Misfires on cold start

I started my 5vz truck up yesterday to notice a misfire that only lasted until I gave it some throttle. it idles fine after and drives good. This is the 2nd time its happened.

My first thought is something to do with valves. I could check compression but again after it goes away It runs normal. I did run fuel injector cleaner in a near empty tank right before I filled up and am currently on that tank. thought maybe injectors, but I would think that a leaky injector would not cause it to last as long as it did. do these engines need valve adjustments or should I run some seafoam into the intake to try and solve any buildup issues with the valves? kind of a rookie here..

no cel or anything like that, just noticed my shifter jumping around more than normal.

 

That is the stereotypical headgasket/ cracked head symptom on a 5vze. Misfire/rough idle on cold start. Typically no codes.

 

I haven't noticed any of the basic head gasket symptoms at all. I've had an eye out for anything to do with head gaskets since I bought the truck. Nothing at all so far. with the way I drive the truck i would be shocked if this were the case. I guess theres never not a possibility. what could I check or do to confirm this?

 

You did a Leakdown test?..what cylinder is misfiring?

 

no leakdown test yet. I have no idea what cylinder because i haven't gotten any codes. Misfire monitor was "ok" on my scan tool. i don't think it lasts long enough for the ECU to give a code anyway.

 

To answer your original question, yes the valves need to be adjusted (FSM states every 60k miles). And no, running seafoam or other additives won't do you any good if the problem is indeed your valves. These valves actually get tighter over time and adjustment is to open up the lash (aka loosen) them. So I'm doubtful your symptoms are related directly to the valves.

Now a cracked head because valves are too tight might explain everything and I agree with others that your symptoms do sound typical of a cracked head or leaking head gasket. Has your coolant level stayed steady? Have you watched the tailpipe right after a cold start to look for white smoke?

 

coolant levels are stable. I have not noticed any white smoke out the exhaust. I will keep a bigger eye out tho as this misfiring just started. I will do a leakdown test. Any other tests or symptoms I should look for? Thank you guys for the feedback.

truck has been sitting since last night. When I'm home from school I'll start it up and see if it happens again. I'll let it idle and see if I can get a cel. leakdown test from there.

 

A really good test you could perform would be to pull the spark plugs and look in each cylinder with a borescope. You'd want to look for a small amount of coolant pooling up on the top of a piston.

If you don't see that in any cyclinders then that would perhaps give you hope that we're all wrong and it actually is a fuel or spark issue. If you see a cylinder that looks oddly cleaner than all the others (i.e. much less carbon buildup), then pay very close attention to that one.

But keep in mind that if this just started it may be hard to find these signs at this early stage.

As others have said, compression and leak down tests would also be a good idea

 

Il keep this thread updated. Thanks again.

 

OBD II strategy changes from year to year so I do not know it the PCM in your truck will show misfire counts* or not. Before you start chasing your tail look for the emission sticker under the hood and she if she is OBDI or OBDII compliant.

*there has to be so many misfires for the PCM to set a code and illuminate the light, this is usually viewable with a better scan tool IF misfire counts are viewable. The only other way I can suggest to determine which cylinder is to disconnect an injector and see if the mis is worse on unaffected. Access to the injectors under the upper intake can be a an issue.

 

do you have a page# in the FSM stating that for reference
too bad the valve cover gaskets don't start weeping every 60k for the efforts to undertake valve check adjustment on the 5VZFE

 

unless they have the same connector, I'm certain my truck is obd2. I'm not sure if my scan tool will tell me exactly cylinder misfire

 

LOL hahahaha, pretty damn close!

 

? ?

 

I was just saying that's funny cause it seems like a problem we've all had if you put miles on your truck. Seems like a 60k problem

 

The valve covers leaking?

 

Yep the valve covers leaking

 

Valves clearances may or may not be out of spec. Mine at 318k were all within spec and were never checked before.

 

after school yesterday I had a buddy look at the exhaust while I started my truck cold. saw nothing, no misfire. started it cold this morning again after using my truck all last evening to pull some trailers in and out of our yard.. nothing. is there anything that could have just caused this temporarily? like my injector cleaner I threw in the tank right before I got those misfires? I am just confused and trying to learn the most I can from this so I appreciate everyone's input. And I haven't ruled out the possibility of any cracked heads, gaskets or whatever just yet.

edit: funny question. what else could cause a vibration similar to a misfire? I haven't even thought about it being anything else.

 

Maybe real bad motor or transmission mounts but that would vibrate constantly at idle. A broken off fan blade can cause a tremendous vibration, but again it wouldn't go away. Can't think of much that would only last a little while after startup aside from misfires