Stumped??????
 

This one has me baffled and so far haven't found what's causing it.

Here's what's happening: (2000, 5.4 engine)
1. Only in cold damp weather (did not do this all summer)
2. Missing at start up, some times one or 2 cylinders and some time 5-6 and it quits.
3. If it quits, it'll start right back up.
4. If I let it run a bit, some times holding it at 2000 rpm, it'll clear it self and run good.
5. If it does not clear itself, if I rev it a few times to 4000 it will almost always clear and run good. If I don't clear it, it will continue to miss.
6. Once it's running good, it will not miss again and is totally normal for the rest of the day.
7. It has 263,000 miles on it and I changed engines last winter, BUT it did the same thing with the previous engine.
8. This engine has all new plugs, coils.
9. It throws a whole row of codes, electrical right down the row on cyl, 1 or two or 5-6 depending on how bad it's missing that day.
10. One day when it was missing badly, I sprayed about every connection I could find with WD-40 thinking some moisture was in a connection.. no change.
11. I put a can of Seafoam through the fuel system thinking maybe water, but no change there.


I'm thinking bad connection some place like the main engine plug, computer connection, possibly a bad ground ???

HELP, this is driving me nuts!!

Is it a vacuum line somewhere

I would suspect bad plugs wires.

I have seen engines act like this if the motor ground is loose or very dirty. Very easy to check for a bad ground. It will take two people. One to start truck while other takes just one side of the jumper cables( either both red or both black). Connect one black to the battery ground on your battery and hold the other about 1/2" from a ground on the engine and brush it across ground on engine. And have other person crank truck. If you get sparks from the engine to the cable you are bumping on the ground of engine you have a bad ground. Probably could have explained better but it is just something I do, not try to explain. May not be your problem but its free to check.

If it's a bad engine ground, would it start so easily??

Reminds me of when my wife's car had a bad head gasket. It would run rough on start ups and then Smooth out once it burnt all the coolant in the cylinder. It was more of a leaky head gasket so it wouldn't over heat just run rough. A test is cheap to have done so you can rule it out.

Exhaust shows no sign of water, no water use either. Wiring or fuel system, I just have to find where it's screwing up.

Ever figure out the issue? My truck is doing the same exact thing. Gonna change the fuel filter and iac valve and see what happens.

sounds exactly like what my moms car did when it blew head gasket it didn't show water in exhaust or using much water for a little while too but then one day when they were off bout 80 miles from home if all hit the wall with smoke and all

Did you replace the EGR valve or use the EGR from your old engine? I am suspecting the EFR is stuck and all it needs is a cleaning. Also make sure you clean the tube from the manifold to the EGR. If you reach under the diaphragm with the engine running you can feel the EGR move. If it does not move, could be your problem (either the diaphragm is bad or stuck valve).

Also, doesnt cost much to check the grounds for clean and tight. do that also as it is good maintenance even if not the problem. Also check and replace if necessary fuel filter and check fuel pressure.