2000 Ranger intermittent stumble on acceleration

[mrln1955]

Over the last 6-8 weeks I have experienced an occasional loss of power when depressing the accelerator pedal. Power typically returns when the accelerator pedal is released. Recently, at 10mph in first gear on level ground, the engine bogged down when the accelerator was depressed and rev'd back up when released. I repeated this cycle 3 times in short succession. During one of these stumble episodes it almost feels as if the throttle response is inverted. The abnormal behavior typically lasts about ten seconds or less.

The engine is a 2.5L with 54,000 miles and starts and idles normally, and between stumbling incidents will rev freely in neutral and reach 80mph on the freeway. The stumble will occasionally occur at speed on level ground but doesn't seem to be a problem going uphill. The engine doesn't stall. About a month ago I added Sea Foam with a full tank and subsequently refilled the tank when it was 1/2 empty. I only drive about 200 miles/month and I want to avoid condensation in the tank since the truck is parked outdoors. Since then I've driven another 1/8 tank. I then changed the fuel filter about a week ago, and today I cleaned the MAF sensor element, but the problem is still there. I have not had an MIL and the problem seems to be getting more frequent.

I have ordered a scan tool from OBDCOM.com and plan to drive around with it to see if I can capture any codes during an event. I was used to doing everything on my first truck (1975 Datsun), but I haven't done anything besides routine maintenance on a vehicle for the past thirty years. The internal combustion engine has become pretty complex while I wasn't paying attention and I've got a bit of catching up to do.

If anybody has had a similar experience or has suggestions on what might be causing this problem, I'd appreciate hearing from you.

 

[steve63]

hard to say without knowing what fault codes you have,check your fuel pressure,to rule out fuel pump issues or clogging,fuel pressure should be 35-45 psi constant.

 

[mrln1955]

hard to say without knowing what fault codes you have,check your fuel pressure,to rule out fuel pump issues or clogging,fuel pressure should be 35-45 psi constant.

Thanks, The OBDCOM scan system should arrive in the next few days. Since the system works with a PC or laptop, it is supposed to be able to do real-time data logging and I'm hoping to monitor the engine during an event. I bought the Haynes OBD-II Techbook as a guide to help interpret the codes.

To give you an idea how rusty I am at troubleshooting, l replaced a starter motor last weekend when it was simply my ten year old battery calling it quits. I hadn't had any trouble with starting the truck until last week when I got a loud chatter when attempting to start it. I assumed it was the bendix failing to engage, or possibly broken teeth on the flywheel. When I heard the same noise with the new starter, I knew it had to be the battery and some sort of oscillatory condition due to low current/voltage. I hooked up my jumper cables to my wife's car and the truck started right up.

 

[mrln1955]

hard to say without knowing what fault codes you have,check your fuel pressure,to rule out fuel pump issues or clogging,fuel pressure should be 35-45 psi constant.

Okay, I hooked up the ODBCOM scanner and there were no stored or pending codes, and no freeze frame data. I have driven less than an hour since the new battery, so that may have an impact. The system can monitor and log up to 10 parameters, selected from:

Throttle Position (%) [0~100]
MAF Air Flow (gm/sec) [0~327.675]
Intake Air Temp (deg F) [-40~200]
Timing Advance (deg) [-64~63.5]
Speed (MPH) [0~158.5]
RPM (1/min) [0~8000]
Short Term Fuel Trim Bank 1 (%) [-100~100]
Long Term Fuel Trim Bank 1 (%) [-100~100]
Torque (experimental) (FtLb) [0~400]
HP (experimental) (HP) [0~400]
Fuel System Status () [0~16]
Calculated Load (%) [0~100]
O2S Voltage Bank 1 Sensor 1 (V) [0~1.275]
Engine Coolant Temp (deg F) [-40~310]
Fuel Economy (MPG) [0~60]

How should I prioritize these parameters for data logging, in view of the symptoms I have? I plan to drive around with my watch synchronized to the laptop clock and note the time when a stumble event occurs, but I want to make sure that I am logging the most important parameters. Although the system can scan ten, it will scan faster if I select fewer parameters. Can anybody recommend a driving cycle for the 2000 ranger 2.5L 4cyl?