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 …

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
Pending checks in order of priority

1) Check ignition coil resistance, check ignition module
2) Check/Replace the second oxygen sensor
3) Replace EGR Valve.

 

Didn't see that the timming was checked. was it and was it advancing when the rpm increased ? just a guess.
Dave 257

 

I checked basic timing at idle and it was within spec. But I didn't check if the timing advanced during accelaration -- good point, I will definitely check and report back! What component would be responsible for timing advance -- computer and the ignition module? Don't you miss the good old vacuum advance?

Thanks for your input

 

I've never worked on a 3.0l, but some of the guys here talk about a "sprot"??. I guess that needs to be disconnected before for you check the timming. someone will come by with a better idea of how to do it.
Dave

 

Hows the fuel pressure?

 

Status : Some improvement in the performance, but still far from normal. Something is improving with constant use -- don't know what that something is to speed up the remedy. Now I have all the (only 2 on the vehicle) O2 sensors replaced. I drove around with a fuel pressure gauge indicating pressure within specification, during accelaration and idle. Also under accelaration the timing advances (no load testing). The timing was checked with the Spout out and then replaced for normal operation. All in all the issue remains.

 

The only thing that makes sense to me is the injectors are slowly cleaning themselves as you drive.You mentioned that you ran some cleaner through it. Was that only once, or did you do it several times. I have found sometimes that adding cleaner to several tanks in a row will help injectors. As far as the power goes, have you looked at the throttle plate while someone holds the pedal to the floor? My '97 felt sluggish until I realized I was only achieving half throttle when I mashed it to the floor. After repairing the throttle cable I feel like I got a new engine.