The car (er...minivan) in question is my Caravan with the 2.5 and auto.

Runs great but seems to be a bit on the 'rich' side. Usually fails NOX at inspection time, tail pipe is sooty, MPG isn't quite what it should be.

Mileage of engine is unknown as I'm not sure if its the original engine. The van shows 110K. Engine uses only the slightest bit of oil between changes.

There are no vacuum leaks and the condition exists even with a new oxygen sensor.

On a carbed engine, I'd know what to look for, but with FI and computer I'm a bit lost.

Any common causes for this? Suggestions? Sage words of advice?

Are there any codes stored ?

Some had a problem with leaky injector.I replace quite a few back in the day at work.I believe the bad ones were black but its been years since Ive done any.Rocky

I have had that problem because of a bad Map sensor and most recently a timing belt that was stretched too much and the timing was off terribly.

Replace the T-belt since you don't have a clue the mileage, check your plugs for a cylinder that is suspect (possible bad wire or injector) and replace the map sensor if they all look the same.

Black injectors?

I vaguely recall something about different colored injectors.

This is TBI.

Timing belt, took a look at it when I had the cover off the replace the valve cover gasket. No cracks, could still clearly see GATES written on it. Still doesn't tell me how old it is, but, at least I know its not the factory belt.

Wouldn't a bad MAP sensor affect drivability too? Van seems to run no different in any temps, any weather, any altitude.

Thanks guys.

Start checking for any vacuum leaks

Dont let the codes confuse you as they are no big deal and do tell you something.

12 - recent battery disconnect....dont worry about this

34- Cruise control...it will set if you dont have cruise control so I assume you dont have it.

37- Part throttle kickdown...it also sets if not equipped and you most likely dont have it. It is a relay that controls the lock-up converter on some models. I would not worry about it as I said you most likely dont have it and even if you did it has nothing to do with running rich.

55- Means end of sequence or all done testing. You will always get this code at the end of checking codes since it means its all done.


51- This is the one that tells you something. If you are running lean for any reason the 02 sensor will drive to low voltage telling the PCM to richen up the mixture. It will drive the mixture as rich as it can until the 02 starts switching. It will also jump to other adaptive cells trying to richen the mixture. If it does all this and is still staying at low voltage it tells you you have a very lean condition that the PCM cant makeup for.


So as was stated look for a good size vacum leak ar a very low fuel pressure. Basically anything that will make it run lean will cause this. If the 02 sensor was actually stuck there and was bad it would be loading up very badly. The 02 sensor needs to be switching from lean to rich for it to work correctly. Basically about .5 is the center so the 02 will go from just below .5 to just above .5 to be working right. Ron

This thing originally had cruise, but, for whatever reason, it was left off when the van was put back together after being wrecked.

I've checked hoses before, and I'll check 'em again.

The O2 sensor has been replaced twice in the short time I've owned it. Both times in an effort to get it to pass emissions testing.

Fuel pressure? Never checked.

Would it run basically OK with low fuel pressure?

The fuel pump is fairly loud on this thing. When standing at the drivers door with it idling, you can hear the pump over the engine.

Hmmmm.....I don't think I've ever replaced the inline fuel filter.

Thanks Ron for explaining things so that I could understand them.

Replaced the fuel filter today. Don't know why I didn't do it sooner. It was pretty plugged up.

Went thru the vacuum lines. No broken lines, but found a couple where the connection was LOOSE. I only replaced one hose, the rest I just trimmed a little to get down to where the hose wasn't expanded to get a tighter fit. On the bigger hoses, I actually put on hose clamps.

First start up, it smelled leaner. I didn't smell the richness I used to. The fuel pump was also MUCH quieter.

Excited, I took it for a bop around town, ran great!

Gave it a five mile run on the freeway..........I now have a 20MPH idle.

No hoses came off, nothing is holding the throttle open. Start the van put it in drive, and it goes 20MPH without touching the gas.

Did I screw something up by giving it 'proper' vacuum?

I've got the battery disconnected right now to reset the computer. I didn't pull codes (again) before disconnect.

Ok, since nobody's said this yet, check and change out the coolant temperature sensor if necessary. It helps regulate the mixture. If it's telling the ECU the engine is colder than it really is, it's going to run rich.

Wouldn't a temp sensor throw a code?

Well, don't know what the heck happened. Left the battery disconnected overnight, runs 'normal' again. Drove around for an hour trying to get it to do it again, nothing.

You know with you saying that it reminded me of the problems we had with leaking injectors on some 2.5 engines. They actually had a recall for some models. But the bottom line was they would come in and we would replace the injector. Then the cars would not idle ?? So we had to unhook the battery for at least 10 minutes to fix it. What happened was the PCM would drive the adaptive memory way lean to make up for the dripping injector. So when we replaced the inj it would run way lean in certain adaptive memory cells because the leaking injector was not leaking now causing it to run rich. So we had to unhook the battery for a good 10 minutes to reset the adaptive memory to 0. Then it would run good and as you drive the car it learns the best setting for the memory cells. So when you unhooked the battery you reset the adaptive memory along with a few other settings. Drive it and see if it comes back. It may after a few days or a week or so but if it does not then dont worry about it unless it ever happens again. Ron

Ron didnt you just love working on those old 2.2s and 2.5s?One of the easiest motors ever to work on.I really like the ones with no AC to do timing belts on.Only problems I remember was the rubber carb base that had to be changed.That and those carbs either worked great or were a total pain in the A--.Rocky

On my old 3.0, the fuel pump was noisy, but seemed to run fine.
On vacation one year, got up north in mountains, on a long pull it started to die out, lose power, but we were nearly where we were going, and for the two weeks of vacation no problems, ran fine. Friend with shop there said tank sock. Ran fine while there.
Return trip home, fine until about 400 from home. Got off interstate, secondary roads for couple hundred miles, ran fine, forgot about it for a awhile.
Had to return up north month later, same symptoms.
Got there, had friend drop tank, the sock was orange. Apparently not clogged entirely, would slowly plug. He said very common, even with plastic tank.
New sock, pump quiet, no further problems.
PITA to change, but the improvement was worth the work.

Been running great.......until a few moments ago. I was in traffic, slowed for traffic, and it stalled. Fired right back up, but, I had to 'two foot' it to get it home.

Once home, I let it die, waited a few minutes, then started it up again. It idled just fine. Drove around the block just fine.

You could check for leaking injectors by pulling the injectors and fuel rail as a unit and cycling the key on and off to prime the system (if the pump runs for a second when you turn it to "On" initially). If any of them drip fuel then there's your problem.

Heck you could even cycle the key without removing anything and see if it burps out some unburnt fuel when you actually go to start it.

Only has one injector.Might have to have it scanned.Not just have codes read.Scanner will show what the computer is actually doing.Rocky