2003 Ranger, 2.3L DOCH ~235K

Goal - diagnose Code 171

Rig is new to me. I have already resolved many codes with new IM, VC, and miscellaneous gaskets, new PVC valve and hose, fixing vac leaks and operation of the IMRC/swirl control system. Sea foamed (intake manifold throttle body and MAP) Cleaned MAF (with MAF cleaner). New plugs and wires.

At that point the only remaining code was 171 and it came on every test drive. The rig was idling rough and having major hesitation problems when accelerating especially in lower gears.

Yesterday I replaced upstream O2 sensor. (Just on principle, no fancy scan software involved).

There was HUGE improvement in drivability. Almost smooth idle and only a little hesitation. The weird thing is Code 171 is certain to come on, but only on every other trip. For example.....

A. Drive until warm then turn off engine

B. Clear all codes

C. Test drive 5-20 minutes more (fast/slow; high/Low RPM; drive 20 minutes, variable conditions, down shifting freeway everything.)

D. Turn engine off 2 minutes

E. Start driving again, and Code 171 comes back within a minute or two. It never comes on during the first drive after clearing codes, but is sure to show up on the second.

Weird, huh?

Ideas?

 

To be honest, to track that one down I think you are going to need some scanning software like Torque Pro on an Android tablet/phone or forscan on a laptop/phone.

Do you know how much vacuum you've got? That P0171 could still be a vacuum leak somewhere albeit a small one. Could also be a flaky injector or EGR problem or faulty coil (although if it were the coil I suspect it would be misfiring or bucking).

How about fuel pressure? Have you tested for that yet? System should run around 55 psi - 65 psi. Mine holds pretty steady at 62 psi when accelerating.

Have you looked at your short term and long term fuel trims yet?

 

Thanks for the input Soledad. Today I made a smoker (cut down soup can holding cone incense, scrap wood handle, inside cardboard coffee can, with couple extra air compressor fittings for air in/out).

Voila! I found a leak. Earlier I had replaced the two hoses on the IMRC system (from IM to solenoid, and from solenoid to actuator) and thought I was good to go. Uh-huh! I have a huge leak out the body of the solenoid itself. Beats me why the code seems to come/go every other trip. I'll replace that part and report again... stay tuned.

 

Nice find! Yeah, keep us updated.

 

Dope!

Vac line attachments for IMRC solenoid is NOT bidirectional! When I cut new hoses to size I was installing them reversed. (For anyone arriving here who does not already know, the nipple that points to the ground runs to the swirl control valve, and the one that points towards the grill runs to the IM.) Correcting that error cleared up the last bit of hesitation while accelerating, but code 171 still returns every otger trip.

I'll get back to looking for vac leaks, but it will be several days. The little time I get to work on her will go after the leaking rear main seal, and other stuff on back of engine while I have the tranny out, like EGR and coolant hose. When I know more about this I'll followup.