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Discussion Starter · #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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With that many miles and the below compression readings, not surprised it's running poorly:

1- 150
2- 143
3- 133
4- 165

You've got a problem in #3 and it's likely a burnt valve. Maybe it's time to take another compression check, with the engine warmed, fuel pump relay(s) pulled, all (4) spark plugs removed, throttle wide open.

Take reading dry and then repeat with a couple teaspoons of motor oil down the spark plug hole of the cylinder under test.

Let's see if the readings come up significantly, if so then you have piston ring sealing problems. If, for example, the "wet" test of #3 doesn't bring its compression up much, that valve is very likely to be burnt. And it's always #3, ain't it!! :roll: #3 & #4 tend to run hotter for some reason. Seems like if the head gasket blows, it's almost always between 3 and 4. And so it goes.

A leakdown test is much more accurate than a compression test. If you have a shop near you capable of performing a leakdown test, shouldn't be extremely expensive.

Or you can do it yourself. An acceptable-quality tester for the layman who won't be using it every day, isn't extremely expensive. Amazon and eBay have lots of them. I would check Amazon, find one with a decent review, and then see if you can beat the Amazon price on eBay.

https://smile.amazon.com/s?k=leakdown+t ... nb_sb_noss

https://www.ebay.com/sch/i.html?_nkw=le ... ition=1000

https://www.hotrod.com/articles/cylinde ... wn-tester/

HTH & let us know what you find out............ed
 

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Discussion Starter · #3 ·
wrong topic? I haven't done a compression test. the car doesn't smoke, when i had the upper oil pan off the engine looked pristine.

I looked into one of the spark plug holes with a torch, and i swear i saw crosshatching.. Back when this car was still in service, I remember making this engine run beautifully by spraying oil into the IAC, and considering it hasn't left my property since 2018, i don't see what could've happened in so little time.

The misfire shown in the video seems to have subsided, though. maybe the cap & rotor needed time to 'bed in'? it runs just fine at high revs now. you'd think a burnt valve would hamper operation across the board.

Here's another piece of information about the fuel mixture, too. when i let off the gas while coasting, it pops and backfires. I think that's strange, since the workshop manual states the ECU makes a 'fuel cut' when the idle contacts are closed above a certain rev range. leaking injectors? i have no clue.
 

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Oops, sorry I was looking thru some of your older posts and the compression test was just a thread in which you had only replied to the O.P. :oops:

Might not be a bad idea to do one, though, especially since it's popping thru the exhaust. Could be a sign of leaky exhaust valve, or perhaps lean fuel mixture.

BTW I did watch the video and the ticking doesn't sound extremely abnormal. Maybe just a bit more than normal, but not to where I'd be worried.
 

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Discussion Starter · #5 ·
Ed Mc. said:
Oops, sorry I was looking thru some of your older posts and the compression test was just a thread in which you had only replied to the O.P. :oops:

Might not be a bad idea to do one, though, especially since it's popping thru the exhaust. Could be a sign of leaky exhaust valve, or perhaps lean fuel mixture.

BTW I did watch the video and the ticking doesn't sound extremely abnormal. Maybe just a bit more than normal, but not to where I'd be worried.
Thanks for replying so promptly, man. It's good to know the ticking isn't worrying for this kind of engine. maybe i didn't have enough drag on my feeler gauge.

Could partially clogged injectors perhaps be causing a cylinder or two to lean out under certain conditions? It'd be funny if that was the case, since all my spark plugs came out black, like its been running rich across the board.

Granted, it's only been doing work around the property for the last 3 years. No long drives, often it doesn't even get up to operating temp. Only been taking it up to temp recently with some proper test drives up and down the country lane. perhaps that may be the reason they're black?

I am surely hoping it isn't a valve problem. If it is, i have a torque wrench -- the head's coming off. I am too far into this project to give up.
I might be getting a job on monday or tuesday, If i'm successful, i'll at least have the money to be doing this stuff.

But let's say worst comes to worst and i do have a burnt valve. what do i need to do? If the head needs to go to a machine shop, i can imagine that'd get very expensive.
 

