Lil'John

This issue is it idles like a champ. But any throttle and it bogs down.

Here is the setup:

• 2004 LQ4 from Silverado 2500HD swapped into an old Toyota Land Cruiser
• NV4500 swapped in place of the stock 4l80e it came with
• e8248 fuel pump
• Corvette regulator and filter combo(AC Delco P# GF822)
• exhaust leak on passenger side
• no cats
• VATS programmed out as well as rear o2 sensor (JET DTS programmer)
• STOCK harness with un-needed junk pulled(autotranny wires, rear o2 wires, and purge valve)... only the VSS wires were removed from the PCM plug and put back on.
• headers
• new hard and flex lines throughout (3/8" and 6an but also about 12" of 5/16" at tank)
• VSS installed
• Drive by wire system installed
• everything else stock
• I've got engine block grounded directly to the battery... all other stock grounds for the harness are at stock locations.

Engine sat for about 8 months before being run. The engine is a returnless style fuel system thus the corvette style fuel filter/regulator.

Things I've done/tested so far:

• fuel pressure is at 60psi
• soaked injectors in sea foam (no change)
• run engine with a can of sea foam and about 7 gal of 87 oct gas (no change)
• no engine codes aside from no MIL (P0650)
• checked the TB butterfly to ensure it opens both with and without the engine running
• replaced a E2000 fuel pump with e8248
• confirmed MAF functionality by pulling MAF away from TB as well as unplugging. Both cause the engine to idle like crap.

Would the PCM not having input from the auto tranny spaz it out?

Would a plugged fuel filter cause this? Even though it is still giving the right pressure reading.

novaflash2002

iTrader: (51)

have you checked or changed the tps? you can verify what it is reading in your jet dts if you run a scan to make sure it is reading that the throttle is opening.

zx9rgreen

iTrader: (18)

Maybe I missed it but is this the stock PCM that came with the engine/trans

Lil'John

The TPS is the one that came with the engine. I'll triple check on the scan tool that it is getting the appropriate results.

As mentioned in my initial post, the TB is definitely moving with the throttle pedal.

I'd give this a resounding sort of. It is the stock PCM for the engine. But the engine came originally with a 4l80e transmission. I am using an NV4500 in place of it.

Would the lack of transmission input cause an issue like this but not throw up any codes?

I've run the engine for about 10 minutes idling and never received any codes aside from the missing MIL.

brandon1566

you should check your fuel pressure at the rail mine did this same thing that was the problem. if you have 60 psi at the rail you said you maf is good and your tps is working idk other than that, but the fuel pressure was my issue.


edit: I would also ground the block to the chassis

Lil'John

Thanks for the input. I did check the pressure at the rail using the fitting. It was 60psi while running. However, I didn't see a method to check while gassing.

Would a clogged fuel filter still give the right pressure but not flow enough fuel?

I will also double check that I grounded the block to the frame. I know the battery is grounded to the block.

Old Geezer

iTrader: (3)

I think that the pcm will put the DBW into a limp mode as described here.
Reduced Engine Power Mode
When the PCM detects a condition with the TAC system, the PCM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions:


Acceleration limiting- The control module will continue to use the accelerator pedal for throttle control; however, the vehicle acceleration is limited.
Limited throttle mode- The control module will continue to use the accelerator pedal for throttle control; however, the maximum throttle opening is limited.
Throttle default mode- The control module will turn off the throttle actuator motor and the throttle will return to the spring loaded default position.
Forced idle mode- The control module will perform the following actions:
Limit engine speed to idle by positioning throttle position, or by controlling fuel and spark if throttle is turned off.
Ignore accelerator pedal input.
Engine shutdown mode- The control module will disable fuel and de-energize the throttle actuator.
If there's no VSS, you may get this type of problem.
A few $$ spent on a yrs sub to www.alldatadiy.com, is well spent. [Like <$40.00]
Do you have access to EFILIVE, etc?

