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Old 05-05-2015, 03:32 PM
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Engine Idles Terrible

Recently installed a magnumpowers supercharger in my TJ. I have a 4.0lengine, auto trans.

I'm not getting any error codes. But it runs terrible. It is loading up, black smoke and idles extremely slow.

I did replace the iac valve because I did have that code previously. But that did not fix the problem.

I installed a 2 bar map and new injectors along with a tune. All three of which came with the install kit.

I know on the map there is to be a ground, hot wire and a signal wire. I am getting the same voltage at the signal wire as the hot wire. 5 volts

I have spoke to the Tech at Magnumpowers and tried a few thing's but no luck.

Any idea's ???

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Old 05-05-2015, 03:37 PM   #2
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What did the Magnumpowers Tech suggest to try?

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Old 05-05-2015, 03:39 PM   #3
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I know on the map there is to be a ground, hot wire and a signal wire. I am getting the same voltage at the signal wire as the hot wire. 5 volts
Sounds like a problem.
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Old 05-05-2015, 04:19 PM
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He gave me a different tune to install. No change. Double checked map to make sure it was wired correctly.
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Old 05-05-2015, 04:20 PM   #5
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He gave me a different tune to install. No change. Double checked map to make sure it was wired correctly.
Im pretty sure the signal and hot should not be the same voltage on the map. Did you tell the tech about that?
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Old 05-05-2015, 04:34 PM
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He also told me that. DO you know where the signal comes from. I am assuming the ecu
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Old 05-05-2015, 06:15 PM   #7
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Im pretty sure the signal and hot should not be the same voltage on the map.
The MAP voltage should read 2.5v when the engine is off on the 2 bar unit. If it is always reading 5v then it is indicating full boost, so the ecu dumps more fuel, and you are running really rich. Might want to triple check the wiring there.
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Old 05-05-2015, 06:47 PM   #8
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The MAP voltage should read 2.5v when the engine is off on the 2 bar unit. If it is always reading 5v then it is indicating full boost, so the ecu dumps more fuel, and you are running really rich. Might want to triple check the wiring there.
Yep.

Related:

Map and tune must be matched. I know you think they are, but since you are having problems, time to double check. Maybe the tune wasnt calibrated right or the Map isnt the one you think it is. Check its part number.

Maybe the Map is bad or hooked up wrong to its vac line. Its hooked up to its vac line, right?
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Old 05-05-2015, 08:37 PM
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I've gone over the wiring numerous times to make sure it is correct. Used a meter to make sure I have continuity. And I checked the vacuum lines a couple times to make sure they didn't come off.

Any thoughts that it might be the ecu ??? Is there a test for the map sensor ?
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Old 05-06-2015, 12:40 AM   #10
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Is there a test for the map sensor ?
You should be able to check that when power is applied, but the engine is not running that you have 2.5v on the sensor output. If that is not the case, either the MAP sensor is bad or something on the other end is pulling that line to 5v.
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Old 05-06-2015, 02:55 PM
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A friend is going to let me borrow his vacuum pump to check the map sensor. See if the voltage changes with the change in vacuum.

Update to come.
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Old 05-07-2015, 03:51 PM
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I checked the voltage on the map sensor and as I added more vacuum the voltage dropped. Is this correct for a two bar map sensor ? Or should the voltage increase ?

If so, does that mean pcm issue's ?
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Old 05-07-2015, 07:17 PM   #13
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I checked the voltage on the map sensor and as I added more vacuum the voltage dropped. Is this correct for a two bar map sensor ? Or should the voltage increase ?

If so, does that mean pcm issue's ?
That is correct. It should start at 2.5v, and decrease as you pull a vacuum.

I dont know exactly what it means, but whatever is on the other end of the map sensor signal wire is doing something wrong.

Do you have anything spliced into the wiring harness?
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Old 05-17-2015, 10:16 AM
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I rewired the stock map. Checked the voltage and is over 4 volts but as I pulled more vacuum the voltage dropped.

I am getting a new 2 bar map.

But it still sounds like it is getting too much voltage at the signal wire.

Any ideas ???

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