what will be the best place to move the MAT and what happens when you move it away from the plenum?

Thanks

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89Iroc, 305 TPI, WC T5, 3.08 Posi, Flowtech Headers 1 1/2, Hooker Y-Pipe 2 1/2, 3 inch over the axle, Flowmaster 80, No Cat, Aluminium Driveshaft, Ported Plenum, Air Foil, MAF Screens/Fins removed, K&N, Gutted Air Boxes, AFPR @45 psi, Ram Air, Throttle Body By-pass, Bumped Timing @12, Bosch +4, MSD 8mm wires, HP Rotor, Cap and Fuel Filter, Sensi Trac rear Shocks.

 

By using the '92 and later MAT Sensor and placing it in front of the throttle body the motor will be more responsive.

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GTA -89:Free flow muffler,dual 3" HF cats, Edelbrock headers, Vette heads, 1.52 RR 7/16, ZZ-9 cam, Big Mouth, AS&M LTR, !plenum, 52 TB, MSD 6AL, TPIS level V prom, Superior shift-kit and all the minor mods. and more to come!
http://www.itv.se/tacs/members_cars/m279/m279.html (Swedish Trans Am Club)

 

"MAT" stands for "manifold absolute temperature. The lower temperature it see's, the more timing, and fuel the ECM will add. The stock location tends to be pretty hot, so the closer it is to the air inlet the better off you are. From what I understand the 92 and later sensors tend to be better as well. The calibration might be a bit closer, who knows. It is worth doing though. Either with the stock one or the later version.

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Torque is KING!
All pray to the god of grunt! When ye thinkth ye has been whupped than shall ye meet the mighty Buick! For none can surpass her majestic power, and all will yet try. All pray to the god of grunt. For the King of torque has arrived!
1. 82 Camaro+ 1. 455" Buick+ 1. N2O plate = YOUR WORST FRIGGIN NIGHTMARE!!!
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I moved mine to my SLP cold air intake. Older 3rd gen V6s that used the same TPI air intake as the 85-92 Camaros have a bung built into the plastic. You could use a V6 airbox top and screw you MAT in and make it look factory.

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Rob P
89RSconvtZZ4TPI
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

The straight dope on MAT relocation:

Before I got into programming my own PROMs and studying the disassembly of the microcode I thought that relocating the MAT allowed the computer to use more agressive timing and fuel. Makes sense right? Well, now I know differently. This subject came up on the GMECM mailing list and several of us studied the disassembly and guess what we found? The MAT is used for nothing except for EGR. That's it. Now - I am saying this in relation to 1990-1992 F-Bodies (speed density). Not sure about the MAF F-Bodies. Haven't looked at that code regarding the MAT yet. Makes sense now why GM put it there.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's after installing Hooker LT Headers and reducing weight.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

So Tim, you're implying that MAT relocation is a basically useless mod for us SD guys at least right...how exactly is the MAT used for EGR, i suppose the ECM waits until it sees a certain intake temp before it allows EGR, so by relocating to a cold place, you may in fact be disabling EGR?
...ed

 

I recently did a Diacom test while we were having a cold spell (-18C or 0F). I have both of my MATs hooked up and I just connect the one I want at the wiring harness connector at the back of the engine.

I discovered that when the ecm detects an MAT temperature around +5C, the EGR ceases to function. Also, when the EGR stops functioning, there was less timing. Further, it appears to have some affect on the duty cycle of the purge cannister. At lower temperatures it drops in its % of duty cycle.

An interesting aspect of the EGR functioning, is that it puts heat into the manifold and thus will maintain it around 5*C even if the ambient temperature gets VERY COLD. Only when I started to climb a very long grade with the cold temperture, (MAT in stock location) the TB opened enough to cool the plenum to below +5*C. When it hit below +5*C, the EGR's shutting off allowed the plenum temperature to drop so far (almost near ambient air temperature) that the EGR would not return on and my plenum remained "supercooled".

I should note that I also have the TB Bypass, so this is another reason why GM has the coolant going through the TB. So the plenum does not fall below +5*C and cause the EGR to cease to function. Remember, that if the MAT reads below -40*C, that you will get an error code.

So while the MAT may only control the EGR, by the EGR functioning, it does have an affect on the timing while driving at part throttle.

