Truck is having ignition problems..any thoughts?
03-11-2013, 10:43 AM
#1
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Truck is having ignition problems..any thoughts?
So 2 years ago when I got the truck (98 f150 4x4 4.6 auto) I was getting a #4 misfire and after some diagnoses I came up with a bad coil, fixed the problem.
Well the truck just hit 170K miles and got pretty dirty this winter so I spent a day cleaning it last week and checking it over.
I washed the motor compartment down like I did many times before and blew out the standing water off the motor and it started running like crap!
Turns out I had a cyl 4 miss fire (same as before and acting like it did 2years before) so I replaced the coil and it still runs like crap but goes away after a few miles.
It was sitting for a week when this first happened so any water should have dryed up by now..
Any thoughts on what else it could be?
Well the truck just hit 170K miles and got pretty dirty this winter so I spent a day cleaning it last week and checking it over.
I washed the motor compartment down like I did many times before and blew out the standing water off the motor and it started running like crap!
Turns out I had a cyl 4 miss fire (same as before and acting like it did 2years before) so I replaced the coil and it still runs like crap but goes away after a few miles.
It was sitting for a week when this first happened so any water should have dryed up by now..
Any thoughts on what else it could be?
03-11-2013, 01:21 PM
#2
Ford Owner
I have a theory. When you washed your engine, did you jiggle the heater hoses in the back next the number 4 cyc and firewall. These heater hoses have quick disconnect fittings on them and as they get old the plastic breaks causing small leaks. These leaks can result in coolant getting into the number 4 plug socket and it heats up, causes steam, and moisture at the plug wire. You say this is a 98 so your have two coils with plug wires between the coils and the plugs?
See if you can feel any leaks from the heater hoses. Also, take out the plug wire, clean the contact on the plug wire. Either take out the plug and clean the socket and plug or just try to put a rag down in the socket to clean it as best you can. Make sure your plug has not come loose. Put a little permatex di-electric grease on the plug wire contact and put it back together.
If your truck runs great for a while and then starts missing again, you have either oil or water getting down in that plug socket. The oil comes from a leaking valve cover gasket, the PCV valve area, or someone not using a funnel when they add oil to your truck. The water nearly always comes from the heater hoses. It could, however, come from a blown head gasket or a leak in the radiator hose. If it is a blown head gasket and water is leaking inside they cylinder, it will run bad no matter what.
You said that you previously changed the coil and it ran great for a while. Based on that, I would look real close at the possibility of a coolant leak.
This is a link to a drawing of those quick disconnect fittings
http://www.f150online.com/galleries/...3442-87148.jpg
That ring on the bottom piece in the drawing is made of plastic and it commonly cracks when it gets old. As such, the tabs on the top piece are not tight when connected to the heater core. To remove, press the tabs on the top piece and pull the disconnect and hose off the heater core inlet and outlet. If you do everything right, it should pull off easily. To reinstall, assemble the o rings, top piece and bottom piece and push the assembled disconnect on the heater core. I add a little grease to the inlet and outlet to help them slide on easily and better seal the o rings for zero leaks.
See if you can feel any leaks from the heater hoses. Also, take out the plug wire, clean the contact on the plug wire. Either take out the plug and clean the socket and plug or just try to put a rag down in the socket to clean it as best you can. Make sure your plug has not come loose. Put a little permatex di-electric grease on the plug wire contact and put it back together.
If your truck runs great for a while and then starts missing again, you have either oil or water getting down in that plug socket. The oil comes from a leaking valve cover gasket, the PCV valve area, or someone not using a funnel when they add oil to your truck. The water nearly always comes from the heater hoses. It could, however, come from a blown head gasket or a leak in the radiator hose. If it is a blown head gasket and water is leaking inside they cylinder, it will run bad no matter what.
You said that you previously changed the coil and it ran great for a while. Based on that, I would look real close at the possibility of a coolant leak.
This is a link to a drawing of those quick disconnect fittings
http://www.f150online.com/galleries/...3442-87148.jpg
That ring on the bottom piece in the drawing is made of plastic and it commonly cracks when it gets old. As such, the tabs on the top piece are not tight when connected to the heater core. To remove, press the tabs on the top piece and pull the disconnect and hose off the heater core inlet and outlet. If you do everything right, it should pull off easily. To reinstall, assemble the o rings, top piece and bottom piece and push the assembled disconnect on the heater core. I add a little grease to the inlet and outlet to help them slide on easily and better seal the o rings for zero leaks.
Last edited by Frank_Ford; 03-11-2013 at 09:12 PM.
03-13-2013, 02:33 AM
#4
Senior Member
Since the inception of OBD II computers in 96, water has become the worst nightmare for our engine compartments. The manuals all say NOT to wash down the engine compartments with water. Too many electronic connections and corrosion possibilites caused by water.