Fueling and Air Gurus please chime in! Odd misfire, running rich. Dismal Mileage.

[redrunn]

Hey Team,

'91 4runner (Pre OBD) . No check engine light, and no codes on the diagnostic.

It has a missfire across the rev range. Past 5.5K rpm, I can't seem to tell anymore. But there is a definite and absolute misfire. The trouble is, I can't isolate a cylinder responsible. Maybe its misfiring because the mixture is too rich? Which brings me to the next point.

It runs pretty rich. My gas mileage is dismal. I get about 3-4KM per liter. I bought it like this. It needed lots of work, so only now have I got to this part after fixing everything else (and doing a lift). The peculiar part is that, it doesn't seem like a complete miss. Its not like one of the cylinders are not firing at all. It is more like it is not firing properly. And the engine is running rich anyway. It could also be that the miss is jumping between random cylinders?

When I bought it, it had a high idle symptom. The idle would be around 900 warm, but occasionally it would idle down to its proper idle which is about 500 warm. This accurate idle would be accompanied with a misfire. The accurate idle would show up randomly on some start ups, or randomly at some parking spots when I switched to park. I corrected the idle last night by adjusting the idle screw. Now it always idles at about 500 warm, but occasionally it drops to a low 250 warm, and stays around there (just like earlier).

I tried to isolate the misfire by unplugging plug leads, but can't seem to find the cylinder that is misfiring. It seems that it misfires only once every two, or three rotations of the engine, but its definitely there.

I'm low on cash, so I don't want to throw parts at it that don't need replacing. I bought some contact cleaner today. I'm open to all advice guys, anything helps.

I replaced the fuel filter with an OE unit, as well as replaced the rusted fuel lines. The ignition coil seems good, I can hold the plug wires 3/4 of an inch away and it would jump spark.
Lastly, a compression test came out surprisingly well. All the cylinders are inline with each other with good compression. I don't have any coolant loss either. Please help.

 

[fourwd1]

You do have OBD, OBD-I. No scanner required, jump 2 terminals on the test connector beside the fuse box and count the CEL flashes.
Search to find exact instructions.

 

[redrunn]

I Did

I did jump the terminals, I have no codes, and no flashes.

You do have OBD, OBD-I. No scanner required, jump 2 terminals on the test connector beside the fuse box and count the CEL flashes.
Search to find exact instructions.

 

[fourwd1]

It should flash at a constant rate to show no codes set.
Sure you're doing it right?

 

[redrunn]

one sec.

I did this a month back so I don't remember. I'm going to go try it again right now. Will update.

It should flash at a constant rate to show no codes set.
Sure you're doing it right?

 

[redrunn]

no codes

nope, the O/D and Check Engine light both flash solid about twice a second.

 

[flyinhawaiian01]

Read the plugs, find out if one cylinder is more wet or black than the others.

Should look like the center plug:

If they are all pretty similar, and they look correct (not lean or rich), then check timing, replace cap/rotor, then go from there.

If rich, have you (or previous owner) played with the MAF? Its very hard to make an efi run rich without touching something one shouldn't be touching!

I won't talk about o2 sensor until we determine whether its really running rich or not.


Oh yeah, if only one cylinder is rich-looking or oily, then there's a bunch of reasons for this, from bad spark plug, to bad plug wire, to cracked dist. cap, to low compression, to cracked head or BHG...

 

[redrunn]

tell me what you think.

all the plugs look identical. one doesn't look any different from the other. these pictures are diff angles of a few plugs.

Postimage.org / gallery - IMG 20150626 180309, IMG 20150626 180315, IMG 20150626 180323

what do you think? should I try leaning out the afm and adding some timing?

Read the plugs, find out if one cylinder is more wet or black than the others.

Should look like the center plug:

If they are all pretty similar, and they look correct (not lean or rich), then check timing, replace cap/rotor, then go from there.

If rich, have you (or previous owner) played with the MAF? Its very hard to make an efi run rich without touching something one shouldn't be touching!

