i have a 91 ford f150 with a strait 6 in it. it has recently been sputtering and stalling badly and shutting off while driving down the road, i replaced the fuel filter yesterday and it is still doing the same thing, any suggestions.
1991 F150 4.9L
I'm having similar problems.
It starts up from cold and runs, drives.
Seems just fine.
When warm(er), it stalls, sometimes intermittently, sometimes immediately after starting, and very rarely it will run for 10-20 seconds with normal power/etc.
Replaced cap, rotor, wires, coil.
Still doing the same thing.
Tried switching fuel tanks, no change.
Montana_1, if you find a fix please post; your email is disabled, so I can't email you directly.
I'm going to mess with the IAC next.
For the past couple of years it's had an occasional intermittent miss at idle, but didn't seem to affect drivability, figured it was the original ignition components. Still does it after the above ignition part replacements.
On rare occasion it would misfire/stumble while freeway driving. Since it's not staying running, I can't check that now after the ignition parts change. When changing the wires I found that #5 and #6 plugs were loose, the service tech probably had finger-tighted them then forgot to torque them. That was a couple years ago!
My F150's situation is definitely engine temperature related.
After it has cooled to ambient, it will start and run , until exhaust starts to heat up. Then it stalls. I felt the O2 sensor, and it was warm but not hot enough that I couldn't touch it.
I can restart it, but as it gets warmer the run-time is shorter and shorter (goes from 10's of seconds to seconds to mis-fires while trying to start).
My guess is a sensor (the O2?), or a wire to one of the sensors. It seems to be electrical/heat related.
Interesting thing: when it dies, if it was running off the front tank, I hear the fuel pump continue to pump for a few seconds, then the pump shuts off; but if it's on the rear tank, the fuel pump isn't running when it dies. Could be the front pump is getting marginal, but the engine still has the same run symptoms running off the rear tank.
Continues to have an intermittent misfire, and stalling, and difficulty starting or no-start during warmup phase.
From cold-start condition:
Started the truck, as it warmed up, I kept the idle up over 2500, and it tried to stall several times, and once or twice did, but I was able to restart and get the rpms up quick enough.
Once it fully warmed up (as measured by coolant temp), it stabilized and ran well enough (still has an intermittent 'misfire'). Drove it around the block, appeared to run well enough (like it has the past year, with an occaional misfire).
Restarted it several times. Each time it would:
Initially run smoothly at just-started advanced idle (initially about 1500 rpm, dropping to about 1000-1200 (didn't write it down)). After about 30 seconds, it would drop to about 800 rpm, and simultaneously begin slight intermittent misfire, and under the hood would be two sounds, a 'humming' and a slight 'rattle' sound. After another 30 or so seconds, the humming and rattle would quit, and the intermittent misfire would continue.
I recall reading a few posts about a 'humming', so I'm going to turn my attention there for the moment.
I also strongly suspect the O2 sensor, which I've also read (if I remember correctly) can act up during warmup, but be fine at cold start and full operating temp.
I have the identical problem Mr23 has written about. If it is a hot day and I start up and drive the truck, I can just about predict when the truck will start losing power and then stall at a stop light. I have gone as long as a year without any problems and then they resurface. In cold weather this problem does not exist. I had the truck at the dealer several years ago and they just asked for my money and did not fix the problem.
A call to the dealer mechanics resulted in comments about various sensors (as described in the thread), but one person said it was highly likely that the intake or exhaust manifold wasn't maintaining a seal through the warmup cycle. Your experience could corroborate that...
I haven't taken it in yet to let the dealer waste time on it, they wanted $99 just to start diagnosing it. I ran a quick test myself the other day: I started the truck and let it run until it killed the first time. Then I took a propane torch and heated the exhaust O2 sensor and surrounding pipe up. Truck restarted immediately, ran for a bit, then died again. Normally the truck wouldn't restart, when I tried restarts on other occasions without heating the sensor. Did this several times, until the engine was warm enough to keep the O2 sensor warm itself. Seems to me to be that sensor, in my case.
I want to run another test, but I need another pair of hands: someone to start the truck (and restart if necessary); I'll run a torch on the sensor starting after the first time it dies off, and see if it stays running until warm. I'm going to do this because I have to hire a shop to replace the sensor. I tried, but I couldn't break it loose (been on there 14 years). Dealer quoted $150 for the sensor, so before I drop $200-250 to 'try' it, I wanted to be more sure that replacing the sensor would be likely to fix it.
try breaking it loose after you put all that propane on it, and put the longest piece of pipe you can fit on your wrench handle. Can also try a monkey wrench on it. That's all they're gonna do at the shop.
When I first starting having my troubles I got a check engine light that I could sometimes reset. I eventually replaced both o2 sensors about 3 months ago and have had no problems since. I had an intermittent failure on one sensor and it ultimately died as indicated by gas mileage going away. I am having problems with stalling and rough running periodically right after startup and during warm up phase but no check engine light has come on.
Why do I not have these problems in lower environmental temperatures? It's almost time for cooler weather and I bet I won't have this problem through fall and winter.
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