Someone in an earlier post said tb coolant bypass cause the engine to stay in warm up mode and causes the egr to sieze functioning.True false?

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1987 Trans AM GTA
305 5SPD
Hypertech airfoil
gutted maf
kn filter
High Flow Cat,
3"Walker pipe
Dynomax Super turbo Muffler
TB Coolant bypass

I'd really like to know how that is even possible.

No, it wont cause problems unless you live in the south pole.

Max, better check again. The MAT does affect the EGR's functioning. That is why in PROM Burning we set the Temp Enable counts to 254, to keep it from enabling the EGR if you don't have one. Setting the "switch" only supresses the Diagnostic. It doesn't stop the ecm from trying to enable the EGR.

And whether or not the EGR functions does affect the calcuations the ECM makes.

Shadow, ask the same question on the DIY PROM Board and see what responses you get.

Say what? The only thing that's going to cool is your TB. I have had that mod on my car since August of last year and did'nt even have a problem when the temps dipped way down in the winter.
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89 IROC-Z 5.7L 2.77 GEARS
130,000 MILES
ALL FREE MODS
K&Ns FILTERS
FLOWMASTER MUFFLER
PERFORMANCE RESOURCE CHIP
AFPR & PORTED PLENUM
Best 1/4 E.T. 14.09 @ 97.2 MPH
Best 1/8 E.T. 9.09 @ 77.4 MPH
Best 60ft. 2.03

[This message has been edited by whiteroc (edited July 03, 2001).]

As per the hacs, address X'247 for 6E/MAF and address X'2B0 for 8D/SD are the hex addresses of the constant to set the minimum MAT temp to enable the EGR. If the MAT is above that value (around 5*C) the EGR is enabled, and below that disabled.

To disable the EGR (for those with a Miniram), hex FD (a very high number) is put in the above mentioned hex addresses. This requires the MAT to read 304*F before the EGR will turn on. At that point, your car is probably on fire.

I found that in colder climates and you have a functioning EGR, that if you don't adjust those values to a lower temp, you EGR will kick out sooner...especially with a TB Bypass or a relocated MAT much sooner.

[This message has been edited by Glenn91L98GTA (edited July 03, 2001).]

What does the MAT sensor have to do with the TB coolant bypass mod? He did'nt say anything about removing the EGR valve. ...Just trying to figure out where you are coming from with this post.

Glenn... 30 to 40 F for EGR enable is what you said on the other post? I havent driven my car in snow with a scanner hooked up, but Ive been in some pretty cold weather and never saw the MAT below 122 at cruise. I dont see the problem here. Even if that was C, its only 104... I still dont see the problem.

White, read my answer above.

The ecm compares the MAT to a minimum (I gave the hex addresses that are referenced in the MAF and SD eproms) before it turns on. A bypassed TB will cause the MAT to read lower temperature than an un-bypassed TB. This will cause the EGR to cease to function sooner in cooler weather as the MAT will be giving a lower reading.

The stock value is around 5*C as read by the MAT before the EGR ceases to function. I have done a hundred tests of this with Diacom when it is winter and that was the value that MAT reading everytime the EGR turned off. I've confirmed it in the code of the eprom.

Is it the open cage style MAT or the closed one thats all brass?

So since you are testing... how much heat does the TB being hooked up add?

...and I assume this also applyies to the remote MAT sensor mod that puts the MAT sensor in from of the TB in the airbox.

Why do you seem to be the only guys that knows about this?

Max, if you start the car when it is "stone cold" and the air temperature is less than 0*C (32*F), unless you drive in stop and go traffic to pick up some "latent heat" from the engine, the bypassed TB (and stock MAT location) will cause the MAT from ever reaching 5*C (just under 40*F). I am use to Celsius, so I just round with Fahrenheit.

I noticed this last fall and that is when I did all my experimenting with the EGR, a relocated MAT and TB Bypass. I did various tests with both locations for the MAT (I have two installed on my car) and with the TB Bypass.

