I already have the resistor chart that Vader distributes. My MAT is going bad I think (I keep getting '25') Can i just go out to Radio Shack and buy a resistor of the right OHMs and hook it up and be done with it? Also, am I correct in thinking that the lower temperature the computer thinks it's getting, the better? Because colder air means more fuel has to be added to compensate = more power, correct? If that is the case then what is the lowest temp I can send to the ECM and still have it 'in range' so I don't get an SES. Or should I just skip the whole thing and buy a new one? Because I was also thinking that the O2 sensor would correct any imbalances... Someone check my logic and slap this around, I wanna see posts with answers.. :-P Thanks for the time though

------------------
1985 Camaro SC - 2.8L, auto.

http://www.xenodrgn.f2s.com/Frontright.jpg

 

well, for one thing, the reason cold air is good is that it is more dense and contains more oxygen. so you actually want it in there, faking it would make no sense. anyway good luck with the rest of that...

 

Exactly. Basically what I'm asking is do these cars inherently run rich or lean? If they ran lean it would make sense to fake a colder temp, adding more fuel, if they ran rich, it would make sense to fake a higher temp, less fuel. Perhaps I should just buy a new sensor, anyone have any idea how much they are? Or should I just go the to the pick-your-part and pocket a few?


------------------
1985 Camaro SC - 2.8L, auto.

http://www.xenodrgn.f2s.com/Frontright.jpg

 

MAT does nothing to determine fuel for a MAF car...it is all done by the MAF. Only SD cars does the MAT affect the calculation for Injector Pulse Width.

Air temperature is a function of the MAF.

 

If that's true then why do maf cars have mat sensors?

 

MAF determines VOLUME
MAT determines TEMPERATURE

MAF does NOT measure the temperature of the incoming air, never has, never will. The only way it deals w/ temperature is that it has to increase voltage to maintain a certain temperature on the wire, but that determines the volume of air, not the temp.

To determine fuel we need to know quantity and temp of the air. (presumably we know how long its in transit.)

Your idea to put a resistor there has merit except for one thing. The incoming temp changes a lot during a given day, not to mention during the seasons. If you put one resistor in there you would at times be running lean, others rich. It might even out , but the fact would remain that it would only rarely, by blind luck, run as efficiently as it could.

My opinion is to just replace the sensor. The performance will pay for it.

Clayton

 

This might be stupid but what about an air/fuel mixture gauge and a remotely adjustable resistance. It would cost quite a bit though and be a PITA I would think.

 

The MAT only controls the EGR on MAF cars. I have searched all refrences to the MAT in the EPROM for MAF cars and that is all it does.

Does a MAF car have a baro sensor? No it does not. Then how does it determine elevation? Guess what...the MAF sensor does.

Think about colder air blowing against the wire and hot air blowing against the wire...you will get a different voltage reading on the MAF.

 

Xeno's car ('85 2.8) does not use a hot-wire MAF. It uses the AC/Delco "frequency-film" MAF.

The MAT might affect the MAF reading on his (and my) engine.

Although, I don't see the point of "fooling it". Let the computer do it's job. Relocating the air inlet and putting the MAT in that cooler spot would be a better idea.


------------------
-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

My 89 v6 had a baro sensor, actually.

Thank you for making by point, BTW.

If, as we know that cold temp and hot temp will affect the drop in the MAF differently, then doesnt it make sense that it would need a sensor (MAT) to tell it the temp of the incoming air so that the drop in the MAF reading can be accurately corrected?

If the MAT only influenced the EGR, then when would the EGR ever open during the winter? No doubt the temps then are might cold. Too cold to need an EGR vavle. So that cant be it.

Clayton

 

The MAT enables the EGR at around 5*C as measured by the MAT, below that, your EGR is disabled. And that is really the only test of the MAT that I can find in the MAF code.

If you can point out where in the eprom the MAT affects the calculation for the injector pulse width, can you please show me so I can review the instruction set? I can show you in the SD eprom, but not in the MAF eprom.

[This message has been edited by Glenn91L98GTA (edited July 06, 2001).]

 

So, what you're trying to say is that GM put a sensor on MAF cars that is used only to switch on the EGR?

Get real. As bean counting as GM, and other manufacturers, are, that makes absolutely no sense what so ever. The EGR also has the CTS to trigger it. So the MAT would be a redundant trigger. No way would GM put it on how many 1000's of cars?

We all know that GM moved from MAF to SD for the reason of money, so if they were that concerned about money, why would they have kept the MAT on MAF cars?

