Severe miss under load.

[x_man586]

Severe miss under load. Solved!

I did a search and am in the process of working out the problem. I was on my way to work this morning and had to stop at a light. When the light changed I accelerated normally I didn't even hear the s/c whine. Out of nowhere the motor started shaking like crazy. I got off of the throttle and coasted and the stumble went away. I can keep a constant speed going down hill and no stumble, but as soon as I start up the hill it starts shaking. The first thing I checked was the vacuum lines, I have one that likes to come off every now and then. They were all connected. After I deleted the E.G.R. I replaced all of the rubber vacuum connectors. Then I looked for a blown plug even though I didn't hear a pop, but all of the coil packs were firmly bolted down. I limped the truck home and let it cool off and pulled the plugs thinking if a c/p went bad the plug would show it. The plugs were a little too white for my taste, but still had a brown tint. I filled up about 1 1/2 weeks ago and the first half of the tank burned fine. The fuel filter has around 3k on it. I went to Orilleys this evening for new TR6's and a new filter. I will put them on tomorrow and see if there is any improvement.

I was wondering if there is anything I am overlooking. Something else that could be causing this problem.
Thanks.
I am borrowing my father in-law's 4.6 F-150 :cryying: until I can fix the problem so I can still get to work.

 

[1990stanggt]

I'm interested to see what people say as well, I randomly have this happen to me as well. Funny thing is, it only does it through a certain range of throttle, if you gas it when it does it, it downshifts and feels great, no miss at all......have you tried that?

bump bump

 

[mcarbine]

Could be a bad COP. Triballightning just went throught the same thing sort of. truck ran normal under light acceleration but once there was a load or if he got the boost up it would miss and stutter etc. We ruled out vacumn leaks and the fuel filter etc so he took it to a shop and sure enough the #4 COP was bad. He replaced it and now its all good. Hopefully yours is something easy like that.

 

[02_lightning_NP]

i went throguh almost the same thing a few months ago and i had to end up changing out my coil packs. and the connectors to them because i had if i remember right four or five go bad over night. I to heard no popping no nothing and accelerating normal - light was fine but anything other than that she would start shaking really bad. get them tested at your local repair shop. trust me

 

[x_man586]

Unless the stealership can do it, there aren't any local shops that can test them.

 

[xonecrazyx]

astealership can test them . orany good scanner can access mode 6 data . if there is a skip it will show in mode 6 way before it sets any lights

 

[1990stanggt]

Is this something I could datalog or check with the Xcal 3 to narrow down which one it could be? I really think that is exactly what is wrong, the symptoms are almost identical to mine.

 

[Mondo1]

Do not overlook a deteriorated rear pcv hose (the desending on behind the S/C ) Mine was worn through from oil and age and the truck was stalling and wouldn't support boost. The fact that you say that there is no S/C whine makes me beleive you have a worn s/c vacuum hose . Check your t-fitting hoses on the passanger side and the desending rear hose is virtually impossible to feel fo unless the S/C is removed. A common problem with bad running Lightnings. Just some FYI.

 

[x_man586]

I said I didn't get on the throttle enough to make the s/c whine when the problem started. On the way home I tried to keep it in the vacuum, but the s/c whined like normal.

 

[slow232]

i had the exact issue and it was a bad COP.

 

[Tazman1]

I too had the same problem back about 3 years ago. Turned out to be a bad coil pack. It was the last one on the passenger side. The one closest to the fire wall. I took it to the Dealership to have it diagnosed. Total bill for fixing it was a little over 200.00

But that was 3 years ago.

 

[LightningLou]

Bad coils same symptoms here too. Went with a set from Weaponx and haven't had any issues since!

 

[matted2thefloor]

Failing coil packs on the 2v 5.4s is a very common problem. It may be different for the L's but the N/A 2v 5.4 had a situation where coolant would leak from a surrounding hose and drip/run down to the last coil on the pass side. I'm not sure if the L has a coolant hose near that coil, but if it does, check it to be sure.

 

[x_man586]

Well. The last plug on the pass. side had rust on it.

 

[x_man586]

Well. I found the problem. The connector on the second coil pack on the drivers side was not completely plugged in. It looked like it was and I pushed on all of them when the engine was off. The problem was that I spent last night and this afternoon changing plugs, the fuel filter, I pulled apart the coil packs and cleaned them and checked their resistance. When I cranked the truck after swapping everything it was still shaking. Then I started unplugging the coil packs while the motor was running. I spent 7 hours when the problem took 5 seconds to fix. I just always work harder than I need to. The good thing is that I know I have good plugs, a new fuel filter, the coil packs are fine. I ran a bead of di-electric grease around the boots where they enter the head so no water can get on the plug.

 

[1990stanggt]

Glad to hear you got yours fixed. I gotta get to work on checking mine out now.

Is the uplugging/plugging the COPS in one at a time while the truck is running the best method to test them? I really can't afford to go to the dealership......

 

[x_man586]

Doing it that way will definitely tell you if one is shot. I pulled them off and used a volt meter to measure continuity. Set the meter to ohms and touch one lead to each of the little prongs. You should get a really low number. All of mine showed .6. Then leave one lead touching the prong and touch the other one to the spring in the boot where the spark plug connects. A stock coil should be 5. something. Mine were either 5.6 or 5.7. The big thing is to make sure they all read about the same. Kind of like a compression test. If all of them are about the same and one is way off that one is probably bad.

 

[1990stanggt]

Thanks for the tips, I'll grab a multimeter and try that this weekend!

 

[1990stanggt]

Great News!!

I went ahead and tried the plugging/unplugging test and located two bad COPS. I replaced them a little while ago and it made a HUGE difference in how smooth the truck runs. If anyone at all is having similiar issues, CHECK THE COPS!!! I can't believe how much better the truck is running, especially under light to mid throttle. I do think I still have one bad COP due to it being rough in a small range of throttle, but, I have a sensor to replace first! Great advice everyone! :rockon: