2001 ranger, at idle, misfires?

keith3232 · 10-10-2007, 07:48 AM

hello, i've had 1 diagnostic and three separate mechanics look at my truck and no luck, under 1200 rpm it misfires on all cyl. over it runs ok, revs fine etc. tested the egr valve, looks good, fuel lines had pressure, new fuel filter etc. pumps working fine. the last 60k miles my fuel cap light has been on, and no one has been able to fix it, cap is fine, idk if it has anything to do with it. plus at the same time this occured my horn/cruise/airbag control blew. idk? please help. thank u

*dogfriend* · 10-10-2007, 09:22 AM

My first thought is that you have a vacuum leak somewhere. It will cause a misfire at idle because it leans out the air/fuel mixture, making it harder for the plug(s) to fire. At higher engine speeds, the vacuum leak will have less of an effect, because the vacuum lowers as the throttle opens.

Regarding the "fuel cap" light; Is the Check Engine Light on, or do you have a separate Fuel light on your truck? If it is the former, I would get the actual code(s) that are set in the PCM (computer). It is very possible that the code(s) are related to the problem you are having and will give a clue to the source of the problem.

If you can report what code(s) are set on your truck, people here will be able to give you more advice on fixing the problem.

keith3232 · 10-10-2007, 09:31 AM

i did put a vacuum tester on, and at idle the needle vibrates like craxy. with gas it levels out. there are no visible line leaks. hope its not inside?

*dogfriend* · 10-10-2007, 09:42 AM

I don't know which engine you have, but intake manifold leaks are somewhat common on the 4.0L as they get older. The 4.0L SOHC engines are famous for leaking o-ring gaskets in the intake manifold.

Check this link for a trick to find a vacuum leak.

keith3232 · 10-10-2007, 09:49 AM

yes, i have the 4.0 v6. any guess on cost to fix?, i can change basic alternater, starter etc, but past that i'm lost

*dogfriend* · 10-10-2007, 09:56 AM

The parts are cheap, but the labor is probably a few hours for an experienced mechanic; probably a couple of hundred bucks. This is something where you can save quite a bit if you are willing / able to DIY.

If you search, you should be able to find some writeups on replacing the intake manifold gaskets.

keith3232 · 10-10-2007, 10:25 AM

just for grins, could the ac have anything to do with it?

*dogfriend* · 10-10-2007, 12:22 PM

Quote:

Originally Posted by keith3232

just for grins, could the ac have anything to do with it?

For a misfire, not very likely that the AC has anything to do with it. However, if the truck idles slower when the AC is on, it could point to a problem with the IAC (idle air control) valve.

If you search on IAC, you should get half a gazillion hits.

10-10-2007, 07:48 AM	#1
keith3232 Wannabe Elite Explorer fort worth tx. 2001 ford ranger Join Date: Oct 2007 Posts: 4 Vehicle Specs (Original Poster)	2001 ranger, at idle, misfires? hello, i've had 1 diagnostic and three separate mechanics look at my truck and no luck, under 1200 rpm it misfires on all cyl. over it runs ok, revs fine etc. tested the egr valve, looks good, fuel lines had pressure, new fuel filter etc. pumps working fine. the last 60k miles my fuel cap light has been on, and no one has been able to fix it, cap is fine, idk if it has anything to do with it. plus at the same time this occured my horn/cruise/airbag control blew. idk? please help. thank u

10-10-2007, 09:31 AM	#3
keith3232 Wannabe Elite Explorer fort worth tx. 2001 ford ranger Join Date: Oct 2007 Posts: 4 Vehicle Specs (Original Poster)	yep i did put a vacuum tester on, and at idle the needle vibrates like craxy. with gas it levels out. there are no visible line leaks. hope its not inside?

10-10-2007, 09:49 AM	#5
keith3232 Wannabe Elite Explorer fort worth tx. 2001 ford ranger Join Date: Oct 2007 Posts: 4 Vehicle Specs (Original Poster)	yep yes, i have the 4.0 v6. any guess on cost to fix?, i can change basic alternater, starter etc, but past that i'm lost

10-10-2007, 10:25 AM	#7
keith3232 Wannabe Elite Explorer fort worth tx. 2001 ford ranger Join Date: Oct 2007 Posts: 4 Vehicle Specs (Original Poster)	maybe? just for grins, could the ac have anything to do with it?

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10-10-2007, 09:22 AM	#2
dogfriend Human-Animal Hybrid Carmichael, CA '97 Sport 4x4 Join Date: Jul 2002 Posts: 8,828 Vehicle Specs	My first thought is that you have a vacuum leak somewhere. It will cause a misfire at idle because it leans out the air/fuel mixture, making it harder for the plug(s) to fire. At higher engine speeds, the vacuum leak will have less of an effect, because the vacuum lowers as the throttle opens. Regarding the "fuel cap" light; Is the Check Engine Light on, or do you have a separate Fuel light on your truck? If it is the former, I would get the actual code(s) that are set in the PCM (computer). It is very possible that the code(s) are related to the problem you are having and will give a clue to the source of the problem. If you can report what code(s) are set on your truck, people here will be able to give you more advice on fixing the problem.

10-10-2007, 09:42 AM	#4
dogfriend Human-Animal Hybrid Carmichael, CA '97 Sport 4x4 Join Date: Jul 2002 Posts: 8,828 Vehicle Specs	I don't know which engine you have, but intake manifold leaks are somewhat common on the 4.0L as they get older. The 4.0L SOHC engines are famous for leaking o-ring gaskets in the intake manifold. Check this link for a trick to find a vacuum leak.

10-10-2007, 09:56 AM	#6
dogfriend Human-Animal Hybrid Carmichael, CA '97 Sport 4x4 Join Date: Jul 2002 Posts: 8,828 Vehicle Specs	The parts are cheap, but the labor is probably a few hours for an experienced mechanic; probably a couple of hundred bucks. This is something where you can save quite a bit if you are willing / able to DIY. If you search, you should be able to find some writeups on replacing the intake manifold gaskets.