Random Misfire Issues - Sometimes will be ALL cylinders, other times just #4-6

Joined
Jul 24, 2019
Messages
70
Location
Denver, CO
Hello All!

As the title states, I'm having a random misfire after changing out the following on my 1995 1fz-fe stock 80 with 252k on the clock:
  • Valve Cover Gasket
  • Spark Plug Seals
  • Injector Service (all new o-rings/seals)
  • Fuel Filter
  • Fuel Pressure Regulator
  • Vacuum Lines
  • New cap/rotor/plugs/wires within the last 3-4 months - new plugs this past weekend
  • Cleaned all upper intake passages and installed new gaskets
Next on the list:
  • Compression Test
  • Valve Clearance Check
Now, on to the fun stuff... I'll try to keep this concise as possible, but I've been working on this for the last week and have changed/replaced/touched pretty much everything on the top half of the engine. I've also done a TON of searching on this forum and other areas and have read through 20-30 posts pertaining to EGR, injectors, HG, etc. For background - the 80 has been running rich for a while with the occasional p0401 code that I was able to fix(new modulator, VSV, etc), but overall it was running well. When I changed the plugs, I noticed oil on the top of several of them and I knew the spark plug seals needed to be addressed as well. So, I figured I would send the injectors to get serviced while I was working on everything else.

:worms:

Here's where it gets interesting. I buttoned everything back up and it was running smooth on initial startup for a few minutes with only one *slight* miss coming off 2k+ RPMs to idle. Almost like a little hiccup. Drove it home without any issues at 65-70MPH for almost 15 minutes, then the check engine light started flashing and engine started missing. (P0300, P0301-p0306) I limped home and here's where I'm stuck - sort of.

Items I've checked off:
  • Wire harness near EGR - nothing was "melted" but there were some cracks in the insulation so those have all been addressed and re-wrapped.
  • No ECU issues with the wiring that I can see at the ECU and coming through the firewall. No grabbing/twisting/etc ever made a difference.
  • Injector clips - there were several - especially #4 - that the wires at the clip had cracked insulation so those are now all new.
  • Injectors - moving injectors had no effect. They all read in spec and are clicking during operation (used my stethoscope for confirmation)
  • Plugs - moving plugs had no effect.
  • All plug wires read correct impedance and cap/rotor look clean inside without any oil.
  • New o2 sensors had no effect but the front sensor was covered in carbon.
  • Cooling system has been effective - no overheating issues after replacing the fluid in blue fan clutch.
Random observations:
  • After getting the 80 home, the battery kept draining quickly - I believe one of the injector clips was shorting and draining the battery immediately - that is no longer an issue.
  • #4 intake tube AND upper intake near throttle body had a significant amount of standing oil/fuel mix which wasn't there after I cleaned it.
  • Top of #4 cylinder was wet - this could've been due to what I think was a stuck injector/short.
  • Upper intake was getting hot almost immediately during idle and misfire - which ties into the next test of the cat
  • I removed the y-pipe and fired her up (sounded like a race car) and I was able to get it to idle smoothly after a few minutes. No bucking, no hesitation, no shuddering. I also heard a discernable "click" once when it was misfiring and it started running smoothly until I drove it down the street.
  • Old test cat(gutted) was used after to make sure there wasn't a restriction, but the miss came back after a few minutes and short drive.
  • When it was misfiring, I pulled #6 lead and could hear it arcing so I know spark is there, but the idle actually came up a bit and was running *slightly* better. Pulling other leads - #1 for example - increased the shuddering.
  • Also NO smoke at startup - just rich fuel smell.
Sorry for the long-winded post. I have a pretty good idea what's going on, but want to seek out the help of the community to see if you guys have any ideas. I'm also going to close this thread out once it's solved - I've noticed there are a TON of dead end threads out there that don't actually list the solution.

Thanks!
Jeff
 
Last edited:
Joined
Nov 9, 2012
Messages
12,444
Location
Olathe, KS, USA
1) What brand of plug wires / CAP / Rotor were installed?
2) Check the plug on the top of the distributor for wires that are pulled, cracked, shorting. I have seen a couple issues with these.
3) The fact that you are getting all cylinders on the PO300 codes, would point to an injector grounding issue to me or the harness by the EGR. I know you've addressed these, but they are still a possibility.
4) Check to make sure all your ground cables are installed. I think there are (6) of them from the engine to various places under the hood.
 
