89 Merc CP Stumbles or stutters 5.0

as stated 89 Colony Park fuel injected 5.0 has a stumble or stutter. i call it intermittant but i know about when its going to come and go, lets see if i can explain it:

After sitting overnight, it starts and runs just fine, no problems for about 2 miles, then the stumble or misfire starts. after another 2 miles it clears up just before i get to work.

for the rest of the day, the stumble comes first, for about 3 miles after each start up, then goes away.

its worse with the Blower Fan, AC, or headlights on, or all 3.

I was thinking it was a voltage issue,since it seems to come when the battery has been put to work and has to recharge, but there was no change with a new voltage regulator. it acts like a bad spark plug, but they are new along with wires, distributor, cap and rotor, ignition module, fuel pressure regulator, fuel pump and filter, all new vaccum lines, new engine temp sensor, and O2 sensors.

add to this, that after the new plugs and wires installed she ran like brand new for about 150 miles. Next day, back to the stumble again.

 

That sounds like something is out of calibration just after it gets to operating temperature, and then when it get to full warm, it works properly. That could be one of the O2 sensors leaning the mixture prematurely, or it could be one of the temperature vacuum switches. My first guess would be O2 sensors. They get dirty and don't read quite right, but there is no 'Check Engine' light because they are still working electrically. The 5.0 has 2, one on the rear of each exhaust manifold. Make sure you get the calibration code of the car to get the right ones. There are at least 4 different calibration codes for the 89 302 engine. Get them directly from Ford as the have the properly calibrated sensors, and are not much dearer than anywhere else.

 

I'd be looking at the EGR. Could have junk in it.

Also, if you haven't gone ahead and swapped-out ALL vacuum lines, with the age of the car, I would. All it takes is one temp-activated switch on a cracked vacuum line to cause problems.

On the spark plugs- if you've made changes such as exhaust, etc., it's always possible you may need to adjust the heat range on your plugs. The 150 miles may have just coincided with a change in weather.

 

entire egr system is new. all new vaccum lines throughout engine compartment.

did a test with #8 plug on saturday, popped a new one in, within 75 miles, the stumble is back and plug is fouled.

plug i removed first had gunk caked up on it, and has less than 2000 miles on it.

SOOOO

:Blasting_anim:
what now? whats causing #8 to be such a PIA and keep fouling my plugs, and im guessing causing this misfire ive been chasing for 2 years.

no changes to exhaust. everything done to factory as i found it. and have known the car since new.

 

Not knowing what your 'gunk' is, I'd say either an issue with getting spark to the plug, or a leak in that cylinder.

Do you have an Ohm meter? You could check the resistance in that particular plug wire. Not only that the resistance isn't too high, but it's possible there is even a break in the conductor wire. It may be ok sometimes and not sending a signal -or proper signal- other times as the engine moves. Might even be shorting to the valve cover, air cleaner lid, etc.

If you have a coolant or oil leak into the cylinder, you should know from the plug. A coolant leak will leave a white crust on the electrode, and oil will usually leave more of a film or gummy lump depending on how long the plug's been in. (I'd be very surprised if it was coolant/head gasket for this long)

If you had access to the gauges, you could obviously run compression or leak-down tests. Any smoke out the exhaust? Blue or white?

 

little puff of blue every now and again. not everytime. and wont smoke at all when i take it to the shop to have them see it smoke.

its a reman engine that has about 6000 miles on it and still under warranty, BUT warranty doesnt cover trouble shooting, and only pertains to the engine itself. Im thinking clogged oil return, maybe missed in the cleaning. have had compression tested its good.

the gunk on the plug looks kind of like a mouse turd glued to the side of the electrode. the wires are all motocraft and have the same stumble with old wires and new wires, so not suspecting wires.

