84 F-150 Only runs when cold
05-19-2020, 07:08 PM
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84 F-150 Only runs when cold
Hey guys, I just bought this 1984 F-150, Straight 6 4x4 Manual transmission.
I'm a beginner mechanic, so please bear with me.
Problem: It starts fine when cold. Sometimes, I need to crank it, turn the key off, wait 20 seconds, and then try again. It always starts by the second try. Once started it runs good. The idle starts high. After it warms up the idle starts to drop. After a few minutes of driving it will start to stutter, sputter, and die. Once it dies, I can usually start it back up after waiting a minute, but it will die again much more quickly. When the idle starts to drop, the headlights will brighten when revving the rpms. It doesn't seem to be a low idle that is the problem, as it's most likely to die when accelerating. When idling, it will usually die slowly, often starting to die when it resumes a normal (low) idle for a few seconds, then trying to die again.
Here are the results of some testing:
-I started out this morning with a battery charge of ~12.4V. After it died, I let the truck rest a few hours and checked the battery again: ~11.3V. So it seems the battery is draining while the truck runs. Keep in mind that this is after maybe 3 restarts, a couple failed starts, and idling and revving for maybe 20 min. The battery will hold a charge when I charge it using my trickle charger. I also took it into Autozone, and they said the battery seems fine.
-I used a multimeter to check the alternator. When starting the truck cold with no load, it's about 14.2 at the battery posts, and 14.5 at the alternator itself. I did voltage drop tests, one at the alternator battery output bolt, and a lead on the positive battery post. That showed a drop of about .15V. I did a test on the neg battery post, with a lead on the alternator housing, and that shows a drop of about .05V. From what I've been reading, these readings indicate that the alternator should be charging the battery. Once the engine starts getting to a really low idle, and dying, I do see the voltage both at the battery and the alternator dropping down into the 12Vs. When the charge dropped into the 12s, I did another drop test on the positive side between the alternator and battery, and it got up to .25V.
-So I'm still not sure if I have a charging system failure here or not. My friend thought it was more likely fuel/carb related, and that was causing the engine speed to drop, thereby lowering the alternator output.
Couple things I did:
- New battery terminals. The old cable leads were really beat up, and there was a lot of corrosion around the posts.
- Replaced the alternator belts and power steering belt. There was a slight squeal at the alternator that went away when I did this.
- New fuel filter and fuel line running from the fuel pump to the filter at the carb.
- The previous owner put in a new fuel pump, but I haven't done any tests on it.
- I did a visual check of all the fuses, they look normal.
- Put a bottle of Seafoam in the gas tank
A couple things to note, the wiring is a mess. There are a bunch of 20 year old farm fixes, and I think it all needs to be redone. But this will take me a while and I'd like to get this back on the road in the meantime. The vacuum lines are also a mess. I don't see any obvious cracks and such, but there are multiple tubes not connected to anything, with stoppers in the ends. The air filter housing doesn't have any hoses/tubes hooked up.
I also noticed that there was a broken wire connected to the Stator bolt on the alternator. From what I gather, this is supposed to connect directly to the choke heater, and helps in opening up the choke as the truck warms up. The wire looks like it's been broken for a while, so I removed it entirely. I ran it with the air filter removed, and the choke plate seems to be working as my Haynes manual says it should.
And finally, some quick backstory that might help. I bought the truck last week. It ran great while I was checking it out. Started it and shut it off multiple times. After I paid the guy and was getting ready to leave, it would not start, like the battery was dead. I had already paid the guy and my ride had left. The guy said it has a crappy battery, and we jumped it no problem. I left his house, and after a mile or two, I noticed that the temp gauge was all the way hot, like as far right as it can go. I'm freaking out at this point, and pull over to check the engine. I pop the hood, and it seems perfectly cool, and running with no issues. I also noticed that the fuel gauge didn't work either. So I figure the gauges are broken. I haven't had any overheating issues since then. I drove all the way home on the freeway, 1.25 hrs going 65-70, no problems. I was still having problems with the battery that night and the next day. I figured it needed a new battery as it would take a jump. A few nights later, I take it for a drive, side streets, then on the freeway, for a good 1/2 hour. I stopped to top off the gas tank. When I was getting back on the freeway it straight dies while accelerating. To make a long story short, I had to tow it back home. That was the first time it died on me. Since then I haven't been able to drive it more than a couple blocks before it starts stuttering.
Well, I hope that isn't too much for people to read. Any help or direction would be greatly appreciated.
I'm a beginner mechanic, so please bear with me.
Problem: It starts fine when cold. Sometimes, I need to crank it, turn the key off, wait 20 seconds, and then try again. It always starts by the second try. Once started it runs good. The idle starts high. After it warms up the idle starts to drop. After a few minutes of driving it will start to stutter, sputter, and die. Once it dies, I can usually start it back up after waiting a minute, but it will die again much more quickly. When the idle starts to drop, the headlights will brighten when revving the rpms. It doesn't seem to be a low idle that is the problem, as it's most likely to die when accelerating. When idling, it will usually die slowly, often starting to die when it resumes a normal (low) idle for a few seconds, then trying to die again.
