mave605

Its had problems since I bought it nearly 2 years ago, with major fixes big and small to no avail! It hesitates after start up! I have replaced nearly everything, including a full engine rebuild! Maybe someone here can help???



The build up for my rig covers much of this. I am working on posting 2 years of build up here. Not sure if I'm allowed to link tech thread to my build up thread, so if I'm not, LMK: https://www.yotatech.com/forums/f199...sitate-283374/



May the trials and tribulations for hesitation issues begin! I am now an expert on almost all types of hesitation issues, just can't fix mine :-( I have checked, replaced, double checked again with new OEM or used parts for the following:



Intake system
TPS sensor
Temp sensors
Ignitor
Coil including grounding wires
Spark plug wires
Spark plugs
Cap
Rotor
Distributor
ECM
Complete throttle body
Vacuum lines
Battery
Starter
EGR system
Upper intake manifold
Lower intake manifold
Knock sensor
Knock sensor wire
Heads
Injectors
Complete engine rebuild from block out
Engine grounds
Exhaust system including exhaust manifolds, CAT, muffler and O2 sensor
Extra wire to 80 amp fuse
Extra wire from 80 amp fuse to alternator
Alternator
Ignition
Fuel pump
Fuel filter
Charcoal canister
Opened wiring harness to check injector wires and other wires for corrosion (None)
Fuel pump switch
Fuel pump grounds
All switches on the drivers side kick panel

Whats left???

JasonYota

iTrader: (1)

I see injectors on your list but what about the cold start injector? Check engine light on or off?
Runs normal when at operating temp but hesitates when cold?

mave605

Yes cold start injector was replaced. Wiring was checked. Amps were tested at the ECU. Check engine light is off. Runs great at operating temp. It runs perfect at 1st start up in the morning. After about 30 seconds after cold start, the clutch fan turns off and then it starts to run like crap. If you hit the gas too hard, it hesitates pretty bad, some smoke, sometimes it dies out and barely wants to start back up. I have to feather the gas peddle very lightly while turning the motor over. But once it starts to warm up, runs perfect.

I think its a temp sensor problem. The temp gauge in the cluster takes forever to get to the middle. Also, after its warmed up, then hop on the freeway, the temp gauge in the cluster gets cooler. I think it might be related, but I've replaced all the temp sensors.

Kiroshu

Check Volume Air Flow Meter for proper specs per FSM.

Possible sticking/stuck VAFM air door..?

Debris/dirt inside VAFM electrical/mechanical..?

Try a few "love taps" to the VAFM when engine performance is poor.

Coolant temperature incorrect signal to ECM is very possible. Verify proper operation of temperature sensors/switches.

mave605

Yes I replaced the VAFM with 2 other ones. My brother tested all sensors at the ECM and he said they are all getting the proper signals. He had the FSM for the 1991 though, only problem. And I know the temp sensors on these things are different. But I swapped in new temp sensors and other temp sensor from my identical 1991 parts 4runner and it still has the same problem.

One point you brought up that could be a problem is output signal from ECM to the VAMF to have the intake increase air with engine temp changes. Do you think the wiring/connector to the VAMF could be an issue?

mave605

This is the sensor block out of my donor. I didn't replace the block with the engine rebuild. I did replace the sensors on occasion. One theory I have is that the coolant does not touch the sensors, that would explain why the gauge is off and why it runs crappy on cold start up.

A wired thing is that when I take a sensor off my 4runner, coolant doesn't flow out of the hole. It does when I remove sensors from other 4 runners. What could cause that?

mave605

mave605

This pic is from a 1991 at the junk yard.

mave605

To make sure the coolant is extra full and touching the sensors, I took this off the junk yard 4runner and installed it on mine. When I did that, I also made sure that the heater core was not clogged and also checked to make sure the rear heater had no clog. Wanted to eliminate those as potential issues in regards to the temp sensors.

I didn't replace the blue vacuum sensor thing. I did check to make sure air flowed through the hoses though and did replace the charcoal canister.

RJR

Just to clarify, there are two coolant temperature sensors, one to the temperature gauge in the cluster, and the other to the ECU. The sensor that goes to the gauge has no effect on engine operation, it only there to inform the driver as to what's going on. The other one that the ECU sees is the one that needs to be working properly in order for the engine to run properly at various temperatures.

Your problem indeed sounds like improper temp information going to the ECU. You may need to check the voltage at the ECT input to the ECU at various operating temperatures to see what's going on. Your Toyota dealer may have a diagnostic reader that could also tell them what the ECU thinks the engine temperature is.

mave605

Thank you for the reply! Yes, your right. The big green sensor is the one that goes to the ECU. The one in the middle that is missing from the block above is a black one that triggers the cold start injector. The one on the right goes right to the instrament panel. I think the whitish color one is for the A/C.


The wiring checks out, signals are getting to the ECU. As to the exact voltages at different temps, not sure. My brother is a master mechanic at the dealer. They only have FSM 1991 diagnostics there because people don't bring these old trucks in there that often anymore, couldn't locate one for a 1990.

Here is the weird thing. With the temp sensor for the gauge, it is not showing that the temp is warmed up even though I know it is for sure. I swapped in another instrument panel to check and same thing, the temp is showing off all the time. I went offroading today, engine was heated up fully while offroading, but only showed 1/4 of the way warm.