Also, if all the MAT was supposed to do was trigger the EGR, then how is that priority enough to trigger the MIL light?

Clayton

 

I cannot answer why GM selected the MAT as the controlling device for the EGR. I have modified the code of my eprom to make it function differently to improve driveability. But it is an "eprom test" that GM has maintained through the various "generations" of ECMs as GM refined their development.

I am just disclosing facts that we in the DIY PROM Burning Board have discovered. We do a LOT of testing and experimenting to see how and why these various sensor work and interact. There are certain code that we have NO IDEA why GM put it in...and then didn't even invoke it.

Did you know that GM put in code to enable Highway Mode/Lean Mode to give excellent gas mileage and never invoked it???? After extensive testing and refinement of my personal eprom, I have enabled the Highway Mode routine to give me US30 MPG from my L98 that does high 13s. Not bad for a 350 c.i. V8 IMO. But why did GM disable this fuel efficient code? There are a variety of theories, but only GM knows for sure.

The thing I find funny about this, is this is the exact opposite of a debate we had months ago on the DIY PROM Board, "Does the MAT serve any purpose other than controlling the EGR?" At that time, that was the ONLY PURPOSE found for the MAT. I was the first to propose that the MAT WAS a factor in metering fuel on SD cars...and found code that supported it. I then went out to prove it. You can do the very same test to prove or disprove how it works on various cars.

You will need a range of various resistors to similate different readings of the MAT and a scan tool. Due to the slow ecm that is in your cars, you may have to do the test slightly differently than I did to prove the effects of the MAT.

With your scan tool, you can monitor a variety of sensor readings to confirm the effects. The actual sensor readings monitored differs from ECM to ECM, so you may have monitor things that are different because your ECM does not output that information to the ALDL. The sensor readings that are of interest are: Injector Pulse Width, BLM/INT values, %TPS (or voltage reading), EGR Operation (On/Off, or percentage of Duty Cylce), MAT value (or resistance), Load or Baro reading (if available), O2 Voltage (if available for WOT Test).

The colder the air temperature, the greater the resistance of the MAT. Just insert a high resistance resistor into the MAT and note (or capture) the various readings. Make sure you get the engine up to proper operating temperature before noting the readings.

The first test is the part-throttle cruise test. Find a long stretch of flat road and maintain a constant speed/%TPS for a period of time and record those values. Then, insert a resistor of lesser resistance an redo the test, and so forth until you have emulated cold to hot weather.

I found the Injector Pulse Width was it greatest, the BLM/INT values the lowest at the coldest readings...and as I decreased the resistance (warmer MAT readings), the Injector Pulse width went down and the BLM/INT values increased.

At around 5*C, I noticed the EGR began to function too. I re-did the test and found below 5*C the EGR would not function and above it did.

The second test is the WOT test. Even with a slow ECM, the first test should show the effects. But with the slow ECM, this test may not be as valid. But try it anyways.

Do a standing start and just acceralate to a "significant speed". Track is the best place to test this. Using the various resistors you should notice that the from "run to run" the Injector Pulse width should decrease for the increase in measured MAT temperature. Also, the O2 sensor will most likely decrease. But the Injector Pulse Width is the key reading to monitor.

Here is a table that corresponds between Resistance and Temperature to help you do the test:

Temp ... Ohms
212F ... 177
194F ... 241
176F ... 332
158F ... 467
140F ... 667
122F ... 973
113F ... 1188
104F ... 1459
95F .... 1802
86F .... 2238
77F .... 2796
68F .... 3520
59F .... 4450
50F .... 5670
41F .... 7280
32F .... 9420
23F .... 12300
14F .... 16180
5F ...... 21450
-4F .... 28680
-22F .. 52700
-40F .. 100700

When I did these tests, I noticed a definite effect that stood out like a sore thumb. You had to be blind not to notice the change in the Injector Pulse Width. But with my ECM I get 6 data captures in 1 second. Some of the older ecms take almost 2 seconds for a single data capture. That is why the part-throttle cruise test may be better to use. But try both.

BTW, I also found that my ECM/EPROM overcorrected when I had a relocated MAT. It ran far too rich in cold weather and too lean in hot weather. That is when I found the Tables that corrected this and now my relocated MAT works perfectly. Prior to that, it caused me more problems (cutting out the EGR at 5*C and mis-managing the fuel mixture). My car is now consistent in hot weather, cold weather, hot operation and cold start operation. I never suffer from the problem of my car feeling like a dog when I turn off and restart my engine in hot weather that plagues so many TPI cars.

