Miss/bucking at low speed & on incline

Windywoes · #1 06-23-2009, 11:30 AM

'99 LX, 3.8L, 132,000 miles: I am getting a miss or bucking action when in 4th gear, low RPM's, and going up a slight incline. This is the only time I am getting this condition. Other than that it runs fine. New wires, new fuel filter, Autolite double platinum plugs with only about 15K miles, Dealer did the 171/174 fix some time ago. Tranny was replaced at 38,000 miles, but no fluid or filter work since (I have the parts to do this).

If I stomp on the gas this never happens.

In other similar threads I have read this condition might be a coil pack or vapor canister purge valve. Can anyone elaborate or share their opinions on this?

BTW-this condition is getting worse each week.

tomj76 · #2 06-23-2009, 02:58 PM

When was the last time your EGR ports (under the upper intake) were cleaned? When clogged, they can cause misfire conditions.

Another couple things to check are spark (coil) and valve lift. The valve covers need to be removed to check the lift.

Andrew1941 · #3 06-23-2009, 05:35 PM

Had the same condition and for ME, it was the DPFE sensor. Build up of oil vapour of the sensor surface causes the sensor to go caput. Then the voltage signal does not change and the EGR valve stays in whatever position it is in when the failure ocurred. For example, the EGR is open slightly, then when you meet all the conditions for the computer to turn on the EGR system, i.e. you are up to speed and the engine is warm etc, then the valve will open to that position causing recirculation of the exhaust gases. By not modulating the amount, you can choke the engine with too much exhaust and then you get the stutter of the engine. If you stomp on it, you put more fuel and oxygen in and the ratio of exhaust gas to the rest is increased and you get a good burn and all is fine.

Like I said, this is what is was for me (I had EXACTLY what you are describing), but it may not be for you as I have heard other people talk about a bunch of other solutions. However, with that being said, a person i work with has an 02 Ford Escape and she has the EXACT same conditions and what fixed ti was a new DPFE sensor. BUT in both our cases, we had the check engine light come on and the P0401 code was thrown. In both cases, I confirmed the sensor was the prblem by testing the voltage. If you do a search on the DPFE in this forumn, you will find one of my ramblings/explanations about testing it. It is a bit of a pain, but the DPFE can be expensive. We paid about $50 each for after market and Ford wanted $140. However, both of our sensors have since failed again after about 6 months use, so maybe the Ford one is the way to go? OR maybe there is something else wrong that is killing the sensors? Not really sure? By the way, on my Deathstar, I have done all the same stuff you mentioned for repairs and then some. All help, but for me the bandaid repair (so far) was to change the sensor.

Windywoes · #4 06-23-2009, 05:53 PM

I appreciate the lengthy reply Andrew 1941. I might start with the DPFE since it is easily accessed. I did not do the 171/174 repair so I do not know if the EGR ports were cleaned.

Maybe I can pull the vacuum line to the EGR and road test for the condition. That could further point to the DPFE, right?

Thanks others for your thoughts as well.

If not for this forum I would be in a deep financial hole with 'ol Windy.

Andrew1941 · #5 06-23-2009, 06:09 PM

Absolutely, pulling the vacuum off the EGR valve should leave it closed and all should be fine while driving at higher speeds. If not, the problem is elsewhere.

Another easy thing to do is to apply vaccuum to the EGR valve with the engine idling. The engine should stall immediately. If it doesn't stall, then you know the EGR valve is stuck (not a likely condition, but nice to rule out). Alternatively, if the engine does stall, then you know the valve is opening just fine. I took the vacuum line off the heater controls and put it to the EGR valve (on the pass side of compartment under the cowel - my line colours were red for heater and green for EGR valve).

Windywoes · #6 06-24-2009, 06:52 AM

Thanks for the confirmation. I will play with it today weather permitting.

I did take the DPFE off and used a cotton swab to gently probe inside the output and ref tubes of the device. The swab came out of the output tube coated with wet looking rust and oil. Not a good sign, is it?

Andrew1941 · #7 06-24-2009, 02:49 PM

Nope...I would bet the sensor is done. The sensor should be relatively clean inside and dry.

I'm going to give Ford a call and get them to re-check the price on the DPFE using my VIN number to confirm they have the right one. In 2001 they started switching over to a sensor that mounted on the side of the manifold. This sensor is more expensive than the one I have which is mounted on the steel tubes on the exhaust recirc pipe. Hopefully the price I was given before was for the more expensive one!