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This guy had a few issues after a "5-tec" mod. Maybe there's something there that would help:

https://www.planetisuzoo.com/viewtopic.php?t=136987

Some very good tips about ITEC running-rich in this thread, pay particular heed to Dennis' words:

https://www.planetisuzoo.com/viewtopic. ... &hilit=MAF

How 'bout the MAF sensor? Overfueling on all 4 plugs might make one think there's something wrong with the MAF, its wiring, or maybe even the ECM itself. Not uncommon to see a hole worn in the air intake tube between MAF and throttle body, where the tube contacts the valve cover. Hard to see unless you pull the tube completely off.

Here's some good newer 2.6 MAF testing info that should be applicable to your older 2.6. AFAIK the only diff between older and newer MAFs is that the hole is WAYYYY bigger on the newer MAF. One would think that could be a performance-adder to an older 2.6, eh? That and a newer-style head with heart-shaped combustion chambers.

Quite frankly, if you do discover valve problems, I wouldn't even mess with the old head. Buy a '93-up 2.6 head, and the smaller combustion chambers combined with earlier 2.6 flat-top pistons gives you a nice bump in compression ratio.

Depending on the casting # of your old head, (such as 1, 2, 3, definitely), they are prone to cracking and valve issues. Later castings are much more stable, if you can find an OE head it's even worth doing a valve job on it. Or get an aftermarket head, the castings are thicker and not prone to cracking. Usually if an older 2.3 or 2.6 overheats badly, it's very likely to blow the head gasket and crack the head.

And just one thought on spark quality; if you put an inductive timing light on each plug wire in succession, you'll get a pretty good idea if there's consistent spark on all the cylinders. Checking while the system is under compression will weed out marginal spark pretty fast.

Another way to stress the ign system to potential failure is to gap-out a plug you don't care about, to at least .080" or as wide as it'll go. See if spark will jump this extra-large gap with force. You should see a whitish or purplish spark, if it's reddish/orange/yellowish, that's too weak and will blow out under cylinder pressure, causing misfire.
 

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Discussion Starter · #7 ·
Thank you very much for the info! i'll be sure to look into these threads right away.

I checked for holes in the intake tube. I found a ***** taken out of a plastic tube, but I couldn't suck air through it, so i assume it's not anything serious.

MAF sensor, eh? I hope there's an easy way to test those. I had a look at the heater and resistor and they seemed to be fine, neither was broken off at all.
I know in newer cars you can unplug them and the engine controller will start reading 'best guess' air values from a predetermined table, but in this thing, the bugger just straight up refuses to run.
It's not as if it can determine throttle position, anyway. the 'sensor' in this thing isn't even a proper potentiometer.
It does have an aftermarket 'pod' filter, though. I don't know if that's skewing the readings or not.

It's a 1990, I know 1988 certainly had bad head castings, but i think they fixed that in 90 and 91..

I don't yet have an inductive timing light. so might just have to make do with my oscilloscope. wrap a coil of wire around a lead, then hook the probe to both ends.

IAC is still attached and hooked up like it's supposed to, btw. High idle is working just fine.
 

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Discussion Starter · #8 ·
I just tested my coil with my bench power supply and an old spark plug i gapped out like crazy. didn't have anyone around to crank up the car for me.

The spark looked orange under a light, but in the dark, it looked purple as it should be. I'm still a little concerned about my coil reading a whole kilo-ohm over its spec, though. Are spark plugs supposed to make a loud snap? or just a quiet little click? :?

EDIT: Tested again with the gapped out plug. spark doesn't make much of a sound. i cant really see it when i shine a bright light on it, looks a little orangey, but not overly so..
 

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aidan7777 said:
I just tested my coil with my bench power supply and an old spark plug i gapped out like crazy. didn't have anyone around to crank up the car for me.

