Got a 88 ford f150 started running like poop last nite seems to be running with choke on, but is fuelinjected so? Im thinking it is not my pressure reg cause in getting like 28 psi and is not peeing gas thru the vac hose. Well atleast it dont appear to. I pulled vac hose off map? sensor by heater motor and didnt change running condition. So im thinking its either that or temp sensor for eec to start. Anybody ever xperence anythink like this?
thanks,allan

 

When was the last time you changed the O2 sensor? I have read that the O2s should be changed every 30 to 40k miles, as they become less responsive over time untill they finally fail. When they fail they usually go one way or the other and tell the ECU the engine is running lean or rich, which causes the ECU to create the exact opposit.

 

O2 sensor won't work until it has warmed up to 600F or so. Does it run fine when cold-then run rich when hot? The temp sensor is easy to test with a miltimeter and basic repair manual-just compare the resistance to what it should be when it's warm. If the sensor is bad and it always is trying to warm the truck up, the computer will continue to dump fuel in trying to get it up to temp.

 

thanks guys, o2 has bout 10,000 miles found a broken vac line to the fuelpressure regulator which might have something to do with it? Anyways i bought a new regulator and fuel filter, and the coolant sensor. going to try those along with new plugs even thou i changed them 2 weeks ago ill post results

 

well wasnt vac hose., im getting steady 28-30 isnt going up and down when giving gas stays steady, so fuelfilter is first then reg then pump. I would think id be running lean, stranger things have happened

 

could it be a leaky or bad injector just spraying fuel so that the FP is low?

 

Do you have the map hose plugged back in? If that doesn't make a difference at all when you disconnect that hose, that is where I would start. The truck shouldn't run if you pull the vacuum line off that sensor when it is running. The 28-30 psi seems to eliminate fuel as the issue-though I don't know the specs it should be within. Do you have a repair manual?

 

the FP should be at ~ 40 psi with no vacuum.

I once miss plumed my MAP on my 88 Mustang Got som vac lines crossed up so that it had no vacuum to the MAP, the rusult was the engine ran extreamly rich like it had a stuck choke, burned my eyes from the exhaust. it ran great at WOT, it took me a few day to figure that one out...

 

no i do not have a manual, but i have the net...lol. Anyways before when i checked pressure it was 35 and jumped to 40 when reving now is steady. I also thought that engine should die when unhooking map and plugging the vac line with finger. there any way to test a map?

 

engine runs ok in a rev but thats bout it. goin to try reg and stuff and if no better then in buyin a map thanks guys

 

the map is much easier to change the the reg...

and about the same cost... try the JY for a MAP... 88-90 is the same one...

 

You can check them by backprobing the wires connected to the map-then compare the voltage to what it should be at that vacuum level. Maybe someone could post what the voltage readings should be for that sensor. I'm not sure on your truck-but on many of them if you leave the vacuum line where it is, and just unplu the sensor, then start the truck-the computer will ignore that sensor and go by all the others. You could try that. Might not start if you do it, but it takes 2 seconds and it's worth a shot before you spend the money.

 

well i changed out regulator and filter, no difference. Tryed the unplugging map and truck wouldnt idle but seemed to have better responce so off to the parts store for a map. I know pressure isnt causing my issues and a map is easy to change. Cant be much else besides the map and the coolant sensor. pressure holds even with engine off so that rules out leaking injector

 

map didnt do it either. im stumped maybe timing chain jumped? lost most of its *****

 

check engine light on?