This is about my personal truck. It's a 1995 F150 / 4.9L / 5 speed / 3.55 /Speed Density / 69,000 miles. Mods include a coil, cat back, quality wires, FIPK, and some other little things.

The problem is a random miss at idle. It has had this miss for several years, but where as it used to only occur one or two times a minute, it now happens every few seconds. It used to have a similar miss on acceleration and during cruise, but I discovered that those were caused by the EGR valve and dirty injectors, and they've been corrected. I still have this random miss at idle. I also have a code 213 (SPOUT circuit open) during KOER, but only a passing code during KOEO.

I suspect that the 213 and the miss are not related. The 213 never shows up during KOEO or as a continuous code, so I suspect there is a fault somewhere in the KOER test, but I can't be certain. I have followed every single flow chart I could find for diagnosing a 213, and the truck passes every test perfectly. In fact, according to the flow charts, the truck is perfect.

Anyway, I can't tell if it's an ignition miss, or a fuel miss, but I'm leaning towards it being a fuel issue. It has no distinct pattern. At first, it will just be a single miss, but the longer it idles, the more it misses, often several times in a row. It has never stalled the engine, but it feels like it might if I let it idle long enough. Feathering the throttle while sitting at a traffic light seems to help. I have tried killing the cylinders one at a time, to isolate the cylinder that is having the miss, with no luck. The miss is random across all/most cylinders, regardless of engine temp.

The miss could best be described as follows; if you've ever had an engine with a Holley 4 barrel on it, and the float was just a hair too high, the fuel slowly drips out of the booster, and when it get's sucked by the throttle plate, the engine often experiences a slight miss. That is exactly how this miss sounds. The longer it idles, the worse the miss becomes, like it's loading up. The injectors don't leak. The fuel pressure remains rock steady for hours after the engine is shut off. Creating a vacuum leak causes the idle to increase by at least 500 rpms, and the miss goes away until the ECM is able to regain control, and brings the rpms back down. That's when the miss returns. I tried adding propane to see if it was a lean miss, and the engine stalled.

I swear I notice an improvement after adding large quantities of injector cleaner to the gas tank, but the injectors have been replaced 3 times, and the problem still remains. It does seem to go away after resetting the ECM, but by the time it's done re-learning, the miss returns.

Fuel pressure is perfect, and the regulator works correctly. Compression is excellent in all cylinders. Vacuum at idle is 20", and at 2000 rpm is 21". Timing is set to 14 degrees advanced, but the problem is identical when it's set to the stock 10 degrees advanced. The problem exists with or without the SPOUT connector in place. The exhaust is free flowing. The distributor passes every test. New parts in the past year include:

Injectors (2 new sets and a rebuilt set)
O2 sensor
Knock sensor
ICM (TFI module)
TPS
MAP sensor
Plugs
Wires
Cap & rotor
Fuel filter
EGR Restrictor plate

Parts that have been tested and cleaned include:

EGR
EVP
IAC
IAT
ECT

The truck runs excellent off idle all the way to WOT. It just has this annoying random miss at idle.

Any thoughts?

 

I have the same truck just a 96. Most people agree to run the stock motorcraft sparkplug. Double check the base timming and ensure base idle rpm is good. My truck makes the same hiccup on occassion, but the idle generally remains strong and fast. About 750 - 900. and is in excellent tune and running condition. I tried the egr block plate and played with the timming many many times. I tow a large boat and need maximum grunt without ping. I am back to running without the restrictor plate.

Mine is only driven when I need it for camping/towing. It just turned 80,000 miles and have only put 15,000 on it since I bought it used in 1999. I am now awaiting a new 22 ft boat. I just assumed the miss is just inherant to the engine monitor design. Remember, none of the smog/pollution/computer/fuel injection stuff existed when this engine was first made. So while it is good, with a better flowing head they really could have made it better. But Ford knew the production end was near and didn't waste any more money on it other than getting it to meet emissions until a replacement was ready.

 

Hi Chris (GREAT name!!!)

There were actually quite a few differences in engine management between 1995 and 1996. Mine is OBDI, with Speed Density, while yours has OBDII, and uses Mass Air. OBDII makes diagnostics much easier, IMO. I wish I had it!



My base timing is 14 degrees advanced, but running it at 10 degrees advanced made no difference. The idle rpm was perfect, but I found that by raising it to about 900-1000 rpm, the miss was less frequent, so that's where the idle sits right now. Reducing it back to stock specs makes the miss worse.

FWIW, I've found that my truck runs it's best with Champion Truck plugs that I sidegap.

Thanks for the ideas!



Take care,
~Chris