Ok, this truck is crazy. Have a 99 Navigator and the instrument cluster and PCM was just replaced (3rd PCM by the way, thank goodness it has a warrantly on it). So Im driving down the hgwy and the engine begins to cut back and my mileage and RPM are slashing back to 0 everytime it cuts back ....so then my theft light starts blinking. The theft light goes out but then when I give it gas and get to about 50 mph then it cuts back again. OK does anyone have any idea whats wrong with this puppy now.

 

As with any diagnosis of electrical issues the first things to check would be as follows;
1. Check the battery terminals for tightness after verifying that they are clean.
2. Check all connections from the battery to the solenoids and as far as you can check to.

Have these things been done by you? Dealer techs can be a bit sloppy at times.

 

Yes, thanks Moto, made those checks and everything in tack. I just got word that if the truck is backfiring or cutting back and usually doing it at about 45-55,that I could have an issue on my cylinder 4 plug or coil. They tell me the this could be triggering a throwback causes the theft light blinking since it has only starting rapid blinking when the backfire or cutback happens then it stops but the truck will still cut back afterwards. It seem once the truck heats up all this starts, but if just cracking and starting to drive with the truck still cold, no issues...besides a slight dragging soon as I have driving a good 40 miles and engine has had time to heat up then it starts. I'm thinkking I need to do a full tune up on this puppy and maybe that will handle the issue. What you thinks guys.

 

A good tune will probably cure the problem. I suggest that you find out who the Ford street racers go to in your area, that has a Dyno, because the dealer tune up could cost over $1000.00. Whatever you do get as firm a price as you can first. There are a lot of really good shops in the Atlanta area. That's Ford Country, for sure.

 

This is not a tuneup issue.

You are getting momentary interruptions in the power feed to the PCM.

Look for a faulty PCM relay, faulty cable or wire connection, corroded fuse or distribution box connections, O2 sensors on the exhaust or drivetrain, etc.

 

OK, will swap the PCM relay and check wiring going to PCM...went ahead and did a tune up since I haven't had one in a long time. The hard cut back has stopped and no theft light blinking lately but it still stalls, drags when changing gears between seems like 3 or 4th gear around 50-60 miles and when hitting 70 and holding steady, but if I hit the gas the gear changes and rolls just fine. Any other suggestions. Will let u know if it get better after checking PCM wires, relays etc.

 

ok, so the truck finally goes out again. Of course the PCM is gone and the dealer for some reason can't seem to find the issue and keeps putting in new PCM but not fixing the issue. I have checked PCM connections, under hood power box, battery connections and etc. Some mention the aftermarket DVD, Nav system that was installed could be the issue. Which after careful thinking, the issues didnt start until I changed from the factory radio. Has anyone ever heard of this causing issues. ....So frustrated but trying to get ride of the vehicle, because when the PCM not acting up, it drives excellent.

 

I'm having (and have been for a while now) a very similar issue, and it's seeming to get worse. I've heard some suggestions of a bad GEM module, but until recently it hasn't been frequent enough of an issue to get any real feedback on.

I'd love to hear if anyone has any input and what was found if Yungking gets it fixed too.

Thanks!