I am currently looking at some older drag runs I did when I first installed the relocated MAT. I had done a couple of runs with both. As I remember, the relocated MAT seemed to have a slightly higher 02 reading than the stock MAT (about 20mV higher if IIRC). Maybe it was just the inaccuracy of the 02 sensor but I want to look at a couple of them to see if it was consistently 20mV higher with the relocated MAT. At WOT, the EGR functioning is not an issue as it does not function at WOT IIRC.

But inspite of what the relocated MAT does (or does not do), and a variety of other "time honored TPI trick", I realize these are all "gerry rigged" means of accomplishing what you really want ... "to burn your own custom chip to obtain optimum performance".

[This message has been edited by Glenn91L98GTA (edited December 22, 2000).]

 

Glenn,

Very good points. But, there is one thing that you are forgetting......

EGR is not used a Wide Open Throttle. So, if we are talking about performance then we need to concentrate on WOT. Your points are absolutely valid for driving around town. But, once your car goes to WOT ... timing is fixed to the timing in the Spark Advance Map and Fuel is fixed via the modifiers. No adjustment is made due to MAT at WOT.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's after installing Hooker LT Headers and reducing weight.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Trax,
On my ZZ4TPI the EGR does not work (of course) and I have removed the airpump and a.i.r. lines. I still have all the vacuum lines attached to the EGR, including those ones back by the distributor. Is there something I should do to disable the EGR so the computer does not see it? This is a MAP set up by the way. Should I get a block off plate and remove all the vacuum lines? What about my MAT sensor? Leave it in place or can I get rid of it? Seems I may be loosing some timing advance with my EGR not working if I'm reading all this correctly.
Tks
ZZ4TPI (MAP) Edlebrock intake, SLP runners, everything ported, 24# injectors, ADjfpr, SLP dual cold air, MSD6AL.

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Rob P
89RSconvtZZ4TPI
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

Physically plug the EGR port, somewhere. Set 02BO to FF to disable the EGR. Course this is for off road use only...

 

I've started to get interested in burning my own chips, and to that end, I've started to look at what happens with the stock calibrations. On a MAF motor, I think this is what happens with regard to the EGR(corrections are welcome)-

- the ECM reads the MAF sensor ro determine airflow and from that calculates the VE
- based on the VE, the ECM varies the EGR duty cycle(up to a maximum of 60%)
- based on the EGR duty cycle, the ECM varies the spark advance(adding up to 2.8 degrees)

assuming the above info is correct(something I'm not positive on), it would seem that relocating the MAT sensor would cause the ECM to calculate a higher VE, and therefore, also increase the EGR duty cycle.

would it then make sense to leave(replace) the MAT in the stock location, to allow the ECM to calculate VE based on air temps in the plenum, and also restrict the flow from the EGR system(which should be limited to a max. 60% duty cycle) or perhaps increase the amount of spark advance based on EGR duty cycle?

in the future I'm planning on coating(ceramics) the intake system to allow cooler air into the cylinders, but it would seem the stock calibrations would negate(via EGR) some of the gain made by keeping intake temps down.

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He who hesitates,... is lost!

 

Rob, the EGR in and of itself does not cause timing advance, the ecm has its own set of advance values to be added in when the EGR is functioning (or when the ecm THINKS its functioning) so the goal is to have NO timing added for egr if you dont have it, the ecm can add timing when the egr is on because it cools the combustion chamber and makes it less detonation sensitive. If you dont have a functioning egr valve, but the ecm thinks otherwise you may infact be running too much part throttle timing.. thats why its important to disable it in the chip

 

With the temp sensor in the stock location the sensor absorbs some manifold heat which throws it off some. I have heard that relocating the sensor will be the equivelent of increasing the fuel pressure by 5 psi and that the computer will be getting sensor readings that are closer to right through all operating ranges. Just my $.02.

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1989 Iroc-Z TPI 350 auto 4-spd Removed MAF screens K & N filters, stock other than that.

 

Traxion, isn't mat used in the v.e. calculation in speed density cars? What would be the advantage of reloacting the mat anyway. Don't you want it to sense the temp of the air as it goes in to the cylinder so that the computer has the most accurate numbers for the a/f ratio that will go into the cylinder. It seems to me that if the mat were in a cooler place the ecm would add the amount of fuel for the cool air air which will require more fuel than the warmer air that actually gets burned. Won't this cause a rich condition. I can see how relocation may fool the computer into allowing more spark advance though.

