Hi folks. I posted this problem I'm having on the Ranger subdirectory but didnt get too many responses.
Was hoping maybe it might get more exposure here.

My 1994 Ranger has the 4.0 v6. After it warms up, the engine sputters, loses power, and the check engine light goes on and off sporadically. When I floor the accelerator, things improve, but it is back to the same old once I ease up on it. At idle, the motor interestingly runs fine, barely hinting of what is to come when things come up to cruising speed. If I didnt know better from the way it's been acting, I would think there is water trapped in the distributor. As far as I can tell though, it's a ditributorless ignition.

Any ideas as to what is causing this problem?> FYI, I already did the usual tune up stuff including changed wires/ plugs, gas-air filter. I also wiggled, unplugged and re-plugged in all sensor connections I could find under the hood in case there was a loose connection there.

Any thoughts would be greatly appreciated.

 

How many miles?? Have you had the scanner
hooked up?? Could be a number of things, need
more data...

 

The presence of the CEL suggests there might be trouble codes to be had from the computer. If you don't have a scanner, you can pull trouble codes with a jumper wire.

 

Sorry, not much more data to give you. I dont have a scanner to read the codes. I tried pulling codes via jumper wire, but couldnt make heads or tails of most of the engine light output. I've pulled codes on other vehicles just fine but this one was erratic.

I checked vacuum lines for any leaks, but didnt find any. I thought the characteristic of running rough while warm and during cruising speeds only might pinpoint the problem to something specific, so that's why I posted.

Guess it's off to the mechanic.

 

Whoa, hold there before charging off to the mechanic. Do a couple of simple things first.

Threre are generally three components that commonly cause your symptoms. Dirty mass air flow sensor(MAF), dirty/worn throttle position sensor (TPS) or the idle air control valve (IAC). The MAF is most suspect based on your symptoms. This is found right after the air cleaner box just before the start of the long air tunnel. There is a two wire connector leading to it and it is held in place with two Torex screws. (They may be the security type with a center pin on your year). Remove the connector and retaining screws and CAREFULLY lift the MAF out. There are several very fine wires on the sensor. Spray these several times with an aerosol electronics cleaner. If there is any dust/dirt/debris in the aluminum housing remove this and check your air cleaner element for tears and the air box to ensure it is sealing properly. Dirty MAF sensors cause all sorts of driveablility problems - but are easily remedied.

The TPS is on the throttle body, a black looking affair, again with a wire connector, usually on the left side of throttle body when facing the engine. Unscrew this and clean with the electronic cleaner and replace.

The IAC valve sometimes causes driveablity problems but usually there are idle problems as well. Since your engines idles fine, this is likely not the problem. There are many postings about the IAC if you need additonal information.

Try cleaning these two items and see what happens.

Good luck!

 

Thanks for the thoughts, aerocolorado. You are correct concerning the center pin TORX security screws on the MAF. Fortunately I have the tool that can take them out. I also have handy some electronics cleaner so I should be able to try all your suggestions in a little bit and get back to you on it.

If anyone else has hunches as to what's going on with my truck, please feel free to jot them down.

 

Well, I pried open all the sensors I could visibly find under the hood (including MAF and TPS) and sprayed them with the 'lectric cleaner. Unfortunately the problem still exists. I havent as of yet (in a sense) pressure tested the air intake tube (post MAF to throttle intake) to see if there are any leaks there. I have a hunch though that a leaky duct would cause engine performance problems at ALL times, not just while warmed up, as in my case.

Since my problem exihbits itself only after the engine warms, I was wondering if perhaps the Engine Coolant Temperature (ECT) sensor might be to blame. It's the only sensor I can think of that has a direct bearing on engine heat.

What do you all think? Have you ever heard of a bad ECT causing running problems? Also, does anyone know if the ECT provides info for the temperature guage, or does that guage use its own seperate varistor? If the ECT is used by the temp guage, I might conclude that that is NOT my problem since my temperature appears to be working normally.

After I check the duct, I'll use my Haynes to check the ECT. If that checks out I'll move on to the MAF & others. Haynes seems to give very good details on how to check these sensors.

Thank you all.

 

Well, ohm readings (cold and hot) and Vref on the ECT checked out.

As I thought for a bit, I recalled one more sensor that is affected by the warming of an engine and that was the oxygen sensor. Since Haynes was vague about checking voltages that emanate from this sensor when operating temp is reached (which I imagine was intentional since amplitudes vary depending on many running conditions), I simply pulled the plug on it to see what happened.

Well, surprise surprise,,,,, 95% of the sputter problem went away. After reading Haynes it started to become clear to me why this may have happened. Simplified for brevity, when cold, the engine runs in closed loop mode which virtually ignores any output from the oxygen sensor. At this time the engine runs based on programmed variables to set fuel/ air mixture. Once things heat up, open loop kicks in and real world variables via the oxy sensor are used and mixture is set by this.

Potentially in my case, a defective sensor may have been giving corrupted info which in turn upset the mixture. By unplugging the sensor, I estimate, the system was locked in a closed loop setting. No voltage was received from the sensor so things were still running on the closed setting's.

Since things arent exactly 100% solved and I am concerned about loss of fuel economy/ pollution issues, I'm going to remove the oxy sensor and take a look at it. Does anyone know if
these things can be cleaned at all? Haynes says not to use solevants to clean them and I imagine a harsh wire brush might remove crictical platnium/ ceramic coatings. I would think gasoline itself could be used to clean it since the sensor invariably comes in contact with it in the exhaust. Maybe this coupled with a nylon brush might bring some life back into it. Any thoughts??

 

I had the same problem on my explorer, 4.0 SOHC. I cleaned and replaced IAC, Cleaned MAF. But today I replaced the DPFE sensor and got great results so far.

 

Well, I found out there were actually 2 oxy sensors in my truck. One in the left header and one in the right. I replaced both of them and I no longer have the problem. For some reason though, the engine light still comes on after everything warms up.

It seems that these sensors need to be replaced all at once. When I 1st only replaced the right side, the truck actually ran worse previously.

Thanks for all the posts.

 

Engine light was on because I didnt plug one of the oxy sensors in all the way. Light stays off now. Nice feeling, since I was dreading seeing it come on previously.