My misfire thread..

[Killdozer1776]

6 months ago I bought a rusty 96 with small issues and rust for cheap. Had a very slight misfire. I had the codes ran, and they were for: O2 sensors, multiple cylinder misfire, and specific codes for each cylinder misfire.

The intake tube was duct taped so I put a new tube on. Then put in new plugs (properly gapped), wires, cap and rotor. Still had the misfire but it was pretty minor and only occasionally would it sputter at idle. Fine under load.

Cleaned battery connections, checked most of the grounds but still need to look at a few admittedly. And look at the fusible links (I actually don't know wtf these are or how many there are.)

Over winter the idle got really bad, it would surge up and down from 400 to 800 and it recently lost power and ran really rough and crazy, sometimes dropping to 400 rpm, sometimes dying at the very rough idle. This was right after I got new brake lines, master cyl, and proportioning valve.

Today I opened up the harness that was resting on the EGR pipe and saw that somebody had already repaired it, but some of the repaired sections were burnt so I replaced them. The previous replacement wires were 16 gauge, while the oem wires appear to be 14 mostly. I unfortunately had bought 16g because walmart didn't have 14g, but I figured new wires of the same size would be better than burnt ones, and the difference isn't -that- large.

I've been asking and can confirm (for people's future searches) that the 96 wire harness uses mostly 14 gauge wires , at least by the EGR pipe. The job is quite easy, just a backbreaker leaning on and over the engine standing on the frame. I also pulled the harness down underneath the EGR junk and over the manifold toward the passenger side, far away from that pipe. Fastened in place.

Anyway it runs much, much better now and actually idles at 600-650 (not completely consistent still). Has lots more power and I'm pretty happy. I also haven't had a trans slip yet (probably just jinxed myself) and may be the cause of the 'solenoid' issue. I hope.

Still a slight stumble intermittently so I waited for the CEL to come back on and had the codes read.

Multiple Cylinder Misfire
Cyl 1 Misfire
Cyl 2 Misfire
Cyl 4 Misfire
Cyl 5 Misfire
Cyl 6 Misfire

I've read that I have to check the harness section in the glove box area, but I don't exactly know what I'm looking for there as I can't imagine what kind of damage could be done away from the engine and probably not rubbing anything.

I was worried about the head gasket, but the oil is still at full and clean from a couple months ago. I DO have my oil idiot light coming on/off in the dash constantly. That wouldn't make it run weird, would it? I doubt it.

There is old oil and crud around the valve cover gasket, and the rearmost bolt for the valve cover is busted off (MOTHERF PREVIOUS OWNER!). It could be sucking in air at the gasket, but I have a feeling that's not it. Yeah one bolt is broke but it's not going to make it that loose. And the problem is intermittent. Sometimes it runs A+. I've had a truck's valve cover gasket fail before and have vacuum issues slowly mess up the idle, then it got worse before it finally died on the road, never to start again until refreshing the top end.

I plan to do the same here just because it needs to be done, and I'm also going to remove the EGR system and as much smog crap as possible, replacing all vacuum lines and gaskets, etc but I don't think any of that's the issue. I'm also going to do the head gasket while I'm down there anyway.

I've pretty much ruled out sensors at this point. They'd be fine or bad, not intermittent for half a year. Plus no CEL for them. Wouldn't hurt to clean the MAF or whatever it's called.

Injectors? I know they clog eventually in diesels but is it really that common w gasoline? So again, I doubt it.

Maybe the head gasket is only slightly bad. Not enough to noticeably burn oil or mix oil with coolant? I'll do a compression check when I finally get around to it, but again, I doubt it. Even the coolant temp is always perfect and never gets hot.

What's left?

Edit to add: The fuel filler neck leaks a little when I put gas in. Perhaps air could get in through that, but I don't see how that would mess up the fuel/air mixture, being upstream of the gas on top of the pump.The vehicle is old and rusty enough that it could use new fuel lines, pump and all tubes. I can't do all of this at once so I need to narrow it down and come up with a plan.

 

[PDoyle]

Check the large air hose going into the air box they tend crack over time. You should get an OBDll scanner to read any codes. As for your back get an adjustable tire step.

 

[Killdozer1776]

Already replaced air tube. That and the codes that were ran are in the original post

 

[Rifleman]

Did you check the main engine wiring harness where it passes next to the EGR tube. It's a known problem with the EGR tube burning through the insulation on the wiring harness thereby causing misfires/shorting some of the injectors. When new the factory installed a plastic clamp to hold the wiring harness away from the EGR tube, but over years of exposure to heat that clamp can fail letting the harness lay against the EGR tube.

 

[Killdozer1776]

Thanks but i wrote about that in the original post

 

[CaptClose]

Lol... I think people are giving you advice after reading only your thread title. You seem to have covered most everything.

With misfires on all cylinders but number 3 (weird), I wouldn’t suspect bad injectors. The odds of 5/6 going bad suddenly are extremely low.

