lq4 swap wont rev over 2500rpm help please

[Liltroy]

Ive been fighting with this thing since I first fired it a month ago and still cant drive it. With key forward, not started I get 99.6% tps but as soon as I start it it will only give me 20% tps and about 2500rpm...thats it! Only code Im getting is P0174(bank 2 lean). Im getting very frustrated and hope someone can help. Ive searched google for weeks and cant find anyone else having this issue!!!

[ls1nova71]

DBW or cable? What's your fuel pressure at?

[Liltroy]

dbw, pressure holds at 58-60lbs(cheapo temporary gauge). New tank,new pump, new lines,new vette filter/regulator. I cant figure out why it will only give me full throttle with the engine off. Its driving me crazy!!!!

[ls1nova71]

What year is it? Did you get the matching TAC module and pedal for the engine from the same truck? PCM from the same truck? Correct tune for your year of TAC and PCM?

[BR3W CITY]

Does it throttle-check when you go key on? (the click-click that you'll usually hear)

What are you monitoring this on? Using HP Tuners you should be able to watch what the TPS is seeing in raw output. If your pusing down 2/3 of the way but getting 20% throttle, then either the TAC, Pedal, or TB has an issue OR something in your tune has been modified.

If your only using a simple scanner or scanguage, try getting it on a dealer TacII or having your tuner run it in VCM Scanner so you can see what its doing or log the TPS functions.

[homemade87]

Sounds to me like it is going in limp mode . The computer is seeing something when running that's only allowing 20% throttle .

Are you sure you have all the grounds hooked up . Also it would not hurt to clean the mass air with the mass air cleaner just to rule it out .

[Liltroy]

Originally Posted by ls1nova71

What year is it? Did you get the matching TAC module and pedal for the engine from the same truck? PCM from the same truck? Correct tune for your year of TAC and PCM?

It's out of an 06 2500hd. Yes, yes, and as far as I know, yes.

[Liltroy]

Originally Posted by BR3W CITY

Does it throttle-check when you go key on? (the click-click that you'll usually hear)

What are you monitoring this on? Using HP Tuners you should be able to watch what the TPS is seeing in raw output. If your pusing down 2/3 of the way but getting 20% throttle, then either the TAC, Pedal, or TB has an issue OR something in your tune has been modified.

If your only using a simple scanner or scanguage, try getting it on a dealer TacII or having your tuner run it in VCM Scanner so you can see what its doing or log the TPS functions.

I'm using a scanner that shows live data and also has graphing. With key forward and engine off I'm getting proper throttle response and tops out at 99.6% (no vehicle in my driveway actually tps's at 100% so I'm assuming that's good). But once I start the engine, no matter how far I put the pedal down it won't open the throttle over EXACTLY 20% and acts as though there's a soft limiter at 2500rpms.

[Liltroy]

Originally Posted by homemade87

Sounds to me like it is going in limp mode . The computer is seeing something when running that's only allowing 20% throttle .

Are you sure you have all the grounds hooked up . Also it would not hurt to clean the mass air with the mass air cleaner just to rule it out .

I recleaned and reinstalled all ground....one on back of each side of engine, one on front drivers side engine, one from engine to body, added another from engine to body, total off three from frame to body, big one from engine to frame, one from batt to block, one from batt to body. MAF sensor is brand new. As are O2 sensors. Passenger side O2 isn't reading....it's staying at .445mv. I thought I might have gotten a factory defect so I swapped sensors side to side but issue remained on passenger side??? Wires are pinned correctly at PCM. I'm going to make sure they're right in the sensor connecter of my harness tonight but even if not, I'm told a bad O2 reading won't cause limp mode.

[BR3W CITY]

02's won't cause limp. If you unhook the battery, let it sit, and hook it back up...does it allow you to go past even ONCE? I'm wondering if its seeing an initial fault, or if something triggers the fault. Generally with intermittent/damaged TAC/Pedal issues, you can trick it into "working" once or twice before the sensors error-out.

Can your scanner command control at all?

[Liltroy]

No, I've reset it several times. It has revved up fully a couple times but not right after a reset. It will give me 99.6% throttle every time if it's not running. If it was a TAC, throttle body, or pedal issue, wouldn't it do it with the key forward but not running as well? I mean, it opens the throttle completely every single time unless I start it. As far as command/control, I don't think so but I'm not sure what that is. I just bought this new scanner a few weeks ag because my old one wouldn't read any vehicle newer than 2004 so I'm not completely familiar with it yet. I only know it reads, records,prints and graphs live data but it has no battery so once you unplug it it loses everything.
Another question.... What should my MAF readings look like? It's new but I wanna make sure it's doing what it's supposed to be doing.

[Liltroy]

And btw, thanks for the help fellas.

[BR3W CITY]

Command/Control is something that only a "full suite" scanner like a Startach or TacII (dealer stuff), or HP Tuners-type systems can do. Basically, it overrides your pedal and can lock-out the TB or change the effective range of the sensor (you can use this to dumb-down the pedal of a super touchy motor).

As for the key on/off thing, I'd generally assume you were correct about working in both positions, however there have been a few situations with the yellow and purple wires on the TB pulling loose or breaking due to the engines motion. Of course, the fact that you can reproduce it EVERY time leans against this theory.

MAF failure will put you into forced SD, but won't limp a car. I'm not running one at the moment so I can't reference my log.

Were there any major changes to your tune, or was it just an emissions/vats delete?

[Liltroy]

Originally Posted by BR3W CITY

Command/Control is something that only a "full suite" scanner like a Startach or TacII (dealer stuff), or HP Tuners-type systems can do. Basically, it overrides your pedal and can lock-out the TB or change the effective range of the sensor (you can use this to dumb-down the pedal of a super touchy motor).

