1986 22re (W56) Random Misfire At Idle and 2000-3000 RPM Range
 

Guys, I've spent the last 6 weeks trying to track down the source of a random misfire at both idle and also (only) in the 2000-3000 rpm band on my fresh rebuild 1986 22re in my 86 4runner DLX. It is definitely ignition related because I'm seeing dropped spark on all 4 cylinders. to keep this simple I will just list all the stuff that tested with high resistance and I replaced along the way as well as some other systems that were replaced.

New parts:
-Distributor cap
-Rotor
-Distributor its self
-coil
-igniter
-igniter wiring between ECU and igniter (found shorts happening between the 3 wires from getting cooked over the years)
-tested plug wires and coil wire, all tested good
-replaced fuel pump
-replaced fuel pressure regulator
-injectors rebuilt
-all vacuum hoses replaced
-intake tube rubber flex tubes replaced also checked for leaks on the PVC intake tube
-replaced and calibrated the TPS with new OEM TPS, old one had mechanical lag
-tested the circuit opening relay
-tested to make sure the AFM opens the circuit opening replay and turns on the fuel pump and it does
-I also ran the truck with the fuel pump jumped (B+ and Fp) just to make sure it wasn't the AFM connector getting intermittent connection and causing the fuel pump to drop out, no change in behavior
-I checked valve clearances several times and they are good
-I also ran compression tests on all 4 cylinders and they are well within spec and only deviate 5psi between all 4 cylinders.
-Tested the EGR valve and the engine stalls when vacuum is applied with my mighty vac tool (according to FSM this is a positive good test)
-also checked that there was no vacuum at idle on the vacuum modulator and tested the Thermal vacuum switch on the front of the lower intake.
-Vacuum at the intake plenum is 21" of vacuum
-Sanded all engine grounds to bare metal and reattached ... tested negative sides for voltage drops all was good.
-tested TPS and AFM pins from ECU side
-Tested Various ECU pins to ground as well as resistance tests
-pretty much every wire from the ECU side checked out ok, the readings were the same for the TPS and the AFM as they were from the pins on the units themselves... I didn't really see any variations in resistance on anything until I noticed the igniter wires were shorting when they got really warmed up ... if I giggled them while doing a continuity test I was dropping tone and the resistance was going to 0.000 that said the voltages to the igniter from the ECU side were within spec listed in the FSM 0.7 volts to 1 volt. I didn't manipulate the wires at all when I tested the voltages though as I hadn't gotten to testing the resistance between the ECU pin side and the connector end of the igniter wiring.

several times in this process the truck ran great as if it were fixed for 1/2 a test run or an entire test run only to start missing randomly the next time it was started or half way through the test. I can recreated the misfire from the engine compartment by manipulating the throttle and it always starts around 1800-2000rpm range and ends at about 3000 rpm. no missing bellow or above those ranges except at idle. it will rev steady then suddenly pop pop....pop...pop pop. most of the time when I've replaced parts I pulled the battery leads which in turn resets the ECU so I'm assuming at this point (since I've gone through the entire list of troubleshooting ignition issues listed in the FSM except for the ECU) that its the ECU. I notice that when I put a timing light on the crank pulley and get the misfire to happen the timing mark advances really far over to the left sometimes taking the timing mark out of sight ... I've read that the ECU's can be faulty and cause the timing to advance too far which will cause a random misfire like I'm having but I'm not really sure what too far looks like. I read a tech bulletin that suggested retarding the timing to 3 degrees instead of 5 (base timing) so I also tried that but it hasn't corrected the misfire. Retarding the timing was one possible solution for the advance issue but the second was a replacement ECU. I'm at the point where I'm going to start looking for a second ECU to test this with but I wanted to ask here just in case there is something else obvious that I'm not seeing? I'm grasping at straws at this point. Any suggestions?


Thanks in advance!

I've got a gauge on the cold start banjo and it's reading within spec. Like I mentioned the fuel system has been gone through as well ... new pump , regulator, injectors cleaned and recapped and new micro screens... also ran a backup set of injectors to be sure and same issue. the injectors fire away with no mis when the engine misses... I listened to all of them with a stethoscope and they never miss. fuel pressure is around 30psi max 40psi and it's a liquid filled gauge using one of LCE's modified banjo bolts. when it's running at idle its around 30 psi and jumps up as throttle applied if the ignition is at the on position and I jump the Fp and B+ ports the pump puts out 40psi. Also watched to see if fuel pressure drops on my gauge when the misfire happens but it's steady. Also I verified the misfire is coming from ignition i.e.: random misses on the plug wires. everything there has been replaced .. distributor, coil, tested a new set of NGK wires for the hell of it, distributor cap and rotor... even went back to my old cap and rotor just to be sure it wasn't a bad new cap and same thing ... second igniter and I rewired the igniter wires to the ECU.

Another thing to note is the previous owner swamped the truck and hydro locked the engine with water then he said he rebuilt the engine but after I had major issues and started tearing into it, it became obvious he just pulled a junkyard engine and put it in. So, the ECU could potentially have gotten wet, actually sounds like it definitely did get wet so that's another reason I'm wondering if these symptoms could be ECU related.

Spark plug gap is correct?
Is the number 3 ground wire attached to the head?

Does it drop idle when you jump the "test connector"?

Verify the female side of the involved electrical plugs are tight. By this I mean tight enough they are a little difficult to put together, this will shave a bit of the prong when they get put together to the bright clean conductor. Just don't deform or break anything.

​​​​​Then pop the cover off the ECU. Take a bright diffused light high resolution photo. Will be looking for water marks (typically white crusty bits), dry solder joints (silver crystalline, not smooth mirror), loose connections (micro gaps), and discolored components.

I'm gonna do that on the weekend just to check it out. Thanks. Great idea. Gonna see if there are any caps on there I could change out. 32yo caps!!

OP, did you measure you have idle on the TPS? (Does it drop RPM when you connect the test jumper, as if you where checking engine timing?

I also have the issue, but here it is more like cylinder just not firing. No "pop" at all to speak of.

On mine it will just "miss" a spark, rpm drop ever so slightly, and it keeps going. It is MUCH better now with the number 3 GND connected, but you already checked that.

I'm uploading my misfire right now.
My plan is indeed the 3°, 2° remedy, after checking the ecu.

Does yours sound like this?

https://www.youtube.com/watch?v=MuAp...ature=youtu.be

Ok so I'm back. I procured a spare ECU for 50$ it wasn't the problem (of course) but still I wanted a spare ECU and 50$ was a price I couldn't turn down. that said I have new info on my problem. I started going through testing the main replay, starter relay, injector solenoid all of that tests good. then I started up the truck this evening and just started shaking the engine wiring harness portion that goes from the firewall to between the intake plenum and the truck died on me. I reproduced this 4 times in a row by touching one area of the harness. Looks like the previous owner was in there at some point because it's sealed up with electrical tape. My bet is ether there is something incredibly jenky going on in the harness with some sensor wiring or ecu grounds or I have the dreaded fuel injector split of death issue going on. I need the truck for the next few days so I can't tear into it now but after Tuesday evening I can pull this apart and correct any issues I find. I'm fairly certain it is the injectors because when the engine died I could hear the injectors clicking and trying to fire if I continued to manipulate the harness. I guess I'm glad this never happened to the point of stalling while I was driving it.