I won't talk about o2 sensor until we determine whether its really running rich or not.


Oh yeah, if only one cylinder is rich-looking or oily, then there's a bunch of reasons for this, from bad spark plug, to bad plug wire, to cracked dist. cap, to low compression, to cracked head or BHG...

 

[redrunn]

bump bump, anyone?

 

[flyinhawaiian01]

Ain't nothing rich about that plug! Those plugs look slightly lean, actually! Since they all look similar and nothing out of the ordinary, you could rule out bad plugs and BHG/rings/cylinder issues. And definitely don't lean out the system any more! No changes to anything until the issue is solved, that would be the wisest thing to do at this point.

Now, next thing I'd check would be timing, play around with it to see if you can get it to change the miss. Stock for a 22RE I believe is 5BTDC, but you can run them up to 10-12BTDC for a bit more power, but we're just trying to see if you can get the miss to go away or be reduced here, we're not lookng for extra anything right now! If no changes, put it back to where it was initially and move forward.

You can then start checking the throttle body, might be dirty or a vacuum hose that's cracked or loose or popped off. These items will give you a leaner mixture (more air into the system than its calculated through the MAF). These can also give you a missfire.

 

[redrunn]

Hey Flyin

Hey, THanks for your reply.


This is probably a better photo of the plug. It has a deep black base and white top. The reason I suspect it running rich is because of the exhaust smell.

I didn't see your post before, so I went ahead and got a timing light, and also decided to adjust the afm. I remember on carb'd engines I was taught to look for a sweet spot where the idle is highest at idle while adding or removing air. I found that richening the mixture would increase idle if anything. But I leaned it out 4 clicks (I DIDN'T SEE YOUR POST THEN), and set timing to 16 advance. The mark was right at 10 earlier.

I came across two clues.
1. missfire is still consistent, and its very noticeable around 2-3Krpm.

2. The timing light would show a jump on plug 1, and it seemed to correlate with the missfire. Every 3-4 revolutions the light would have a miss a flash, or jump retarded. I know this because on cylinder #6, there is a continuous stead spark/flash. Maybe it is a bad plug? I remember replacing all the plugs on that bank with dealer denso ones. I ordered new OE plugs anyway. I also know that cylinder #2 has a loud injector.

3. Unsettled Idle rpm. I brought the idle down from 900 when warm, to 700 when warm. I noticed when it was 900 warm that occasionally idle would drop to 500 (once a week breifly). Now its more commonly occurring. Mid drive it would drop down to 2-300 randomly and start burbling. Adjusting the idle screw out would bring the rpms back up, but then again randomly the idle would get up to 1100, and I'd have to adjust it back down to 700. Very odd. I suspect the TPS, or a sticky throttle body. Going to clean the TB today.

I ordered the following parts from rockauto.com for now.

AIRTEX / WELLS 4S6 Distributor Rotor
AIRTEX / WELLS 5D1307 (JP942) Distributor Cap
DENSO 3119 Spark Plug x6
DENSO 6716173 (671-6173) Spark Plug Wire
DENSO 2344055 (234-4055) Oxygen (O2) Sensor
MANN Air Filter

Ain't nothing rich about that plug! Those plugs look slightly lean, actually! Since they all look similar and nothing out of the ordinary, you could rule out bad plugs and BHG/rings/cylinder issues. And definitely don't lean out the system any more! No changes to anything until the issue is solved, that would be the wisest thing to do at this point.

Now, next thing I'd check would be timing, play around with it to see if you can get it to change the miss. Stock for a 22RE I believe is 5BTDC, but you can run them up to 10-12BTDC for a bit more power, but we're just trying to see if you can get the miss to go away or be reduced here, we're not lookng for extra anything right now! If no changes, put it back to where it was initially and move forward.

You can then start checking the throttle body, might be dirty or a vacuum hose that's cracked or loose or popped off. These items will give you a leaner mixture (more air into the system than its calculated through the MAF). These can also give you a missfire.

