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post #1 of (permalink) Old 06-14-2009, 06:07 AM Thread Starter
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Map Sensor

What would cause the map sensor to give a code 14, saying it is bad if its not? I know from the wiring diagrams, it is connected to and works in conjunction with the O2 sensor and crank sensor. I replaced the map sensor, won't correct the problem, swap back the old one, same systems. The jeep also gives a code 33 which is faulty a/c clutch relay and or faulty a/c clutch engagement, I don't have/need a/c. I figured it was a problem with the gas, checked it completely, no water anywhere, (it acted like there was water in the gas) checked all vacuum hoses, found one bad one, replaced it, some improvement, the biggest improvement was when I put an adjustable pressure regulator on the fuel rail. (I had one laying around) that made the most significant improvement of all but I've reset the computer 3 times so far and the problems still come back before I leave the driveway. The Jeep is the 1995, 2.5 litre, 5 speed, "the rare bright Mango colored with all had pinstriping and scenes, from the factory" you know, the bastard year for jeep it don't know whether its a Wrangler or YJ. Do ya think the computer bit the dust, but it still runs great but idles at 1K RPM's and the idiot light drives me crazy, got plenty of spark all injectors are firing, any ideas. Thanks to any help in advance.

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Last edited by Booger; 06-14-2009 at 06:11 AM. Reason: Because I can
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post #2 of (permalink) Old 06-14-2009, 02:12 PM
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The MAP sensor code is thrown because the computer doesn't believe the reading - it's not in the range it expects based on other things. Since it's running fine it's still using the MAP input, but it's wary of it.

Have a close look at the vacuum line feeding the MAP. It should be the thin hard plastic line. Sometimes that line gets replaced with a rubber hose - small ones collapse and trick the MAP, big ones dampen the signal too much. Either can set the code.

The ECM may have had a glitch inadvertently loaded into the memory - an electrical spark from somewhere - radio station, welding, lightening etc. who knows. Just clearing codes quickly won't get rid of it. Disconnect the battery overnight - it takes several hours to get ALL the memory to erase.

Try it then, let us know.
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post #3 of (permalink) Old 06-14-2009, 04:02 PM Thread Starter
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Thanks RRICH, I'll have to maybe downsize the hose a tad, the old one was as you speak, but it was rotted and I replaced it with a standard vacuum hose, and it ran fine for a few thousand miles before now, I was begining to think no one knew about their function, thanks again, I'll try this and we will see.

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post #4 of (permalink) Old 06-14-2009, 05:42 PM
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The thin hard plastic don't collapse like rubber will, that's why they use it.
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post #5 of (permalink) Old 06-15-2009, 01:27 AM
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Quote:
Originally Posted by RRich View Post
The thin hard plastic don't collapse like rubber will, that's why they use it.
Yup, had that same talk with people time and time again!
Sometimes, you should just save your breath...

*IF* you take the hard lines off the sensors (heat. vibration problems, there are reasons to be cheap and not use the hard factory lines)
Try using a stiff WOVEN SUPPORT FUEL LINE instead of cheap vacuum line.

To be real about this,
Even the not too bright ASE mechanics are warned NOT to use rubber vacuum line in place of any line that will carry GASOLINE VAPOR!

(and if you don't think the MAP sensor 'Sees' gas fumes, just take the line off and smell it!)

The stiffer FUEL PRESSURE RATED LINE will do a better job than the vacuum line some kid at the parts store gave you.

Ideally, you should bend up some metal tubing and just use fuel line on the fittings,
Barring that, you should go back with the factory 'Plastic' lines,
And if you are not going to do that,
Try FUEL PRESSURE line, NOT VACUUM HOSE!

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post #6 of (permalink) Old 06-15-2009, 12:20 PM
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I had to get creative when plumbing the MAP during the recent TBI swap. Ended up reusing the hard line & elbows (had several of these extra) along with a short section of FI rated hose (cut from what I used to plumb the external pump). The hardline fit into the elbows (still pliable), but used a bit of O2 safe RTV to "glue" them up. I searched for weeks looking for a new section of tube (figuring it could be bent using heat like PVC), but never found anything.