I found the solution was simple, since I wanted a functioning EGR, I just set the temperature setting lower. Also, since the MAT is a factor in calculating air flow for SD cars (which I have), I found I had to adjust a table (MAT Inverse Compesation) to make my ecm calculate properly for the lower temperatures when using a relocated MAT. Those changes to the eprom fixed those problems.

When I searched the "hac" for the 6E/MAF, I never found any similar compensation code for the MAT for air flow. But, then I realized it was not necessary as air temperature is measured as the MAF anyway.

A relocated MAT is just a fancy thermometer on a MAF car and does nothing to increase performance (as it is not a function for air flow) and the EGR makes a relocated MAT actually a problem.

I'm looking at a 90 L98 hack and it says 30 C not F. ANHT4298 bin

So which MAT sensor is it?

The documentation in the "hac" is incorrect. The algorithym for the constant is not normal. It equates to 5*C.

If it was 30*C (as the hac suggests), that is almost 90*F...trust me, the EGR is functions BELOW 90*F. 5*C on an F-body.

When I mentioned this to TunerCat (as the variable is defined in the 8D TDF), they explained that is why they use "counts" instead of the actual temperature as no one has REALLY cracked how the algorithym works. I just know that the stock value equates to 5*C as measured by the MAT through testing.

[This message has been edited by Glenn91L98GTA (edited July 04, 2001).]

The 32B has it too, says 30 but no reference to F or C.

so if im in temperature above 5'C im ok for my egr still working right.My car will never drive in winter again so im ok then.

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1987 Trans AM GTA
305 5SPD
Hypertech airfoil
gutted maf
kn filter
High Flow Cat,
3"Walker pipe
Dynomax Super turbo Muffler
TB Coolant bypass

If your coolant is flowing through your TB and you have the MAT in the stock location, this will never happen.

The more surprising thing is that the MAT relocation is a useless mod on a MAF car. Other than affecting the EGR, it does nothing for performance on a MAF car as it is not a factor (from what I can see in the "hacs") in calculating Injector Pulse Widths or Spark (expect if the EGR is affected).

So Glen,
You're saying my relocated MAT mod is useless? It makes no performance improvement?

See sig for other mods....


I also have TB coolant bypassed. Should I be eliminating the EGR also?

You seem to know your stuff. Your input is appreciated.



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Mike L.
It ain't pretty.......

1987 IROC Z TPI 350 A4 3.27 Borg-Warner.

Mods: 2300-2500 Stall Converter, Shift Kit(GM parts), TPI Specialties Stage 3 PROM, Modified Airbox w/ K&N's, homemade cold air, Relocated MAT sensor, Gutted MAF, 160* thermostat, Accel 8mm Wires, bypassed TB coolant, Flowmaster 3 chamber single 3" in/out muffler, 3" MAC mandrel intermediate, custom dual !cat Y-pipe. airfoil, ported plenum. !smog

http://www.MichaelLasiuta.home.att.net

**BOYCOTT LAPEER DRAGWAY**

There are 2 different styles of MAT sensors that were used and are available. There is an open style, and a closed style. I know the closed style was used up until at least 1988 on TPI cars, it shares exactly the same part number as the CTS. I am assuming the SD cars got the open style one although I am not positive. Why I am asking...

Air does a lousy job of cooling metal off for the most part. A radiator is a good example of this, it works but only to a certain degree and it requires a bunch of airflow to do so. I have the closed style in my intake, and as such its not really a MAT sensor but more appropriately an MT sensor. This makes sense with the scanner readings and infared thermometer readings I have gotten before, and the fact that rapid acceleration does little to the reading from the MT sensor. The open style however, is much more reactive to the amount of air moving in the engine and the actual AIR temperature and not the manifold temperature since the sensing element is exposed to the air and not really exposed to the heat from the brass housing its in. It actually works as a MAT sensor unlike what I have. I'll experiment with the TB bypassed and not bypassed and see what, if any, different readings I get from my MAT sensor. I'd venture to guess the readings will not be significantly different due to the design of the sensor itself and its location. I would also assume that the open style will not react the same but I have no idea what difference there might be.

