I have a 4.6L that runs great when cold. After warming up you gradually feel hesitation when accelerating. Continue to drive and the problem gets worse, especially on inclines when the engine comes under load. Bad fuel is ruled out as this has been going on for months. Engine Service Light has not come back on since I change all EGR components. I would think it is an injector issue or a COP, but why does the ruff running only occur after the engine gets hot?

 

BAd plugs will do this they will lite off a rich mixture ie when an engine is cold and are more likely to miss under load.

 

Can you be more specific about the EGR problems you had and what you did?

 

The Truck had been running bad for sometime. Eventually the Service Engine Light came on. I went to the Auto Zone free diagnostic and it showed an EGR issues. I replaced the EGR Valve and it did not fix the problem. Light was reset and came back on as problem continued. I cleaned the old valve and tube (not dirty at all) reinstalled and returned the new valve. I purchased and installed an EGR regulator. Seemed to fix the problem. Had the Engine Service Light reset (and it has not come back on to date). Truck ran good for about 100 miles. Then the problem resurfaced. The parts store allowed me to replace the new EGR Regulator - still had problem. Replaced the DPEE - still had problem. I have not check current going to these components yet. No apparent vacuum leaks….

 

It could be something as simple as your battery terminals. Before you change plugs or something else check out your battery terminals, a loose or corroded connection will cause hesitation, loss of power travelling up inclines. This happened to me this spring on my 97 5.4 expy, no engine light came on either.

 

Did you every pull the throttlebody elbow off and clean the two egr holes out?

 

torkum

I assume the throttlebody elbow is what the EGR Valve is attached to. If this is the case, then no, I did not inspect/clean those ports. I will do that this evening....Thanks...

 

waboose:

I did not even suspect a bad battery connection as a culprit. I did coincidentally clean the terminals and connectors a few weeks ago just because I was working under the hood – no change in poor performance.

I have a twenty mile drive to work, mostly interstate / highway with one large bridge. The vehicle hesitates a little on the way to work going over the bridge and has extreme hesitation on the bridge heading home. The weather here today 100% humidity/rain and the hesitation is barely noticeable. It almost seems like the problem is worse on hot/dry days. Sounds crazy but it’s the truth …

 

Try cleaning the MAF with CRC brand MAF cleaner. Read the instructions before starting.

 

Did you find the problem yet? If cleaning out the EGR ports did not work and you double checked your EGR components you changed. It could also be the fuel filter, pcv valve or a loose spark plug boot. Hope this helps.

 

Waboose

Last night I removed the EGR and most compents around the throttle body and cleaned (not dirty at all). That did not fix problem. I will check the PCV valve. Fuel filter was changed recently and I verified it still had good flow last week.

 

MAF dirty?

 

Exactly...

 

Torkum

Removed the MAF and it looked brand new. Cleaned it anyway with the CRC. Also verfied the PCV was operating properly. Vehicle runs great when cold - still sluggish after warming up (takes about 15 miles of highway driving before it starts cutting out)....

 

If someone else didn't already mention, check the fuel pressure, both with the engine running and with the engine off/key on.

With the engine running, you should see 28-30psi, and with the engine NOT running, it should be about 40.

Also, if possible, try to check the pressure when the engine is under load and "cutting out"...

Did you ever change the fuel filter?