Help! LQ9 Won't rev
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 89
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Help! LQ9 Won't rev 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 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.
Does anyone have any thoughts on what else might be causing the issue?
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 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.
Does anyone have any thoughts on what else might be causing the issue?
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 89
Likes: 0
Parts aren't common over here in the UK so trying another pedal isn't an easy option. I'd assume the pedal itself is electrically the same across all years as it's essentially just two potentiometers. Also the fact that (engine not running) the throttle plate responds accurately to the pedal suggests to me that the pedal is ok. I'm willing to be corrected though!
The ECU and harness is the standard one from an 2007 chevy silverado that's had the VATS and rear O2 sensors switched off. It's the blue and green plug type.
The ECU and harness is the standard one from an 2007 chevy silverado that's had the VATS and rear O2 sensors switched off. It's the blue and green plug type.
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.
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Staging Lane
Joined: Sep 2018
Posts: 89
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I'm not sure about fuel pressure, but I had wondered myself. I've just ordered another gauge kit so I can test that in a couple of days.
The map sensor appeared to be ok on a pre run check - it was reporting 101kpa. I'll confess I haven't checked it with the engine running.
The map sensor appeared to be ok on a pre run check - it was reporting 101kpa. I'll confess I haven't checked it with the engine running.
Thread Starter
Staging Lane
Joined: Sep 2018
Posts: 89
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Hi Joz,
I've checked the wiring diagrams and it suggested that the pins B(purple) and D(tan) required swapping over. I tried this but then the pedal stopped responding at all and it threw error codes.
Would you mind asking your harness builder for more information please?
I've checked fuel pressure and the MAP sensor and they're both fine.
I've checked the wiring diagrams and it suggested that the pins B(purple) and D(tan) required swapping over. I tried this but then the pedal stopped responding at all and it threw error codes.
Would you mind asking your harness builder for more information please?
I've checked fuel pressure and the MAP sensor and they're both fine.
On The Tree
Joined: Sep 2010
Posts: 197
Likes: 1
From: Phoenix, AZ
Not sure what I’d ask him. It was actually his mistake that I found after comparing the schematic against the wiring. In my case it’s a little complicated as I was converting an 06 GTO harness. My harness guy had to splice in the OBDII and pedal stuff into the the main engine harness as that part is in a separate harness in the GTO (part of the dash harness I think). This was a couple of years ago so.
He just got two of the pedal wires switched when he was finishing it up.
If your pinout/wire colors match your schematic, that’s probably not the problem.
Wish I could be of more help!
He just got two of the pedal wires switched when he was finishing it up.
If your pinout/wire colors match your schematic, that’s probably not the problem.
Wish I could be of more help!