1993 L27 MAF sensor Frequency or volts?

So just bought this awesome 93 Riv with only 60k on it and no rust. I am only getting about 19MPG though. So going through things and found an Actron scanner that seems to read the live data ok, but the MAF readings are from 1700-11000? The scanner says it is gr/sec, but I am thinking that it is Hz? Anyone know if this is supposed to be in Hz? I have the 93 service manual, and it says it should be in grams. I can not seem to find much info, except that if in Hz, it should run about 5000 hz at 3500 rpm? Mime is way over that. It does seem to be pretty smooth increase and decrease when I rev it up and down, and cruising down the highway at 1900 rpm, 65mph, MAF stays around 7500.

Any thoughts would be greatly appreciated....

I also read somewhere that these don't get the typical MPG of 30+? I had an 86 Old's and it was great on fuel.

The MAF measures the mass of air entering the throttle body. It uses that to set up the fuel injection. The signal is in Hertz. According to my 1998 FSM, the reading should vary from 2000 Hz at idle to 10,000 Hz at maximum engine load.

Ah, this is the confirmation that I needed. Thanks Larry.

https://www.aa1car.com/library/maf_sensors.htm

You need to look through your 93 FSM and see what normal readings are. I quoted 1998 figures, apparently, it varies.

Quote :

So just bought this awesome 93 Riv with only 60k on it and no rust.  I am only getting about 19MPG though.  So going through things and found an Actron scanner that seems to read the live data ok, but the MAF readings are from 1700-11000?  The scanner says it is gr/sec, but I am thinking that it is Hz?  Anyone know if this is supposed to be in Hz?  Essay writing service at https://homework-writer.com/ you will find I have the 93 service manual, and it says it should be in grams.  I can not seem to find much info, except that if in Hz, it should run about 5000 hz at 3500 rpm?  Mime is way over that.  It does seem to be pretty smooth increase and decrease when I rev it up and down, and cruising down the highway at 1900 rpm, 65mph, MAF stays around 7500.

Any thoughts would be greatly appreciated....

I also read somewhere that these don't get the typical MPG of 30+?  I had an 86 Old's and it was great on fuel.

mine stays around these numbers too
always thought its normal

One reason the Rivieras are so good on gas is the gearing. 60 MPH is about 1600 RPM, at 2000 RPM, I am very near 80 MPH.

LARRY70GS wrote:

One reason the Rivieras are so good on gas is the gearing.  60 MPH is about 1600 RPM, at 2000 RPM, I am very near 80 MPH.

Really? Now this if one of the 1st comments about the Riv's getting great MPG? And your rpm's/MPH sounds more in line of what I thought I would see too... I wonder if they changed the gearing between the 93 and 98 models? I envy you man....

waynehere wrote:

LARRY70GS wrote:

One reason the Rivieras are so good on gas is the gearing.  60 MPH is about 1600 RPM, at 2000 RPM, I am very near 80 MPH.

Really?  Now this if one of the 1st comments about the Riv's getting great MPG?  And your rpm's/MPH sounds more in line of what I thought I would see too... I wonder if they changed the gearing between the 93 and 98 models?  I envy you man....  

Yes, the gearing was a bit different. According to what I could find on the net, the 93 Riviera had a differential ratio of 3.06, and a .70 overdrive gear for a final drive of 2.14. The 98 Riviera has a 2.93 and a .70 overdrive gear for a final drive of 2.06.

To figure RPM at speed, use the following formula,

336/tire height X gear X MPH = RPM

The stock tire for your 93 is a P205/70R-15. That tire is 26.3" tall

336/26.3 X 2.14 X 65 = 1777 RPM


For my 98, the stock tire is a P225/60R-16. That tire is 26.6" tall.

336/26.6 X 2.06 X 60 = 1561 RPM

336/26.6 X 2.06 X 80 = 2082 RPM.

...at 55 MPH the '98 Riv is not that far off cold idle... the secret is that the standard cam is ground to give low end **grunt** and torque. The 3800 will rev 5000 RPMs but its power band so to speak is way lower.

