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Bizarro intermittent misfire, Poor idle, & Concerning tick

8K views 68 replies 6 participants last post by  aidan7777 
#1 ·
Hi guys. Just got my trooper back together after a long while. While my rust repairs have been holding up pretty good, i can't say the same for the engine, it still runs just as poorly as i remember..

I have tried each and every single thing i can think of, and i'm pretty much out of ideas.

For a start, it idles terribly. On both high and low idle speeds, the RPM constantly dips due to misfiring. (can hear popping from the exhuast) At high idle, it runs with the misfire but doesn't stall due to the high RPM, at low idle, the misfiring often stalls the engine outright.
Recently, it started consistently misfiring over 2500 RPM. After replacing the cap and rotor, it still continued to do so for a while, then subsided, but i still have an extremely poor idle.

It cannot POSSIBLY be a vacuum leak. I have replaced all the lines, including all the fat ones, i have completely torn apart the intake to replace every gasket (and do the '5-tec' mod for serviceability's sake). Unless i somehow made a mistake reinstalling the intake manifold, i just don't think it can even be possible. this problem was the case long before i did the job.
EVAP canister can't be causing a leak internally, either. I've tried pinching the lines to it closed to isolate the issue, and the condition didn't change at all.
If it somehow is a vacuum leak, it'd be injector seals as i didn't replace them. even then, they looked just fine.

On another note, the engine also makes this concerning ticking noise that increases in frequency with RPM. Word has it that the 4ZE1 always has a ticking sound, and that when it runs right it should sound like a sewing machine.
I adjusted the valves a while back, and it didn't seem to help with very much at all. I shot a video of it doing its thing, if it's of any use.

Here's all the information i have about this car.

All my fuel injector and spark plug wires are hooked up correctly.
I have tested the IAC, and it is working just fine.
IAC is mounted in the right direction.
Throttle position ""sensor"" (read: single pole double throw switch) is positioned where it should be. idle contacts have continuity.
All plug leads are reading around the range of 2.5 Kilo-ohms.
Spark plugs are fairly new, however every single one has a uniformly black, sooty tip, as if the engine's running rich all across the board.
Injectors are ticking as they should. although #2 sounds like it has a weaker click than #1.
Service manual says the secondary winding of the ignition coil should measure at 9.4 kilo-ohms, however, mine reads 10.4. (could that cause a weak spark? or is that within manufacturing tolerance?)
I've fiddled with that idle air mixture screw on the back of the throttle body til the cows came home, and it hasn't made a lick of difference. The 'ghostbusters symbol' o-ring on it isn't perished, i don't see any compression set on the edge either.
Ground on the rocker cover is not weak. I ran a wire from the ignition transistor to the intake manifold just to be extra sure.
The car does not smoke, There is no coolant in the oil or oil in the coolant, When my family bought the car 8 years ago the P.O said the engine was rebuilt, whether that means rings and bearings or something more, i don't know. Can't possibly have a bad head gasket.
All valves are adjusted to .008, or 0.2mm.
Exhaust manifold gasket is new.
I welded the crack in the exhaust manifold that was making an alternative annoying ticking noise upon acceleration.
When i had everything apart. I sucked and blew on the vacuum hose that actuates the diaphragm in the fuel pressure regulator, and wasn't able to get any air out of it. Maybe its different when everything's under pressure, though. doubt the human lung can top 60 PSI of fuel pressure, or 17 PSI of vacuum. (don't any of you dare make jokes about ex girlfriends!!!!!)

I'm stumped, guys. The only thing that comes to mind now is taking all those injectors out and bringing them to the local injector shop to be tested. They may very well be original, and this car has 405,000 something kilometres on it.

Any ideas? :(
 
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#27 ·
Sorry about the job thing.
It's been a long time since I had a 2.6 dizzy opened up, but I thought I remembered a LOT of slots. I could be wrong on that.
Page 43 of my build thread shows where I was having a vacuum leak problem. Includes injector stuff and before and after vacuum gauge readings. Hope it can be of help or encouragement. Dennis
 
#28 · (Edited by Moderator)
Yep, you're right. It's got several. This makes a lot more sense to me. guess the 4 slots are just a sync' signal of sorts?

IMG_20210506_234129[1].jpg

I took it apart last night to have a look, and saw the sensor was covered in oil. Strange, considering all the o ring does is seal the oil from leaking outside the engine, not inside the distributor.

I guess this means i need a new distributor? I haven't tested the sensor waveform yet, But this is concerning.
 

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#29 · (Edited by Moderator)
Pulled the distributor and figured out why the oil's coming in. Distributor bearings feel very smooth, no rough spots or anything else suspicious. But..

