1993 Fj80 Rough Idle, runs great other than that

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I just had another thought.... Is there any smoke from the tailpipe at all? If you put your hand over pipe with the engine idling rough, do you feel any "pulses", as if it's dropping a cylinder or two at idle only?
And.... if you have a stethoscope, you might want to listen to each injector at idle, to make sure you're getting a good solid click sound from each one.
I have a couple of injectors that have some internal fouling causing a poor spray pattern, which at idle speed results in a very slight misfire, not enough to give the symptoms you have but enough to be felt. This can sometimes be confirmed or eliminated by getting your engine hooked up to a good oscilloscope and reading the pattern of each cylinder's spark. Some of the old scopes could also do a "cylinder balance test", killing each cylinder in order and measuring the immediate rpm drop. Old school for sure, but sometimes the best way.
 
I tinkered a little more today, I noticed as soon as i block off the fuel pressure regulator vacuum line, it idles perfect and drives perfect hot and cold, I doubt the brand new denso fuel pressure regulator i just bought is bad, so I'm thinking the fuel pump is week and not putting out enough pressure, so when the fuel pressure regulator is under vacuum at idle, it is essentially just opening the return back to the tank and reducing pressure, the fuel pump is original and probably week, does this sound like this could be the problem?
 
It could be a failing fuel pump or related to it. In a properly working system with the vacuum applied at idle should drop the pressure ~7 psi. (no vacuum 38 - 44 with vacuum 31 - 37). The fuel pump runs at two voltages, 12V at startup and heavy load otherwise the fuel pump relay routes voltage through a resistor. In your case the resistor, the relay, wiring or grounds could be reducing the voltage as well.

The voltage supplied to the pump can be measured from one of the pins in the diagnostic connector. I would measure the voltage to see if that corresponds to when the idle drops/fluctuates. You can measure resistance across the terminals of the pump. I it should be 0.2 to 3 .0 Ohms. You could also bypass the relay and keep voltage at 12V and play with the vacuum line on the regulator.
 
It sounds like the inverse of your problem. Your engine needs an absolute minimum of fuel at idle, and by removing the vacuum line to the regulator, you're increasing the amount of fuel pressure delivered. If you had a problem with fuel delivery, either volume or pressure due to a failing pump, your engine would also run very poorly in all conditions other than idle, and probably idle okay.
Every time you increase throttle opening, you decrease manifold vacuum, and increase fuel requirement. Agreed? So if you increase the amount of fuel to your delivery system (injectors) in a low-need setting (idle) you are most likely, and I stress this, most likely covering up another problem. Since additional fuel is lessening your problem, I strongly suspect your root problem is too much air in idle condition. I would seriously look for some way that un-wanted air is getting in the intake tract, ie a vacuum leak. This can be anywhere from the engine side of the air flow meter to the cylinder head/intake manifold gasket, and includes the EGR system.
A hand-held propane torch is a workable way to look for this "leak", if you know what you're doing and exercise proper safety precautions.
 
Well there are several current rough idle threads floating around on here, so if i slightly turn the TPS clockwise and put it out of spec, i hear the iac click and it runs great, with a slightly higher idle, so would that indicate a vacuum leak for sure? Your probably right about a tiny vacuum leak somewhere, that would make since as to why it idles rough when it's warm not cold when it's using way more air/fuel, at warm idle is when it would require the least amount of fuel/air correct?
 
When cold, it's enriched, correct. Also when cold, you're at a higher idle speed, which will cover up your problem.
Warm idle requires the least amount of fuel/leanest mixture, correct.
Removing the vac line from your fuel pressure regulator causes the fuel pressure to max, correct. Moving your TPS so that the PCM sees a throttle open past idle enriches the fuel mixture, correct. These two also can cover up a lean mixture due to a vacuum leak.
 
Hi all, this thread seams to be on the same vein as what I'm dealing with. I'm hoping that some of your knowledge can point me in the right direction.

I recently completed (rather, almost completed) a bunch of maintenance on my FZJ80 that I bought last month.
The maintenance items I just completed:
- Oil change
- Drained the coolant system, currently has distilled water in it as I was about to perform the flush
- Replace main crank shaft seal
- Replace oil pump gasket
- Replaced the belts
- Change silicon grease in the fan clutch
- Replaced valve cover gasket
- Replaced valve plug seals
- Replaced dizzy O-ring
- Replace PCV valve and hose
- Cleaned the throttle body
- Replace the PHH
- Replaced the FHHs

In doing this, I had the throttle body off and cleaned it as best I could. I touched all the common things associated with the throttle body, hoses, throttle cable, accel cable, EGR hoses, etc... I also had the dizzy off and feel like I got the timing back correct, to within a cog I'd say.

Last night I fired it up for the first time since all the maintenance. It started pretty easy but idled rough. I only let it run for a minute or so before shutting it down to do some research. Unfortunately I didn't look at the RPMs but I'm quite confident they were low and I didn't think to rev them higher to see if it would run smooth :doh:. My initial thought was that timing was causing the rough idle. Now I'm thinking it was rough simply because of low RPMs (I hope).

