Have a 1998 F150 that just started to backfire and will barely do 30 MPH. Haven't checked anything yet, but is there something particular that suddenly cause such an event. I read through the threads and saw one dealing with backfire on a 1996 which the individual found out the battery was at fault. What is it with a battery that could cause this effect? Any help anyone!

 

I'd start with a general tune-up.......plugs, wires, cap, rotor, injectors, air filter, throttle body....etc.

 

Hi Guny and welcome to FTE

What size engine in your truck? How many miles? Has it had a tune-up?

 

I've done the tuneup route! And things did get a little better, but still not drivable no power of idle, will not accelarate. Things I've changed are both O2 Sensors; Fuel Filter; Air Filter; Plugs (these were in real bad shape). This vehicle has coil backs so there is no distributor. I've checked the fuel pressure and it is 31 psi at idle and 41 psi with vac hose detached. Engine idles beautiful and will accelarate if I playing with throttle. It will rev and then act like it runs out of gas and starts to bog. I'm looking at the fuel pressure when I am coxing the throttle to accelarate and pressure increases as throttle is opened to around 40 psi, but engine continues to bog; I'll back off throttle and the engine seems to recover, but then as soon as I start opening the throttle it starts to not want to accel. Sometimes I can *** the throttle and get the engine to rev steady at about 3,000 RPM, but eventually it starts to bog. It's not backfiring any more, but there is no power off idle. I've tried disconnecting and plugging vacuum lines some lines cause some difference in engine run but the off idle bog is always there. Exhaust gas coming out of tailpipe seems forceful at the times I was able to *** some RPM; it blows fallen leaves on my lawn a few feet. I don't see how exhaust blockage could be a problem. I'm thinging it has something to do with timing advance, but then why no back fire? Electronics are great until they start going batty! I cleared the codes from the computer by disconnecting Battery, and no new codes have appeared... of course I haven't tried to drive it.

I was hoping some one would recognize the symptom and how they fixed there similar problem. Can anyone advise anything else to try.

 

I would first clean the mass-air sensor. Then I would suspect the TPS sensor could be bad. It is what tells the computer how much fuel and timing to give when accelerating.
Jimmy

 

If the plugs were real bad maybe a cat or cats are now plugged and the engine can't rev over it. Since your fuel pressure isn't dropping off, but it sounds like its starting to loose it, bang on the cats and see if any are loose or rattling inside.

 

I am not sure if this is related to your problem or not, but I recently had my 2000 F150 5.4L in the shop for a bad coil. The truck would start and idle. You could drive it, if you wanted to feel like a milkshake. Trying to do a slight acceleration, the entire truck would shake and rattle the change out of my dash cup holder. The dealership told me it was a bad coil and one of the plugs was finger tight.

Hope this helps!

-dave

 

Sorry I forgot to mention its a 4.6 L.

Replaced The Spark Plugs and yes they were in real bad shape more the .100" gap on all of them due to electrode and graound tang wear. Check spark jump on a snap on tester and spark in blue, strong, and jump a gap of .250 (1/4").

I removed EGR to check for blockages and leaks. All looks good EGR opens when vacuum applied and holds. Plunger moves open and closes normally with vacuum application and release. Blew shop ait through EGR tube and DPFE sensor hose and all seem open. Starting to test each sensor for related input output signals, ground, etc. Will try removing "SPOUT" shorting bar next to see if PCM is controling spark timing.

Guny

 

I check the Battery Voltage, ohms, reference signal, ohms, etc. of the various input / output sensors. The unit that would most likely cause the effect and that was not displaying the proper output voltage was the Mass Air Flow (MAF) Sensor. Voltage across the YEL / RED (sometimes BLU / RED) and the BLK / TAN (ground) wire at the MAF harness (via back probing) should be 0.2 - 1.5V at idle and move up to 2.0V as engine RPM is raised. Engine warm in closed loop status. It was rather difficult to get RPM out of the vehicle particularly with all the other issues it had (i.e. worn out spark plugs, etc). With all the routine maintenance issues taken care off I was able to coax the throttle to increase RPM long enough to confirm a suspension that the MAF sensor was at fault. I took a closer look at the HOT WIRE filaments of the MAF and could see that some kind of debris got onto the at least one of the two filaments and burned (melted) on to it. I tried gentle cleaning, but in the end replaced the MAF ($60.00, remanf.). After replacing the MAF the engine would rev normally. Took the vehicle for a test drive and got whip lash acceleration. This issue was not showing up as a Check Engine light trigger. After fixing all the preventive maintenance issues, which had been neglected by the owner; the check engine light was not coming on even though the vehicle was not performing properly. The vehicle was acting as though the throttle was only being barely opened, even though half or more throttle actuation was being applied.

At-a-boy Guny!

Oh! and Lxman1 for the MAF suggestion, and Jeremy for the tune-up reminder.

Keep it tuned and save yourself a big surprise $$$. That dirty air filter let something get through and on to the hot wire elements of the MAF!

 

Thanks for letting us know what fixed it

 

Glad to help, and glad you got it fixed.
Jimmy