Rough Under Load - Fuel Smell - No Codes

[rangerpilot]

Truck starting jerking a little a few days ago at highway speed and then continued even at low speed. First thought was bad fuel pressure or blocked fuel filter.

While driving/under load: Heavy vibration and sometimes jerks/bucks. Feels drive train related.

At idle or rev up while in neutral: No sign of engine vibration. Minor sound like the exhaust pipe is coughing. Heavy fuel burn smell like running rich. Bad catalytic converter??

All conditions: No knocking or sounds of misfire. No OBD codes! Puzzling!

Feel free to ask questions...tomorrow is troubleshoot day...repair shop on Thursday if I don't figure it out. Not too keen on driving it but engine sounds all right.

 

[RonD]

Clean MAF sensor and unplug it and see if engine runs better, CEL should come on, so that also tests if computer is working like it should and setting codes.
Without MAF sensor data computer runs pre-set factory fuel mix based on RPM and throttle position, so may be sluggish but shouldn't misfire

1999 Ranger will run 65psi fuel pressure so did you test that or??
You mentioned it but then didn't say if that was tested.

With engine warmed up and idling, unplug the 2 wire connector on the IAC Valve, idle should drop to 500 or engine may even stall, either is good it means no vacuum leaks.
If idle stays up, 700 or higher, then you have a vacuum leak

Misfires means no fuel was burned so you would smell that in the exhaust

 

[rangerpilot]

Hi Ron! Thanks for the reply. I tried the fuel pressure check and while I had done it before with another problem, a few days ago it would not register at all. Luckily that wasn't the problem but it just burns me up that the dang Schrader valve is so difficultly placed next to a large wiring bundle. Ugh!

So...in fact the engine WAS misfiring. No code was thrown [scratching head] but I replaced all the spark plugs. Here is my findings:

#1 Gap .56 - fairly clean
#2 Gap .52 - fairly clean
#3 Gap .50 - very clean

Here's the doosey ....
#4 Gap .76 - burned up
#5 Gap .58 - noticeable buildup
#6 Gap .48 - heavy buildup

All new plugs along with standard maintenance of fuel filter and oil change and everything is running well.

Certainly there is an underlying problem with Bank 1 cylinders 4,5,6 and a compression check is in order but I didn't feel comfortable doing that by myself. If the misfire returns in a short period of time then I will have to do some deeper investigation.

As a side note, I don't see any evidence of burning/consuming oil but I do leak a couple quarts (have to add) in between each oil change. I have recently had the real main seal replaced but it appears to still be leaking there as well as from the front near the crankshaft pulley or maybe the around the oil pan up front. Do I really have to take the engine out to remove the oil pan and replace the seal? If so, that is not going to happen and I will just deal.

Thanks for the help!!!




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