germ

Hey guys, I hope this post offers enough mystery to elicit some response because its got me stumped.

My 2001 2.3 Ranger bucks fiercely under "heavy" acceleration. I can avoid the bucking so long as I'm careful to accelerate the truck easily and slowly. I get the best performance in the higher RPM's. If I try to press the gas too much I get the bucking.

The thing that baffles me is the check engine light remains off. I've tried to get the check engine light to come on by purposely pressing the gas pedal to the floor while in high gear at low RPM, which induces the bucking the most. Still no check engine light, thus no codes to help me pinpoint the problem.

The truck only does this while driving. I can't get the symptoms to surface in the driveway while opening the throttle.

Any ideas?

(Obviously I'm avoiding the shop. I'm in my last year at college and money is tight. I'd love to fix this on my own if possible. I do have some mechanical experience)

Bert

I'd start with changing the fuel filter. See how it runs then. Try blowing through it when you get it off. As for codes, there could be some even without a light. AutoZone will chack for free.

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Bert

djames28

That was "one" of my symptoms, too.

After replacing fuel filter, cleaning injectors (using strong concentration of additive to little fuel), changing spark wires, diagnosing fuel regulator/damper and fuel pump, compression testing, vacuum testing, fuel pressure testing - and noticing sooty tail pipe,
I finally spark checked my ignition coil pack.
It had little noticeable spark (although the engine easily started and idled well).
On close inspection, the coil had visible cracks.
If you can find a Kilovolt meter to read the output voltage - you can know what your coil is putting out and check the specs. New coil is around $100.

germ

thanks for the advice. I'll let you know how it goes.

I did go by Hi Low and had them check for codes. There were none. Do you think a better scanner would pick up codes thrown while the CEL is out? as in my case? Thats is to say, do you think there might be codes that the Hi Low scanner didn't pick up because its a cheaper scanner.

I changed the fuel filter, but i guess its been over a year and couldn't hurt to change it again. Actually I guess its a little over due. Has anyone heard if the newer ethanol blended fuels are harder on fuel filters?

Whats the voltage output supposed to be on the coil? I wonder if I could apply the spark to some high voltage resistance dividers to measure the voltage indirectly with a standard multimeter.

Bert

The coil Primary resistance is 0.5 ohms and the Secondary is 12 to 14.5k ohms. Ignition peak amps- 6.50-7.50 A, 4.1-4.6 msec rise time.

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Bert

djames28

I'm told odb scanners won't show a code for coil problems.
Coil juice is in the neighborhood of 30-40,000 volts - and more.
There are a lot of internet "how to spark check a coil" helps - to give you some good detail for the spark test (with or without a spark tester unit).

germ

I changed the fuel filter and there is no noticeable improvement. I blew through it like you suggested Bert (I remember that from shop class) and didn't notice any problems. I think its working better, but it might be my wishful thinking. I still have the hesitation and bucking performance.

I also cleaned the mass airflow sensor. I don't think that did much good, but it can't hurt.

I checked the ignition coil as best as I could. The way they designed these things! sheesh. Why couldn't they orient the ignition coil such that the primary connection wasn't butted up against the intake manifold! I had to do some real acrobatics but I eventually made some confident measurements. The meter and leads measured .9 ohms, and the middle pin to outside pins measured 1.6 and 1.2 ohms (there were three pins, so i made two measurements. Please let me know if I've done this the wrong way.) So I end up with .7 and .3 ohms for the primary windings. I'm thinking this is pretty close to the required .5. The secondary windings, I'm told, are to be measured in pairs, 1-4 and 2-3. For both I measured about 10.8 kohms which seems a little low. I haven't yet tried to measure current or voltage. I'm not quite sure how to do that.

Thanks for the posts. Let me know what you guys think so far.

Bert

If the coil is leaking spark, the ohms may be okay and they still can be bad. Sounds like you're on the right track and doing things the way I would have. As djames28 said, it's a very good chance that the coil is bad.

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Bert

germ

FIXED!! Its been a while, sorry. It took me a little bit of time to get the money together. Hey! if the trucks moving?! its not a priority right? Hopefully this post will help out someone. Turns out it was the coil the whole time. Bad coils don't throw error codes. At least, mine didn't. Thanks for the tip guys! Truck is running great :)

Bert

Glad you got it going. Thanks for the update.

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Bert