1996 Dodge Caravan 3.3 intermittent rough run at speed

Tiny
RAUSCS
  • MEMBER
  • 1996 DODGE CARAVAN
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 148,000 MILES
Hi,

Strange happenings with the old beast yesterday. Driving down the freeway at 70, power suddenly dropped to nothing, engine still running but idling rough, no power, chuffing and missing big time. Can get forward motion, but 10 MPH and sounds awful. Let it sit at idle for a few minutes, starts running OK. Ran for another 30-40 miles fine, same thing happens again. Had it towed to a mechanic at 1:00 am. Gas tank at 1/4 full.

Once the mechanic arrived at 8:00, battery was dead (probably has NOTHING to do with the problem). No codes, replaced battery (bad cell) and test drove a bunch. Could not repeat the problem, so got back on the road. Same problem half an hour later. Waited a few minutes, started running better, so I drove the rest of the way home (300 miles!) Like a little old lady, very easy on the gas, stayed under 70, and made it home OK. Filled tank about 50 miles after the last episode. Check engine light was on, only code is a misc misfire code.

Mechanic here at home can't find a problem, suggests plugs and wires (probably not the problem, but needs it anyway).

Thanks in advance for your help! Steve in Costa Mesa.
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Sunday, October 10th, 2010 AT 1:46 PM

11 Replies

Tiny
BMRFIXIT
  • EXPERT
Misfiring codes check for tune up 1st
pay close look at the coil, high rate of failure also check fuel pump and do a fuel pressure and fuel flow test
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Monday, October 11th, 2010 AT 6:52 AM
Tiny
RAUSCS
  • MEMBER
Replaced wires and plugs, ran fine for a few weeks, but had the same problem again. Had it towed into my mechanic, but everything runs fine. They tested the fuel pressure, and it checks out. Mechanic says it COULD be the catalytic converter heating up and plugging up. Any more ideas?
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Monday, November 8th, 2010 AT 1:57 PM
Tiny
BMRFIXIT
  • EXPERT
This may help its from

converters. Com

Tech Tips How do I know if my catalytic converter is defective?

How do I know if my catalytic converter is defective?

Catalytic converters are defective when they become clogged or poisoned. You may sometimes be able to feel when a converter is partially clogged, or defective, when you do not go any faster when you step on the throttle. This may also be accompanied with a noticeable drop in gas mileage. A clogged converter will cause increased backpressure in the exhaust system. This increased backpressure prevents the engine from breathing properly which in turn may cause the engine to quit after a few minutes of driving or feel like an engine governor limiting the RPM's the engine can achieve. You may actually hear a whistling or choking sound when applying the throttle.

A catalyst that has broken apart internally and is loose in the system or has worked its way back to the muffler can also cause rattling noises. This rattling may be prevalent at idle but go away as speed is increased. Sometimes you may tap on the converter with a rubber mallet and hear the core rattling. If you discover any of the above your converter needs to be replaced.

Since there is no inspection port for you to see if you have an actual clog in a converter there a couple things you may try to help diagnose a defective converter. Many mechanics will remove the oxygen sensor and look for a change in the vehicles performance. If a performance change is noted, your converter needs to be replaced. You must be extremely careful if you run the engine with the oxygen sensor removed since there is a risk of fire and asphyxiation caused by escaping engine exhaust and exhaust gases.

A vacuum gauge that also has a fuel pressure gauge, or a pressure gauge that has a 1 to 10 pound scale, may also assist you in diagnosing a clogged exhaust.

If you connect the gauge upstream of the converter, either in an emission test port or by fashioning an adapter in the oxygen sensor hole, you can measure the exhaust backpressure. A general rule of thumb is no more than 1.5 pounds of backpressure. Another test, using a vacuum gauge, is to measure the engine vacuum at curb idle and at 1600 RPM. If engine vacuum is 21 inches at curb idle and 15 inches at 1600 RPM then there is a good possibility your catalytic converter needs to be replaced.

