408 LQ4 problems

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.

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.

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!!!

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

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Originally Posted by 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.

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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?

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Originally Posted by mr2cam

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?

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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.

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Originally Posted by 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!!!

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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.

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Originally Posted by pl4yboy

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

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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.

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Originally Posted by pl4yboy

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.

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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!

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.

Since the hesitation went away when pulling disabling the maf, might be a dirty maf or the PCM thinks there is a lean condition or there is one.
A map sensor doesn't respond the same way to a vac leak.

What are the ltrims showing when the ma is plugged in?

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Originally Posted by farmtruc

Since the hesitation went away when pulling disabling the maf, might be a dirty maf or the PCM thinks there is a lean condition or there is one.
A map sensor doesn't respond the same way to a vac leak.

What are the ltrims showing when the ma is plugged in?

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You mean the fuel trims? This morning before we did any revisions with the base tune it was showing good, I think one bank was 0 and the other was -3 on the Verus. Also when I sent Vince the first data log he thought the fuel trims looked good, but the truck does act like it is running lean.

I should also say that once the truck is driving it is smooth as silk, drives very nice..

There are so many things that could be going on.
Good ltrims indicate there is no leak and the o2's are working.
The fact that the engine runs with the maf disconnected means the map is working, actually since the trucks starts at all means the map is working.
Good ltrims also means the fuel pressure is ok, as long as the ltrims are around 0 during idle and normal driving (loaded).
o2's good, map good, no leaks good, fuel pressure good, only thing is the maf, be sure you swap it out just to make sure it's not that. I've seen weird things happen due to a maf.

Well we put a brand new MAF in the truck and still does the exact same thing, kinda stuck here :\.

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Originally Posted by mr2cam

Well we put a brand new MAF in the truck and still does the exact same thing, kinda stuck here :\.

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sounds lean, have him richen it up quite a bit, and lower PE threshold to 30

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Originally Posted by farmtruc

sounds lean, have him richen it up quite a bit, and lower PE threshold to 30

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K, he sent me another tune and it made things even worse, truck barley ran and died at almost every stopsign, I datalogged it for him and he will hopefully have another one back to me soon.

not sure what to tell you on the tuning side, i know i take offense when others recommend without knowing the full details, so i don't wanna do that.

just be sure all the mechanical stuff is in order, or the tuner will have a nightmare trying to tune around it.

i'll keep racking my brain and try to suggest some stuff.

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Originally Posted by farmtruc

not sure what to tell you on the tuning side, i know i take offense when others recommend without knowing the full details, so i don't wanna do that.

just be sure all the mechanical stuff is in order, or the tuner will have a nightmare trying to tune around it.

i'll keep racking my brain and try to suggest some stuff.

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We have checked just about everything we can, here is what the tuner said last.

"It is not running lean. Fuel trims look good. It’s just that the PCM isn’t adapting for the idle properly"

I'm wondering if it's having a problem with the 102mm throttle body and huge intake..

Well after talking to Vince we decided that this tuning through e-mail isn't working out, so were going to trailer the truck over there after we get the fuel pump in and have it dynod and let him fix the issues, he said it will go much faster with him there.

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Originally Posted by mr2cam

Well after talking to Vince we decided that this tuning through e-mail isn't working out, so were going to trailer the truck over there after we get the fuel pump in and have it dynod and let him fix the issues, he said it will go much faster with him there.

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I agree 100%. It is so much faster when someone is right there able to change things instead of waiting for that PCM in the mail or wait on an email. Hopefully you don't have a bad MAP something so it goes very quickly.

Since the injectors have been swapped out it could simply be injector timing issues. Make sure he knows the exact brand, part number and fuel pressure the injectors are seeing. If you can, get the all the injector flow data you can from the manufacturer. I see the brand of injector is Precision, is that Precision Turbo? Contact the seller and see if they can give you all the injector data you need relating to a Gen3 engine. If the injector offset voltage is wrong the truck is going to run like crap. Injector timing is very tempermental. If he can't get you the data and your tuner can't get it worked out I'd ask for your money back and get injectors from someone that can provide the data you need. Injector Dynamics is probably the best companies to get larger injectors from because they have all the equipment to get all the data required to make injector swaps pretty much plug and play.

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Originally Posted by RedHeartbeat

Since the injectors have been swapped out it could simply be injector timing issues. Make sure he knows the exact brand, part number and fuel pressure the injectors are seeing. If you can, get the all the injector flow data you can from the manufacturer. I see the brand of injector is Precision, is that Precision Turbo? Contact the seller and see if they can give you all the injector data you need relating to a Gen3 engine. If the injector offset voltage is wrong the truck is going to run like crap. Injector timing is very tempermental. If he can't get you the data and your tuner can't get it worked out I'd ask for your money back and get injectors from someone that can provide the data you need. Injector Dynamics is probably the best companies to get larger injectors from because they have all the equipment to get all the data required to make injector swaps pretty much plug and play.

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I believe these are the injectors

http://www.nolimitmotorsport.com/prod/041-0420

contact NLM or Precision Turbo and see if they'll supply you with the data you need. Not all 42lb injectors are created equally, some are pintle, some are disk some have short coils, some have long coils... the specific data you need for these is really important. Also, he will need to know the flow rating is at 3 bar fuel pressure. If the injectors are reboxed Ford Motorsport injectors then he may already have the injector data.

FWIW, I would contact Precision Turbo directly and see if they can supply you with the data.