Hello all:

I am flummoxed. The Ranger is a 1986 2.9, and I've been chasing an idling problem. A few days back I pulled an 18 trouble code. Went off in search of an IDM resistor. Found one at a salvage yard and installed it. I had also reset the ECM memory by removing the negative battery cable. That 18 hasn't shown up. My idle isn't the best... seems different. As I went in search of a grounded spout wire, (the yellow wire going to #5 on the pin connecter), I was hoping that some of the foil shielding might be the culprit. I've dug into the loom all they way from the distributor to the alternator. In the past, I've seen some wire wrapped in this foil shielding, and thought that it was just part of the shielding. On doing some tests, I find that if I put my neg lead of the multimeter on that wire, and power the positive lead, I get batt voltage. So, is this a ground wire that's been ignored. Never saw a lead attached to this. Can't understand the reasoning behind a thick metal wire running along the insulated wires and the shielding.

Also, I test about 7 volts at the SPOUT connector when the engine is running. Is that normal? Isn't it supposed to be battery voltage?

thanks in advance.

tony

 

Yes, 7volts is what it should be engine running

Yes, there are a few shielded wires around an engine bay, they are grounded but ONLY at one end, but can be grounded at both ends, doesn't hurt or help
A shield is what it sounds like it shields the circuit FROM outside electrical interference AND it shields other circuits from the shielded circuit

So you are thinking the spark system is causing an idle issue, not the IAC Valve, which computer uses to control idle

When you start cold engine computer should set idle at 1,100rpms or so
Computer is also in Choke Mode because ECT(engine coolant temp) sensor is under 160degF
As coolant/ECT sensor warms up computer will start to lower idle(close IAC valve bit by bit) and Lean out the fuel mix, exit Choke Mode

Once engine is at operating temp, 185-195degF, idle should be 650rpms, for manual trans, 750 automatic

 

Thanks for that explanation, Ron. I couldn't understand why there was a bare metal wire running through that shielded section. No, I've never replaced the temp sensors. Maybe that's the next thing. The 7 volts number you gave me sounds like I'm target there. I couldn't find any grounded part of the #5 wire in that loop. So, maybe I should move on to the temp sensor? Never got a code for that... not sure if there is one????


tony

 

Oh, I forgot to ask if that sensor is the one closest to the front of the engine... right there on the top of the intake manifold?


thank you!


tony

 

ECT sensor will have 2 wires its close to thermostat housing

ECT sender, will have 1 wire, its for the dash temp gauge only

Sender runs on 12volts

Sensor uses 5volts from computer

So these are not interchangeable, different parts

Unless the ECT sensor fails completely or is unplugged there won't be a code, the computer has nothing to compare it with

 

Thanks for that, Ron. That's the next direction I'll go. It's the one sensor I haven't replaced. Thanks for the specifics.

tony

 

I've replaced an IAC that wasn't that old to begin with. I went on the dwell/timing journey because of the obd 18 code.

The engine at cold is at an idle (no tach meter here), and will eventually ramp down. It will hold a good idle UNTIL I manually move the throttle cable and then it will go to putz... very low... then die.

Thanks again, Ron. With your help, I'm getting there.

 

It reads like throttle plate or TPS may be sticking, if moving the cable caused it to close more, and maybe Computer can't open IAC valve fast enough to keep engine idling

warmed up engine, shut off
Remove TPS
start engine
See if its idling lower, move cable

There is an anti-diesel screw on the throttle linkage, it can be used to set minimum idle of 500-600rpms

After engine is warmed up unplug 2 wire connector on IAC Valve
RPMs should drop to 500-600rpms
If engine stalls turn screw in a bit and restart
This is NOT an idle screw, fuel injection can't work with an idle screw
But it can be used as anti-stall for warmed up engine

 

Ron, I'll follow that to a tee, because I know you are the Ranger expert. My one question is that when you say "remove TPS" are you just talking about taking off the connector, or removing the whole unit?

Tony

 

Remove the whole unit, 2 bolts
It may be sticking and holding throttle open a bit, when it "unsticks" idle stumbles

 

Thanks, Ron. First thing in the morning, I'll do that.

tony

 

Thanks Ron,

I've definitely got a better idle, but after a test drive, she still did the issue. Wouldn't start when I got her back home. In another thread I remember you stated that the ETC was like the automatic choke for these systems. As she was idling rather rich before I took her out, and she had a starting issue after she'd warmed up more, does it seem plausible that the ETC may be the final puzzle piece? The sensor and sender for the temps have never been replaced, and this girl has a lot of miles on that part.

thanks so much.

tony

 

ECT sensor is not an expensive part, and while it can be tested with ohm meter and boiling water on a stove top, just replacing it is probably best

If you want to test it heres the specs: https://www.freeautomechanic.com/images/ect3.gif

 

Thanks for that, Ron.

I took your suggestion and replaced the sensor yesterday. Well, dunno what's next... seems after I replaced the sensor that my idle was higher on the start side. Tried to drive it and it kicked down. I've tested good voltage at the spout. Taking off the IAC connector gets a reaction. Same for the TPS. Every damn sensor on this truck is new now. I've even swapped out computers. Now, back when I put the long block in and the issue turned out to be plugged up catalytic converters, they were also telling me that the muffler might be plugged. They replaced the cats, not the muffler. As I've noticed this issue has gotten progressively worse, I flashed back and thought, "hey, maybe it is a plugged up muffler." I've got a hole going in this one, gonna need to get it done and made an appointment. Told the shop guy over the phone about the issue and he says mufflers don't normally choke up. So, I dunno. I'm not pulling any more codes and I'm stuck. After this, I'm at the mercy of another shop. Damn it.

 

Is the Air Charge Temperature Sensor worth the time. There is some surging that MAY indicate that as the culprit?


Thank you, as always.

Tony