Blinking Check engine light on RPMs 2000 above; sputtering, shaking and loss of power

I am not sure whether there is a definitive and vehicle model-specific answer to this issue so I am posting this thread in the hope of finding answers and solve this problem. These are the details:
1. 2007 Toyota Tacoma PreRunner 4.0L Long Bed, Dark Blue(rear wheel drive)
2. History of blinking check engine light upon acceleration greater than 2000 RPMs, no codes.
3. When CEL blinks, driveability issues pop up--shakes, hesitates, rough idle below 1000 RPMs, and compression and power suffers especially uphill; feels like something is stuck or plugged that the engine could not cough out. This issue started late 2018, continued to 2019 and for some reason, got better in 2020.
4. When CEL was not flashing, I get code DTC P0306. I delete the code and drive normally with both A/C and heater on full blast until vehicle reaches normal operating temp.
5. What was done:
a. removed the lower intake manifold 3x and cleaned the injectors; regularly applied fuel injector cleaners on the gas tank. Performance improved both times that I cleaned the injectors and the sputtering and uphill choking/shaking went away during the pandemic.
b. checked and inspected all spark plugs, can't see any arching inside the coils
c. chemical test for possible oil in coolant returned negative last time I tested it in 2019
d. compression test done with an average of 145 PSI on all 5 cylinders, the 6th cylinder reading a close 135 PSi. According to the mechanic that I consulted it was still within normal specs.
e. I replaced the water pump as the after market pump that I installed in 2018 failed in 2019. Actual replacement was during the beginning of the stay at home orders in March 2020. The drive belt I replaced like last summer since for no reason it was shredded to pieces.
f. I adjusted the timing chain when I replaced the valve cover gaskets since I was already there and placed Cylinder 1 to TDC. I reinspected the shims and there were no indications of adjusting it since all readings for the Intake and Exhaust valves were within normal specs.
g. I reinspected for leaks; no evidence of loss; In 2020 I thought the problem self cured itself. Occasionally the DTC P0306 would show but the truck had no issues in terms of traveling as it run normally, even faster for its specs in the highways. I just erased it using my OBD scanner. It would run with no incident.
h. Lastly, before all these started, the wife was responsible enough not to notice that the coolant reservoir was empty in the summer of 2016, I think. When she returned after picking up the kids, there was smoke coming from the engine. I quickly did damage control and applied, after flushing the radiator, Blue Devil. Thought the damage control went well as we even used the Tacoma driving to Potland, OR in 2018, without any incident and before that, in December 2017 to Las Vegas. Truck never had any problems when it was running in the highways.

Now I am back to square one. For the 4th time, I removed the whole lower intake manifold, since it started sputtering again last week, when I drove the wife and the wife's cousins from Oregon to Mission Viejo, CA to attend the interment of their cousin. This was last Sunday. Going there was unincidental. Ride was smooth. On the way back, near my place the dreaded CEL started to blink again, this time the sputtering was worse. I was able to drive it short distance enough to the parking space. Last Monday, the sputtering had been so furiously consistent that it stalled after dropping my son to school. Once back I ran the CRC Intake and Valve cleaner and let it have it all! White smoke all over the place after the one hour heat soak. Thought I just solved my issue. Wrong! Tacoma stalled on my way to the funeral. I was unable to attend the funeral of their cousin as a result, them being dropped off by another relative to our place.

I know that the other discussion for 1st Gen Tacomas involved replacing the the wires. But mine has COP, distributor-less. I have a replacement wire ready to replace, but when I did my electrical check with the multimeter, the coil had power as well as the wire connector had resistance below 10 ohms and although I am not sure, this would still read as normal. So why replace something that's working?

I hope this time I can decipher some answers. Some of you will probably say to cut the OEM wire connectors for the ignition coil. But hey, all 6 of those connectors had the same resistance readings below 10 ohms. The repair manual has parameters one has to follow before cutting those wires. What am I missing? Please help and share your solutions. I am quire sure I will return the favor if I find the one solution to this age old, crippling, travel preventing issue of blinking CEL. Thanks.

 

Have you swapped #6 coil with a different coil?

