1990 3.0 Running Very Rich

Hey all! I just purchased a 1990 4runner 3.0 for a pretty good price. The body is in great condition but the engine seems to be running verrrry rich.
Upon accelerating *unless i very slowly ease into the accelerator* the car will stall for a second, shoot a small ploom of black smoke, then continue on its way. You can also smell the unburned fuel just having the car idle
This has caused the car to stall out completely when trying to accelerate from a stop, especially going uphill.

I had just changed the spark plugs today to no prevail, and the old ones were wet upon removal.. I also checked compression on each cylinder and compression is just fine.

Any ideas on why the car would be running so rich?

 

Vacuum leak? Fuel pressure regulator?

 

Both my 3VZE equipped 4Runners are of this age and many of the vacuum lines at this later great date are beyond their useful service life if they are original. The pvc line vac booster and usually the lines that go to the PS pump are often no longer flexible. There is a real spiders web of hoses and vacuum switches for all of the OBD1 smog stuff to operate properly. So, diagnosis can be tricky! Assuming the hoses are not cracked or broken off on the plenum, then there are several things that the OBD1 engine control microprocessor (MP) uses to adjust the ignition and fuel injector timing. For the ignition side the distributor handles the spark distribution via the cap and rotor but it is also a crankshaft position sensor and that signal is sent to the MP for base timing adjustments which is why you have to place the jumper on the diagnostic connector when you set the ignition timing to 10° or the MP will alter things while you're twisting the distributor. Three things are on the fuel side to meet the engines demanded power when you step on the accelerator. The first is the throttle position sensor (TPS) that rotates on the same shaft as the throttle plate. This rotation of the throttle plate is going to tell the microprocessor how your asking the engine to respond to throttle changes. So the TPS is key for acceleration signaling to the MP. The second is the air flow meter (AFM) that is going to follow the TPS and open up more as you open up the throttle plate with your right foot when you accelerate. So if one or both of these i.e. the TPS or the AFM are failing to report correct information the fueling is going to be wrong and especially under acceleration the engine speed is changing so the system has to respond accurately which seems it is not doing. The third component would be the oxygen sensor which will be engaged once the operating temperature has been reached and the MP will then be running in a closed loop where the O2 sensor will give the MP feedback on rich/lean conditions. Then the MP's algorithm can adjust the injector timing to get the ratio corrected. Certainly with off-idle-stumble and black smoke it would seem that perhaps the ability to change in the engine speed is the problem. Also the fuel rail is a regulated pressure fed affair and that fuel pressure regulator is quite loud when it is working properly and if it is not then your injectors might be getting too much fuel pressure and are having trouble stopping the fuel flow i.e. black smoke!...

 

I was told by a muffler shop my truck is running too rich. Mine seems to bog down a little. I have replaced all Mass Air Sensor rubber ducts. Should I advance my timing to 12 degrees TDC from 10 degrees? I do have a air leak in the brake booster. I hear whistle at pedal sometimes.. I brake fine. 320K on rebuilt 3vze and orig 5 sp manual tranny

 

If the plugs are wet with fuel then the first thing to look at would be the cold start fuel injector that is adjacent to the area on the plenum were the EGR feeds its exhaust gasses into the plenum. This injectore is perhaps leaking or the logic in how the MP tells it to stop flow after its warmed up is not working. There is a thermal sensor at the back of the engines intake manifold that alerts the MP to the motors overall temperature which is key in getting the MP to go into closed loop. If this has failed then after warm up the cold start injector will not turn off and over fueling will result. How is your CAT handling things because it will get very hot trying to process an over rich condition? A Toyota FSM is your best friend for troubleshooting problems.

My 91's exhaust pipe tip is black inside the pipe and is basically due to the fact that OBD1 fuel management is perhaps not quite as good as OBD2 and so the spotlessly clean exhaust you can observe on newer vehicles will never happen on our 3VZ-E's.

If you have a leaking brake Booster the idle speed will be irregular and higher than it should be which should be 700 to 900 RPM when its warmed up with the AC off.

 

