miss @ cruising speed

[basilfaulty]

I have a 99 3.0 with what seeems to be a miss @ cruising speed. You can be driving along fine and hit a hill and it develops a miss under load. If you accelerate it goes away or if you shut off the OD it goes away. No CEL, almost like a lean miss but I can't find a vacuum leak anywhere. Sometimes it does shudder a little bit just off idle if you take off on a hill and sometimes it seems like it has a miss when you first start it cold but it goes away in a minute. What gives? TPS? coil breaking down?

 

[Rearanger]

You can be driving along fine and hit a hill and it develops a miss under load. If you accelerate it goes away or if you shut off the OD it goes away.

Usually misses under load is electrical issue. When was last time you changed wires, plugs?

 

[adfav1]

i agree,sounds like the same problem i had with a set of year old wires and plugs.the wires were a set from autozone though when i bought the truck.i replaced them with a set of motorcraft wires and plugs and took care of it.

 

[Airmaster]

Check the following, make sure you do the easiest things first when troubleshooting...

Spark Plugs, Spark Plug Gap
Fault in fuel or electrical system
Faulty Spark Plug Wires
Vacuum leaks at the air intake
Uneven and/or low cylinder compression
Fuel filter clogged
Faulty emissions components
Faulty ignition

 

[basilfaulty]

Well I just put the motor in this thing. Other motor ran good just had a bunch of miles and an oil leak. Got this motor in a wrecked truck REMAN 5k miles ago. Put this motor in and started having this issue. I retained most of the original components from the current truck. Upper intake, harness, coil, wires, egr, etc to avoid this problem. Anyhow I got it figured out. It was a combination of a couple things. I put the coil and wires from the donor truck on this, checked and gapped the plugs....solved most of the problem. Still had a slight problem, started looking at egr. Vacuum gauge at idle shows slight vacuum 1 or 2 inches at idle, I thought it should be 0 at idle? Changed out the vacuum controller for the egr from the donor...same reading. Compared egr valves, both work, both hold vacuum, both seal when closed....worked the valves manually the one in the donor is noticeably firmer spring action...hmmm. Changed out the egr and all is good. Original valve getting weak I guess and the new motor had enough pressure to overcome the spring? Ran fine with the original motor. Glad I had all the donor stuff here to experiment.