I was just doing some testing and my LTFT is way high.  Like 148, where 128 is supposed to be "0".  STFT was bouncing above and below 128, which I think is normal.  That was sitting still and revved up to 2500 rpm for 45 seconds.  I also have recorded going down the road and it runs high, like 138 or higher. This is supposed to mean it is running lean? It never does get back down to 128. I took it on a 100 mile trip on the expressway and only got 21 mpg. According to the original sticker on it, supposed to get 27 on highway.

I tested the fuel pressure and it starts out at 43ish and drops down to 38ish when I start it.  All within specs according to the shop manual.  Also have put a new GM O2 sensor, fuel filter, MAF sensor, PCV.  Tested exhaust pressure and less then 1.5#.  So not plugged.  About only thing left is Vac leak or fuel injectors.  I tried starting fluid around the engine, but never noticed any change in rpms...

So looked into getting the fuel injectors cleaned and tested, then found some reman injectors on Rockauto for $21/injector.  Cleaning was going to be about $18 a piece.  This way, not much of a down time swapping them out instead of sending them out and not getting them back for a couple of weeks.  Should get them next week sometime. Also, going to build a smoke machine to see if I have any Vac leaks.  

Interesting fact is there is no EGR valve on this?  Someone told me maybe it was built in Canada, but the VIN shows it was in the USA.  Weird...

Thanks to all of your responses...

On my 98, Fuel trim is expressed in a percentage, and it can be positive or negative. Typical values range from -10% to +10%. Negative values indicate the PCM is pulling fuel in response to a rich condition, Positive values indicate the PCM is adding fuel in response to a lean condition. One of the indicators of a bad MAF is large negative fuel trim numbers.

waynehere wrote:

I was just doing some testing and my LTFT is way high.  Like 148, where 128 is supposed to be "0".  STFT was bouncing above and below 128, which I think is normal.  That was sitting still and revved up to 2500 rpm for 45 seconds.  I also have recorded going down the road and it runs high, like 138 or higher.  This is supposed to mean it is running lean?  It never does get back down to 128. I took it on a 100 mile trip on the expressway and only got 21 mpg.  According to the original sticker on it, supposed to get 27 on highway.

I tested the fuel pressure and it starts out at 43ish and drops down to 38ish when I start it.  All within specs according to the shop manual.  Also have put a new GM O2 sensor, fuel filter, MAF sensor, PCV.  Tested exhaust pressure and less then 1.5#.  So not plugged.  About only thing left is Vac leak or fuel injectors.  I tried starting fluid around the engine, but never noticed any change in rpms...

So looked into getting the fuel injectors cleaned and tested, then found some reman injectors on Rockauto for $21/injector.  Cleaning was going to be about $18 a piece.  This way, not much of a down time swapping them out instead of sending them out and not getting them back for a couple of weeks.  Should get them next week sometime.  Also, going to build a smoke machine to see if I have any Vac leaks.  

Interesting fact is there is no EGR valve on this?  Someone told me maybe it was built in Canada, but the VIN shows it was in the USA.  Weird...

Thanks to all of your responses...

Your post jogged my memory as to some chit chat with the service manager at my local GM dealer. We were talking about the low quality of certain aftermarket EGR valves, and he explained about the tuned port version of the 3800 not having EGR valves installed, from MY 1990 thru MY 1992, and that depending on how you looked at it the EGR was not really a need. SO... I did a quick web search and found that GM also deleted the EGR from the 3300 v6 from 1989-1993. Both engines passed emissions without EGR valves, but over time (I imagine, longer than the warranty period and internal testing, shorter than lifetime testing and field experience) GM found burning exhaust valves and cracking exhaust manifolds due to higher combustion temperatures. So, in MY 93 GM put the EGR Valve back on the 3800 Vin L Tuned Port. They did not bother putting it back on the 3300 because they stopped using that engine.

