Adding MAT to 350 TBI $0D/7247

[JeepsAndGuns]

So those spark tables could be set up/adjusted to remove or add a few degrees of advance across the board when temps are high or low? That does seem like a very handy feature, as back in my carb days, I would get a little part throttle ping in the summer, that wasnt there when colder.
I have a feeling this is going to be a good thread!

[JeepsAndGuns]

Ah! Missed that part, yes from evaporting fuel!

Just thought, my LT1 has no hot air tube! But does have a heater hose to TB which guys remove... but I don't remember any MPFI having hot air tubes? Now I'll have to start looking at other MPFI as I don't remember any others having heater hose water running through them... why would there be icing issue in MPFI TB if no gas evaporating making it colder like TBI or carb.

The mpi in my wrangler has no hot air inlet or any type of coolant going to the tb or the intake.
I have seen some of those GM TB's and wondered why they had coolant running through them, any idea?

[woody80z28]

The mpi in my wrangler has no hot air inlet or any type of coolant going to the tb or the intake.
I have seen some of those GM TB's and wondered why they had coolant running through them, any idea?

I've wondered that myself...because IIRC (haven't had either stock TB for some time now) the 3100 in my '95 Beretta had the coolant pipe to the TB, but the 3400 from a '04 Impala did not. And both engines are nearly identical aside from displacement...both SFI.

There is no doubt though that once the truck is running, the TBI unit is colder than ambient temp under most - if not all - circumstances.

[PJG1173]

The mpi in my wrangler has no hot air inlet or any type of coolant going to the tb or the intake.
I have seen some of those GM TB's and wondered why they had coolant running through them, any idea?

my TBI jeep has/had a hot air tube going to the airbox from the manifold. I'm almost positive my buddy's MPI had one too.

Wondered why the TBI adapter I took off a 454 had coolant lines going to it. I'm still on the fence on whether or not I should hook the lines up to it when I put it on my other truck with the air gap intake. if I can ever find time to convert it to EFI.

[EagleMark]

Strange finding as to why MPFI/TPI/CPI had hot water tubes and some did not? Don't see the need as icing would not occur with just air? Or maybe it did? But now they do not? But having a hot air tube could be for drivibility on earlier ECM/PCM. Or did the ones with hot air tubes not have MAT/IAT? Guess it's just all part of the evolution of EFI...

But we do know adding MAT/IAT sensor input to the equation will be a benefit!

As for the Truck TBI to spread bore intake adapter having hot water. The engines at that time were used in HD trucks with a carb and light duty trucks with TBI. So they made an adapter for that time period. I was told by an GM engineer at that time the hot water was added during testing on there in house engine dynos, climate controlled, because TBI truck engines at highway speed were still getting icing as they were running higher RPM and pulling more load, hence using more fuel and air, causing more icing. Hot air tube from exhaust was insufficient at highway speed do to wind in engine compartment blowing hot air past hot air tube, instead of being drawn through hot air tube to incoming air to TBI. So they warmed the TBI this way. Later improvements to intake design cured this and the adapter was no longer needed as they now had a TBI intake manifold.

[woody80z28]

Strange finding as to why MPFI/TPI/CPI had hot water tubes and some did not? Don't see the need as icing would not occur with just air? Or maybe it did? But now they do not? But having a hot air tube could be for drivibility on earlier ECM/PCM. Or did the ones with hot air tubes not have MAT/IAT? Guess it's just all part of the evolution of EFI...

But we do know adding MAT/IAT sensor input to the equation will be a benefit!

As for the Truck TBI to spread bore intake adapter having hot water. The engines at that time were used in HD trucks with a carb and light duty trucks with TBI. So they made an adapter for that time period. I was told by an GM engineer at that time the hot water was added during testing on there in house engine dynos, climate controlled, because TBI truck engines at highway speed were still getting icing as they were running higher RPM and pulling more load, hence using more fuel and air, causing more icing. Hot air tube from exhaust was insufficient at highway speed do to wind in engine compartment blowing hot air past hot air tube, instead of being drawn through hot air tube to incoming air to TBI. So they warmed the TBI this way. Later improvements to intake design cured this and the adapter was no longer needed as they now had a TBI intake manifold.

I played around with the idea of swapping in a BBC TBI adapter since my manifold is spreadbore. My thoughts were that it wouldn't make any difference for my short 1-mile trips and might actually hurt max power on a loaded hill climb, etc. but maybe during cruise at low temps it would help.

[JeepsAndGuns]

my TBI jeep has/had a hot air tube going to the airbox from the manifold. I'm almost positive my buddy's MPI had one too.

Yea the TBI ones were diffrent, they were older. But all of the 91 and up 4.0's I have ever seen (in YJ's, ZJ's, and XJ's) I have never seen a hot air inlet. Now the pre 91 XJ 4.0's with the renix injection might be diffrent, I have not worked on or really seen any of those.

[FSJ Guy]

If you look up a 92 Chevy Astro Van with the 4.3L TBI engine, you will find an "Air Charge Temperature Sensor" for under $20. BWD part # WT3036 or the O'Reilley's house brand (Master Pro) # 2ATS7.

The plug looks SIMILAR to the coolant temp sender plug, but it is NOT THE SAME!!! Look at the different pictures on the parts store website and you'll see that the plug you want has two rectangular channels on the short side of the plug. One channel is wider than the other. The CTS plug has channels that are half-round. This is the sender that the plug needs to fit:


You can get the pigtail for $20 or from a junkyard. I found several simply wandering around the mid to late 90's TBI Chevy's in the yard.

[EagleMark]

Found a thread on Thirgen by RBob on exactly what we are looking for when using or changing MAT/IAT has all the numbers !

http://www.thirdgen.org/techboard/di...sation-8d.html

[woody80z28]

I went to the local jy and found nothing with a MAT, so I just snipped the half rounds off a CTS plug and it works fine. The pins engage and the clip holds it together, so I don't forsee any issues.

[woody80z28]

Found a thread on Thirgen by RBob on exactly what we are looking for when using or changing MAT/IAT has all the numbers !

http://www.thirdgen.org/techboard/di...sation-8d.html

I got the table from the 4.3 bin for mine as a starting point since it is TBI and not MPFI, so I think it should be closer. I'll post it up when I get back to my home PC.

[EagleMark]

4.3L came as TBI and CPI. In the $OD bin there seems to be numbers for both depending on what bimasks are selected determines what is used. As mentioned MAT and IAT would be 2 differant sets of numbers. If using as IAT I would start with IAT numbers. If using MAT I would start with MAT numbers. Now because TBI is wet intake and MPFI/TPI/CPI are dry intake numbers would be differant because intake manifold temps would be differant. So IAT numbers from a TBI engine would be best starting point!

[woody80z28]

I am going TBI MAT though, not IAT. So I'll probably just have some tweaking to do.

[EagleMark]

Probaly more then you think! MAT numbers are all from dry intake, TBI is wet intake. So you would have to find numbers from a MAT TBI bin. Does anyone know of a MAT factory on TBI engine?

The only TBI I know of that used this was B and F body $61 and that is IAT.

[woody80z28]

I guess that makes it a good thing to play with, so it can be helpful to the whole community!