1997 ford f150 v6 4.2 mis fire code at cylinder 6

Got a serious problem here, hope anyone can/will help! I have a 1997 Ford F150, V6, 4.2. Has about 180k miles on it. I just had a new engine installed. All components off old swapped to new. Put in new spark plugs & wires, ignition coil, fuel injector @ cylinder 6, and a water pump. My machanic is getting an error code that shows a mis-fire @ cyl. 6, (which is why we replaced the plug wires, coil, and fuel injector. When the engine is comming to an idle(stopping at a stop sign),it shakes and shudders like its going to die. When driving, it seems to run great, until you start to slow down. Any ideas as to what this could be? Note: The engine light came on earlier this year, well before the engine replacement, showing the same code. I had it checked at a local shop where they couldn’t find anything. I’m $2600 in to this one which has me over budget already. HELP!!!

The next thing to check is the electrical connector for fuel injector #6.


thanks tester, i’ll have that checked next.

Clean the throttle body bore and throttle plate, and idle air control valve with Throttle Body Cleaner. Clean the MAF (Mass Air Flow) Sensor with MAF Cleaner.
Check the wiring to the ignition coil. Check the smoothness of the ohms check on the throttle position sensor (tps) from idle to off-idle position.

Further checks should be in the Haynes, or Chilton’s, repair manual. There is, also, alldata HD and HE diagnostic charts.

Just a few follow-up questions. The “new” engine means an actual new or reman one correct? Some consider a low miles engine a “new” one, which it is not.

New long block or new short block with cylinder heads changed over?
Should I ask if this new engine was installed because of the chronic never diagnosed cylinder msifire?

If the problem is not the fuel injector wire connector or an ECM fault I believe I would run a compression test at least on that particular cylinder. If the figure is questionable then I’d check every cylinder and possibly start questioning the quality of the new or reman engine.

(I’m just bringing up the compression scenario because it’s possible to have a very weak cylinder which will cause a rough idle and can smooth out when the RPMS are raised.)

Thanks for the advice/info, I appreciate that.

Thanks for the advice and input. I really do appreciate it!

The engine is a reman long block, heads included, from Grooms of Nashville. I had it replaced due to piston damage (broken sleeve) and because of the high milage.

valves do a cyl leakdown.

In theory, a reman engine should not be a cause for worry when it comes to compression. In practice however, anything is possible. When wrestling a chronic performance problem a compression test should always be performed (at least on the one questionable cylinder). The plugs are out anyway so get that possibility out of the way right off the bat.

I’m also leaning towards a wire harness, injector connector, or even possibly an ECM fault (which controls the injector opening/closing) but what could be done is simply connect a vacuum gauge. If there is a mechanical problem (low compression, etc.) then a vacuum gauge will show it instantly. The sad part is that many shops/techs do not use a vac. gauge. It’s one of the most valuable tools around in my opinion, it only takes seconds to connect one to the engine, and cam tell so much about what is going on inside the engine.

A Noid light can also be connected to the injector connector and this will show whether there is a pulse or not.
You can also use a long handled screwdriver as a stethoscope, place the tip against the injector body, and listen to the injector with the screwdriver handle against the ear while the vehicle is idling. You should hear a faint steady clicking sound. Hope that helps.

Again ok, thanks so much.
I will have these issues checked. I will do the screwdriver test. I am in need of a trustworthy shop eqipped with the diagnostic equip. I have a great, honest mechanic, but he does not have all the hi-tech equip. I will post my findings ASAP. I am moving a family member this weekend and thru the week, so time is not on my side. Thanks again.