91' F250 problem
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Elder User
Joined: Apr 2006
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From: South Dakota
91' F250 problem
Hello everyone, I'm new to the forum and have a question or two about my diesel that I hope ya can help me with. I am the proud owner of a 1991 Ford F250 2WD with a 7.3L engine. The truck is very clean and is in great working order (is for the most part stock). From when I first bought it up till now it makes a rattle noise under the hood when I am in any gear and my tach is at about 900-1200 rpms. I suspected that this was in the exhaust system, so I looked it over but could not find any loose parts. I also went ahead and replaced the stock muffler with a flowmaster 40. I examined the engine compartment and found a few loose parts, went ahead and tightened those up. After all that it still makes the same rattle. Any ideas of what this could be and how to fix it?
Senior User
Joined: Mar 2006
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well i have a 91 f-250 with the 7.3 myself. unlike yours mine is not clean and not in good condition. it makes all kinds of sounds that i cant locate so no sorry i cant really help you. -but check inside the side panals. my buddie danial had his brand new truck that made a rattle and there was a pop bottle with a note in there it said "took you a while to find it dident it?"
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Elder User
Joined: Apr 2006
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From: South Dakota
haha, I never heard of that. I have looked around under the hood, even tightened down the tire-tools. One more thing, is that flowmaster 40 bad for a diesel? says its for off-road/universal applications but a friend of mine says it will plug over time from the diesel smog...
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Elder User
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From: South Dakota
I looked around today and I can't find much for performance parts for this truck. I heard that I might be able to get my injectors tuned at a local diesel shop but thats about it. Anything I can do to give the engine a little more power...besides putting in a turbo?
Post Fiend
Joined: Nov 2003
Posts: 21,285
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From: Nutter Fort, WV
If it is RPM related it may be the dual mass fly wheel starting to go bad.
If I remember right, remove the dust cover on the bell housing.
Truck in neutral, engine off.
Free play in the flywheel is to be less than 5/8" rotation wise.
More power,
Air intake mods
Exhaust mods
Timing adjusted
Injectors rebuilt
IP recalibrated
Turn just a bit more fuel to it.
How many miles on the engine/truck?
Do you have any black smoke when you are pulling the hills or taking off or driving down the road?
A turbo is the biggest bang as far as more power goes.
I had a rattle under the front of my truck going over bumps that I could never find.
Last year I changed my front springs, when I dropped the front spring shackle down out of the frame I found my rattle. The top bushing in the front spring shackles was completely gone on both sides. But that was at 300,000 miles on the truck. I had been trying to find it for close to one hundred thousand miles though.
If I remember right, remove the dust cover on the bell housing.
Truck in neutral, engine off.
Free play in the flywheel is to be less than 5/8" rotation wise.
More power,
Air intake mods
Exhaust mods
Timing adjusted
Injectors rebuilt
IP recalibrated
Turn just a bit more fuel to it.
How many miles on the engine/truck?
Do you have any black smoke when you are pulling the hills or taking off or driving down the road?
A turbo is the biggest bang as far as more power goes.
I had a rattle under the front of my truck going over bumps that I could never find.
Last year I changed my front springs, when I dropped the front spring shackle down out of the frame I found my rattle. The top bushing in the front spring shackles was completely gone on both sides. But that was at 300,000 miles on the truck. I had been trying to find it for close to one hundred thousand miles though.
Last edited by Dave Sponaugle; Apr 27, 2006 at 09:29 PM.
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Elder User
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From: South Dakota
Well the truck has just over 53,000 miles and the oil was changed about 1000 miles ago. The truck does not smoke at all. A friend did tell me that flowmaster 40 would plug up after a few months use due to diesel smog, any fact to that?
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Post Fiend
Joined: Nov 2003
Posts: 21,285
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From: Nutter Fort, WV
I can not say about the Flow Master, I am running no muffler on mine.
No chance for it to plug up that way, and I don't have to haul so much weight around.
The turbo is a good muffler all by it's self.
No chance for it to plug up that way, and I don't have to haul so much weight around.
The turbo is a good muffler all by it's self.
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Elder User
Joined: Apr 2006
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From: South Dakota
I see what ur sayin, I was debating putting 5'' stacks on my diesel earlier this year. I did read your previous post, I don't have much for experience with diesel engine tuning but how would I go about adjusting the timing and recalibrate the IP? could this be professionally done?
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Joined: Mar 2006
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i can't see a super 40 plugging up, because all that is in there is steel. correct me if i am wrong, but those super 40s are all steel, right? if so, i can't see it plugging up.
if i were you, i would save up some dough, and just buy a turbo, it is worth your money.
if i were you, i would save up some dough, and just buy a turbo, it is worth your money.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
With a 5 speed you should be doing better than 12 unless you are running it real hard.
What size tires are you running?
Give me an RPM and speed at that RPM in which gear.
I will figure out the rear axle ratio from that.
What size tires are you running?
Give me an RPM and speed at that RPM in which gear.
I will figure out the rear axle ratio from that.
Last edited by Dave Sponaugle; Apr 30, 2006 at 11:51 PM.
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Elder User
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From: South Dakota
I don't run the truck hard at all. I am running 235x85x16LT tires all the way around. In 4th gear I am at about 2000 rpm's going 45mph. The transmission is 4spd with Overdrive and the truck is 2WD. Air filter, oil and oil filter has been changed during the last 1000 miles as well.
Last edited by Dave7.3; May 1, 2006 at 12:06 AM.