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-   -   Two different Hot Air MAFs? (http://gnttype.org/forums/showthread.php?t=14374)

jiho 05-31-2011 08:31 PM

Two different Hot Air MAFs?
 
I have a MAF of uncertain origin that was sold to me as "84/85". The problem is that, although they appear identical from the outside, there are two different part numbers for '84 and '85, and I've never been able to find out why.

This one is in the original-style case. It has a plastic sticker on it that reads:
/--------
| 25007653
| SERVICE
|
| BP [rotated and large]
|
| 25007651
\--------

25007653 is the '84 number. 25007699 is the '85 number.

My ECM has the '85 PROM (CMM broadcast code). What difference could it possibly make, using one Hot Air MAF versus the other?

This (apparently '84) MAF has a removable lid on the electronics box. Is there something in there I could learn something from?

I've been banging my head on this for a while. I can't find any information to resolve it. And I know reman MAFs are a crap shoot, probably dicier than just using this one.

jiho 06-01-2011 02:27 AM

Re: Two different Hot Air MAFs?
 
Here's a link to www.turbobuick.com where I just posted a pic of the MAF, with focus on the sticker:

http://www.turbobuick.com/forums/hot...nal-reman.html

Keller 06-01-2011 01:04 PM

Re: Two different Hot Air MAFs?
 
You do realize you can post pictures here, right?

My guess is that whatever changes were made from 1984-1985 were minor, and either done to enhance tuning or to simplify the construction of the device. There is a very good chance that both are essentially interchangeable.

On the 1984-1986 cars vs. 1987/1989 cars there was a change to the knock sensor filter. The change was to simply go from a four-pole filter to a two-pole filter. It was determined that a two pole filter performed well enough, and four were overkill.

A good source for this answer might be Eric Fisher. Or possibly Eric Marshall. Actually, Tom Chou would probably be the best to answer this, but I doubt you'd be able to find him...

jiho 06-01-2011 04:02 PM

Re: Two different Hot Air MAFs?
 
Quote:

Originally Posted by Keller (Post 58839)
You do realize you can post pictures here, right?

I couldn't figure out how, presumably because it's not exactly the same as over there, but I did notice later that people here do.

Quote:

Originally Posted by Keller (Post 58839)
My guess is that whatever changes were made from 1984-1985 were minor, and either done to enhance tuning or to simplify the construction of the device. There is a very good chance that both are essentially interchangeable.

The parts catalog claims there was a "2nd design" '85 with a ThermAC air cleaner setup, controlled by a coolant thermal vacuum switch. Maybe when the snout door opened the MAF got a blast of cold air.

But if it was any kind of "backward compatible" improvement, you'd expect GM to specify the same service part for the '84. The various service MAFs all listed for exactly the same price.

My concern at the moment appears to be "forward compatibility" of the '84 MAF to the "1st design" (non-ThermAC) '85. PROM-specific tuning might be an issue, however small. This is for a driver, I'm in California, and we do have smogcheck.

Quote:

Originally Posted by Keller (Post 58839)
On the 1984-1986 cars vs. 1987/1989 cars there was a change to the knock sensor filter. The change was to simply go from a four-pole filter to a two-pole filter. It was determined that a two pole filter performed well enough, and four were overkill.

You mean the ESC module, right?

Overkill for '84-'86, or for '87/'89 as well? Would you expect the '84-'86 ESC to drop into an '87/'89 and work fine with no complaints?

Quote:

Originally Posted by Keller (Post 58839)
A good source for this answer might be Eric Fisher. Or possibly Eric Marshall. Actually, Tom Chou would probably be the best to answer this, but I doubt you'd be able to find him...

Maybe you can't find him because he did know, and GM found him first....

Keller 06-01-2011 04:44 PM

Re: Two different Hot Air MAFs?
 
Quote:

Originally Posted by jiho (Post 58843)
The parts catalog claims there was a "2nd design" '85 with a ThermAC air cleaner setup, controlled by a coolant thermal vacuum switch. Maybe when the snout door opened the MAF got a blast of cold air.

