Engine Hesitation under Medium Acceleration (Ignition Coil?)

I would have taken your advice, a year ago when I wrote it. But as I was new to the forum I was just looking for answers and many 2nd gen owners also own or have owned first gens and a thread talking about spark plugs seemed like a good place to get info. Instead of starting a new thread that most people won't look at. So there was a reason to my madness and if it's not the way you would do it , then you know what they say.... Now if you think it was rude then all apologies. BTY I'm a professional highjacker when I comes to getting the info I need and hopefully I don't hurt anyone's feelings , it just seems like a better way to get an answer when someone else is kinda already on the subject. And yes that post was a little too long. I agree with breaking it up. I'm a beginner editor.

 

I think

A lot of the hoses are form fitted... the hose going to my throttle body was practically falling off. Stuck that back on and clamped the hell outta it, resetting ECU and UCON now with a 10 minute power down, and trying again.

side fact, there are a couple form fitted hoses that appear to be Toyota items only.

 

Ok, so fixing the TB vacuum hose and ressetting the ecu/ucon didn’t resolve the hesitation from stop, and through gears.

Only other things I can think of would be to replace the throttle body and MAF sensors, both I recently cleaned..

News.. after digging deeper (going on days of digging now), I found a couple causes for hesitation this thread hasn’t touched on yet.

1. brake sensor and the accelerator interlock kicking in. See this thread for details: https://www.tacomaworld.com/threads/stall-during-acceleration.377040/

2. Oil Control Valve. Yeah I had to look this up to understand (which I still might not) this valve controls the Variable Valve Timing based on oil pressure. There are also OCV Filters that need to be replaced/cleaned. See this thread for the details: https://www.tacomaworld.com/threads/oil-control-valve-location.270960/

and this thread for details about the filter location/replacement part number:
https://www.tacomaworld.com/threads/this-is-why-you-need-to-replace-your-vvt-screens.639996/

 

Ok, so fixing the TB vacuum hose and ressetting the ecu/ucon didn’t resolve the hesitation from stop, and through gears.

Only other things I can think of would be to replace the throttle body and MAF sensors, both I recently cleaned..

News.. after digging deeper (going on days of digging now), I found a couple causes for hesitation this thread hasn’t touched on yet.

1. brake sensor and the accelerator interlock kicking in. See this thread for details: https://www.tacomaworld.com/threads/stall-during-acceleration.377040/

2. Oil Control Valve. Yeah I had to look this up to understand (which I still might not) this valve controls the Variable Valve Timing based on oil pressure. There are also OCV Filters that need to be replaced/cleaned. See this thread for the details: https://www.tacomaworld.com/threads/oil-control-valve-location.270960/

 

Have put this in at least one other thread...so just a thought, another possiblity??.......

Maybe not exactly the same but this might be worth a read...check the 6th post from "Nutsy" I had the "hesitation on acceleration" symptoms and a new fuel pump fixed it.

........oh, sorry...post number 9 by "blacktaco07" in this thread mentioned it as well..

 

Thanks for the add!!

my truck has a brand new walbro fuel pump, I did the work myself so it’s rock solid (unless it was defective from the factory).

I purchased a ton of stuff last night for the Tacoma and will get around to systematically working through possibilities when I wrap up with work travel in a couple weeks.

 

Replaced all Vacuum lines, except the brake booster line because I missed it when placing the order, with new ones.

Replaced the OCV solenoids and filters (which weren’t that bad).

Replaced the Throttle Body with a new one, definite change in responsiveness there, but still same underlying issue.

Checked my brake sensor to ensure the ECU wasn’t cutting fuel from detecting ‘braking’ when I wasn’t..

still no beans. Near consistently stumbles if I try to give it a medium amount of gas when launching. Acceleration that feels great sometimes when gassing it, but like crap others. It still accelerates and pulls, just feels like crap compared to the good moments.

the stumbling from a stop feels like my engine is cutting power entirely/down to idle levels (but in gear-MT) before it starts yanking.

did the gasket work myself, tightened intake and plenum down to torque with new gaskets..

Very frustrating.. will figure it out even if I have to tear the damn engine out, but don’t think I should need to.