I’m thinking electrical gremlins. Perhaps go back and check your work near the EGR harness again. Also test your MAF, there’s a procedure in the FSM for that.

I’m curious to see how this ends up. I’ll be watching.

 

[Marine7]

I “second” Captclose, go thru the wire bundle by the egr again, maybe you ( or PO) missed a wire that’s cut short?. Injectors on these do go bad, but 5 out of 6 sounds suspicious. Good luck! I’ll be following.

 

[PDoyle]

Just a thought. What kind of new wires and plugs did you buy?

 

[Killdozer1776]

All NGK. Its not plugs or wires

Still running much better after the harness fix but today the surging in gear at idle reappeared for about 5 seconds.

Still misfiring

 

[PDoyle]

NGK wires? Check their connections. OEM is your best bet to eliminate any question.

 

[bigredmachine]

is the egr getting partly stuck open, I realize that you don't have egr codes but open egr at idle will cause your symptoms.

 

[Killdozer1776]

the symptoms are exactly the same as they were with OEM plugs and wires before changing them. my money says that's not it.

as for the egr, does anybody make plates for fixing it?

 

[Killdozer1776]

Has been running fine after patching the harness. Until this morning, after it rained overnight. Surging, bucking, popping, zero power.

These vehicles are said to be extremely reliable, but I think it's dishonest to not mention the very very common electrical gremlins

 

[PDoyle]

The vehicle is 25 years old. You bought one that needed work you knew that at the beginning. Don't blame Toyota. Fix it.

 

[bubfuji]

Misfire...relates to spark. Bad injectors would not trigger a misfire since the plug would still be firing. Bad idle yes, but not misfire
A blinking oil light would not cause this condition. You mentioned rust...how about the hall sensor inside the dist. I don't remember the exact terms for the components inside the dist. But there is a sensor-trigger combo under the rotor that tells the igniter (ignition module) to fire the coil. Needs to be nice and clean with the correct air gap to trigger a spark signal. Check the igniter condition, wiring . It needs a good ground. Finish checking the engine grounds. There are several grounds. Your ignition loves a good ground. Did you mention the coil itself...connections/conditions. You talked about harness issues. Maybe a wire is shorting to ground and missing up the igniter...The igniter is crazy expensive for what it does.

When I got water in my dist...i got the same misfire codes across all cylinders. So look for spark issues. The spark circuit... Dist signal to the ECU, The ECU to the Igniter, the igniter to coil, the coil to dist....spark!

A fuseable link is a wire designed to melt apart during a short circuit. Just like a blade or glass type fuse. You can buy a new fuseable link from Toyota. Or go to your local....Oreillys (parts store, or amazon) and buy fuseable link wire and fix it yourself. The fuse wire needs to be 1 or 2 sizes smaller then the wire it's supporting (connected to). People say replacing the fuse link helps....and it does because the connection gets refreshed. But....this would not cause a misfire.

Dumb question.....did you clear the codes. Its late here..., the codes may clear when the misfire stops. I can't remember.

Since your refreshing things. You can also clean (carefully) the MAF fine wire sensor with a q-tip. Lets the engine see how much air is getting to the engine. However...this would not generate a misfire. Only helps the engine efficiency.

Still thinking.......

 

[bubfuji]

Just saw your later post.....is misfire gone.? With the exception of the surging issues.

 

[Killdozer1776]

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.

 

[ccslider]

You can swap in a used harness and an ecu... I have both for you

 

[ppc]

That sounds like an ignition problem not an ECM. Have the ignition wires been replaced? The OEM wires have the date printed on them. On a dry, dark night open the hood and spray/mist some water over the wires, distributor etc. with the engine idling. If you see sparks then you have isolated the problem area.

 

[Killdozer1776]

That sounds like an ignition problem not an ECM. Have the ignition wires been replaced? The OEM wires have the date printed on them. On a dry, dark night open the hood and spray/mist some water over the wires, distributor etc. with the engine idling. If you see sparks then you have isolated the problem area.

I've ruled out ignition at this point.
Full and thorough tune up has been done with no change. The issue is wonky and intermittent.

When it's really acting up, it'll surge up and down 500rpm or more in an analog manner. Sometimes throwing it into neutral makes it smoothe out completely. It's more than an ignition misfire.

I wouldn't suspect the ecu without going through everything else first.

Older threads in this forum and others indicate that the ecu can definitely be the culprit. Very similar symptoms. I hadn't heard of this until recently.

Apparently capacitors in the ecu of old toyotas degrade after 10 years or so. If they're bad enough, they leak and damage the board. Oftentimes they're bad but look fine.

If it ever stops raining cats and dogs I'm pulling it to take a look. I think I might end up grabbing ccsliders spare ecu (dibs).

I just don't understand why moisture and humidity makes the issue SO much worse. Aside from my condensation-going-where-not-supposed-to theory.