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82 z28 350cid, vortec heads, comp 262h cam, Holley 600cfm carb, 2in twice pipes, MSD ignition, turbo 350 trans, 3.73 posi, manly b&m megashifter

 

So...when I get my custom chip burned, I'll have them disable the EGR function or at least set it to no recognize it. I am halfway thru my header install, driver side done, now on to the bad side.


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Rob P
89RSconvtZZ4TPI
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

Traxion/Tim, yes...when I gave my observations of what I noticed about my MAT I was discussing strictly part-throttle. In my second to last paragraph, I began to discuss WOT and said in the last sentence that the EGR ceases to function @ WOT. I was alluding to my next set of observations as to whether a relocated MAT does ANYTHING @ WOT, or just a fancy thermometer to tell you the incoming air temperature. I don't think there is a question that the MAT is needed at part-throttle for the EGR to function.

I realize TunerCat does not allow you to make any adjustments for the incoming air temperature. And in reviewing the Tables of the hack for the 8d, there does not appear to be any tables that can be modified to adjust for the MAT (PW or Spark). However, I have plenty of WOT runs I've done at various MAT readings (many on the same day, done with the stock MAT, relocated MAT and 4.7K resistor to make the ecm THINK I had a specific air temperature.

And I can tell you for a fact, that a relocated MAT DOES affect the injector pulse width @ WOT (on my SD car anyways). It does not appear to do anything to the spark advance. I offer the following Diacom+ data I have taken from a number of runs I did while doing these tests.

MAT*F CTS*F InjPW
108.....179.....10.8ms
93......163.....11.1ms
75......172.....11.4ms
64......163.....11.8ms
55......176.....11.8ms

I realize the CTS also has a great effect on PW and spark, but my CTS readings are fairly close in range. Also my CTS readings varies both Up and Down...but regardless of the CTS reading, a lower MAT ALWAYS results in a longer Injector PW. So I have to conclude that GM has some algorithm within the 8d code for the SD cars that adjusts the PW based on a given MAT.

All of these tests were done at the same location within a few days of each other and with relatively the same ambient air temperature. The only major variable was the MAT reading. Also, the order that I performed these tests are not in the order I gave the data (I sorted in in descending sequence on MAT*F).

And for those that may doubt this data, I have a conclusive test that I would like to offer. (For SD cars and users of Diacom, I cannot say whether MAF cars will get similar results...but it would be interesting none the less).

Get 3 resistors, 1.5K (105*F), 4.7K (55*F) and 16.2K (14*F)...I've included the MAT temperature reading those resistors should equate to. Do back to back runs, using each of the 3 resistors...do it twice...do it thrice for each resistor if you wish...the more the better. I am willing to bet that you will have a higher PW reading for the higher resistance resistors (lower MAT temp).

I plan to do this very test in the spring with my Diacom and I would be interested if others would be willing to participate to get independent confirmation. You must have a fan switch or some means of maintaining a constant CTS for the test to be truly valid as a higher CTS will result in shorter PWs.

Of course, if others do this test, get the same observations (longer PWs with lower MAT readings), that still does not solve the problem of where GM embedded this algorithm in the PROM and how to use this information to our advantage.

Further analysis that I am working on, indicates that the change in the PW is too long for the given change in temperature. As the MAT temp goes down, the ecm adds too much fuel. Until the algorithm can be modified to give a better correction factor, it still would appear the best solution would be to burn a specific PROM for a given range of ambient air temperatures to obtain optimum performance @ WOT at a specific temperature.

Again, I am only saying this with SD cars. For MAF cars, a relocated MAT may only be a fancy thermometer of your incoming air temperature...unless some MAF person does a similar test with Diacom.

[This message has been edited by Glenn91L98GTA (edited December 25, 2000).]

 

PS: On the test data (for those interested) I did the 108*F (stock MAT), 75*F (relocated MAT) and 55*F (4.7K resistor) on the same day within a relatively short time of each other...about 30 minutes apart.

The 93*F (stock MAT) and 64*F (relocated MAT) was done a few days later with the conditions about the same, except a little earlier in the morning, hence the slightly cooler incoming air temperature. Again, about 30 minutes apart.

