Engine Sputtering (Sometimes Dies) When Warm

This is kind of a long story, but I will try to condense it as best I can.

My 86 Ranger 2.9L had a hesitation upon accelerating that had bugged me since I bought the truck. So I asked my Ford ASSET instructor to come out and take a look at my truck, and we discovered that the vacuum line to the fuel pressure regulator had come unplugged. After plugging it back in and "giving the computer time to 're-learn' how to run right again" as my instructor put it, the skip didn't go away, so we brought it back in, and after checking for trouble codes, we found out that the Throttle Position Sensor and EGR Pressure Feedback Sensor were both faulty, so I replaced them both and also repaired another vacuum line that had snapped in two (one of those plastic ones, the green one to be specific).

Now, to back track a little bit, after I plugged the FPR's vacuum line back in to start with, my truck had a strange condition where once it got hot, after starting and stopping a few times (I.E. city driving) it would not accelerate, but instead it would sputter and backfire and then just die until the Lord felt sorry for me and allowed me to finally limp it back to the house. Fast forward to where I left off, and the problem has not gone away, so I replaced the two faulty sensors and limped the thing to school so we could run further tests on it. After getting the thing warm and hooking a fuel pressure gauge up to it, we determined that the in-line fuel pump was not putting out enough pressure when it got hot, but if you went underneath and tapped it a couple times, it would start working again for a few seconds, then just die off. So back to O'Reilly I went, and I dropped another fuel pump in it. After putting everything back the way it was and checking that the timing and idling were correct, everything was peaches and cream. For about a week....

Fast forward again to the way it sits today. When I start the truck up first thing in the morning, you can hear it sucking in air through the air filter quite loudly. I do have a high flow K&N air filter on the truck, but I'd never heard it doing this before until just recently. After letting the truck warm up a bit, when I go to take off the acceleration hesitation is back, and there is a slight skip for like the first half-second. It does this the first few times, then goes away mostly. After driving back to my hometown of Columbus to start back to work at the Ford dealership here from Birmingham (about a 3 hour drive), it's getting to where now when I drive into town or something, the sputtering/backfiring/dying has returned, and I have no idea what's causing it. This morning I went outside and pulled the following Key On Engine Running DTC's:

25 - Knock not sensed during Dynamic Response Test
33 - EGR Valve fault / Not closing properly
74 - Brake On/Off (BOO) Switch fault; not actuated
77 - Wide Open Throttle not sensed / Operator error

I'm guessing my EGR valve is gone or going? I'm just starting out with actually doing this for a living, so I'm not really an expert with this sort of thing (hence why I'm going to school for it, Lol). If anyone can help me out, I would greatly appreciate it. Rusty (my truck) is my daily driver and the only vehicle I own, and besides which, that truck is my baby and I can't stand to see it running the way it does (literally; it kinda pisses me off). So again, to recap everything:

-Brand new Throttle Position Sensor, EGR Pressure Feedback sensor, In-Line Fuel Pump

-SEVERAL vacuum lines repaired

-Engine sputters/loses power/backfires/dies when hot and driving in city conditions (of course, I haven't really tried to take it on the highway while it's screwing up).

-DTC's 25, 33, 74, 77 pulled with scan tool (as listed above)

-Only transportation

ANY and ALL suggestions are GREATLY appreciated, because as the old saying goes, your guess is as good as mine (probably better than mine at this point).

DTCs 74 and 77 are tests you need to take part in so ignore those.

The symptoms and then the DTC 33 would point to the EGR valve acting as a vacuum leak and sucking in exhaust not air.
EGR valve needs to be closed at idle, it should only open when engine vacuum is lower(higher RPMs) and engine is under load
You may be able to remove it and clean it, but removing it would be the first step.
You could put a "gasket/block" between EGR valve and intake to get you running again, thin pieces of metal, like two layers from pop cans cut to fit, until new EGR valve can be installed.

RonD said:

DTCs 74 and 77 are tests you need to take part in so ignore those.

The symptoms and then the DTC 33 would point to the EGR valve acting as a vacuum leak and sucking in exhaust not air.
EGR valve needs to be closed at idle, it should only open when engine vacuum is lower(higher RPMs) and engine is under load
You may be able to remove it and clean it, but removing it would be the first step.
You could put a "gasket/block" between EGR valve and intake to get you running again, thin pieces of metal, like two layers from pop cans cut to fit.

Click to expand...

Code 74 isn't a concern right now, my BRAKE light stays on all the time, so it didn't surprise me. When the engine starts dying off, the sucking air/exhaust gets very loud and it sounds like it's coming from the throttle body, not the EGR valve. I'm going to hook a Mity-Vac up to it later and see what I get; I found the test procedure in my Haynes manual. As far as cleaning the EGR valve is concerned, would Carburetor Cleaner do the trick?

Yes, small screw driver and carb cleaner will work, make sure to rinse off the carb cleaner from diaphragm.
Then put a vacuum line on it and suck valve open and closed a few times to make sure it isn't sticking.
Also before removal, start engine and test EGRs vacuum line for 0 pressure, there should be no vacuum on that line at idle, if there is then the EGR control valve is the issue.

I often remove/loosen the water pump belt, so fan isn't spinning, and remove the air tube(plenum) from the intake manifold.
Then start engine, cold engine can run for a few minutes without water pump(or alternator).
I put my hand over intake to restrict air flow, and at that time you can often hear a vacuum leak, then spray some carb cleaner at that location to narrow it down.

Some EGR valves are open on the bottom.
This allows you to (cold) press the diaghram up/down to exercise its actuation/travel. Spray the carb cleaner on the shaft and exercise it a few strokes (use the Mitivac if it's not open on the bottom). That might clear out the carbon blocking it from fully closing.


I didn't see any fuel pressure testing, particularly testing the function of the Fuel Pressure Regulator. It might be bad, failed at high pressure. IIRC, test fuel pressure with engine running. Then disconnect the FPR vacuum line, pressure should change significantly (Don't recall if it goes up or down).


http://oldfuelinjection.com/?p=35 EGR test

http://oldfuelinjection.com/?p=41 Fuel Pressure test does not include changing the vacuum input to the FPR though.

http://www.autozone.com/autozone/repairinfo/common/repairInfoMain.jsp?targetPage=productsHowToInspect&leftNavPage=productsHowTo&pageId= 0996b43f80a01350&subtitle=test
"Test 2

High pressure is usually caused by a bad pressure regulator or when a pressure return line to the fuel tank is kinked.
When there is a vacuum line to the pressure regulator, part of the procedure is to pull the vacuum hose off while the engine idles.
The pressure should rise about 10 psi in most systems when the hose is pulled.
If a pressure regulator requires adjustment, something else might be wrong with the system. On non-adjustable systems, the regulator must be replaced if the pressure is not correct.
Repeat the test by pressurizing the system and then pinching off the fuel line from the pump. If the pressure remains steady, the check valve is leaking.
To test to see if pressure is leaking through the pressure regulator, plug the fuel return line and repeat the test. If the pressure remains constant, the pressure regulator is leaking. "

As far as fuel pressure is concerned, I'm now kicking myself in the butt because I didn't replace the fuel filter when I replaced the pump, which I should have done. I'm going to replace it today as soon as I get up to the store to buy it.