nice descriptor of what various sensors and actuators do. It's a nice compliment to the FSM.

http://www.lovehorsepower.com/ToyotaPDFs/24.PDF