L6 Falling on its Face
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New User
Joined: Apr 2009
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From: Amherst, MA
L6 Falling on its Face
Ive got a 89 F-150 with a L6 4.9L 5 Speed. I recently bought this truck and have yet to been able to figure out what is causeing some of the problems im having. when you start the truck after it has been run and warmed up it hunts at idle for 15-30 seconds before leveling out but if you throddle it up any and let it back to idle again its gone. The other problem i have been noticing is that when shifting through the gears once i get about 1800-2000 RPM the engine seems to loose all "top-end" even though that isnt the top end at all. So far i have replaced the fuel pressure regulator wich seemed to help out the falling on its face, but its still not entierly gone, i just replaced the O2 sensor due to the lousy gas milage, 12-13. I have a new stock replacement exhaust system, a new TPS sensor and a new EGR vaccuum solonid regulator. I have pulled off the throddle body and throughly cleaned it as well as check for any vaccuum leaks and i cant find any for the life of me. any one that could leand a new imput in to what mught be my problem would be greatly weclomed.
Thanks much!!
Thanks much!!
Post Fiend
Joined: Jan 2005
Posts: 8,402
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New stock exhaust system, did that include the cat?
You may want to clean the Idle Air Control valve and pull any stored error codes. Go to fordfuelinjection.com for instructions on both.
Check the PCV valve and piping.
It might also be worth pulling the EGR valve and cleaning it.
You may want to clean the Idle Air Control valve and pull any stored error codes. Go to fordfuelinjection.com for instructions on both.
Check the PCV valve and piping.
It might also be worth pulling the EGR valve and cleaning it.
Laughing Gas
Joined: Oct 2005
Posts: 1,226
Likes: 42
From: The OC
Definitly check for codes first prior to spending $$$ on parts. Many problems are solved by replacing items that come up with an error code. Sounds like you have an EGR issue or possibly a bad cat. Like Lazy K said, clean your throttle body and don't be shy with the cleaner, soak it. Make sure you disconnect your negative battery cable when you replace parts to erase old codes. A can of Seafoam in the tank and 1/2 a can through the vacuum hose off the brake booster may help too.
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New User
Joined: Apr 2009
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From: Amherst, MA
I have pulled the codes before and got nothing, but the exhaust didnt include a cat, ive looked at them and their pricy *******s. any way i hope that tomorrow ill get a chance to pull off the egr itself to inspect it, i have already removed and cleaned the throddle body and the IAC valve when i first bought the truck.
Thanks, any other ideas, keep em comin!!
Thanks, any other ideas, keep em comin!!
Post Fiend
Joined: Jan 2007
Posts: 7,021
Likes: 5
From: Almost Heaven
Have you ever had an I6 before? It falls on it's face a lot. It's picky about what gear it wants to go WOT in. Just drive her easy. The 300's torque starts falling off at 2,000 rpm. It gains HP up till 3,400.
My 300 idles decent but shudders every second or two. I used a couple bottles of gummout fuel system cleaner in my front tank and the shudder went away. Maybe try that in your efforts.
Sorry I couldn't aid much in this, just giving my $.2!
My 300 idles decent but shudders every second or two. I used a couple bottles of gummout fuel system cleaner in my front tank and the shudder went away. Maybe try that in your efforts.
Sorry I couldn't aid much in this, just giving my $.2!
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Posting Guru
Joined: Jul 2004
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From: Cottage Grove, WI
ive got a 95 I6, new plugs, wires cap rotor, coil, timing set to 10*, air filter, fuel filter, fuel pump, 5 speed trans, all new vac lines, seafoamed it probably 3 times in the last 3 years, and i still only get 13mpg. and yeah, above about 2400, they dont accelerate fast at all.
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New User
Joined: Apr 2009
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From: Amherst, MA
Thanks for the imput, no i haven ever had a 300 before, my last truck was an 89 F-350 with a 7.3L IDI. I guess ill have some getting used to having a 6 cyl as apposed to a diesel too.
Thanks!
Thanks!
Elder User
Joined: Nov 2005
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I agree the 4.9 is not a race truck, and mine does not get good gas mileage, but there are a couple things you could check.
This link describes how to use a vacuum gauge to check a multitude of things. Real quick and cheap test.
How to Use and Interpret a Vacuum Gauge
I would take a hard look at the timing. Should be at 10 or even 12 deg BTDC with the spout out. When the spout is back in, the timing should move way past where you can read it. I helped a friend with his 4.9, and he accidentally timed it with the spout in. Ran a lot like you described. Some people have erroneously timed them using the wrong timing indicator. Make sure you are using the one on the passenger side of the engine. I don't know what the other thing is used for, except to confuse the unwary.
Good Luck Frank
This link describes how to use a vacuum gauge to check a multitude of things. Real quick and cheap test.
How to Use and Interpret a Vacuum Gauge
I would take a hard look at the timing. Should be at 10 or even 12 deg BTDC with the spout out. When the spout is back in, the timing should move way past where you can read it. I helped a friend with his 4.9, and he accidentally timed it with the spout in. Ran a lot like you described. Some people have erroneously timed them using the wrong timing indicator. Make sure you are using the one on the passenger side of the engine. I don't know what the other thing is used for, except to confuse the unwary.
Good Luck Frank
Post Fiend
Joined: Jan 2007
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From: Almost Heaven
The 300 is one of Ford's best motors. It acts JUST like a Diesel. I don't want you to think the 300 is a bad motor. It's slow and gets poor fuel mileage but it'll always start.
Postmaster
Joined: Jun 2007
Posts: 2,621
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From: Sweetwater Texas
That puts it +1 on the IDI he just had, I never once had problems getting my F100 to start, but my 88 7.3, well hope I don't need it started in under 10 seconds.
Post Fiend
Joined: Jan 2007
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From: Almost Heaven
My 300 has never not started for me. Once I had to give it fuel on a really cold night but that was it. I'm sure the OP will miss the raw power of his IDI but the 300 is a good motor. Who knows, maybe his really is falling on it's face more than normal? I've found mine does a lot better if I keep it out of OD.
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New User
Joined: Apr 2009
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From: Amherst, MA
i havent heard hardly one bad thing about these motors which is why i bought one, bu from the girl i bought it from she was claming that she was getting 16-17 out of it, its only got 68,500 on it, all orignal miles and i checked out the rear end, its got 3.08's in it, so i guess i was kinda expecting a little better fuel economy out of it, i know ill never see 20 mpg but 12-13 to me seems kinda low. I do love having a inline 6 though, someday maybe ford will smarten up and make their diesel a 6, but oh well, doubt that'll ever happen
Posting Guru
Joined: Feb 2007
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It should do better than 12-13 on the highway. My '94 F250 with the 351, C6 (no overdrive), and 4.10s gets 13 or 14 on the highway when you drive 55. Those 3.08s should help highway mileage, around town they are going to make your mileage worse by putting more stress on the motor to get the truck moving.