IMG_20210507_180012[1].jpg

O ring looks to have failed from 'compression set'. the most common failure mode of o-rings. The rubber is so hard and brittle that it split in half when i tried to pick it off.

And the oil is coming in through the crank position sensor's plug socket.
distributorleak.PNG


My hypothesis is that the oil is coming in and skinning over some of the fine little slots on the trigger wheel. It'd explain why the problem comes on after it's run for a minute, or about the time it takes to start kicking down into low idle.
 

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#30 · (Edited by Moderator)
Okay, I got a new O ring and replaced a cracked hose which was going from the middle of the intake tube into the valve cover. While i dont think that could cause a vacuum leak, i'm sure it'd definitely lean things out.

Now all that's troubling me is the distributor timing. I have done it exactly as the manual has told me to twice, and both times it simply refused to turn over, occasionally trying to fire on one cylinder only.
I know for a fact that cylinder #4 is at TDC. Both valves closed, Cam timing mark on the cam belt pulley is lined up. (pulley mark isn't but thats because the balancer's slipped 20 or 30 degrees :evil:)

I tried pointing the rotor at the stud that locks the distributor down like JLEMOND recommends, and that did make it fire up, but only for a short while before it dies again. Backfired a bunch, too. (perhaps i was a tooth off? i can't really get a true line of sight.)

manualdistributor.PNG

settingmarks.PNG


Is the workshop manual wrong? :?
 

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#31 ·
Guess it is wrong. I turned the distributor a tooth clockwise from that mark, and it fired right up. Is it any better? Absolutely not.

It still has a serious misfire at 2500 RPM that stops it from going any higher, even though i have a brand new cap and rotor, and have cleaned all the carbon off the plugs.

I got a vacuum gauge the other day, and it fluctuates around 17-18. DSUZU's truck got around 22, so I'm hoping this is because he's at sea level, and i'm a kilometer above.

if i somehow STILL have a vacuum leak, i have absolutely no idea where it is or how on earth i can have one. I have sprayed oil over EVERY gasket, EVERY seal, EVERY hose, and none of what i did changed a damn thing in the vacuum reading. Looks like i'm due to spend even more money..

I have replaced everything seal related on the intake side except for the injector seals, and i didn't replace them because they didn't look bad.

I am getting so fed up with this. I'm going to take the intake off again, inspect the injectors and the seals especially well, and perhaps even shell out ANOTHER 120 bucks to get the stupid things tested.

EDIT: Went over to the injector shop today and handed them in, they'll be phoning me tomorrow to tell me how it went. Least it'll be 100 bucks. not 120.
 
#32 ·
I got a vacuum gauge the other day, and it fluctuates around 17-18. DSUZU's truck got around 22, so I'm hoping this is because he's at sea level, and i'm a kilometer above.

I have a vacuum gauge hooked up and mounted in my dash. My engine has the carb conversion but I'm thinking the readings should mean the same. The barametric pressure changes about 1 inch per 1000 feet, so yea, at 3000 feet (1 kilometer) your reading is going to be lower. Shouldn't fluctuate, at least not much. Mine reads 22 to 23 at idle, engine warmed up. And it's steady. Just pulling out the manual choke will cause the reading to drop and the more air I take away the lower the reading goes. I'd be curious to know just how much the vacuum reading would change for every 1000 feet above sea level. I'm at 500 feet so that's basically sea level.
 
#34 ·
Thanks for the words of encouragement, guys. I think the vacuum's just fluctuating due to the misfire.

Now, I wonder.. Since the misfire's at its worst at 2500 RPM, it makes me think this might perhaps be a fuel pressure issue? I've already had a couple of fuel filters get blocked up, one time while i was on the road, and both times it completely killed all my power if i tried to give it any reasonable throttle. My tank might be getting rusty.

The tan tops on the injectors also lead me to believe they are the originals. 30 years and 251,000 miles are LONG past when the automotive grim reaper starts calling, so i'm hoping the fuel injector people come back to me with some bad news! :D
 
#35 ·
Just got my fuel injectors back last night. The man told me they were within 10% of eachother, and that he got them within 1. He demagnetized them, ran chemicals through them, replaced the screens, replaced the bottom seals, even cleaned the dirt off the casings, Did a very good job of it.

Did it fix the problem? No. The misfire seems to have moved up to 3000 and seems a little less nasty, but it is still there. I haven't tested the idle yet, but i'm sure it'll be just the same.

132 bucks, and for what? Either there's something strange going on with my fuel system, I have a vacuum leak in some unfathomable place, or i have a burnt valve 20 something thousand kilometers into a rebuilt engine.

