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Discussion Starter #1
As much as I hate to start another thread on this subject, I am stumped and I just can't afford to pay any more mechanics to guess (wrongly!) about what is causing this issue.

The problem first manifested a year ago. While high-speed freeway driving I would occasionally feel a momentary misfire. On secondary roads (40-60 mph) the car would randomly surge and lose power, then pickup and run smoothly for a while. Over the last year the problem has got much worse--to the point where it will suddenly start surging and stumbling in in-town traffic and will sometimes just quit at red lights. My no. 1 mechanic (30-yr relationship) replaced coil pack, plugs and wires, IAC, had the intakes off and checked gaskets, did a smoke test and over time did a bunch of other stuff that made no difference. The car runs perfectly for him. It stumbled, surged and quit on the way home. I let my no. 2 mechanic take it home several times (he has a 45 minute mixed city/highway commute). He experienced no problems. Lately the problem can even appear when starting the car in the morning--it will 1) start and run perfectly, 2) start and rev up to about 1500 rpm and immediately quit and not fire again until I wait a few minutes. 3) Start and run on what sounds like 3 or 4 cylinders and limp along for a minute until it finally quits. With option 3 there is black smoke out the tailpipe and a strong smell of gas so I don't think fuel delivery is the issue. I broke down and paid my Ford dealer for a mechanic to ride with me for 2 hours with his laptop all plugged in. There was ONE stumble that registered on his computer with no indication of why. It almost died on me on the way home. I have changed the computer (used), the throttle body (used), the cam position sensor (the one in the end of the head, not the old-style distributor shaft kind) fuel pump, coil pack (again!). Probably some other stuff too but I can't remember right now.

Now, when the car decides to run it will run perfectly and smoothly and it goes like hell. It will sometimes run for days without any issue. I noticed that any time I disconnect the battery and discharge the computer it seems to run well for about a week before it starts acting up again. (Just long enough to make you think you fixed it!) Then the problem manifests slowly and, over the course of a few days builds up to undriveability again. Like the computer is taking a week to learn bad behavior again. That's the only way I can describe it.

Note: During this time there has NEVER been a check engine light or any codes displayed. NEVER!

I'm stumped. And broke. Any advice would be welcome, short of being told to go out on the freeway and stop in front of a Peterbilt. (which I have been tempted to do. LOL)
 

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Welcome to the forum. If it were my car I would be very frustrated also! Sounds like you've replaced almost everything on the ignition side but I wouldn't rule out a fuel related cause. I would recommend to replace the fuel filter if you haven't already done that and stick a fuel pressure guage on it while it's acting up and see if it could be a fuel pump not providing enough pressure. I'm sure others will chime in with other possibilities also.
 

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I have heard of someone who had a bad coil pack, so they bought one that was ALSO bad, and the next one bought was finally good. You could do the spraybottle water test on the coil pack, since the new pack is after your no.1 mechanic doing his thing.

But that doesn't sound like the problem with the situation of resetting the computer and eventually going back to the original bad state. So it has something to do with the adapation system. Bad O2 sensor(s)? Bad pcm?
 

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I have heard of someone who had a bad coil pack, so they bought one that was ALSO bad, and the next one bought was finally good. You could do the spraybottle water test on the coil pack, since the new pack is after your no.1 mechanic doing his thing.

But that doesn't sound like the problem with the situation of resetting the computer and eventually going back to the original bad state. So it has something to do with the adapation system. Bad O2 sensor(s)? Bad pcm?
'03 DOHC pic shows an issue not new to the Ford Tec who did the diag for me. I replaced the wires and plugs and it returned one year later. No codes but it ran horrible. Then coil crack and real misfire, no codes. Just because the wires and plugs are new, does not make them good. Tec told me this only happens on the rear bank.


'03 DOHC wagon bought used, had coil, plugs and wires replaced just over 80K. "03 Taurus bought used, had the same things done before 100K. There must be a reason.


-chart-
 

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I would look at ground cables and straps. Check where the cable hooks up to the body frame and the one going to the engine. Grounds cause lots of weird problems and your car is hitting that age.
 

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I would look at ground cables and straps. Check where the cable hooks up to the body frame and the one going to the engine. Grounds cause lots of weird problems and your car is hitting that age.
One in the pic, firewall, Alt negative to body, PCM, and sensor return all bond here. All bolted over painted metal, then rust and corrosion. I sanded the paint off, coated all with anti-ox compound and it fixed my irregular idle speed. Erratic sensor signal at the TPS found.


-chart-
 

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Discussion Starter #7
Thanks guys for all your input!

When the fuel pump was replaced all the filters were checked and replaced. The previous fuel pump was only a year old and had been pressure tested. The pump was replaced because while out one day we heard a chirping noise coming from the back of the car, both while driving and sitting idling. The only thing back there that could chirp was the fuel pump so I decided to change it if only to eliminate it as a source of the problem.

I have spent so much time with a water spray bottle I might as well have used a garden hose. No effects.

The current coil pack will now be the 3rd one since the problem started. I doubt both replacements are duds.

I will spend the next couple of days investigating all the grounds I can find. I will also pull the back plugs and check them and their wires.

To recap:

Changed plugs & wires--no difference

Changed coil pack (2x) --no difference

Changed computer--no difference

Changed throttle body--car ran fine for a week or so before starting to act up

Cleaned MAF sensor--ditto

Unplugged camshaft position sensor--ditto, so I ordered a new one which made no difference

Probably done other things that I just can't remember right now.