As for the key on/off thing, I'd generally assume you were correct about working in both positions, however there have been a few situations with the yellow and purple wires on the TB pulling loose or breaking due to the engines motion. Of course, the fact that you can reproduce it EVERY time leans against this theory.

MAF failure will put you into forced SD, but won't limp a car. I'm not running one at the moment so I can't reference my log.

Were there any major changes to your tune, or was it just an emissions/vats delete?

That I'm not sure about. I told him I had shorty headers and cai but that's it so I'm not sure if it's some kind of performance tune or not. It was done by wait4me. I called Jesse last week and he pulled my tune up and said everything looked good but since it has done this from the very first start, I'm starting to wonder is something is off. Another member here offered to look at it for me if I shipped him the PCM so if I can't come up with anything else in the next couple days, I'll probably ship it and maybe he can find something that has been overlooked.

[ls1nova71]

This really sounds like a mismatch of parts, or the tuner flashed in the wrong year OS for the parts you have. With the engine not running, you say the throttle goes to 99%, is that commanded, (what the pedal is saying) or actual (what the throttle body is doing)? Have you looked at the throttle body to make sure that its actually opening that much? I have seen throttlle bodies stick and go into limp mode. Does it open and close smoothly by hand?

[Liltroy]

Originally Posted by ls1nova71

This really sounds like a mismatch of parts, or the tuner flashed in the wrong year OS for the parts you have. With the engine not running, you say the throttle goes to 99%, is that commanded, (what the pedal is saying) or actual (what the throttle body is doing)? Have you looked at the throttle body to make sure that its actually opening that much? I have seen throttlle bodies stick and go into limp mode. Does it open and close smoothly by hand?

All parts came from the same donor vehicle. this was out of someones wrecked truck and did not come from a junk yard so I donts think mismatched parts would have been possible. With the key forward, scanner says 99.6%tps and throttle blade looks to be fully opened.I have verified this at least 20 times with either my buddy or my wife watching it. When you say it opens smoothly I assume you mean aside from the fact that I can feel that I'm pushing against the motor inside of it right? Because other than that it is smooth. When I first start the engine, tps is at about 15%....as it warms up it drops to 5 or 6% after a few minutes. Starts easily and idles well....just limits me to 20% and 2500 rpm. My last work vehicle was a chevy colorado....if you tryed to rev it in neutral or park it would respond slowly and only rev to 4000 rpm and hang there...this feels just like that but a lower rpm. it doesnt studder or bounce...it just revs slowly to 2500 and holds it until i let off the gas.

[BR3W CITY]

There is no neutral limit on these, you can rev them to the limiter in neutral.

When Nova was asking about smoothness; IMO he meant when you press the pedal from 0-100%, did the blade respond by going from 0-100 like it would on a cable throttle? OR did it move around, act notchy, skip around etc?

[Liltroy]

Originally Posted by BR3W CITY

There is no neutral limit on these, you can rev them to the limiter in neutral.

When Nova was asking about smoothness; IMO he meant when you press the pedal from 0-100%, did the blade respond by going from 0-100 like it would on a cable throttle? OR did it move around, act notchy, skip around etc?

oh ok. I really dont know cause I cant see the tb while im working the pedal. I may pull the tac harness back through the firewall tomorrow after work so I can operate it and look at the tb at the same time. Just a question...would my uncles 04 throttle body work with my 06 tac and pedal? I may be able to talk him into letting me switch some parts around for testing....

[BR3W CITY]

I believe the 04 is metal-stalk pedal, which has a single 0-10v sensor. The 06 would have been plastic stalk with a 0-10v and a 10v-0. Short answer, no I don't think they'll swap and function.

[Liltroy]

Mine is the 06 plastic pedal with small connector on pedal side and "K" TAC module. As far as I know the K TAC module and plastic pedal was only used on 06-07 so I'm pretty sure I've got the right parts. Since this was an issue immediately from the first fire up I REALLY feel like this almost has to be something software related since it really didn't have time to read anything to throw it into limp mode?wish I knew a local tuner that could take a look at my tune. I guess I'm gonna ship my ecu to someone to take a 2nd look aat it and if something is wrong then I'll contact wait4me about it and see if they'll fix it so I don't have to put anymore money out. If it's not tune related then I'm not sure where to go from here.

[Clyde65]

I used Nelson performance in San Antonio, I bought one from them, with the specs I gave them and they shipped it to me. When I got it ( Couple days) I plugged it in, ran it for a couple days and shipped my old one back to them, easy peasy!

Good luck!

[aknovaman]

Call me when you get a chance. I'm back in country.

[Liltroy]

Originally Posted by aknovaman

Call me when you get a chance. I'm back in country.

Outstanding! I've got one more thing I'm gonna try first. My buddy that works for Lokar just texted me and said his boss told him that they have ran into this 20% throttle thing a couple times before and it never throws a code but it's usually the tps's sensor on the pedal! They're going to program one of their billit pedals and let him bring it home to test it tomorrow. Have I mentioned how awesome my buddy john is? Lol hopefully that's the issue cause I can get a new pedal for $60. If that doesn't fix it then I'll be shipping my PCM!

[BR3W CITY]

Otherwise if you have a log of it or an HPT file I can look at it here if you just email it to me.

[Liltroy]

Originally Posted by BR3W CITY

Otherwise if you have a log of it or an HPT file I can look at it here if you just email it to me.

wish i did but no. Also turns out that Lokar only makes a pedal for the 07-up silverados so of course the one he brought home was the wrong harness. Im starting to think this project is cursed.