I went out to start again a few minutes later and couldn't get it to start.

This morning I tried again, and got it started for a few seconds with very low RPM before it died. Most times when I try it won't start and if I let it crank too long or too many times, it will stop trying.

Giving it some accel pedal while cranking doesn't seem to help.

Your insightful and brilliant cruiser thoughts?

Thx
 
MtnCruise said:
Hi all, this thread seams to be on the same vein as what I'm dealing with. I'm hoping that some of your knowledge can point me in the right direction.

I recently completed (rather, almost completed) a bunch of maintenance on my FZJ80 that I bought last month.
The maintenance items I just completed:
- Oil change
- Drained the coolant system, currently has distilled water in it as I was about to perform the flush
- Replace main crank shaft seal
- Replace oil pump gasket
- Replaced the belts
- Change silicon grease in the fan clutch
- Replaced valve cover gasket
- Replaced valve plug seals
- Replaced dizzy O-ring
- Replace PCV valve and hose
- Cleaned the throttle body
- Replace the PHH
- Replaced the FHHs

In doing this, I had the throttle body off and cleaned it as best I could. I touched all the common things associated with the throttle body, hoses, throttle cable, accel cable, EGR hoses, etc... I also had the dizzy off and feel like I got the timing back correct, to within a cog I'd say.

Last night I fired it up for the first time since all the maintenance. It started pretty easy but idled rough. I only let it run for a minute or so before shutting it down to do some research. Unfortunately I didn't look at the RPMs but I'm quite confident they were low and I didn't think to rev them higher to see if it would run smooth :doh:. My initial thought was that timing was causing the rough idle. Now I'm thinking it was rough simply because of low RPMs (I hope).

I went out to start again a few minutes later and couldn't get it to start.

This morning I tried again, and got it started for a few seconds with very low RPM before it died. Most times when I try it won't start and if I let it crank too long or too many times, it will stop trying.

Giving it some accel pedal while cranking doesn't seem to help.

Your insightful and brilliant cruiser thoughts?

Thx
Click to expand...

A video of the start noise
 
Wonder if you got the dizzy/timing off. Place motor in TDC, and check rotor position under dizzy. Should be at #1 or #6.

Here is what one tooth off looks like at #1.

IMG_8191.webp


Here is what TDC looks like with dizzy correct.

IMG_8192.webp
 
Timing Mark

Timing Mark

  • Media owner MtnCruise
  • Date added
Notice the timing mark in the middle is aligned.
Hey brizzlygibbs,

A couple of thoughts and questions...

What is TDC? I'm assuming this is when the timing mark on the harmonic balancer aligns with the 0-mark indicating that the stroke is on the first cylinder. I did this when I was getting the dizzy back installed. In setting the crank shaft position back to "TDC", I assume I need to take the fan back off and get the 30mm socket back on the crank manually?

When I was installing the dizzy, I first set the main crank to the 0 position with the timing mark on the outside. I had to rotate the crank another full rotation to get the gear marks aligned as seen in the picture. After that I proceeded to align the groove of the dizzy with the protrusion on the driven gear. Here's where it to a little uncertain for me... (FSM page IG-13), inserting the distributor I align the center of the flange with the bolt hole. This is what determined how the dizzy worm drive aligned with the timing gear. I felt like there was a possibility to be one cog off here. After it was fully inserted, I rotated the dizzy such that the two frames were flush at the top. It shouldn't have affected the gear cog location. This is what I mean by one cog off. Effectively it would be a few degrees rotation of the dizzy rotor, which is much less than your pictures show.

I can go back and check the timing, but I was pretty careful the first time. My first thoughts would be, how far off would I have to be before seeing this type of behavior? If a single cog (~5 deg on the dizzy rotor) is enough to do this, then maybe that's the problem. If the dizzy rotor would have to be off by 30 degrees, then I'm skeptical that this is the solution path.

FZJ80_TimingMark.webp
 
TDC= top dead center. The mark, when set to the zero (0), timing mark, will put either #1 or # 6 cylinder at TDC. Fan should not need to come off to do this. A 1-3/16" wrench works as well. I am guessing your timing is off. I marked where my dizz hold down bolt was, as well as marked where dizzy met valve cover area on the head as rotating the dizzy regardless if it is in the right tooth would change your timing. The fsm does state to put dizzy flange in center of the hold down bolt hole.

Do you have a timing light?

I hope i am of help but it sounds like you know what you're doing. I just do this stuff as a user and enjoy working on my lc so i am not an expert. Please Post up your findings.
 
grizzlygibbs said:
TDC= top dead center. The mark, when set to the zero (0), timing mark, will put either #1 or # 6 cylinder at TDC. Fan should not need to come off to do this. A 1-3/16" wrench works as well. I am guessing your timing is off. I marked where my dizz hold down bolt was, as well as marked where dizzy met valve cover area on the head as rotating the dizzy regardless if it is in the right tooth would change your timing. The fsm does state to put dizzy flange in center of the hold down bolt hole.