*IF* it becomes a problem, any issue using steel brake/fuel line to make a new pipe?

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Last edited by Caver Dave; 06-15-2009 at 12:22 PM.
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post #7 of (permalink) Old 06-15-2009, 01:06 PM
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Steel lines, like a brake line? Maybe if the run is really short.

The hard plastic line has a very small inside diameter - for a reason.

Remember the MAP controls the amount of fuel being injected. When you mash your foot down it needs to "know" the vacuum dropped instantly and how hard so it can add the appropriate amount of fuel. It needs to know all the subtle changes in the vacuum all the time.

The longer it takes for the vacuum to change in that line the more delay, and the more the stumble. A small line reacts almost instantly, where a bigger one will be slower. The larger volume in a larger line acts like a buffer and slows the changes down considerably.
Brakes lines are considerably bigger inside than the plastic lines.

If you can get very small steel lines like the plastic ones they would be better - lifetime lines that don't melt or get brittle with time and heat.

Most parts houses don't carry the plastic line in bulk, you have to search around - a PITA.

I bought a small roll of it on the internet once, but I don't remember where. Maybe do a search.

Parts houses do have the rubber ends and splices though.

I was working on a customers truck (street) - he'd installed a "hot?" cam with lots of overlap and a long duration, on ported fuel injection. It ran terrible, about the only time it ran good was WOT.

The big cam was driving the MAP nuts - I used a vacuum transducer to see the pulses.
I tried using a bigger and longer vacuum hose to the MAP, I think it was 3/8 about 6 feet long. It buffered the pulses fine, engine ran fairly smooth. But it created a very bad stumble, too much to drive.
The final cure? - We put in a cam without near as much overlap or duration, and it had very steep ramps on opening and closing, and more lift. It did the trick!
It was an interesting project to play with, especially with a vacuum transducer where we could print the pulses and see how much the vacuum line size dampened them.

Even when using a regular vacuum gauge, you want the hose as small and short as possible so you can see the "ticks."
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post #8 of (permalink) Old 06-15-2009, 03:58 PM
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Yup, we do it all the time,
but on the show cars, we used polished stainless lines.

On a lot of 'Utility' vehicles, I use copper or aluminum tubing since it doesn't rust up and close off as easily as brake line does.

Steel brake lines is what I use for 'Beater' vehicles that we aren't spending much on...
Works OK, is cheap and effective, but will RUST like crazy inside if you aren't careful to tilt it so it drains to the vacuum source!

Use the small diameter lines, and you will have virtually the same inside diameter as the hard plastic lines.
-----------------------------

Just keep in mind that the MAP sensor needs to be mounted NIPPLE FACING DOWN!


GM had a REAL problem with mounting the MAP sensors with the nipple facing UP, or the MAP sensor on the end of a 'Down Hill' run of lines.
Drove us crazy at DFI also until we figured it out!

Fuel condenses from vapor, and stands in the sensor or in the lines...
So you wind up with all sorts of strange readings!


Of course when you open the lines, the fuel evaporates quickly, so you don't find it by the time you unbolt and test the MAP sensor to see if it's reading stupid...
And you are left with a trouble code, a compute stuck on open loop, and a bald head from all the hair pulling!

Make sure you don't have a 'Dip' in your vacuum signal line so fuel/moisture can collect in the line either or you will get some pretty strange vacuum readings!

Early electronic fuel injected vehicles
(yes, I'm old enough to remember MECHANICAL fuel injection on vehicles)
were a REAL PAIN in the beginning!
All kinds of unforeseen problems with plumbing, wiring, materials, ect.
----------------------------

I spent almost a week trying to find a problme with a girlfriends car she bought used for a "Really good price..."
Turned out the moron had used silicone sealer and some had got in the vacuum lines!.
He had chased a phantom problem for MONTHS, then just sold the vehicle to get rid of the headache!

Changed out all the vacuum lines and the vehicle decided to work correctly after that! (and a change of O2 sensors)...
If she had been paying by the hour, she would have had more in the labor bill than she paid for the vehicle!

