Cold start issues...

[A.Wilson013]

Awhile back I posted in my build about an issue I was having every now and again where my 4Runner would run really rough for about 5 - 30 seconds after starting if it had been sitting for a few hours, or a few days. After that short amount of time it runs PERFECTLY normal.

Well, I pulled a plug to run a compression check and found the iridium tip on my spark plug was completely gone, so I thought, "cool, there's my issue" and replaced all plugs and wires. The probably appeared to be gone.

But now it's back.

Up front:
Fuel trims are normal
RPM is normal
New Plugs
New Wires
New PCV Valve
Have done EXTENSIVE searching for a vacuum leak. There isn't one.
Cleaned (and swapped with another) MAF
Fluids are all at their normal level and color
Fuel trims are normal
RPM is normal

I have tried countless times to get a video of the issue, but all the other noises associated with a cold start (mostly the loud fan) cover and sign of the strange running.

Basically, it sounds like a train- chug chug chug chug, and the speed of the chugging increases with the speed of the engine until it goes away completely. Sometimes it takes a couple seconds, other times it has taken as long as about 30 seconds. ONE time it threw a code for a random misfire. However, the next day I changed the plugs and wires and it has never come back.

I am leaning toward a leaking fuel injector but I am skeptical because I feel my wifeband AFR would show it running real rich on start up, which it doesn't. Any thoughts on this?

 

[ShooterMcGavin]

This may be a ridiculous guess, but...
I had a car in the past that had a leak-back valve for the fuel line, in order to keep fuel pressure when the car was off for some time. When that valve went bad eventually, if left sitting for some time (a day or more), it would have problems starting and would run very rough for some time as the fuel pressure was built up again. Do our 4Runners have anything like that?

 

[A.Wilson013]

This may be a ridiculous guess, but...
I had a car in the past that had a leak-back valve for the fuel line, in order to keep fuel pressure when the car was off for some time. When that valve went bad eventually, if left sitting for some time (a day or more), it would have problems starting and would run very rough for some time as the fuel pressure was built up again. Do our 4Runners have anything like that?

I don't believe they do, but if a fuel injector were leaking it'd have a very similar outcome.

I just feel like my wideband O2 would show it running way rich if that were the case, and it doesn't.

 

[LittleCaesar]

Aging fuel pump? What is the fuel pressure KOEO?

 

[A.Wilson013]

Aging fuel pump? What is the fuel pressure KOEO?

I have been reading up on fuel pressure testing and it seems like it'll be pretty spendy... Theoretically if I had a leaking injector it'd be nothing after sitting for awhile, right?

I test the resistance at the plug on my pump and it was well within spec. I'm also having no issues running lean at WOT. I think if my pump were going out id be leaning out quite a bit especially around 9psi of boost.

 

[SpidermanGeek]

What Oil Weight are you running?

 

[A.Wilson013]

What Oil Weight are you running?

Shouldn't matter as I live in Seattle. However, I run Mobil 1 5-30 synthetic.

 

[LittleCaesar]

You should PM the great him. He just put in a fuel pump over the weekend and is able to test fuel pressure. His father or FIL is a master toyo technician so I have read so he may have everything accessible.

In all the tester and extras would run ya no more than $60. At least it would rule out fuel.

Fellow member JasonofRedwood is having a fuel problem, most likely a leaking or failing injector even though his ohm readings are within spec.

 

[SpidermanGeek]

Shouldn't matter as I live in Seattle. However, I run Mobil 1 5-30 synthetic.

True. I thought about it afterward. It's just cause I've had the "train chug" experience with a previous car on really cold Ontario mornings and it's due to a combination of cold air and thick cold oil. It would take a good 15-20 seconds sometimes before the engine would start idling smoothly. It never sounded good, that's for sure.

My fault though, I never bothered to plug the block heater overnight.

Anywho, I don't think I have much more to add. Sounds like a mystery to me.

 

[rideexileex]

Fuel pump isnt going to affect a cold startup for a few seconds - It's either good or bad... Same with fuel injectors - they'll be good or bad, regardless of warmup.

Does it run similar to when you disconnect the PCV hose?

Have you looked at the IAC valve, or the vacuum hose with the check valve in it to see if its dirty?