I usually like to swap coils at least 1 cylinder apart. In your case , 6 with 2.
Then see if the problem moves to #2.

It’s probably not going to be as simple as a coil. As # 6 seemed to have lower compression as well. You might try a leak down test in #6. Maybe you have a bad valve?

Maybe even and injector flow test?
But that will require special tools and a scan tool that can perform a flow test.

I hate to mention it, but here still may be a possibility it is the head gasket.

 

According to the FSM 145 psi is the minimum specified compression, standard is 189 psi, low compression would definitely cause driveablity issues at low RPM.
Since the engine was overheated you may want to do a leakdown test and see where the compression is leaking off to.
Also you said the engine seems "constipated" I would pull the O2 sensors and do a backpressure check on both banks to make sure you don't have a plugged catyletic converter.

 

No, the P0300 doesn’t really change anything.
It’s still associated with the P0306.

I noticed after rereading your 1st post.

1. The truck lost coolant once before, correct?
2. You said you tested for oil in the coolant.
You typically test for exhaust gasses in the coolant. Not oil.
3. Has it lost any coolant since the last time?

 

That compression sounds low

I agree with Dm you should pull a 02 sensor and check backpressure

This really sounds like clogged cats

 

My money is on a head gasket issue. That’s fairly low compression for the 1GR…even if it is technically within spec. I say this because the motor was clearly overheated without coolant to the point it was producing smoke.

Easy place to start would be by having the coolant checked for ignition byproducts to check for head gasket. I’d also move the #6 coil pack over to opposite side of the motor to see if the issue follows the coil pack.

 

@Dm93, @TnShooter, @b_r_o, and @tacoman45 -->I appreciate your inputs, suggestions and diagnostic opinion. For the first time since I posted my problems in 2019, I got replies that were really pinpoints what I need to do, revisit what I previously did and move forward as to whether it would still make sense pursuing this on my own vs letting a mechanic do it for me. I didn't want to deal with this on a tight budget now. I wished last year during the height of the pandemic, these actions I could have done as I had a little $ to spend for major repairs. I did a chemical test on the radiator, to check for exhaust gases in the coolant both done in 2018 and 2019. Negative for both. Time to do another one. I may have overlooked something.

@TnShooter, yes, the truck lost coolant to the point that the reservoir or overflow tank was empty and smoke was seen in the front when I lifted the hood, thanks to wife who only knew how to drive but no thanks when it comes to checking fluid levels before use, LOL. Lately, I asked her and my son to check the coolant level before driving. No check, no drive. It is safe to say that on a daily bases, I lose coolant at/or about 240-300 ml when I remove the radiator cap. Little loss on the reservoir though. They have to share responsibilities now, esp that I had gone back to my home health visits as a nurse, and I really need a reliable vehicle to take me anywhere the rubber meets the road.
@tacoman45, I tried to swap coils back in 2019 before we moved to this apartment complex, from a thread I read somewhere on this site, but did not get to complete it. From the swaps I did on with cylinder 4 and 2, however, it was clear the misfire stayed on #6. I removed and replaced the valve cover gaskets on suspicion that engine oil was seeping through the plug on 6. No evidence of seepage.

From the actions that you folks suggested, @Dm93, I have not done that backflow test on the catalytic converter, I will post a freeze frame reading when I get a misfire on 6. I noticed that prior to misfires, the short term fuel trim would be running rich, then normalize when a CEL is set. I am neither a newbie nor am I an expert either on performing these tests--I am just an avid learner. As I am up and running after getting COVID-19 last September, which put my world on hold for 26 days with no income, I hope it wouldn't be a burden on your end to show me, or give me resources, how it is done as I had been on the road the past 3 weeks, trying to recoup from that loss. I try to read threads here before working and continue to test before I drive, which means time wise, I am time constrained. I know it has to be done.

