Trying to figure out what this is

[DrPizza]

Problem with my older grand caravan, nearly 145,000 miles on it. I drove about 40 miles the other day, and after I came to a stop sign, as I started accelerating away from it, the van started lurching; the RPMs were bouncing all over the place. The problem has been sporadic ever since. Sometimes, as soon as I attempt to go, it starts lurching, with the RPMs bouncing from 500 to 2500 and back. If I let my foot off the gas, most of the time it'll resume idling just fine. But, sometimes it idles way below where it normally idles. But, if I turn it off and immediately turn it back on, the problem goes away and it idles just fine. Accelerating up a hill is a bit of a problem - sometimes. But, other times, it accelerates just fine.

At first, I was thinking it was a fuel pump problem. But, if I get out of the van after it has just done that, you can detect the smell of unburned fuel. Before I throw a ton of money at things that don't have to be changed, any best guesses?
A sensor? Plug wire? Distributor? That the problem is so intermittent is what's making it tough (for me) to figure out. I don't recall that I've had any trouble whatsoever, once I'm up to speed (90% of my driving is at 55-65 mph). Most of the time I just put on cruise control and have yet to have a problem while cruise control is on. But, that's not to say that I can't force a problem - after traveling on a 55mph road, and slowing down to make a right turn onto another 55mph road, it started doing that again. Right after I got up to 55mph again, I was on a hill. I tried to floor it going up the hill to see how well it accelerated at that speed, and I got it to start that 500rpm to 3500 rpm lurching again.

 

[IcePickFreak]

What year is it? It's always hard to say without actually seeing it, but my first inclination from what you're describing would be to check the EGR valve.

 

[alphatarget1]

any CEL?

 

[Bartman39]

I`m thinking EGR as well but year and CEL we need to know for sure... If no CEL then possibly even an ECU, have seen the older Chrysler products have strange issues due to the ECU... Partial failures or intermediate issues with no CEL can be caused by them as well...

 

[Greenman]

If it's not throwing any codes, I'd check the fuel filter and pump.

 

[exdeath]

Smell of fuel doesn't mean the fuel system is working, it could mean that the fuel is leaking out somewhere else and not making it into the engine. First thing to do is monitor fuel pressure, during the condition if possible, and monitor rails, injectors, regulator, vacuum line, etc for leaking. If you can get the problem to occur and the needle on the fuel pressure gauge isn't budging, you can rule out fuel. If fuel system is a problem, you'll observe the needly descend just before it occurs.

Next, check that the EGR valve is free to open/close and staying closed under spring pressure, then remove the vacuum line and plug it. This prevents the EGR from opening at all, even if commanded. If the problem remains, it's not EGR, as the EGR won't be able to open at all. Make sure to restore the vacuum line once finished testing.

Monitor engine vacuum on a gauge during idle and normal driving and verify it's normal.

Intermittent erratic stumbling under load can also point to an ignition issue, particularly the coils. Look for cracks or burn marks in the coil packs, particularly around the brown resin and the terminals. Ignition problems will be be difficult to observe without a scope. Inspect plugs for fouling. I'm going to assume this is a V6 with 3 coil packs and no distributor. If one coil is bad, two cylinders will be taken out and that will cause noticeable stumbling and fuel smell. What year is this?

What happens if you put it in neutral when it starts to stumble or idle low? Transmission issues related to fluid and torque converter lockup shouldn't be overlooked.

Some simple things to do that don't require any parts and only require cheap tools that you should be able to rent/borrow (vacuum and fuel pressure gauge) You would be fortunate if you could antagonize the problem and force it into a stall and no start, would be much easier then.

To get more advanced, assuming all the above is ok, you'd need a scanner with datalog ability to monitor vital sensors and look for anomalies when it happens.

 

[brblx]

sounds like it's misfiring under load to me. CEL should be on, if not, it probably has at least stored a code (but might not see the problem often enough to flag it as active/continuous).

most common causes would be ignition related- bad plug(s), wire(s), or coil (iirc that car has three waste spark coils combined into one assembly). this stuff is easiest to find if the car has set a code for a particular cylinder- if it hasn't set an DTC's, or if it just set P0300 (mult misfire), you're almost certainly looking at a problem that is affect all cylinders. that means it's less likely to be spark and a lot more likely to be a fuel issue. a quick fuel pressure check (hopefully it has a test port on the fuel rail) should rule that out as an issue. the spec varies between engines, but 30-50psi is typical. should be able to rev the engine up all you want without it dipping significantly.

shouldn't be a vacuum leak, that would cause an abnormal idle and probably set a fuel trim code. also would highly doubt an EGR problem (some of those vans don't even have it).

