Car throttle body closing at WOT and backfire
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Joined: Mar 2023
Posts: 8
Car throttle body closing at WOT and backfire
After a strenuous and lengthy diagnostic with my 05' Ford Focus, I'm left stumped.
Originally, my car has been bogging whenever I tried accelerating. I brought my car to my local mechanic and a Ford service shop and they both came back with the same response, the fuel pump needed to replace.
After getting it replaced, the car has been running much better but the same issue of my car bogging keeps happening. The problem now only happens when I'm at WOT or heavy on the throttle. Whenever my car bogs, I hear a weird air suction sound from the engine bay. At first I thought it was just my CAI, but after taking it off one night, the sound is apparently coming from my throttle body as if it's closing on itself. The problem eventually fixes itself when I ease off the throttle or turn off the car. I haven't gotten a SINGLE code or a CEL...
I have already replaced the MAF, checked the MAF harness, tested my engine pressure (150 PSI each), did a intake vaccum test (which came back with possibly a clogged converter), changed my air filter, and checked for vaccum leaks. I'm gonna check the TPS and throttle body when I get back.
Upon testing, I also found out my car has a quiet backfire as I hear a puff from the throttle plate and out the exhaust.
Anyone have any clue or insight on what may be going on? Should my throttle body be doing that?
I have a video of the problem happening here
https://youtube.com/shorts/DSqnyCOTDFc?feature=share
Originally, my car has been bogging whenever I tried accelerating. I brought my car to my local mechanic and a Ford service shop and they both came back with the same response, the fuel pump needed to replace.
After getting it replaced, the car has been running much better but the same issue of my car bogging keeps happening. The problem now only happens when I'm at WOT or heavy on the throttle. Whenever my car bogs, I hear a weird air suction sound from the engine bay. At first I thought it was just my CAI, but after taking it off one night, the sound is apparently coming from my throttle body as if it's closing on itself. The problem eventually fixes itself when I ease off the throttle or turn off the car. I haven't gotten a SINGLE code or a CEL...
I have already replaced the MAF, checked the MAF harness, tested my engine pressure (150 PSI each), did a intake vaccum test (which came back with possibly a clogged converter), changed my air filter, and checked for vaccum leaks. I'm gonna check the TPS and throttle body when I get back.
Upon testing, I also found out my car has a quiet backfire as I hear a puff from the throttle plate and out the exhaust.
Anyone have any clue or insight on what may be going on? Should my throttle body be doing that?
I have a video of the problem happening here
https://youtube.com/shorts/DSqnyCOTDFc?feature=share
Last edited by sarxworks; Mar 8, 2023 at 06:31 PM.
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Joined: Apr 2019
Posts: 1,236
Does sound like a converter issue to me. Confirm it with a vacuum gauge to monitor the manifold vacuum. You should have a steady 18-22 inches of vacuum at idle. As you increase the engine speed, the vacuum may quickly drop and quickly bounce back up. If it drops and doesn't bounce back up, an exhaust restriction is a good possibility.
Thread Starter
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Junior Member
Joined: Mar 2023
Posts: 8
Does sound like a converter issue to me. Confirm it with a vacuum gauge to monitor the manifold vacuum. You should have a steady 18-22 inches of vacuum at idle. As you increase the engine speed, the vacuum may quickly drop and quickly bounce back up. If it drops and doesn't bounce back up, an exhaust restriction is a good possibility.
I thought the vaccum dropping off as I accelerated signified a clogged converter (a problem but now I realize that doesn't make sense as the vaccum should be falling off as the speed increases) . So my test came back normal then.
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Joined: Jun 2010
Posts: 16,662
Do you think you could do the test over again with the vacuum gauge connected to intake manifold vacuum ?
The results you posted seem a little incomplete.
With the gauge connected, engine running, raise the RPM to around 2500 and watch the gauge.
Hold the RPM there and the gauge will continue to go down because the engine is having difficulty breathing ,IF,,, there is any restriction in the exhaust.
What result did you get?
How did you know the puff was coming back thru the throttle body if you were driving the vehicle?
There are some addl questions that come up and let's take them one at a time,OK ?
