I need help! My 1999 F350 V10 6.8L is sputtering, backfiring, and lagging at low speeds and when taking off. Once I get above about 15-20mph it smooths out and runs perfect. Sometimes it even makes the tranny jump and shift hard. If I turn it off and then back on it will usually fix the whole problem. I just had the transmission serviced, the gasket between the tranny and transfer case replaced, oil is clean, replaced EGR valve, EGR vacuum solenoid, DPFE, Cleaned air intake system including MAF sensor, replaced fuel filter, and replaced vacuum lines to PCV valve. I have no idea what is causing it! It has no check engine lights. The olnly lights I have had are speed sensor, and EGR low flow. Both are gone now.

Any ideas?

Thanks,

James from Texas

 

A good recheck of all the vacuum lines you removed might reveal something you overlooked.

 

Yeah I did that because it was doing this before I replaced them.

 

Is the engine backfiring into the exhaust or into the intake?

As you have probably learned from this site. The coils on these vehicles are giving a lot of people heartburn. I would suggest you make sure the coils are making good connections with each spark plug. This requires removing each coil and checking the spring contact from the coil to the spark plug . I have seen the contact where the spring makes contact with the coil secondary tab on the coil get corroded from moisture intrusion. Try the easiest ones first and see if you notice any difference. The contact has to be good and positive.

 

I here it in the engine compartment more so than the exhaust

 

Ok i will try it

 

Sometimes if the EGR valve is receiving vacuum when it should not that can cause problems similar to what your vehicle is giving. A quick check of disconnecting the vacuum hose from the EGR valve and plugging it will eliminate that as a possible cause. This may cause the check engine lite to come on. but after reconnecting it the light should go out. Unless you have found the answer to the problem, this may help.