Escalating Hesitation-Then-Jerk-Forward Issue

Maintenance/Repairs
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  1. About 2 months ago I started having a problem with the car sometimes hesitating, then jerking forward a little, especially when almost stopped. Also engine died once when going very slow < 5 MPH. Tried fuel injection cleaning; no difference.

  2. Problem started happening more frequently. Engine died a few more times when going slow, though not very often. Also started hesitating and then going forward a little when going at faster speeds (20-30 MPH), though not as noticeable then.

  3. Recently started doing the hesitate then jerk forward thing more frequently, including when just driving normally. Also, in addition to that, a new thing: sometimes when driving it will out of nowhere decelerate a little. Like all of a sudden I’ll start going slower, though not really noticeable speed-wise. More of just a feeling that something’s pulling it back.

  4. Then, last night, I was driving at about 15 MPH when this deceleration thing happened again, but much stronger than before. It was a strong, sudden deceleration, and my small dog was pushed forward off the passenger seat onto the floor by it, and there was a slight squealing sound for 2-3 seconds, which then went away. (My foot was on the gas the whole time.)

So, at first I thought this might be the fuel pump, but now I’m don’t think so. Belt? Transmission? Any ideas? No check engine light at all these past few months. 2003 Dodge Caravan SE 3.3L flex fuel.

Thanks!

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Clean the throttle body, and go from there.

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Actually, already did that. When I said that I tried fuel injection cleaning, what I meant was
it was a fuel system service cleaning – throttle, intake, and air flow injector cleaning.

Thanks.

4

New crankshaft position sensor, then fuel pump.

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Thanks for the reply. Two questions.

  1. If the crankshaft position sensor was bad, wouldn’t there have been a check engine light?

  2. If CPS or fuel pump were bad, would that cause the car to suddenly decelerate, like one was applying brake (but without applying brake) as described in #4 in my original post? Seems a fuel pump issue would cause the car to slowly decelerate, not suddenly decelerate, no?

Thanks!

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I think this is where y0uor shop should focus their diagnostic attention. Problems with the fuel injectors, coils, crank/cam position sensors, throttle position sensor, any of those could indeed could cause such a symptom, but wouldn’t likely cause a squealing sound. Squealing sounds occurring during an unwanted deceleration make me think of a brake, transmission, or driveline problem. Or possibly a problem with the AC compressor. If it was a brake problem and affected just one wheel, you’d get a pulling sensation too, which I presume you don’t get. So if it is a brake problem it would have to be something affecting all the wheels. Like a brake master cylinder or power brake booster, or ABS problem. For the transmission, that really requires somebody experienced listening to the sound. Shops have gadgets they can attach to your vehicle that helps them narrow down where a sound is coming from.

ABS systems can usually be disabled by pulling a fuse, so that might be something to try. Brake boosters can be checked pretty easily, at least for diaphragm leaks. You could experiment with the AC controls, see if that makes the problem better or worse. Or have a shop inspect the AC compressor for signs of it binding up.

Asking a shop to do a basic transmission inspection makes sense, and of course reading out all the diagnostic codes both active e and pending. The check engine light might not come on even when there are codes, so the only way to tell for sure is to read them out from the computer memory.

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Not necessarily

Probably 1/2 or more of the bad crankshaft position sensors never generated a check engine light or fault code

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It’s difficult for the engine computer to tell if the crank position sensor is failing intermittently. If it totally fails, the computer can determine that straight-away; but if it drops 10% of the timing pulses, not so easy for the computer to determine that.

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If it was a brake problem and affected just one wheel, you’d get a pulling sensation too, which I presume you don’t get.

Right. No pulling to the side. Just a sensation of the car suddenly decelerating.

For the transmission, that really requires somebody experienced listening to the sound.

Only thing is, all of this is intermittent. I’ve been waiting until it got worse, so that a shop could diagnose it. But that thing last night with it suddenly decelerating forcefully makes me not feel safe driving the car anymore, so I need to take it in. Not sure if it’ll make the sound, though.

You could experiment with the AC controls, see if that makes the problem better or worse.

If I felt safe driving the car, I might. But right now, I’m just hoping I make it to the shop tomorrow. LOL

Or have a shop inspect the AC compressor for signs of it binding up.

Wouldn’t think the A/C would have anything to do with the drivetrain or brakes, such that it would cause a sudden deceleration.

Asking a shop to do a basic transmission inspection makes sense,

I was thinking of taking it to a transmission shop, since it seems possible it could be a transmission issue. There’s a shop nearby that specializes in transmissions and general auto repair. Haven’t been there before. But they have good reviews on Google, so I think they might be the best bet, given the possible transmission issue. The regular shop I go to is tiny, and I just don’t think they’re equipped to deal with transmission issues, if it’s that.