Are you not bothered that it could also be a fuel pump issue and injectors related and an electrical issue? Here's the specific symptoms lately: when I accelerate uphill, the truck shakes like something is clogged somewhere, then the blinking CEL is triggered, then continues to choke as it struggles, then breaks free, as if something was let loose. You know the feeling when when you unclog a drain right? That's the feeling. Don't forget that for some reason in 2020 this problem went away and continues to do well uphill, until last week, when it was back to its old, choking self. I did check the wires as I read in 1st Gen problems that plug wires where corrosion and erosion could easily snap a wire. But these 2nd Gen wires are innervated by only one IGF source and they're sturdy too. I tested the power on the red wire (key on, engine off) on the connector on 6 and there was light. It has power. I have reserved a cylinder head and will order a head gasket for the driver side, although I am not ready to pull the trigger. I don't want to think that after all my troubles, it would still be the head gasket, et al. And a possible toasted cat. Yet. I will keep you updated. Please share your opinions here. I will do my best to take pictures on the next threads. As I said I will post results here. So others will get an insight if they were having the same problems but are stuck because they don't know where to start. Thanks for all the help. I appreciate.

 

Update on this thread. Unsure which is really the culprit. I decided to put my money on the injectors. To my surprise, #6 injector appeared sluggish when I decided to re-clean the injectors without removing it from the lower intake manifold. I removed the entire lower manifold without removing the injectors and decided to bench test every single injector and spray cleaned all of it, starting with #6 injector. I took my time cleaning each injector. Did it for a day then decided to put it back. Switched #6 to #1. Misfire stayed on #6. I have not examined the wire connectors for the ignition coil on Cylinder 6. It's time to take a peek. I have a Dorman made coil wire connectors to replace it. If by this action I still see misfire I will have to redo what I I missed. Will keep you posted. I replaced the plugs all with factory made Denso. Will check the gap once again.

 

Put a scope in the cylinders and see if any look really clean vs the others. Also, I had one with a minor head gasket leak that didn't show on leak down test, but when we hooked an air compressor to cylinder 6 and rotated the crank to close the valves bubbles started showing up in the radiator fill hole.
In general cylinders 5and 6 do run hot because they are so close to the firewall. Overheating can damage the injectors on those cylinders pretty easy, but it sounds like you ruled that out. Maybe watch for any members that install a super charger, I got a set of almost new injectors for $50. If I think of anything else I'll post.

Also, is the level of coolant staying consistent or going down over time?

 

IMHO. A significant clue is the constant consumption of coolant. Along with the history of overheat, coolant loss and 5h in the OP's post #1.

I suspect a head gasket, prolly close to #6, is the problem.

Once upon a time ago, we had an Chevy Venture. It started consuming coolant. It showed no signs of problems. Long story short, it was a head gasket problem. We paid for all the tests,no indication of problem.......until I discovered a Warranty TSB on the problem.

Possible scenario......
On the intake stroke of #6 there is a slight vacuum pulled. This vacuum could allow the coolant into the cylinder, remember the coolant system is pressurized to about 15 psi. Then on the compression stroke, the cylinder pressure forces the gap closed. Essentially, the gap is acting like a check valve to open on vacuum. The coolant in the cylinder could be interfering with the ignition of the fuel/air mix, leading to the misfire codes. The coolant can flash to steam inside a cylinder, 1 drop will expand to displace alot of volume.

 

Get a bore scope and remove the plugs . If the piston tops have no carbon chances are your head gasket is toast.

 

I’d stop throwing $$ at it until you rule out the head gaskets.

 

Purely FWIW: I ran into the P0306 code yesterday morning when my 2000 V6 started having the same issues described here (shudder, misfire, shaking, rough idle). Figured it was over my head so I made an appointment with a mechanic but he didn't have openings 'till later this week so decided to just replace the 6th cylinder spark plug. That didn't do anything. So figured what the heck I'll replace the wires since mechanic not available for a couple days. Miraculously that cured it--I cleared the code and it didn't come back, smooth running engine again. That may not be helpful since it looks like your wires have already been replaced, but just noting here in case someone else can find useful (this particular thread has the most hits when you search for the P0306 code on TW).

Open to feedback on the routing for the wires--could figure out the tidiest way to do it so went with a diagram from YotaTech. I can see why people do the NGK wires--the color contrast is pretty sick.