93 FZJ80 - Advanced timing now have rough idle (1 Viewer)

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mudgudgeon

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On Saturday I fitted new air filter, spark plugs, plug leads, dizzy cap, rotor button and distributor o-ring.
I also advanced the static timing to 10 degrees BTDC.
Throttle body was cleaned about 6 months ago.

Truck is running crisp, and pulling a lot stronger, and picks up better at low RPM.
No pinging. All seems good, except I now have a rough idle.

Truck is manual, and with AC off is idling at 650-750 rpm, but it's a tough idle.
Apply a little right foot and bring rooms up to 8-900 rpm, its still rough.

Runs well when off idle.

Thought I may have an unmetered air leak from intake hoses, but it seems ok.


What have I missed? Do I need to increase the idle? And if so, how?
 
Check all the vac hoses?
 
You might revisit the distributor installation.
 
If you were off a tooth on the distributor it wouldn't be slightly rough, it would barely run properly and certainly not have good power off idle. I have my timing set slightly advanced as well and it still idles very smooth. I would suspect a possible bad spark plug or wire. New out of the box can sometimes be bad.
 
If you were off a tooth on the distributor it wouldn't be slightly rough, it would barely run properly and certainly not have good power off idle. I have my timing set slightly advanced as well and it still idles very smooth. I would suspect a possible bad spark plug or wire. New out of the box can sometimes be bad.
Not necessarily, when I bought mine it was off one tooth but ran ok. I knew it was off because of how far the lock down bolt was from the center of the adjustment slot.
 
Can do. What am I looking for?

I marked a tooth, and the housing before removal. I'm confident I got it back in right, but may be worth another look
With number 1 at TDC on the power stroke, the rotor button should point to about 11 O’clock and the lock down bolt should be pretty much in the middle of the adjustment slot.

CABF2929-852C-4D91-A864-8D8551E2E5A8.jpeg
 
With number 1 at TDC on the power stroke, the rotor button should point to about 11 O’clock and the lock down bolt should be pretty much in the middle of the adjustment slot.

View attachment 2142159

I think I'm golden then.
I set the crank at TDC with number 1 cylinder on compression stroke before I shifted anything.
The rotor was pointing at the number 1 contact on the dizzy cap, but off by a few degrees for the advance.
I marked a tooth, and the housing, and the clamp was more or less centred.
 
I'd pull the wires off the distributor one at a time. These engines can run pretty smoothly with one cylinder not/barely firing. I wonder if you got the plug on the spark plug fully seated on all but one. I literally did this yesterday (sunday) as the farthest back did not connect with a sharp click. Later as I was double checking things, I pushed on them all before putting the cover on and found the rear one had "felt" seated but then clicked when I pushed really hard. If you pull a wire and it barely makes a difference or does not at all, that's your suspect cylinder. If its the rear one, perhaps you damaged the ignition wire as you have to kind of pull hardest on that one to get the plug connecter oriented in the seat hole and I worry about that stress each time I do plugs. This check would be quickest. Unclip all distributor wires so you can easily move them before starting the engine.
 
So I spent a chunk of time on this this arvo. Kind of stumped at the moment.

It still has a stumble at idle. It's inconsistent. Sometimes it stumbles every half second, other times is maybe every 5-10 seconds. Just a little stumble.

I think driving it, I've been coaxing it off the line a little, it's running fine otherwise.


I rechecked the dizzy. Had the teeth lined up right. Tried shifting one tooth in either direction just to be triple sure

Checked all the plug leads were plugged in properly. All were solidly in place.
Tried removing one plug lead at a time with the engine running. This has me puzzled as there was not the slightest change in engine speed or idle. No stumble at all when any of the plug wires was pulled.
I checked all plug gaps when I swapped the plugs over a few weeks ago. And all the old plugs looked good.

I rechecked the main intake hose for splits or cracks. Is old and hard, but not cracked.

Also checked all the vacuum hoses, replaced one that looked pretty sad.

Not sure where to go next with this.

Thinking maybe compression test.

It is burning a bit of oil. Not a huge amount, but I do need to keep an eye on it
 
With no check engine light to reference, and with out access to sophisticated diagnostic tools, it may be prudent to go back in with the old parts that you removed at the time of the maintenance you did. Perhaps begin with just the cap and rotor at first in an attempt to get back to running like it was previously. Is there a possibility you bought inferior parts?

It would be worth removing the intake tube and either replacing it or at least giving it a thorough inspection along with making sure it the throttle body is secured and well sealed to the plenum. I assume these components were removed for access to the plugs and wires.
 
All parts were new OEM. didn't keep any of the old parts. The dizzy cap and rotor were beyond what I'd keep as spares.
Kicking myself for being too hasty tossing stuff out.

Is there anything fuel system wise that I should look at?
Injector wiring? Injectors?
 
This problem arose with your “tune-up” I gather? It idled better before? If this be the case, you installed a defective part or your activity upset a fragile wire harness or there was a lack of attention to detail with regard to component installation at some point. I would be redoing it all over again.

A mechanics stethoscope or, if you can manage by feel with a finger, will help determine if there is an injector misfiring.
 
I would be suspect of the coil. With your test pulling off one wire at a time, it seems like the coil could be weak. Probably not but might be worth a try to at least swap it out with another used one and see if it improves
 
When I did my distributor o-ring, it took my rig a few cycles and miles to settle its idle back to normal, but that was under 24 hours. Usually the computer takes some time to settle in. You can adjust the idle my adjusting your idle cable (IDK what it's called, the one that doesn't move when the gas is pressed)...but you only want to adjust that if you're consistently never near 650 on idle when warm.

Does setting the timing to -10 degrees maybe impact things a bit? I mean, you're sparking pretty early...I set mine to -3, per FSM, though I've seen many guys on here ignore the -3 for a variety of reasons.

You could also run live data off an OBDII scanner and get some data points to compare to the FSM's guidance on various systems...may show you if your running lean or rich, or if MAF is bad, etc... (see: "Engine Operating Condition" section in Engine part of FSM to get started...my scanner gives tons of data and records it to compare when at computer to look things up).

Good luck.
 
This problem arose with your “tune-up” I gather? It idled better before? If this be the case, you installed a defective part or your activity upset a fragile wire harness or there was a lack of attention to detail with regard to component installation at some point. I would be redoing it all over again.

Yep, it occurred after tune up. I'm thinking the same as you, but at a loss what else to check. Kind of at the point of throwing parts at it.

I've rechecked distributor orientation. I'm confident I have it right.

Adjusted the timing back to 3°BTDC, no change. Miss is still there.

Plugs were Denso. Set gap to 0.8mm before installing.
Haven't pulled and checked plugs yet.

I checked plug leads were all connected properly. Pulling plug leads one at a time with the engine running made no difference, but I could hear each one sparking against the inside of the plug tube.

I wrapped the intake hose with duct tape to eliminate it as a possible vacuum leak. No change.

I've sprayed ether around the manifold, throttle body etc to try and see if it has a vacuum leak. No indication of a leak.
 
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What would I be feeling for?
The injector pulse can be felt. A resistance check across the injector is also outlined in the FSM. Are you positive that there are no damage/melted/exposed wires in the harness near the the egr valve?
 

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