Hello and thanks in advance.

In my continuing journey, I'm on the trail of solving what MAY be the crux of my warm idle issue. It seems there is a resistor on the lead to the negative side of the coil that is "supposed" to be the main culprit of the 18 trouble code. I haven't dug into this yet as tonight's project is replacing an exhaust manifold gasket, but I've got to make a plan as the salvage yards seem to be short of potential Rangers for a replacement. Does anyone of you have experience with this issue? I've replaced a ton of sensors and other stuff and this is the latest bridge to cross.

thanks so much

tony

 

What year and what engine?


On the TFI system there was a 22k ohm resistor on a spliced wire from TFI to coil "-", it was for RPM to computer and if its failed it could set that code, shouldn't cause running issue unless it was grounding out

Its seen here: https://cdn.shopify.com/s/files/1/02...ngIGN.gif?1317
Bottom center

It was a part that was not sold separately, basically people got replacements at wrecking yards
Ford used same resistor on all TFI systems up to 1993 on some cars and trucks, not a Ranger thing


Picture of one here, with damaged wire: https://www.therangerstation.com/for...607174&slide=1

 

Thanks, Ron. 1986 and 2.9. I appreciate that very much. If you have anything to add on what might cause the 18 code, please let me know. I'm not so electrical, trying to get up to speed.


Tony

 

Code 18 means computer thinks there is a problem with spark timing
Computer has two sources for spark/distributor timing, the actual signal from the sensor inside the distributor, and the "fire" signal, Coil "-", from the wire with resistor

Code 18 means they are not "matched" to the computers timing "suggestions" to TFI module


To run well a gasoline engine needs "vacuum advance" spark timing or it will hesitate when accelerating
A distributor has weights and springs inside for RPM advance, i.e. the faster the distributor spins the more advanced the spark timing gets to keep up with piston speed

In the old days there was a vacuum advance on the distributor hooked up to intake manifold vacuum, when you opened the throttle vacuum in intake drops and spark timing was changed for the Richer fuel mix, with out that engine would stumble a bit and hesitate

Computer uses the throttle position sensor(TPS) and the MAP sensor, instead of a distributor vacuum advance, to change spark timing by "telling" TFI module to advance or retard timing

It compares what it "tells" TFI do, to what TFI does via the feedback from RPM info via that resistor

The SPOUT connector and wire is how the computer "tells" the TFI module how to adjust the timing, which is why you need to disconnect SPOUT to set base spark timing

 

 

Great

Yes, all the "new stuff" on engines today just replaces the "old stuff" but is more reliable than the old stuff, and like you say it is just a newer skill-set to understand how it works to accomplish the same thing the old stuff did
Anyone who had to change points and adjust dwell will agree the new stuff is better in that respect, lol

Fuel injection does what a carb did but does it better because it can adjust air/fuel mix "on the fly", in the "old days" we had to adjust the carb and choke for different times of year(summer/winter) and driving conditions, like higher attitude/elevation

Many say the older stuff was easier to work on, but I think that comes from having to work on it all the time, so you learned it by shear repetition, lol
Newer systems just don't need that constant attention so we forget some of the stuff we learn because we just don't have to repeat it all the time

 

Well said, Ron, and good to hear! I'll report back in a day or two how this went.

Thanks again for your guidance.


tony

 

I found two resistors on different 5-150s at the salvage yard yesterday. It sure helped to know that they weren't unique to Rangers. Did a test today... truck did a high idle for about three minutes that was solid. Kicked down the idle, then a minute later, it died. So, no, the resistor was not the problem.

Seems the other half of the code 18 might be a grounded SPOUT circuit. I'll dig into this, but not super good with searching out voltage drops or tearing into wiring. Ready to learn. If I can get some direction, that'd be much appreciated. I know this can be fixed; I just have to find the culprit. Thanks again. Oh, once again: 1986 2.9. Ignition module is a few weeks old. Distributor. cap and rotor and wires... all new or replaced recently.

Thanks so much.

tony

 

I've replaced the resistor, and I still have an issue. Today's action is that I've tested the voltage on the SPOUT connector while the engine is running. Doesn't equal battery voltage, reads 7 volts or below (I've tested it a couple of times. I guess the next thing is to get into the wiring harness and follow the yellow wire down to the ECM and see if it is grounding somewhere? ? ?


tony