I have NO idea how the vacuum hoses are supposed to be routed. I only have one vacuum switching valve on the starboard side of the engine bay for some odd reason. does that mean somebody's been fiddling with it before me and routed everything wrong? I get vacuum at the regulator on a cold start, The line coming from the bottom of the throttle body goes into a T plug. one end goes to the canister line (???), and the other end goes into this mystery VSV.

Anyone have a picture of what the vacuum switching valve's supposed to look like on a 90? This is weird!
 
#37 ·
I don't think so. I'm sure i would've seen it when i was working around the frame a few months ago.

Never seen vacuum lines go down there at all.
 
#39 ·
I just went out and tested it out. Good news is the injector cleaning really brought the ticking noise down. it's nice and quiet now, only ticking now is from the valvetrain itself.

Bad news is it still constantly tries to die at idle. The high speed misfire seems to clear up when the engine starts coming up to temp, but no matter how high i turn the idle screw, it'll still misfire a bunch and start to stall.

Still hear popping out the exhaust when it does it. I guess if the vacuum lines are misrouted, that could lean out my idle too much. That's all i have at this point.

I'll be going to my dad's place in a few days, and i'll be staying for quite a while. So if this topic goes dead, i haven't given up on it. I'll update if i find anything wrong.
 
#40 · (Edited by Moderator)
Here's a picture of the valve. None of vacuum hoses line up at all with what i see on the diagram, and i get vacuum at the FPR on a cold start. Clearly something is amiss.

IMG_20210516_123920[1].jpg

I sent JLEMOND himself an email asking about this mystery VSV. Hope to hear back from him soon.
 

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#41 ·
aidan7777 said:
i get vacuum at the FPR on a cold start.
You SHOULD have vacuum on the FPR on a cold start (or any start). Some have hooked the FPR vacuum hose directly to the plenum chamber, and theirs ran okay that way.
What you DON'T want is vacuum to the EGR valve on a cold start and be sure your EGR transducer is working and plumbed properly. If you suspect you have an EGR issue, just unplug the vacuum hose at the EGR valve, plug the hose, and see if that makes a difference. Dennis
 
#42 ·
Fair enough. Most cars have constant vacuum to the FPR, anyhow.

Here's the thing, though. I don't HAVE an EGR. Either it wasnt standard equipment here in the first place, or it was removed when the calmini tri-y's went on.

One of my EVAP lines is going straight to the T joint on the end of the throttle body line, though. something's clearly wrong with the way this system is routed, and that single vacuum switching valve only makes me more suspicious.

I'll see if i can find a proper VSV from a wreckers yard up at my dad's place. If not, I have a terminal crimping tool and a wiring diagram, Any pair of valves from any make and model will do.
 
#43 ·
Checked spark plug wires today. I see a little cut on one, and long flat spots on the rest where the cables have been rubbing on things, but when i bend them around with the multimeter hooked up, I dont see the needle fluctuate. around 2 to 2.5 kilo-ohms per wire. None of them show conductors.

Only trouble is they fit sort of loose on the plugs. The wire on #3 is noticably looser than the rest, and has a distinct bend in the spark plug boot, like somebody stepped on it or something.

Just ordered a compression tester and a neat little chinese boroscope. When i get back from dad's place, i'll post compression test results + photographs of the combustion chambers and valves.

If i do find a burnt valve, I don't think i'm going to throw away this head. the rest of it is in really good condition.
 
#44 ·
Oh yeah, one piece of information i forgot to add earlier, if its of any use.

My dipstick keeps popping out, and the PCV valve on the top is wrong. its port is differently sized to the corresponding port on the plenum.

Can that cause problems with the vacuum system, or not? apart from plug wires, i am completely out of ideas.
 
#45 ·
Sorry for spamming up this board, just want to make a quick update on where i'm at right now.

I made a little homemade smoke machine out of a glass jar, a piece of hose, and an old schrader valve from a dry rotten inner tube. Lit up some shredded cardboard in there, made it smolder, then hooked up a little 12V air compressor and went to town.

That intake had more smoke in it than cheech & chong and i still couldn't find anything. both RUN and ACC gave me pretty much nothing at all.

The only smoke that came out was from the throttle body. Couldn't get that sealed perfect, even with tons of layers of glad wrap AND a nice tight constrictor knot. (i had so much pressure that the elastics kept blowing off). Didnt see smoke coming out of anything else at all.
It was well in the little hoses. pull one off the top of the FPR and it would BILLOW out.

