Need help with this misfire.

[Grandlooser]

Ok, I dont typically look for assistance, as a mechanic myself I rarely need it but this one is bugging me, and since my father has gone sick I dont have the time or patience sometimes needed for this kind of thing. Im going to lay out as many details as possible to see if anyone can assist here.

So I have a medium level misfire / stumble that is happening ONLY at between 1850-2000 rpm, very narrow range. To further narrow the range it is only under medium load conditions and with the pedal depressed lightly. I am going to reiterate the RPM range because it is very consistent and in my eyes MUST eliminate some possibilities. It has become pretty consistent but doesn't always do it, at this point probably 80% of the time, has been increasing the past week or so. I have a low miles 2nd truck that is going under the knife so for the time being I have access to every part for exchange and the truck runs perfect so all parts are known working parts.

Vehicle details:

97 with 250k
EGR delete
Full baseline a few months ago ( I mean damn near everything but the HG)
Compression numbers 190 190 190 190 190 160 ( I know this is below spec for difference but truck runs perfect outside this RPM and no signs of HG)


This is what I have replaced / changed recently either before or during this process in no special order:

Fuel pump OEM
Fuel filter OEM
Plugs and wires
Distributor
D. cap
Rotor
TPS
All vac lines ( including manifold removal for PHH ETC.)
All injector seals
Timing checked multiple times ( about 2-3 degrees over stock)
All grounds clean and intact
MAF cleaned
New front o2 but a cheaper replacement
EGR delete
Crank position sensor

No DTC codes that pertain to anything of this sort ( I no longer have a second 02 so thats always there)

All of these things have so far made zero change, or were done prior to the issue becoming. I have also chased a few things despite not believing they could be an issue due to the specific nature of the problem. For example this seems way to narrow an issue to be a fuel pressure issue or an injector issue, Ive not seen these things act up only within a 2-300 RPM window and at lower loads. Unfortunately I feel like possibly some kind of harness issue or short somewhere which is a PITA because Im not sure the best way to proceed with that given my time and shop space. If anyone has experienced anything like this, please do speak up.

 

[OffRoadScott]

Ok, I dont typically look for assistance, as a mechanic myself I rarely need it but this one is bugging me, and since my father has gone sick I dont have the time or patience sometimes needed for this kind of thing. Im going to lay out as many details as possible to see if anyone can assist here.

So I have a medium level misfire / stumble that is happening ONLY at between 1850-2000 rpm, very narrow range. To further narrow the range it is only under medium load conditions and with the pedal depressed lightly. I am going to reiterate the RPM range because it is very consistent and in my eyes MUST eliminate some possibilities. It has become pretty consistent but doesn't always do it, at this point probably 80% of the time, has been increasing the past week or so. I have a low miles 2nd truck that is going under the knife so for the time being I have access to every part for exchange and the truck runs perfect so all parts are known working parts.

Vehicle details:

97 with 250k
EGR delete
Full baseline a few months ago ( I mean damn near everything but the HG)
Compression numbers 190 190 190 190 190 160 ( I know this is below spec for difference but truck runs perfect outside this RPM and no signs of HG)


This is what I have replaced / changed recently either before or during this process in no special order:

Fuel pump OEM
Fuel filter OEM
Plugs and wires
Distributor
D. cap
Rotor
TPS
All vac lines ( including manifold removal for PHH ETC.)
All injector seals
Timing checked multiple times ( about 2-3 degrees over stock)
All grounds clean and intact
MAF cleaned
New front o2 but a cheaper replacement
EGR delete
Crank position sensor

No DTC codes that pertain to anything of this sort ( I no longer have a second 02 so thats always there)

All of these things have so far made zero change, or were done prior to the issue becoming. I have also chased a few things despite not believing they could be an issue due to the specific nature of the problem. For example this seems way to narrow an issue to be a fuel pressure issue or an injector issue, Ive not seen these things act up only within a 2-300 RPM window and at lower loads. Unfortunately I feel like possibly some kind of harness issue or short somewhere which is a PITA because Im not sure the best way to proceed with that given my time and shop space. If anyone has experienced anything like this, please do speak up.

It may or may not be your wire harness where it passed by the EGR but I would also check the injectors and have them cleaned.

 

[Saito]

I had the exact issue you’re describing. Little stumble at exactly 1800rpm and under light load. I loosened my distributor and advanced the timing just a tad(with no light, just stopped where vacuum on the gauge was highest). Issue is gone now.