Windywoes · #8 06-26-2009, 12:42 PM

I ordered an Airtex unit from Rock Auto. Not the cheapest and not the most expensive. Mine mounts to the front of the manifold. Takes about 2 minutes to change out. The new one is the molded version. I will report back when the new one is installed and road tested. This would be an easy fix to this problem-if it works. Oh me of little faith........

Windywoes · #9 06-29-2009, 06:04 PM

I installed the new Airtex DPFE from Rock Auto (wow-fast shipping) and test drove it. Now I cannot get the van to buck or miss like before. So far I would say it was a bad DPFE that was causing my problem. I will test drive Windy again tomorrow to verify.

Thanks for your help on this!!!!!!

Windywoes · #10 07-03-2009, 08:44 AM

ALAS! With 3 days of problem free driving after replacing the DPFE the bucking/missing has returned. One thing I noticed after installing the new DPFE is how well the engine ran at very low RPM's and high gear, but yesterday I started to notice that it was really dragging again. Today, the bucking/missing is back. As always, it only happens in 4th gear and RPM's below 2,000 and while going up a slight incline. Windy has 132,000 miles on her

I guess my next course of action is as follows:
- check the coil pack
- plug wires are new and good quality
- plugs have 30,000 miles on them, but I will check the gap
- look for a vacuum leak in the EGR line and the intake manifold
- inspect IMF-doohickeys again

Any other ideas?

BTW, yesterday I replaced the trans filter and changed out 7 quarts of Mercon V. The old fluid and filter had about 100,000 miles (not the original tranny) on it and it was surprisingly clean.

wiswind · #11 07-03-2009, 10:24 AM

If it has not been done, I would remove the upper intake manifold and clean the EGR ports.
The tend to clog, starting with the ones closest to the EGR valve (driver side) and leaving the ones on the passenger side as the only ones open.....which gives cylinder's 3 and/or 4 all the EGR flow, which robs them of oxygen....causing them to not fire correctly when the EGR system is activated.
This will be more noticable at low RPM when the EGR system is activated.

Also, checking the IMRC linkage is advised, as the 1999 and newer have nylon clips that are known to break, or fall off.

Andrew1941 · #12 07-03-2009, 10:26 AM

I would 1) test the new DPFE and see if it is still functioning; Whats to say it didn't fail already? Search the forumn for DPFE ( I have explained the testign a few times...I can again if you really need me too)
2) if you are going to pull the plugs, check the ceramic section of the body very closly on every plug for a hairline crack. Been there too, but mine were Bosch (now Motorcraft). Anyway, one of the back plugs on mine and others ended up with a crack around the same time as the DPFE issue cropped up. In my case, the plugs only had about 40,000km, but they were not the AutoliteDP you mentioned, so??? I would just look real close at those.
3) you could have a vacuum leak somewhere in the system
4) did you test the EGR valve is functioning correctly? You can disconnect the vacuum line to the valve and if your problems go away, then at least you know the problem is with the EGR system. Then if while idling, you hook up vacuum to the EGR valve and you make the engine stall, you know the valve is working, if not, then the valve is not working and may be stuck part way open or something? This rare, but it can happen. I used the vacuum line from the heater controls on the passenger side of the engine under the cowel. I hooked the red vacuum line to the green which was the EGR valve.

Good luck.

Windywoes · #13 07-04-2009, 06:48 AM

Thanks much Andrew and Wiswind for your helpful insights. All though I gave you my plan my gut says this problem is related to the EGR system. It did hit me when the problem re-occurred that the new DPFE could have failed. I will check the DPFE and EGR functions as suggested, but for now I cannot afford the parts needed to do the lower intake manifold/EGR port cleaning so that will have to wait. I will also check for codes pending even though the CEL has not come on.

Windywoes · #14 07-06-2009, 07:15 PM

I was inspecting the vacuum lines at the rear of the engine and got a little encouraged when I found that the line from the manifold to the green hose was almost falling off the connection at the manifold. I pushed it back on. The problem now seems better, but it is still there on occasion. I am still going to do the tests Andrew suggested when time permits.

Wow, Windy will be 10 years old in a few weeks. I washed and waxed her for her birthday. She has given is fits in the past, but lately has been fairly well behaved. Thank the Lord for that!

Windywoes · #15 07-08-2009, 05:37 PM

Andrew: Can I ask what may seem like a dumb question? How do you hook up the meter to measure the voltages of the device while it is connected?

Another thought on this problem: Do you think the bucking/missing feeling I get is actually an attempt of the tranny to down shift to 3rd gear, but for some reason it does not happen? Bad programming of the tranny perhaps?

Sorry to keep bumping this thread.

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