Lil'John

Old Geezer thanks for that.

On the TAC module, I've got a few questions:

• Is there a way to verify it is the correct one for my PCM/engine(p# or something)?
• Will leaving all the cruise control wiring unconnected effect its function?
• If the throttle pedal causes the throttle body to move, does this say the TAC module is good?
• Does the TAC module require a special ground? Or is through the bolt to the mount sufficient?
• If the TAC is bad or faulty, wouldn't it throw a code? (as mentioned, I get no codes besides the missing MIL)

FWIW, I do have the FSM for this engine. All 5 thick books worth.

AFAIK, every thing attached to the engine came from the donor rig(ie MAF, TB, TAC, o2s, all sensors) The only thing that didn't come from the donor rig was the VSS and it was a new one from an autoparts store in a custom housing.

Jet DTS confirmed the PCM is what I was told the engine is from.

Lil'John

Would this off idle issue be a sign of the abuse mode function coming on?

fast83z28

This may sound dumb, but have you checked to make sure the MAF is installed in the correct direction? I had a car once that was doing exactly as you described and that was the problem.

Bo185

John,

I did you flash the PCM with a manual tune. I still think that might be your the problem if its still has the 4l80 tune.

The TAC should be OK, but read this! Info on DBW and TAC

Also let it idle and watch the TB and have someone get the gas and see if it moves and the engine dies or if it doesn't move and dies.

Lil'John

Not 100% sure it is the correct direction. But mine has the word Flow and an arrow. I assumed the arrow points toward the throttle body.

I have not flashed the PCM for a manual tranny.

On the TB, I tested it without the engine running and it followed the pedal. Would this change while running?

Bo185

You said you used a JET DTS programmer right. I am thinking your going to have to have the PCM flashed to a manual tune. The LQ4 had the NV4500 as a option for a number of years. I bet that will fix the problem. The PCM mostly thinks there is a problem with the trans (4l80) since it doesn't see one. It in limp mode.

Lil'John

Yes, I've got the Jet DTS programmer.

I've also got a scanner with real time data logging. Diagnose by B. Roadman.

I'm currently looking at trying to convert my PCM for manual trans functionality. But Jet DTS documentation is a bit sparse so I'm being careful with what I change.

I did get a 4.8L manual tune and I'm currently checking differences.

chadeberly

Hey guys figure I'd share some input. I am having the same problem. I have 04- cts-v ls6. I currently have a fast 90/ls2 90 mm throttle body with piggyback harness. I bought a 90mm TPIC throttle body so I could go back to my original LS6 IAC and tps because I like the drive by wire response on the ls1/ls6 style better. Anyway, my car is going into limp mode also, I double checked everything and it was all good but still in limp mode and no cel. So.... I put my ls2 back on and no more problem what gives? The LS6 TB will open fully and close fully when the key is in ON mode, but when its at idle (which it barely does) it will not move. The check oil level kept popping up on the nav screen too. But when I went back to ls2 all was good.

GA95DCMSS

iTrader: (13)

That sounds about right. Seeing as the NV4500 isn't an electronic controlled tranny, I'm betting you'd have to run a manual tune to get it to work right. Kinda like doing a TH400 swap, same thing applies here.

Lil'John

If I am understanding this correctly, if an automatic trans tuned PCM sees no transmission input, the PCM will go into limp mode. Is this correct?

If so, it sounds like a simple one parameter change using DTS

Bo185

I think so as it thinks the trans is toast.

I don't think the DTS will do it. I would contact them and tell them your problem.

Lil'John

DTS has one section dealing with Transmission Parameters that lets me pick the transmission type(4l60,4l80, or manual)

I believe I set that on my intial tune but won't swear 100% to that. The problem is I am not sure if there are any related parameters that need to be set(if any) when the transmission type gets changed.

poconojoe

iTrader: (43)

Did you try the stick shift tune?
Do you want the copy converted to a 5.3?