Actually Max, from what I understand the MAT sensor used in the LT1s (and installed on some 1992 SD cars) is the best one and reacts the quickest. That is the one I am using for my relocated MAT and I will admit that I can notice the effects of cooling if I have been stuck in traffic and then start moving on the open road.

I have noticed that even the new type is STILL subject to "heat soaking" from just my plastic intake track. It still takes 10 minutes of driving on the open road to get the relocated MAT to read the same as the ambient air temperature. Its the old "80/20" rule...80% of the effect is noticed within 20% of the time, the remaining 20% of the effect takes the remaining 80% of the time.

On the subject of relocated MATs, I break my opinion of them between MAF and SD cars. On MAF, they are a useless mod for any type of performance. If anything causes problems with the EGR IF you do not adjust the Minimum EGR Enable Temp counts down to single digits, especially if you live in colder climate.

On SD cars, the relocated MAT is only useful IF you adjust the MAT Inverse Compensation Table to account for the fact that the MAT is now measuring the actual air temperature coming into the engine. Once adjusted, it actually is beneficial in that you have a precise calculation made for the incoming air flow. You no longer have "heat soak" from the plenum giving you a "leaner" condition. GM took this "leaning effect" into consideration when they developed the MAT Inverse Compensation table, with a relocated MAT you tend to run overly rich without adjusting this table.

On the EGR issue, my opinion is the same regardless of whether you have MAF or SD. Whether you bypass the TB or run a relocated MAT, you MUST reduce the Minimum MAT EGR Enable temperature counts if you want your EGR to function in colder weather. This is one of the reasons many guys get horrible gas mileage during winter driving. Once I made these adjustments, my gas mileage during winter returned to the same levels I got during the summer.

If you do not have an EGR, disable the EGR properly by increasing the Minimum MAT EGR Enable temperature to a very high number (dec 254 or Hex FE). This is the only real sure fire way to make sure the eprom does not execute any of the code involving the EGR. Turning of the EGR Diagnostic Code or setting the %TPS constant can still allow the eprom to execute the EGR code...it just suppresses an SES code related to the non-functioning EGR. When the EGR code is executed, it has an effect on both the spark advance and fuel, depending on whether the EGR is enabled or not.

This will allow for more consistent tuning. Tuning around a "working EGR" and then not enabling it causes tuning issues. Tuning around a non-functioning EGR and then having the code exectuted also causes tuning problems.

Just figure out what you want (EGR or no EGR), make sure it is enabled based on what you want, and then tune around it.

So what I hear you guys saying is for those of us that DO have basically stock MAF based TPI's and DON'T have engineering degrees this brings our list of "totally useless" mods to five?

MAT Relocation
MAF Screen Removal
Throttle Body Bypass
Throttle Body Airfoil
160° Thermostat (for horsepower purposes)

You don't need an engineering degree to burn proms. Go to the PROM board and click on the link at the top of the page, this will take you to an Intro to Prom Burning article written by Traxxion. It's simple, I can do it.

i was about to do TB bypass but luckily one of the hose clamp bolts were broken to it's hole so i pass the mod this time. anyway, i'm pretty sure that passing coolant is a good mod since intake is really hot after taking some smooth and gently runs (have you adjusted timing after taking best 0 to 60 few times -> even the runners are warm enough to fry your hand

EGR will functioning in weather you're able to drive your TPI car. i wont even consider below sub zero celsius. scary enough ride when it's raining i'll take a bus.


- P

There's no engineering degree's required. I understand fully what glenn is saying and i just got into eprom's last september/october. Alot of reading to do but even a dip **** like me can burn eproms. btw, if you didn't pass 6th grade math you might have problems with a few things...

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89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Gutted cat
-!AIR
-Gutted Air Boxes

agree, Glenn have an idea how's engine is functioning

i also understand that cooler intake is better than hot. i run 200F+ thermostat currently, so i believe MAT will recognize quite high temps even TB coolant is not heating the intake.

-p