GRM Rocket Surgeons, speculate about my Ford

Subject is a 1993 Ford F-250, 2WD, 5.0, E4OD.

The original engine failed. I replaced it with another 5.0 out of a 2000 Explorer. In order to take advantage of the differences between the two motors, I retained the explorer's intake manifold. I also deleted the air pump, and EGR system. The original injectors were those old yellow bosch 19 lb things. I had some newer style ones out of my 2002 P71 that I installed as well. The only other change that I can think of is the addition of long-tube headers.

The symptoms; It starts easily and doesn't hesitate to drive even in 5 degree weather. As the engine begins to warm up, it will develop a tendency to stall at idle. When this happens, it is reluctant to restart unless I floor the accelerator. Once it's restarted it may very well stall again unless I keep it revv'd. When this is happening the exhaust is black.

On warmer days, like 30 degrees or better, none of this happens at all. I've been driving it since this summer and didn't have any trouble, or notice particularly poor fuel economy. So why now, when it's cold out, is it running so rich it can't idle?

Another symptom that could be unrelated, or the cause, or idk what... The temp gauge floats around between really cold and barely warm. It takes a long time for the engine to warm up, and there never really is good heat in the cab. Even when it does, it isn't uncommon for the needle to all of a sudden drop from the middle of the gauge down to cold side of normal. The thermostat was a new Stant, and then I swapped it out for a new motorcraft. No improvement. I even removed the radiator fan in an attempt to keep warm. Didn't change anything.

Lukewarm heat can be a symptom of a blown headgasket. I'd run a compression/leak down test just to rule that out.

You replaced the original injectors. Are they larger? If so, the combination of parts issomething like this: A 1993 ECU, which is about as smart as a brick when it comes to adapting fuel trims, a set of long tube headers that takes a long time to build enough heat to get the O2 sensor working, and bigger than stock injectors that will be running off a static fuel map intended for a smaller injector. I'd say you are running in open loop far too long when its cold. I'd put the original injectors back in.

In reply to Streetwiseguy:

This is what I was thinking, too.

One reason- you mention having to run wide open to start the engine after stalling- this is actual pedal to the floor- which turns the injectors off. Of course, if it starts, you had too much fuel there in the first place.

I'd put smaller injectors back into it. Unless you are maxing the smaller ones out, there's no real advantage to running the big injectors.

I would also check to see if you have an air bubble in the cooling system. Did you turn on teh heat when you burped teh system?

Could this the "rich when cold" situation also be from a bad thermo sensor?

Streetwiseguy wrote: You replaced the original injectors. Are they larger? If so, the combination of parts issomething like this: A 1993 ECU, which is about as smart as a brick when it comes to adapting fuel trims, a set of long tube headers that takes a long time to build enough heat to get the O2 sensor working, and bigger than stock injectors that will be running off a static fuel map intended for a smaller injector. I'd say you are running in open loop far too long when its cold. I'd put the original injectors back in.

The replacement injectors are the same size as the orginal ones, so the open-loop fuel map seems like it should be okay. I think. In my mind it should be lean, if anything, since this engine could be making as much as 20% more power than the original one. Plus it all worked okay when tempatures were above freezing. Wouldn't the rich condition be less of an issue when it's sooo cold out?

Streetwiseguy wrote: You replaced the original injectors. Are they larger? If so, the combination of parts issomething like this: A 1993 ECU, which is about as smart as a brick when it comes to adapting fuel trims, a set of long tube headers that takes a long time to build enough heat to get the O2 sensor working, and bigger than stock injectors that will be running off a static fuel map intended for a smaller injector. I'd say you are running in open loop far too long when its cold. I'd put the original injectors back in.

Everything he said, plus check the O2 sensor to make sure its actually working, and the engine coolant temp sensor. Also double check all sensor connectors, the cold could be leading to a bad connection due to things contracting.

double check the cold start. It might not be turning off and just dumping extra fuel into the engine

Are the new injectors the same Ohms as the old ones?

I agree with others sort out the sensors dealing with tempature. The gadge moving all over the place can be a HG but it would usually result in overheating. Sounds more like a air bubble in the system. Are there any differences in the gasket sets and / or the intake manifolds? What I am thinking is that there may be a difference between the two and one of passages in the intake for coolant or something is blocked. Did you use the gasket set for the truck or for the explorer and is there a difference?

All the answers have been hit on, open/closed loop & EEC problem with the injectors. The warm up cycle/temp gauge still screams bad t-stat/air bubble.

Differences in latency times between those injectors could result in a pretty huge proportional difference in fuel delivery at idle since the pulsewidths are so short there.

If you still have the original injectors, i would put them back in.

Vigo wrote: Differences in latency times between those injectors could result in a pretty huge proportional difference in fuel delivery at idle since the pulsewidths are so short there. If you still have the original injectors, i would put them back in.

Yeah, thats probably it. Can't this ecu be tuned the same way as the mustang ones? Would generate a nice power and fuel economy bump.

Will they go back into open-loop if the coolant temp drops too far? For some reason I thought once it went closed loop it would stay there, but I have nothing to base that on.

Depends on the logic in the ecu.

I want this truck.

Could be a failing coolant temp or intake air temp sensor.

fix the stuff you know is wrong, see what else happens.

I noticed the cooling lines were hooked up wrong to the heater core. It's supposed to come out of the intake manifold for one, and out of the water pump for the other. I can't even describe what was done instead, suffice to say, It was circumventing the thermostat, sort of. Now that it's all hooked up correctly the engine comes up to temp normally, and runs great.

I have to guess it was falling out of closed loop every time the temp would swing back cold.

...and you now get really warm air from the dash vents consistently?

warm~ish. but way more consistent.

Correct temp thermostat?

The Super Stant I tried at first was a 195. The Motorcraft one I bought at the dealer later on was not marked, but presumably.

MAP sensor is hooked up to vacuum and not leaking?