460 hesitating rough idle
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460 hesitating rough idle
I have a 1990 460 that has a rough idle and hesitates / misses slightly when starting off. This only happens after it is warmed up. It will clear up when I am driving. It will come back after I stop and/or turn off engine and start back up again. No error codes. I have check for vacumm leaks, replaced plugs and wires. I have been putting up with this for several years.
Any suggestions would be greatly appreciated.
Any suggestions would be greatly appreciated.
Senior User
Joined: Dec 2011
Posts: 366
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From: Harlingen,TX
I have a 1990 460 that has a rough idle and hesitates / misses slightly when starting off. This only happens after it is warmed up. It will clear up when I am driving. It will come back after I stop and/or turn off engine and start back up again. No error codes. I have check for vacumm leaks, replaced plugs and wires. I have been putting up with this for several years.
Any suggestions would be greatly appreciated.
Any suggestions would be greatly appreciated.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
I have a 1990 460 that has a rough idle and hesitates / misses slightly when starting off. This only happens after it is warmed up. It will clear up when I am driving. It will come back after I stop and/or turn off engine and start back up again. No error codes. I have check for vacumm leaks, replaced plugs and wires. I have been putting up with this for several years.
Any suggestions would be greatly appreciated.
Any suggestions would be greatly appreciated.
Define "No error codes". How did you check for vacuum leaks? Have you checked the fuel pressure? How about checked/changed filters?
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I forgot to mention this is fuel injection. I have replace the fuel filter, air filter, Oxygen sensor, plugs wires. I also checked for vacumm leaks. Including spraying carb cleaner around the engine. I tryed unpluging the vacumm hose from the EGR, and pulling vacumm to open EGR.
Fleet Owner
Joined: Oct 2005
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From: Kentucky
I asked in Post#3, define "no codes". Nothing at all indicates your scan tool is garbage. At the very least you should get the system pass code of 11 repeated (11/11) for the KOEO tests. The same for Continuous Memory (CM). and a Third time for KOER tests.
As far as spraying carb cleaner around the engine goes, that is inconclusive as well. There are several vacuum reservoirs in the engine bay, not to mention the HVAC system, that can cause a vacuum leak. NO amount of spraying with cleaner will find the problem.
You need to put a fuel pressure gauge on the truck then drive it under load to see if it is dropping out of specification.
As far as spraying carb cleaner around the engine goes, that is inconclusive as well. There are several vacuum reservoirs in the engine bay, not to mention the HVAC system, that can cause a vacuum leak. NO amount of spraying with cleaner will find the problem.
You need to put a fuel pressure gauge on the truck then drive it under load to see if it is dropping out of specification.
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I don't remember what the codes were. However, there were no problem codes. As far as vacuum leaks I have done a visual check and the carb cleaner trick. do you have any other suggestions on how to find a vacuum leak? I agree that these simptoms point to a possible vacuum leak. Or maybe something related to smog equipment. Thanks for your advice!
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Fleet Owner
Joined: Oct 2005
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From: Kentucky
I use a handheld vacuum pump gauge to test each vacuum circuit. You could try isolating each circuit by unplugging it from the vacuum source then cap off the port.
As far as codes go did you check using the KOEO/CM tests or KOER? You should start with the engine off checks before moving on to the engine running tests. We ask for codes because many times an OP overlooks what may appear to be insignificant code to them, but in reality is a key indicator of the root cause.
The 7.5L engines do have a reputation for vacuum leaks internal to the engine, i.e. under the intake from a leaking intake manifold gasket. I have no first hand experience to validate that reputation, but I have read more than a few posts here of others with that issue.
If it were mine I would do a compression check and leak down test before tearing into the engine. Also check the plugs to look for signs of misfiring or perhaps an injector may be weak or stuck open causing a lean or rich condition on one or more cylinders.
As far as codes go did you check using the KOEO/CM tests or KOER? You should start with the engine off checks before moving on to the engine running tests. We ask for codes because many times an OP overlooks what may appear to be insignificant code to them, but in reality is a key indicator of the root cause.
The 7.5L engines do have a reputation for vacuum leaks internal to the engine, i.e. under the intake from a leaking intake manifold gasket. I have no first hand experience to validate that reputation, but I have read more than a few posts here of others with that issue.
If it were mine I would do a compression check and leak down test before tearing into the engine. Also check the plugs to look for signs of misfiring or perhaps an injector may be weak or stuck open causing a lean or rich condition on one or more cylinders.
Senior User
Joined: Feb 2012
Posts: 223
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From: Baltimore MD
89 460 and I've had the same problem for quite some time. New cat, old one was not only clogged but when I pulled it a socket wrench fell out of the back of it. Better. Cleaned my K&N, found out you have to use the kit, tapping on the workbench only gives you an insect collection. Better. New IAC, Better. Last night, I replaced some lingering vinyl vacuum hoses with really good silicone. Problem resolved. All of these things can contribute to bad idle, and all commonly need fixing after 23 years. I still want to go through my fuel system front to back and make sure everything's totally clean.
More Turbo
Joined: Jun 2012
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From: Deepwater Mo.
I put a 160 degree Thermostat in my 92' f150 about a week ago and replaced it with a 180 degree Thermostat today do to that similar issue of yours on my 92 f150 but, "I do not think that is your problem."
I think the problem with your truck is the Throttle Position Sensor or a vacuum leak. Try unplugging that sensor and see what happens.
I think the problem with your truck is the Throttle Position Sensor or a vacuum leak. Try unplugging that sensor and see what happens.
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Timing?
Took the truck in for a smog. They said it failed due to a visual inspection. They said that the timing was set at TDC not 10 BTDC. (tailpipe emission were good.) I dont understand how it could of changed. I've owned the truck for 10 yrs and it has always passed smog. Can anyone tell me if 10 degres is correct? I know how to change/check the timing however, I don't know how to test it to determine it is functioning correctly. i.e., the time should advance at different rpms.
Lead Driver
Joined: Jul 2007
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From: Rhode Island
A stretched timing chain and worn distributor gears can retard ignition timing.
I have a hard time believing they actually went through the trouble of unplugging the spout connector, marking the harmonic balancer, and setting up the timing light for a visual inspection.
I have a hard time believing they actually went through the trouble of unplugging the spout connector, marking the harmonic balancer, and setting up the timing light for a visual inspection.
Fleet Owner
Joined: Oct 2005
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From: Kentucky
Fuel Injection Technical Library » Setting the timing
And 10 TDC is correct
Unplug the SPOUT the timing should return to base timing. Plug the SPOUT in the timing will advance to whatever the computer thinks it should be.
And 10 TDC is correct
Unplug the SPOUT the timing should return to base timing. Plug the SPOUT in the timing will advance to whatever the computer thinks it should be.