Do you have a timing light?

I hope i am of help but it sounds like you know what you're doing. I just do this stuff as a user and enjoy working on my lc so i am not an expert. Please Post up your findings.
Click to expand...

I do not have a timing light, but it looks like I'll probably get one. I'll keep you posted what the solution is when I hopefully get to it later this week.
 
I think I've overcome a little bit of ignorance. I won't get to try it out until at least tomorrow, but I'm pretty sure the issue is timing. Hopefully the only issue. Despite literally being a rocket scientist, I missed this fact. The FSM says to insert the dizzy with the mounting bolt in the center. I did this, but then my OCD made a crucial mistake. I said, "gee, this sure would look nicer if the dizzy mount was flush with the block mount". So I rotated it to be flush, thinking that once the worm gear was engaged that the timing has been fixed at that point. Oh contrare pierre... though the gears are linked I still rotated the stater pickups and this "dorked" up the timing:bang:. I didn't count the cogs on the dizzy but I've read elsewhere that each cog represents 14 degrees. It's possible I'm off one cog there plus the 10ish I added to make it flush, so maybe 25 deg. I'm hoping this solves things and I can unleash my happy dance.

It seems like a timing light is the only way to know down to the single degree range. Can anyone confirm the stock timing? 3 deg retard? Anyone set the timing simply by observing/hearing the engine smoothness?

Distributor in a 3FE - Hypothetic
 
It happens. I used to set it on my 1977 Small Block 350 Chevrolet by sound. I would invest in a timing light though. It doesn't have to be fancy. I am looking at a 50 dollar one. I am. It sure if that is a good one or. It, more research.
 
No happy dance. I set the harmonic balancer back to TDC. Ensured that the dizzy rotor was up as you've shown and set the mount back to center. I tried rotating the mount through it's full range to see if maybe I was a cog off on the worm drive. No dice. I had my timing light all ready to go "star wars" on this thing, bummer. While I'm sure I will need to tune the timing still, I don't think that's my issue with it not starting. The sound remains similar to video and I'm confident the issue is not the battery.

I guess I need to start testing individual ignition items like the spark plugs, wires, etc... Maybe a dizzy rotor cap? Perhaps the rotor is no longer connecting with the 6 prongs?
 
brandonatx13 said:
Well there are several current rough idle threads floating around on here, so if i slightly turn the TPS clockwise and put it out of spec, i hear the iac click and it runs great, with a slightly higher idle, so would that indicate a vacuum leak for sure? Your probably right about a tiny vacuum leak somewhere, that would make since as to why it idles rough when it's warm not cold when it's using way more air/fuel, at warm idle is when it would require the least amount of fuel/air correct?
Click to expand...
Now it’s an old thread but thought I’d ask anyways…@brandonatx13 I literally have exact same symposiums in my 80…what was your final solution? Did you just roll with TPS adjusted or find the vacuum leak? Thx!
 
Rusco said:
Something to consider: after years of operation, battery disconnects, other variables and and wear factors, the Idle Air Controller (IAC) can be operating at one end of its range of travel. To correct this, the valve must be "centered". If you've had the throttle plate sticking slightly open due to the recently replaced throttle cable, the IAC system has been trying to slow the idle speed down and is probably out of whack.
Not sure if the LC PCM has this capability or not, pretty sure it does since it's OBD1 and this should be universal , but here it is:
To center the IAC, you'll need to cycle the ignition switch from "off" to "run" at least 14 times within 20 seconds. Do not start it, just go from "off" to "run". This will cause the stepper motor in the IAC to center the air valve. Wait about five minutes, ignition off, then start the truck. Most likely the idle speed will then be so low it won't even run, so you'll need to drive it right away, with plenty of idle and stop-and-go situations. Around the neighborhood, with plenty of stop signs, usually works fine. Be prepared to drive the thing for 20-30 minutes before the idle stabilizes at the correct speed. If the idle is still too low, there's a good chance the air passages are clogged with soft carbon and oil vapors, not unheard of, but by centering the IAC, you've eliminated one variable from the equation. Come to think about it, you may want to remove and inspect the operating part of the valve and then do the centering procedure.
Another cause of rough or low idle is an EGR valve that's not completely closed at idle. This is also very common, and the fix is to remove it and clean the valve and seating area. If you've ever been in a highway speed situation for a long time, abruptly gone to a stop-and-go situation and experienced a low and rough idle when you've previously had no problems, this is the first likely culprit, and holds true for pretty much any engine with an EGR that's vacuum controlled.
I know you're wondering "who's this guy, come out of the blue with all this drivel", as well you should. But I've had a couple of these things myself, and spent a few years at a Lexus dealer as a Lexus and ASE Master Tech. The last ten of close to 30 years in the business was at my own shop, which I sold five years ago. I'm sort of semi-retired now, and it's a slow time of year at work, so I'm on the internet. Hmmm....
Click to expand...
Good...God man. 14 times in 20 seconds. And it's fixed. Jesus.
 
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