Anyone else with a different setup that is willing to do this test, I would be interested in it too. If you have Diacom, e-mail the GDF file to me.

[This message has been edited by Glenn91L98GTA (edited July 06, 2001).]

 

Wow, thanks guys! I didn't except so much info. It's become apparent that using a resistor is more trouble than it's worth. So my last question is, how much is a new MAT sensor going to cost me?

------------------
1985 Camaro SC - 2.8L, auto.

http://www.xenodrgn.f2s.com/Frontright.jpg

 

Hehe, not me! I wouldn't have a clue as to where; and I'm not saying you're wrong, either. I'm just saying that the V6's use a different MAF than V8's.. and maybe the V6 prom's are burnt differently. I don't think anyone's attacked a 2.8L PROM; that's all I'm saying.

The V6 MAF has an orange flat film (flat is the key, if it's wrinkled, your MAF is busted and it's time for a new one). The film vibrates due to incoming air flow. Low vibration = low frequency = low air flow. High vibe = high freq = high air flow. Too low, and trouble code 34 sets. Too high and code 35 sets.

I've never considered it before now, but I imagine that the film will vibrate differently according to incoming air density. Does that make sense? Considering airflow at the same speed: A cooler, more dense air might make the film vibrate higher (and thus read high air flow). More air molecules would be hitting the film and raising it's frequency. And conversely, a warmer less-dense air would make the film vibrate lower due to less air molecules.

Xeno, there's no reason you can't hook up a resistor as a "sensor by-pass", just to test out the problem. Go to Radio Shack, and pick up a 2-pack of 2.2K ohm resistors for 50 cents. Hook it where your sensor went, and start the car up. If the SES light goes out, you had a bad sensor... the guys here helped me do that with a knock sensor on another car. The computer kept saying "bad knock sensor, bad knock sensor!" even though I tested the sensor out to be working. I checked the wire leading back to the ECM too. The guys told me how to bypass the knock sensor, and sure enough, the code was still being set- the ECM was fried.

Oh- I just checked carparts.com; looks like they want $25 for an "air charge temp sensor". I'm sure an Autozone or Pep Boys price is similar.

------------------
-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

[This message has been edited by TomP (edited July 06, 2001).]

 

Tom, I can't find any information on the "early" MAF V6s (can't find anything on the V8 either). Generally, the V6s shared a lot with the V8s though. In fact, V6s are an excellent choice to find 7730 SD ECMs.

But the problem is these older MAF systems. There appears to be three types, Pre-1986, 1986-1987 and 1989. V6s were the first to go SD (even before the V8s), but the SD version is very similar to the V8 version. Tables have different values, but the EPROM machine code is still the same if it is a 7730 SD ECM.

As MAF goes, the pre-1986 seems to be the one with the least information and guys wanting to mod their pre-1986 ECM have the most difficult time. Converting to a 1989 type system or 7730 SD is the only two real options open to a person who wants to mod their engines that have these older systems.

But, if some guys are willing to do some of the tests I outlined above, then at least we can see if there any differences. I would be interested in information from ANYONE doing the test...just tell me the year, and type of engine. I know that the 1987+ SD V6s definitely will notice a relocated MAT as they are the same type of system as the 1990-92 TPI SD system. I haven't checked out the 3.1 F-body yet as it uses the 404. Not much information on the 404, though I would like to check it out and see what I can find.

No V6 guys are really into PROM Burning (which is a shame as we do have a lot of infomation on the 7730 used on the 87-89 2.8 V6). I realize isn't much information that we can offer them if they have the 404 used in the 90-92s. But I would like to change that.

 

Thanks Tom, and everyone else. The CEL light doesn't stay on, however I am getting both codes 23 and 25 (used to be just 25). I'll go buy a resistor at radio shack to be sure it's not just faulty wires, and if that solves the problem, I'll go ahead and buy the sensor. Thanks again, I never figured I'd start such a debated/techy post.

------------------
1985 Camaro SC - 2.8L, auto.

http://www.xenodrgn.f2s.com/Frontright.jpg

 

Ok Glenn, in light of all the testing and all that that has been done by yourself and others, I will go w/ the idea that the MAT has no other purpose than an EGR switch on the MAF vehicles.

Also, you did a good job of keeping the topic civilized. Thanx

Not to start another debate, but my 89 2.8 was MAF, not SD, so was the SD a secret/special option in 89?

Clayton

PS The MAT thing still doesnt make much sense

 

According to the GM P4 ECM Cross-reference Table http://www.cruzers.com/~ludis/p4xref.html the 87-89 2.8s used the 7730 SD ECM. Not having actually had the opportunity to yank out the ecm and look at the ecm/memcal, I cannot say for sure.

