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Red hot exhaust

Tiny
WHITESHIRTSAMMY
  • MEMBER
  • 1996 FORD F-150
  • 4.9L
  • 6 CYL
  • 4WD
  • MANUAL
  • 150,000 MILES
I rebuilt the 300i 4.9l straight-six in my truck listed above. It has a new crankshaft, new camshaft, all around new bearings, and new cylinder head. Initially, when I was revving the engine to break-in the camshaft, after 10 minutes, the exhaust manifold attached to the cylinder head got red hot. It melted my vacuum lines. I repaired all the damage but if I have the engine on for more then 10 minutes it continue to happen. What could be the problem?
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Monday, June 14th, 2021 AT 4:58 AM

48 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,813 POSTS
Hi,

If the exhaust manifold is getting red hot, either you have a restriction (possible catalytic converter) or excessive fuel is entering the combustion chamber.

Have you checked fuel pressure to make sure it isn't too high? Here is a link showing how:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Also, when it's running and the manifold is red hot, check the catalytic converter too. See if it is red hot.

Take a look through this link as well:

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

Let me know.

Joe
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Monday, June 14th, 2021 AT 9:11 PM
Tiny
WHITESHIRTSAMMY
  • MEMBER
  • 60 POSTS
When I turn on the truck, I get regular steam output out the muffler. Also, I had a fuel pressure gauge attached to the fuel rail and was getting the require 50 PSI for when the vehicle was running. I forgot to take it off before the exhaust overheat and now damaged.

I forgot to mention that I have a P1507 code displayed.

I can double check the catalytic converter when I get home today and report back.
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Tuesday, June 15th, 2021 AT 6:19 AM
Tiny
WHITESHIRTSAMMY
  • MEMBER
  • 60 POSTS
I was doing a visual inspection and found that the overheat was reaching the cheap muffler I installed. This is beyond the two catalytic converters. Where do I look to solve this problem?
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Tuesday, June 15th, 2021 AT 6:40 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,813 POSTS
Wow, that is a concern. Let's start with a few basics. Recheck engine timing to make sure it isn't off. Also, if you have a live data scan tool, let me know what the short-term fuel trims are. If the timing is correct, either it is running extremely lean or rich. One other thought. If you remove the oxygen sensor before the converter, does the problem change?

Let me know.

Joe
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Tuesday, June 15th, 2021 AT 10:03 PM
Tiny
WHITESHIRTSAMMY
  • MEMBER
  • 60 POSTS
This is the timing.
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Wednesday, June 16th, 2021 AT 5:19 PM
Tiny
WHITESHIRTSAMMY
  • MEMBER
  • 60 POSTS
The fuel trim with engine off: STFT B1 0%, STFT B2 0%, STFT B1S1 0%, STFT B1S2 99.2%, STFT B2S1 0%. When I turn on the engine, they all start at 18% and slowly lower until they are in the negative and the engine stalls but STFTB1S2 stays at 99.2%.
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Wednesday, June 16th, 2021 AT 5:56 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,813 POSTS
Hi,

THe B1S2 @ 99% is normal. That is the sensor after the converter. The 0% are perfect. When it goes negative, that tells me the computer is trying to lean the fuel mixture. How far into the negatives does it go?

Are there any misfires? Have you checked the timing? Also, it could be dumping fuel. The code you gave me, P1507, is related to the idle air control valve. It could be choking the engine not allowing enough air which in turn would cause a rich fuel mixture.

I attached the diagnostics below specific to the code. Take a look through them and let me know if you are comfortable doing them

Let me know if that helps. In my mind, if the converter is good and fuel pressure us good, something is causing it to dump fuel or the timing is retarded.

Take care and let me know the results.

Joe

See pics below.
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Wednesday, June 16th, 2021 AT 7:38 PM
Tiny
WHITESHIRTSAMMY
  • MEMBER
  • 60 POSTS
The voltage is 12.3v and the resistance is 2.11m ohm.
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Friday, June 18th, 2021 AT 4:09 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,813 POSTS
Hi,

If you are getting 2.11 m ohms, the IAC is bad. The flow chart indicated it should be between 6 and 13 ohms. Have you tried replacing it?

Here is a link that shows how it's done in general. You can use this as a guide.

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

The directions specific to your vehicle are attached below.

Let me know.

Joe
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Friday, June 18th, 2021 AT 6:44 PM
Tiny
WHITESHIRTSAMMY
  • MEMBER
  • 60 POSTS
I think I misread something. I need to double-check my work.
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Friday, June 18th, 2021 AT 6:56 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,813 POSTS
Hi,

No problem. Let me know when you recheck. Also, let me know if I can help.

Take care,

Joe
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Friday, June 18th, 2021 AT 8:57 PM
Tiny
WHITESHIRTSAMMY
  • MEMBER
  • 60 POSTS
Okay, the IAC has 9.4 ohms across the pins. I was doing it wrong. What is next to check?
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Saturday, June 19th, 2021 AT 8:21 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,813 POSTS
Hi,

That sounds a lot better. What I would do next is remove it and inspect where it mounts on the throttle body. It isn't uncommon for carbon and dirt to build up and restrict airflow. Keep in mind that I am basing this on the code you provided.