Where I ended up -- the original EGR on my car gave out after several years, and I was venting to the service manager because the replacement (A Standard T-series) quit after 2 years and cost a good buck (at retail, locally). He quipped that an earlier version of the 3800 didn't even have the EGR on, and the electronic version on my car was there (instead of a vacuum operated version) because if you controlled the EGR electrically rather than by vacuum you could get the computer to run it so as to improve performance... or at least, to not be such a drag... With that in mind, I put on a BWD, which itself only lasted about 45,000 miles... SMH... I replaced that BWD with a new Delphi and installed a gasket with screen because I had heard that one think killing the EGRs was soot getting in. How that screen stops anything I have no idea BUT I have not had to mess with the EGR since I did it about 100,000 miles ago, in 11/2014.

Interesting with the adding an EGR valve. Do you remember what all was involved? Did they replace the exhaust manifold with one that has a port on it? Where did they hook into the intake manifold? Is there a kit?

Thanks for all this info.. Never too old to learn things..

waynehere wrote:

Interesting with the adding an EGR valve.  Do you remember what all was involved?  Did they replace the exhaust manifold with one that has a port on it?  Where did they hook into the intake manifold?  Is there a kit?  

Thanks for all this info..  Never too old to learn things..  

Easiest and best thing to do is look at any '94 or later 3800 engine in a junkyard GM car -- Camaro, Firebird, Olds 88, 98, Pontiac Bonneville, Buick LeSabre, some Grand Prix, some Buick Regal, some Buick Century.

So just a little update. I changed out my injectors and a couple of small Vac lines that broke taking the fuel rail off. MPG went up to about 23. Up from 19. Still going to change the intake gaskets too. Hopefully this weekend...

waynehere wrote:

LARRY70GS wrote:

One reason the Rivieras are so good on gas is the gearing.  60 MPH is about 1600 RPM, at 2000 RPM, I am very near 80 MPH.

Really?  Now this if one of the 1st comments about the Riv's getting great MPG?  And your rpm's/MPH sounds more in line of what I thought I would see too... I wonder if they changed the gearing between the 93 and 98 models?  I envy you man....  

...check me on this, but I think there were changes in the 3800 engine. Not to mention that for it's size the 8th gen Riv does not weigh very much at all and is aerodynamic. My '98 gets better highway mileage than my '90 Subaru Legacy 4-banger did (5 spd manual, FT AWD), on highway. (city, not so much). It got 22-23 MPG at posted highway speed, my Riv gets a very solid 27.

Finally got the intake gaskets replaced as well as some of the other little hoses and o-rings. I did find some leaks around a couple of the intake ports where some sludge had built up, probably water getting into the oil. The antifreeze was really dirty too, so flushing that out too.

Still had a really bad stutter when warmed up at idle, so put in a new IAC valve and that seems to have cured that problem. Now to run it for a few hundred miles and see what the MPG gets.

So an update is in order.  The rough idle was still there, so I started unplugging sensors to try and find the culprit, and when I unplugged the MAF sensor, it calmed the engine right down.  I looked up when I replaced it and it was back in Dec, and the problem started about 2 weeks after it was installed.  Looked up the warranty from Rock Auto and it was only 90 days.  Ugh.  I usually look for that too..  So instead of just getting it replaced and dealing with it failing again, I bought one from Advanced Auto with a limited lifetime warranty.  Of course then it started to stall after I installed the better one and gave me a code about the MAF sensor.  So I did a soft reboot of the computer and this morning it was running great.  When I did the intake gaskets I had the battery unplugged for a week and it did a hard reset on the computer and was running rich for over a week.  Apparently if unplugged for more then 2 hours it will do that.  The soft reset just reset some of the minor sensors is all and was just the trick I needed.

So now my fuel trims are finally in line too.  So I think I finally got it back into shape.  Now to put some miles on it and see if I can get the 27MPH, or higher, on the highway like it says on the dealer sticker...  

Update. Seems to be running just fine now. I have a 18 mile trip to work, mostly expressway, and am getting 22-23mpg. Took it on a 200 mile trip on the expressway and got 27mpg. So I seem to have fixed my poor fuel economy... Now the wife wants me to look at her subaru... I just want to stick to the Buick....