I have replaced that sensor with a known working one, and a brand new one. I know that doesn't control anything, but wouldn't it be logical if that one isn't showing the proper temp, with good wiring and a signal at the ecm, that the other sensors are having a similar issue too?

Kiroshu

Have you verified temperature at the engine with a temperature gun/thermometer..? The odd temperature reading in the instrument cluster could be a fault with the gauge in the cluster and or the engine may very well be having issues reaching operating temperature.

How long does the engine take to reach operating temperature..?

pewdiepie

Op i believe i know what your problem is. You would need to remove your air intake. then remove the throttle body. Then With a flash light look inside and inspect if there's sludge build up. ive had my 95 4runner since 2011 and sometime last year i checked it out and it turned out it was full of sludge(i was driving with bucking and kicking for 3 years) took me about 4-5 hours to clean out with a toothbrush and carb cleaner. Also i used a screw driver to gently scrape the thick gunk out.
Also just the other day i added new grounds.
Motor to chasis
Chasis to battery
and i also re surfaced any what seem to be a ground. turns out it fixed a headlight problem i was having and helped alot with other issues such as hesitation, random shifting etc.

mave605

I haven't used a temp gun, but it takes about 10 minutes to warm up. I swapped the instrument cluster out, both read the same, so I know that's not the issue.

Detail on warm up. It runs perfect on start up, no hesitation at all. Runs perfect for about 30 seconds. Once the fan clutch turns off, it starts to hesitate if you hit the gas hard. If you don't hit the gas hard, its OK. However, stuck on a hill or when you need to accelerate quickly, it sucks! Hesitation goes away after about 10 to 15 minutes of moderate driving, once its warmed up. I can tell its warmed up because the heater blows hot air, despite what the temp gauge says. After warmup, runs perfect. Temp gauge fluctuates to medium and cold, depending on speed, mostly goes cold when driving faster.

pewdiepie

You should try what I mentioned earlier, sounds like two thing's one is that your grounds need to be resurfaced and add new grounds from the chasis to neg terminal, and when I mean chasis I mean the full Metal not the frame, then ground the engine block to the chasis as well, I literally had the same problem your having and just two days ago I got it fixed by adding new grounds and just sand papering all the other grounds. If you need pictures I'll be happy to post how i did mine. Also number 2 reason is the air intake manifold, pull the throttle body off and inspect it!!! Most likely this will be fun of sludge, same with mine and others I've delt with. I'll post pictures of my air intake that was full of sludge which would have the same problems your describing

Resurface Grounds
Add new ground's 0,4,2 gauge wires and sand the terminals of the new wires and pre existing wires while you resurfacing the factory grounds.
Clean air intake manifold
Thank me later

This picture is the cause of most problems in 4runners

mave605

Yes I cleaned out my intake and throttle body very well before installing again during the rebuild. I also tried another cleaned intake and throttle body off my parts 4runner which didn't hesitate, but still had the issue.







I checked the fuel pump circuit last weekend and it did have some voltage loss. I added a ground from the fuel pump to the seat belt bolt. It helped but still had a little voltage loss.

Do you have those photos or a link where you added the extra grounds? It may help because I added the extra power cable to the alternator. Thank you again for your advice!

pewdiepie

Sorry I couldn't respond quicker. I tried taking pictures of how I did mine, but basically I just did the "Big 3 Upgrade" which amazingly helped with shifting, bucking, misfires, bogged down power. Completely changed the power.



I also repaired the old wire that connects to my alternator, which at times, if I use my windows the headlight fades, but that's just due to my alternator dieing, but the big 3 is helping it by giving it more of a break and more flow of power to the alternator without much resistance. Also just go through all the grounds you see in the car and just take them off, sand the base where there connected, and the terminal of the ground it's self, and just reconnect. I'll get more pictures of how my connections are, since there very well hidden. Also make a ground from your tranny to the chasis of the truck. I'm about to do that, but I know it will help, also with vaccum's Which play a big roll in the 3.slow, to check the metal tubes and see if there not clogged up. If they are just run 2ft of vaccum lines to where ever they connect to.

oldblue

i really don't intend to be a dick, but maybe its time a professional stepped in. it looks like you have spent thousands of dollars and still the same issue. you need to find a really good diagnostic technician and have them look at it. it may cost $300-$500 for them to figure it out, but it may save you a lot more money and headaches in the long run. btw, you will not find a good diagnostic tech at a dealer. ask around for a good shop.

pewdiepie

Where's the fun in that? You'll just spend more money on a baboon that will have to start with figuring out the history of the car, and chances of spending more time plus having to pay labor. Just to do what Op is already doing. After maybe a year, and even a mechanic who looked at my truck couldn't find the problem. I acually did find what was wrong, and it was as simple as cleaning the air intake. Little things that other people's expierences have on yota tech help people like OP and myself to give a description of what's happening to the vehicle and to help out with past expierences that would help him with his problem. I have the exact same problem he is having with his truck and just crossing out things that he should look for. And if your willing to spend thousands of dollars on your truck, than by all means do it. But if op cannot find out what's going on, then his last resort should be a mechanic. (Which are useless) since op knows what he's doing

nv4runner

I think you were on to something with no coolant reaching the sensors. New sensors and different gauges don't give you correct temp readings... maybe there is a clog in your coolant passages to the sensor block? Maybe your water pump is on the weak side and doesn't give enough flow to efficiently circulate the system? Just thinking out loud.