Cause for fuel cutout? Like speed limiter, but at low speeds.

[JoshT]

This about the 2000 Explorer 5.0L drivetrain swapped into my 99 Ranger. As we know, all systems compatable between the two, same fuel system, pats, etc.

What I am experiencing I can best describe as a fuel cutout. It literally feels like what it does when I hit the speed limiter, except I'm moving about 5 mph, not 105 mph.

Fire the truck up and it seems to idle fine, it free revs fine. Place into reverse and it starts off ok then quickly acts like fuel is cut out or a speed limiter has engaged. Sit still at an idle or into neutral it clears up and idles fine. Shift into drive is like reverse, but seems to happen quicker.

Did the initial swap last spring, new "performance" engine went in around September. It was driving fine until Thursday. So what changed Thursday you ask? Installed Ford Performance 24lb/hr injectors and a tune from a reputable tuner.

So far I've checked over everything I touched to make sure I didn't miss something obvious. I checked all of my wiring and plug wires, everything is correct. I checked fuel pressure and it's solid in thelow 60s, even when the cutout issue is happening. I've done a smoke check on both intake and exhaust side, no meaningful leaks. I swapped from the Screaming Demon coil packs I installed a few weeks ago, back to the old Motorcraft coil packs, it behaves exactly the same. I swapped the aftermarket IACV that was working fine on stock tune for a known working Motorcraft IACV, same behavior. I swapped from the 91 octane tune that the tuner provided to the 87 octane tune they provided, again no improvement.

Having a wideband hooked into the SCT tuner for datalogging, I can see that when it does this fuel cutout that the AFR is pegged lean. I just can't figure out if there is anything that I could have done when swapping in the injectors that could have caused this.

I sent a datalog of it doing this to the tuner to get their input, but don't expect to hear back before next week. Trying to identify other potential causes in the mean time.

 

[SenorNoob]

Can you tell what the AFR is at idle? I ask because I've seen small engine seem fine at idle but fall on their face with ANY load because they were lean.

 

[Uncle Gump]

Traction control?

Speed limiter going active?

 

[JoshT]

Can you tell what the AFR is at idle? I ask because I've seen small engine seem fine at idle but fall on their face with ANY load because they were lean.

14-14.5 according to the datalog of the installed wideband.

Traction control?

Speed limiter going active?

No traction control on a 1999 Ranger or 2000 Explorer, and I didn't mix in anything else. Not going to say it isn't possible, but if that's the case I'd like to know how.
Speed limiter getting triggered might be possible, but don't know how, why, or what could fix it.

 

[alwaysFlOoReD]

You installed the 24# injectors before or after the tuners did their work?

 

[JoshT]

With...

Stock injectors are 19lb. Would not be good to run the 24lb on the stock tune. Likewise not good to run the 19lb on the tune for the 24 lb.

Emailed remote tuning, once I had the tune in hand I swapped out the injectors and installed the tune.

 

[Uncle Gump]

I was just thinking out loud...

I would bet it has something to do with the new tune.

 

[JoshT]

That's great. Might stumble over something, or trigger other ideas.

After my last post, I think I'm going to put the stock tune back in and see if it behaves better. It's not good to drive with the injector to tune missmatch, but 19 to 24 is not a huge increase. As long as I'm not trying to go down the road and get a lot of speed, it should be ok. All I'll need to do it basically put into gear and let it get just above an idle to see if the problem persists.

With a huge injector jump there would be some concern about being pig rich and washing down the cylinders with fuel and thinning the oil. This is a small change and I was getting ready to do an oil change on it in the next week or so anyway.

 

[Uncle Gump]

That sounds wise...

Revert back to your last known tune that worked.

 

[JoshT]

Tune appears to be the problem. Reinstalled stock tune and it performs like it is supposed to. Something is set wrong in the received tunes and has them cutting fuel like crazy.

 

[JoshT]

Tune problem. They sent new ones today, loaded the 91 octane and it works like it should.

Now to figure out how I'm going to improve brakes. Brakes function like they are supposed to, and plenty of vacuum to operate them. Being an AWD, they just don't have enough holding power for launching. I think they'd do fine on a 2wd, but since the fronts are trying to turn and pull too...

Was already in the plans to swap knuckles and install the slightly larger 04+ brakes the next time that it needs them. The Explorer discs are on the to-do list too. I'll be investigating upgrades beyond those as well. Maybe just improved pad material will suffice.

Somewhere down the road I'm going to need to take a look at transmission improvements too. I think I'll be happy with the engine as-is, if I can just get better shifting. J-mod would probably do the trick, but it is already a high mileage transmission so a little leary of doing it. Maybe next year after other projects are to a stopping point and/or finished.