1990 F250 4x4. 5sp manual trans.


ok, i have decided to keep my FI. now i have problems. this is what i have done; changed cap, rotor, plugs and plug wires as they looked bad (burnt, cracked...) i found some bad vacuum lines and replaced. antifreeze is up in radiator. i cleaned the first half of the IAB, and sprayed brake cleaner followed by carb cleaner in to the second half and blew air into it till stuff came out looking clean out of throttle body.

i go and start it and does the same as it did before i started replacing bad finds. i have to feather the throttle to make it run. once warm it will idle rough at 500 rpm, i push on the gas and rpms don't go up unless i "pump" the gas pedal and when i get the rpm up say like 3,ooo and hole the pedal there motor rpm goes down. and i also hear like a backfiring in the motor or in the intakes, meaning i am not hearing it out of the exhaust. i then poped the cap open, remind u it is new, and on the contacts there is like a whitish looking residue.

the check engine light isn't on.

where do i go from here?

am contaplating going back to 80's model f250. anyone want to trade. been at this now for couple of weeks.

 

did you replace your IAC . O2 sensor or TPS sensor? and FPR?
sounds more like the FPR/

chek the fuel pressure at Rail
should be 36 at idle ant 40 at WOT


but before you replace anything else chek for codes if you dont know how here is a helpfull link

http://www.fordfuelinjection.com/?p=13

 

First of all, what engine is this? DJdemon has some good suggestions.

I would start with pulling the codes, checking fuel pressure, and checking your timing. It should be at 10 BTDC but you have to pull the spout connector to check it.

 

no codes are stored. the motor is 351w.

 

Then check timing and fuel pressure.

The timing marks on a 351w are hard to see. You will probably have to crawl under it and use a brush on the balancer to find the marks. They are there, though. Once you find them, mark it with whiteout. Either the bottle kind or the tape kind works great.

Unfortunately, if you don't have the tools you need to test these things, they will cost you about $60 to $80 to buy. I don't think Autozone rents them. I would try to find a buddy or family member to borrow them from.

 

So start with the basics...
Does the motor have good compression on all cylinders?
Are you getting 32-35psi fuel pressure at the fuel rail? 40-45ps with vacuum removed?
Air and fuel filters are clean?
Exhaust isn't plugged?

Check the codes anyway, if it's clear that's fine, but there could be something stored, and if you can't read them or get garbage this may indicate a processor problem.

 

Something is wrong with the timing.

A backfire occures when ignition happens, and a valve is not closed.(intake or exaust.

If your F-250 has a 5.0-302 Motor , your timing should be set at 10* (14* for towing and stop and go driving).

Also pull the vacuum line off of your PCV and plug it with a bolt (or your thumb). The engine should smooth out . All too ofen you can have an internal leak from the PCV allowing to much air into the intake.Don't buy cheap PCV's because of this.

I don't use my PCV at all. I have plugged the back of the intake manafold with a double male brass plumbing fitting and a cap. (Home Depot) Make sure to use hi-temp thread tape.

I left the PCV in the cover and attached a 3" hose or so , run it down to the frame and attach it with zip-ties. It needs to breath, I just let it go in to the air , instead of being sucked back into the intake.

 

noneshere, thank u for the advive on the pcv on the back of the motor. that wasn't what is was but investigating it i removed a vacuum line of the MAP and when i went to start it i forgot to put the vacuum line back on and the motor ran! i hooked the vacuum up and it died. i unhook and it and put my finger over it and it runs. if i unplug the electrical off the MAP, the motor dies. so i am thinking this is my problem, bad MAP.

but why didn't it throw a code? and why does it run with vacuum line off the MAP? and if it is running can i just plug off my vacuum and drive that way or am i going to run into more problems down the road? my guess is if i replace it and it is the problem i will probally get better gas mileage

also can a person throw a code. i unplugged the O2 senor and started it. no code thrown.

 

It shouldn't run at all without the MAP. No MAP, and the computer has no idea how much load is on the engine, how much air is being drawn in, and therefore no idea how much fuel to inject. The fact that it runs without the MAP being plugged in suggests that there are problems elsewhere, possibly in addition to a bad MAP.

When you say there are no codes, are you pulling the codes and getting 1-1 for each test? Or are you getting no response at all? Can you explain in detail how you are pulling the codes?

 

Mine runs without the MAP but idles like a BIG cammed monster!! and smokes black


i think no codes.. so maybe bad EEC??

 

You've received lots of good advice so I won't repeat it.

It's highly unlikely the EEC itself is bad, because they typically work fine or are completely dead. There have been exceptions over the years where the mosfets driving the injectors, EGR, or other higher-current devices pop, but generally it's an all or nothing deal. All things considered they are fairly reliable as far as electronics go.

I am curious about the 500rpm idle... that's quite a bit below the ford recommendation of 700-900 depending on the year. 500 is well in the "stumble and die" RPM as anyone who has forgotten to shift out of overdrive while coasting to a stop would know

Is the 500 rpm figure accurate? A guess? Read off the factory "approximation" tach? Or did you use an external tachometer?

 

Mine dies the second I unplug the MAP. From what I've read, that's what most people's trucks do, and from what I know of Ford's EFI, that's what supposed to happen.

It wouldn't be the first time I was wrong though.

 

i don't know if i am doing the code reading right. i was doing with the wire to the battery and count the blinks. but i get no light. i would like to plug in a regular reader. anyway the 500 aprox idle, yes very low. when i unpluged the vacuum off the MAP the idle jumped to 800 to 900 approx. i am going to get a new MAP tomorrow and see what happens. when i did unplug the vacuum from the Map it had pretty good throttle response and no smoke. would hold an rpm of approx. 2500 using the throttle cable. i will post what happens when i put on a new MAP.

 

Sounds like the code plug ground wire doesn't have a good connection on one end or the other.

 

have you ever reset the computer?