 

[flyinhawaiian01]

Yep, that's a better pic of the plugs. They actually look pretty good, I wouldn't worry much about them being too rich or lean for now.

Go ahead and get those parts installed, then see where it goes from there. As for 16º advance, that's a bit high for the engine, I wouldn't go much over 10º. Getting it to fire that early can screw with your idle and knock sensor, which I believe will pull the timing down when set off, as you're basically igniting your fuel mixture before the optimum spot in that cylinder's revolution of its stroke.

This can also create a rich mixture as you're not burning the fuel in the cylinders at its peak, which would also give you a richer smell at the exhaust tip and will also overheat your cat and deteriorate your o2 sensor.

Now, if you're seeing a missing fire with the timing light, that could be a couple of things here. If it coincides with the sound of a missfire (but not exactly at each revolution but more sporadic), then I'd look at distributor first, see if cap/rotor are good, check wiring to distributor for cracks or bad connection, then move up to the ignitor.

If it does NOT coincide with the missfire, then check your inductor of the timing light to the #1 spark plug wire. They don't always pick up the spark on every revolution. Run the test again after moving the spark plug wires around.

Let's see what happens with the new parts first, and hold off on installing the new o2 sensor just yet. I've had issues with the Denso o2 sensor from RockAuto, have a brand new one sitting here that doesn't read correctly, and I wouldn't want you to have to deal with another anomoly with your issues!

If you have time and wanna do something on the 4 runner, you could always pull the throttle body off, give it a really good cleaning with TB cleaner and a toothbrush, then clamp it down on the workbench and test the TPS!

 

[redrunn]

thanks chris!

I'm going to dial the timing back down to about 12. I didn't know about advancing causing possible richness because of an incomplete burn! Good knowledge!

Did rockauto refund you? I read around and ppl advised to stay away from bosch, so I went ahead with the denso unit, and at about CAD $66, it was a steal. Going to bring the afm back to stock as well.

I read somewhere that someone had to replace their distributor. I checked the cap and rotor. They are the stock denso units. They have some wear, but no bridging or serious corrosion. It doesn't seem like it would cause a missfire, but I ordered the part anyway. Once I get the cheap things like plugs, wires, cap and rotor out of the way, I'll dig into more things and get the multimeter out.

I read about a bad tps? I saw a few write ups on adjusting it but can't for the life of me fully understand what is going on. My dad didn't teach me much wiring so I'd always been a little weary. But I'll pull the TB out when the parts arrive and give it a once over.

I'll keep you posted.

Yep, that's a better pic of the plugs. They actually look pretty good, I wouldn't worry much about them being too rich or lean for now.

Go ahead and get those parts installed, then see where it goes from there. As for 16º advance, that's a bit high for the engine, I wouldn't go much over 10º. Getting it to fire that early can screw with your idle and knock sensor, which I believe will pull the timing down when set off, as you're basically igniting your fuel mixture before the optimum spot in that cylinder's revolution of its stroke.

This can also create a rich mixture as you're not burning the fuel in the cylinders at its peak, which would also give you a richer smell at the exhaust tip and will also overheat your cat and deteriorate your o2 sensor.

Now, if you're seeing a missing fire with the timing light, that could be a couple of things here. If it coincides with the sound of a missfire (but not exactly at each revolution but more sporadic), then I'd look at distributor first, see if cap/rotor are good, check wiring to distributor for cracks or bad connection, then move up to the ignitor.

If it does NOT coincide with the missfire, then check your inductor of the timing light to the #1 spark plug wire. They don't always pick up the spark on every revolution. Run the test again after moving the spark plug wires around.

Let's see what happens with the new parts first, and hold off on installing the new o2 sensor just yet. I've had issues with the Denso o2 sensor from RockAuto, have a brand new one sitting here that doesn't read correctly, and I wouldn't want you to have to deal with another anomoly with your issues!

If you have time and wanna do something on the 4 runner, you could always pull the throttle body off, give it a really good cleaning with TB cleaner and a toothbrush, then clamp it down on the workbench and test the TPS!