az00Convt

Let's start from the beginning. Every once in a while (I beleive three times in the past 6 months) when I start the car in the morning when I press the gas down the car would hesitate and have no power. Once I punch the gas, it will sort of sputter then get going. After this little routine everything would be fine.

A week or two ago I had the A/C on and was idling and I noticed that it was idling a little rough. Nothing horrible, but noticable. Turn the car off and come back later and it was idling fine.

Now I was driving home yesterday and when I was driving normally my car was fine. Now on the highway I was trying to do a moderate pass and the car would hesitate and start bucking. So I dropped it into 4th and hit the gas and no problem. So I was keeping it in fourth and no problem. So I put it back and 5th and let the RPM go to 1700 I think and give it gas and it would start doing the bucking thing. Once I got off the highway, anytime that the car was under a moderate load it would start bucking. WOT no problem, or pretty much if the RPMS were over 2300 it was fine.

So I parked the car and it was idling rough. Again nothing hugely bad but definately noticeable. I parked it and came back later and started it and everything was idling fine. I didn't get a chance to really drive it to see if it was still bucking under load.

So just a little backround. I replaced the spark plugs (platnium), and boots about 40,000 miles ago. I probably changed the fuel filter around the same time I think. Trying to get an idea of where to start.

devongarver

The first part could be from fuel pressure bleeding off over time, this is corrected once the pump is on long enough to catch up. It can be prevented by turning the ignition to ON and pausing for a second before starting it, giving the pump a chance to kick on.

The hesitation under load would normally be ignition and/or fuel related, however, the fact that you say it is at low rpm only has me thrown for a loop. For it to work fine at WOT, but not at low rpm would lead me to believe it isn't a fuel supply issue. I'm kinda stumped....Cliff? Help?

EDIT: what about the TPS??

smitty2919

Check your FPDM (Fuel Pump Driver Module). It's in your trunk on the driver side behind the wheel well cover. This tells the pump how much fuel to give the engine at any given RPM. Mine was getting wet from a hole in the wheel well when it would rain. Causing the random low rpm sputtering/bucking.

My thread when it was happening.
https://mustangforums.com/forum/4-6l...lp-needed.html

Edit: Here is a referance pic. There are 2 in this pic...you only have 1. It's the black/aluminum looking part with the connector.

cliffyk

MAF (dirty), PCV (sticking/stuck), EGR (sticking/stuck valve), and/or EVAP (sticking/stuck valve)

devongarver

cliff, is that a pee joke picture in your signature? If so I approve!!

cliffyk

Yup it's a urinal strainer, and fully represents what I would do in moment if given the opportunity...

devongarver

ya know cliff, if you didn't live 1500 miles away, I'd buy you a beer. You sir, are a stand up guy!

az00Convt

I live in AZ and it has not been wet out here, so that will be my last resort. If nothing else works.

Guess I'll have to break out the TB cleaner and go to town. I don't remember the EGR being plugged up when I changed out the TB but I guess 40,000 can do that.

az00Convt

I looked at the MAF and it didn't look dirty and the tube was clean so I think it is ok. But I don't have any cleaner so I can't clean it yet. Any tips on cleaning that anyway. Never had to do it before.

PCV - Looks like it was not seating correctly because there was a good amount of oil residue on it and around the PCV valve. So cleaned up around it, cleaned the pcv valve and seated correctly.

EGR - Didn't have time yet to take it off and check it. I did clean the TB and all the ports on the TB though.

EVAP - Not even sure where that is located.


So far still no change except it idles fine right now. If I accelerate it seems fine but I didn't get it up to highway speeds yet. Now if I am going 20 mph and I put it into third then give it a lot of gas it will speed up slowly and start bucking like it is missing a cyclinder for a brief moment. I'll know more when I go to work tonight and see what it does. At least I got the cleaning out of the way.

cliffyk

If the MAF looks OK don't clean it, it's somewhat delicate and one of those "if it ain't broke" things;

Make sure the valve rattles when you shake it--if it's one of the newer heated valves the heater may be bad, but that is not a common issue of which I am aware;[/quote]

Mine got sticky and caused a lot of misfiring at low revs and loads--I disabled it in the tune and the problem went away (no inspection here in FL)[/quote]

Most of it is on the passenger side fender--I don't have any good photos of the components, but here's the description of how it works from the '00 shop manual.