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This is a general question to identify a low rough idle. Over the last two years I have installed a new ICM, EGR, Cap & rotor & plugs (all last week). I cleaned the throttle body and have new IACV. All in all these were items that needed to be done and not to solve any major problems. The only item that was needed was the new fuel tanks and fuel pumps. I have system pass III and III with the code reader so nothing is pointing to any major issues. But, I do feel a low rough idle when I am sitting at the light when I can see the tach sitting rock solid on appx. 700RPM. It is peppy and got no problems at all. So, is this low rough idle TPS maybe or distributor which are both 25yrs and original equipment. Like I said there are no codes telling me either item is bad or out of range, but could they be something that I NEED to replace. Again, it does not stall or fink out on me but looking for some thing that might need to be adjusted or replaced.
No codes. I did a couple of things this morning. I put dielectric grease on the list cap and ignition coil. Sprayed some WD40 in the cap and wiped it down. I also did some checking of the TPS resistance. Closed it reads 3.3K and WOT it reads about 422 ohms. This is within the spec from Haynes. Although the WOT is supposed to be around 350ohms, but will not quibble right now. Oh, and also put some black RTV around the dust cap to seal out any moisture. Just seems that the dist cap is so dang loose as it sits on the dist.
I went and looked at a new dist to see how it sits and I noticed that the center pin that touches the rotor it solid with no movement. But aftermarket cap there is a spring loaded center connection. I am considering getting some decent quality cap/rotor like MSD just to see if it sits solid on the dist.
No codes. I did a couple of things this morning. I put dielectric grease on the list cap and ignition coil. Sprayed some WD40 in the cap and wiped it down. I also did some checking of the TPS resistance. Closed it reads 3.3K and WOT it reads about 422 ohms. This is within the spec from Haynes. Although the WOT is supposed to be around 350ohms, but will not quibble right now. Oh, and also put some black RTV around the dust cap to seal out any moisture. Just seems that the dist cap is so dang loose as it sits on the dist.
I went and looked at a new dist to see how it sits and I noticed that the center pin that touches the rotor it solid with no movement. But aftermarket cap there is a spring loaded center connection. I am considering getting some decent quality cap/rotor like MSD just to see if it sits solid on the dist.
Some caps have a spring loaded center pin, some do not. I've never had an issue with either. You say that the cap sits loose on the distributor, exactly what do you mean? The cap itself should have no looseness on the distributor when the two attachment bolts are secured, regardless of cap type. If it was replaced, check the part number to make sure it is correct. That dust cap isn't actually a dust cap, its a vent and needs to be unobstructed. As far as the TPS, check the voltage readings with the engine off and the key on. The voltage with the throttle blades closed all the way should be just under 1 volt. As you open the throttle blades, it should steadily increase in voltage with no dead spots. The best way to test this is with a voltmeter that has a needle, not a digital one. Bad spots will be very apparent. Have you verified your ignition timing? There should be a sticker under the hood with the spec, but I believe that most if not all fuel injected fords with the EECIV computer should be set at a base timing of 10* BEFORE top dead center with the SPOUT plug out.
Well, when I say loose, I mean that when I clamp it down with the two clips I can rock it some what with the pivot point the imaginary line between the two clips. Last year I got a new adapter for the cap to sit on the dust and that seemed to be a nice fit. But after 18 months or so, that became loose as well. So, when I replaced it again a few weeks ago I got both the cap and adapter and it was loose. So, I figured I would live with but then the low rough idle became noticeable. The reason I replaced the cap, rotor and adapter was because I had that carbon buildup and instead of cleaning it I figured I would get new stuff. Also, got new plugs as well. Then I started looking for a felt gasket for the cap to sit on the adapter and when I tried to find one the websites were all sold out or discontinued, so I went ahead and did the Black RTV this morning. When I RTV'd it and it became tacky I put it on and it was a firm fit. Also, sprayed some WD40 in there as well.