The results you posted seem a little incomplete.
With the gauge connected, engine running, raise the RPM to around 2500 and watch the gauge.
Hold the RPM there and the gauge will continue to go down because the engine is having difficulty breathing ,IF,,, there is any restriction in the exhaust.
What result did you get?
How did you know the puff was coming back thru the throttle body if you were driving the vehicle?
There are some addl questions that come up and let's take them one at a time,OK ?
Thread Starter
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Junior Member
Joined: Mar 2023
Posts: 8
Do you think you could do the test over again with the vacuum gauge connected to intake manifold vacuum ?
The results you posted seem a little incomplete.
With the gauge connected, engine running, raise the RPM to around 2500 and watch the gauge.
Hold the RPM there and the gauge will continue to go down because the engine is having difficulty breathing ,IF,,, there is any restriction in the exhaust.
What result did you get?
How did you know the puff was coming back thru the throttle body if you were driving the vehicle?
There are some addl questions that come up and let's take them one at a time,OK ?
The results you posted seem a little incomplete.
With the gauge connected, engine running, raise the RPM to around 2500 and watch the gauge.
Hold the RPM there and the gauge will continue to go down because the engine is having difficulty breathing ,IF,,, there is any restriction in the exhaust.
What result did you get?
How did you know the puff was coming back thru the throttle body if you were driving the vehicle?
There are some addl questions that come up and let's take them one at a time,OK ?
For now I can answer you question.
"How did you know the puff was coming back thru the throttle body if you were driving the vehicle?"
I heard the puff(s) after getting back from driving the car. After parking, I decided to look under the hood to listen for any vaccum leaks and heard the puffs from the air filter. I decided then to take it off because I was curious if it was the filter and after doing so, I still heard the popping. The sound is similar to water boiling in a covered pot with the throttle plate acting as the cover. I also heard the puff in the exhaust and felt the air pop whenever I heard the noise. I will definitely record it when I test for the vaccum.
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Joined: Jun 2010
Posts: 16,662
Maybe being a little premature, but it sounds like a misfire.
That could be caused by spark getting to the wrong cyl at the wrong time or maybe a possible valve system problem,
Do you know how it was determined to be a fuel supply problem?
Was the vehicle checked for any codes present or history ?
How many miles on vehicle and last time plugs were replaced? This does not necessarily mean a spark plug problem , but could be related to that system when it MIGHT have been done.
What engine is in the vehicle?
That could be caused by spark getting to the wrong cyl at the wrong time or maybe a possible valve system problem,
Do you know how it was determined to be a fuel supply problem?
Was the vehicle checked for any codes present or history ?
How many miles on vehicle and last time plugs were replaced? This does not necessarily mean a spark plug problem , but could be related to that system when it MIGHT have been done.
What engine is in the vehicle?
Thread Starter
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Junior Member
Joined: Mar 2023
Posts: 8
Maybe being a little premature, but it sounds like a misfire.
That could be caused by spark getting to the wrong cyl at the wrong time or maybe a possible valve system problem,
Do you know how it was determined to be a fuel supply problem?
Was the vehicle checked for any codes present or history ?
How many miles on vehicle and last time plugs were replaced? This does not necessarily mean a spark plug problem , but could be related to that system when it MIGHT have been done.
What engine is in the vehicle?
That could be caused by spark getting to the wrong cyl at the wrong time or maybe a possible valve system problem,
Do you know how it was determined to be a fuel supply problem?
Was the vehicle checked for any codes present or history ?
How many miles on vehicle and last time plugs were replaced? This does not necessarily mean a spark plug problem , but could be related to that system when it MIGHT have been done.
What engine is in the vehicle?
The problem was first determined to be a fuel problem after Ford and my local mechanic did a fuel pressure test and they both told me that with key in, ignition off I had 0 PSI. This was further supported as my pump was making a terrible squealing at start up and the car wouldn't even start sometimes.
The car has been checked for codes/past codes by me, my local mechanic, a transmission specialist, Ford, and a exhaust mechanic who also test drove the car.
