Hissing.
Thread Starter
|
New User
Joined: Apr 2013
Posts: 3
Likes: 0
Hissing.
Hello, I have a f250 5.4L V8. I have been having some issues with it, it is making some hissing sounds when it is underload. I have noticed that It is worse when I am pulling a trailer, my RPM's are about 3500 and then instantly drops 500 rpms when the hissing starts.
I am not sure if a vacuum leak could cause that or in that sense really where to start looking for the problem. I would like to diagnose it myself without having to take it in. If there is anyone that has any input that would be great.
I am not sure if a vacuum leak could cause that or in that sense really where to start looking for the problem. I would like to diagnose it myself without having to take it in. If there is anyone that has any input that would be great.
Fleet Mechanic
Joined: Aug 2008
Posts: 1,446
Likes: 9
From: NE Iowa JD Country
Hello, I have a f250 5.4L V8. I have been having some issues with it, it is making some hissing sounds when it is underload. I have noticed that It is worse when I am pulling a trailer, my RPM's are about 3500 and then instantly drops 500 rpms when the hissing starts.
I am not sure if a vacuum leak could cause that or in that sense really where to start looking for the problem. I would like to diagnose it myself without having to take it in. If there is anyone that has any input that would be great.
I am not sure if a vacuum leak could cause that or in that sense really where to start looking for the problem. I would like to diagnose it myself without having to take it in. If there is anyone that has any input that would be great.
1st suspect area is a elbow of the PCV line near the firewall that connects to the throttle body.
Vacuum leaks can be anywhere though...so check things over closely
does it hesitate or shake during this? or just drop RPM?
Thread Starter
|
New User
Joined: Apr 2013
Posts: 3
Likes: 0
Just drop in rpm along with a loss of power. It hisses more, like I said earlier, when it is under load, like when I am towing something up hill. You can hear it now and then when I am just driving, but it is more pronounced when I am pulling. I will check the vacuum system for leaks. Thanks.
Fleet Mechanic
Joined: Aug 2008
Posts: 1,446
Likes: 9
From: NE Iowa JD Country
Just drop in rpm along with a loss of power. It hisses more, like I said earlier, when it is under load, like when I am towing something up hill. You can hear it now and then when I am just driving, but it is more pronounced when I am pulling. I will check the vacuum system for leaks. Thanks.
when it is the most "pronounced" can you still change where the air is coming out?? Defroster to the heat, or heat to the dash output of air?
Thread Starter
|
New User
Joined: Apr 2013
Posts: 3
Likes: 0
It is a 2001, with an auto transmission. It is most pronounced at around 3500 rpm and while it is under load. Yes I can still change the air on my dash to whatever I need. I know that is one of the main ways of knowing you have a vacuum leak on fords. My brother just had a leak and he could only use his defrost, it was a line that was loose behind the battery.
I used some carb cleaner around my engine and couldn't find a leak. I did take a line off of the vacuum box behind the battery and sprayed the cleaner directly on the elbow line and there was no change in the idle of my truck.
I did notice though as I was sitting there listening to the engine it would rev a little bit and then let off. Almost as if the ac was on but I had turned off the ac and the air. So I don't know if that could be another sign of a leak, an intermittent idle. Now it was not cutting in and out only a slight change in the rpm.
Let me know, thanks.
I used some carb cleaner around my engine and couldn't find a leak. I did take a line off of the vacuum box behind the battery and sprayed the cleaner directly on the elbow line and there was no change in the idle of my truck.
I did notice though as I was sitting there listening to the engine it would rev a little bit and then let off. Almost as if the ac was on but I had turned off the ac and the air. So I don't know if that could be another sign of a leak, an intermittent idle. Now it was not cutting in and out only a slight change in the rpm.
Let me know, thanks.
Fleet Mechanic
Joined: Aug 2008
Posts: 1,446
Likes: 9
From: NE Iowa JD Country
It is a 2001, with an auto transmission. It is most pronounced at around 3500 rpm and while it is under load. Yes I can still change the air on my dash to whatever I need. I know that is one of the main ways of knowing you have a vacuum leak on fords. My brother just had a leak and he could only use his defrost, it was a line that was loose behind the battery.
I used some carb cleaner around my engine and couldn't find a leak. I did take a line off of the vacuum box behind the battery and sprayed the cleaner directly on the elbow line and there was no change in the idle of my truck.
I did notice though as I was sitting there listening to the engine it would rev a little bit and then let off. Almost as if the ac was on but I had turned off the ac and the air. So I don't know if that could be another sign of a leak, an intermittent idle. Now it was not cutting in and out only a slight change in the rpm.
Let me know, thanks.
I used some carb cleaner around my engine and couldn't find a leak. I did take a line off of the vacuum box behind the battery and sprayed the cleaner directly on the elbow line and there was no change in the idle of my truck.
I did notice though as I was sitting there listening to the engine it would rev a little bit and then let off. Almost as if the ac was on but I had turned off the ac and the air. So I don't know if that could be another sign of a leak, an intermittent idle. Now it was not cutting in and out only a slight change in the rpm.
Let me know, thanks.
Have you had the codes scanned?...there can be stored codes without tripping the CEL (Check Engine Light or Service Engine Soon) on the dash.
Prolly got more than one gremlin in there giving you fits.
A fluctuating idle, hints that the IAC is need of some cleaning, maybe replacement, but shouldn't come into play around the 3500 rpm and load situations.
If you have some higher mileage on this...then the best way to clean and or replace the IAC is to remove the whole throttle body housing. This not only will get to the IAC but allow you to check/clean the internal EGR ports that are inside the housing too. also give you a real good look at the elbow on the PCV line ta boot.
Once you have the Throttle body housing off then remove the IAC and clean it...small plunger inside that needs to move freely, and any built up carbon good ole WD40 works pretty well for that.
then clean the throttle body housing and back side of the throttle butterfly plate, carb cleaner can used here. IF the EGR ports are pretty well clogged up...then you turn your attention to the EGR itself & its plumbing
Fleet Owner
Joined: Aug 2010
Posts: 21,254
Likes: 1,656
From: Reynoldsburg, Ohio
Trending Topics
Fleet Mechanic
Joined: Aug 2008
Posts: 1,446
Likes: 9
From: NE Iowa JD Country
possibly...but would that explain the hissing The OP originally brought to light? ( Not trying to be smart A$$ here)
Non the less you make a good point JWA as to cleaning it (MAF sensor). Certainly could not hurt to clean it
Non the less you make a good point JWA as to cleaning it (MAF sensor). Certainly could not hurt to clean it
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
Fleet Owner
Joined: Aug 2010
Posts: 21,254
Likes: 1,656
From: Reynoldsburg, Ohio
No No No No--absolutely NOT being a smart azz----'tis all good!
Also odd is how those "lights" can sometimes make all us somewhat dim bulbs huh?
Fleet Mechanic
Joined: Aug 2008
Posts: 1,446
Likes: 9
From: NE Iowa JD Country
....thought I was missing something 
Thread
Thread Starter
Forum
Replies
Last Post
ritechous_26
1968-Present E-Series Van/Cutaway/Chassis
2
Mar 19, 2013 03:22 PM
coachtap76
1987 - 1996 F150 & Larger F-Series Trucks
8
Sep 27, 2004 08:40 PM