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1997 4.2L Ford F150 rough idle / miss. Sometimes shakes at start and stalls.


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#1 jeffceo

 
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Posted 02 October 2007 - 01:09 PM

1997 F-150 4.2L
This is one for the experts! I have been trying to troubleshoot this problem for the past year without much luck, in fact it seems to be getting worse.

The main symptoms:

-Rough idle (seems to be when warm, engine vibration almost seems like an occasional miss) you can see the engine shake and feel it with your hand on the engine or while holding the steering wheel.
-about 1 out of every ten times I start it, it shakes violently and stalls after about 5 seconds. If you press the gas it usually will not stall.
-Poor gas mileage?
-The old autolight platinum plugs were pretty carboned up but the engine doesn't consume any oil.
-No check engine light

Recent mechanical history:
Hydrolocked, coolant in #1 and lower intake gasket replaced last year. (no damage to engine as engine barely turned and did not fire and bend a rod, etc) Coolant temp sensor, idle air control IAC and intake temp sensor changed. Fuel filter changed. Cleaned PVC and checked for leaks. Cleaned throttle body with seafoam multiple times. I also tested the throttle position sensor, coolant temp sensor and intake temp sensor with a multimeter and they were all in the normal range. I also replace one of the vac hoses on the intake manifold and inspected the others and they seem fine.

I tested the coil pack. The coil pack secondary resistance (between adjacent coils ie 1-5). The resistance is supposed to be 8,000-11,500 but I get 13,600 and 14,600 when it is warm. I swapped the coil pack for a new one and it made zero difference. I though I might have a problem with the EGR system so I spent a while troubleshooting that (DFPE, coolant temp sensor, EGR control valve, MAF, air intake temp sensor, removed and cleaned EGR) and everything seems to be working perfectly. I checked vacuum pressure at the intake manifold and I am getting a pretty steady 18.5-19.5 in. of pressure which is what a healthy engine should get and this hopefully also means that there aren't any vacuum leaks. I also cleaned the MAF with special CRC electronics cleaner and no difference. New spark plugs and wires.

I tested the fuel pressure at the rail: 38-40 psi with key on engine off. 32 at idle (should be 30-45) and 42 at idle with vacuum line off fuel pressure regulator (should be 40-50 according to haynes manual). It increases slightly when you rev the engine.

Even though I cleaned and tested the MAF several times I figured I would try a new one since it seems this sensor causes a lot of trouble. Zero difference.

One key symptom I am wondering about here and I hope someone can help is that the plugs were in my opinion very dirty after approx 12K miles. here is a picture of them: http://picasaweb.goo...765817055358610
The plugs closest seemed slightly dirtier and are from the drivers side. Most people may say it is burning oil with 89,000 on it but it does not burn any noticeable amount after 3k mi. The exhaust pipe opening also seems excessively carboned up.

Along with the symptom of poor gas mileage, this leads me to think it may be running rich.

Does anyone know what is wrong? any-help.gif

Thank you

#2 Warren Johnson

 
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Posted 02 October 2007 - 01:24 PM

The #1 thing that I don't see here is when the intake was off did you/they clean out the EGR ports. From what you are discribing is what we see with plugged EGR ports.

Also you link is not working for the image.
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#3 jeffceo

 
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Posted 02 October 2007 - 02:31 PM

Thank you for your response. Here is the link for the spark plug photo, it got cut off before for some reason:
http://picasaweb.goo...765817055358610

A pretty good mechanic did the intake gaskets. At the time I didn't realize there were multiple EGR ports but I did ask him how dirty the intake was and the intake valves. He said they weren't bad but the throttle body was and he cleaned that.

When I had the EGR valve off I sprayed some seafoam into the intake where the EGR bolts up and it sat over night although I am not sure if this would do much. Is there any way to test for plugged EGR ports without taking apart the whole intake? I know that if I apply vacuum to the EGR valve at idle the engine starts to run really rough and will probably stall if I continue giving it vacuum.

Thanks for your help

#4 Warren Johnson

 
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Posted 02 October 2007 - 02:36 PM

How many miles on the truck
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#5 jeffceo

 
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Posted 02 October 2007 - 02:52 PM

89,000 miles. Probably 10-12k on those spark plugs.

#6 Warren Johnson

 
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Posted 02 October 2007 - 02:53 PM

In my opinion you need to pull the upper intake and inspect the egr ports
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#7 jeffceo

 
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Posted 02 October 2007 - 05:46 PM

Thanks Warren. I am going to try doing this in the next day or two and I will post the results here. Is it worth popping out a couple of fuel injectors while I am in there to see if they are being a problem?

#8 me6894

 
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Posted 02 October 2007 - 08:49 PM

QUOTE (jeffceo @ Oct 2 2007, 06:46 PM) <{POST_SNAPBACK}>
Thanks Warren. I am going to try doing this in the next day or two and I will post the results here. Is it worth popping out a couple of fuel injectors while I am in there to see if they are being a problem?


looking at them wont do anyting, but you could always test the resistance and do a drop test or whatever its called

#9 jeffceo

 
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Posted 03 October 2007 - 05:27 PM

UPDATE: I pulled off the upper intake manifold/ plenum. The EGR ports seem pretty clear to me, there is some buildup but none seem to have a serious restriction. I will clean them before I reassemble anyway.

Please see pictures:
http://picasaweb.goo...239818236079778
http://picasaweb.goo...239822531047090
http://picasaweb.goo...239826826014402

Any more ideas? Anything I should check while the intake is off? Thanks

#10 tsd98

 
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Posted 05 October 2007 - 12:27 AM

I am not a tech but had a '97 with the 4.2. I had the same problems you're having. I ended up changing the upstream O2 sensors on both sides and sold the truck with over 200K, never having the shaky idle again. Never got a "check engine" light while this was happening and no ford dealer I tried could duplicate. Later, a local mechanic described this situation as a "lazy" O2 sensor. Might be woth a try cause it only cost me about $100.00. By the way, watch the gaskets on that 4.2 and it might last forever. I sold mine to a guy locally and it now is almost at 300K. Good Luck!




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