The car is going on 79k miles now. I have personally pulled and charged the spark plugs at about 65k after I did a valve cover change. Since then the car was running fine until now.
The engine is a 2.0L Duratec with California Emissions.
Thread Starter
|
Junior Member
Joined: Mar 2023
Posts: 8
Maybe being a little premature, but it sounds like a misfire.
That could be caused by spark getting to the wrong cyl at the wrong time or maybe a possible valve system problem,
Do you know how it was determined to be a fuel supply problem?
Was the vehicle checked for any codes present or history ?
How many miles on vehicle and last time plugs were replaced? This does not necessarily mean a spark plug problem , but could be related to that system when it MIGHT have been done.
What engine is in the vehicle?
That could be caused by spark getting to the wrong cyl at the wrong time or maybe a possible valve system problem,
Do you know how it was determined to be a fuel supply problem?
Was the vehicle checked for any codes present or history ?
How many miles on vehicle and last time plugs were replaced? This does not necessarily mean a spark plug problem , but could be related to that system when it MIGHT have been done.
What engine is in the vehicle?
I thought it could have been the same thing as I heard the exact same sound when I didn't tighten one of my plugs when changing them. Except, unlike that time, I got a code.
The problem was determined to be a fuel problem after my local mechanic and Ford did a fuel pressure test on my car. They stated I had 0 PSI at key in, ignition on. This is further supported as my pump made a terrible squealing noise at startup and the car wouldn't start sometimes.
The car has been checked for present/past codes by me, my local mechanic, Ford, a transmission mechanic, a exhaust mechanic, and a friend mechanic so I can say there are definitely no odd codes stored lol.
I should also stated the exhaust mechanic ran a few tests and stated my cat is fine but I'm a bit skeptical as he didn't do a intake vaccum test or even touched or looked at the cat, only going based off his scan tool
The car is packing about 79k miles and the spark plugs have been changed at about 65k with the valve cover, the valve cover gasket, and coils also being changed. I've been getting no problems after that until now.
The engine is a 2.0L Duratec with California Emissions
Last edited by sarxworks; Mar 9, 2023 at 11:51 AM.
Senior Member
Joined: Apr 2019
Posts: 1,236
I start with a steady 22 inches. The vaccum drops and snaps back quickly.
I thought the vaccum dropping off as I accelerated signified a clogged converter (a problem but now I realize that doesn't make sense as the vaccum should be falling off as the speed increases) . So my test came back normal then.
I thought the vaccum dropping off as I accelerated signified a clogged converter (a problem but now I realize that doesn't make sense as the vaccum should be falling off as the speed increases) . So my test came back normal then.
I do not think you have a misfire. If that happened long enough, a code would be set . A misfire on a four banger would result in a very rough, shuddering engine.
I would be curious as to what your fuel trims are at to actually see how the engine is performing.
Also you might want to test your air pump's check valve. They can cause a backfire when you back off the throttle.
https://www.rockauto.com/en/moreinfo...vmMfS8ANlMpp8g
Last edited by raski; Mar 9, 2023 at 03:09 PM.
Senior Member
Joined: Jun 2010
Posts: 16,662
When you changed the spark plugs did you do one at a time or all at once?
Air coming from the AIR pump usually goes to the exhaust manifold only or is diverted out of the system. Should not be noticed or felt at the intake or throttle body, but anything is possible until we determine why you are feeling puffs at the throttle body AND the exhaust. This engine does have a dual overhead cam system with a timing chain.
Variable valve timing could be involved here too. 76,000 mi is not a lot of miles, unless regular oil changes were not done to which the VVT system becomes susceptible to excessive wear and clogging problems.which may or may not throw any codes.
Air coming from the AIR pump usually goes to the exhaust manifold only or is diverted out of the system. Should not be noticed or felt at the intake or throttle body, but anything is possible until we determine why you are feeling puffs at the throttle body AND the exhaust. This engine does have a dual overhead cam system with a timing chain.
Variable valve timing could be involved here too. 76,000 mi is not a lot of miles, unless regular oil changes were not done to which the VVT system becomes susceptible to excessive wear and clogging problems.which may or may not throw any codes.
