What the heck is wrong with my truck? It will run great for several days, sometimes several hours and other times just won't start. It will run great then all of a sudden start chugging and sputtering while belching out black smoke out the exhaust. Sometimes when it stalls it will not restart. Has been towed home on a number of occasions. Several days later it will start like it was never screwed up and run fine. It even passed NJ state inspection (at a time it was running ok) that is performed with an emissions dyno run. I have replaced: ignition module on distributor, MAP sensor, plugs, wires, cap, rotor, and several other sensors little black thingies. I'm thinking the CPU but have not replaced it yet due to cost, but thats the next step. Has anyone come across this behavior in their truck? And if you did, what steps corrected the problem. The erratic/intermittent nature of this problem has me going nuts. Thanks in advance for any advice.

OBTW it is a 1988 F150 w/5.0 automatic

 

does your computer need resetting?
Disconnnect negative terminal and turn ingition to 'on' and turn the headlights on, and let sit for a half hour. Then turn lights and ignition to 'off' and reconnect battery. Then start truck and drive for 20 mins or so.

 

Sounds like you narrowed it down to the culprit, a bad computer. Perhaps it is loose and not grounding correctly. That is usually a cause of intermitten things. Check all of your electrical connenctions, battery, alternator, computer. If anything pick up anpother computer at a junkyard, they may let you test it to make sure it works with your truck

Good luck

Brian

 

I say bad Disturbtor or TFI module.The hall sensor in the dist might have gone south.

 

Thanks for the advise. Tried pulling the batttery cable off etc. Didn't help. TFI module has been changed. Computer I guess is next. Not sure about the distributor itself. May be worth a shot. I'll keep on plugging away.

 

I dont want to sound like a smart *** but I think maybe you guys are on the wrong track with the ignition related probs. If it is blowing BLACK smoke while the problem is occuring then we know that there is way too much fuel getting to the cylinders. We also know that it is getting partially burned because it is black. If we just had a bad miss we would get very little noticable smoke. My guess would be a bad connection on the coolant temp sensor. Maybe a bad sensor itself. I believe when the temp is cold the voltage getting back to the ecm is low. So if you have a connector not sufficiently connected and you get no voltage to ecm, then the ecm is going to see very cold engine temp and pour the fuel to it. If I were you, I would check the wiring from the ecm to the coolant temp sensor. Or just pull on the wires while the engine is running smooth and see if you get any changes. You might just wiggle all the wires up under the hood and see if you get any changes. When the truck does this again, and doesn't restart, plant you foot to the floor and crank it for about 30 seconds or so. Then let the starter rest a while. And do it again. Then wait a while and start like normal without any action of the pedal. If it does start back up, then you know for sure you are getting a flooding condition. What you are doing by doing a WOT at crank is actually shutting the fuel supply completely off. This is designed like this from the manufacturer just for the sole purpose of clearing floods. Your truck has probably never had this prob when the engine is cold has it? Hope this helps ya.

 

It could be a bad fuel pressure regulator. I've seen these stick closed causing the fuel pressure to go way higher than the normal 40-50 PSI. Too high fuel pressure will cause the injectors to flood & will cause rough running & black smoke. The next time its doing this connect a fuel pressure guage to the fuel rail & read fuel pressure,if its too high, like near 90-100 PSI then the pressure regulator is bad.

 

Good thinking Tailgator, i would definetely check that as well.

 

I believe when the temp is cold the voltage getting back to the ecm is low. So if you have a connector not sufficiently connected and you get no voltage to ecm, then the ecm is going to see very cold engine temp and pour the fuel to it.


Here are some sensors and data to look at on a hot engine.


Typical Diagnostic Reference Values
SENSORS/ INPUTS Signal Pin # KOEO Units HOT IDLE 30 MPH 55 MPH Units
TP 47 .58-1.3 DCV .58-1.3 1.0-1.2 1.2-1.4 DCV
EVP 27 .3-.4 DCV .3-.4 .6-1.3 .6-2.8 DCV
ECT 7 .5-.7 DCV .5-.7 .5-.7 .5-.7 DCV
IAT 25 .7-2.8 DCV .7-2.8 .7-2.8 .7-2.8 DCV
MAP 45 157 Hz 106-110 112-122 118-138 Hz
IDM 4 0-12 RPM 750-850 1250-1480 1600-1750 RPM
PIP 56 0-12 RPM 750-850 1250-1480 1600-1750 RPM
HO2S 29 0 DCV switching (4) switching (4) switching (4) DCV
FPM - red 8 0 DCV VBAT VBAT VBAT DCV
ACCS 10 0 DCV VBAT (1) 0 0 DCV
PSOM+ 3 1 MPH 1 30 55 MPH
CPP 30 5.0 DCV 0 (2) 5.0 5.0 DCV
STI 48 5.0 DCV 5.0 5.0 5.0 DCV

 

Thanks guys for all the info. There are some very good ideas here. Looks like we might have a break in the weather this weekend so I'll have my work cut out for me.