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1997 ranger occasional skip


wa1vvs

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I have a 1997 Ranger with the 3.0l engine and 5 speed manual trans with 210,000 mi. I bought it for $400.00 at the end of winter. It had no oil pressure. I took the engine out and found that the camshaft position sensor gear was worn. I replaced the sensor and the oil pressure was back to normal. I had a burnt exhaust valve on #4 cyl so replaced both heads with reconditioned heads. Now the engine runs good except for an occasional skip. I have driven it for about 200 miles like this and the CEL does not come one. I installed new Motorcraft AGSF 32FM sparkplugs. I tested the sparkplug wires with known good ones, I replaced the coil pack with a known good one. I changed each plug one at a time with a known good one. I bought the new plugs at the Ford dealership and the told me that the plugs that they sold me are replacements for the AWSF 32PP plugs.
When the engine was out, I tested the fuel injectors and they checked ok.
Bob
 


ratdude747

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Did you do a compression test? I wonder if there is something worn (cams, etc) that's doing that.

Are you sure everything electrical was properly connected? Loose connections (this include body grounds) can cause all sorts of oddities.
 

wa1vvs

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Hi ratdude,
There is no need to check the compression. If there was a bad lobe on the cam, It would have a steady skip. I have an OCCASIONAL skip. It will do it when I have the rpm between 1200-2000 when I am in 4th gear going up an incline. It may do it 2 to 3 times till I reach over 2000rpm. The motor was out 2 times so all electrical connections were done twice.
Thank you for your help.
 

wa1vvs

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Hi all,
After 3 weeks, I guess everybody on here is as smart as I am. No one knows the answer.
 

RonD

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Well not to easy to diagnose "occasional skip".

There are only 2 reason but several possible causes.
Fuel or spark are the reasons
For fuel:
Perhaps fuel pump is losing power momentarily, could be fuel pump relay, but that would seem odd to occur only under load in a specific RPM range.
TPS, throttle position sensor, this is a simple variable resistor like a light dimmer or volume control, and it is a mechanical device so can get "dead spots".
It could have a dead spot that you would only notice at a certain RPM range and only under load since you wouldn't feel it otherwise.
Best way to test TPS is with a volt meter and sewing pin(needle)
It will have 3 wires
Top wire will have 5volts when key is on
Center wire tells computer the position of throttle.
You want to test top wire first, use battery or engine metal as ground
Use pin to pierce wire to test "+" voltage, do the same for center wire.
So you test it with wires still connected to TPS and key on/engine off

Center wire should have .69-.99 volts when throttle is closed, under 1 volt.
As you slowly open the throttle manually the voltage will increase, look for jumping or dropping of voltage as you open throttle, replace TPS if you see that.
At wide open throttle voltage should be 4.5 or higher.

If voltage changes rapidly(jumps or drops) computer thinks you let your foot of the gas or pressed to the floor, either will cause stumbling, since throttle plate has not actually changed position.

Clean MAF(mass air flow) sensor and check its connector, RPMs have a specific air flow for engine size, i.e. a 3 liter engine will pull in a certain amount of air at a certain RPM, if MAF sensor was not reading air flow correctly at certain levels then engine could stumble, again you wouldn't feel this unless under load.

Spark is harder since computer controls it all after 1994, no separate modules, just coil and spark plugs.
There are 3 separate coils in the coil pack, one could fail and cause the stumbling, but would be harder to be RPM range specific.
But it could happen, a weaker spark has a harder time igniting a Richer mix, and when accelerating the mix gets richer, so could cause stumbling until mix leaned out a bit.
Video here on testing coil packs: www.youtube.com/watch?v=c1zhgsnyZWw

Problem with testing coils is that a bad one will test bad, but a good test doesn't mean "good", lol, because of the low OHMs even a little heat can cause problems if a coil is starting to fail, so worth testing but doesn't mean 100% good
 
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pjtoledo

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going by past experience with a different engine/car, misses at low rpm with lots of throttle was plugs & wires. but you already swapped the wires.
I'm a stickler for wires that fit tight, here is something to try. Use needle nose pliers to get into boots to bend the metal clips for a good fit. use a bit of electrical grease to seal the boots. also play with the plug gap by .005 smaller and larger and see what happens.
some fuel injector cleaner won't hurt anything.
 

wa1vvs

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Hi all,
When I tried the sparkplug wires, I did one at a time using only one wire at a time. I took the truck to a garage and had them check it on there scanner. It checked that the #3 and 6 wirers were misfiring.
They replaced all of the wires and it is running fine now. I guess when I replaced #3 wire, #6 wire was misfiring and when I replaced #6 wire, #3 wire was misfiring. I am not one to go and buy a hole new wire set if I am not sure if that is the problem.
Thank you all for the help.
 

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