408 LQ4 problems

[mr2cam]

Hi guys, my dad built a mild 408 for his 99 Silverado 1500 (use to have a 5.3 in it). Anyway I will explain the problems were having and at the bottom I will list the mods on the engine and specs. I am not so sure this is a tuning issue, right now Vince at Trifecta is working with us and e-mailing us tunes to try to make things right but I think it might be something else, hard to say.

When you start the truck up a lot of times it will sit there and idle fine around 800rpms, then when you put it in reverse or drive it immediately dies, then there are other times it will be fine and go right into drive or reverse, it seems to do it worse after the truck is warmed up all the way. Also when you stab the throttle it hesitates for a second then it wants to take off. So far no pinging that we can hear at all so we know the timing is probably retarded quite a bit (running on 87 octane). Let me know what you guys think, here are the mods.

Eagle 408 Stroker with stock LQ4 aluminum heads (mild porting)
10:1 compression ratio
224/220 Comp Cam
Fast 102 Intake Manifold (ported)
Fast 102 Throttle Body
Precision 42lb injectors
Fast Billet Fuel Rails
Fuel pressure set at 61psi
AEM Intake with stock MAF (Will we need to upgrade the MAF?)
Stock fuel pump (for now, have a walbro 255 waiting to go in)
13 inches of vacuum at idle

I believe that is it, if I can remember anything else I will add on to the list, thanks for the help in advance and thanks again to Vince for working his tail off trying to help us get this thing right.

[RedHeartbeat]

sounds like a bad TPS or MAP sensor. Disconnect the MAF sensor and see how it runs when it runs off the open loop base tune. It may be nothing more than a dirty MAF sensor. The map could also be defective or plugged.

[skeet]

id have to agree with greg, check the little things, hows the fueling on the gauge when giving it gas? like when you punch it? are ya'll logging during start up then sending tunes by mail? or is the tuner kinda somewhat guessing with the info youre giving him? that could be a nightmare for the tuner!


man that setup would be a beast with some nice 243 heads ( i take it thats the FAST truck intake? ) a nicer size cam!!!

[mr2cam]

id have to agree with greg, check the little things, hows the fueling on the gauge when giving it gas? like when you punch it? are ya'll logging during start up then sending tunes by mail? or is the tuner kinda somewhat guessing with the info youre giving him? that could be a nightmare for the tuner!


man that setup would be a beast with some nice 243 heads ( i take it thats the FAST truck intake? ) a nicer size cam!!!

Yes we are logging and sending it to Vince, he has sent us 3 revisions, and it seems to be getting better the more we try things. It is the FAST truck intake manifold, my dad doesn't want too big of a cam or heads because it is his daily driver and hes pushing 60 :p. He just wants some nice bottom end TQ.

[pl4yboy]

Yeah, also I really wouldn't do too much WOT with that stock pump. Who knows how lean it'll get.

[mr2cam]

Yeah, also I really wouldn't do too much WOT with that stock pump. Who knows how lean it'll get.

We havn't gone WOT at all, we will stab it for like a millesecond then let off, we are babying it quite a bit.

[mr2cam]

sounds like a bad TPS or MAP sensor. Disconnect the MAF sensor and see how it runs when it runs off the open loop base tune. It may be nothing more than a dirty MAF sensor. The map could also be defective or plugged.

Thanks for the quick responce, I unplugged the MAF, at first it didn't want to idle, after a few restarts it I let it idle, one thing it did fix was the hesitation when I stabbed the gas for a sec, it went away, I then turned it back off, plugged in the MAF, and the hesitation was back. Do you also think that the stock MAF is a big restriction with all the mods I have listed?

[pl4yboy]

Thanks for the quick responce, I unplugged the MAF, at first it didn't want to idle, after a few restarts it I let it idle, one thing it did fix was the hesitation when I stabbed the gas for a sec, it went away, I then turned it back off, plugged in the MAF, and the hesitation was back. Do you also think that the stock MAF is a big restriction with all the mods I have listed?

The stock MAF is fine. It's probably either dirty or bad. See if you can get another one to try out of a different truck. Also, try cleaning that one carefully.

[mr2cam]

The stock MAF is fine. It's probably either dirty or bad. See if you can get another one to try out of a different truck. Also, try cleaning that one carefully.

Ok, we will clean it first and see how that works, thanks for the help guys, I will report back, and if anyone else has suggestions let me know, thanks a bunch!

[mr2cam]

One weird thing is though it never did this with the 5.3, and it's the same MAF from the 5.3. But the MAF did sit around for quite a bit before we got the motor in the truck so it could be quite dirty, guess we will find out tomorrow.