1998 Ecm Replacement Programming? - JeepForum.com
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post #1 of 18 Old 06-06-2020, 10:03 PM Thread Starter
Xj98Classic
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1998 Ecm Replacement Programming?

I just bought a 98 cherokee 4wd 4.0 automatic.
Guy sold it because it was misfiring, stalling, and stuttering.

I bought it and tried to figure the problem out. What I found was when
I touch the harness for the ECM it would die. I found a messed up wire
and fixed the wire.

It would still stutter and miss and randomly cut out.
I hit the ecm with my hand and it died. Wouldn't start after. I hit it again
and it started. I squeeze it and it dies.

I figure it was a faulty ecm. I went to a junk yard and pulled one from an
identical jeep, year engine and trans. It was a different shape ecm but I
checked 2 different identical jeeps to mine (maybe not trim level) and they both have different than what was in mine.

I bought one installed it. The car starts and instantly dies. If I rev it it will rev barely stay on and die when I stop.

Am I missing something? Do these ecms need programmed to the car Vin?
I read online about vtss? How would I know if my car has it?

Any info would help. Its hard to find on Google.
Thanks guys.

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post #2 of 18 Old 06-07-2020, 02:38 AM
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keep your original .

others will post ideas.
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File Type: pdf 1998xj_PCM.pdf (83.9 KB, 5 views)

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 18 Old 06-07-2020, 05:40 AM
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XJ Cherokee or ZJ Grand Cherokee ?

There is only one shape of 1997-2001 XJ Cherokee PCM, does yours look like the picture ?

What was the part number of the original PCM, and what is the part number of the junkyard PCM ? A 1998 XJ Cherokee PCM should have a Chrysler P/N P56041 534 on the ID label. If the Part Number is correct, the PCM does not require programming

ZJ Grand Cherokee could have vtss, XJ Cherokee never had vtss, but SKIM Chip-in-Key anti-theft was optional in an XJ CHerokee.

Having the engine stall and having to nurse the gas pedal for a minute or two until the Jeep will idle by itself is normal after re-booting the PCM by extended storage without battery voltage.



.
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post #4 of 18 Old 06-07-2020, 10:13 AM Thread Starter
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It is a 98 cherokee classic. The junkyard ecm looks like the one in the picture. The one that was in it was rounded with bend over tabs that hold it together. I took the cover off and it is full of solidified jelly.

After swapping the ecm it will not idle. It will bearly stay on when i rev but constantly try to die and then die when i stop touching the gas.

Could the SKIM be causing it shut it off?
The ignition was replaced by previous owner.
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post #5 of 18 Old 06-07-2020, 10:14 AM Thread Starter
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Original vs one from junk yard
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20200605_171152_1591546454612.jpg   20200606_111657_1591546474836.jpg  
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post #6 of 18 Old 06-07-2020, 10:15 AM Thread Starter
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Damaged purple wire on ecm harness i fixed.
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post #7 of 18 Old 06-07-2020, 10:28 AM
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The symptoms are not SKIM related. The old PCM looks like a refurbished unit. The junkyard PCM is for 1998, is Calif emissions, but should work.

It is very likely that the PCM has re-booted and deleted the idle settings from sitting with no battery. Go for a test drive to restore the idle settings. You will very likely have to start out with one foot on the gas pedal to keep the engine running, and the other foot on the brakes.


The new For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM or poor battery charging. Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem. A faulty Coolant Temperature Sensor may also cause similar symptoms. Testing of the CTS is recommended as part of the diagnostics. A poor ground at the ignition coil can also cause similar symptoms.

The reboot symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal. (3) The ECU will relearn the idle settings after a short period of driving and the engine should start and idle normally.

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post #8 of 18 Old 06-07-2020, 10:35 AM Thread Starter
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Nice. Thanks for the info. I'll go try again and see what haplens.
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post #9 of 18 Old 06-07-2020, 08:06 PM Thread Starter
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So I ran the codes and it is throwing the cts circuit high. P0118.

I replaced the sensor cleared the code and same problem. After it warms up it idles perfect. But any touch on the gas and it stalls.

I checked the fuel pressure and at the rail its showing 4. Than 10psi. Crept up to 20 once but usually sits at 10ish.

I tested the pump and I know it turns on. I hear it.
I am looking into the fuel pressure regulator. Where is it located? Its not on the rail like what I find on Google.
And there is no serviceable filter? Just a strainer?
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post #10 of 18 Old 06-07-2020, 09:52 PM
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fuel pressure 49psi +or-5, regulator in tank on pump module.
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #11 of 18 Old 06-07-2020, 11:03 PM Thread Starter
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Yea I was looking into that.

Would there be any reason why there would be low fuel pressure besides a bad pump?

Pump turns on.

Does the tank need to be pressurized?
Pressure leak?
Clogged hose?
Signals from computer?
Voltage or ground issue?
Pressure regulator signal? (Part of the pump?)
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post #12 of 18 Old 06-08-2020, 04:52 AM
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Failure of the fuel pump assembly is somewhat common. Low fuel pressure would be a primary symptom of failure, and would explain the running/stalling symptoms.

Check the CTS wire plug for bent pushed back or corroded wire pins. Check the CTS wire harness for damaged wires or chafed/melted wire insulation.

The fuel pump is mechanical and doe not rely on the PCM to function. If you think it is necessary you could open the fuel line and blow it out with compressed air. Test the fuel pump voltage, amperage draw, and continuity to ground.

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post #13 of 18 Old 06-08-2020, 11:03 AM Thread Starter
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Would the CTS cause no fuel fressure?
I just replaced the sensor. Pins looked fine ill check fir damage. When I disconnect it the fan turns on so it seems like it gets a readjng.
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post #14 of 18 Old 06-08-2020, 11:12 AM
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Quote:
Originally Posted by Xj98Classic View Post
Would the CTS cause no fuel pressure?
.
No.

Quote:
When I disconnect it the fan turns on ...
The operating circuits are good. The e-fan engages as a safety default when no CTS signal is present. Inspect to confirm the CTS signals can get to the PCM.

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“When the people find that they can vote themselves money, that will herald the end of the Republic.”

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post #15 of 18 Old 06-08-2020, 11:30 AM Thread Starter
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Alright. Thanks for all the info. Going to check everything on the fuel pump and possibly replace it. I'll let you guys know if that fixed the problem. Might take a day or 2. To many kids around my house to take care of haha

Thanks.
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