1988 F150 problem....

[FordGuyF1504X4]

Ok I have a 1988 f150 302 4x4 auto.. I got the truck and was told it needed a new fuel pump.. Well it was the fuel pump relay that was bad but the pumps were weak so I went ahead and put a new pump in the tank and on the frame... Got the correct pressure now.. But to my problem... My drive to work is 15 miles from my house and when I am 1-2 miles from work or on my way home it starts to run really rough like its only hitting on a few cylinders.... Also the smell of raw gas is strong... After it sets for a hour or so it will start up and run great.... I put in new plugs, coil, cap and button replace module and pick up coil in the distributer... and still acts up... The check engine light comes on for a few seconds and goes out when its running bad... Any ideas?

 

[5.0Flareside]

first and foremost easiest thing to do to start off with is pulling codes. you can either buy a cheap OBDI code reader or go to Fordfuelinjection.com to learn how to pull them yourself with a paper clip.

but after all that the only thing i can think of is maybe you got the plug wires in the wrong firing order. yours needs the older 5.0 firing order thats different than the 351W and 5.0HO and post 94 5.0 order.

 

[FordGuyF1504X4]

Well I would pull the codes but on the truck the self test plug is there but the single self test input is not... (Another mystery of this truck) ..... And the plug wires are in the right order... Like I said it runs great but after about 13 miles of driving it just starts to mess up..... Then a hour of so later after it cools down it will start and run fine....

 

[5.0Flareside]

ok next thing i can think is a fuel filter. cause i know that if the fuel filter is dirty and it gets heated up the gunk gums up and does let the fuel run freely to the motor.

 

[FordGuyF1504X4]

Changed them when I changed the fuel pumps....

 

[5.0Flareside]

hhhhmmmmmm..... heck idk. are your gauges showing anything weird. like high water temp or low alt. output. etc. but it still sucks that you cant check codes. that would make it tons easier to figure this problem out.

 

[FordGuyF1504X4]

My gauges are all working and not showing anything odd... Water temp is normal... Keeps great oil pressure.... And charging is good.... Yea the wire missing really sucks... I borrowed a tester from a friend and went to hook it up and couldn't find the STI wire....

 

[5.0Flareside]

ok. well that elimates it getting hot and cutting out. and oil pressure dropping causing it to run rough. what bout your vacuum hoses?

 

[FordGuyF1504X4]

All the hoses look fine... None look dry rotted or cut... I have looked at just about everything.... I did have a buddy just say that it might be the MAP Sensor making it run this way......

 

[5.0Flareside]

thats what i was fixing to bring up next. cause if wasnt anything simple like ive been naming wont solve it its just bout gotta be the MAP sensor

edit. had to find this i had read it a few weeks ago. this is an easy way to test the MAP sensor.

To test the MAP, unplug the ELECTRICAL connector, not the vacuum and go for
a ride. If it is bad it will run better when unplugged. Plug and unplug with
the key off.

 

[FordGuyF1504X4]

I just read in my shop manual how to test them... I will give that a try tomorrow... I will post back with my findings...

 

[5.0Flareside]

how does the shop manual tell you? cause i know of unplugging the electrical connector. Prior post....

 

[FordGuyF1504X4]

It says "using a tachometer probe the backside of the MAP Sensor MAP/BP SIGNAL wire and SIGNAL RETURN(ground wire) and check for frequency voltage. It should be between 300 and 320 rpm depending on the altitude"

It says alot more but I would be here all night typing...
I have a Haynes Repair Manual Page 4-21

 

[5.0Flareside]

thats complicated sounding. like i previously post you should just go for a ride with the electrical connection unplugged and see how it feels after the 13 mile mark.

 

[FordGuyF1504X4]

I will take it out today and play around in the snow...

 

[5.0Flareside]

let us know how it goes.

 

[gonente23]

ya

Ya i would check the map sensore to i had worked on a 91 f150 that had that same problem and i went through all those porsedures and eventualy change the map sensore and it worked. what i do when looking for parts is go to www.autozone.com and create a logina count and ad your vehical and they have a trouble shooting part wear you select three option, sounds like, feels like, and smells like it is realy help and it gives you a list of all the things it could be, also its noce becuase you can look up parts you need with out having to call it will tell you if it is in stock or if its in another store or if its a special order its realy nice check it out, Nathan

 

[Skandocious]

Could be the MAP sensor, but it sounds more like an ICM to me (ignition control module). On your truck it may be mounted on side of the distributor but I believe it should be remote mounted on the drive fender near the firewall. Looks like this:

If yours is gray then make sure you replace it with a gray one. If it's black, replace with a black one. Different colored modules have different signals coming out on the pins and the wrong color will make your truck behave strangely.

 

[FordGuyF1504X4]

I drove it around with the MAP sensor unplugged and it still acted up.. Well It wasn't causing the problem... So when I got home I took the control module off and had it tested at autozone and was bad... It smelled burned..... I put a new one on last night... I will see show it runs this morning on my way to work....

 

[wizzard351]

not bein around the truck id have to go with skan's idea or mabe the ignition coil is goin bad, when it acts up stop and touch the coil(shut truck off 1st) and see if its hot if it is replace