 

[Wanderlust4]

Well, I pulled a plug to run a compression check and found the iridium tip on my spark plug was completely gone, so I thought, "cool, there's my issue" and replaced all plugs and wires. The probably appeared to be gone.

Did you end up running the compression test then? If so, what were the results?

If you didn't then and end up doing a compression test now/soon, do a leakdown as well.

How do the plugs look now? How many miles on the engine overall? After the initial 5-30 seconds, does the engine still run perfectly?

Basically, it sounds like a train- chug chug chug chug, and the speed of the chugging increases with the speed of the engine until it goes away completely. Sometimes it takes a couple seconds, other times it has taken as long as about 30 seconds. ONE time it threw a code for a random misfire. However, the next day I changed the plugs and wires and it has never come back.

Is the sound only RPM dependent? Does the sound change if the engine is under load or when there's no load (coasting in gear)? Does the engine seem to choke/stutter/misfire at a certain RPM or RPM range?

If you have another set of known good plugs that you can borrow, I would put those in and see if the issue goes away again. It almost sounds like something is eating your plugs.

I am leaning toward a leaking fuel injector but I am skeptical because I feel my wifeband AFR would show it running real rich on start up, which it doesn't. Any thoughts on this?

If it's not showing up in the AFR, then I don't think it would be a leaking fuel injector. Also, if you have a cleaned/swapped MAF and the O2 sensors aren't throwing any codes, that should be a secondary indication that your AFR should be within acceptable range.

 

[JFinns]

It's a long shot but, if the coolant temp sensor or even the intake air temp sensor were way out of range it might cause the engine to start rough and then seem to run fine, or If one of the 2 sensor had a open circuit it would read -40 deg that would definitely make it run rough, but you would probably get a code if one of them failed like that.

 

[A.Wilson013]

Well, I had my first VISUAL and OLFACTORY symptom tonight.

I let my 4Runner sit for just about 24 hours. I went out tonight, popped the hood and smelled fuel which seemed to be more pronounced on the driver's side of the engine. Interesting. Fired it up and it ran rough as expected, AFR was normal, BUT my scangauge showed that the computer was pulling 18 units of fuel in the short term fuel trims. As I backed up I noticed the steam/smoke from my exhaust had a very blue tint to it when my headlights hit it.

I need to find some time to actually trouble shoot this stuff, but I am really leaning toward a leaking injector now...

Also guess I am done driving the 4Runner for a bit.

 

[jeremyc74]

I think you really need to be able to see the fuel pressure on start-up, and then you can see if it's leaking down.

In the near term I'd probably pull the plug that was bad out again and see what kind of shape it's in.

Aside from fuel problems, you could have oil or coolant pooling in the cylinder and the plug might show that.

 

[gamefreakgc]

I was going to say you are probably losing fuel pressure due to a leak somewhere like others said, but you just figured it out.

If it were a fuel leak from a line somewhere, you'd smell it non-stop. Seeing that's not the case, time to pull those injectors and have them flow tested and rebuilt. Your 4Runner will run better after you do that anyway so you'll be happy you did it.

 

[A.Wilson013]

Just pulled all the spark plugs and jumped the fuel pump to see if any fuel would spill into the cylinders. It didn't.

I can hear the fuel running through something with the pump on so I pulled the 7th injector. No fuel coming out of that either with the pump going.

Pretty irritated as I move back to square one. No idea what it is/could be.

 

[nely]

I'd check your fuel pressure regulator. If it's leaking into the vacuum line you'll have fuel smell and rough startup.

It should be on the rear of the driver side fuel rail. I'd pull the vacuum line and start the truck. If it's bad you'll see some fuel squirt out of the hose.

 

[nely]

Also you won't see fuel in the cylinder if the valves are closed. You'll maybe only have 1 or 2 cylinders to likely have the intake valves open. You really need to pull the fuel lines and injectors to find a leaking injector

 

[A.Wilson013]

Also you won't see fuel in the cylinder if the valves are closed. You'll maybe only have 1 or 2 cylinders to likely have the intake valves open. You really need to pull the fuel lines and injectors to find a leaking injector

That's a good point that I didn't consider.

I pulled the vacuum line off of the FPR and there was nothing to be seen for fuel. No scent either.

 

[nely]

You stated that the fuel trims where -18. Was that on both engine banks? Just 1 or just 2?

And when you stated you changed wires is that just the 3 wires or wires and the coil boots?