LQ4 swap issues

[Red Alert]

Hi everyone, name is Craig and I am a new member here obviously, and have some issues with my latest project that I sure hope some of you can assist with

Details, my son and I are working on a 1979 Olds Cutlass with the factory Hurst option (gold/white car), bought it with no engine and transmission, after finding a donor 2005 Silverado HD with the LQ4/4L80 and all needed parts to complete this swap.

I have a 1971 C10 that I did a previous LQ4 swap into with great success about 4 years ago still running strong so I have done this before.

All harness mods were done by me referring to LT1swap.com, great site BTW.

Anyhoo, we got everything bolted in, very little custom work to make it drop right in, except the exhaust which I struggled with but after denting up a used set of Chevelle Edelbrock LS1 swap headers fit right in. The engine runs good, fires right up, idles high but smooth. BUT, here is the issue, we cannot get the drive by wire throttle to work. Well, it did work for a short period of time, then very intermittent, now nothing. We get key on trigger to it (hear the motor closing the blade when the key is turned on) but very quickly after the engine fires we have no throttle.

SO far this is what I have done, replaced the pedal sensor, we modified the pedal and did some welding to the arm so I just bought a new sensor thinking that might be it but no change in anything, so back to square one.

I have read the codes, and here they are:
P0120
P0220
P0758
P1516
P2761
P2101
P2135

Lots of codes, any direction that I can start with? I have not replaced the throttle body OR the TAC module which match the harness and computer (came out the donor truck)

[joecar]

Great project

So engine, trans, PCM, throttle pedal, TAC all came from same donor vehicle...?

Hi idle indicates an air leak.

[Red Alert]

Thanks joecar, we just kind of stumbled on this car on CL when we were looking for a recipient for the engine/trans/

Yes, all of the systems came from the same truck, nothing has been changed. High idle, I guess I should have explained better, the idle when I first fire it up is normal, then when the throttle decides it does not want to work (which is all the time now) it will go from normal to higher like around 1200 rpm.

[Red Alert]

One of my sons friends are bringing by a data reader today so I can dip further into this. I just read a P1125 now, this thing is a mess What info do I need to pull from the PCM?

[Jetmech442]

Aside from rpm and ect, I'd say grab the 5 throttle pids :SAE .App_A and b, as well as sae. Tp(absolute, B, and relative).

Sorry I just have a second to post, so search absolute and "B", iirc they should be exact opposite of each other or else the tcm thinks it's a pedal issue and freaks out.

I haven't looked up those codes to see what they mean, maybe someone else has and it will point to showing me definitive.

Sent from my Nexus 6P using Tapatalk

[Red Alert]

I put a multi meter on the A and B circuits off of the pedal key on, A has about .80V at rest and evenly rises to over 3V. Circuit B has the exact same, not the opposite, this would be my issue? It's a brand new pedal sensor, why would this be different than designed?

[Jetmech442]

No, I must be remembering wrong. I thought they were opposite. I'm under the car right now, or I'd check.

You can log these channels if you feel it is connected. Obviously getting a capture of the right pids when it shuts itself off would be ideal. Sorry if there's any typos in having Google do the speach to text...

Sent from my Nexus 6P using Tapatalk

[joecar]

Is this your vehicle:
2005 Chevrolet Chevy C Silverado - 2WD - 4.8L, 5.3L, and 6.0L


The attached files may help.

[Red Alert]

Thanks for the links and info, sorry for the delayed reply I have been a busy employee this week...

I have a scan tool today (Bosch OBD1150) so if that has the ability to read what the throttle body is seeing I will post the results here tonight.

[Red Alert]

This code reader is not giving me the info that I need, but it does say that the TPS is at 99.6%? Dunno what that means