I have a 94 ranger 4x4 5speed. My CEL is on all the time. I'm pretty sure I have a obd1 system and the only code I get is 335 EGR PFE out of self test range. I've checked my MAF, AIT, Coolant, TPS, and DPFE sensor's. All seem to check out fine. My truck lacks power, knocks pretty bad and my fuel mileage is down. Also, I've applied vacuum to my EGR vavle and I know it's working. I'm wondering about the 02 sensor but wouldn't the CEL come on after the engine warmed up? Or can a bad or slow O2 sensor(s)cause the CEL to stay on all the time? Mostly, I haven't checked it because it's a pain in the *** to get to. I am new to this site and have read most of the threads but haven't quite found my identical problem. I would appreciate any help or links dealing with this. Thanks

 

Welcome to FTE!

Which motor do you have?

It'd be the 2.3 Lima, the 3.0 Vulcan, or the pushrod 4.0

I had a similar symptom on the big brother of the 2.3 Lima and it ended up being the DPFE. I have an OBDII system.

 

Sorry, I forgot to say what engine. It's a 4.0

 

http://www.niehoff.com/techtips/n_sen.html

 

"Our testing has found that contaminant build-up in the area of the EGR pintle shaft, or pintle seat...."

The pintle shaft is the line from the exaust manifold to the EGR? Or, is it from the vacuum to the EGR? My guess would be cleaning said shaft and seat should eliminate your problem.

 

And, since you asked

How can I test my O2 sensor?
They can be tested both in the car and out. If you have a high
impedence volt meter, the procedure is fairly simple. It will
help you to have some background on the way the sensor does
it's job. Read how does an O2 sensor work first.

Testing O2 sensors that are installed
The engine must first be fully warm. If you have a defective
thermostat, this test may not be possible due to a minimum
temperature required for closed loop operation. Attach the
positive lead of a high impedence DC voltmeter to the Oxygen
sensor output wire. This wire should remain attached to the
computer. You will have to back probe the connection or use
a jumper wire to get access. The negative lead should be
attached to a good clean ground on the engine block or
accessory bracket. Cheap voltmeters will not give accurate
results because they load down the circuit and absorb the
voltage that they are attempting to measure. A acceptable
value is 1,000,000 ohms/volt or more on the DC voltage.
Most (if not all) digital voltmeters meet this need. Few
(if any) non-powered analog (needle style) voltmeters do.
Check the specs for your meter to find out. Set your meter
to look for 1 volt DC. Many late model cars use a heated
O2 sensor. These have either two or three wires instead of
one. Heated sensors will have 12 volts on one lead, ground
on the other, and the sensor signal on the third. If you have
two or three wires, use a 15 or higher volt scale on the meter
until you know which is the sensor output wire.

When you turn the key on, do not start the engine. You should
see a change in voltage on the meter in most late model cars. If
not, check your connections. Next, check your leads to make sure
you won't wrap up any wires in the belts, etc. then start the
engine. You should run the engine above 2000 rpm for two
minutes to warm the O2 sensor and try to get into closed loop.
Closed loop operation is indicated by the sensor showing several
cross counts per second. It may help to rev the engine between
idle and about 3000 rpm several times. The computer recognizes
the sensor as hot and active once there are several cross counts.

You are looking for voltage to go above and below 0.45 volts.
If you see less than 0.2 and more than 0.7 volts and the value
changes rapidly, you are through, your sensor is good. If not,
is it steady high (> 0.45) near 0.45 or steady low.

Testing O2 sensors on the workbench.
Use a high impedence DC voltmeter as above. Clamp the sensor in
a vice, or use a plier or vice-grip to hold it. Clamp your
negative voltmeter lead to the case, and the positive to the
output wire. Use a propane torch set to high and the inner blue
flame tip to heat the fluted or perforated area of the sensor.
You should see a DC voltage of at least 0.6 within 20 seconds.
If not, most likely cause is open circuit internally or lead
fouling. If OK so far, remove from flame. You should see a
drop to under 0.1 volt within 4 seconds. If not likely silicone
fouled. If still OK, heat for two full minutes and watch for
drops in voltage. Sometimes, the internal connections will open
up under heat. This is the same a loose wire and is a failure.
If the sensor is OK at this point, and will switch from high to
low quickly as you move the flame, the sensor is good. Bear in
mind that good or bad is relative, with port fuel injection
needing faster information than carbureted systems.

ANY O2 sensor that will generate 0.9 volts or more when heated,
show 0.1 volts or less within one second of flame removal, AND
pass the two minute heat test is good regardless of age. When
replacing a sensor, don't miss the opportunity to use the test
above on the replacement. This will calibrate your evaluation
skills and save you money in the future.

There is almost always *no* benefit in replacing an oxygen sensor that will pass the test in the first line of this paragraph.

