My misfire thread..

[fjbj40]

Why don't you spray WD40 on various harness areas? It will displace the moisture. When you hit a spot and it improves the idle then dig into that area.

The fact that its raining now is a bonus, as you stated it runs alright when dry but not when wet.

 

[Killdozer1776]

Harness portion behind glovebox is fine, but what's this gray wire for? Radio antenna? I can't find the other end of it and the antenna is gone so it seems most likely

 

[Killdozer1776]

it runs so well when it's warm and dry. hard to even feel a misfire at all

one new symptom though, when shifting to park, idle jumps up to around 1000 and climbs slowly or stays right around there. also odd considering when it does act up, a percentage of the time the rough idle clears right up at a stoplight if i shift to neutral.

i'm certain this is not an ignition issue. harness issue seems less likely now. i'd think it would be always bad if wires were burnt. i don't see how the wiring would hold water without the sheathing being cracked or split. all wires look good, but when it acts up again i will be trying the wd40 test

there is an absolute ton of oil and power steering fluid caked all over the bottom of the engine from years past. if that sparks any ideas, please let me know. obv i'll be degreasing it very soon

 

[OffRoadScott]

I was having some serious misfires/stumbles shortly after I had my head gasket replaced on my LC. Right before the head gasket died I was planning on doing the cap/rotor/plugs. So when the dealer did the work they installed the cheaper plugs I bought. Recently I replaced them with some nicer NGK plugs and OEM cap/rotor and the misfire went away.

When I went to replace the cap/rotor I noticed some oil residue in the distributor. I cleaned the contacts that are associated with the distributor shaft and the misfire went away. I still have a misfire every so often, honestly, I think that the seal inside the distributor shaft seal is bad.

Check what the other guys/gals say to check but I would check for condensation/oil inside your distributor.

 

[BILT4ME]

My first few thoughts were going to be about the valve cover gasket and the spark plug tube seals, as both of those can allow free air into the engine and jack with A/F ratios. That MAY affect the surging.

However, since it appears to be heavily affected by high humidity, I would be thinking an electrical connector.

One possibility is the Neutral Safety Switch (NSS) connector under the center console. There have been a few folks here lately stating they took apart the plug, cleaned it and put it all back together with a bit of dielectric grease and it solved all the world's problems!

Another possibility would be the O2 sensor plugs since they can affect the A/F ratios based on their changes and I know moisture affects them and how they read. Maybe pull the plugs, clean them, put in some dielectric grease, and see if it helps.

 

[OffRoadScott]

Another possibility would be the O2 sensor plugs since they can affect the A/F ratios based on their changes and I know moisture affects them and how they read. Maybe pull the plugs, clean them, put in some dielectric grease, and see if it helps.

True story. Here in AZ, we have some crazy rains in the summer months (aka Monsoon). Last year after monsoon I hit a large puddle and shortly after my car ran like crap. It ended up being the O2 sensor plug got wet, I unplugged both and let them air dry, and then put the dielectric grease on them both.

 

[Killdozer1776]

I messed with unplugging the oxygen sensors last year to see if it would make a difference. So today I found the first O2 sensor somehow unplugged, open to the elements. The second O2 sensor was hanging out of the exhaust, it had rusted and fallen out with the piece of pipe that has the bung.

Last year I had a couple quick fill welds put onto the (downpipe?) that was cracked. Exh system is deteriorating fast. Rear muffler is missing lol. Going to have to piece together a whole exhaust and new O2 sensors asap. For now I reconnected the first one. The rearmost one that fell out is removed and the connector on harness side is sealed up. These appear to be the OEM O2 sensors.

I forget how closed/open loop works with a 96 OBD2. without the rear O2 sensor I hoped it would run a predetermined fuel/timing 'map/code'. Ironically after all this today I still had a slight misfire randomly at idle and sometimes low idle (~450rpm in gear)

The exhaust and o2 sensor issues were making the problem worse, probably contributed to the surging. But I don't think it's the cause of the misfire issue. Something still underlying. I can see the fueling being messed up because of the exhaust, but not ignition?

The valve cover is bad and I'd like to replace that and the intake plenum gasket, and whatever else I should do while there, later this summer. I considered the vacuum issues that could cause misfires, but I think it would be bad all the time, and not intermittent. Still has to be done, as well as new vacuum hoses, and 4000 other things.

I'd like to seal up the distributor where necessary to eliminate that as an issue. Does anybody have a picture of which part we're talking about?

Also, @BILT4ME can you tell me where exactly the neutral safety switch is located or do you have a diagram? I'd like to check this out too.

 

[BILT4ME]

Under your shifter.

Search NSS on here and you'll get detailed threads.

 

[ppc]

On our trucks the NSS is referenced as the Park/Neutral Position Switch in the FSM and is located on the side of the transmission where the shift linkage attaches.

 

[Killdozer1776]

I will do that tomorrow.

With the rear O2 sensor removed, it ran like a top today. I actually didn't feel a single misfire and the engine was much smoother.

Is it running predertimed fuel/timing? I thought it only would with the upstream one removed

I can't imagine erroneous air/fuel readings would cause a misfire

 

[Killdozer1776]

Ran like a top today in the rain and puddles.

I don't think all my issues are solved, but there's now light at the end of the tunnel.

Now I wonder if it's not misfiring due to the removed oxygen sensor, and running predetermined fuel/timing.

I'm a diesel guy, so help me out here.. Can/how does a bad air/fuel reading affect ignition? Does timing change as well as A:F to compensate?