Joined
Jul 24, 2019
Messages
70
Location
Denver, CO
1) What brand of plug wires / CAP / Rotor were installed?
2) Check the plug on the top of the distributor for wires that are pulled, cracked, shorting. I have seen a couple issues with these.
3) The fact that you are getting all cylinders on the PO300 codes, would point to an injector grounding issue to me or the harness by the EGR. I know you've addressed these, but they are still a possibility.
4) Check to make sure all your ground cables are installed. I think there are (6) of them from the engine to various places under the hood.
@BILT4ME

All good questions here - I have been replacing everything with OEM parts, and have utilized the knowledge on this forum pertaining to the fickle nature of certain components.

OEM cap/wires/rotor with Denso K16-RU plugs - gapped to .031
I have a new 4pin harness on the way for that plug on the top of the distro - similar cracked insulation to other plugs on the vehicle right at the base of the connector.
I checked impedance on all injector wires running up to the firewall, but will check to the ECM next.
I'm also in the process of replacing grounds as that's also on the list. Again, this wasn't an issue until doing the top end work, but I understand how important grounds are to electrical systems - I ran a car stereo shop for a lot of years, and electrical is my specialty.

I will say this... most of the time when I'm getting p0300, it is mostly 0304 or 0304-0306.
 
Joined
Jul 24, 2019
Messages
70
Location
Denver, CO
Here are some images of the shenanigans.
20211225_103321_resized.jpg
20211222_171524_resized.jpg
20211218_121458_resized.jpg
20211128_131203_resized.jpg
20211128_122908_resized.jpg
20211128_123118_resized.jpg
 
Joined
Jul 24, 2019
Messages
70
Location
Denver, CO
Good thing you LIKE electrical!
I know it's weird to say, but I do. Haha!

I was putting in remote starters in cars in the late 90's, TV's in headrests before they were a factory option, etc. I have a EWD and have followed that in the past to fix some other electrical gremlins in this 80 Series.
 
Joined
Jul 24, 2019
Messages
70
Location
Denver, CO
I'm leaning toward stuck exhaust valves due to the intake getting extremely hot when it's misfiring. Without restriction - when I pulled the y-pipe - there wasn't any opportunity for backpressure or for exhaust from other cylinders to flow back into #4.

Question - would incomplete combustion (lack of spark, for example) fill the intake with hot gasses??
 
Joined
Nov 9, 2012
Messages
12,444
Location
Olathe, KS, USA
I'm leaning toward stuck exhaust valves due to the intake getting extremely hot when it's misfiring. Without restriction - when I pulled the y-pipe - there wasn't any opportunity for backpressure or for exhaust from other cylinders to flow back into #4.

Question - would incomplete combustion (lack of spark, for example) fill the intake with hot gasses??
The valve are not going to stick unless you are referring to the EGR valve.

There is not "adjustment" to the valves on your engine unless you go through the entire re-shimming process. NOT common on the 1FZ-FE.

The timing could be an issue. Retarded timing will show up as red-hot exhaust manifolds and will cough through the intake under hard, fast acceleration blips.
Too far advanced timing will result in pinging (pre-ignition) or knocking which the knock sensors are supposed to adjust out of it.

Check your timing

None of the items I listed here will change as soon as the engine comes to temp.

The only things that change are due to the ECU telling it to change due to other inputs.

Keep it simple. Don't try to make it harder than it should be.

From the FSM:

1640631160925.png
 
Joined
Jul 24, 2019
Messages
70
Location
Denver, CO
The valve are not going to stick unless you are referring to the EGR valve.

There is not "adjustment" to the valves on your engine unless you go through the entire re-shimming process. NOT common on the 1FZ-FE.

The timing could be an issue. Retarded timing will show up as red-hot exhaust manifolds and will cough through the intake under hard, fast acceleration blips.
Too far advanced timing will result in pinging (pre-ignition) or knocking which the knock sensors are supposed to adjust out of it.

Check your timing

None of the items I listed here will change as soon as the engine comes to temp.

The only things that change are due to the ECU telling it to change due to other inputs.

Keep it simple. Don't try to make it harder than it should be.