The check engine light might not come on even when there are codes, so the only way to tell for sure is to read them out from the computer memory.

That’s good to know. Thanks!

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On my son-in-law’s car it “totally failed” several times causing him to coast to the side of the road. The car would restart after 15-30 minutes. No check engine light. New crank sensor fixed it.

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Update. Took it to the transmission shop and they said that it didn’t sound like a transmission issue. Said it could be a bad coil or crankshaft sensor. (Forgot to note: had crankshaft and cam sensor replaced a couple of years ago.)

Took it for a test drive with the mechanic, but it wasn’t doing it, though it did it while i was driving over there.

So, seems to do it more after the car’s been sitting a while, it seems. So, perhaps debris in the fuel pump? After it sits a while the debris settles and clogs the intake or output? (On my model, the fuel pump is inside the gas tank.)

Anyway, since it didn’t seem to be a transmission issue, went to my regular mechanic and dropped it off there. He said he didn’t know what it could be, but would take it for a test drive in the morning.

Still curious about George’s comment about the AC compressor, and how the AC would be affecting this.

Thanks!

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The AC compressor is a pump gadget that periodically engages and disengages, & is powered by the engine via the crankshaft pulley & accessory belt. Even in normal operation it puts a noticeable load on the engine. You’ve probably noticed when your turn the AC on while you are coasting, once the compressor engages you’ll slow down a little. Many modern cars prevent the AC compressor from engaging in idle, b/c the extra load it causes could stall out the engine. If the AC compressor was broken & started to lock up in a major way, rather than turning freely, that would put a big mechanical load on the engine which was trying to turn it, and could cause the car to decelerate rapidly & cause a squealing sound from the AC compressor belt slipping on its pulley.

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I can see how the engine computer might not be able to figure that out if the crank sensor totally failed while the engine was running. The computer might see that as just the engine was running fine, then it stalled out, or ran out of gas. The best way to determine there’s a crank sensor problem is to see if there’s pulses coming from it when the engine is turning. But the computer doesn’t necessarily have another way to determine when the engine is turning. Unless there was a cam sensor too, then maybe it could see it was getting cam sensor signals, but no crank sensor signals, & that something was wrong with the crank sensor. But even if it had no other way (besides the crank sensor) to determine the engine was turning, you’d think it would notice the lack of crank sensor signals during cranking, the next time you tried to start it, and turn on the CEL then.

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I assumed the AC compressor was powered by electricity supplied by the alternator. I didn’t realize it was connected to the engine itself. So that makes sense. Thanks for explaining!

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Here’s the thing. I talked with two mechanics today and both said it could be the crank position sensor or a bad coil. I replied, if they failed, wouldn’t it cause the car to just coast, like taking your foot off the gas (as it did with your son)? Why would that cause it to decelerate suddenly, as it did with me, causing my dog to fly forward off the passenger seat?

They both insisted that, yes, if it failed, it could cause the engine to just not go and would be a sudden deceleration. But that doesn’t really make sense to me.

Anyone have any thoughts on this, and why it would cause such a sudden, abrupt deceleration?

Thanks!

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If it feels like the brakes are coming on, after an episode, feel all the wheels. If one is hot, there’s a likely culprit.

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I agree w/you poster enargins. If the engine totally stops running while driving down the road b/c of a crank sensor etc problem, I wouldn’t guess that itself would cause the rapid deceleration as you describe. It would be just like running out of gas, you’d gradually slow down and coast to the side of the road. The dog would only figure something was up if you happened to stop in front of a McDonalds. Golden arches!! Yipee. Burger Treats!! … lol …

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Update. Shop has had the car since yesterday. Mechanic drove it home last night. Drove it in the evening, in the morning, drove it fast, drove it slow. Couldn’t get it to reproduce the problem!! I’m going to go down there in a little while and drive it with him and see if it’ll do it with my foot on the pedal. Maybe something about the way I drive triggers it.

This is very frustrating. I would just wait until it gets worse, but I’m afraid to drive the car now. Given how it suddenly decelerated when going 15 MPH, causing my dog to fly off the seat, what would’ve happened if I had been going 30, 40, or 60 MPH?? Would be like hitting a brick wall.

So this is very frustrating.

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One other place to attain some well-informed advice is at allpar.com. They focus on Chrysler products and have a discussion board devoted to minivans. I have found help there over the years for questions about my 2007 Town and Country and previous 1999 Plymouth Voyager. Best wishes.

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Thanks! I’ll definitely post there as well.