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post #9 of (permalink) Old 06-15-2009, 05:41 PM Thread Starter
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Ok, did a new plastic vacuum line, disconnected the battery overnight, started right up and then cut right off, 2 times, when the check engine light came on it runs fine at 1K rpm's. Sitting at a light or stopped it will idle down to 800 rpm's and run for a few seconds and then back up to 1K rpm's. Still reads the same codes, a 33 for the A/C and a 14 for the map sensor. I'm figuring an O2 sensor, but I'm not sure yet. I'll find out, going on an 800 mile road trip tomorrow, we shall see. Anyone, ideas?

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post #10 of (permalink) Old 06-16-2009, 12:14 AM
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Quote:
Originally Posted by Booger View Post
Ok, did a new plastic vacuum line, disconnected the battery overnight, started right up and then cut right off, 2 times, when the check engine light came on it runs fine at 1K rpm's. Sitting at a light or stopped it will idle down to 800 rpm's and run for a few seconds and then back up to 1K rpm's.
When it idles down to 800, that's a try at closed loop mode, and something is throwing a large enough trouble code to kick it back into 'Open Loop' or 'Limp Home' mode.

When in closed loop, you are working from all the sensors and the engine is trying to do optimum fuel mileage comsumption.

When enough trouble codes flash, or you have one major sensor that isn't working, then the system goes into 'Open Loop',
Which is nothing more than dumping enough fuel for the Engine RPM (Speed) and usually the supply entering the engine (Density/Volume) and the computer can determine how much air is getting in by one of three means,
The O2 sensor, the Throttle Position Sensor (Throttle Angle) or if equipped, the Air Density Sensor that also tells volume of air.

My guess is you have a wire that is disconnected, grounded, isn't making a good connection, or you have a sensor unhooked somewhere,
OR,
You are running the sensor wires (Low Voltage) next to something that is causing INDUCTION, creating current in the wires that shouldn't be there.

More problems on swaps crop up from bad grounds,
(people simply WILL NOT run dedicated grounds to the computer, engine block, transmission case, ect. so the computer sees the same electrical potential at all inputs)
Or bundling the sensor wires with high current wires, like wires to the coil, heater motor, or running them too close to things like alternator and coil/spark plug wires.

One knucklehead actually bundled his computer wiring with his speaker wiring for his base speakers!
Car ran fine as long as he didn't turn on the subs,
but as soon as he fired up the 'Rap Crap', the car would do STUPID things!
(I told him it was "God's Way" of telling him he shouldn't listen to 'Gangsta Rap', wear his pants around his knees and his hats on sideways!)

Anyway, make sure your wiring is sorted and shielded for the sensors,
Make sure everything is soldered with SILVER BEARING ELECTRIC SOLDER, not the lead/tin crap off the discount store shelves,
And sort through to see if your sensors are all working (usually done with a multi-meter or laptop with a Calibration Mapping program which you can find on the internet for free now)

Quote:
Still reads the same codes, a 33 for the A/C and a 14 for the map sensor.
A/C reading, is it an open circuit code, or is there more than one code, like for over limit on the A/C for the donor vehicle?

MAP sensor problems are almost ALWAYS either the MAP sensor it's self,
Or the connector to the map sensor.

Since you did a swap, you might want to check the connecting wiring all the way back to the computer along with checking the physical things at the Sensor it's self...
(Make sure there it's mounted NIPPLE DOWN, make sure there are no 'Low Spots' in the lines leading to the sensor, so vapors can't condense into liquid and plug things up,
Ect...

Quote:
I'm figuring an O2 sensor, but I'm not sure yet. I'll find out, going on an 800 mile road trip tomorrow, we shall see. Anyone, ideas?
It will probably make the 800 miles, but my guess is it will have horrible fuel mileage if it does the entire trip in open loop...
------------------------------

One other thing you might want to check,
A clogged converter or smashed pipe will cause high back pressure,
And that will throw a vacuum (MAP) trouble code,
So will a IAC motor not working correctly...

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