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View Full Version : keeps throwing MAP sensor codes... poss. ECU problem



Hurricane 4x4
10-17-2005, 09:35 PM
i'm having some issues with my 1996 4.0 grand

About 3 months ago i started to randomly have engine problems... it would run really rich or lean all of a sudden and then go back to normal... it finally threw a code 14, MAP sensor... so I went and bought a cheapo pep boys sensor... works ok for 2 months... then completely dies... so i break down and shell out $80 for a mopar part... works for a few days, then mysteriously has problems on/off whenever it feels like it.

I have taken the connectors off of the computer and sprayed with electronic cleaner... and i have taken the connector apart that hooks up to the sensor and cleaned and inspected that as well... all the connections look great... no dirt or corrosion at all.

here is what strikes me as odd... when i hook up my original sensor and with the replacement mopar sensor, it will start, but it will run real rich and idle poorly... with the pep boys sensor it will not start at all

I have checked the connectors and all looks well... and a visual inspection of the wiring shows it to be in excellent shape also. My multimeter was broken when i pulled it out today, so I could not do the 5v test... i will get to that tomorrow... but now I am thinking it may be my ECU that has gone bad?

any insight?

thanks

TrojanMan
10-17-2005, 11:17 PM
I'm not entirely sure what to tell you, but you might want to try an adjustable MAP sensor http://www.angelfire.com/my/fan/MAP_adjuster.html

That will adjust your fuel curve effectively. The only thing is that will patch the problem rather than fully repair it.. I'm not sure what to tell you otherwise. You might want to try cleaning the intake manifold with seafoam and make sure you're getting enough air.

Hurricane 4x4
10-18-2005, 01:28 PM
I like the idea of an adjustable sensor... however I dont think it would really patch the problem since it is on/off

The motor is getting plenty of air.... and I checked the little throttle body elbow and the passageway on the TB... its fine.

I may just take it to the dealer... it would be the first trip in 170,000 miles

For those of you who have had an ECU go bad... did it act up like this?

Hurricane 4x4
10-18-2005, 01:30 PM
I read in my haynes manual that the code 14 means that the 5.0 v circuit is "open". Could this mean a bad ground somewhere?

Hurricane 4x4
10-19-2005, 11:04 PM
Ok... well i dropped it off at the dealer yesterday... went back to the stealership today to get the lowdown... the guy looks at some papers... says my computer is fucked... then punches some numbers in on a calculator and hands it to me, and says "this is how much before tax" I did a double take. $950... I almost dropped a log right there on the floor. Fortunately they had not ordered the new PCM yet and i was able to get out of there and only spent $150 on a diagnosis... the part itself was $420 from them. And as most of you know it takes 20 minutes TOPS to swap out a PCM

I bought one from a junkyard for $150 and it will be here friday.. then I am taking it to another dealer who said they would program it with my VIN number and factory settings for $40

Hurricane 4x4
10-21-2005, 11:37 PM
Well i got my new computer today from a used parts place... it was pulled from a 96 Jeep Grand Cherokee 4.0 and came tested and with a 30 day warranty.

It still runs like poop... albeit different poop

computer now throws a code 24... map and TPS sensor do not correlate

Guess I will check the TPS?

Hurricane 4x4
10-22-2005, 10:22 AM
TPS sensor is fine...

this is keeping me awake at night

Hurricane 4x4
10-29-2005, 10:32 AM
Got new PCM, new MAP sensor... TPS checks out...

Jeep runs good MOST of the time. Every now and then it will have some trouble. For example... I started it up to go to lunch the other day and it fired and died. I tried again, same result. I finally got the thing going by giving it a little gas, but if i let off It would die. After a few seconds nursing it at low rpms, the IAC kicked in and it idled just slightly higher than normal. When driving, it would almost stall when I came to a stop... and while on the gas the power was decent, and it ran smooth, but it would get stronger and weaker at times... seemed like it was going rich/lean. After that, when I started the motor, it would start and run right at idle speed... not rev up a bit and then drop like it usually does. Next day it runs fine... but i'm sure this problem will revisit me.

Right now I am thinking Fuel pump? any ideas? Batt is new, charged, and the connections at the battery are good.

OverkillZJ
10-29-2005, 11:06 AM
Torch it.


Frankly, beats me. When you've replaced that much junk maybe it's better junk interacting with the same wiring problems. Total guess though.

Fuel pump would make sense though, I guess.

dkreuzen
10-31-2005, 08:48 PM
I had a similar problem with my MAP sensor on my 96 4.0. I replaced two sensors (Mopar) then I decided to look really good at the connector. The connector looked good and was clean but the contacts were loose. I crimped the pins just a little so I could feel them making good contact, no more problems. Remove the seal on the connector and you will be able to feel if the connector is loose or not.

