Hello Ford Fans,

I'm trying to help my nephew with his 97 Explorer, 4.0 SOHC, Auto, 4X4. Truck runs fine cold. The following problem occurs after warm-up.

The truck starts and idles fine in Park or Neutral. As soon as you put it Reverse or Drive, it stalls. But sometimes, it will run in 1st. This first occurred about one month ago. We limped it up to Autozone. They pulled the codes. Crank Shaft Position sensor and Mass Air Flow sensor. We replaced both of those and it ran well for 3-4 weeks.

Now we're having the same problem. Check engine light back on. Codes 171 & 174. Lean on banks one and two. Carried it up to Pep Boys. They can't locate the problem, but suspect the Torque Converter.

I've been researching the forum, and found several posts about the IAC, so we definitely need to check that. Is it possibly the torque converter? That doesn't make sense to me.

Thanks

 

The codes you have are indicative of an air leak (vacuum) between the MAF and the intake valves.

The truck will never run correctly until you locate and fix the leak, look for chaffed disconnected tubing, intake manifold, PCV.

The parts you replaced probably were not at fault, just a symptom (did you test them??)

 

Got to spend a little time on the truck tonight. Too dark to look for vacuum leaks, but did get to test the IAC valve.

The harness going to the IAC checked out at 12 volts.

The two pins on the IAC valve measured approx 10 ohms. Supposed to be between 6 and 13 ohms.

The third check was for an internal short to IAC case. One probe on the IAC case, the other probe on one of the connector pins. Supposed to be 10,000 ohms. I couldn't get any reading.

So I'm still suspect of the IAC valve, but need to look for vacuum leaks.

Any other ideas?

 

The reading of "OL" on your meter when checking for an internal short to IAC case is not suggesting a problem. The spec is a minimum resistance. Your meter is suggesting you have an open circuit which is a good thing. One quick test for the IAC would be to start the truck and with it idling, unplug the IAC. The engine will probably stall, but at a minimum the idle will drop. If so, the IAC is working.

As Aquanaut mentioned, the codes are not for a torque converter but rather suggest a vacuum leak. There are several common sources for vacuum leaks on the V6 Explorer. Certainly fix the vacuum leak before doing anything with the torque converter. Since you have codes for both banks you're probably looking for something that is common to both banks such as the EGR system, intake manifold gasket, PCV, or intake air tubing.

-Rod

 

Thanks Rod.

The guys at Pep Boys said that the truck also had an intake vacuum leak, but they didn't think that was the cause for the stalling.

Could this vacuum leak be the cause? I don't understand why the truck idles fine until you put it in gear. The vacuum leak would be occuring all the time. What's the difference?

 

I'd certainly start with fixing the vacuum leak before pursuing anything else, especially since the leak is bad enough that the PCM is picking up on it. At idle there is essentially no load on the engine. As soon as you shift in to Drive or Reverse the load increases on the engine. Since we're not able to hear how the engine is idling it's tough to draw a conclusion on if it is actually idling fine or not. With a working IAC the PCM can attempt to compensate for some amount of vacuum leak.

If you find a large parking lot with no cars around you could try "power braking" the engine - hold one foot firmly on the brake pedal, then give the engine some throttle with your other foot, maybe to 1000 rpms, then shift to drive. If you are able to keep the engine running doing this, the problem is not the torque converter. But don't do this for long otherwise you will have transmission problems. You might find that the engine runs quite rough when in gear this way too, further suggesting a vacuum leak.

-Rod

 

I actually tried the power braking yesterday. (In a safe place of course) The truck would still stall. I tried shifting at RPMs up to 1500 and it would stall every time I put it into gear.

Does this suggest torque converter?

 

You could always have a guy from a reputable tranny shop connect a scan tool to it and check the transmission for diagnostic codes. The standard scan tools like what's found at most parts stores will not access the transmission-specific codes.

It depends a bit on the way in which it stalled, if it was like it was choked out or if it was like a switch was thrown. Without witnessing the way the engine idles and runs in park versus the way it stalls it would be very difficult to point you in the right direction. If you want to condemn the transmission and have it pulled that's up to you, but, once again, I would start by fixing the source of the lean codes.

-Rod

 

Thanks again Rod,

Now that we've ruled out the IAC valve, I agree with you. The intake leak needs to be addressed whether the tranny is good or bad.