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Bob
Bob, Ford Technician
Category: Ford
Satisfied Customers: 205
Experience:  23 years @ Ford, 1997 Ford Master Technician Specializing in Engine,Transmission & Electrical Repair
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1994 Ford Ranger: 4.0L..running rough..(seems to be rich)..pinpoint

Customer Question

<p>I have a 1994 Ford Ranger, 4.0L that is running rough (seems to be rich) and I'm trying to pinpoint the problem. I have tried hooking up the OTC4000E, but I can not get any data from the computer. The 4000 IS registering the Key off / on status and it is registering when the vehicle is started, but the 2:00 minute counter counts down to zero and shows "NO DATA". Any ideas as to what the problem is or a next step?</p><p> Additional info.  This morning (after the truck sat unused all night) I hooked up the scanner again.  Did the KO/EO test, showed code 111, no faults.  Did the KO/ER test. Ran at 2k rpm for 3 minutes.  Went through pressing brake, turning wheel, goose throttle, complete test.  No faults found.</p><p>Drove the vehicle a short time and the "check eng" light comes on.  Hooked the unit back up and started KO/ER test sequence again.  Currently the "Check Eng" light is not on.  While running the eng at 2k rpm, after about two minutes, the "Check Eng" light comes on adn stays on, and the truck begins idling rough, smells like it is running rich.  The tester, after answering it the vehicle has been running for 3 minutes, advises to start the vehicle.  The tester then shows "the codes are " and the two minutes count down to zero, and no data.  It seems that the computer is now not communication with the tester.  No instructions to press the brake, turn the wheel, etc.  What could the problem be.</p>
Submitted: 3 years ago.
Category: Ford
Expert:  Bob replied 3 years ago.

Bob :

Hello, this is Bob. I will do my best to assist you.

Bob :

If it is running rich have you checked the fuel pressure? If the pressure is too high it will run rich. Did you check the fuel pressure regulator to see if fuel is present at the vacuum port? You should NOT have fuel at the vacuum port.

Customer:

Don't have a fuel pressure gage avail right now. There is good fuel pressure at the schrader valve on the fuel rail (checked by depressing valve with nail) but i don't know if it is excessively high. The truck ran fine first thing this morning, didn't seem to be rich. It started during the 3 minute fast idle prior to the attempted KO/ER test. I don't believe the fuel press reg or fuel pump or system is the problem.

Bob :

Did you pull the vacuum line off of the regulator while the engine was running? There should not be any fuel at the vacuum port.

Bob :

Also if the regulator sticks the fuel pressure will be very high and cause it to run rich. I want to cover the easy and common failures first.

Customer:

Haven't tried that yet. Is the vacume line teh stainless braided line on top.

Customer:

My SVO mustang had a rubber line on top. But I don't see anything like that on this truck.

Bob :

No, it is a red plastic 1/8" vacuum line with a 90 degree rubber end that attaches to the vacuum port on the regulator.

Bob :

It may be hard to see because it is on the passenger side of the regulator if I remember right.

Customer:

Is the reg on the front pass side on the top of the engine, kinda tucked up under the intake at the throttle body?

Bob :

Yes, in that area. It is attached to the fuel rail. Here is an image of the fuel rail.

Full Size Image

Bob :

The regulator is hard to see in this image but it is right below the schrader valve where you check for fuel pressure.

Customer:

Found it. I think the stainless line is from the fuel pump. There is a vacuum line that runs out the rear side. pulled it off, there is NO fuel there.

Bob :

Do you have a Mass Air flow sensor on this 4.0L?

Bob :

It looks like the one in the photo but your should be bolted to you air filter box.

Bob :

As far as having no data from the PCM, it could be that your vehicle PCM does not have that capability.

Customer:

Same sensor, but with the factory style air filter box. It seems like the computer is locking up for some reason. This morning after the truck say unused all night, the reader worked. I went through the quick tests and hooked up to the dcl test also where I could see all the voltage levels etc. But after the short drive to set a trouble code, now it seems that the codes can't be read.

Customer:

Vehicle is idling right now, about 750 to 800, and very rough. I can rev the engine to 3 to 4 thousand and it runs very smooth. Take foot off accel, it returns to idle and is still rough.

Bob :

It could be a connection problem. Is the self test connector terminals clean?

Bob :

One other common problem with the 4.0L was the fuel rail gasket would fail. Do you have a can of carb cleaner?

Customer:

Yes. I sprayed a little cleaner on them yesterday. I also had full connectivity this morning. The code reader is also detecting the key on off status, and engine running status, but I'm getting no code info from the computer.

Customer:

Yes, I have some carb cleaner.

Bob :

What did you spray the cleaner on?

Customer:

I used some Contact Cleaner to clean the EEC and STI connectors. Haven't used the carb cleaner yet.

Bob :

Try this with the carb cleaner. With the engine running and the air intake in place, spray the cleaner along the fuel rail on both sides and see if the engine picks up speed and runs better when you are spraying. You are checking for vacuum leaks so if the cleaner is sucked into the engine it will change speed. The cleaner need to be flamable.