Dennis

JeepinHank
11-01-2005, 10:21 AM
Stupid question, and possibly not at all related to your issues, but how does your exhaust manifold look? Is it cracked? Above the upstream O2 sensor? I'm running about 15% richer due to the O2 sensor showing its lean (Because of a bad crack in the manifold) - no check engine lights tho.

Hurricane 4x4
11-03-2005, 11:30 PM
the manifold i'll give a look over... i dont think its my problem but hey, it could happen


The dealer actually cut the wires at the MAP sensor and replaced the connector with another one... i haven't touched it, i assume its good.

Today, the problem revisited me for a short time. I drove from my house to the local blockbuster... went in, came out, started it up, and bingo, goes straight to 800 rpm and idles right there. I shut it off, and cranked it back up only to find it go straight to 800 rpm again.. i try this a few more times at stoplights, same thing. Seems to run ok though. So i boogie on over to the auto parts store, and buy a fuel pressure tester.. hoping to catch it in the act... i start it up and it acts normally again.. going to about 1400 rpm and then dropping to a normal idle

could it possibly be that my new computer is just "learning"? even though i've been driving on it a week now.

TrojanMan
11-04-2005, 01:07 AM
you bring up a good point about learning. with my dad's 01 montero you have to let it idle for like 15 20 minutes to let it relearn. Try disconnecting the battery for 30 seconds... then let it idle for 20 minutes or so. With any luck that'll solve the problem. If not, I suggest cleaning the intake manifold out with seafoam. Search for my post on how to use seafoam the best. Upstream O2 sensor is another good possibilty. Those things do go bad with time.

Willy's
03-08-2007, 05:01 AM
:smt101 Have you checked the O2 sensor. they are know to have problems on Jeeps

PassRunnerZJ
03-09-2007, 11:14 AM
Since this is an old post I don't know how much good it will be to the original poster, but when my 95 was throwing a MAP sensor code (voltage high I think) it turned out to be a broken wire from the MAP sensor to the PCU. Instead of ponying up $1200 for a new wiring harness I just probed it to the break, stripped it back, and solderd a new short piece of wire in and then sealed it with shrink wrap.

One way that I found to test the broke wire theory was to remove the MAP sensor from the firewall and zip tie it to one of the heavy duty vaccuum lines moving it closer to the engine which pushed the wires together. I ran it this way for a few days before soldering the break.

Oh yea, when my O2 sensor was failing it just threw codes, but didn't make it run like shit at idle and just off idle like the way I thought the idle air screw would do (which I changed out too as well as a new MAP sensor). Once I got to speed on the highway it ran fine as I was able to drive home from Moab which is were the final wire broke in the middle of the Seven Mile Rim trail. Autozone can test MAP sensors which they did and both my old one and new one were good.

DansZJ
03-21-2007, 07:52 PM
I found this thread looking for solutions to my similar issue. I have a 93 4.0L 4wd Auto. Two weeks ago, my check engine light came on and the Jeep started running like crap. I was on the freeway and could feel it wasn't shifting or idling correctly. My temp gauge was bouncing around, and would peg to the red when I let off the gas. I wasn't far from home, so I was able to limp it back there safely.
I obtained the TC - 24 by doing the ignition on, off routine. So I swapped the TPS. No Change so I swapped the MAP sensor. No change, and since the coolant gauge was bouncing around, I replaced the temperature sensor in the thermostat (hoping to at least get my coolant gauge to quit bouncing around).

Still ran like crap, and it wouldn't idle in park, only in drive. It would die in reverse too.
The frustrating part was there was no rhyme or reason to it. In the morning it would run fine, no light. The next morning, MIL light was on and ran bad.
Driving around town, the light would come one and then go out.

I pulled the new sensors, returned them to Autozone (they refunded my money) and put the old ones back on since there was no difference.

After 4 nights and a saturday of checking circuits, voltage, resistance, I gave up and took it to my shop. Handed over the keys and and described what I had done to diagnose it.
3 days of diagnosing, testing, etc, I got it back.

The cause of all this trouble? The wiring in the harness that connects the sensors to the main harness was melted together and shorting out. They repaired the wires that needed it, heat shrinking, etc, and that resolved all the issues. They recommend that I still replace that section of the harness (plugs in to the main harness) but that was it. They also replaced the coolant gauge sensor (back of the engine) since it was bad.

I wouldn't have opened the harness cover to inspect these wires. The tests that I performed to check voltage from the ECM were correct at the time when I checked them. I guess the wires were not shorting out when the engine was not running, but as the engine shifted, it would pull the wires enough to cause a short to open.
Interesting thing is I've never had an engine fire, and can only remember once overheating it. But maybe the AZ summer heat, cracked exhaust manifold, and ??? caused the melted wires.

I hope my experience helps someone else in diagnosing a similar issue.
Man, what a pain the in the ass.