i have an 87 ford f150 4wd, exhaust fell off right b4 the cat, have not got to fix that yet, and now i have a miss fire under load, no backfiring, not sure what to start with


my guess is something with the injectors

 

I would start with putting the exhaust system back into place.

 

What he said X2. Plus the Cats are probably TU and/or the EGR could be burned out.

 

Have the computer scanned to see if there are hidden codes.

 

no cats on the truck and the egr valve isnt hooked up but i think the head gasket just went gonna do a compression test and go from there

 

I would check spark plug gap, it's quick and cheap, head-gaskets, not so much...

Sam

 

just changed the fuel filter, i did a compression test on cylinders 2 thru 6 (my adapter wont fit into cylinder 1 without removing the pwer steering pump) all cylinders are within 20psi of each other averaging 125psi new plugs wires rotor and cap still sounds like my camed 390

 

gapped the plugs at 0.44 still sounds camed and it doesnt go away when reved up or driving

 

No oil in water or water in oil?

It sounds like the head gaskets are ok, here's where I would look:

Check for vacuum leaks, the brake boosters on these can leak really badly, throttle body gasket can leak, any hoses or gaskets that are on or around the intake can all leak and cause trouble. EGR could certainly be bad.

Also, is the thermostat bad? A new one (195* only) can make a massive difference, so can temp senders.

Are you sure that the plug wires are all good? Also check the timing and make sure the spout connector is unplugged when you do.

I just worked on an 87 F150 (i6) that had similar problems, turned out to be a combination of bad brake booster, bad thermostat, bad EGR valve and a bunch of miscellaneous gaskets.

Good luck man!

Sam

 

that sounds likley, i just bought the wires and put my timing light on them they all work, there is no water in the oil i checked numerous times today, i will start lookin at vacuum leaks and the egr....not sure how to test them but ill look it up, i never thought about the thermostat ill replace it tomarrow...ill do the timing right now, i dont understand this spout connector u mention

 

well i cant say much about the timing, there are no timing marks or resemblance of timing marks on the harmonic balancer so i just turned it till it started loping faster, sprayed some brake cleaner in the intake with it on high idle and now it actually has rhythm i also put a stethoscope on the injectors they sound slow compared to the engine, as far as vacuum leaks there is so much air flow and noise i cant pinpoint anything so im going to look into an emissions delete kit and some vacuum hose see what i can get. gonna try and test the injectors tomorrow.

 

Here's what I like to do to check for vacuum leaks, I take some carb cleaner and just start spraying around the gaskets, hoses, EGR valve brake booster and such, and if it smooths out when you spray one spot, you've got a leak.

Is there also a loud tapping, like a lifter tapping? A push rod could have jumped out of the rocker, that would definitely make it miss.

Sam

 

omg the pushrod makes a lot of sense, ill pull the cover tomarrow morning, and ill spray her down, any ideas on testing injectors while still in the head my intake will b off anyway might as well test them while its off

 

well got the intake off and number one cylinder had an exhuast valve stuck open and a bent pushrod...ended up finding a 77 300 in my price range and now shes on my trailer to say the least, bought a new ignition module and scavenged the distributor/coil to ignition module wiring harness from a 400m but theres 2 wires from my ignition module unaccounted for. one is red and 0ne is white, according to my hanes manual, the whit one is supposed to b blue and go to the alternator regulator and the red wire is supposed to go to the S terminal on my starting solenoid. im want to make sure it runs b4 i put it in my truck. any ideas

 

Ouch, do you know what stuck the valve?

Also, do you plan to run fuel injection or carb on the new motor?

Sam