Im thinking the oil is gathering and pushing thru the valve trying to burn off causing this intermittent mess. (maybe this weekend i can get the valve cover off)

with a new plug it runs great, and i may stop in and pick up a platinum plug to see if its hot enough to burn thru the oil, JUST FOR TESTING to see if im correct on where the misfire is coming from.

 

Perhaps a loose valve guide in the head? Maybe just loose enough to cause the intermittent puff of blue smoke and fouling of the plug, but secure enough to maintain compression in that cylinder.
If it is a remanufactured engine, I would be curious if they were replaced or not. On that same idea, I wonder if when the rings were installed on the piston if they were installed properly/staggered.

 

When i was shopping for the engine, i read off the lists of rework that each company offered on the engines they were selling.

The company i ordered from advertises they replaced valve guides, pistons, rings and warranties them.



on a side note, a friend asked me if the computer had been changed out, i said no that it couldnt be the computer. i say that because with a brand new plug with correct gap, the car doesnt misfire until it has had enough miles to foul the plug.


I am curious, has anyone ever had an alternator cause a misfire?

 

A couple of things JUST this minute hit me. First, if the coil is not new, slap one one. IF you can't get one that uses the factory horseshoe connection, make sure the polarity is correct. The will work with the negative and positive reversed, just the voltage output will be WAY down. I would put in a new coil as a matter of course on a vehicle that age, anyway. I'm putting an Accel into the Thunderbird next week.

The other idea I had is that it could be the ignition control module getting weak. They can start to fail, and cause weak spark that allows plugs to foul. Not difficult to change and they are notorious for failure anyway.

If the injectors weren't cleaned or replaced when the new engine went in, I would run a container of injector cleaner through the tank and see what happens. The injector could be a bit dirty. Also, have you flushed the crankcase since the engine was installed. That may just help, too. I normally do a flush and double oil change at about 1,000 miles on a new or remanned engine.

 

I have a newer coil on, but im not sure what brand. its from advance or autozone. need to find a motorcraft.

the ignition module, distributor, rotor, cap, are all new motorcraft parts.

i have done the oil changes since the engine swap. and i have ran some injector cleaner thru the fuel.



my next step is to test the fuel pressure while driving, and possibly pull the fuel rails and hand clean each injector.

ps, this misfire was present before the engine swap. So we are chasing two problems. 1 is the misfire, the other is the fouled plugs.

i can pull a hill and be misfiring like crazy, then suddenly all 8 kick in just fine. it just goes and comes like something turning on or off, and thats with AC on or off.:banghead3:

can a bad alternator cause a misfire? just asking. it always tests good, but i can hear the power draw from the turn signals and brake lights in the fuel pump noise.

 

New info, for anyone whos following and is as curious as i am as to whats going on.

Yesterday after work, the car stumbled all the way to home depot. i left there drove a mile and a half home and still had the misfire. my plan was to listen, then pull and replace plug wires till i could find which cylinder was misfiring. when i got to the exhaust pipe the misfire had stopped.

I turned on the headlights , the AC was already on, and the misfire came back for about a minute, long enough to pull 1 plug wire and run to the back of the car and put the wire back on.
Next i shut the engine down, left the headlights on high beam for a minute, then restarted. BAD misfire, was able to pull 3 more plugs and run to the exhaust pipe between each to listen. then just like a switch flipped, it smoothed out, no more misfire. so just for giggles i shut down and restarted immediately. bad misfire again.

 

I thought you found that the problem was #8 fouling??

 

i think #8 fouling is a separate problem now. Or is fouling because of the misfire (maybe) im ready to take it to a shop, but i know as soon as i do, itll be something dumb and theyll over charge me for beign dumb.

im trying to figure out what is causing the misfire since there was a misfire present on the old engine and the new one, under same circumstances. Im going to try putting a good alternator in to see if that could be the issue.

 

OH! I didn't realize that the problem existed in 2 different engines! Now I understand why you are searching all the peripherals.

 

Got to be something electrical....voltage drop....bad coil....bad distributor even........