Initially, I was under the impression that the V6s always used the same ECM as the TPI system, until I saw the cross-reference chart. If the cross-reference chart is indeed wrong, then it needs to be corrected.

I do notice that the 90-92 3.1 V6 used a completely unique ECM which little information is known. This is one thing I would like to find more information on. I would like to find someone local with an 89-89 2.8 V6 so I could pull it and verify what ECM (and memcal) came in it.

As I said, nothing saying that the Cross Reference Table for ECMs is correct.

 

So GM used a MAT sensor to turn on EGR and a temperature switch in the EGR base to verify it's on? Imagine how much cash they could've saved by eliminating both and using CTS and TPS to operate EGR... and who cares about verifying it's working.

But then again looking at the 9th injector says it all... what were they thinking?

 

You know, glenn, if I had a scanner, I'd gladly mess with different MAT resistances for you, and if I knew anything about the prom burning biz, I'd help you out with the different computers. But as it is, I can't, so therefore I apologize. Supposing I did get a scanner in the sometime near future, what is a good one to get?

------------------
1985 Camaro SC - 2.8L, auto.

http://www.xenodrgn.f2s.com/Frontright.jpg

 

Well, if you cruise over to the DIY PROM Board, you could enquire about Craig Moates' FREE Scan Tool Program. The only thing you need is a special cable WHICH you can either build yourself or there is a link somewhere to a guy who will build it for you. Under $100 for the "ready to use" cable as I recall. About $25 to build it. I cannot confirm because I use Diacom Plus.

It works great with the MAF 165 ECM. Not sure about your ECM. I am thinking it MAY be the "870". If your car is the 870, unfortunately it is not a great ECM. The alternative for 85 TPI cars are either "upgrade" to the MAF 165 or "since you are in there all ready", just go SD 730.

Any chance of you pulling your ECM and reading the ID tag on the ECM?

 

Joel, if you get into the actual machine code, you can change ANYTHING. Personally, I cannot see a reason for the EGR to turn off except the coldest of temperature. Which I won't be driving my car in anyways. But 5*C was just too unreasonable, especially since I had a relocated MAT.

I actually found controlling the EGR based on MPH made for better driveability. I can actually FEEL the EGR kick in-out when I drive over "rolling hills" which we have a lot where I live. Combine this with a "locking/unlocking TCC" and this gives you a real jolt in the butt.

The EGR is primarily controlled by the MAT and %TPS. I found just relying on MPH and not engaging it until 15 MPH made a much smoother part throttle start. Then my EGR is "locked on" except for deceleration or WOT or if my speed drops below 15 MPH.

With my TCC locked at 45 MPH, this makes a much smoother drive. It greatly improved the driveability over rolling hills.

 

Glenn, if you gimme a short tutorial on how to get at it, and tell me what I'm looking for, I'll do it for ya. As far as I remember, it's in the passengers side kickpanel, with a bolted down plastic cover over it, correct?

------------------
1985 Camaro SC - 2.8L, auto.

http://www.xenodrgn.f2s.com/Frontright.jpg

 

Actually Glenn, all 2.8 (1985-1989) were MAF-based. SD on v6's started in 1990, with the 3.1l. Note that I'm talking about the f-body; other 2.8 V6 platforms might've moved to SD prior to 1990.

So those 3.1 "404" chips are the only ones with the SD software, unless, like I said, you're using other 2.8 chips from other platforms....


You've gotta be talking about a different platform... cavaliers, maybe? Although my dad's old '87 Oldsmobile Cutlass Ciera originally used a MAF sensor, it had a "service bulletin" issued, and a speed density system installed. The MAF was bypassed, a MAP sensor installed; the MAF chip was yanked and a SD chip was put in. Are these the '87's you mean?

Plus, like I mentioned, the MAF used by the V6 is entirely different than the MAF used by the V8's... do you mean the programming between V6's and V8's is similar in areas "other than" the MAF?

By the way, I told my import-owner friend about what you were talking about- it impressed the hell out of him! He didn't know stuff like that was possible.


------------------
-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

Tom, as I stated above. I need to take a gander at one of these 2.8 V6s and see what is REALLY up. I don't doubt what you guys are saying as I was under the same initial impression that 87-89s were MAF until I read the Cross Reference Chart above. I also would like to look at a 3.1 V6 F-body to see what they REALLY have as there is incomplete information on it.