Will update once I replace the brake booster vacuum line.

Will also take some more UCON data for Scott to catch the stumbles.

 

Replaced all vacuum lines, ensured no vacuum leaks. (Even the EVAP likes)

did the electronic cleaner spray test while idling around everything vacuum related (no surging)

compression test yields 182 to 187 PSI on all cylinders.

no CEL codes.

working with gadget on a timing position verification now (still have one question unanswered).

fuel pressure is rock solid and never less then 43 PSI at the end of the fuel rail. Vacuum appears to be rock solid as well.

spark plugs all look identical.

Verified all fuel injectors are the proper part numbers for URD’s mkIII kit. (Still way to do @torpsd recommendation with stock fuel injectors and bypass the UCON, but don’t have stock injectors, don’t want to use crappy Amazon ones, and don’t want to dish out $700 for new OEM/NAPA ones unless I realllly need to..)

with the exception of rare cold engine moments, if I drive and only use the first 50% of the gas pedal range, there aren’t really any issues.

 

Its been awhile since I've seen this thread but is the only problem ur having us hesitation in throttle? Ive kinda read back through what youve done and seen checked for vac.leaks and fuel pump and alot of other things but im sure you did the gas filter? And also ground wires? Every time i had to fix a missing or hesitation issue, its been a fuel filter or plug or plug wire or coil or ground. Since you don't have a distributor then thats out. But that ground that goes from the head to the fender ir firewall will definitely cause a miss. If you already done all if that then just disregard this.

 

Checked the ground below the starter on the block.. you know which head has the ground you’re referencing (even if electronically speaking one ground theoretically grounds the entire metal structure — heads, block)

 

Fuel filter is relatively new, and I get solid pressure regardless (even during hesitation

 

This is exactly what I am now experiencing with my 2015 Tacoma. 84,000 miles. V6 TRD 4D OR. Runs great under light throttle. Medium throttle up a slope and it cuts out, usually during upshift. No CEL. It's maddening. I don't want to head down the whole trial and error road seeing that others have had mixed results. This started (coincidentally I believe) after changing the thermostat and coolant. I changed the thermostat because the engine was not reaching operating temp in normal time and the heater was not getting warm. The new thermostat solved that. I had Toyota mechanics check it out too and of course it ran fine for them.

 

It is maddening!

However, I’m hoping my stubbornness might be paying off to some extent. I believe my issue miiight be from a faulty fuel injector set, not performing to spec and just fucking dumping fuel causing it to run rich to the point of fuel in oil smell (which leads to bad things).

I’ve had a master tuner for these trucks have issues tuning my truck because against all attempts, my truck still registers as rich. This poses an issue in theory though, as our entire engine management and fuel management systems (from the factory and in nearly all aftermarket solutions) depend on two points of measurement for the current air fuel ratio using the exhaust output of banks one and two. This setup assumes that all cylinders on each bank are running about the same, where in reality one injector running rich beyond the bounds of the others will cause an increase in A/F ratio detected. The Engine control unit (ECU) would see this and determine it needs to cut back on the fuel input (which actually leans things out for the previously ‘good’ cylinders), and THEN your other cylinders start running hotter which leads to premature ignition and knock, which our ECU detects (from other vibration type sensors for this reason) and goes “oh shit, cut ignition timing levels to reduce power” which I believe can in some cases result in what I’ve been experiencing. This is from an at home mechanic who’s taking theory and measurements to draw conclusions to the best of his ability. I do NOT have the engine diagnostic experience or tuner related experience to KNOW, so don’t hVe blind faith in my ‘ideology’.

I’m hoping some guru jumps in with some “that makes sense” or “you’re talking bubbles, but here’s where you’re wrong” advice in this here forum.

strongly suggest you more frequently check your oil levels as you may be burning more if you’re having the same result until you figure this out. If it starts smelling gassy, change more frequently (within reason). DONT use non oem or Amazon cheap fuel injectors.

that’s MY troubleshooting, and I actually have a set of 650cc (NOT the size for stock) injectors I bought from the fuel injector clinic sitting in my PO Box and can’t wait to see if how this affects the fuel issues I’ve seen during tuning (even when justDSM has really tried squelching them), which could explain all my woes in the past.

for you, I’d focus on why your truck stopped warming up. I’d throw your old thermostat in a boiling pot of water to see if it was failing or not (though you prolly threw it away).

cheers to weird issues!