 

Wow! Thanks aquanaut20, I will follow your instructions to the letter. I'll try to find time to test my sensors this weekend and post my results.

 

OK, natebaker and 96_4wdr I got your posts and I'm going to look into my possible false PFE sensor codes. (Oh, by the way I checked my 02 sensors and according to Aquanuat20's info they check out good, thanks for the info) Tomorrow I'm probably going to take apart the pintle shaft and seat and check for contaminants because at this point I'm at a loss. My only question is that somewhere on this site I can't remember where but somebody was posting a similiar problem. They, however unplugged their MAF sensor and their truck seemed to run great! Well, what the heck, I tried it, same scenario my truck runs great when I unplugged my MAF sensor. It doesn't knock and my power is all back, the check engine light is still on (to be expected) but can somebody explain this. I'm no expert on electrical device's by a long shot, but if the pintle shaft or seat was clogged and my PCM was trying to adjust by commanding more vacuum wouldn't my problem still exist? Even with the MAF sensor unplugged. Just looking for answers, thanks.

 

I do have to fess up and say I haven't check my codes for a long while. A couple of months ago I did check my PFE sensor and I wasn't getting the correct readings so a couple of weeks ago I finally decided to get a new one. Well, now after deciding to check my codes again, the fault code for the PFE doesn't come up. Now, I get a 121 (Indicates TPS voltage inconsistent with MAF sensor) and a 421 which I don't know what it is for a OBDI. I do believe in the last couple of months I have developed a new problem causing my CEL to stay on.(Buy the way I did clear my codes and I checked my new codes with the MAF sensor plugged in). What's still weird is that my truck still runs pretty good (no knocking, no loss of power) with the MAF sensor now plugged back in. If I could just get that darn CEL light out I'd be happy. Any suggestions?

 

In order to CORRECTLY diagnose the problem, you need to follow the diagnostic steps in order.

First, determine if you 121 code is a continuous memory code, a KOEO test code, or a KOER test code. Each has its own diagnostic procedure to correctly pinpoint the problem.

Continuous Memory Diagnostic Trouble Code (DTC) 121 indicates TP was inconsistent with MAF value.


KOEO/KOER: DTC 121 indicates the Throttle Position (TP) sensor's rotational setting may be out of Self-Test range.


Are you sure that's a 421 (non-existant) and not a 412 code? If it's a 412, fix it first.

FWIW, I'd clean the MAF sensor element as a preventative measure.

Steve

 

Ok, All I have to go by is my Haynes Repair manual. I'm pretty sure I'm following it as it reads but is there a better diagnostic procedure you could give me? I'm not sure but wouldn't my codes have to be a continuous memory code if my CEL is on all the time? The one thing that's got my curiosity is the 412 instead of a 421. After I get into the KOER test and into the Computed timing test my Haynes manual says it will advance the timing and hold it there for approximately 2 minutes. What I have observed is that it only holds it there for maybe 15 to 20 seconds at the most. I don't know if that's normal or not. I don't know if I'll get time this week to run through the diagnostic spill again but would appreciate any advice. Thanks.

 

If you are concerned about your tp sensor it is easy to check. Back probe with an analog volt meter and the needle should swing smooth from idle to wot. If not, replace it. At closed throttle, you should read .95 to .98 volts. The mounting holes should be loose enough to adust to this voltage and a digital voltmeter is best for this part of the check.

 

Thanks for the post super 6.8. I do have a digital voltmeter and I plan on checking the TPS sensor again, since I haven't checked it for awhile. Thanks for all the posts guys! There's some very useful info on this site.

 

Unplugging the MAF can set a code... because you run the engine (change TPS value) without the MAF value changing, therefore the code (tps change no maf change).
TPS can develop a 'glitch' that you won't see on a sweep test. Even the special tester you can buy to test emission components may miss it. If you have an auto with torque converter lockup and O/D, it may make the lockup come and go because the TPS drops to idle or WOT (sure) and the ECM is supposed to unlock the torque converter then. Weird symptom until you know.
CLean the MAF with brake-cleaner GENTLY, and give it a go.
tom

 

Just so I'm clear, I still get the same code 121 with my maf sensor plugged back in. I've cleared my codes several times(running thru the entire diagnostic procedure) with it plugged in and my truck up to operating temp.(CEL still on all the time. It's definetly a continous memory code cause it stays in there all the time. Basically, I just don't believe in changing parts to fix problem. I have cleaned my MAF sensor with electronic cleaner and I'm sure I'm getting the right readings when I check the Vref voltage, sig volt, etc. I did check my TPS sensor and seemed to be getting the right readings as well. Has anybody changed a sensor that they thought was OK and it fixed the problem? Are some of these sensors beyond the scope of a DIY mechanic? If I take it to Autozone, or Ford(God forbid!) can they pull codes that I can't read with my digital voltmeter? Any help would be appreciated.