The problem I see is that enough V6 guys are not into PROM burning and we need more feedback.

 

Would it help if I got you any numbers from the top of my original GM prom, before I put it back in? I'm yanking the ADS chip because of what you told me about it.

Plus, too, I'm in junkyards a lot, if the numbers off the top help you, I could pop open some 85-89 2.8 computers and get those chip numbers, or ECM numbers, or etc... would any of that help?

I'd love to get into PROM stuff, but I'll probably tackle that after I rebuild my motor. Looks like that won't happen this summer (dammit); I need to do a mass-clean of the basement to convince my dad to let me keep a motor down there.


------------------
-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

An easier thing to get is the "Broadcast" code from the BIN (along with the ECM lable).

Go here http://holman.cs.uml.edu/~sdurphey/bccfind/ to see where the Broadcast Id is located on an eprom.

An interesting note, a person on the DIY PROM board ran a 1989 2.8 V6 Broadcast Code and this site is ALSO saying the SD 7730 ecm is used in 1989.

So if you can grab some of this information that would be great, I could check them. Pity you don't have access to a Prom Burner, then you could read the BIN and I could look inside to see which it is.

It has been my impression that the GM V6s were actually a "little ahead" of the V8 guys. Lots of theories as to why. I suspect it is because of the shear number of V6s are greater than the V8s...so GM does the development there as this is their "bread and butter".

It is quite surprising on how many different cars/trucks and engine combos many of the same basic eprom works on. Also, a different ECM is often a "reworked version" of another ECM. A great example is the 749 ECM used on Syclones/Typhoons is a "derivative" of a 7730 ecm used on Speed Density Vehicles. The 749 just has a "driver" for the waste gate of the turbo.

I feel part of the reason that there is so little info on V6s is also because there has always been very limited aftermarket parts, so the V6 guys don't face the same "tuning" issues us V8 guys do.

But, I hope to change that as I believe that once the proper ecms are known, then all the tuning tricks within the eprom available for V8s is available for V6s. It's just a motor with EFI as far as I am concerned.

Just have to know WHICH ecm.

 

Wow, my chip is half the size of the one at that website, but hopefully it's got the sticker on it. I'll see if I can find my ECM label too; it fell off four years ago, and I put it in a safe place- wherever that is!


------------------
-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

Glenn, according to what you have typed, you have only done the above test to see if the MAT sensor affects fuel enrichment on a MAP equiped car, like yours. As I understand it you have not done the test on a MAF car, correct?? If not, all you are going by to say that the MAT sensor does not affect fuel enrichment on MAF cars is that "you cannot find code for it", correct? Well I have frequently visited the DIY PROM board and repeatedly read that there is much, much more code that you guys have not even looked at yet, let alone deciphered to find its function. I believe you cannot say the MAT does nothing for MAF cars except control the EGR because PROM burning has STILL not become perfected yet. There is much to learn and find in the MAF PROM. Since, no one has done any conclusive testing on MAF cars like you have done to you MAP car, I believe your statements have no foundation. Also, considering that 95% of the experienced people on the DIY PROM board use the SD ECM, there is much less known about the MAF ECM and very little research being done on its code than SD. So in my opinion you cannot come here and write the say all to end all arguement about the MAT on MAF cars. To put it lightly you do NOT have the experience with or knowledge about the MAF code to make the assumption that the MAT only controls the EGR.

 

Great, do the test that I have previously outlined on this subject and give us the results.

But the evidence is against the MAT doing anything other than the EGR for a MAF car is not supported in the hac.

I used a "search funciton" of the "address" referenced in the "hac" for the MAT. It finds ALL occurances of that address, where it is tested in the code and what is done with it.

For MAF, there is lots of referencing with the EGR. Nothing for fuel correction. With SD, lots of referencing with the EGR and Fuel Correction.

FYI, I use the "search function" all the time to find out what happens with in the code. It is how I found the "Octane Retard Routine" that mysteriously pulls out 4* of timing.

If the "search function" can't find a reference to something, it is a excellent bet that it is not there.

But do the "resistor" test of varying resistors that emulate a specific Temperature for the MAT. Then just "scan" the results and you will immediately notice the effect of the MAT. If you put in higher restance resistors, it will make the ecm think it is colder outside and it would increase the Injector Pulse Width to compensate. This is what it does on SD cars. And would do the same on a MAF car if the MAT has an effect.

Also, if you use resistor that will give a value below 5*C and then above 5*C, you will see the effects on the EGR.

The table for Resistance vs MAT temp is above. I look forward to your results.