I have an 81 C10 I just installed an aluminum 5.3 in. Motor is basically stock with LS1 intake, fuel rails, injectors, and throttle body, stock LS1 cam. Basically a mini LS1. The truck Idles smooth as silk and runs great at low RPM whether under a load or not. My issue is when I give it much more than quarter throttle, it starts cutting out. I can ease into really slow and eventually work the pedal all the way down with no breakup, but I can't just nail into it. Where should I start?

PS - No mass air, IAT or rear O2's

 

Is it tuned?

 

I am going to guess not.

 

The computer doesn't know what is going on so drivability will be sub par at best.

 

I sent the computer to get a "startup" tune but I haven't taken the truck for a final tune since its been running. Its only been done a few days. I just wanted to make sure my ducks were in a row before I went back. It's tuned as a stock 04 GTO right now

 

Mass air, etc was removed in the intial tune but my scanner is saying "mass air low voltage". Should I assume that it's still trying to read mass air Like it still has it or is it just normal for it to still try and read mass air even though it's deleted? The motor Idles super smooth and runs really well under half throttle so surely it wouldn't run that good if mass air was still in the PCM... Basically I wanna make sure I did my job right before I waste time getting the final tune and something on my end still be wrong...

 

Why not plug the MAF in and see what happens?

 

No mass air and no IAT? Someone correct me if I'm wrong but I doubt that will ever work as I'm fairly certain speed density will still require IAT readings.

If I were you I would correctly install both.

 

It's deleted from the PCM so I'd have to wire it back up. I was just wondering if anyone had seen this same situation. Maybe the final tune will fix it. Just wanted to make sure this was a normal. I'm big into LS stuff but this is my first swap, especially with speed density, so I wasn't sure what to expect

 

I was wondering the same thing. This is my first swap with speed density so I wasn't sure. Ive heard I can run with or without IAT but I can't get a concrete answer from someone I trust. IAT has been deleted from the PCM. I can re-pin it and try that if I need to but I didn't wanna go through the unnecessary work if not...

 

What fuel pressure are you sending to the rails? You need to have 58psi at all times to the rail.

 

I have just a hair over 60 psi at idle and I put it in gear and hold the break to simulate a load, the pressure stays at 60. I haven't driven it with a gauge on it so I'm not sure what it actually does going down the road

 

Does the pcm programmer know what he is doing? I had Brendan at LT1 Swap program my pcm. He tells you in his site that he recomends running the mass air flo sensor. I think you need to talk to him on your programming.

 

I agree. Hook up the IAT and MAF. Have it tuned and leave both of them on there. You will have a smooth running/driving truck that will always be ready to crank and go.

 

You can run without the Maf but no mail order is gonna be close enough to run well. As far as the iat I believe to have any kind of accurate tune it will have to be functional. I'd just put the Maf and iat back and call it a day

 

Yeah he knows what he's doing. I may just go ahead and run mass air/IAT. I was trying to keep it neat and as clean as possible under the hood... May not work the way I want it to without it. Thanks for your help

 

I may just go ahead and do that. So much cleaner without it but oh well. If it dont run good, it dont matter good it looks! Thanks for your help

 

Wow lot of random info in here.
Lets get to the heart of the matter.
You are running currently in SD mode since there is no MAF.
Speed Density requires two things (actually several things but for simplicity here) it needs to know the Manifold Absolute Pressure (MAP) and it needs to know the Intake Air Temp (IAT). It uses this information combined with a few other things to figure out fueling when running in SD mode.

You have no IAT connected. So the PCM is getting no reading from the IAT and when this happens it assumes that the car is in a cold environment and defaults to the bottom of the IAT fueling enrichment table for fueling requirements. I don't have my HPT in front of me to look but I know from memory it's well bellow -32 as I recall. This means your car will fuel based of this table which in cold environments makes the car run very rich.

So its able to idle but doing so in a rich afr most likely. Light throttle transitions work as it doesn't call in any other enrichment tables but as soon as you given it any real throttle it calls in different enrichment tables which only continue to add even more fuel. Your flooding the engine to a very rich Afr and it's dying out because of that.

That would be my guess based on the info your giving us.
SD mode needs the MAP sensor and the IAT sensor to function. With out the IAT the PCM can' not figure out the density of the air as air molecules get more dense the colder they are ... and less dense the warmer they are so for proper fueling it must have an idea what the temp of the air coming in is. It makes a big difference. And on the stock o/s if it does not see an IAT reading it assumes the coldest setting possible.

Wire in the IAT it' is a necessity for SD mode.

 

That's what I expected. The IAT is small so you should have no trouble hiding it on the underside of the filter or intake tubing if you just don't want to look at it.

 

On the truck motor the IAT is integrated in with the maf. You will need a new IAT sensor that is separate from the Maf. I know the early Camaro's had the iat in the intake tube.