I have an '86 4x4 Ranger w/2.9L V6.
When I stop at red lights, (sometimes) the engine idles down and wants to stall out. Usually, I just punch the gas pedal and it gets okay. Most all the time it runs fine, I have noticed a slight lack of power on the highway when punching it to pass or something, but the idle problem when I stop is puzzling me. Also, on a cold morning, you can crank it, and it runs at high idle like it should, for about two minutes, then the RPM's drop, and it acts like it wants to stall. If it were not fuel injected, I would look to the electronic choke, or carb problems. Does anyone have a suggestion? I'm guessing it's possibly a bad O2 sensor.

 

I would check your fuel pressure, I beleive it should be around 30psi.

The FPR is on the drivers side on the fuel rail.


,86 2.9L Flowmaster 40 series, MSD 6A, Free floating Rockers, Intake spacers, K&N Filter.

 

You can also check your base idle speed, this is controled by the IAC. The IAC is the canister looking thing on the passengers side of the uper intake manifold. Disconnect it and check the speed, around 800 auto, a little higher for manual. You can adjust the idle speed using the screw under the black cover on the throttle body. If this doesn't fix it the IAC might be dirty or you may need to pull the codes. FYI fuel pressure is 30-40 psi.

 

Made a mistake, the base idle is NOT controled by the IAC, my bad.

 

Clean the mass air flow sensor, dirty ones will cause all kinds of idle problems.

 

>Clean the mass air flow sensor, dirty ones will cause all
>kinds of idle problems.

Just a FYI a 86 2.9 doesn't have a MAF.

 

Okay, after further diagnosis his weekend, I have ruled out fuel pressure and idle sttings, they appear normal. The phenomenon has gotten rather predictable, it always happens just after cranking, and following a period of stable idle. As I said, it is similar to an electronic choke letting off. There is also a strong raw fuel smell when it happens. It seems as if something is not cutting the fuel when it should. I'm not familiar enough with vacuum problems, a friend suggested it may be vacuum related, also suggested it could be an igniion problem, if the spark plugs don't fire, or stop firing, it would cause unignited fuel to be dispersed. Anybody have any ideas of what to check next?

 

I would see if there are any codes. Wouldn't hurt to make sure the FPR isn't leaking fuel.

 

No fuel leaks at the FPR. I have a dumb question; how do you check the codes? I'm not familiar with the Ranger, this is my first one, and I've only had it a few weeks. My Toyota Supra has a diagnostics block where you connect a lead between two terminals to get the codes, I suspect the Ranger would have something similar, but I'm lost. HELP! Thanks Ken, you've been wonderful!

 

The codes are easy check, it can be done with a scanner, which is about $30 at the parts store, or an analog meter, I don't think an 86 can be done with the CEL. Do you have a meter? A few more things that I missed, cleaning the IAC, take it apart and clean the valve not the solenoid. Disconnect the battery for 15 minutes to reset the computer after this or any other sensor repair/replacement, it may run a little funny after resetting while it relearns things. Do you have any vacuum leaks or exhaust leaks? When you say it's rich, is this black smoke, or...? I'll keep thinking in case I missed something else to check.

 

 

14 Feb
I have had an intermittant problem similar to yours. The water temperature sensor (there are two - the other sends a signal to the gauge on the dash) was not sending the right info. This sensor is underneath the intake hose at the front of the engine. It turned out to be a dirty contact only. I was able to clear the problem up by simply spraying penetrating oil on the sensor. I spray from both sides although the intake is directly overhead. It is easiest to spray from the right side.
My symptoms were this: engine would start fine and run smoothly sometimes. A few minutes later, it would stumble while waiting at a stoplight - the symptoms were just like water in the gas. Other times it would suddenly start acting up after being driven a short distance, stopped, and then re-started. Since it was still cold out, I would just shoot the WD-40 on the sensor and restart the truck. The stumble would disappear immediately, even though just a minute before it acted like I was running it on 99 per cent water. I had tried fuel line antifreeze and gasoline water removing products because the symptoms were like a bad tank of gas. I had replaced the O2 sensor,wires, plugs, cap, and had new fuel injectors installed prior to a recent emissions test (btw, passed with flying colours at 318,000 kms).
Now that the weather is warming up, I'm going to take the sensor off and give it a closer inspection - possibly replace it if necessary. If you haven't solved your problem, you might try this. Obviously, don't spray the oil over everything, but try to confine it to the sensor.
I take no credit for the tip - I read about the sensor elsewhere on this site and was pleasantly surprised to find it worked.

 

There is only one temperature sensor and it's where you said but the other unit is called the temerature sender for the dash guage. The "only" reason I know this is that I was just looking at the 1997 Electrical TroubleShooting manual for the first time since I bought it back then! Although I was looking at the layout for the 4.0L, the 2.9L should be the same. This manual shows the location of all the sensors which is very helpful.

 

Just an FYI, there are two sensors, one for the gauge and another for the computer. The gauge sensor has one wire and the computer one as two wires.

 

[updated:LAST EDITED ON 16-Feb-02 AT 00:08 AM (EST)]Ken:

The electrical print for a 4.0L shows the location of both but they call the one for the guage, a sender. They always called them sending units for temp, oil pressure, etc.

There is one strange thing! The electrical print shows both ECT and IAT as having two wires. I was looking where the ECT might be seen a unit with what appeared to be one wire near the thermostat housing with another on the other side with two wires or more. This manual shows the ECT to be at the location of the single wire unit and the other unit to be the IAC, if these arrows/lines are accurate!

The temperature sending unit is shown to be between injector #1 and injector #4. I'd have to compare this pictorial to the real thing!!

I just got that electrical manual out again. The second wire shown on the IAT, ECT, OSS, ODS and the third wire on the DPFE and TP all are GRY/R circuit 359, pin 91 PCM, signal return to the PCM. Since all tie into that circuit, it's just ground anyway but I guess they just want to eliminate any chance of losing a ground connection. It doesn't show any sensors with just a single wire but I swear that I seen two, the ECT and IAT. If it wasn't so late, I'd go out there and pop the hood!!