 

[Grandlooser]

I had the exact issue you’re describing. Little stumble at exactly 1800rpm and under light load. I loosened my distributor and advanced the timing just a tad(with no light, just stopped where vacuum on the gauge was highest). Issue is gone now.

I have played with the timing a bunch to no avail so far.

 

[leonard_nemoy]

My rig had a misfire just like this for about 3 weeks. Right at 1800-2000 rip ems at medium throttle. Than the spark plug boot melted and arced out on cylinder 3 and it threw a code for cylinder 3 misfire. New plugs and wires and the misfire disappeared completely.

I figure the boot was very close to arcing out when the misfire started. 3 weeks later it went full on misfire.

What kind of plugs are you running?

Verify that your injector harness is on in the correct order. A quick visual is all that should be needed for this. Make sure the injector plugs are alternating colors.

Wiring harness by egr?

Unfortunately I feel like possibly some kind of harness issue or short somewhere which is a PITA because Im not sure the best way to proceed with that given my time and shop space.

Have you ever heard of a short finder?

Power Probe 3 PPKIT03S Master Kit with ECT3000 - https://www.jbtools.com/power-probe-3-ppkit03s-master-kit-with-ect3000/


Good luck

 

[Grandlooser]

My rig had a misfire just like this for about 3 weeks. Right at 1800-2000 rip ems at medium throttle. Than the spark plug boot melted and arced out on cylinder 3 and it threw a code for cylinder 3 misfire. New plugs and wires and the misfire disappeared completely.

I figure the boot was very close to arcing out when the misfire started. 3 weeks later it went full on misfire.

What kind of plugs are you running?

Verify that your injector harness is on in the correct order. A quick visual is all that should be needed for this. Make sure the injector plugs are alternating colors.

Wiring harness by egr?







Have you ever heard of a short finder?

Power Probe 3 PPKIT03S Master Kit with ECT3000 - https://www.jbtools.com/power-probe-3-ppkit03s-master-kit-with-ect3000/


Good luck

Bkr5egp ngk's

Connectors are good, just verified. All injectors check out for resistance unsurprisingly. Plugs are 3 days fresh and took wires from my donor with no change. My egr is removed and the harness never got burned by it. Just peeled back the insulation to verify no heat damage to any wires.

Thanks for the post however.

 

[Grandlooser]

Well, while the TB was off for inspection of things I decided to swap out the FPR. So far it's behaving as good as it can. I know better than to conclude too soon so I will update after more miles.

Edit:

Update. Got a good 30+ mike's without a single hiccup. Looks like I nailed it on a hunch, and wasted a bunch of time using logic

 

[FJ80 Money Pit]

Definitely a fuel issue. Fpr sounded like half of it, but i would also clean the oem 02 sensor with mass air flow cleaner and put it back on with copper anti seize and new nuts. You dont need to buy new 02 sensors when you can clean the oem ones. My pinging/ misfire went away completely after doing this and only went away a little after i changed my fpr and fuel pressure dampener.

 

[kambei]

I have this exact issue on my '92 3FE. Mechanic thinks its the MAF, but I replaced it and continues to happen. Also have done several sensor/ECU/plugs etc. I was going to try the FPR, but I just noticed that this is for a '97. Do you think the same resolution may apply?

 

[Grandlooser]

I'm not sure but probably unlikely. I was meaning to update this thread to say that this issue persists and has worsened. New 02 sensor on the way and am planning an injector swap soon. After that.....

 

[BILT4ME]

A few things off the top of my head. I realize you may have done some, but, go back and look again with a fresh set of eyes and perspective. Maybe something you already looked at and assumed it was good because you've changed it.......

Plug wires:
OEM or not?
Is each end of EVERY wire set and snapped in correctly on BOTH ends? A certain RPM range could correlate to a frequency on a gap on the coil or cap even.

I was thinking TPS, but I think you've already addressed that.

Crank sensor. Check the plug on it, maybe swap with known good one to check.

Check the ground wires on the engine and especially the coil.

I'm guessing since it's a very specific range, it's electrically related.

 

[Grandlooser]

My Wits' end sticker has really taken new meaning with this thing. Thrown a few new things and time at it with zero change in fact seems to be worsening.