 

[Killdozer1776]

It runs beautifully and I don't feel a misfire. Bump for if it's only running well because it's in open/closed loop ?(if it is with rear o2 s removed)?
I might just run in it like this haha

Sometimes at a stoplight in gear or when parking, the idle will be kinda high. 850ish. Sometimes at 1050 or so. But mostly perfect at 675ish steady.

Today in the heavy rain and puddles it was idling at the higher 1050. Once when I pulled in and parked (after deep puddles) the idle shot up to 2000 automatically before i could turn the key to off.

 

[tjones8]

It runs beautifully and I don't feel a misfire. Bump for if it's only running well because it's in open/closed loop ?(if it is with rear o2 s removed)?
I might just run in it like this haha

Sometimes at a stoplight in gear or when parking, the idle will be kinda high. 850ish. Sometimes at 1050 or so. But mostly perfect at 675ish steady.

Today in the heavy rain and puddles it was idling at the higher 1050. Once when I pulled in and parked (after deep puddles) the idle shot up to 2000 automatically before i could turn the key to off.

what ended up solving this?

 

[alia176]

I just read this entire thread and confused by one thing. The rear O2 sensor does ZERO engine control. It's purely there to let you know when the two cat converters are going tits up. So, how is it being unplugged and making his misfires disappear?

 

[RobE30]

I finally had time and weather to clean and check all the grounds I could find. No difference. Looked over the harness and all wires again. Looks fine. Inside the distributor cap looks new and clean, just as it did when I did the tune up.

I'm leaning towards an ECU issue after a ton of research and seeing how common it is on old toyotas and lexus'.

However theres a piece to the puzzle that's driving me nuts and I can't make sense of it.

In dry weather, it runs great with only a rare misfire. Mostly perfect idle etc.

When there's moisture.. Any rain or snow.. Its a bucking, surging, sputtering, powerless stalling pile that's not safe to drive in traffic.

This doesn't require going through puddles or anything. As soon as I start it up, if it's raining or recently rained, the issues arise as I put it in gear and pull out of the driveway. The worse it's raining/snowing, the worse it runs.

Perhaps the computer is damaged enough to where it somehow acquires condensation internally.

I've heard of bad/old wires soaking up moisture, but I'm not seeing any wires that look bad.

WHAT DOES MOISTURE AND HUMIDITY HAVE TO DO W ANYTHING?

At this point I'll have to try an ecu and/or new capacitors for it. If that doesn't work, it'll have to be sold for parts at a significant loss.

I haven't finished reading your entire thread but similar things happened on my friend's VW GTi. Even though we did a recent tune up, it would act stupid, falling flat on it's face when rainy. Ended up being a bad distributor cap AND a crack in the coil housing. Neither could be seen with the naked eye, replaced them out of frustration and it worked just fine after that.

 

[sbman]

This was a bit of a thread resurrect, but there seems to be some mis-understanding of what a 'misfire' code means. A misfire code does not directly relate to whether or not a spark at occurred at the spark plug.

The computer has no way to know what causes a 'misfire'. A misfire as detected by the computer is a failure for a cylinder to produce power at the time that it should produce power. The computer measures the velocity of the crankshaft at all times. When a cylinder fires, the crankshaft will change it's rotational velocity. If an expected fire event doesn't occur, the velocity of the crankshaft's rotation doesn't match the computer's expectations and can be labeled as a 'misfire'. This can be caused by having a non volatile air/fuel mixture (not enough fuel or too much fuel), not having a spark, or lack of compression.

To illustrate, think of someone with one leg riding a bicycle. This person would accelerate their bicycle when pushing down with their one leg, and then slow down until their leg came back around to push down again. Someone riding a bike with two legs will produce power twice for each revolution of the pedals, one push for each leg. If you graphed the speed of the bicycle against the pedal rotations, you could see in the graph each 'push' from the legs and easily identify 1 legged riders vs. two legged riders.

The computer does analysis like that in real time, looking for missing 'pushes' from the various cylinders and flags misfires when they occur.

 

[Rifleman]

Ended up being a bad distributor cap AND a crack in the coil housing. Neither could be seen with the naked eye

There's a very simple old mechanic trick to test for problems like this. Park the car in a garage, then wait until dark, start the car while keeping all the the lights off in the garage.

Inside that dark garage if any of your spark plug wires, or coil lead are leaking spark, those spark leaks will stand out like a sore thumb as bright blue flashes at the site of each leak.

 

[Killdozer1776]

A couple years later now. I was searching the archives of this forum and came across my own thread. See that 3 people are viewing it. Funny (not) how common this problem is with these trucks. 50 people will say 70 things fixed their problem, but it's intermittent (random misfire) so it's hard to be certain. And sometimes what seems like a fix really is just temporary coincidence.

Anyway I have done a lot of maintenance during this time but still have the misfire issue. It had gotten pretty bad recently.

Pulled the cap off the distributor as I hadn't checked that since I replaced it. Oil from inside the cap poured onto my hand as soon as I pulled it off. So the shaft seal is shot.

I imagine oil in the distributor could cause misfires? But the contacts in the cap seemed dry except for the center one. It hasn't been ran in a couple weeks so that's to be expected. The oil inside would cause issues besides the leak itself, right? I'm not sure if the oil just pools at the bottom or gets "sprayed" all over the contacts and eventually drips off of them. If this is the case, I'll get a new distributor.

Wiped it all out and it ran better. I hope I'm getting close.

 

[Rifleman]

I'll get a new distributor.

If i remember right, new one's from the Toyota are NLA.

 

[Rifleman]

Looks like i was wrong, Toyota is still showing DISTRIBUTOR ASSEMBLY P/N 19100-66020 as good for the low, low, retail price of $819 dollars.