This is topic Backfiring F-150 in forum Tech Talk at Northern California Ford Owners  .


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Posted by ilikefastcars (Member # 3479) on :
 
I followed the link for the I Love Mustangs thread here from www.zcar.com I think the thread is pretty funny. Anyway, I have a 99 F-150 with the 4.2. It backfires when I accelerate. First I pulled the injectors and took them to a shop to be cleaned and tested. When that didn't cure it I pulled the heads thinking that maybe a busted valve spring was causing the burn to blow by on the power stroke. All the springs were good. Then I pulled the front cover and checked the cam. That was in time and no slack in the chain. I'm still getting the backfire. The exhaust was replaced 25,000 miles ago by me due to leaks and a broke exhaust manifold. The engine doesn't use a drop of oil. I even did a complete tune up new plugs, wires, filters, oil, coil/distributor pack. The fuel injection timing and spark timing is controlled by the ECU and there were no codes present. Any ideas? This really has me stumped because it's fuel injected and not carbureted. Honestly this is the first late model fuel injected ECU controlled vehicle I've seen backfire. That's why I assumed it was a hard part. How do I figure out if it's a line of code or a sensor? I even replaced the timing sensor on the crank and the oxygen sensor. To be blunt I have reached the point where I am throwing parts at it. Can anyone suggest a more scientific approach?
 
Posted by 99gt-UJSTLST (Member # 584) on :
 
when does it back fire
at idle, on the road, or when you let off he gas ?

also does it back fire from the intake or exhaust

how many miles does it have

and whats the last thing you did to it before it started to back fire
 
Posted by ilikefastcars (Member # 3479) on :
 
quote:
Originally posted by 99gt-UJSTLST:
when does it back fire
at idle, on the road, or when you let off he gas ?

also does it back fire from the intake or exhaust

how many miles does it have

and whats the last thing you did to it before it started to back fire
It backfires loudly evertime I accelerate. Kind of embarrassing actually. It sounds like it's coming off the left (drivers side) bank exhaust.

It has 85,000 miles on it.

It started to backfire right after I towed a 8,000 lb trailer from Dallas to Oklahoma City. I thought maybe I bent or broke or warped something but every part I took off I checked with a Snap-On straight edge, feeler gauge, or a dial gauge. Everything seems fine. I left it out of overdrive, ran the engine at 3,000 rpm, used the cruise control, and watched my gauges. Truck didn't even come close to overheating.
 
Posted by Jdub07 (Member # 2728) on :
 
Does it "hesitate" when accelerating? I have never heard of backfire when accelerating before. What about your fuel system? filter maybe...hopfully its something easy.
 
Posted by Black94 5.0 (Member # 655) on :
 
Sorry, I dont know much about the 4.2 V6 engine, but when an engine back fires the main cuases are bad timming or an exhaust leak....

Check and see if all the smog equiment is working..Like the EGR and the diverter valves comming off the air/smog pump...

Good luck! [patriot]
 
Posted by ilikefastcars (Member # 3479) on :
 
OK, I'll check the smog stuff. Life was easier before cars had this stuff. When I accelerate the engine stumbles and then theres a loud bang/pop noise and then the truck accelerates like normal. I changed the fuel filter 1,000 miles ago. It's a Motorcraft just like everything else on the truck. I've used Super Premium gasoline since new because I tow and haul frequently with this truck. I only use factory replacement parts so it kind of surprises me that the truck acts like this. This truck doesn't even have a distributor I can turn to fiddle with the timing. The timing is controlled by the ECU right?
 
Posted by 99gt-UJSTLST (Member # 584) on :
 
quote:
Originally posted by ilikefastcars:
OK, I'll check the smog stuff. Life was easier before cars had this stuff. When I accelerate the engine stumbles and then theres a loud bang/pop noise and then the truck accelerates like normal. I changed the fuel filter 1,000 miles ago. It's a Motorcraft just like everything else on the truck. I've used Super Premium gasoline since new because I tow and haul frequently with this truck. I only use factory replacement parts so it kind of surprises me that the truck acts like this. This truck doesn't even have a distributor I can turn to fiddle with the timing. The timing is controlled by the ECU right?
one more thing to try is the fuel pump, maybe its not working properly, and your not getting enough fuel
 
Posted by ilikefastcars (Member # 3479) on :
 
That's a good idea! I'll put a pressure tester on the Schraeder valve and see what it says. If I post the PSI will somebody here be able to tell e if it's good? I don't have a specification book for my truck.
 
Posted by ilikefastcars (Member # 3479) on :
 
OK, the trucks fuel pump makes 58 psi from idle to redline. I ran the truck for twenty minutes and monitored it just to be sure. Is this enough fuel pressure?
 
Posted by st5150 (Member # 51) on :
 
Have you checked the computer for codes? I'm not familiar with your engine, but overly retarded ignition timing will cause back fire durring acceleration. does your motor even have a distributor?
 
Posted by JEO (Member # 2918) on :
 
load test your ignition coil. put it in drive and step on brakes at the same time and load it up and see it it starts missing. try that also.
 
Posted by ilikefastcars (Member # 3479) on :
 
No coil and no distributor. It's that coil pack thing. I wanted to turn the distributor to see if that made it go away but I couldn't. The distributorless ignition coil pack is brand new Motorcraft. I replaced it just for the heck of it. Along with new plugs and wires. The ECU has no codes. I even checked all the fuses. I also disconnected the battery and taped both terminals together overnight to give the ECU a hard boot.
 
Posted by JEO (Member # 2918) on :
 
maybe you flattened a camlobe on your cam!
 
Posted by ilikefastcars (Member # 3479) on :
 
Is there any way to check for that without pulling the cam out of the engine?
 
Posted by st5150 (Member # 51) on :
 
You really went overkill on the ECU. Simply disconnecting it for ~20 seconds is more than enough. You could have a dead or weak coil pack.... but its really just guess work until you pull the codes from the computer.
 




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