1999 F250 SD CC 2WD shortbed 100,000 miles
5.4 Triton
"L" factory designation

I've been fighting this for some time now and am beyond frustrated. I can't reproduce the problem on every drive, but when it does occur, I can reproduce it for the entire drive (sometimes the entire day). Of course, it won't happen when I've got it at the shop.

Symptom:
Under light/slow acceleration, and right at 1450-1500 there's a significant stumble. It will stumble bad enough to stall about 1 out of 10 times. Symptom is worse when pulling - which is when we are slowly accelerating more often (horse trailer). Also, on the occasions where this stumble does occur, the transmission shifts very hard up and down.
When not pulling, simply accelerating just a little faster (leaving a stop at 1700+ RPM) there's no stumble and it runs like a sewing machine.
I absolutely *cannot* get any CEL codes, even "predictive" codes (per my mechanic).


Repairs (so far):
New:
Plugs, COPs, Fuel pump, fuel filter, Idle Air Control Valve, Throttle Position Sensor, Vehicle Speed Sensor

Repaired:
Vacuum leak at PCV to intake 90 degree boot
Vacuum leak at one injector (there is one injector different from the rest, and apparently whoever replaced it did not get it inserted straight, and it cut the bottom o-ring)

Any, any, any advice is MOST appreciated at this point!

 

Saw a post over on F150online that referenced possible EGR and/or DPFE problems, I can troubleshoot with these steps, does that make sense?

http://easyautodiagnostics.com/ford/...e-egr-system-1

 

Are you measuring fuel pressure at idle and WOT? Was the fuel pressure regulator changed along with the pump?

Can you run a fuel pressure gauge or your OBD0II scanner to get real time readings while driving?

 

I don't have a fuel pressure gauge, I'll try and see if I can get that checked at the shop. I did follow all the testing steps in the link referenced earlier, and during this test I found that there was no vacuum on the EGR valve. The article is implying that the EGR Solenoid is bad, so I was going to replace that next. All the other tests from that site came out perfect, EGR, DPFE, voltages, etc.

Here is the test procedure:

The third part of testing the EGR Vacuum Regulator Solenoid is done while road testing your Ford (or Lincoln, or Mercury) car or truck. This test will let you know beyond a shadow of a doubt if the EGR Vacuum Regulator Solenoid is BAD or not.
The engine in your Ford (or Lincoln, or Mercury) car or truck has to be at operating temperature before you start your road-test. This is important, since with a cold engine, the PCM will not activate the EGR valve system.
Disconnect the vacuum line or hose that is connected to the EGR valve (see photo 2 and 3 in the image viewer).
Connect a piece of vacuum hose (that should be about 2 feet in length) to the vacuum line or hose you just disconnected as shown in photo 3.
Snake the vacuum hose under the Hood and secure it under the wiper arm.
Connect a vacuum gauge to the end of the vacuum hose that's under the wiper arm.
The vacuum gauge must be in such a position that you can easily read the Gauge's needle as you're driving down the road.
OK, your mission is to verify that the vacuum gauge's needle moves up to 5 in.Hg only when you start to accelerate the car or truck (whether it's from a stand-still or you're already cruising). After the needle moves up to 5 in.HG, the vacuum gauge's needle should always drop down (immediately) to 0 (zero) in.HG when you let go off the Accelerator Pedal.
CASE 1: If the vacuum gauge's needle moved up to 5 in.HG when you accelerated the vehicle and then dropped to 0 in.HG when you released the accelerator pedal... this indicates beyond a shadow of doubt that the EGR Vacuum Regulator Solenoid is working correctly.
CASE 2: If the vacuum gauge's needle DID NOT move up to 5 in.HG when you accelerated the vehicle and then dropped to 0 in.HG when you released the accelerator pedal... this indicates that the EGR Vacuum Regulator Solenoid is BAD, replace it.

 

From what little I know of the EGR's proper operation that pass/fail test seems very spot on.

Won't hurt to measure the fuel pressure if you're able.

 

Appreciate it. I should be able to pick up the EGR solenoid tomorrow and get it swapped this weekend. Passenger side fuel rail has a schrader valve, going to have a pressure gauge put on it this afternoon.

What about exhaust restrictions, what's the best way to check for clogged a catalytic converter?

 

Was able to get by a friends shop where he hooked up a full laptop to the truck and put up a monitor that was watching the COPs firing live - of course, that's when the truck decided to run like a top! Hopefully it will act up again on the way home today, I can stop by again.

On that note - is it feasible to assume that it's somehow electrical related? If it was truly mechanical in nature, shouldn't the issue be present all the time? Because it happens randomly makes me think that there may be some type of electrical/connection/control issue.

 

I'd agree this issue could be and probably is related to an electrical glitch of some kind. First thought was the PCM itself (or its connector to the chassis wiring harness) is faulty.

If time permits inspect that connector along with the one on top of the engine feeding the COP's---if there's one for the injectors also check it. Unfortunately if there is a connector terminal fault or a wire or wires along the harness length it might be difficult and time-consuming to find what's causing this.

Could your catalytic converter's be clogged?

Could this be related to valve timing?

Can you view or retrieve live data while driving during these stumbles?

Its odd there are not DTC's thrown, even pending ones in memory.

 

Did you ever figure out your issue, I had a similar issue it turned out to be a weak spring inside the egr valve causing it to open too much during pcm command for testing and normal calling for, causing a stumble, I went around the entire motor to find this as the aftermarket egr was weak too, replaced it with oem and it fixed the issue

 

kbsupercrew - what kind of problems were you having?

 

I had a stumble between 1200 and 1500 rpm, went thru everything and found by unplugging the green line from egr and plugging it the stumble when away, then after much reseach found that the aftermarket egr and evr from autozone werent up to factory spec. replaced them with oem and it solved my issue, i started a thread about it years ago.