The spark looked orange under a light, but in the dark, it looked purple as it should be. I'm still a little concerned about my coil reading a whole kilo-ohm over its spec, though. Are spark plugs supposed to make a loud snap? or just a quiet little click? :?
You might not get much of a snap out of a spark plug. If you were to unplug the coil wire from the distributor, and place the free end of the wire about 1/2" from the block, you should get a pretty decent spark jumping the gap when cranking-over the engine. It might snap at you a bit!

If you get decent spark jumping 3/8" to 1/2" off the coil wire, that should be good enough.

Dunno about the coil being a bit high out-of-spec, how accurate is your meter? Temperature plays a factor in resistance values, as well.

BTW I've put a remote starter switch to good use when by myself, needing to crank over the engine. Or, with the hood open, position a plug wire close to the cowling so you'll be able to see it when you crank via the ign switch. If you're handy, you can rig yourself up any old normally-open pushbutton switch that's rated for 12VDC and maybe 10 amps or so, just disconnect the solenoid power wire at the starter, and hook-up the switch wiring between positive battery terminal and solenoid.

.
 

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Discussion Starter · #10 ·
Hmm. Would it be possible for a weak spark to be aggrivated by distributor contacts?? I sanded down the points and the rotor arm on my old distributor, and that's around when the 2500 RPM misfire problem happened.

Now, with the new cap and rotor it's still there in small part, but it's not as bad as it was prior. I really bent out a spark plug to the point it occasionally doesn't fire, arc looks slightly reddish, but i'm still not too sure on it. Perhaps the sooted up plugs might be interfering with it as well.
 

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Discussion Starter · #11 ·
Hold the phone, i've been doing some research about poor idle in these motors, and word has it if you have leaking distributor shaft seals, the oil will emerge into the distributor mounted crank angle pickup and foul up the signal, causing the ECU to not fire at the appropriate interval.

When i remove the cap, i often see a film of oil around the lower lip, but never any on the points. I also see oil sitting under the 'flange' that houses the bushing the rotor shaft rides in. Very suspicious. :|

I'll investigate tomorrow. if i find anything off when i pull out the distributor, i'll let it be known so others will know where to look.
 

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From the sound in your video, it sounds like when you rev it and back off, it takes a few seconds for the revs to drop. Is this accurate? If so, that is classic evidence of a vacuum leak. Do you have access to a vacuum gauge? A vacuum gauge can tell a lot about an engine. There should be a certain amount of vacuum at idle, a certain amount when cranking (w/ fuel or spark disabled) and a certain amount on deceleration.
You mentioned having the intake off. I had an issue with the gasket between the lower manifold and my common chamber. Dennis
 

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Discussion Starter · #13 ·
Thanks for checking in.

In my testing of this engine, i never really noticed it take particularly long to come back down to idle, however. if i've had a vacuum leak all this time, i might not know how it's supposed to behave when everything's right.

I indeed did have the intake off, manifold and all. Every gasket has been replaced, so if the leak's there, i'll be astonished.

i'm hoping it's something easy(ish) like that, though. my alternatives are not looking good, or cheap.

Unfortunately, i don't own a vacuum gauge or any other piece of automotive test equipment aside from a couple oscilloscopes. This is the first car i've ever gotten this far into, and i haven't picked up all the tools of the trade yet.
 

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Alright, I just went out today and got some more information on the vehicle.

When i started it up, it misfired a bunch on start, then went to high idle. creeping from 1500 up to 1800. I guess that's because i have the idle air screw adjusted improperly? (although, i also remember taking that thing all the way in to quell a high idle, and i couldn't get it below 1100. if this is a vacuum leak, i don't see how on earth i can have one after everything i've replaced. :( )

Here's a video of my tach.
Don't mind the rattle. That's just something in the back.

Cranking:
Doesn't sound like it's got a burnt valve, sounds fairly uniform throughout. Car is also very easy to start.

It doesn't try to suck the rag back through the exhaust, either.

