I have a 99 Caravan 3.0 with no power. It winds up to high rpms when accelerating then levels out. Even worse with the AC on.

Took it to a shop, they kept it for a week. No engine codes, their computer did not give any either. If you rev it up by hand with it in park I hear a muffled backfire noise. The cylinders were found to be running at 120psi and they said that is too low and needs an engine rebuild and that is my problem. Could it be something simplier??

It has new air filter, cleaned the throttle body, new plugs, rotor, distributor and wires. Will low compression cause an engine to do high rpms when leaving a red light and hardly accelerate to the desired speed??

Thanks,
Bo - Houston, TX

 

A clogged catalytic converter is a possibility.

 

I agree with cat. or exhaust restriction which not only will show up with a compression test, but will show up with low manifold vacuum.

this is such a basic test.

the problem with efi is soooooo many people think that the computer will give all the answers... and then when they don't get the answers they give up or say it needs a computer.

KISS problem solving methods. always refer to the basics and work toward the harder/more expensive answers last

 

To run an accurate compression test, the cat must be by-passed.
120 PSI is plenty to run OK. I've seen engines with 90 still running and driving.
Test the vacume as suggested.

An easy test for a plugged cat is get a complete exhaust system from the bone yard.
Cant imagine they'd want more than a couple 20s for one.

Keep us posted on what you find,
PinCup

 

why can't people spell VACUUM?

you can't buy a complete exhaust system from a junkyard as it is ILLEGAL to sell used Catalytic converters.

I have never seen a compression test procedure list the requirement of removing the cat for the test. They all say the hold throttle WOT, disconnect fuel and ignition.

How I test for a bad cat is I remove the upstream oxygen sensor and install a pressure gauge.

 

OK, everything points to the catalytic, even you guys. The van is undriveable so I have nothing to lose at this point. The whole system is welded and I can only get to two of the four bolts where the cat bolts to the header.
So, I took my sawzall and cut the pipe behind the cat. Using a 24 inch long, 3/8 diameter drill bit I drilled 4 wholes from one end to the other. Ran the engige to blow it out then put the pipe back together.
Not one bit of improvement.

I threw a MAP sensor in it when this started happening via someone elses suggestion, so that is new as well.

 

after that bit of hack work, I'm done with this post.

 

Well... now that the spelling ***** has retired, let's progress.

I don't think 4, 3/8" holes are enough to get a by-pass effect.
There has to be a way to get that cat off.
Maybe some heat and liquid wrench will help loosen them.

A pressure gauge in the O2 hole would work if you have one.

We all know a junk yard would NEVER break the law... and I have ocean front property in Kansas for sale.
It never hurts to ask the bone yard if they will sell an entire exhaust system.
Tell them the wife ran over a huge rock and flattened yours.
I'm pretty sure they aren't supose to sell air bags from a wreck either, but I've got them before telling them I wanted the leather wrapped steering wheel and my AB wouldn't fit it.

Good Luck,
PinCup

 

Thanks Pincup for your help. Drilling the 4 holes through the cat was just a hail-mary shot. It didn't have to significantly fix the problem, just see if there was a change in performance so I could see if this part is what needed replacing. And there was absolutely no change. I am shooting this horse.

I am a capenter, not a mechanic, so I am calling it quits and calling the "We buy junk cars" guy and get me $500.
Between it not running, the cash I have spent already, rear seal leak, power steering leak, and a/c compressor leak. It's done. Can not complain. Bought it with 12,000 miles on it, ran it up to 170,000 miles only doing oil changes, brakes, and tires.

And don't konck sapporo too much. That's how people like him make themselves feel good. One can not argue with obvious professional advice as they will lose trying, and he knows this. I am sure we all know were to go for professional car advice but, most of us realize that places like this forum are places to try and find affordable/termporary work-arounds so we can get our crap running and get to work on Monday. Because if we could afford a real mechanic to do it, it would be there and I wouldn't be here.

Thanks again,
Bo
Houston,TX



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