I recently began to have a very bad hesitation in my 4.6 Expy. After it warms up when I come to a stop and get back on the gas it hesitates for about 1 sec. Its like there is no fuel for a moment then all is fine. Its not all the time but usually happens 2 to 3 times a day. I have cleaned the TB, new air filter, pcv, fuel filter, had tranny serviced, and run 2 bottles of FI cleaner thru it. I suspect it might be the TPS or fuel pressure regulator but would hate to spend money on these parts if they're not needed. I just reset the computer and its still there. The only mod is I cut off the end of the air filter box. Please help!

Luke

 

did you check for cracks in the intake manifold?

Some 4.6L V6's (I can't recall which years) had problems with it.

 

I had some hesitation problems in my 97 4.6. I did a few of the tricks you thought of FI cleaner, etc. The check engine light finally came on and I went straight to the dealer. The fix they gave me was a new plug and wire on the #2 cylinder, and cleaned all the injectors. I haven't had a problem since. Just a thought.

 

Sorry, I forgot to mention that I changed all the plugs. It really doesn't feel like a misfire but more like lack of fuel. I guess it could be electrical. I don't want to visit the dealer unless I have to since I'm out of warranty. Thanks for the replies.

Luke

 

Do you know what is used for timing advance???? I might be completely off the mark, but years ago I had an older jeep that would do the exact same thing on acceleration. It turned out to be a semi-clogged vacuumn hose that wasn't allowing proper advance to the distributor, thus when you first accelerated, it mimicked a loss of fuel for just a second or two.......Don't know if this may help or not

 

The timing issue:
Timing is set at a base time of 10* BTdC and is non-adjustable. The PCM controls all timing curves to meet the A/F ratio and load present on the vehicle. However there is one trick to adjust/check timing and that is the shortning bar. It is just a small 1inchX1inch cube that is plugged into a harness (spout connector). Mine (97 4.6) is located behind the battery near the firwall. If you pull this it will retard the timing 2-3*. Basically removal of this shortning bar justs takes the PCM out of the timing control loop. From there you can check base timing with a inductive timing light.

If timing is incorrect you will have to see a dealer, from there I don't know if they can adjust timing or if it means the PCM is bad.

I personally have what some might call a hesitation ( i call it a surge or jerk) at around 1100-1500 RPM, when crusing at 40mph with light acceleration and in OD. I have also felt this ( not as much) at around 70mph and 1900rpm. Another note to this is I have a vibration so this may be more tranny/rear axle related more than engine.

 

I have found that just about all surgeing is due to the EGR valve. Disconnect it and plug the line and take it for a drive and see what I mean. You can install a new valve but it will probably not help. All EGR valves suffer from this problem no matter what make or model it is installed on. The nature of the beast but some are worse than others. It is your call if you want to leave it disconnected ....it will make more smog but again you decide....but try it just to confirm it is the cause....

 

if you don't allow EGR into the engine, your exhaust temps will go up which can cause problems.

 

Sorry, it ran fine at one time with the EGR on it, it whould run that way again. I would think unhooking the EGR would cause more problems than it solves. Like the the temp. issue, constant check engine light, and poor performance. I could unhook it and try it. I might also take it off and clean it. Can you get a EGR gasket at a parts store or does only Ford have it?

 

Exhaust temp would be higher, but the real concern would be higher combustion chamber temps. That is exactly what EGR is supposed to do, keep combustion chamber temps down to reduce NOx emissions. Now it does use up a bit of that precious combustion chamber volume with useless inert gas. But that is nothing compared to the spark and fuel delivery "tweaks" the computer will do if it senses knock with the knock sensor. And that will happen if the combustion chanber (that was built to support EGR) gets to hot from no EGR.

So unilke the junk of the 1970's, you cannot pull the EGR off an engine (or disable it) and expect any performance gains unless you have an engine management system and combustion chamber designed to support it.

Also the EGR valve is a part that rarely fails. It gets blamed on all kinds of stuff, but is almost never the real cause of the trouble. I workd as a mechanic for almost 8 years. Of the 10,000 or more junk piles I worked on (independent shops) I only encountered real EGR problems on less than 10 occasions as long as you don't count Fords EVP sensors. Even in those (EVP) cases the EGR system worked fine, just the feedback to the computer was defunct. Amazingly the most common failure is a leak of exhaust when the valve is closed (carbon in valve seat). If you unplug the vacuum to the valve it will still leak exhaust, so it doesn't help a thing (unless you goal is pre-ignition).

I'm so glad that you can't rip off plies of emissions devices from cars any more. For the 1% it helped (racers and cars with serious engine mods), it screwed up 99% of the cars that got "the treatment". The manufactures made their own mess here with the "bolt on" emissions components of the 70's and earily 80's.

The "EGR" effect can be achived my intensional ineffective exhaust scavanging of the cyclinder (valve timing). Many manufactures have done this. The problem is you are stuck with this ineffective exhaust scavanging all of the time. If you use an EGR valve you can turn it off (the EG flow) when you don't need it. Typically the EGR is off at idle and WOT. At idle there isn't enough heat to cause NOx and at WOT you want maximum performance.

Anybody ever had a chance to ride in a F150 with the Rotunda computer on data stream? I'm betting at WOT EGR is near 0%. On most engine management systems its rich enough to keep the temps down.

So why would you unplug it again?

Anyway I better get off this soapbox now. I hope you figure out your problems with your truck. Its very likely not an EGR problem, so I'm really not helping anyway.

 

if the exhaust temp is higher, that means the combustion chamber temp is higher.

heehe
toe-may-toe, tuh-mah-toe.

 

Plug wires?

I've diagnosed myself to death on my truck twice now. Both times eventually giving in and deciding that it was plug wires. In both cases it fixed the problem, they seem to last almost exactly 30,000 in my truck.

 

I don't recomend removing or plugging off the EGR permanently at all, just a way to confirm or illiminate that as a posible cause.