It's got to be either misrouting (as i said before, the hoses do NOT match up with the diagrams), a leak in the PCV line, a result of it having the wrong PCV valve(even though it rattles. i can still suck a fair amount of air through the barb side, though.), or something very very serious. I have a reading of 17-18 in/Hg at 3500 feet, which should be well within the normal range.

EDIT: Just replaced a dodgy homemade cap on the intake with a proper rubber plug. It was an old battery terminal connector over a coil of tape tightly wound over the outlet, sealed off with a screw clamp. I dont think it'll help, but if not, it'll at least rule it out.

EDIT 2: It didn't
 
#46 ·
aidan7777 said:
Sorry for spamming up this board,
NOT! This is EXACTLY what this forum is about - helping people solve problems. There have been "problem child" problems that were SEVERAL pages long.
Now. First on the PCV - try just removing the valve and plugging the hose. This should give you a lower, rough idle.
Another thing. After re-reading this entire thread, I have to ask (suggest) are you absolutely sure the timing belt timing is right. A tooth either direction and they can run, but have all kinds of symptoms. It really isn't difficult to check, just the top cover and align the mark (if your balancer is still accurate (crank should be at zero). Just sayin. Dennis
 
#47 ·
Thanks, dennis.

I removed the PCV and just capped off the port yesterday, the high speed misfiring seemed to subside, but that could be because the engine wasn't stone cold. the issue is at its worst on a cold start. idle really didn't seem to change, still had an erratic 500rpm dip on high idle.
It's obviously the wrong valve. the barb is a different size to the port on the plenum. god knows how wrong the flowrate might be.

Timing, huh? i never would have thought of that, I'll check the timing today.
My balancer is seriously out of whack, though. will that be a problem, or no?

I remember getting this car to run well by spraying oil down the IAC line a few years ago, can't imagine what might've happened in the meantime. crank angle sensor still dirty? i couldn't get the sensor wheel off because the screw stripped.
I'll run another smoke test, too. this time i'll plug up the throttle body extra tight. Vacuum leaks still aren't ruled out.
Can misrouted hoses do the same thing as a leak? i've been having no end of trouble finding them.
 
#49 ·
I only had one VSV for some odd reason, so I can't match the diagram in the first place. The EVAP canister line goes straight into the T on the end of the hose coming out under the TB instead of going through a VSV with a 'hat' on one end, but crimping that line doesn't seem to do any good.

The problems only really seem to manifest at high and low idle, and intermittently around 2500 RPM as a misfire. but above that everything runs just fine. I took it to 6000 on a test drive and it didnt complain about that at all.

The single VSV i DO have matches up just fine with the diagram, but the fact that i don't have another one on top is what's bugging me. Everything else seems to match ok.

I broke off the straight part of the "T" while i was taking it off, What looked like a nut holding its bracket onto the wheel well of it was actually a captive one, and i thought it was siezed, so stupidly, I put some muscle into it and broke it. Never work angry..
Can't find the piece anywhere on the floor, so it looks like i'll be buying one anyway. In the meantime, i'll route the fuel pressure reg straight to the intake plenum and run it that way if i need to do work around the property.
Despite that, i put it on my test bench and put power to it, it clicked, so it was working fine before i screwed it up, but the thing that interested me was the way it directed the airflow. powered off, it directed air from the 'bent' section of the T to the line behind the solenoid, and powered on, it directed it from the bent section to the plastic line INFRONT of the solenoid which i broke off.
This would give the ECU the choice of taking vacuum from either the intake manifold itself, or the port underneath the throttle body that goes into the T fitting. (NOT the one that if equipped, would go through a thermal vacuum valve, then through a back pressure transducer. word has it those ports have different characteristics of some kind.)

I don't understand what difference it would make. everything behind that butterfly valve is under the same vacuum, isn't it? is there something special about that particular port?

I also ran another smoke test, still didn't find anything. but there was smoke leaking out the top of the dodgy jar setup i was using, so maybe that could've covered something slight.
And as for timing, i'll have to take a bunch of things off to remove the lower part of the cover. Need to rely on both the timing mark up top and the one on the crankshaft pulley if i want to make sure everything's right.
The belt IS tracking a little to the side facing the engine, though. I don't know if that's bad.

All in all, thanks for the suggestions. each and every one counts, as i really don't know where to go next.
 
#50 ·
Is your truck a NON air conditioned one? Dennis
 
#51 ·
No, it's air conditioned, but it doesn't have the little AC idle solenoid.
Do the manual trucks not have that one?

I also noticed my throttle body has a little up and down play. I know worn throttle shaft is a classic area for vacuum leaks, but for whatever reason i didn't see any smoke come out of it.
Then again, my setup wasn't exactly the best way of doing that test.
 
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