Here are the results of some testing:
-I started out this morning with a battery charge of ~12.4V. After it died, I let the truck rest a few hours and checked the battery again: ~11.3V. So it seems the battery is draining while the truck runs. Keep in mind that this is after maybe 3 restarts, a couple failed starts, and idling and revving for maybe 20 min. The battery will hold a charge when I charge it using my trickle charger. I also took it into Autozone, and they said the battery seems fine.
-I used a multimeter to check the alternator. When starting the truck cold with no load, it's about 14.2 at the battery posts, and 14.5 at the alternator itself. I did voltage drop tests, one at the alternator battery output bolt, and a lead on the positive battery post. That showed a drop of about .15V. I did a test on the neg battery post, with a lead on the alternator housing, and that shows a drop of about .05V. From what I've been reading, these readings indicate that the alternator should be charging the battery. Once the engine starts getting to a really low idle, and dying, I do see the voltage both at the battery and the alternator dropping down into the 12Vs. When the charge dropped into the 12s, I did another drop test on the positive side between the alternator and battery, and it got up to .25V.
-So I'm still not sure if I have a charging system failure here or not. My friend thought it was more likely fuel/carb related, and that was causing the engine speed to drop, thereby lowering the alternator output.
Couple things I did:
- New battery terminals. The old cable leads were really beat up, and there was a lot of corrosion around the posts.
- Replaced the alternator belts and power steering belt. There was a slight squeal at the alternator that went away when I did this.
- New fuel filter and fuel line running from the fuel pump to the filter at the carb.
- The previous owner put in a new fuel pump, but I haven't done any tests on it.
- I did a visual check of all the fuses, they look normal.
- Put a bottle of Seafoam in the gas tank
A couple things to note, the wiring is a mess. There are a bunch of 20 year old farm fixes, and I think it all needs to be redone. But this will take me a while and I'd like to get this back on the road in the meantime. The vacuum lines are also a mess. I don't see any obvious cracks and such, but there are multiple tubes not connected to anything, with stoppers in the ends. The air filter housing doesn't have any hoses/tubes hooked up.
I also noticed that there was a broken wire connected to the Stator bolt on the alternator. From what I gather, this is supposed to connect directly to the choke heater, and helps in opening up the choke as the truck warms up. The wire looks like it's been broken for a while, so I removed it entirely. I ran it with the air filter removed, and the choke plate seems to be working as my Haynes manual says it should.
And finally, some quick backstory that might help. I bought the truck last week. It ran great while I was checking it out. Started it and shut it off multiple times. After I paid the guy and was getting ready to leave, it would not start, like the battery was dead. I had already paid the guy and my ride had left. The guy said it has a crappy battery, and we jumped it no problem. I left his house, and after a mile or two, I noticed that the temp gauge was all the way hot, like as far right as it can go. I'm freaking out at this point, and pull over to check the engine. I pop the hood, and it seems perfectly cool, and running with no issues. I also noticed that the fuel gauge didn't work either. So I figure the gauges are broken. I haven't had any overheating issues since then. I drove all the way home on the freeway, 1.25 hrs going 65-70, no problems. I was still having problems with the battery that night and the next day. I figured it needed a new battery as it would take a jump. A few nights later, I take it for a drive, side streets, then on the freeway, for a good 1/2 hour. I stopped to top off the gas tank. When I was getting back on the freeway it straight dies while accelerating. To make a long story short, I had to tow it back home. That was the first time it died on me. Since then I haven't been able to drive it more than a couple blocks before it starts stuttering.
Well, I hope that isn't too much for people to read. Any help or direction would be greatly appreciated.
Last edited by xenophon; 05-19-2020 at 07:12 PM.
05-28-2020, 05:05 AM
#2
Senior Member
I believe your charging system is functioning and indicates a low output because the engine is sputtering and about to die.The voltage measurements you made do not make a lot of sense and hopefully you are not using a $10 DVM. A fully charged battery should measure around 12.7v no load. A few tenths of a volt means a lot when checking battery status.You need to also go through and clean all electrical connections, B+ and grounds.The engine should run much longer than a few minutes off the battery if the charging system falters. Resistance with a corroded connection will increase with heat. .What do the plugs look like? You never mentioned any ignition related tests performed which could act up when warm. A heat gun can be used to test the distributor mounted ignition module, ignition coil and pickup coil.I really doubt the carb would act up when warm except for a choke that is not opening as it should.
Last edited by raski; 05-28-2020 at 05:18 AM.
06-01-2020, 06:00 AM
#3
Senior Member
to me it sounds like the choke is sticking closed. I would take the air filter off and see if the choke opens after it is warmed up. I removed the automatic choke and put it on a cable. Very seldom do I need to use the choke.