Hey guys I actually have a 95 Silverado running a 16197427 ECM. Wasn't having much luck on another forum so I figured I would try over here as anytime I've looked up how to do something it's always a link to this site. I really appreciate any help/advice.


So about the truck, I did a really mild 355 build with an ATK short block from summit, summit vortec heads, factory lt1 cam, ls7 lifters, factory rockers and pushrods, bored out factory 350 tbi unit with 350 cop car injectors at 16 psi, 30 psi big block fuel pump edelbrock performer intake (vortec carb style with tbi adapter), ebay shorty headers, high flow 3" cat, built the factory 4l60e up, ordered a chip burner and everything for tuning from Moates as well as an AEM wideband and went through tuning the VE table and AE/PE and used the bluecat trans tuner to dial in the trans to where I want it.


Now to my problem, the truck runs great as long as the ambient temperature is above 55F or so outside but as soon as the temps start to dip into that range I get a bad lean stumble because the AE isn't enough with the cooler air coming in. I've read that this may be due to my intake manifold combo not being able to keep the tbi/intake air heated up like the factory intake. I did confirm one day that after I got into stop and go traffic where the engine could heat soak my AFR's fell right back into line.


So here's where I'm stuck. I found several threads about people having this issue and those people added in an IAT or MAT sensor and enabled the MAT and populated the MAT/CTS blend table as well as populated the MAT AE correction factor table. I tried populating the table with what the people in the threads had used and no change at all so I found a stock 4.3 CPI bin (think it's BPLH) and tried those tables and it made no difference.


So here's my actual question...is there another table that has to be populated in order for the IAT to actually modify the AE? I've maxed out the correction factor to 2.0 and tried all kinds of different values in the CTS/MAT blend multiplier table and it has absolutely no effect at all on the AE. What am I missing here, why isn't the IAT input working at all? Also the IAT sensor and everything reads fine in Tunerpro so the circuit/sensor are fine. Sensor is installed in the air cleaner near where the factory thermo valve was that opens/closes using a heat tube off the header. Even tried going back to that style intake after the IAT didn't work and it didn't help any.


Sorry for the long post, I'm just not an expert on this system by any means and I've reached the extent of my abilities for trying to figure out why the IAT isn't modifying the AE like it should. I even went out on a limb and tried using another PC with a fresh Tunerpro download thinking something was maybe corrupt or something and it didn't help at all, even tried another ECM I snagged out of the local pick n save.


Please help lol

 

I'm not an expert on the TBI mask, but in TPI 8D, the MAT/CTS blend table is used because the MAT sensor comes factory in the upper plenum, and therefore the MAT sensor gets influenced by the coolant temp (via heat conduction through the metal).

When you relocate the MAT sensor out of the upper plenum into the air duct, you're supposed to disable the MAT/CTS blend table.

Where is your MAT/IAT sensor located?

 

Ok now that makes sense. I'm running $0D I can't say I've seen a way to disable that table but I haven't looked for that specifically so I may have missed it. Here's where my sensor is installed:

 

Yeah I don't think that should be taking coolant temp into account.

 

Cool I just looked and didn't see any way to disable the table but I can set it all to 0 which I imagine does the same thing since the lower the value the less CTS is blended in. I'll give that a shot in the morning, supposed to be in the upper 40's so should be plenty cold.

 

You gutted the heated air-intake provision on the air cleaner housing?

In combination with the Vortec heads that don't have an exhaust crossover to warm the intake manifold, and using a non-OEM TBI intake manifold that doesn't have the hot-coolant passage from thermostat area to the outlet fitting for the heater core?

No wonder that engine is "lean" when the ambient temp is cool. There isn't enough heat in the manifold to vaporize the fuel. Point being, you've got enough fuel, it just doesn't vaporize properly; leads to poor running but also leads to liquid fuel washing the oil off the cylinder walls.

It'll be tough (not impossible, but also not practical) to get exhaust heat or heated-coolant under the runners in the intake. About your only real option is to enable the heated-air intake on the air cleaner, and hope for the best.

 

Yeah after what I had been reading I kind of figured that was a lot of my issue, I didn't really realize how big of a deal it was going to be when I did all the mods unfortunately. At this point I wish I had just done a stock rebuild and got a different truck 🤣 or done an engine swap to something newer/better.

Also just to explain the timeline a little better, I started with my original air cleaner fully functional and had made an adapter and plumbed the heat pipe off the cylinder 2 exhaust header pipe but was running lean so I tried the IAT add on which didn't really help (for the reasons you mentioned). This past week I grabbed another stock air cleaner from the junkyard and ran it along with the IAT and it didn't really help unfortunately. So at this point the only other options I can really find are the old spread bore to tbi adapter from the older bbc trucks that has coolant flow through it and plumb it to the unused port i have on the crossover at the front if the intake or the gm performance vortec to tbi intake manifold that's $$$, I'm assuming it has coolant flow through it but I haven't looked into that intake too much.

 

I never had an issue from lack of intake heat running TBI. My 350 had a Victor jr 2bbl on it. I put an IAT on it, enabled it, shifted the blending heavily toward the IAT adjusted the AE vs Temp multiplier and it ran great. I ran mine down to ~10°F at times with no manifold heat. Later I put the TBI on a Holley Projection 2" to 2bbl TBI adapter that was water heated. I did not see enough of a difference to make it worth my time. Atleast the adapter was off someones failed Analog Holley Projection system and cost me literally nothing because it was getting thrown away. I never had an issue running the Weiand 177 either. Tuned it and it worked.