Did the 85s ever really have the thermal door? Regardless of what the parts catalog said, I think this was something never produced, much like the water/alcohol injection that was stillborn and the reason for the "Power Injection" section that has no illumination on the Regal dash.

Quote:

Originally Posted by jiho (Post 58843)
My concern at the moment appears to be "forward compatibility" of the '84 MAF to the "1st design" (non-ThermAC) '85. PROM-specific tuning might be an issue, however small. This is for a driver, I'm in California, and we do have smogcheck.

I doubt it would be an issue. Comparison might be the only way to check.

Quote:

Originally Posted by jiho (Post 58843)
You mean the ESC module, right?

Semantics.

Quote:

Originally Posted by jiho (Post 58843)
Overkill for '84-'86, or for '87/'89 as well? Would you expect the '84-'86 ESC to drop into an '87/'89 and work fine with no complaints?

Absolutely. It was probably more of a financial issue. By saving a few cents or dollars per vehicle, such a change can be justified. Especially with repair parts stock on the shelves.

Quote:

Originally Posted by jiho (Post 58843)
Maybe you can't find him because he did know, and GM found him first....

Huh? Tom has been to my home. I don't think he really is so much an 'out in public' sort with his knowledge and talents as he perhaps once was.

jiho 06-01-2011 05:27 PM

Re: Two different Hot Air MAFs?
 
Quote:

Originally Posted by Keller (Post 58844)
Did the 85s ever really have the thermal door? Regardless of what the parts catalog said, I think this was something never produced, much like the water/alcohol injection that was stillborn and the reason for the "Power Injection" section that has no illumination on the Regal dash.

It's in the illustration section, but not in the listing section. And I don't know of anyone who has seen it in an actual vehicle.

Of course, that wouldn't rule out the possibility that GM developed a MAF to accommodate it and stuck with it anyway.

Quote:

Originally Posted by Keller (Post 58844)
I doubt it would be an issue. Comparison might be the only way to check.

Probably. Getting one's hands on known-good comparison units is the problem.

I would not be surprised if the '84 MAF was used in '85 production cars. I would not be surprised if the MAF and ECM in my photos came in the same '85 car from the factory.

Not knowing is eating my brain....

Quote:

Originally Posted by Keller (Post 58844)
Huh? Tom has been to my home. I don't think he really is so much an 'out in public' sort with his knowledge and talents as he perhaps once was.

Sorry, that was a lame joke, along the lines of GM putting a hit on him to keep him quiet about the real truth behind all of this.

jiho 06-03-2011 05:44 PM

Re: Two different Hot Air MAFs?
 
....which in turn was a wry commentary on how difficult -- impossible -- GM made it to get this kind of information about these particular units.

jiho 06-03-2011 06:03 PM

Re: Two different Hot Air MAFs?
 
Quote:

Originally Posted by Keller (Post 58839)
A good source for this answer might be Eric Fisher. Or possibly Eric Marshall.

These gentlemen, while they might have useful knowledge and try to be helpful, are mainly occupied with selling alternatives to the original factory configurations. As noted, this isn't really a viable option for me in this situation at this time.

Keller 06-03-2011 08:00 PM

Re: Two different Hot Air MAFs?
 
Um...not really.

Honestly, I'm not sure you know who Eric Fisher or Tom Chou are, what they do, or what they have done. While Eric Marshall sells aftermarket chips, I do think he has appreciation for the delicate (and antiquated) nature of the technology involved in making these cars run.

I'm pretty confident at least one of those listed knows the answer to your question.

jiho 06-03-2011 11:18 PM

Re: Two different Hot Air MAFs?
 
At the risk of getting an even angrier looking smiley....

You aren't showing much interest in the answer yourself, despite having been around these motors a lot longer than I have.

I'm just amazed this is not a point of interest for people. As far as I can tell, I'm the only person who's ever expressed any interest. :dunno:

I'm certainly not very enthused about bugging people who aren't interested enough to engage in this thread of their own volition.


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