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Old 06-11-2019, 08:26 AM   #1 (permalink)
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Default Rebuilt Motor Startup Issues

Hey guys, quick question- the car is fully assembled, and it even starts.....sort of. We tried starting it up with the AEM EMS, and it instantly blasted up to 5k rpm and held there steady. The throttle wasn't stuck, no real issues, but we couldn't shut off the engine. Tried the ignition, didn't work, then pulled the battery leads, and a lot of the fuses, but it kept running, so I then yanked the plugs into the EMS and that finally killed it. We reconnected everything, and I swapped in the original ECM, and now it has issues staying started, runs rough, surges a couple times, backfires a bit, and dies. Should I focus on the EMS, or ECM to troubleshoot, and what do I need to do for the selected choice? Doesn’t seem like it would be the spark plugs due to it running so well on the EMS, so not sure what is quite happening. Thanks for the help!
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Old 06-11-2019, 09:29 AM   #2 (permalink)
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Default Re: Rebuilt Motor Startup Issues

I assume you did a boost leak check? Was one thought for the high idle.
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Old 06-11-2019, 09:49 AM   #3 (permalink)
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Default Re: Rebuilt Motor Startup Issues

Quote:
Originally Posted by CntrlSwitch View Post
I assume you did a boost leak check? Was one thought for the high idle.
Admittedly, I forgot to do that, but could it cause THAT high of an idle? I didnít think it would get that high.
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Old 06-11-2019, 09:59 AM   #4 (permalink)
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Default Re: Rebuilt Motor Startup Issues

The only way for the idle to be that high is either an open throttle plate, or vacuum leak after the throttle body. A missing or backed out biss screw, clutch booster leak, or brake booster leak is probably the culprit.
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Old 06-11-2019, 10:07 AM   #5 (permalink)
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Default Re: Rebuilt Motor Startup Issues

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Originally Posted by donniekak View Post
The only way for the idle to be that high is either an open throttle plate, or vacuum leak after the throttle body. A missing or backed out biss screw, clutch booster leak, or brake booster leak is probably the culprit.
Thanks Donnie! Would that also explain the difference between the EMS and ECM as well? I could see how unmeasured airflow would screw with the ratio and cause it to predetonate and stall, or am I off my nut there?
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Old 06-11-2019, 10:40 AM   #6 (permalink)
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Default Re: Rebuilt Motor Startup Issues

Make the throttle is closed and that the throttle cable hasn't popped out and got hung up.
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Old 06-11-2019, 11:02 AM   #7 (permalink)
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Default Re: Rebuilt Motor Startup Issues

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Originally Posted by Chris @ Rvenge Performance View Post
Make the throttle is closed and that the throttle cable hasn't popped out and got hung up.
That was my first thought as well when it was revving that high. Looked good, no issues, seated properly with proper tension on the cable.
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Old 06-11-2019, 12:36 PM   #8 (permalink)
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Default Re: Rebuilt Motor Startup Issues

Quote:
Originally Posted by Hackurs View Post
Thanks Donnie! Would that also explain the difference between the EMS and ECM as well? I could see how unmeasured airflow would screw with the ratio and cause it to predetonate and stall, or am I off my nut there?
With aem and speed density the airflow isnít measured, itís calculated from manifold pressure, air temp, and rpm.
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Old 06-11-2019, 12:58 PM   #9 (permalink)
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Default Re: Rebuilt Motor Startup Issues

Quote:
Originally Posted by donniekak View Post
With aem and speed density the airflow isnít measured, itís calculated from manifold pressure, air temp, and rpm.
Gotcha, so an unregulated air flow after the throttle body wouldnít stop the EMS, it would compensate fuel to much the manifold pressure, hence the 5k idle, but it would mess with the ECM which does measure airflow? Am I understanding that right?
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Old 06-11-2019, 03:41 PM   #10 (permalink)
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Default Re: Rebuilt Motor Startup Issues

I see two problems in this post... 1: where is all the air coming from? 2: Why isn't the MPFI turning off?
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