You may also take the converter off the vehicle and check it for damage or clogging. Shining a flashlight into the core of a honeycomb style converter will reveal whether the honeycomb is partially clogged, damaged, or loose from the edges.

Finally, a converter can be defective because it has become poisoned. When a catalytic converter becomes poisoned it loses its ability to effectively control emissions. Some common causes for poisoning and converter degradation are using leaded fuel, fuel additives containing lead, an out of tune engine, engine management system failure, faulty engine sensors, just to name a few.

If your vehicle is burning an excessive amount of fuel or misfiring, due to some of the reasons above, it is just a matter of time before converter failure. A constant rotten egg smell emitting from the tailpipe is a sure sign of the impending failure of your converter.

If you do determine that your catalytic converter is defective, it is extremely important that you determine the reason for its demise. Always have your emissions checked on an exhaust gas analyzer after the new converter is installed to ensure your engine and engine management systems are operating at their peak efficiency. Failure to find and repair any fault will result in a premature failure of your new converter.
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Monday, November 8th, 2010 AT 5:52 PM
Tiny
RAUSCS
  • MEMBER
Thanks for the info. After reading that, I am doubting that the converter is the problem. The car runs fine, then the issue comes on fast, and the car just barely runs, won't raise the revs over 1000 even with the pedal floored. Then it's fine again. I'm going to look for bad grounds and tight wiring connections this weekend - any other ideas?
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Tuesday, November 9th, 2010 AT 3:55 PM
Tiny
BMRFIXIT
  • EXPERT
You said they check the fuel pressure
i would recheck it again and check fuel flow too
take it for a run and retest the fuel pump( pressure and flow)
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Tuesday, November 9th, 2010 AT 6:30 PM
Tiny
RAUSCS
  • MEMBER
Are you thinking that the cause is a flaky fuel pump or something in that system? The car is back out of the shop, they charged me nothing and gave it back. If this occurs again, is there anything that I can do while I'm sitting at the side of the road, and the car is acting up, to help troubleshoot this?
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Wednesday, November 10th, 2010 AT 6:04 PM
Tiny
BMRFIXIT
  • EXPERT
I do suspect fuel pump
tool needed to check is a
fuel pressure gauge
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Wednesday, November 10th, 2010 AT 6:21 PM
Tiny
RAUSCS
  • MEMBER
More data! I got a fuel pressure tester, and the pressure running is about 60, not running about 50, and it holds that pressure for an hour when turned off.
I got it to fail when driving on the freeway today. Running really rough, shut it down, attached the tester, 20 psi! Let it idle for about 5 minutes, and the pressure slowly built up until it was 50 - and the car was running fine. I could hear the fuel pump whining with a varying pitch while the pressure was low. I turned the engine off, and when I used the pressure relief valve on the tester to bleed off the pressure, there was a lot of sputtering, and it took a while to relieve the pressure down to zero - seemed like there was air in the line.

It appears that I can drive all day on the freeway going 55 - 65, but the problem seems to occur if I go 75+ for a period of time.

May not relate, but when it was running bad and I was pulling to the side of the road with my foot still hard on the throttle, but the car slowing, it seemed that there were times that the engine revved up in neutral - like the tranny wasn't connected.

Thanks again for your help, hopefully this data will be enough to get this solved.
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Friday, November 19th, 2010 AT 9:22 PM
Tiny
BMRFIXIT
  • EXPERT
Need to have the fuel pump replaced
its located in the fuel tank
run the tank low on gas make it easier to handle when dropped down
i some cases you can lower the tank enough and remove the pump with out dropping the tank
but be prepared to drop the tank
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Friday, November 19th, 2010 AT 10:43 PM
Tiny
RAUSCS
  • MEMBER
Great! Should I replace the filter while I'm in there?

Is one brand of pump/filter better than another?
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Friday, November 19th, 2010 AT 10:55 PM
Tiny
BMRFIXIT
  • EXPERT
Change the filters for sure (you may have two)
one inside the tank and one on top of the tank
No preferences on brand name go with the better warranty
good luck
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Friday, November 19th, 2010 AT 11:16 PM

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