 

Glenn,

Awesome data. I really like the idea of using a resistor and doing back to back tests. I'll have to bookmark this page so that whenever I get my car back together I can run these tests. It would be 'cool' to prove the Hack wrong. However, as you saw, there doesn't seem to be anything within the hack that explains the adjusment of PW for different MATs. Hmmm. I can't wait to do this test.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's after installing Hooker LT Headers and reducing weight.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Ive read all the post but dont really understand alot of it. So whats the final verdict? Good or bad to have it relocated? I am curious to know as I have mne relocated...thanks

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wishmister@yahoo.com

1987 White IROC-Z
305 TPI LB9 273 Rear Gear
700-R4 auto tranny
97,000 miles
KYB's
Performance Resource Chip
Flowmaster Muffler
Ported/Polished Plenum by "Daniel Burk"
Holley AFPR
Throttle Body Coolant bypass
TPIS air Foil
TPIS MAT Relocation Kit
K&N's
Gutted air box
Accel 8.0 plug wires
Moroso Super Coil
Blue Streak Cap and Rotor
Boush Patinum +4's
Mobil 1 15/50 Synthetic motor oil
Mobil 1 synthetic Trans fluid.

 

I've been doing more tests and my conclusion that it is bad to relocate the MAT sensor unless you burn a PROM. You should adjust the PROM's fuel delivery so that you have near perfect 128s with the normal ambient air temperature AND possibly have 2 (for winter and summer) should you live in a climate that has extreme differences between summer and winter.

When GM designed the MAT sensor, they made their calibration such that the MAT is in the plenum WITH the TB being warmed by coolant. Thus the stock MAT readings detected by the ECM are very much higher than with a relocated MAT and a TB bypass.

I believe I found an area of the SD 8d code that uses this data. But it appears to use a "net difference" between the incoming MAT and the CTS as part of the calculation. I suspect that when GM wrote this code, the only time there would be a huge difference between MAT and CTS would be when the car was warming up. Because with the stock MAT and coolant in the TB, the temperature reading of the MAT gets quite high.

Overall, a relocated MAT causes the ECM to over compensate and richens the PW far too much for what it really should. This is especially true in cold weather. For every drop in 10*F, the ecm should increase the PW by approximately 1%. But I'm finding that it is increasing the PW by around 2-2.5% for every 10*F drop.

So, I believe the relocated MAT conflicts with the Prom's code as you are bringing in a set of temperatures that was never intened when GM originally designed the code. The ecm is expecting the MAT to be reasonably close the the CTS temperatures on a fully warmed up engine with the stock MAT and the coolant flowing through the TB.

Probably the only persons that may benefit with a relocated MAT are those that have heavily modified their engine and they need extra fuel going to the cylinders (via a longer PW). But they could also accomplish this (getting more fuel to the cylinders) by increased fuel pressure or using larger injectors to get larger flow in a given PW. But regardless, they are just doing a "work around" the REAL SOLUTION, which is "they need a new PROM".

Bottom line, if you NEED a relocated MAT to lengthen you Pulse Width, you really need a new PROM. If you install a relocated MAT you should install a new PROM and be prepared to do two for winter and summer.

 

I should add, that I have found a table in the SD 8d's code that appears to be a multiplier table for a given temperature of the MAT. It is HEAVILY skewed for lower MAT temperatures which would account for the very high over-compensation I am finding with my relocated MAT and the cold weather we have been experiencing where I live.

This table is not accessable with Tuner Cat (the editor I use to modify the PROM tables). But I plan to decrease the "multiplication factors" for the lower temperatures in the table to see if I can decrease the amount the ecm increases the PW to more reasonable (1% change in PW for every 10*F change in MAT temp).

I will keep you posted on what the results are. However, this is all quite time consuming, and I am a fanatic for detail. So I probably won't have any answers in awhile.

 

By the time you include the Reed Presure Levels and stuff of the fuel, you'll probably be back to square one (oem). There are bigger fish to fry, IMO.

I did fire up the ecm bench but just had a 749 glowing, was about .7msec from 0 to 80dF at 100% TPS (@3K)

 

PS. don't forget in the Winter Gas brews they change the aromatic *boil off* temps of the fuel.

Fuel temp also plays a role in detonation.

So what you gain lose at one end you'll probably lose gain more at the other.

There are some things just left better alone.

What is needed is a MAT timing correction. On some of the newer cars that table is for like 10d difference in timing.