Engine Loping
Thread Starter
Member
Joined: Jun 2017
Posts: 42
Likes: 1
From: Tennessee
Engine Loping
1987 F-150 XLT Lariat, 2 WD automatic, 302 5.0
I've replaced a lot of things under the hood with this "barn find" truck and it was running great, then suddenly it started having an issue. It had driven just fine throughout the day, then in the evening, it started to feel like it was losing power and struggling as I drove (35-45 mph). When I drove back home and parked, it stalled. Upon restarting, the engine loped and the headlights dimmed. The engine went from about 300 rpm to 1500 rpm and everywhere in between, sounding like it was going to stall before it would rev back up. I noticed the battery's needle on the dash fluctuated a small amount, but it was indeed moving.
I parked it and replaced the alternator a couple days later, and the problem is persisting. The battery needle isn't fluctuating this time, but the engine is still revving up and down and shaking the truck a bit. It revs up and down and stalls. It starts just fine, and when it stalls, the headlights still stay on.
Any ideas? Over the past 9 months of owning the truck, I changed the spark plugs, distributor cap, starter solenoid, ignition coil, radiator, fuel filter, thermostat, water pump, oxygen sensor, battery, battery terminals, PCV valve, IAC valve, cleaned the throttle body, and Seafoam'd the brake booster vacuum line twice.
I've replaced a lot of things under the hood with this "barn find" truck and it was running great, then suddenly it started having an issue. It had driven just fine throughout the day, then in the evening, it started to feel like it was losing power and struggling as I drove (35-45 mph). When I drove back home and parked, it stalled. Upon restarting, the engine loped and the headlights dimmed. The engine went from about 300 rpm to 1500 rpm and everywhere in between, sounding like it was going to stall before it would rev back up. I noticed the battery's needle on the dash fluctuated a small amount, but it was indeed moving.
I parked it and replaced the alternator a couple days later, and the problem is persisting. The battery needle isn't fluctuating this time, but the engine is still revving up and down and shaking the truck a bit. It revs up and down and stalls. It starts just fine, and when it stalls, the headlights still stay on.
Any ideas? Over the past 9 months of owning the truck, I changed the spark plugs, distributor cap, starter solenoid, ignition coil, radiator, fuel filter, thermostat, water pump, oxygen sensor, battery, battery terminals, PCV valve, IAC valve, cleaned the throttle body, and Seafoam'd the brake booster vacuum line twice.
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Joined: Jan 2018
Posts: 11,256
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From: Memphis, TN, Earth, Milky Way
"A lot of things" is pretty vague. We need specific details to give you specific suggestions. The truck's details (ALL of them), its history (miles, maintenance, damage, repairs), and for EACH part that has been changed: why, when, by whom, with what (brand & PN), from where? What test did it fail, and did the replacement part pass the same test?
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The more we know about it, the more likely we can help you.
Do you have a Haynes manual? Have you read it? Do you have a common auto tools, a digital multimeter, a vacuum gauge, fuel pressure gauge, mechanical oil pressure gauge, compression gauge...? Have you measured fuel pressure recently - particularly when it's NOT running right?
Stop replacing parts - the voltage fluctuated with engine RPM because the alternator can't work at 300RPM. The alt. was not the CAUSE of the loping, so you wasted that time & money. But if you ever replace the alt again, you should upgrade to the 3G because that 2G is known to set vehicles on fire.
(phone app link)
(phone app link)
The more we know about it, the more likely we can help you.
Do you have a Haynes manual? Have you read it? Do you have a common auto tools, a digital multimeter, a vacuum gauge, fuel pressure gauge, mechanical oil pressure gauge, compression gauge...? Have you measured fuel pressure recently - particularly when it's NOT running right?
Stop replacing parts - the voltage fluctuated with engine RPM because the alternator can't work at 300RPM. The alt. was not the CAUSE of the loping, so you wasted that time & money. But if you ever replace the alt again, you should upgrade to the 3G because that 2G is known to set vehicles on fire.
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Thread Starter
Member
Joined: Jun 2017
Posts: 42
Likes: 1
From: Tennessee
It's a 30 year old barn find that sat for many years, thus I don't know the maintenance records of the previous owner. I'm changing old corroded parts with new ones because it had old, neglected corroded parts. It's an old truck, and a barn find at that. I'm not going to leave cruddy old parts in the engine when I can replace them and know what is under the hood for such things. THAT is why parts were changed. They are various brands but they were all specific to this truck. I don't know the particulars about each and every piece, but I wanted to get rid of potentially worn out and dangerous parts.
It has literally ran perfectly fine for months until Sunday night (today is Thursday) and it had the symptoms of a failing alternator. I don't want to drive it to town and have it die on the road, nor do I have equipment/ gauges to measure with, nor can I afford to take it to a mechanic. I use the Haynes and Chilton books, yes, but for learning how to find and change things. I'll see what those books have to say about these symptoms in their troubleshooting sections.
Also, *"A lot of things" is pretty vague.*-I listed the parts I changed out.. Not model number and all of that, but I was specific as to what parts were replaced. It doesn't run at 300 rpm, that was just the low point it hit when it was revving itself back and forth, it usually hovered between 700 and 1100 rpm during its fluctuating fit. Trying to be specific with that as far as the numbers go.
It has literally ran perfectly fine for months until Sunday night (today is Thursday) and it had the symptoms of a failing alternator. I don't want to drive it to town and have it die on the road, nor do I have equipment/ gauges to measure with, nor can I afford to take it to a mechanic. I use the Haynes and Chilton books, yes, but for learning how to find and change things. I'll see what those books have to say about these symptoms in their troubleshooting sections.
Also, *"A lot of things" is pretty vague.*-I listed the parts I changed out.. Not model number and all of that, but I was specific as to what parts were replaced. It doesn't run at 300 rpm, that was just the low point it hit when it was revving itself back and forth, it usually hovered between 700 and 1100 rpm during its fluctuating fit. Trying to be specific with that as far as the numbers go.
Martin
Joined: Jan 2011
Posts: 3,036
Likes: 260
From: Lehi, Utah
Why Steve was asking about the replacement parts is that many times they can be the problem. Most notably the coil as the factory unit will rarely go bad and aftermarket don't have the same quality and this causes problems. Aftermarket PCV can cause idle problems, really want OEM replacement only. Some brands or types of spark plug can cause idle problems. Just trying to back up and make sure it's not a replacement part causing the issues, it can take time for the symptoms to show doesn't have to be immediately after a part swap.