Here are a couple pictures of the suspicious things i found.
IMG_20210502_125717[1].jpg

Will this cause a vacuum leak? This open port was 'fixed' with a zip tie over a tube before i pulled it off. and I see it capped off in all the vacuum diagrams i see.
I only ask since i remember putting my finger over that dodgy tube fix a few years ago, and not feeling any vacuum.

oil.PNG

Here's the oil i found in the distributor. Very sus
 

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Discussion Starter · #15 ·
Alright, I DO have a vacuum leak..

I heard hissing from the intake side, went in with a doctor's stephoscope, and found that one of my new hoses was leaking because it wasn't tight enough.. :evil:

I got the vacuum hose off the top of the fuel pressure reg. Tried it on the spigots and it's the exact size i need. Will keep posted if it works or not.

Said hose also smells of petrol. bad fuel pressure regulator, perhaps? would explain my poor fuel economy and rich condition.
 

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aidan7777 said:
Alright, I DO have a vacuum leak..

I heard hissing from the intake side, went in with a doctor's stephoscope, and found that one of my new hoses was leaking because it wasn't tight enough.. :evil:

I got the vacuum hose off the top of the fuel pressure reg. Tried it on the spigots and it's the exact size i need. Will keep posted if it works or not.

Said hose also smells of petrol. bad fuel pressure regulator, perhaps? would explain my poor fuel economy and rich condition.
Yeah, fuel on the vacuum side of a diaphragm-type fuel pump or regulator is a pretty good indication of a leaky/ruptured diaphragm. It'll suck fuel right into the engine, makes it run nice n' rich!

I've worked on too many outboards to count with that problem. The pump comes off of one cylinder, and it's a lot harder to diagnose a cylinder that's not running because of overfueling, than one that's running lean. Alcohol-laden fuel is Death on rubber hoses and diaphragms.
 

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Discussion Starter · #17 ·
That, and the regulator putting out WOT pressure instead of the proper idle pressure actuated by the vacuum. probably explain the popping on deceleration if it's leaking particularly badly, though.

If it idles properly after i change out the hoses(again), i'll take the hose off the top and see if petrol drips out after a few minutes of running. if it does, it's time to hit rockauto again.

There is no easier person to fool than yourself..
 

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Discussion Starter · #18 ·
Alright. I replaced ALL the vacuum hoses with the 'right' ones. Engine seems to run a little better at high idle. Still misfires a bit, but it seems better.

However. low idle still stalls out JUST like it used to.

It doesn't seem to matter what i do with that stupid idle air screw. It will still randomly drop its guts and attempt to stall out.

WTF is going on?! If it turns out to be the new intake gasket leaking i'm gonna be so pissed off. I spent hours upon hours getting that thing off and back on again, even broke one of my AC lines trying to bend it out of the way of my 1/4 ratchet.
Could it even be my injector seals? I can't hear anything in there with my doctors stethoscope, the engine is just too loud.

i DID replace the studs with bolts to make it easier to take off in the future, though.. maybe i didn't tighten them enough? God damn!

Can a bad FPR do this? I put my finger over the little hose on top of the FPR when I disconnected it, and it didn't have much of a 'bite' to it. are they supposed to really suck onto your finger? or is it just a mild sensation?
I'm hoping my longer crank time after i replaced all these small hoses points to that. I didn't see any petrol come out the top, but I hear that leaky fuel pressure regulators can take quite a few minutes of idling to show that symptom, and this thing doesn't even want to idle for one.

This is driving me crazy!
 

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Discussion Starter · #19 ·
Oh dear.

I just came out to have another look at the thing. I see i have this wicked oil leak, so i think. hey, maybe i didn't tighten the valve cover enough? Let's take a look, i say. Seems like it's coming from the back.

Why was it coming from the back? STUPID here forgot to make sure the half moon seal on the back of the cylinder head was in place before he put the head back on, and now it's been lost somewhere unfathomable. Hope it hasn't gotten itself wedged somewhere it shouldn't be.

Gee wizz. I wonder if THAT might be my vacuum leak.. :oops:
 

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Oof, we've all done stuff like that, especially when you are tired and exasperated with a problem.

BTW do tell what exhaust system you have. Yours sounds awesome compared to mine. Headers?
 
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