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MAF Sensor values on Scanner


venturenot
04-05-2010, 09:07 PM
The manufacturer advises that on a fully warmed engine the MAF Grams per second values should be between 4 and 7. My readings are around 3.75. Does this mean that my MAF is on its last leg? .....Just curious.

I cleaned the sensor to see if I could get the values to change, but they did not.

"The scan tool reads the MAF value and displays it in grams per second (gm/s). At idle, it should read between 4gm/s - 7gm/s on a fully warmed up engine. Values should change rather quickly on acceleration, but values should remain fairly stable at any given RPM. A failure in the MAF sensor or circuit should set DTC P0101, DTC P0102, or DTC P0103."

dewaynep
04-07-2010, 11:08 AM
I wouldn't say it is on its last legs. From the text you provided yours is a little low, but that could be from a dirty air filter, low idle, loss of vacuum, low compression, etc... As long as it is steady I wouldn't worry about it, but I'm not you. What's the long term fuel trim look like? If it's negative then you may have a point, but if it's positive or close to 0 then I wouldn't worry about it, but again, I'm not you.

venturenot
04-07-2010, 11:58 AM
The fuel trim bounces from about -11 to -25 but it does not throw a code. Engine occasionaly stumbles upon acceleration and whenever I try to sustain a speed of 55mph it stumbles like crazy.

dewaynep
04-07-2010, 01:14 PM
You may be right then, perhaps the MAF is getting weak. You should be able to disconnect the MAF sensor and the engine will still run based on the map sensor readings. Throttle response will be non-existant but you should be able to get up to speed as a check of the MAF.

venturenot
04-07-2010, 07:08 PM
Disconnected the MAF and it ran exactly the same as with it connected. The only difference was the long term fuel triim, it was not quite so bad. The readings bounced back and forth from -12.

Car really stumbles when I try to maintain 55 mph speed. No codes have been thrown ( except when I disconnected the MAF)

lesterl
04-07-2010, 10:27 PM
Had a very similar issue, cant remember what my MAF values were, but I told my uncle (GM mech) and he said Plug wires, I didnt believe him, so decided to do it to prove him wrong, all I can say is damnit, should have tried his idea earlier, now smooth as silk, a set of Bosch wires from autozone for $32 cured my issue (no codes either.)

venturenot
04-08-2010, 08:52 PM
Could be the wires, although my wires are fairly new AC Delco wires with about 50,000 mostly highway miles on them.

Funny thing today.. I took the van out on the highway and absolutely no problems. No hesitation or stumbling even the LT fuel trim was reading about -8. The only difference between today and the past week is that the air temperature dropped this afternoon into the 50's. It has been an abnormally warm April and earlier this week when I was having this problem the temps were in the 80's. I wonder if this is just coincidence or if the warm temps are helping to cause the problem?

dewaynep
04-09-2010, 06:47 AM
Well, that's some new info. Have you looked at the IAT and ECT values? They should both be about the same before starting the engine. Then the IAT should go lower and the ECT should go higher. Sounds like maybe you have a bad temperature sensor causing a rich condition.

lesterl
04-09-2010, 10:02 AM
The IAT sensor wont change alot, the CTS however will change in a pattern of ohms like in this link -> http://www.s10forum.com/forum/attachments/f107/98606d1222052466-little-help-needed-gm-sensor-chart.gif

venturenot
04-09-2010, 10:33 AM
At startup the IAT numbers are the same as outside temp. However, after the car is warmed up the IAT goes up to 30 to 40 warmer than outside temp. Is this normal? The coolant temp seem to be pretty normal.

lesterl
04-09-2010, 10:55 AM
Does this warmup cycle involve driving the van? If you just sit and idle it could very well warm up, altho I think a 30-40* warmup is kinda excessive for the IAT. I will check mine later, but I suspect maybe you have a sensor issue or something like sitting still and you are getting heat soak from the exhaust that passes under the intake tubing where the sensor goes in the top.

venturenot
04-09-2010, 11:00 AM
The warm up involves driving the van. The other day it was about 80 degrees out and my IAT was reading 120 degrees while I was driving. This morning outside temp was 44 and after 20 minutes of driving my IAT was at 70 degrees.

I think I will just go buy a new sensor, they are only about $20.00. After disconnecting the electrical sensor do you just pry out the old sensor with flat head screwdriver?

lesterl
04-09-2010, 12:08 PM
We are talking about the IAT in the rubber boot right? Just pry it out, can pull out by hand, be careful if you are prying on it, might twist it Clockwise/ CCW to loosen it before tugging on it. Keep in mind you sensor may be good, it may just be getting excessive heat. The PCM does sit in the air box, perhaps it is getting too hot? Perhaps the EGR is not fully closing and the exhaust mixture is getting in the intake? Have you done a mechanical check with a thermometer? Pull the sensor out and use one of the probe style thermometers, will have to put some packing around to eliminate a vacume leak. Keep the old sensor hooked up but sitting over to the side, run it to where you were having misreadings and see if it is bad on the thermometer.

venturenot
04-09-2010, 09:00 PM
I just went ahead and bought a IAT sensor at Advanced Auto for $14.00. No change, IAT values are still about 40 degrees warmer than outside temperature. I think that it is safe to assume that the original sensor was not faulty.

lesterl
04-09-2010, 09:15 PM
On my 97, or the 00+ motor the EGR is firewall drivers side of motor.

I checked mine, it was reading (in town traffic) ~ 20* warmer...... Good luck.

venturenot
04-11-2010, 08:35 PM
I found an article online that said the IAt and coolant values should be the same at startup. However, once the engine is warm the IAT value should be 100 degrees less than the coolant value. If both criterion are met, then most likely both sensors are OK.

dewaynep
04-12-2010, 01:35 PM
Are we still trying to diagnose the stumble at 55?

venturenot
04-12-2010, 03:18 PM
It has been running well with the cooler weather. I will wait until it gets warm again - 70's or 80's and see if it acts up.

lesterl
04-12-2010, 08:52 PM
What does the Ignition timing look like on your scanner?

venturenot
04-12-2010, 09:04 PM
There is a reading ignition DE? (not sure if that is correct)is that what you are talking about? If so, what should I look for.

Scrapper
04-12-2010, 09:08 PM
have you tried cps.? i never seen it on this thread but i could have misted it.

venturenot
04-12-2010, 09:10 PM
What is CPS?

lesterl
04-12-2010, 09:52 PM
CPS??? CTS?

IGN timing is degrees advance/retarded ( 2 decimal places either negative or positive. )

venturenot
04-15-2010, 11:16 AM
Had a very similar issue, cant remember what my MAF values were, but I told my uncle (GM mech) and he said Plug wires, I didnt believe him, so decided to do it to prove him wrong, all I can say is damnit, should have tried his idea earlier, now smooth as silk, a set of Bosch wires from autozone for $32 cured my issue (no codes either.)

You were right, it was the wires....thank you.

venturenot
04-15-2010, 11:20 AM
Had a very similar issue, cant remember what my MAF values were, but I told my uncle (GM mech) and he said Plug wires, I didnt believe him, so decided to do it to prove him wrong, all I can say is damnit, should have tried his idea earlier, now smooth as silk, a set of Bosch wires from autozone for $32 cured my issue (no codes either.)

You were right, it was the wires....thanks.

dewaynep
04-15-2010, 01:52 PM
Sometimes we overlook the simplest items. Glad it works now. By the way, what brand were the wires you used? 50,000 miles isn't much on a set of wires.

venturenot
04-15-2010, 02:44 PM
They were AC Delco and replaced them with Belden.

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