Customer:

Ok. I aslo talked to another friend who works for Chrysler. He told me he thought the Ford and Mazda's made in the 90's were sometimes extremely difficult to retreive the codes from. Do you know if there is any truth to that or have you had similar experiences or information?

Bob :

If the check engine light comes on there will be a code set. Never had any trouble retreiving the code if the light came on. Have had the wiring or the self test connection cause problems but it was rare.

Bob :

One more thing that you should do is clean the MAF Sensor. Here is a link for instructions: http://www.fordf150.net/howto/clean-maf-mass-airflow-sensor.php This may prevent other problems.

Bob :

Let mr know what your results are with the vacuum leak check.

Customer:

Vacuum check did not seem to change anything. I will clean the MAF sensor. Is there any way to test the unit with a DMM to see if it is bad?

Bob :

If it fails you will get a code, if it is dirty it will not correctly calculate air flow.


TESTING MAF



  1. With the engine running at idle, use a DVOM to verify there is at least 10.5 volts between terminals A and B of the MAF sensor connector. This indicates the power input to the sensor is correct. Then, measure the voltage between MAF sensor connector terminals C and D. If the reading is approximately 0.34–1.96 volts, the sensor is functioning properly.
    Full Size Image

Bob :

Did you check the PCV valve to make sure it is good?

Customer:

Ok. Where is the PCV on this vehicle?

Bob :

Drivers side valve cover towards firewall.

Customer:

Checked it. Its not clogged.

Bob :

If it is running rough at idle then how does it run when you drive it, does it miss?

Bob :

You said the check engine light would come on after driving it. What code is set?

Customer:

When I drive it, it seems to run fine, accel is good, and no misses. I don't know what code s being set. I can't pull the codes up. That's why I initially came online. I have cleaned the MAF sensor. i'll let you know what happens next. I was also able to hook up some jumpers up to the sensor so I could watch the voltages from a DMM thats inside the cab as I drive. The check engine will come on during nornal cruising or light decell. Doesn't come on under hard accell or WOT conditions. What do high voltage readings, then low voltage readings from the MAF indicate. Would that cause a rich or lean condition, then vice versa?

Bob :

If it runs rough at idle it problably is not a sensor problem. The EGR valve could be stuck open or you have a vacuum leak.

Bob :

If a vacuum cap is missing or a vacuum hose came off or has a hole in it it will run rough at idle. Do the spark plugs look white, black or have a brown build up on them?

Customer:

Updated info. I finally got the code reader to work. Still not sure why it wouldn't earlier. The codes I got are 172, 173, 176, 177. These are for a rich condition on bank 1, bank 2, and lean condition on bank 1, bank 2 (maybe not in that order, but that is the info.

Bob :

Does you scanner read the sensor data?

Bob :

Like the values for the engine coolant temp and Air temp?

Customer:

The KOER did not indicate any codes. I have also looked at the data stream. The voltages and operation of the following components look normal and within spec - TPS, MAF, ECT, IAT, and the IAC varies from about 45 to 60 %. The problem seems to be with the O2 sensor. When the vehicle is running, the voltage will either stay at or near .01 v (lean) or at .89 to .9 v (rich). There does not seem to be any middle range and when the truck is idling, the Rich/Lean indicator is not alternating between the two showing the computer is trying to keep the proper 14.7 to 1 ratio. When driving, if the O2 sensor voltage is around .89 volts, suddenly opening the throttle does not cause the voltage to drop, as I believe it should. Also, if the sensor at around .01 volts, closing the throttle and going to idle does not cause it to go to a high reading, which again I believe it should. There does not seem to be any middle range for the O2 sensor. I have seen a few values of .68, .4, and .7 and similar, but most of the time it is either .01 or .9 v.The truck runs good and pulls hard under WOT, and I can see on the monitor that the engine is in Open loop operation. I have changed both O2 sensors, and the problem is still there. I have done a quick underhood check for vacuum leaks and have not seen any yet, but I have not done a full deep inspection, nor have I ehecked the EGR valve yet.

Customer:

Also once again yesterday, the truck (after driving approx 45 minutes) began running very rough, almost to the point of stalling. The check engine light was on (and stayed on). I could not get any connectivity with the code reader to look at the codes or the data stream. The vehicle would accelerate at all, and the endine would rev up at all. It almost seemed like a clogged muffler or cat situation. I parked the truck for three hours. I went back and started the truck. It idled fine, connected the reader, read the test (showed no codes) adn looked at the data stream. This was before I changed the O2 sensors. But after changing the sensors, last night I got the same codes (172, 173, 176, 177), with the check enginr light coming on and going out several times as I drove the vehicle home. The O2 voltages were again changing between .01 an .9 v, as I was driving. It wasn't a rapid change either, it would stay at one or the other for 4 or 5 minutes or longer, and then change. I also observed the SFTRIM values at about 43% and -23%. I believe the values should generally only be + or - 5% range. Any ideas as to what is going on or why the code reader will no connect sometimes?