Take a look through this link and let me know if it helps:

https://www.2carpros.com/articles/idle-air-control-valve-service

Joe
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Saturday, June 19th, 2021 AT 8:16 PM
Tiny
WHITESHIRTSAMMY
  • MEMBER
  • 60 POSTS
Okay, this is where am at: I removed the IAC and the throttle body and found no noticeable accumulation of carbon deposit. Blew air through all the orifices and did not find any obstructions. Put it all back together. Disconnected the air filter. Turned the vehicle on, turns right on, no problem. The STFT starts at 36% but in less than a minute, they lower to the single digits but not zero or negative. It idles really rough. The check engine light has not turned back on.
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Sunday, June 20th, 2021 AT 6:36 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,813 POSTS
Has the check engine light turned off (is the code gone for the IAC)?

I rewatched your video of the timing. In the video, I don't see the marks. Also, I'm hearing a strange noise (not a knocking) but something that sounds like it's hitting?

It's a video so I may be totally wrong. But, have you noticed it?

The fuel trims (in a perfect world) you want at 0. Up to 10% positive or neg are normal. The cold start +38% isn't out of the ordinary. So, I'm to the point that I'm thinking it isn't a fuel-related issue.

I think we need to start over. We are missing something.

Are there engine vacuum leaks? Any possibility of internal timing issues when it was put together? Any chance of the exhaust being plugged?

Let me know.

Joe
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Sunday, June 20th, 2021 AT 8:06 PM
Tiny
WHITESHIRTSAMMY
  • MEMBER
  • 60 POSTS
This is my first time rebuilding an engine myself. Even though I got the timing marks, on the gears, aligned and it makes a straight line between the two shafts, I am still not confident on the timing, in general. Particularly with the lettering being upside down on the crankshaft pulley when you hit it with the timing light. I sent you a still picture, of the timing marks with the video so you get a reference to where the timing was hitting, on the pulley, because it was hard to see the lettering on the video. The pointer from the crankshaft sensor bracket is landing on the 10-12% BTDC. To my understanding, this is where it is supposed to be.

There is a clicking sound coming from the engine. I do not know where it is coming from.

I erased the error codes before I reassembled everything back together. I have not given the engine enough time to display any code. I only ran the engine for a minute or two.

I can double check the vacuum line. I have had to replace them everytime I run the engine for more than 5 mins. Because of the heat.

Let me work on checking the exhaust manifold for blockage.

The primary purpose of this project was to learn engine rebuilding. I just wish I had chosen a smaller engine to work with. I do not mind starting over but at some point I need to make a Lowe’s trip. The secondary purpose for the truck.
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Monday, June 21st, 2021 AT 5:29 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,813 POSTS
Hi,

The timing you mentioned is correct. However, that is where the distributor is set. That can be adjusted. The timing chain, if not perfect, can't be adjusted externally.

Take a look at the pic below. Is that how you had the timing marks aligned?

Let me know. Also, I listened again to the video of the engine running. Do you have good oil pressure? Is the sound coming from the top end? Did you do anything as far as the valve lifters?

I'm glad you decided to rebuild this engine. The problems are how you learn. My biggest concern is something catching fire due to how hot the exhaust is getting. When you have it running, do you feel a misfire? I'm wondering if there is a stuck fuel injector dumping fuel.

Let me know.

Joe
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Monday, June 21st, 2021 AT 9:41 PM
Tiny
WHITESHIRTSAMMY
  • MEMBER
  • 60 POSTS
-The timing illustrated in the picture is exactly how I set my timing.

-I do have engine oil pressure.

-I believe the tapping sound may be coming from the power steering pump but am not confident.

-The cylinder head is a reman from AutoZone. Other than transferring the lifters to the new cylinder head and torquing them, I did not do anything else to it.

-For the first 1-2 minutes I start the engine, it runs perfectly then the RPMs go down. It does not feel like misfiring. I took off the fuel pressure regulator vacuum line and glued the ends to make sure it was not leaking (I rebuilt the vacuum line because it got melted) and reinstalled the line. I got better results with the RPMs, but it still lowers below 500 RPMs. Let us concentrate on the fuel system.

-Do you have access to info on the temp range for the exhaust manifold?

I must purchase a new fuel pressure gauge so as to install and monitor the pressure while it is running. I will make a video of it and report back.
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Wednesday, June 23rd, 2021 AT 7:08 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,813 POSTS
Hi,

You have lifters and pushrods. Neither are in the head. When you adjusted the valve lash, how was it done? We may have hit on something here. If they are too tight, once the engine warms up and expands, the valves may be staying open too long or not full seating. There could be unburned fuel getting into the cylinders on an exhaust stroke. Did you check valve lash?

If you didn't, that needs to be done. Also, if you used the original pushrods, they needed to be reinstalled in the same location as they were removed from as well as the lifters. Adjustment is done by using shorter and longer pushrods.

Starting with pic 3 below are the directions for valve adjustment. You may have already done this or this may be the problem. Finally, I think I know what is happening. I suspect you have pushrods that are too long. They are causing the valves to hang open slightly. And fuel is getting into the cylinder on an exhaust stroke. It's a theory at this time, but I have a feeling this is the issue.

Let me know if you already did this.

Joe

See pics below.
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Wednesday, June 23rd, 2021 AT 9:34 PM
Tiny
WHITESHIRTSAMMY
  • MEMBER
  • 60 POSTS
I saw the valve adjustment in the repair manual but since I was working on my driveway ( I don't have a garage) I was anxious to put it back together. I ordered all standard parts and assume they would fit correctly the first time.

I skipped the valve adjustment part.

Sorry, I confused the rocker arm with the lifter. All I did to the cylinder head was transfer over the rocker arm and torque them to spec.
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Thursday, June 24th, 2021 AT 6:20 PM

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