Insufficient RPM, low power and low MPG

[rantruck]

I have a 94 V6-3.0 ranger 4x4 truck, automatic OD, which is showing intermittent lack of power. On a full tank of gas (15 Gallons), I can never get more than 240 miles (Approx. 16 MPG). Some days (very seldom) and for a brief moment the truck has adequate power. I have changed a number of parts on it and have done a complete tune-up. I will attach the parts changed and items verified in this posting below. There are no engine codes (Check engine light is not lit!). However during a diagnostic scan, under the dynamic response section of the scanner, the following codes showed up. 1) Insufficient RPM change, 2) BOO switch open, 3) Bad/Missing CID sensor.

I had read in one of the repair manuals that the CID sensor is optional and may be present only on CA emission compliant vehicles -- I am not in CA. I think the BOO switch open may be okay as well, as I was not pressing the brake pedal during the test. The insufficient RPM change is what I am concerned with and it could be (may be) leading to the lack of response and hence the power.

While driving, the RPM seems to develop to a max of 3500, but the engine produces no torque -- leading me to believe that the engine is running very rich (which may explain the poor mileage). Also, on initial start up, I get adequate power for the first minute and then the power drops rapidly. Could it be the computer running in closed loop mode with a defective O2 sensor and erratically setting the air / fuel ratio? The truck also exhibits difficulty climbing inclines. All-in-all acceleration is very poor and sluggish. At driving speed between 35 & 45 MPH, the engine exhibits a low frequency audible type power fluctuation. It seems like the engine is loosing power on one or more cylinders by a fixed amount (May be the whole left bank of cylinders are told by the computer to run lean or rich? Is that why I feel the surging?)

Also, when I bought this truck used, the problem was much worse that I could not push the RPM past 2000. It looks like something has cleaned up/ improved over time with regular usage that the RPM now can be as high as 4K.

Here is a question that gets to the heart of the matter: What one component would attribute to low mileage and low power (acceleration) simultaneously and does not impact cruising speed (50MPH +)? Also, the issue has improved over time, through usage. If you had to suspect two components, O2 sensor and the EGR, which one could be better blamed for the behavior at hand?

Any help in identifying the problem and recommending a solution is greatly appreciated. Also, I am posting a complete list of things done, as best as I can, so that other can benefit from my learning experience. And when I find a fix, I will report the actual problem and solution here – for the next wave of technical advancements in any field, be it automotive or medical science, will be through shared knowledge and the internet is a great tool for sharing; only if people would share …

Thanks for your time and help …



Outstanding issues summary:

1) Poor throttle response
2) Lack of power, running lean
3) Pinging.
4) Poor gas mileage

Now for the things replaced and verified through test procedures. Please advice if I should do additional checks.

1) New platinum plugs, cap, rotor and wires. Plugs gapped to specification (44mils)
2) Fuel filter PCV valve and air filter
3) Replaced one defective 02 sensor (Required to clear check engine code)
4) Replaced EGR DPFE sensor (Required to clear check engine code)
5) Replaced catalytic converter (Adequate exhaust flow)
6) Replaced EVR (Required to clear check engine code)
7) Serviced automatic transmission with new filter and fluid
8) Cleaned Fuel injectors with fuel additive.
9) Cleaned MAF and checked voltage/resistance
10) Cleaned throttle body to new condition, checked throttle plate opening/closing action.
11) Cleaned IAC valve to new condition
12) Checked IAT resistance to ensure specification
13) Checked Coolant temperature sensor to ensure specification
14) Checked for vacuum leaks; replaced most hoses; others are in good condition; also sprayed Carb cleaner around hoses to identify leaks which would increase engine RPM (make shift leak detector)
15) Cleaned EGR valve and tube, ensured basic functionality
16) Reset computer and ensured proper battery terminal connection
17) Checked transmission, no slips and shifts through all gears fine. The transmission shifts are delayed but that is because the engine is not producing torque appropriate for the RPM.
18) Ensured brakes are not dragging and the wheels turn freely.
19) Checked intake air diverter operation
20) Throttle position sensor (Was defective and caused engine to idle @ 2500 RPM)
21) Checked timing at engine idle RPM -- Within specs.
22) De-carbonized the combustion chamber, cleaned the injectors using special equipment (cleaned by shop mechanic)
23) Replaced ignition coil
24) Checked Ignition control module (ICM tested with specific tester @autozone)
25) Vaccum modulator in the transmission replaced.


Pending checks in order of priority
1) Check timing advancement during accelaration -- Timing retards before advancing!!! Why?? Reason to trouble shoot!!!!!
2) Replace EGR Valve.
3) Check/Replace the second oxygen sensor

[roadhogg]

Check fuel press regulator if the diapram is leaking it will dump fuel straight into the intake and cause most of those symptoms, if this is the problem the 02 sensor will have to be replaced,also check the brake booster for fuel

[chaser29]

http://members.cardomain.com/12311974

Check your fuel filter.

For more HP:
K&N air filter
Tornado
Modify your air box or purchase a new K&N air intake box & pipe. There are others, so depending on your $$ check out other item for this. They are costly!!
AirRaid throttle spacer, SP wires, radiator and engine flush. These are just a few simple things within a decent budget price range. There are more modified areas, that you could take, but the $$ goes UP!!

Keep in mind with the fuel additives, yes you might feel a slight difference, but with simple engines such as these, they could do more harm then good.

This site might help with some of your answers.
http://www.therangerstation.com/forums/index.php
Good Luck

[rantruck]

I did a timing check, and found the timing to be at 10 degree BTDC. But when I accelarate, the timing retards all the way before advancing to 30 degrees BTDC. Is the timing reversing in this manner normal? This test was performed with the truck in park and reving up the engine. It consistently retards timing before advancing. So, I removed the SPOUT jumper and drove, to see if there is any difference. The vehicle exhibits no appreciable difference in power (the condition is that bad -- I still have to stand on the gas pedal). Once the timing has advanced, it sticks and does not return for about 3 seconds after releasing throttle; I thought it would return to 10 BTDC immediately; so that the engine can quickly rev. down. The RPM changes are sluggish both ways. Is the PIP (CID or CMP) sensor bad? Or is it the ignition module. Worse yet, is the distributor shaft slipping?

[chaser29]

O2 sensors run around $51/52.
I really dont know that answer, and I dont want to say something that may do more harm than good.
Harm always costs more $$
I would ask the ford dealership machanic for some ideas.

[Bulldog Brewer]

Did you find out what was causing this problem?