Bob :

Seem like you may have a bad connection or loose ground in the electrical system. The O2 sensors should switch from a low voltage .01v (lean) to a high voltage .9v (rich) . They should switch high to low ever few seconds.

Bob :

Have you tested the fuel pressure? You want to make sure it is not too high or that it holds pressure.

Customer:

Checked the fuel pressure yesterday. it was right at 30 PSI. I also cleaned the injectors with a can of OTC Injector Kleen that you use with the pressurized can that is hooked up to the schrader valve, with the fuel pump disabled. I didn't leave it on there long enough to test for any leakdown.

Bob :

I would put the fuel gauge back on and turn the key on. The pressure should go up to 30 to 40 psi and then watch it to make sure it holds pressure at about 30 psi. If it is bleeding down to zero you could have an injector that is leaking or the fuel pressure regulator leaks. If the pressure is good and holds then you eliminate that as a problem.

Bob :

You may want to drive it with the gauge hooked up because I have seen the fuel pressure regulators stick intermittently and the fuel pressure will spike to 100 psi then it will run rich.

Bob :

If the fuel pressure is good then we need to look at other sensor output to determine if sensors are functioning properly.

Customer:

I can check that later on today. But would a leaking injector or sticking reg cause the stuck O2 readings? I indicated earlier the the O2 sensor does not change at all with quick changes to the throttle.

Customer:

all the other sensors look to be ok. MAF varies from .8 at idle to 2.5 v at 2500 to 3000 rpm. IAT is at about 90 degrees. TPS shows correct C/T, P/T, and WOT with varing voltages that look to be correct. ECT is at 190 to 200 degrees. Most everything else seems to be correct.

Bob :

The O2 sensors read the oxygen content in the exhaust so if the exhaust is rich the O2 will stay high and low if lean.

Bob :

The O2 sensor can also switch slowly if the get fouled with fuel.

Bob :

A bad ground to the O2 sensor will also cause incorrect O2 readings.

Bob :

Have you looked at the spark plugs?

Customer:

I have found a connector that is unplugged. It is a round connector that is about the diameter of a tube of chapstick. It is located between the intake manifold and the firewall, just under the hood. It has two wires only. I cannot find a matching connector for it. Any idea as to what the connector is for?

Customer:

I changed the spark plugs out a few weeks ago. The ones that came out appeared to be normal. No heavy fouling or buildup, and none were white or glazed.

Bob :

No brownish build up on spark plugs?

Customer:

If the O2 sensors were getting fouled with fuel, the new ones would have had to get fouled immediately, as the slow readings persisted after the sensor change.

Bob :

If it is running rich they should have been black.

Customer:

No brown buildup. Looked like nornal, worn plugs.

Bob :

Do you have a way to take a photo of the connector? You can send photos to me by clicking on the tree icon in the chat tool bar.

Customer:

I can get it to you later. Don't have access to the vehicle now.

Customer:

How would the O2 sensors be grounded

Customer:

I suspect the loose conection theory is most likely cause. Or could the computer be going bad?

Bob :

Do you have a wiring diagram of the sensors? It will show the grounds for the O2 and PCM.

Customer:

Mechanically speaking, I thing the engine is fine. Evew with a small vacuum leak or a leaking injector, etc., it would not be enough to cause the extreme voltage readings from the O2 sensors, with no middle range.

Customer:

Is the ground on the sensor side of the connector, or will it be on the wiring harness side?

Customer:

I have the Haynes manual for the vehicle, which I believe has the diagrams, but I do not have access to it right now.

Bob :

My experience with the computer is they don't fail very often. The O2 normal operation is to continually switch from .1v to .9v.

Customer:

Fyi - the O2 sensors that came out did not appear to be oily or have buildup or fouling. Kinda had that brownish spark plug look, and the outside appeared to be free from any other contaminants.

Bob :

Check out this site for O2 sensor operation: http://fordfuelinjection.com/?p=31

Bob :

Does the engine use any oil?

Customer:

No. No coolant leaks either.

Bob :

Asked because some intake gaskets did fail but they consumed oil when a failure occured.

Bob :

The Ford Fuel Injection site lists all the possible causes for the codes you received.

Bob :

Send me the photo of the connector and check the fuel pressure again.

Customer:

I'll start checking for a ground problem or connector problem, as well as the fuel pressure adn I'll try to get a photo to you. What should the fuel pressure be and how long should I check it for any signs for leakdown?

Bob :

You could also grab the wiring harness in different places and move it around to see if it runs differently. This is a way to find a intermitant wiring problem.

Bob :

The pressure should be 30 to 40 psi and it should hold pressure at about 30 psi for several minutes.

Customer:

I'll try that and get back to you. Thanks.

Customer:

Would a leaking or stuck open injector cause those codes?

Bob :

Yes

Customer:

I'm signing off now, but I'll get back to you later. Thanks.

Bob :

Keep me updated!

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