From the FSM:

View attachment 2876181
@BILT4ME - I have seen this chart as well, but will retrace my steps once again to see if I disturbed any other electrical connections while I have been working on it. I have been trying to "check the simple things first", but that only goes so far... especially when I've discovered multiple connectors that have wires with broken insulation at the base of the plug. I feel like my troubleshooting skills are pretty solid, but I finally broke down to start this post.

I'm also leaning toward spark/timing/electrical, but the hot intake and the fact that it was running after pulling the y-pipe yesterday (the first time it has run without misfiring since this debacle started) made me lean toward exhaust restriction/blockage. This could be also a bad rear o2 sensor. I didn't change the timing, but will check it with a light as well.

If EGR is stuck open, I see how that would dump hot exhaust back into the intake. I can't explain the "wetness" on top of #4 unless it's still just residual from a stuck injector and because I haven't had the engine up to running temp. It has been dumping a TON of water out of the muffler, but not coolant or oil.

Thank you for the input to this point, it's appreciated!
 

TomH

SILVER Star
Joined
May 14, 2003
Messages
1,262
Location
Seattle
Check the engine coolant temp sensor. If it is telling the ECU the engine is cold then it will add fuel and probably adjust timing. If you have a temp gauge or Scangauge/Ultragauge then you can watch the temp jump all over the place if the sensor is bad.
 
Joined
Jul 24, 2019
Messages
70
Location
Denver, CO
Check the engine coolant temp sensor. If it is telling the ECU the engine is cold then it will add fuel and probably adjust timing. If you have a temp gauge or Scangauge/Ultragauge then you can watch the temp jump all over the place if the sensor is bad.
@TomH Good call - I have one on order from Toyota already so I'll pick that up this week.
 

alia176

SILVER Star
Joined
Aug 21, 2003
Messages
14,135
Location
Tijeras, NM
Sorry if this was mentioned but does the ECU have any other CEL codes besides cylinder misfire codes (P3xx)? If so, what are they?

Since the OP is checking electrical stuff, please check the single wire that on the right side of the dizzy. It goes into a off white color plug with, three terminals (I think) but the other two are capped off. If this wire is flaky, it'll kill the engine or make it misbehave.
 

SNLC

OCD
Supporting Vendor
Joined
Sep 9, 2004
Messages
9,067
Location
Boise - Idaho
Website
www.snlandcruisers.com
Random misfire can be traced to coil or igniter, sometimes. I have had an aftermarket igniter do this. I have also found cracked wires at and near the igniter plug.

You can work through the FSM flow chat for trouble shooting the ignition system. Crank position sensor, coil, dizzy cap/wires and associated wires, plugs, igniter, ECU and wiring harness. Simple test can tell you if these parts are good or bad. Once you have eliminated these, move on to another system like fuel/injectors and work through the tests. Process of elimination will reveal the issue. Bouncing around all over the engine does not seem efficient to me in trouble shooting a problem and narrowing it down to the actual issue.

Cheers
 
Joined
Jul 24, 2019
Messages
70
Location
Denver, CO
Sorry if this was mentioned but does the ECU have any other CEL codes besides cylinder misfire codes (P3xx)? If so, what are they?

Since the OP is checking electrical stuff, please check the single wire that on the right side of the dizzy. It goes into a off white color plug with, three terminals (I think) but the other two are capped off. If this wire is flaky, it'll kill the engine or make it misbehave.
@alia176 No other ECU codes, just the p03xx.
 
Joined
Jul 24, 2019
Messages
70
Location
Denver, CO
Random misfire can be traced to coil or igniter, sometimes. I have had an aftermarket igniter do this. I have also found cracked wires at and near the igniter plug.

You can work through the FSM flow chat for trouble shooting the ignition system. Crank position sensor, coil, dizzy cap/wires and associated wires, plugs, igniter, ECU and wiring harness. Simple test can tell you if these parts are good or bad. Once you have eliminated these, move on to another system like fuel/injectors and work through the tests. Process of elimination will reveal the issue. Bouncing around all over the engine does not seem efficient to me in trouble shooting a problem and narrowing it down to the actual issue.

Cheers
@SNLC - Thank you for the info!