 

[DrPizza]

It's a 2001. I didn't even think of it earlier, but one time when I was having trouble, I put it into neutral, revved the engine as much as I wanted, but as soon as it was back under load, the problem started again. But, I've only done that once, and there have been other time where it was bad, then good for 20 seconds, then bad again - so it could be coincidental timing when I tried that.

 

[brblx]

so does it feel like a misfire to you? does the engine 'skip' akwardly, possibly bucking and jerking, or is this more just an issue with the speed of the engine, i.e. it's surging ahead or rapidly dropping in RPM without throttle input?

 

[DrPizza]

bucking and jerking

 

[exdeath]

Starting to sound like ignition. I suspect coils.

 

[BUTCH1]

Starting to sound like ignition. I suspect coils.

I agree, I had a plug wire that misfired under load, whenever I drove over a bridge with a steep grade #4 would arc to the head and it would drop a cylinder, kinda noticeable in a 1.9L Escort!. I resolved the issue with a coating of dielectric grease on the plug boots, never did it again.

 

[7window]

I am not certified but a diy. I would start on the easy ones first like the fuel filter, plugs and plug wires. This kind of problem sometimes hard to diagnose because it could be electric or fuel. This type of problem happened ones to me and it was as simple as fuel filter. The fuel filter back then was still clear and you can see there was fuel and not a whole lot of dirt but when I replaced it the problem went away.

Now with the bouncing up of the RPM, indicates now to me that its electrical such as coil, wires. Thats why I preface that this problem is somewhat difficult and just start replacing the easy cheap parts first. Like plugs, wires, fuel filter, injector cleaner, regular tune ups stuff then work you way to fuel pump(still easy), coils and possibly injectors.

Check the fuel pump wiring too that is in the engine bay not the one attached to fuel pump. Sometimes they get old and frayed that the connection goes bad. Locate the fuse to the fuel pump and behind the box where the fuel pump wire is, just do a visual check and just follow the line to it. I had that problem once with my car. On a real hot day my car would run fine and 3rd gear the car would just cut off. It would surge and then sputter then just dead. It took me five days to find out it was the wire.

 

[boomerang]

Dodge Caravan?

Sounds like transmission problems. I think the fuel smell is a red herring. It's the result of the problem not THE problem.

My $0.02.

 

[twinrider1]

How old is the battery?

 

[Ronstang]

Torque converter?

 

[DrPizza]

Couldn't find anything wrong with the plugs or plug wires; didn't have much time to monkey with it today (wife had a huge honey-do list for me for mother's day.)

 

[Ronstang]

You need to check the transmission. If it is the torque converter you will not have a problem at cruise because it is "locked up" and thus a direct coupling between the engine and the transmission.

 

[Rifter]

Sounds like a ignition issue to me, make sure the coil(s) are functioning properly.

 

[BUTCH1]

Sounds like a ignition issue to me, make sure the coil(s) are functioning properly.

I found mine by parking the car in a dark garage with the parking brake on and have someone slowly bring up the rpm's, that's how I spotted the arcing to the head..

 

[SandEagle]

sounds like cylinder misfire. had a similar issue due to carbon buildup in the engine

 

[Eli]

If it was misfiring, his check engine light would be very angry at him...

 

[DrPizza]

You need to check the transmission. If it is the torque converter you will not have a problem at cruise because it is "locked up" and thus a direct coupling between the engine and the transmission.

But, would that explain it barely idling with it in drive and at a stop (before ever going forward), but then, after clicking the ignition off and immediately restarting it, the problem vanishes?

Drove to work this morning, absolutely no issues with it. It accelerated just fine - 0 to 60 in just a few seconds. Maybe moving spark plug wires around while examining them resulted in one being displaced by a centimeter that was sufficient to stop arcing (that I didn't see any sign of while examining?) Maybe one was partially disconnected from the plug? I hate intermittent problems like this.

 

[Zargon]

it could definately be as simple as a loose plug wire

sadly only time will tell

 

[mike2fix]

Check the Ignition Control Module, pretty common problem on these.