4.6 DOHC Stumble
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4.6 DOHC Stumble
I have a 2000 Lincoln Continental with the 4.6 DOHC Intech. It has a stumble while accelerating you can feel and hear it in the intake tone. The dealer is stumped. So far have replaced fuel pump and filter, fuel rail pressure sensor, throttle position sensor, plugs and coil boots, cleaned mass airflow sensor, reflashed PCM. None made any difference at all. It only has 98k on it, and this started all at once. Does anyone have any ideas.
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Does it have a butterfly in the intake to shut one of the intake ports off at low RPM? I think the 4-valvers do...
Sounds like that butterfly is stuck closed or open and causing the computer to have hissy-fits.
Does it do it at a certain RPM, like 2000 or 2500 or 3000 consistently? For instance, when you slam the gas pedal from a light, as it revs up, does it stumble when it hits a certain RPM?
art k.
Sounds like that butterfly is stuck closed or open and causing the computer to have hissy-fits.
Does it do it at a certain RPM, like 2000 or 2500 or 3000 consistently? For instance, when you slam the gas pedal from a light, as it revs up, does it stumble when it hits a certain RPM?
art k.
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I don't think it has the butterfly valves in it. It has a two barrel progressive throttle body, I think one barrel feeds half the valves when you get about 1/3 throttle the other one starts to open and feed the rest. In answer to RPM it starts at off idle to 3000RPM then pretty much goes away. It feels like a misfire. Just for grins I got a known good MAF sensor today and tried it no change.
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First, you gotta get the misfire counters read - just checking for "codes" is not good enough. You gotta buy a good scan tool, or have a dealer or good mechanic check them. That'll tell you if you have a misfire... and specifically which cylinder!
That progressive throttle body is kinda what I meant - how is that second butterfly controlled?
3000RPM might be the magic # where it opens the second butterfly...
Is the second butterfly open?
That progressive throttle body is kinda what I meant - how is that second butterfly controlled?
3000RPM might be the magic # where it opens the second butterfly...
Is the second butterfly open?
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Not yet but I'm going to. What's strange about this whole thing is it was fine one day and doing this the next.
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Originally Posted by William D
Ran compression test lowest 155/160 after a squirt of oil highest 170. Double checked throttle butterfly purely mechanical, both are opening.
You're supposed to do it DRY first, and if it's low, put oil in it, and try it again. If it comes way up, the rings are bad.
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Only put oil in lowest cylinder, it only came up 5psi. Dry pressures 155-165-165-165 front bank 165-165-165-170 rear bank. The service writer at my local Ford dealer thinks it may be the torque convertor causing it, but says they have no one certified to work on this engine tranny combo. Because it's only used in Lincolns. I am wondering if I may have a floppy timing chain / bad tensioner. I know the SOHC 4.6L has a problem with the tensioners getting weak, but haven't heard of this on the DOHC 4.6L. I know they're spring loaded and oil pressurized when running. I run Castrol SYNTEC 5W-30 changed every 5K and you can still see through it when draining. So it's clean and not sludged up inside.
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Good going on the compression test, re-reading what you posted makes sense now
Doesn't sound like the TC but anything is possible.
If it was a timing chain tensioner, you'd hear the noise way before it actually effected engine performance. Likewise, chains stretching. And that only happens if you don't change the oil regularly... at least until well over 150K miles.
Gee, I'm stumped... did you (or they) check spray pattern and flow on the fuel injectors? One thing you can check is the injector ticking - using a screwdriver against the bone in front of your ear, or a stethoscope, check that each injector is ticking...
If it just started doing it out of the blue, after all you've gone through, it's electrical - coil or injector, I'd think. Can you test the coils with a multimeter?
Doesn't sound like the TC but anything is possible.
If it was a timing chain tensioner, you'd hear the noise way before it actually effected engine performance. Likewise, chains stretching. And that only happens if you don't change the oil regularly... at least until well over 150K miles.
Gee, I'm stumped... did you (or they) check spray pattern and flow on the fuel injectors? One thing you can check is the injector ticking - using a screwdriver against the bone in front of your ear, or a stethoscope, check that each injector is ticking...
If it just started doing it out of the blue, after all you've gone through, it's electrical - coil or injector, I'd think. Can you test the coils with a multimeter?
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Checked the coils with a meter all check the same, can't find any specs as to what they're supposed to be. Talked to a Lincoln dealer he suspects one or more coils are breaking down under load. All the injectors are ticking. He said an injector should set a code in the PCM.
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The dealer didn't find any cyclinders misfiring? Does it seem to do it worse under light load (acceleration)? Mine was doing this, drove me nuts!!!! Finally had it scanned at Ford and found two COPS were bad. I swapped out the COPs and everything is fine now. Checking them with a ohmeter will not tell you anything unless it is completely shot. They usually have to get warm before they start acting up (breaking down). Hope this helps.
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Thats what they said, does it under load also at low speed steady (ie 30-35mph). It's mainly between 1000-3000 RPM over 3500 it goes away completely. Replaced all 8 COPs no change, pressure cleaned injectors using OTC System no change. I'm about ready to blow it up.