Help-hesitation under load

[Tickle]

My 1996 Cobra has 91k miles. On the way home, it started sputtering/hesitating during acceleration, mainly in gears 2-5. I also noticed the voltage meter on the car a little to the left(R in NORMAL), but it went back up and stayed.

I made it home and did a basic check. It revs fine when stopped, idles fine, doesn't try to stall.

My plugs and wires are 2years/20k old.
2k on new O2 sensors.
IMRCS were deleted last year and I have a tune for it.
Fuel filter is 2-3k miles old.
No DTCs are showing.

Updated:
Things I have checked:
-fuel pressure is 29-30 psi at idle, goes up to 39 when I disconnet vacuum from FPR. This eliminates fuel pump IMO.
-I used a mechanics stethoscope and checked each injector, they all were ticking steadily and sounded the same.
-Battery is at 12.6V off, 14.1V at idle
-Both ignition coils read primary resistance 1 ohm, secondary of 13-14.5 K-ohms on all pairs
-All spark plug cylinders/tunnels were clean and clear of oil, no leaks in grommets for valve covers
-all spark plugs were normal and gapped correctly.

5/11/15-next thing to try: replacing spark plug wires, maf cleaning, then datalog, then mechanic after that--my local dealership is awesome and priced reasonably thank goodness. I'm stumped but I'm also just a shade tree mechanic. This may be a job for the pros because I'm out of ideas.

5/13/15: problem solved. It was the wires. Only 20k miles on FRPP 9mm wires. Twice now i have been fooled to think it wasn't wires.

 

[cbrown9064]

Check fuel pressure when this happens.

 

[Tickle]

Is this as simple as renting a gauge and connecting to the schrader valve on the fuel rail? The Haynes manual referenced taking the vacuum line off the regulator?

 

[Tickle]

Updated:
Things I have checked:
-fuel pressure is 29-30 psi at idle, goes up to 39 when I disconnet vacuum from FPR. This eliminates fuel pump IMO.
-I used a mechanics stethoscope and checked each injector, they all were ticking steadily and sounded the same.
-Battery is at 12.6V off, 14.1V at idle
-Both ignition coils read primary resistance 1 ohm, secondary of 13-14.5 K-ohms on all pairs

I am going to let the engine cool then check the spark plus/wires to see what they look like. I am suspecting bad wires, even though I bought them in 4/2013/20K miles ago.

Any other ideas?

 

[cbrown9064]

What kind of wires? That certainly could be the problem...check them out.

If you can test fuel pressure when this happens (not just in the garage), that would eliminate a pump that couldn't put out volume or Id a portion of the fuel system was plugged.

CB

 

[Sn8kebitten]

My cobra was doing the same. Only under acceleration but was fine when revved up in neutral. Turned out to be several of the valve cover gaskets that go around the spark plug holes were leaking oil down into the spark plugs over several months. Replaced the gaskets and cleaned the plugs and haven't had any problem since. But I doubt your car with much lower mileage than mine has this problem

 

[Tickle]

FRPP Wires.

Sn8kebitten, I thought about that, I heard from a friend that had the same problem.

I'm going to check the plugs tomorrow to see if there's any oil leaks in the spark plug area.

Wouldn't this cause smoke?

 

[ZeroDCX]

FRPP Wires.

Sn8kebitten, I thought about that, I heard from a friend that had the same problem.

I'm going to check the plugs tomorrow to see if there's any oil leaks in the spark plug area.

Wouldn't this cause smoke?

If plugs are torqued to spec, this would not cause smoke. Oil would not seep past the spark plugs. It would cause oil to pool in the spark plug cylinder/well, which would act as a conductor against the heads. With our waste spark ignition (two cylinders are fired at once, but only one cylinder actually ignites and combusts) and pooled oil in multiple spark plug cylinders, it could cause other cylinders to fire out of order among other issues. So in essence it would cause a misfire condition.

I'm going with spark plug wires being your issue. Do you have a Motorcraft or FRPP set?

 

[Tickle]

Frpp

 

[ZeroDCX]

Do you have datalogging capabilities? You can monitor misfire counts on each cylinder to isolate the problem. Then try swapping spark plugs, wires and/or injectors with other cylinders in order to isolate the issue. Also you can monitor STFTs to see if the ECM is pulling fuel during the event (spark plug(s) not firing causing a rich condition). You could also monitor LTFTs. But I don't think the condition would last long enough for the system to adjust for long term.

 

[Tickle]

I have a tuner that I can datalog with. What data points do I need to log?

 

[95mustang_gt]

i would check for a bad or dirty mass air flow sensor(maf) .

 

[Tickle]

Just checked all spark plug cylinders. No oil or evidence of leaking oil in there. All spark plugs look good and are gapped at .54-55.

 

[Tickle]

i would check for a bad or dirty mass air flow sensor(maf) .

I'll clean the MAF, couldn't hurt.

This reeks of spark plug wires. Guess I'll try replacing those if the maf doesn't work.

 

[Tickle]

Ordered a new set of frpp wires. We'll see how it goes...

 

[Tickle]

It was the wires. Damn, only 20k miles on them(FRPP 9mm).

Glad this is over. Thank you all for your help and suggestions.

 

[ZeroDCX]

Glad you got your issue fixed.