What is causing an intermittent misfire only when engine is started & cold?

toyota
tundra

#1

2008 Tundra 5.7 only 55K miles – What is causing an intermittent misfire at startup? It’s been running great, then 2 weeks ago when I started it up I could feel a misfire. By the time I backed out of the driveway the check engine light came on. This is what I have learned so far:

•It only happens when you start the engine and the engine is NOT at operating temperature.

•The engine code always reports misfire on Cylinder #2 I put in a new plug and swapped coils but it still reports the misfire on cylinder #2.

•Once it starts to misfire it will continue to misfire until the engine is at operating temperature and you restart the engine. NOTE: You MUST restart the engine for the misfire to go away. It will be running rough, turn engine off/on once it is at operating temperature and it’s as smooth as can be, no more misfire.

•One time I started the truck, I felt the misfire and drove it to a parts store to read the code. Engine was fully warm by the time I reached the parts store. I did not power off the engine, plugged in the tester and read the code which was a misfire on cylinder 2. I cleared the code and within 2-3 seconds it logged the misfire on cylinder #2 again. Cleared the code several times and it kept reporting misfire on cylinder 2. You could also feel the misfire happening. Turned engine off, started it right back up, like before no misfire, cleared the code and it no longer reported a misfire.

•This just started intermittently happening. This morning it happened again, I drove it for about 5 min, engine was about 75% it’s normal operating temperature, powered it off/on, still had the misfire. Once engine temp reached normal temp (about 9 min), I turned off engine, started it back and like before problem was gone.

Any thoughts on what is causing this to happen?


#2

Does this engine have spark plug wires you can look at without taking a lot of stuff apart? If so, that’s the first place I’d start. Carefully bend them and see if there is any cracking of the insulation, esp in cyl number 2’s wire.

Changing parts, like wires, coils, plugs, from one cylinder to another is a common way to diagnose this, so to the extent it is possible swap parts between cylinder 2 and the others, see if the code move to the other cylinder.

I’d also be suspicious of the crank sensor on the fritz. Do the shop manual tests to verify it is fully functional.

A faulty injector can cause this. There’s a test where you fire the injectors using a test gadget and watch how the fuel pressure drops. You’ll likely need to bring in an expert to do that test, but it might be worth it to prove/disprove the injectors being the cause.


#3

Code reader says misfire? What type of misfire? Fuel, injector or ignition, plug? How does code reader determine there is a misfire?


#4

@Cavell, usually the misfire is diagnosed by the engine computer (ECM), not the code reader. The ECM then posts the corresponding diagnoistic trouble code(s)> The code reader simply reads the codes (DTC’s) posted by the ECM. A misfire generally means the crankshaft (the position of which as it goes round and round is measured by the ECM) fails to accelerate at a time when it should accelerate, due to the spark plug firing. That is, if the spark plug fires, it should give a kick to the crankshaft. So a misfire means either there is a problem with something basic, something which is fundamental to makes the engine work, like spark or the fuel/air or the timing or the compression.


#5

No spark plug wires, code reader is always reporting cylinder #2 misfire and I have swapped plugs and coils on cylinder #2 just to eliminate it. What I find strange is the engine will be misfiring, you can feel it, if you turn it off/on and it is below standard running temperature it continues to misfire, once the engine reaches running temp and you turn it off/on the misfire stops. If it was a bad plug, coil, injector or something like that I would think it would continue to act up or fail some time while the engine is running. I do not know what is causing the misfire, but it whatever is causing it only happens intermittently when the engine is started and not at running temperature and the misfire will only go away by restarting the engine after it is at running temp. Once it is at running temp and you restart it you can drive for 200+ miles and it will not miss a beat, will not misfire and run perfect.


#6

I would find a tech who knows how to use an oscilloscope.
When it’s misfiring look at the lines driving the fuel injector and the coil for that cylinder, compare to the others.


#7

Apparently the ECM is doing something different (setting up the engine operating parameters differently) on warm starts compared to cold starts, and whatever that is, it’s sticking for the duration of the trip. So on warm starts, it starts up fine, and runs fine indefinitely.

On cold starts, another parameter set is being loaded, but the ECM never transitions to the warm parameter version for some reason.

Maybe there are two problems. The first is that the car should run fine even on cold starts. That could be due to an air leak, or a fuel pressure problem, either could cause a lean mixture, which would be most noticeable when the engine is cold. The second is that the car’s ECM fails to transition automatically from cold to warm operating parameters. If there was a problem with the engine coolant sensor, or the connection from that sensor to the ECM, that could be a cause.

As mentioned above, this can be solved, but you will probably need to find a tech with expertise on this make/model/year, and who can hook up some real-time engine diagnostic equipment.


#8

I’m having the exact same issue with my 2011 Tundra. Same cylinder and everything exactly as you described. What was the fix for the truck?


#9

my first guess is fuel injector, is there a recall for reprogramming?


#10

Were there any other codes?

A vacuum leak might be causing your problem. While the engine is missfiring spraying carburetor cleaner at the #1 intake port and around the #1 injector will cause a noticeable change in the idle if there is a leak. Of course there could be leaks elsewhere that show up on #1 cylinder also.


#11

Don’t you people look at the time stamps on the original posts?

Tester


#12

no, guess it is off my radar @tester


#13

2013 seems like yesterday @Tester… My how time flies when I’m having fun.

But old threads do seem to often be thrown up into view and I sometimes don’t pay any attention to the fact that they are from the 20th century.


#14

Long story short, it was a broken spring on the intake valve causing the whole intermittent issue only when cold.


#15

That sounds reasonable, I have found broken valve springs in Toyota engines from that year. Lexus recall 138,000 vehicles to replace valve springs in certain 2006-2008 vehicles.

This is something that requires diagnosing, a person shouldn’t just dive in under the suspicion of a broken valve spring.

Now we will need to quietly disappear before we get in trouble for discussing broken vehicles on Car Talk.


#16

How was that broken spring diagnosed to be the problem? Someone very familiar with using a vacuum meter might have found that somewhat quickly but otherwise it seems it would have been a real needle in a hay stack mystery.


#17

Where is irlandes when you need him?

He would have had this properly diagnosed several years ago…


#18

OP responds with the solution after a 4 year delay? Seems in this case anyway it was indeed very worthwhile to the community to invoke an older post. Old or new thread, if somebody has something informational to say on the issue, why not say it?


#19

A compression test would show-up that problem, right?


#20

Compression test showed cylinder 2 was a little low, removal of the valve cover allowed us to verify the Crack in the spring. Had to look real close to see the crack. Was able to just replace the spring to fix the issue.