To date:

TPS changed and checked the circuit and adjustment per FSM.
CPS changed
MAF changed
Plugs and wires
Entire distributor
Coil
02 sensor
Timing set
Vacuum good, all new hoses, no crack in intake boot.
New temp sensor
New fuel pump (previous to issue)
Fuel filter.
Grounds all in place and cleaned.

Really hesitant to pull everything apart again to swap injectors as it makes no sense to me to be that but not sure what else. Really wish I could monitor and data log log like I could on my old Megasquirt car. Issue can't be replicates anywhere but on the road and idles fantastic and accelerates and runs at higher RPM like a boss.

 

[OffRoadScott]

My Wits' end sticker has really taken new meaning with this thing. Thrown a few new things and time at it with zero change in fact seems to be worsening.

To date:

TPS changed and checked the circuit and adjustment per FSM.
CPS changed
MAF changed
Plugs and wires
Entire distributor
Coil
02 sensor
Timing set
Vacuum good, all new hoses, no crack in intake boot.
New temp sensor
New fuel pump (previous to issue)
Fuel filter.
Grounds all in place and cleaned.

Really hesitant to pull everything apart again to swap injectors as it makes no sense to me to be that but not sure what else. Really wish I could monitor and data log log like I could on my old Megasquirt car. Issue can't be replicates anywhere but on the road and idles fantastic and accelerates and runs at higher RPM like a boss.

As mentioned earlier I do have similar issues with my LC as well. Mine is the wiring harness but I am going to pull the injectors as well and have them cleaned at the same time. While you are in there I would do some preventative maintenance and wrap your wiring harness to protect it from the EGR.

Scott Higgins @Cruiserhiggs told me he has seen Land Cruiser experience a miss. Once they removed the injectors and had them cleaned the issue went away. Maybe Scott can or will chime in.

 

[Grandlooser]

That's really my next and only remaining move. Pull intake again, fully check entire harness and swap injectors while I'm in there. There is really nothing left. I can swap the ECU but I have never fixed any car out of thousands by replacing an ecu.

 

[bigredmachine]

i would check the harness for the o2 sensors, i had a similar issue that resolved temporarily after replacing both sensors. after the issue came i found that at some point before i bought the truck the wiring harness had to have been rubbing on the front drive shaft or was burned by the exhaust and i found two crusty, green "wire repairs" in the harness. wires werent even soldered or crimped just twisted together and taped up and it was pretty far up the harness so it wasnt really all that obvious at first

 

[Kernal]

May have missed it, but does this happen only while driving (under load) or also while not moving and just racing the engine? And does it happen 100% of the time the engine reaches that rpm range? Same symptoms for a cold engine (rich) and warm engine?

 

[Grandlooser]

May have missed it, but does this happen only while driving (under load) or also while not moving and just racing the engine? And does it happen 100% of the time the engine reaches that rpm range? Same symptoms for a cold engine (rich) and warm engine?

Cannot replicate the issue in the shop at idle....until a while ago when I parked at the store it was missing at idle. Can't force it to do it again however. Also just had a pretty hairy ride home and wasn't sure I'd make it. The rpm range of missing has definitely widened and seems more like 3-4 cylinders missing as opposed to 1 now. Seems like an easy find but I'm tearing hair out at this point.

 

[Cruiserhiggs]

So I have seen this before many times. The two culprits are always the harness by the egr pipe and the injectors. You can try a wiggle test of the harness and see if it does anything. It won’t always but I have had some luck with that. We also have seen injectors cause this. I pull the upper intake and take them to get flow tested and cleaned. We usually have 1 or 2 that get replaced totally.

 

[Grandlooser]

So I have seen this before many times. The two culprits are always the harness by the egr pipe and the injectors. You can try a wiggle test of the harness and see if it does anything. It won’t always but I have had some luck with that. We also have seen injectors cause this. I pull the upper intake and take them to get flow tested and cleaned. We usually have 1 or 2 that get replaced totally.

Ive got a low mile set of injectors from a great running motor that will be swapped in soon (possibly tomorrow). Every time I open the hood i wiggle stuff to no avail. The wires near the EGR are great and due to the EGR being removed are easy to access and inspect, the sheathing was barely even heat damaged and wires are all intact and not brittle at all.

 

[FJ80 Money Pit]

Plug a T into the vacuum line and run the vacuum gauge into your cab and see if the issue is vacuum related during that RPM range. My truck had this problem during a light hill climb with light throttle input. Also replace your fuseable link because some electrical gremlins are related to this.