LQ4 Swap Not Running Right
Thread Starter
Teching In
Joined: Jan 2016
Posts: 7
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LQ4 Swap Not Running Right Alright everyone, I need help. I am at a loss as what to do next.
I have been searching here, google, ShopKeyPro, and anything else I can.
Here is what I have.
71 C20
2001 Silverado LQ4 6.0/4L80E.
Computer done by Brendan and LT1Swap
Wiring harness cleaned up per his website.
My problem I am having, short of the couple oil leaks which I can deal with easy.
The truck starts fine when cold and idles great for about 30 seconds to a minute. Right around 600 RPM. I am using a Snap-on Modis Ultra to view live data. However, after that time the idle starts going low and the engine starts chugging and shaking. If I let it keep doing that, it'll die. If I press the gas it takes a minute and then catches up but once I let off, it goes to the same thing and dies.
If I try to drive the truck, once I let off the gas it dies. Common problem here is, it dies.
I have pulled the throttle body, cleaned it using a parts washer, pulled the IAC and cleaned it. Put new AC Delco plugs and wire on the truck and I am not getting a single misfire.
Just can't seem to figure it out.
As for codes, the only ones I get are when I unplug a sensor to see if something changes. No MAF code, no IAC code, infant the readings on the IAC are on spot with what it is requesting and what it is giving. I have checked the fuel pressure, 55psi at idle and 58psi when I unplug the vacuum regulator on the rail.
This is a drive by cable engine as well.
Any advice is greatly appreciated and if anyone who knows a lot about this on the west side of Houston, feel free to invite yourself over, I can provide beer and BBQ. I just need to figure this out by Sunday night, This is suppose to become my daily driver.
I have been searching here, google, ShopKeyPro, and anything else I can.
Here is what I have.
71 C20
2001 Silverado LQ4 6.0/4L80E.
Computer done by Brendan and LT1Swap
Wiring harness cleaned up per his website.
My problem I am having, short of the couple oil leaks which I can deal with easy.
The truck starts fine when cold and idles great for about 30 seconds to a minute. Right around 600 RPM. I am using a Snap-on Modis Ultra to view live data. However, after that time the idle starts going low and the engine starts chugging and shaking. If I let it keep doing that, it'll die. If I press the gas it takes a minute and then catches up but once I let off, it goes to the same thing and dies.
If I try to drive the truck, once I let off the gas it dies. Common problem here is, it dies.
I have pulled the throttle body, cleaned it using a parts washer, pulled the IAC and cleaned it. Put new AC Delco plugs and wire on the truck and I am not getting a single misfire.
Just can't seem to figure it out.
As for codes, the only ones I get are when I unplug a sensor to see if something changes. No MAF code, no IAC code, infant the readings on the IAC are on spot with what it is requesting and what it is giving. I have checked the fuel pressure, 55psi at idle and 58psi when I unplug the vacuum regulator on the rail.
This is a drive by cable engine as well.
Any advice is greatly appreciated and if anyone who knows a lot about this on the west side of Houston, feel free to invite yourself over, I can provide beer and BBQ. I just need to figure this out by Sunday night, This is suppose to become my daily driver.
Did you check if your injectors are spraying ? Sounds either like no fuel getting to it/clogged, try spraying some starter fluid and see if it stay on longer. That or you have a big vacuum leak.
Thread Starter
Teching In
Joined: Jan 2016
Posts: 7
Likes: 0
G-X-P you are probably right.
I was playing with it some more. I saw some smoke coming from under the passenger side intake between 2-4. I assume once it warms up it is loosing its seal and causing a leak.
I also tried spaying carb cleaner all over the intake looking for a vacuum leak but the idle never changed.
Here is a video of the idle. It ran like this for about 6 minutes then finally cut off.
Sorry for the shakiness. My camera on my phone is messed up.
I was playing with it some more. I saw some smoke coming from under the passenger side intake between 2-4. I assume once it warms up it is loosing its seal and causing a leak.
I also tried spaying carb cleaner all over the intake looking for a vacuum leak but the idle never changed.
Here is a video of the idle. It ran like this for about 6 minutes then finally cut off.
Sorry for the shakiness. My camera on my phone is messed up.
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Thread Starter
Teching In
Joined: Jan 2016
Posts: 7
Likes: 0
So I put some exhaust on the truck and pulled the IAC once more and really cleaned it and pulled it apart then tested it and the little black thing moved in and out when I cycled the ignition. Put it back in and the idle smoothed out. Not it is idling around 515 RPM which is 50 less than what the PCM is requesting. But it doesn't die now.
I have read that these 6.0s like to idle a bit rough. Is 515RPM normal? or could there be something else I am overlooking?
I have read that these 6.0s like to idle a bit rough. Is 515RPM normal? or could there be something else I am overlooking?
Thread Starter
Teching In
Joined: Jan 2016
Posts: 7
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I have now driven it and got a real exhaust put on at the shop down the road. Runs great now and staying cool. Idling like a champ. It might have a little bit of work to be running 100% but I would say it is running 90% now.
Thanks for the help!
Thanks for the help!