Horn noise
 

First off, I drive my truck maybe once a week. It is a 97 f150 4.6, 4x4, 5spd, with full length headers (EGR deleted) and K&N cold air intake. For the past 2 or 3 months it has made this horn or kazoo noise starting at 2k rpms and changes pitch from there. Now it is affecting power at random when trying to accelerate below 2k rpms. I replaced pvc valve, cleaned IAC, and checked intake clamps. This only happens once it gets warmed up. Any and help is appreciated.

Appears you have a vacuum leak. The main suspect is the elbow on the firewall side runs to the PCV and connects to the intake. BUT, check all over for vacuum leaks. You mention that you cleaned the IAC. maybe that is leaking where it connects/ reattatches or there is a diaphragm can tare inside the IAC, then you just need to replace it.

IF, you go to replace the IAC....remove the whole throttle body housing. Inside there is 2 internal EGR ports that can also get crusted over with carbon build up. The IAC should come off with it to and make cleaning it or replacement a bunch easier and you get the whole back side of the throttle plate and housing clean.

https://www.youtube.com/watch?v=Td8j...ature=youtu.be


Here is a video of what is happening. The check engine light is just from rear 02 sensor wiring for ignoring the cats being deleted years ago went faulty. Light has been on for years before this current issue.

Please read out all the codes and post them.

Codes ended up for Bank 1 sensors 1 and 2 (sensor 2 has always thrown a code since I bought it in 2003) and Bank 1 sensor 1. Have no cats, but wired rear O2 sensors with capicitor and resister to make them act like normal. Then it thru P1100, intermintent MAF, which could be what is causing the random acts of low power below 2k rpms. I will try cleaning the MAF.

Frustrating thing with that noise is you can't really hear it with windows down or outside with the hood up. It's only with doors closed and windows up.

Please post all the code P-numbers.

agreed you'll get the most help.
Have you doubled checked all your incoming air plumbing to make sure that it is all secured and attached properly?

Will this do it without being driven, just goosing the throttle? If so, then maybe remove the serpentine belt, then start it and see if it is still there. If not, then its down to something on the belt driven items, maybe the alternator or A/C, or tensioner

I'll have to get them from my brother who took pics of the programer when we scanned and I all ready cleared the codes. We quit taking pics of the O2/heater circuit codes refer to just that, the O2 sensor, which will have nothing to do with the noise. But, from what I remember and looking them up:
P0131
P0135
P0151
P0155
P0156
P0401(EGR is deleted, dummy circuit could be faulty)
P1000
P1100


I pinched off the tube to to IAC, and it didn't stop the noise, but did make it run rough while my brother was holding it above 2k rpm. Will do it sitting still just revving the motor, its no different then driving. Also, I gave every clamp a couple of ratchet turns to make sure they are snug.

Now clear the codes and see which ones come back.

You have problems with both front O2 sensors, which have to be fixed or it will run terrible.

Just now did a warm up run and took the belt off. NO NOISE!!! I will investigate further tomorrow, and I do have a stethoscope. My suspect problems is idler or tensioner. Any other theories?

O2's are most likely cause the previous long tubes rusted holes earlier this year, and have since replaced with ceramic coated ones. But codes are cleared.

It could be any of the driven pulleys - idler, tensioner, alternator, A/C compressor, power steering pump.

Let us know which codes come back.

Sorry it took so long. Since I hardly drive it, its not high on priority list.
Here are the codes, all begin P0:
133
136
141
153
156
401
1151

I believe my noise is from the alternator. Very faint to here with stethoscope.

Turns out to be the water pump. Will clean MAF to see if that clears up O2 sensor check engine codes

Arrrrgggg. Started making the noise again. So it is something coolant wise related, I think. Any ideas?

Update: After discussion with my brother I tried a new coolant overflow cap, didn't work, and have put a new thermostat in. Initially, this could have been it, which is weird.