One thing I forgot to mention: When driving at highway speeds, when it does start to buck and surge the car noticably jerks and it sounds like it is firing at the wrong time and burbling through the intake or the exhaust. Not a loud bang like a typical backfire but loud enough so that the neighbours will look around if they're outside. Is it possible that there is a sticky valve or am I way off base?

Thanks again!
 

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Did you check the engine side of the ground strap? Even though it is an aluminum block, they still corrode. Then check where the negative battery cable joins the car frame. That is where my Granddaughters PT Cruiser had problems that sound very similar to yours, her cruiser is an '07.
 

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Discussion Starter #9
Well, I have inspected and cleaned all the ground straps mentioned. Didn't see any issues and it hasn't made a difference. I have come to the conclusion that the car is actually running worse since I installed the last coil pack (https://www.amazon.ca/dp/B004A6BHA2/ref=pe_3034960_233709270_TE_item). I have no idea what brands the previous coil packs were. I am considering ordering a new one from Ford but I don't have an extra $225 right now. I have also discovered that I seem to have the wrong plugs installed (NGK TR5GP) which I believe are for Vulcan, not Duratec. I will change them but I'm not in a panic because the problem existed before they were installed. What plugs would you recommend? I'm going to pull the UIM to make installing the new plugs easier and also so I can see what I'm doing with the coil pack. One of those Torx-head bolts is becoming stripped from being in and out so many times and I don't want to take any chances.

I haven't done much of my own mechanical work for pushing 40 years but I have all the basic tools and there's lots of good how-to info here.

Thanks again.
 

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You can visit a junkyard place and take a torx bolt or two you need.

As for the coil pack, mine is stock and is still running like it should at 129k miles. Just look for a coil pack at a junkyard that's stock, and to be safe check the sparkplugs of a car you want to take the stock coilpack from and see if they are finetip or not. If they are finetip then get the pack, assuming it's free of any cracks. The fine tip requires less voltage to make the spark so the coilpack will have not been AS stressed and will have heat up less through its' heat cycles.

Always get finetip, for the same reason. Coilpack will last a lot longer, sh***y spark plugs are a common cause of cracking packs.
 

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Discussion Starter #11
Not quite so simple. We don't have a lot of junk yards around here and none of them keep stuff that old. Pretty much anything I need I have to order from out-of-town (and take the risk of receiving the wrong thing or just junk) or keep driving around hoping I can find one in a back yard somewhere. However, I don't doubt I'll at least find a bolt with the same threads somewhere. Although it's more expensive it's so much easier to get the parts new.

Car stalled in the drive-through this morning. Embarrassing but the guy in front of me paid for my coffee. I guess there's an up side to this. LOL.
 

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Reaching the back 3 spark plugs is hard; especially the one in the middle. One of the back plugs might be loose and thus only misfires when a bump makes the plug wire and spark plug loose contact.
 

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Well you've certainly shot the parts cannon at it. Have you done a compression check? Smoked it? Checked for clogged cats?? All of these tests are cheap or free.
 

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Discussion Starter #14
Smoke test was done. No vacuum leaks found.

Remember, the car will run perfectly for several days and go like a scalded cat, then, out of the blue, suddenly start surging and stumbling and quitting. It doesn't matter if you're doing highway speeds, in-town traffic, or simply trying to start it one morning. Once I get it running again it might run problem free for 5 minutes or 5 days. No telling!

The car has never displayed symptoms for a mechanic no matter how long they have had it. It has never thrown a code. No CEL. Nothing.

I have bitten the bullet and ordered new plugs (the right ones!) and yet another coil pack. All Motorcraft. I will be attempting this myself this weekend. I have read a lot of input from members here and I'm quite confident I can handle this. If not, well I can always yell for help.
 

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Discussion Starter #16
In a word: No. I have eliminated that by buying gas at various, top-line stations. No discount gas.

But it was a good thought. Thanks.
 

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What are the long term fuel trims on both banks at idle and with the engine under load? You need a scan tool that will show PIDs to chase down weird problems on any modern vehicle.

Stall at idle could be a dirty / sticking IAC. Remove it, clean and lube it.
 

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Discussion Starter #18
IAC was replaced. Twice. Forgot to mention that. :(

I have to assume that, during the days (weeks? months?) it's been under a mechanics care and not displaying any symptoms somebody would have run that scan. Ford dealer mechanic had his laptop hooked up for over 2 hours while we rode around and it was programmed to look for all kinds of stuff that just left me confused. During that 2 hours the car stumbled once--a quick hit that registered on his computer but with no indication of what the possible cause might be.

I am about to install new AGSF32FM plugs and a new Motorcraft coil pack. One of the upper intake manifold gasket/O-rings was pinched so I have ordered new ones which will take a couple of weeks to get here. A complete set of upper and lower gaskets from Rock Auto will cost me just under $40 Cdn mailed to my door. Local Ford dealer wanted $40 for EACH gasket. At that price I can afford to wait a couple of weeks. :)
 

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Discussion Starter #19
So, I changed plugs and made an interesting discovery!

My old plugs (which have only been in there for a few months) were very oily, particularly 1,2,3 & 5. I suspect the oil was in the wells and ran down the plugs when I pulled them, also the outside of my plug socket became very oily most noticeably in #5. All the plugs were black and sooty from running rich but, as I mentioned, they were the wrong plug and gap for a Duratec.

So do I get new cam/valve cover gaskets? Anything else? Is this the type of job a guy can do at home? I'd hate to wait two weeks for UIM gaskets, put it all back together and take it to a shop so they can take it all apart again.
 
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