Operation: Smooth Idle

[waskly]

these are not silent non vibrating motors.

are the motor mounts good? and your sure its not a misfire?

 

[98EdBomber]

these are not silent non vibrating motors.

are the motor mounts good? and your sure its not a misfire?

Motor mounts are fine. And how many 2nd Gen Explorers do you know of that have had bad mounts? I think Id notice a bad mount.

I guess I can't say for SURE it's not misfiring.

It doesn't have the inconsistent symptom of a misfire. The idle is stable but the damn thing just vibrates steadily. It's so hard to describe it until you sit in the seat and feel it yourself. I climbed underneath when it was warming up and i could feel the exhuast vibrate pretty hard and then when it warmed up and dropped rpm the vibration lessened quite a bit. I checked all my exhaust hangers and its nice and secure.

When I changed the plugs I noticed #1 cylinder looked a little dark. When I changed the pcv valve i took the intake manifold off and looked at all the valves and they had some minor buildup or "varnish" i guess.But like i said very minor and mainly just on #1 cylinder. I think if i was low on compression i would lose lots of power.

I don't see how a misfire could be present and yet still have good gas mileage and a steady warm idle. Also have power off the line.

She didn't vibrate like this when I bought it. This started to occur in the last 1000 miles or so. Which raises the question - What causes an engine to run worse over time?...LOL....This is why I am going crazy. It could be so many things. As you see in the first post, I have replaced quite a few parts.

VERY FRUSTRATING!

I called to get a "diagnostic" ran today for $75. They would have to keep it overnight to check it when its cold.

Anyone know how a diagnostic could possibly help point out the probl;em. Do they just check voltages, fuel trims?

Can anyone elaborate why a diagnostic may be worth it???

THANKS

 

[waskly]

well we are talking about something that is over 10 years nothing lasts forever and i have seen mounts busted. i swapped enough 4.0's out in my time

 

[98EdBomber]

Motor mounts are fine as I said before.

Anyone else?

 

[syn-]

Well, I just came in from the garage where I have been cursing the napa employees for about an hour. Any how, one thing that I would like to contribute to your quest to find that perfect idle is the ASP UDP (underdrive pulley). The harmonic balancer is part the crank I am suspecting? With this on the SOHC as well as the OHV. With that said the motors share quite a bit other than being from Ford and 6 cylinders. I would give it a try, I replaced my motor with a reman. that came out of a 96 ranger. The odometer said 96k on the body so I am unsure when that motor was taken apart though with the stamp on the block and on one of the heads. I can imagine that there would be less mileage than 96, in short to put sense to the ramble. My idle has greatly improved with this addition as well as a blackmagic 180 xtreme fan. Even with a belt that was an inch long the idle was noticeably calm and I felt the difference instantly after taking the truck for a spin around the hood. Good Luck. Oh and run some seafoam gastank, crank oil, brake booster, the whole 9 yards.

 

[98EdBomber]

Well, I just came in from the garage where I have been cursing the napa employees for about an hour. Any how, one thing that I would like to contribute to your quest to find that perfect idle is the ASP UDP (underdrive pulley). The harmonic balancer is part the crank I am suspecting? With this on the SOHC as well as the OHV. With that said the motors share quite a bit other than being from Ford and 6 cylinders. I would give it a try, I replaced my motor with a reman. that came out of a 96 ranger. The odometer said 96k on the body so I am unsure when that motor was taken apart though with the stamp on the block and on one of the heads. I can imagine that there would be less mileage than 96, in short to put sense to the ramble. My idle has greatly improved with this addition as well as a blackmagic 180 xtreme fan. Even with a belt that was an inch long the idle was noticeably calm and I felt the difference instantly after taking the truck for a spin around the hood. Good Luck. Oh and run some seafoam gastank, crank oil, brake booster, the whole 9 yards.

I BELIEVE I have the one piece harmonic balancer and upon inspection I have found no problems.

I know some have a 2 piece design which can separate and fail.

Ive done sea foam, twice, but this time through the throttle body.

No change. But thanks for the input. Greatly appreciated.

 

[syn-]

My point of my post was not that anything was wrong with your crank pulley. It was that I had similar issues and did not do half of what you did, simply upgraded to something with less drag on the motor and it seems to have taken that vibration away completely. Please also note that a UDP is quite useless without an electric fan, I mean it works but your cooling temps will be higher due to slower rotation.

 

[Alaskanredneck]

96 xlt ohv 210,051 miles same problem

 

[Pontisteve]

My 98 SOHC 4.0 has had a rough idle for a long time. I threw money at it, in the form of new Ford O2 sensors, plugs, wires, cleaned the MAF, throttle body and IAC, and it still shakes around at idle, somewhat intermittently.

Ironically, I tune EFI cars. I would think that with my skill set and equipment, that I would have been able to cure this. But it seems to me that it might not be curable. It may be in the design... 6 cylinder engines are not like V8's. The engine balance in a 6 cylinder is much more of a challenge for the designers, and it is possible they will just never be dead smooth.

What bugs me about that theory is that sometimes it does very well. I looked in the tune file, and at the live data, and I don't see a thing wrong with it. But every once in a while, looking at mode 6 data in my scan tool, I catch some misfires adding up. It could even be a design flaw in the sensor wiring. Maybe they didn't run shielded cable to the crank sensor or something. Very frustrating!

