I have a 1988 F-150 4x4 5 speed manual with the 302 motor. I have owned it about 3-4 weeks and have only had one problem and it now has the truck where it will not start. Let me give you the details and see what you think.....

When I would drive it around town here and go over decent size bumps while accelerating it would hesitate while going over them but instantly clear up when I got clear of them. It would not buck, backfire, or anything like that, it would just act like it momentarily lost power. Then yesterday as I was coming home from work it did it but this time it just quite all together. I went over the bump, it hesitated and then went into limp mode and then just wouldn't run all together. I had it towed to my house and worked on it a little last night. It will turn over, no problem there. I replaced the fuel relay pump, no good. I replaced the external fuel pump, no good. At that point it was late and I went to bed. I looked for the inertia switch in the left kick panel but could not find it. Did these models have one, and if they did where in the world is it?(lol) Any ideas of what I could check would be appreciated. Thanks.

 

hmm sounds kinda like a loose connection possibly. i would start looking at the ignition. see if any ries are broken, disconnected. also check all the other connections too. since your in there i would replace your cap/rotor/plugs/wires also. did you also test for fuel pressure? easy way to test is press on the schrader type looking valve(looks like a valve on a tire) on the fuel rail and if it sprays out then you have pressure. thats my 2 cents. good luck

 

oh and yes they did have an inertia switch. but the inertia switch wouldn't make your truck seem powerless then regain power after a bump. it would shut down completely. you would have to reset it and if my memory serves me correct it will throw a check engine code for the inertia switch.

 

I believe the inertia switch is behind the right kick panel.

 

Mine is located on the firewall just to right of where the cab harness plugs in(black case with a red pop-up button).
I would look for loose or corroded grounds, especially on the computer and on the back of the intake manifolds, there should be one on each corner and the bolt to the firewall. There is a ground near the computer plug on the engine compartment side and the case of the computer behind the Left Hand kick panel is grounded by mounting contacts.

 

Not all trucks will have fuel pressure at the rail. Mine doesn't, and it runs fine. It only has fuel pressure when the truck is running. I have a problem with the fuel returning to the tank, which causes it.
I'd look at the inertia switch first, then the ignition. Check all the wires going to your distributer.
Good luck.

 

Well, you have to have spark and fuel for it to run. Before you throw any parts at it, or any more, check for spark at plug wires. If you have a good hot blue spark, then move to fuel. Check pressure at the rail. Just pressing the shrader valve doensnt show theres much for pressure, it would squirt out even just at 5 psi. Put a gauge on it and look for 35/40 is pressure. If you have pressure, check for injector pulse. Put a NOID light on the injector plugs, and crank it. It should flash for each signal to that injector.

 

Thanks guys, I'll give these suggestions a try here in about another hour once I get off work. Maybe I've knocked a ground off somewhere. I'm gonna get out a test light and check the connection on the external pump I put on last night. If I don't have any power there I guess I will have answered my first question in many that will need answering. Hopefully I will have some good news before the night is over. If anyone else has any more suggestions please feel free to add to this thread. Thanks guys.

 

You will not find any power at the pump after the key is turned to run for one second.
Look under the EEC Power relay for bad wiring.

 

on an 88 the inertia switch i above the steering coumn under the dash.

 

quit screwing around with the inertia switch. It's not gonna reset itself anyway.

go wiggle the wires that go to the distributor. might even want to tug on them a tad (don't ask me how I know)

 

actually the connector could be loose or corroded on the inertia switch.

 

I have the same problem with my 1990 5.0 Mustang LX, I would hit a bump and it seeemd like everything would momentarily shut down, lights would come on in the dash like I had just started it..air bag, etc. Then it would come right back to life. I thought I had a clogged fuel filter, replaced that and it was still doing it.
I am following these posts with great interest because I have not yet fixed it and it could possibly be one of these solutions. Let us know if you discover what it is Mob, mine hasn't died completely yet, but the inertia switch with bad connect could be my problem (if there is one in the LX), it does it sometimes when I make a hard U-turn also. Damn complicated machines....but I love em'.

Johnny



1988 Ford F-150 Custom 4.9L 4 speed with solid alloy Ford wheels
1990 Ford Mustang LX 5.Whoa Hatchback AOD
1993 Ford Mustang LX coupe 5-speed


..................................God Bless Henry Ford........................................

 

every fuel injected vehicle has an inertia switch.

also the ignition actuator in the steering column could be bad.

 

Just wanted to update you guys on what ended up being the problem......

A wire running to the battery got pulled off due to the battery not being secured to the mounting plate on the truck. The battery was bouncing around when I was hitting bumps and just eventually came loose from it. I didn't spot it because it broke loose right there at the clamp and fell down beside the fender area, so I just looked right over it. I did end up finding the inertia switch, it was attached to the firewall just left of the steering wheel. I checked it and (of course) found it okay. Thanks for the help guys, just thought I would update this just in case anyone else just happen to have this problem.