Although it may seem like it, I've been very systematic in my approach to troubleshoot what is causing my misfire other than the two items I mentioned above - compression test and valve clearance check. I can definitely be more thorough with some of these items, but I've gone by the FSM some of these already i.e. checking impedance at each injector, voltages, grounds, etc. I've also checked and replaced plugs, tested all wires to make sure they are in spec, etc. I started with the areas of the engine I "disturbed" and have found several electrical issues from moving wire looms out of the way to gain access to bolts. Other items that have been replaced recently haven't had as close of a look because the engine was running fine before doing this maintenance. (or so I thought)

When I finally figure this out, I will post my findings to hopefully help the next guy down the road.

Thanks!
 
Joined
Aug 6, 2021
Messages
2
Location
bay area California
A similar thing to this is currently happening to me. I replaced

-Spark Plugs
-Valve Cover Gasket
- Spark Plug Seals

And After this, when I started the car it sounded rough so I drove down the street, and eventually, a P0303 code popped up.
I assumed the Coil Wires must be old so I replaced those after.

The first few cranks when I replaced the coil wires I had the firing order mixed up so I am wondering if something within the distributor may have gotten mixed up because the wires were in the wrong place. Because when I drove around after fixing the order, The code did not come back But My normally silky smooth 1-FZ is still feeling a little rough so I'm convinced I have not fixed the problem.

One thing I noted is that I may have had the 2 Vacuum Lines on top of the throttle body mixed up. I corrected that for the second time I drove it around but I felt no difference
 
Joined
Jul 24, 2019
Messages
70
Location
Denver, CO
A similar thing to this is currently happening to me. I replaced

-Spark Plugs
-Valve Cover Gasket
- Spark Plug Seals

And After this, when I started the car it sounded rough so I drove down the street, and eventually, a P0303 code popped up.
I assumed the Coil Wires must be old so I replaced those after.

The first few cranks when I replaced the coil wires I had the firing order mixed up so I am wondering if something within the distributor may have gotten mixed up because the wires were in the wrong place. Because when I drove around after fixing the order, The code did not come back But My normally silky smooth 1-FZ is still feeling a little rough so I'm convinced I have not fixed the problem.

One thing I noted is that I may have had the 2 Vacuum Lines on top of the throttle body mixed up. I corrected that for the second time I drove it around but I felt no difference
@whiteFZJ80 - That's interesting for sure. What did you remove in order to replace valve cover gasket/spark plug seals? Just the throttle body or the upper intake as well?

Let me know if/when you are able to trace down the cause of your misfire and I'll post my results as soon as I figure my issues out.
 

alia176

SILVER Star
Joined
Aug 21, 2003
Messages
14,135
Location
Tijeras, NM
@whiteFZJ80 - That's interesting for sure. What did you remove in order to replace valve cover gasket/spark plug seals? Just the throttle body or the upper intake as well?

Let me know if/when you are able to trace down the cause of your misfire and I'll post my results as soon as I figure my issues out.

Valve cover project just requires the removal of the TB, no need to touch the upper intake. Be sure to order new PCV grommet, both new PCV hoses, all new vac lines that live UNDER the TB. Also, there's a PITA to access two rubber coolant hoses that feed the TB on the underside. These two hoses holds on to the TB something fierce until you disconnect them. I bypassed this long time ago as I don't need to heat up my TB on cold winter mornings since I live in the SW. If the TB is bypassed in this manner, it makes the removal of the TB in the future a piece of cake. If the TB is easy to remove, then you end up doing PMs in this area much more easily.
 
Joined
Jul 24, 2019
Messages
70
Location
Denver, CO
Valve cover project just requires the removal of the TB, no need to touch the upper intake. Be sure to order new PCV grommet, both new PCV hoses, all new vac lines that live UNDER the TB. Also, there's a PITA to access two rubber coolant hoses that feed the TB on the underside. These two hoses holds on to the TB something fierce until you disconnect them. I bypassed this long time ago as I don't need to heat up my TB on cold winter mornings since I live in the SW. If the TB is bypassed in this manner, it makes the removal of the TB in the future a piece of cake. If the TB is easy to remove, then you end up doing PMs in this area much more easily.
I've already done the job, I was just asking what you removed/replaced during your VC change. I'm still working though some electrical troubleshooting and found more than one injector harness wire with cracked insulation from moving it around.

Seeing if yours could also be electrical.
 

Users who are viewing this thread

Top Bottom