 

[98EdBomber]

Zombies!!!

I don't mean to recover this thread from the dead but its been 5 months and I am still having these same issues with the idle and vibrations.

If there is anyone out there that happens to read this and would like to add any input it would be greatly appreciated as this is my sole mode of transportation at the moment and Id like to solve the issue.

Ive read around that possibly it may be a fuel issue.

Any advice?

Thanks

 

[Pontisteve]

Check your harmonic balancer and make sure that at idle, it isn't wobbling around abnormally. Beyond that, a tune up never hurts. Beyond that, you need a scan tool. Also inspect motor mounts.

 

[kdbstl]

I've noticed when my dpfe sensor is faulty(cel on now) that it seems better. Not perfect but one option that that whole egr system. I don’t know if that happens with your. I haven't tried anything yet since dpfe is $40 and who knows about the other sensors. I like the balancer thought. It seems this is an expensive problem. I put new plugs and wires a few months back and now have a surging idle issue. Good Luck

 

[Pontisteve]

DPFE is a common sensor to go bad on Fords, since exhaust heat gets to the sensor. Ford tells me they replace them all the time. The DPFE basically tells the PCM how much EGR is flowing, and the PCM adjusts EGR flow (via pulsewidth to the EGR vacuum regulator) to achieve the desired EGR flow based on that sensor.

EGR basically makes a motor run rough, which is why they don't engage the EGR valve at idle or at WOT, only at cruise speeds. An incorrect amount of EGR flow stemming from a bad DPFE could have the effect of making the engine run rough, most likely at cruise speeds. It could also cause improper spark advance, leading to pinging or possibly low power. I never thought about the DPFE causing a rough running condition, but it could I suppose. But Im not as sure that it could at idle.

If the DPFE code comes on because the DPFE correctly detects EGR flow at idle, thats a different story! EGR valves should never be engaged at idle, so any EGR flow whatsoever at idle will cause stumbling. A simple check here would be to unplug the EGR valve and cap off the vacuum line at idle, and see if the misfire immediately goes away. You could also monitor DPFE voltage and see if you're getting any flow at idle (if the sensor is good). Mine is normally around 1v at idle, which is zero EGR flow, so that's not my issue.

For plugs and wires, PLEASE stick with motorcraft wires, and either motorcraft or NGK or some other quality plug. No Bosch, no champion, etc. Any ignition misfire, whether due to plugs, wires, coil or whatever, will cause the engine to run bad in two ways. First, it's a misfire, that's obvious. Second, a misfire sends unburnt Oxygen right out the tail pipe, where the O2 sensor detects this unburned Oxygen, and assumes it's because the engine isn't rich enough, so it will increase the short term fuel trims to richen the motor up on that bank.

If the motor gets too rich, it will fuel fowl the spark plug, making the engine miss even more. The O2 sensor will see even more oxygen, and throw even more fuel at the engine, and this cycle repeats itself over and over. At some point, it's possible the O2 sensor throws a code, and once it does that, the computer will ignore that sensor and run on the base tune, which will return the truck to smooth operation. After restarting the truck, the computer tries to use the sensor again, and the whole thing repeats.

Idle surge can be caused by 3 different things: An increase or decrease in air, fuel, or spark advance. Since fuel is calculated based on airflow, the MAF sensor or vacuum leaks are the culprit here. Spark advance is based on load, which is determined largely by the MAF sensor as well. The computer will also use spark advance to raise the RPMs to compensate for a sudden drop in RPMs from some other problem. This sudden increase in spark can cause a rapid increase in engine RPM by a couple hundred. The PCM sees this overspeed condition, and pulls timing to fix it. Then, the RPM drops and the situation repeats itself. The idle speed basically "hunts" for a correct RPM.

Usually fixing the underlying problem fixes this condition. Typically, a misfire elsewhere.

As always, a good place to start looking for idle issues is to clean the MAF sensor, Idle Air Control motor, and put in new motorcraft plugs and wires if they're suspect. If you have a scan tool, pull codes and also look at the live data.

 

[pcsullivan91]

try replacing your intake gasket rings. I did this after changing most of what you listed above with no results and it fixed the problem.

 

[Dono]

Have you done a compression check on the cylinders? A mismatch in compression will definately cause a motor to shake.

 

[Pontisteve]

I believe the intake gaskets is a very good suggestion. They're a known issue on these engines apparently. If the intake gaskets do leak, they should leak worse cold than warm. This fresh intake air leak would be unmetered airflow, and the EFI's mass airflow sensor won't be reading this air, which means the PCM won't be fueling for it.

That means the engine will run lean, especially when cold. That should show up in the fuel trims as a lean condition during warmup. I need to log STFTs with my Xcal3 during warmup and see if that's happening.

How hard is the intake gasket job? I haven't done one of these before. Is it the upper to lower intake, or lower to cyl head that's the issue?

 

[Erik727]

If you're going to do intake manifold gaskets ,,do yourself a favor..Do the upper and lower.The kit ,Felpro ,comes with upper and lower gaskets for under $20. Once the upper manifold is off,it's only 12 more bolts to get the lower intake off..They're all easy to get to and there's nothing in the way...Just did the job a couple weeks ago on my 99 SOHC..Easy,,it was only a 4 beer job.

Don't know about the OHV or the V8