Misfire and Bucking with temperatures under 40 degrees

Walker Mechanic South Carolina Posted   Latest  
Resolved
Driveability
2003 Ford Ranger Edge 3.0L (U) 5-spd (5R44E)
Misfire

I am just an equipment mechanic trying to help a neighbor so bear with me. I only have a scanner to check codes it doesnt show any live data. Anyway this little truck bucks and misfires sharply with temps under 40 degrees. It only does it under a load for the first quarter of a mile. It then runs perfectly. I have replaced the plugs, wires, and coil with Motorcraft parts. I have physically checked the grounds I see and found no faults. The fuel pressure is 65 psi when the misfire is occuring under load and acceleration. Could this be the PCM or computer. Any input would be helpful. It has a manual trans also.

0
Aaron Owner/Technician
Kansas
Aaron
 

I would start by checking for vacuum leaks and intake leaks. I’ve noticed a lot of 3.0 having issues With this. Do you know how many miles The truck has? Also experienced 2003 3.0 having low compression on bank 2 cylinders so don’t rule out low compression being an issue.

0
Ð Awarded
Walker Mechanic
South Carolina
Walker
 

The truck has 205,000 miles. I will check for vacuum leaks and check the compression on all cylinders. Good excuse to buy a decent scanner also. Thanks for the input. Any recommendations on a decent scan tool.

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

Since this has issues only when cold/Open Loop, it's a basic issue. From your description, once it's in fuel control, the system is able to compensate for the issue. Without scan data, you're flying blind…

+1
Ð Awarded
Agree
Timothy Owner/Technician
Wisconsin
Timothy
 

And, just because the parts are ‘new’ does not mean that they are good. NEW can mean Never Ever Worked. This sounds to me like a spark issue, but that's just a SWAG.

0
Ð Awarded
Mihail Technician
Maryland
Mihail
 

Hi, you need to find a way to check the engine coolant sensor temperature. Good luck.

+2
Ð Awarded
Agree
Robert Diagnostician
California
Robert
 

Since it runs well after it warms up and goes into closed-loop fuel control I would be looking for a vacuum leak or a sensor misreading like a MAF sensor that would make it lean. It would help if you could look at fuel trims in data.

0
Ð Awarded
Ronald Owner/Technician
North Carolina
Ronald
 

Compression reading cold then warmed up. Sounds like carbon.

0
Ð Awarded
Kevin Technician
Maryland
Kevin
 

Carbon on the valves will cause misfire when first started cold. Try a good carbon cleaning.

0
Ð Awarded
Marc Technician
New Jersey
Marc
 

I maintain a fleet of theses Relics which all have about 212,000 miles or more on each , they are security vehicles so that means they would have about 400,000 miles on the engine . { idle Time } I Can honestly say i have never seen much carbon build up on the intake valves .

0
Ð Awarded
Kevin Technician
Maryland
Kevin
 

Ford also has an issue with intake gasket leaking when cold. Check fuel trim when cold if adding then improves as it warms up needs intake gasket

0
Ð Awarded
Gary Owner/Technician
Colorado
Gary
   

Hello, Walker. I don't know how your 3.0 L is configured, but the old 4.0L Explorers had a recall problem with the the upper intake plenum o-rings losing their sealing ability in cold weather. This symptom is very difficult to detect because the symptoms quickly disappear after the engine is started. Smoke or propane testing is usually a waste of time because you're usually working outdoors…

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

Since it does it under load, with the throttle open, I'm doubtful you're looking at a vacuum leak. It would be present on first start cold, without load, if the vacuum leaks were causing it. It would have to be a fairly large vacuum leak to do it under load…coolant sensor is possible, but again, I'm doubtful about that as well, because it wouldn't cause it to be lean but rich, in most ECT…

+1
Ð Awarded
Agree
Gary Owner/Technician
Colorado
Gary
 

Hello again Walker. The PCM would be the last place I'd look, It sounds like a lean fuel problem caused by a sensor. The reason you're probably not setting any codes is because the engine is still cold. Here again, you really need a scan tool with a data stream that gives you positive or negative fuel trims...

0
Ð Awarded
Randall Technician
Pennsylvania
Randall
 

Walker, Keep it simple. I agree that it sounds like a lean condition, typically intake gaskets cause a rough idle on cold start but are ok under load. Clean the MAF sensor, check it for debris. Try running with it disconnected. Fuel quality. Take a sample, check Ethanol, water content, and volatility.I recently was beat up by a Nissan with bad fuel. Some of the 3.0 Rangers had an ethanol…

0
Ð Awarded
Chris Technical Support Specialist
New York
Chris
 

FORScan and a ELM device might be just the tool you need to diagnose this and for under $50.00 The code scan and data side of the software will allow you to see what you need and the hardware required is pretty cheap. Check out their site for hardware recommendations.

0
Ð Awarded
Walker Mechanic
South Carolina
Walker
 

I think it is the PCM. I got the bright idea and took the PCM off and kept it in the house overnight on two occasions and put it back on when the temp was in the high 20 degree range and it ran perfectly on both occasions. Left it on overnight when the temp was in the high 30 range and the truck bucked and skipped for about a quarter of a mile. I dont know driver or something failing. Owner is…

0
Ð Awarded
Randall Technician
Pennsylvania
Randall
 

Walker, I had to put a PCM in the freezer a few times. GREAT CALL!! Thanks for following up! Randy

0
Ð Awarded
Walker Mechanic
South Carolina
Walker Resolution
 

The PCM fixed it. Thanks everyone for the input.

0
Resolution Ð Awarded