 

Pretty sure I have mine fixed. Was following this thread because I was having issues that sound similar. Got around to spark plugs and searched the forum to get the factory part number and ran across several posts where people were saying they were having similar problems with Irridium plugs, notice the plugs shown in a previous post are Irridium. Anyway, pulled my 24,000 mile Denso Irridiums and put Denso copper in and haven't had an issue in two months.

 

I read thru all of this again and saw where one person replaced a coil they thought was bad and the problem did not go away. Has anyone tried buying one coil and moving it from cylinder to cylinder to see if the problem goes away? I suppose this could work to identify a bad coil if only one of the six is not fully functional.

Since there are so many things or combination of things that can cause these issues, alone or together, trial and error is a slippery slope to head down. Faulty plug, faulty coil, dirty fuel injectors, fuel pump/filter, faulty TPS, dirty throttle body or MAF, faulty 02 sensor, restricted CAT, etc. I change my air filter often and every time I do I feel a change for the better. I can always tell when it needs to be changed as I can feel it in the reduced responsiveness. Every time I change the engine air filter I see that secondary filter/screen thing (charcoal filter for gas emissions?) downstream of the air filter and it looks filthy and clogged. I guess that is just the way they look because Toyota claims it does not restrict air flow.

Only one person in this thread seemed to resolve the hesitation and that was with a new fuel pump. I believe the filter is in the fuel pump assembly? No in-line filter, correct?

The most disappointing thing is there is no CEL, thus no code, to even give you an idea of which component/s might be failing. And it sounds like it never will code so we just keep chasing a ghost.

I have learned to drive in such a way as to minimize the hesitations. I don't want this to be the norm going forward so it looks like trial and error is the only option.

 

RocketTaco808; I changed the thermostat because I suspected it wasn't closing because it was difficult for the engine to reach operating temperature in the bitter cold weather and so my heater was not working well. It works as it should now and the engine reaches operating temp quickly. I have owned numerous Toyotas and have never had a bad heater. I threw the old thermostat away but I did look at it and it was partly open. I replaced it with an OEM thermostat. It seemed to be the only option for this engine.

 

Cool, you went OEM, heating problem solved, makes sense.

I did replace my coils with denso coils and still had my issue. They looked like they’ve had better days and the insulators were cracking so I don’t feel too horrid about doing this. Definitely wouldn’t foot for OEM though, but also wouldn’t stray from Denso either.

how’s your mileage and fuel trims looking when driving? (OBD2 scanner required for fuel trims). Looking for STFT and LTFT values.

Also you saying the secondary filter is filthy and it being ok because toyota said it would never impede airflow borders on blind faith. Got any pics? If your truck is getting up there in age and it’s (for whatever reason) clogged, Reality < Toyota’s words.

 

filter downstream of the air filter. Whatever this thing is called and whatever it is supposed to do.....

 

@RocketTaco808 its likely the UCon is causing your stumble from a stop. Mine had a similar issue and it was the boards in the UCon were bad. URD replaced them and it’s been smooth sailing since. I would highly recommend trying driving the truck with something like HP tuners or going back to stock if that’s an option.

 

@Dergibog, looks like fine desert sand is all up in your taco. It sounds silly, but I’d leave that in place from seeing how silty it looks and maybe try vacuuming it clean with a good shop vac.

@BassAckwards ripped the ucon out (as I’m literally running out of things it could be that make sense), have an hptuners dongle, but tunes from justdsm (who definitely knows his stuff), weren’t running right at all, truck was chugging gas and trying to cut back, even when the pulse widths were very short on the injectors.

hence my FIC injectors that are tested good.

just hoping justdsm resurfaces otherwise I’m going to venture on figuring the tuning side out with the base tunes he gave me and support/knowledge from reading through the hptuners thread on here.

reading a book on tuning is great, until you see options in hptuners in toyota jargon and blank out on what most of the stuff actually does