Help! LQ9 Won't rev
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 89
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Help! LQ9 Won't rev It was suggested that I post this in here rather than the LSx conversions section...
I've just got my 2007 LQ9 in my project car running, it starts instantly and idles no problem. I can't get it to rev up though, either in neutral or when attempting to drive.
It'll rev up to 1500rpm or so but over that it cuts and drops back to idle. If I keep my foot on the pedal it revs up and dies back to idle, revs up and dies back.
I'd describe it as feeling like its an unmapped car that's way too lean off idle.
I don't know what year the TAC module and pedal are from as they came separately. I'd wondered if that might be causing an issue but the pedal actuates the throttle plate accurately enough from closed to wide open. Plugging in My OBDII scanner only shows o2 and evap faults. The readout on the scanner shows the throttle position at around 18% at idle and I can get a full sweep reading with the engine switched off.
,I've connected in the brake light switch and the TCC switch and I've connected the CPP switch to C1 pin 35 in a clutch released Normally Closed, 12v fed/ Clutch pressed, Open circuit configuration as that's what the wiring diagram suggests it needs. I have seen suggestions that it expects to see a ground when the clutch is pressed, but i've not found any wiring diagrams to support that.
It's a 2007 PCM and loom from a Silverado. The PCM is the green and blue plug type. I don't know what they call tat model designation as I'm very new to the LS.
Does anyone have any thoughts on what else might be causing the issue?
I've just got my 2007 LQ9 in my project car running, it starts instantly and idles no problem. I can't get it to rev up though, either in neutral or when attempting to drive.
It'll rev up to 1500rpm or so but over that it cuts and drops back to idle. If I keep my foot on the pedal it revs up and dies back to idle, revs up and dies back.
I'd describe it as feeling like its an unmapped car that's way too lean off idle.
I don't know what year the TAC module and pedal are from as they came separately. I'd wondered if that might be causing an issue but the pedal actuates the throttle plate accurately enough from closed to wide open. Plugging in My OBDII scanner only shows o2 and evap faults. The readout on the scanner shows the throttle position at around 18% at idle and I can get a full sweep reading with the engine switched off.
,I've connected in the brake light switch and the TCC switch and I've connected the CPP switch to C1 pin 35 in a clutch released Normally Closed, 12v fed/ Clutch pressed, Open circuit configuration as that's what the wiring diagram suggests it needs. I have seen suggestions that it expects to see a ground when the clutch is pressed, but i've not found any wiring diagrams to support that.
It's a 2007 PCM and loom from a Silverado. The PCM is the green and blue plug type. I don't know what they call tat model designation as I'm very new to the LS.
Does anyone have any thoughts on what else might be causing the issue?
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 89
Likes: 0
Bit of an update. Unplugging the MAF makes no difference.
It appears I have an 03-05 throttle pedal. Looking into wiring diagrams it appears that the TAC module is the same for trucks from 2003 on (same part number), but the throttle pedal is different in that the early (metal, 03 - 05) pedal has 3 variable resistors, whereas the later (plastic 06-07) pedal has 2 variable resistors. I've unpinned the 3rd resistor but it hasn't made a difference.
I've had the engine running with the maf off so I can see the throttle plate moving and it IS moving proportional to the pedal and the scantool readout correlates to the actual position so I'm doubtful the throttle or TAC module is at fault.
The only thing I can liken it to is a bad fuel map that isn't providing enough fuel.
It appears I have an 03-05 throttle pedal. Looking into wiring diagrams it appears that the TAC module is the same for trucks from 2003 on (same part number), but the throttle pedal is different in that the early (metal, 03 - 05) pedal has 3 variable resistors, whereas the later (plastic 06-07) pedal has 2 variable resistors. I've unpinned the 3rd resistor but it hasn't made a difference.
I've had the engine running with the maf off so I can see the throttle plate moving and it IS moving proportional to the pedal and the scantool readout correlates to the actual position so I'm doubtful the throttle or TAC module is at fault.
The only thing I can liken it to is a bad fuel map that isn't providing enough fuel.
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 89
Likes: 0
It doesn't have a wideband. Should it?
I hooked up my innovate LM-1 and it's showing it snapping very lean at the moment the revs die. The MAF and MAP both seem to be working correctly and returning sensible data. I know it's a long shot, but could the people who reconfigured the ECU for a manual setup and removed the VATS have accidentally corrupted the fuel maps?
I hooked up my innovate LM-1 and it's showing it snapping very lean at the moment the revs die. The MAF and MAP both seem to be working correctly and returning sensible data. I know it's a long shot, but could the people who reconfigured the ECU for a manual setup and removed the VATS have accidentally corrupted the fuel maps?
