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Smoke but not overheating?

Tiny
SHEESHAPANTS
  • MEMBER
  • 1997 FORD MUSTANG
  • 3.8L
  • V6
  • 2WD
  • AUTOMATIC
  • 165,000 MILES
Recently replaced my lower intake manifold. The car was not started for about 30 days during replacement. Upon restarting there is a small but steady amount of white smoke coming from under the hood. I can't pinpoint where it's coming from or why? Also, the RPMs are normal when starting (1,500) then after about 1 minute they go down to 1,100 and it idles pretty hard but doesn't shut off. (Which it did not do before the replacement). Meanwhile there's smoke coming out.
There is no smell of burning or antifreeze or anything else, nor is there blue smoke. No smoke from exhaust and all fluids are at full line with no visible leaks. I'm at a loss what to do here.
Update: the car is now showing a p304 code (it wasn't before lower intake replacement)- cylinder #4 misfire.
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Wednesday, August 3rd, 2022 AT 11:23 AM

9 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,901 POSTS
Hi,

I suspect you have an intake leak causing the idle issues. As far as the white smoke, does it seem like steam or smoke? The idea that you replaced the manifold leads me to think something didn't seal. Closely check all around the manifold where it mounts.

When you installed the lower intake, did you use a sealant on the end rails? Also, if you took anything off the manifold, such as the heater elbows, coolant temperature sensor, and so on, they should have been sealed with a sealant.

Take a look below. Did you use a sealant at the ends of the end seals?

Let me know.

Take care,

Joe

See pic below. Also, with the hood open, let me know approximately where the smoke comes from.
Image (Click to make bigger)
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Wednesday, August 3rd, 2022 AT 8:07 PM
Tiny
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Everything was sealed/reattached as per Ford repair manual specifications, including the sealant used on front and rear seals. The smoke has stopped since the 2nd startup since replacement. It might have been dirt/fluids burning off top of engine. It just started throwing the p304 code (cylinder #4 misfire)i double checked wires and replaced spark plugs and coil, which I think narrows it down pretty well to a vacuum leak for the RPM lag/rough idling problem. Thanks for the help/advice! I didn't want to take it all apart again without a second opinion.
Will update after double checking all seals on the lower intake /if the problem persists
Thanks again!
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Thursday, August 4th, 2022 AT 3:35 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,901 POSTS
Hi,

As you said, chances are the smoke was something left behind. As far as the rough idle, a vacuum leak is most common.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know what you find or if you have questions.

Take care,

Joe
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Thursday, August 4th, 2022 AT 5:03 PM
Tiny
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  • 5 POSTS
I rechecked (and tightened one loose) bolts on lower intake, then reassembled engine etc.
Now it starts and runs fine, the previous codes are no longer coming up. No more rough idle woo-hoo!
There is still a small amount of smoke, it looks like it's coming from the exhaust manifold on the driver's side. There is nothing visibly touching it. I can't be sure anything spilled on it as I was working on the car though. Still no exhaust smoke or fluids in places they shouldn't be, everything else seems fine.
It is also now showing a code p0340 which it did not have before. I double checked the sensor, it's connected, and wires seem fine.
I'm unsure if this is due to car relearning running/idling etc, like the repair manual says or what.
I haven't let it run until the thermostat opens up yet because I'm worried, I'll blow something out letting it get hot.
Any advice on what I should do?
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Tuesday, August 23rd, 2022 AT 4:23 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,901 POSTS
Hi,

You didn't do anything with the timing chain, correct? I suspect you already know the code is for a cam sensor. If you clear the code, how long does it take (or does it) to come back?

I suspect by tightening the lower intake, you eliminated a vacuum leak, so that is good news.

As far as the smoke from the exhaust manifold, it is likely just a residue on it. If you can make a video of the smoke and upload it, I may be able to tell.

Be confident in yourself and allow it to warm up. If it's running well, you did a good job and I'm sure it's fine.

Let me know.

Joe
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Tuesday, August 23rd, 2022 AT 7:34 PM
Tiny
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I didn't do anything to timing chain, no. The sensor was unhooked to replace the lower intake manifold, since I had to move the wiring harness aside. The smoke has stopped, I had someone less nervous run it for a while for me.
I have driven it a few times (all less than a couple miles jic) and it is idling hard. Chugs and bogs down anytime I'm not pressing the gas. It does not stall out though.
The code reappears about 2 minutes after starting, about 1 minute if it's just sitting in the driveway idling.
There are no other codes.
Thanks for all the help (so far)!
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Thursday, August 25th, 2022 AT 5:41 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Okay, since the sensor was disconnected, recheck the connection. See if there is any damage, a loose connection, corrosion, or if one of the pins is pushed in and not making good contact. I realize you have checked it, but I have a feeling the issue is there or a leak.

Next, it truly sounds like you have an engine vacuum leak. At least that is a theory at this point. By any chance do you have a live data scan tool? If you do, I need you to check two things for me. First, what are the short-term fuel trims when it's warm and running? Next, before starting the vehicle in the morning and the engine is cold, check the coolant temperature sensor signal. It should be signaling approximate ambient temperature.

Let me know.

Joe
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Thursday, August 25th, 2022 AT 6:03 PM
Tiny
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I checked all wires and hoses again (triple check). I also took off the upper intake manifold again and found a couple bolts about half a turn loose (or under torqued) on my lower intake manifold. I put everything back together and still had the same code/issue.
Because you suggested vacuum leak, I did an at home smoke test, which revealed a small air leak between EGR and upper intake.
Problem Solved!
I just wanted to reply to say thanks! I don't know any mechanics and without the money to go to a shop for diagnostics. It's awesome how easy and helpful and quick to respond ya'll have been!
Thanks again!
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Monday, September 19th, 2022 AT 12:09 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,901 POSTS
Hi,

You are very welcome and thank you for the update. I have a feeling your post will be helpful to others in the future. Also, I'm glad to know you got it taken care of.

Please feel free to come back anytime in the future if you have questions. You are always welcome here.

Take care,

Joe
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Monday, September 19th, 2022 AT 7:20 PM

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