Yes last year at the end of last year I had to put another muffler on there because it developed a crack at the inlet which was strange and boy that cat was getting very hot I seem to remember I could feel heat radiating off of it. I was able to get historic vehicle collector car plates and so I had the cat removed since I only have one denso O2 sensor prior to the cat. That muffler shop said the knockoff magnaflow Muffler that was on there which it was pretty loud, that it was getting too hot and he told me I'm running too Rich.... They installed a quiet muffler yesterday. Its poor idle and it's below 500rpm after braking and while the truck is sitting at idle for a minute or two it'll idle up by itself and go up to like 700 RPM. I'll look at the BKR5EYA NGK V Power plugs. I have a Toyota OEM water temperature sensor and also another Toyota exhaust o2 sensor on order. I need to start looking at that cold start injector what you're saying it seems to be controlled by the engine water temperature sensor correct? I have the factory orange/black Toyota service manuals that I bought back in
1995 or so at the dealer. I do have an old OBD1 Snap-on Red Scan Brick MT2500 that lives in a hard briefcase. I used it once in awhile I acquired it at low cost. There is a Toyota module for it. On youtube I see videos of heating the o2 sensor & checking voltage from it. I have a Denso o2 on there. But 4Runner sat for 5 years after Cyl 6 blew the gasket. Do you think its worth pulling that o2 sensor off the exaust and trying to test it? Or maybe just i could just focus on the Water temp sensor of that flange back by the brake booster, and the cold start injector?

 

There are two temperature sensors on that funky manifold that is behind the plenum as well as some thermal vacuum switches for the carbon trap and other things. One temp sensor goes to the gauge in the dash and the other talks to the Micro Processor (MP) that is behind the passenger side footwell cover. This one helps control the cold start injector for getting pulses to help with cold starts and will add fuel until the engine is warmed up. So if that sensor is shot it won't stop fueling after its warmed up and throttle response will suck. I run a Flow-Master HP-2 at the CAT location and a FLOW-FX where the OEM muffler went all plumbed with 2-1/2" pipe. Sounds great and flows well. Easy things to verify are fuel pressure in the fuel rail. But you have to drill and tap the banjo bolt next the oil cap in the fuel rail so you can install a schrader valve for a gauge to access the pressure. The diaphragm on the fuel rail is quite noisy when the motor is running and it reduces the fuel rail pressure upon deceleration when the throttle plate is shut. You get good manifold vacuum when decelerating from high engine speed and the diaphragm will open and dump some of the fuel pressure back to the tank and relieve the fuel rail from some of the pressure the spec is in the FSM. Too much pressure all the time in the fuel rail can overwhelm the injectors and create a rich running condition. Check the metal tubes that are about the plenum and make sure they are open and not plugged up with rust like mine was for this diaphragms operation. The Denso 02's are the only ones you want to run on these trucks and they are pretty robust and don't really do much until your cruising at speed and then it can help manage giving the MP some needed correction for injector duration to help keep the mileage up and the emissions down. The FSM has a bunch of stuff you can check for suspected rich running conditions. The Volume Air flow Meter (VAFM) and the throttle position sensor (TPS) both have a lot to do with getting the motor to respond to acceleration. The thing that is important is that the air pipe/s between the VAFM and the TB have to be airtight and leak free. Otherwise the VAFM's flapper and the TPS will be giving mixed information to the MP and it will not go or respond to the accelerator pedal. If you have the OEM air box this is hard to do but if you have easy access to the opening of the VAFM you can mess with the flapper with your finger while its running to get feel for how important this relationship with the engine being able to correctly suck that dam thing open as you increase engine speed. The VAFM flapper also turns on the fuel pump when the engine first turns over and it sucks the VAFM flapper open a bit it which closes a switch inside the housing and the fuel pump then runs.

 

Thanks for your input, regarding: "The thing that is important is that the air pipe/s between the VAFM and the TB have to be airtight and leak free. "
This i am certain of. This year I replaced both of the stock 4" rubber ducts with OEM Toyota rubber air ducts , and not Dorman junk.
Rubber is the weakness where I live. Rubber does not last long if not Toy branded. I have the new green oem Japan coolant Temp sensor coming from a Toy dealer in Calif, and a Toy O2 sensor coming. Was about $160 for both but not getting burned again as when i used non OEM back in the day, I got burned /paid twice and usually had to re-do the repair later. I am suspicious of that existing water temp sensor. I saw a little bit of black smoke at tailpipe today at start up. The existing Denso O2 sensor I had replaced in 2015. But maybe the excessive heat might have affected it. Who knows? I have the old red MT2500 scanner OBD1 and an Actron CP9690 Scanner which is supposed to be OBD1 capable. I wonder what they will tell me? I may hook them up before I change any parts.

 

I Like: The FSM has a bunch of stuff you can check for suspected rich running conditions. The Volume Air flow Meter (VAFM) and the throttle position sensor (TPS) both have a lot to do with getting the motor to respond to acceleration.

And I also have a spare MAF/VAFM... but that is rarely a problem. I plan to review the Orange FSM manuals

 

I don't know how useful the scanners will be unless the check engine light is blinking. The OBD1 was anything but a standard and so all the diagnostic methodology was very manufacture specific. So making a scanner that was universal was difficult from what I have been able to understand. That sensor may be the answer for getting the MP to be able to get into closed loop mode after warm up. Fingers crossed on that!