But there has to be a good quality cap that sits on that adapter without wobble. I got motorcraft this time and it does it as well. Seems odd to me...I would pay money to find good quality that keeps out the moisture and sits tight.
I'm not sure what you mean by an adapter.... you shouldn't need any adapter for your cap and rotor, and from the factory they SHOULD seal out moisture and dust well enough. I've wheeled through pretty damn deep water in quite a few vehicles with stock caps, and never had an issue with moisture...
The cap sits on a plastic adapter and does not sit directly on the distributor. This is a 5.0L and there is not enough room to sit all eight plug wires on top of the dist so ford created this adapter, It is sold as as an adapter for distributors for this ford engine. When you buy a dist package for this engine it comes all as a unit: dist, adapter, cap, rotor.
AH I see. I keep forgetting that they had the huge, wide cap. I think that if the cap is loose, there is an issue with the clip tabs and their tension. They may not be gripping the cap as tightly as they should. Regardless, those joints should be tight enough to seal out any serious moisture. I think it was a good idea to use the RTV to seal the cap to the adapter, but I would have put an even bead around the edges, Let it fully dry, and then attached it. It might be a bit of a pain in the *** to remove next time if you put it on tacky.
Regardless of all of this I still don't think that its the cap/adapter and rotor that would be your issue. Have you verified that you have spark on all 8 spark plug wires? How old is your ignition coil? Do you have a bluetooth dongle for your truck to monitor some things like fuel trims and timing while driving? I use a cheapo bluetooth dongle and the OBD Car Doctor app. While the majority of the information is general and useless, it helped me pinpoint a seemingly impossible to fix misfire on my 96 5.0 Explorer. I eventually noticed that my long term fuel trims on bank 1 were WAY out of wack. While not enough to set a CEL, it was enough to enrich fuel to the point of an annoying misfire at idle or at a stoplight. It rally wasnt a misfire at all, just the computer no knowing what the hell to do. Turns out it was a cracked exhaust manifold.
Anyways, I would start with verifying that you have decent spark to all 8 with a spark tester, and then verify your ignition timing. After that, try to see what your short term fuel trims are doing at idle, and see if something is out of wack with your long term trims.
No codes. I did a couple of things this morning. I put dielectric grease on the list cap and ignition coil. Sprayed some WD40 in the cap and wiped it down. I also did some checking of the TPS resistance. Closed it reads 3.3K and WOT it reads about 422 ohms. This is within the spec from Haynes. Although the WOT is supposed to be around 350ohms, but will not quibble right now. Oh, and also put some black RTV around the dust cap to seal out any moisture. Just seems that the dist cap is so dang loose as it sits on the dist.
I went and looked at a new dist to see how it sits and I noticed that the center pin that touches the rotor it solid with no movement. But aftermarket cap there is a spring loaded center connection. I am considering getting some decent quality cap/rotor like MSD just to see if it sits solid on the dist.
Don't waste your money on a MSD cap. Just get a Motorcraft (no aftermarket junk)and you will be fine. DO NOT RTV the vent cap.It fits loose and will even spin on the cap, as it should. Seal it up and moisture will appear itself inside the cap as temperatures change. I would RTV the adapter or any part of the dist. Get an OEM cap/rotor and things may fit perfectly.TPS sounds fine. What you look for is a "dead spot" as you go through its rotation. Don't get hung up on exact restance readings because parts/manuals are constantly revised.You only want a thin layer of dielectric grease INSIDE each plug/coil wire boot.
You are kind of limited to what information you can read w/o some special equipment because it is a 94. If it were a 96 and up, you can read live data, fuel trims etc.
You have a 25 year old vehicle and do not know how good things are such as compression. If the compression readings are not within ten percent of each other, you will never get a very smooth idle.Look at manifold vacuum, and verify it is steady from 18-22 inches at idle. If it is good and your tach is steady, you do not have any misfiring taking place at idle.
BTW- what does your engine decal under the hood indicate what your idle speed should be?
01-02-2019, 07:38 PM
Low rough idle 5.0L 1994 F150