On another note my son and I put some cheap $150 chinese headers on his 3.0 90 4Runner last year and did an EGR delete. We bumped the static initial timing to 14° BTDC and it is a completely different 4Runner. Now it hauls butt like mine does. The key is getting the heat out of the engine and these headers really help a lot with that when joined with 2-1/2" exhaust. It is truly the best mod you can make on the 3.0. Putting a shroud around the K&N FIPK offered by Summit is another good mod as well.

You have some miles on that motor now, so how is the oil consumption? I've put a little over 30K on my rebuild and just put half a quart into my engine a week or so ago and am doing 2500 mile change intervals with oil filter every 5K. Been running 10W-40 with this cooler winter here in Southern CA and suspect it burned more easily than the 20W-50 I run in the summer.

 

Nice & i am still waiting for parts to arrive. I'm interested in what you have done to get a little more HP. My motor was rebuilt by an outfit in west Phoenix, with in-house machine shop at beginning of covid. at 304,000 mi. I put about 240,000 of them miles as the 2nd owner. It took 1 year to get vehicle back due to parts shortage/labor problems. They convinced me in the beginning, it would be worth doing & 2yr warranty. It was gambling a bit. So I had cam wear probably due to Castrol oil, so new Toy cams, pistons, an outfit certified at rebuilding motors. Thus far its held up. in the beginning I made a mistake of using synthetic. I'm now using elevated ZDDP conventional 10w-40 oil after consulting with Driven oils. I'm using a little oil likely due to not using conventional oil in the beginning. I suggest elevated zinc & moly oils to contribute to cam life. Since in the 90's oil had more zinc/moly than the current off the shelf oil due to cat

 

Get the headers and do an EGR delete the OBD1 won't know the change to the engine just keep the temp prob attache'd to the header to keep the MP happy.

Over head cams with buckets and shims like ZDDP. But a CAT does not like seeing that stuff go through it over time. As I swap in my CAT at smog time it doesn't get much exposure. I drop some of that STP oil treatment into the engine with oil change so as to get that into the motor.

 

Where did you find quality, reliable headers for the 3VZE? If I could fild QUALITY headers then I would like to investigate further.
I have historic lic plates, and drive maybe 3000 mi year
Hastings has collecter car insurance for AZ, I showed MVD and emission inspection is "supposed" to be waived in 2024. I can vouch for the ZDDP and need for it, since my previous oil was off the shelf Castrol Syn Blend 20-50. I see now Castol coming out with oil "classic" with higher levels of zinc.
Previously I didn't know anything about ZDDP. I use now since 1300 mi ago Driven HR5 10w-40 conventional they say:

the product data sheet for HR-5.
Zinc is around 1600ppm (Mobil1 Syn 10w-40 is 900ppm )
Phos is around 1500ppm
Hr5 does contain about 2500ppm of detergent, and it is a conventional oil.
HR-5 is about $10qt

I'm getting some of their GL-4 oil for my 5sp trans & transfer case. Getting rid of the Lucas GL-5

 

Hello,
My name is Dan.
I also have a 90 3.0l that is running rich. Did you figure it out? If so, what was the cause?

 

I have on order a genuine oem Toy water temp sensor made in Japan. I'm starting there. I'm changing over to 60% Toyota long life coolant the other 40% distilled water ....and I'm doing it myself to be sure its done correctly. I already have the fluid and I have a slight leak in the radiator it's very small but I have to take the radiator out and go get the brass radiator evaluated. I have a backup Denso oxygen sensor and I'm going to also look at the cold start fuel injector

 

Hello Tony,
Dan here.
Thank you for your response. I appreciate any and all the advice I can get. I'm new to this forum. I posted a thread a week or so ago before I read yours. It's about 14 down on the 2nd gen page, if you're interested in reading it. I spoke with a mechanic from Phoenix a few days ago and he recommended the temp sensor, so hopefully we are both on the right track. His buisness is called Totoworks and he seems very knowledgeable. Keep me posted on your progress and I will keep you posted on mine. Two heads are better than one.
Thanks again, Dan

 

Atgparker I have the orange FSM and I don't have time today or this week, but I would like to find the circuit details either on-line or in FSM on how that watertemp sensor ties into the ECM/ ECU engine control module and all the circuitry like the o2 sensor "reporting" its voltage to the ECM and what actually makes the fuel/air ratios. I want to see if there are low micro farad capacitors tied into that circuitry which would likely be in ECM. In the 90s Toyota had issues on some vehicles and leaking Japan sourced capacitors in ECU/ECM on many vehicles related to quaternary ammonium salt capacitor issue. I am familiar with this problem as I have a 95 LS400 .....
https://www.clublexus.com/forums/ls...exus-issues-solved-ecu-leaking-capacitor.html
Another:
https://www.flickr.com/photos/162334321@N05/48723450378/