Have not looked at the MAP in such detail. Was not aware that oil could could clog it. If this is the case, why would oil be getting up that far in the intake? Does that just happen over time? Also, in the event no oil in the MAP, should I get an AC/DELCO part or an aftermarket brand from a local parts store?

Thanks

 

My opinion is always use the factory brand on the sensors. Mine was $40 from the dealer and with aftermarket you never can be sure the part worked correctly to start with. The orange map seal is $5 and should be replaced at the same time.

 

Ok, that's what I was thinking. I'll order an AC/DELCO.

Thanks.

 

ok, i just replaced the MAP sensor with a new AC/Delco part.

voltage readings are basically the same - i'm stumped???.

Engine running idle: 1.19 - 1.2 v
Engine running WOT: 0.96 V

the granatelli is still in there but fred has mentioned that would not cause the readings to be off.

please help

 

I had a similar miss too, I replaced the MAF instead of cleaning it. Put on a new one and problem went away. I stayed with stock, from the dealer. I heard LT1s can reject aftermarkets sometimes but that is just rumor, don't know from personal experience. Hope this helps.

 

thanks for the suggestion. i still have my old stock MAF that i will put on. but i'm still puzzled at the erroneous MAP readings??

 

Are you sure that you are getting an accurate MAP reading with your meter? The reason I ask is that if your new MAP sensor is functional and your replacement harness is providing a good connection, unless there is some other fundamental that I am missing you should get not get .96 at WOT. I am far from being an expert, but your problem sure stumps me.

 

I think there in lies the rub. How can it be tested UNDER LOAD with a voltmeter????? Aren't you just blipping the throttle while it sits in the driveway?

I would also like to know what the PCM is reading real time while all this is going on?

The test done directly to the MAP is to apply 10" Hg vacuum to the sensor and confirm the voltage changed by at least 1.5 volts(sensor signal on the green wire to ground on the black wire). If the change in signal is less or the voltage changes slowly, that indicates the sensor is defective. This is directly from the GM shop manual.

If the signal is less, confirm the 5 volts and ground at the MAP. Confirm the same voltage at the MAP that you read at the PCM. If it's different, you have a wiring issue. If it's the same, test the MAP by applying 10" HG to the sensor and confirm it rises quickly. If it's a lower voltage or rises slowly, replace it.

The MAP signal on the light green wire goes to the White PCM connector pin 23.

Sorry this reads confusing. I sent this information to someone that has incorrect readings at the PCM so he would be checking with the voltmeter. You already looked at the MAP so now you have to check what's at the PCM and then test the MAP for correct response.

 

don, the multimeter is pretty new and i can only assume its correct. it give correct voltages for the battery and some other components.

 

speedy, correct - the test is in the driveway blipping the throttle car in neutral.

a few things: what instrumentation do i need to apply 10" HG vac? i've never gone to the PCM to do any testing....how is this connector pin test done?

 

The measurement is done at the pin on the PCM just as you did the measurement at the MAP.
Anytime you have what appears to be a sensor problem. You should be sure the sensor has power and ground if applicable. Then be sure it's outputting the correct signal and then be sure it's getting to the PCM. If you had a scanner, you wouldn't have to trace the signal all the way back to the PCM.

To apply vacuum you could use a Mity-vac or other brake bleeder. Shown here:
http://www.mityvac.com/images/products/hvpo_04010.jpg
and
http://www.lislecorp.com/tool_detail.cfm?detail=1317

If you have a certain voltage on the green wire of the MAP connector, then be sure by probing or back probing the same wire on pin 23 of the white PCM connector. This tells you the signal is getting to the PCM. If the voltage is different at the PCM then at the MAP, it's probably a wiring issue.

To kill 2 birds with one stone, Pull the MAP from the intake and put the hose from the vacuum pump on the MAP. Set it to the equivalent of 10" of mercury and see what the voltage is at the MAP connector. Now measure the same thing at the PCM end of the green wire.

 

ok, continuation to this story: last year i had mac headers installed along with new plugs and the stumble essentially vanished. car still felt a bit rough in 5 and 6th gear, but no noticeable stumble. i assumed my old plugs were bad.

now the stumble is coming back. the car seems down on power too, with all the mods in my sig, if i drive off in 1st gear, then and smash the gas i don't even chirp tires - just stumbles from 1500 rpm to 2500.

i spoke to a friend who's a mechanic and he thinks it's either the opti is worn out, or my timing is off. i mentioned to him that when i installed the 1.66 roller rockers, i recall the arrow on the crank hub being off by 90 degrees. #1 cylinder was closed (valves all the way up) with arrow at 3 o'clock. he thinks the timing chain skipped because the pulley arrow can never be at 3 o'clock and #1 cyl closed? is this true? or do you guys think it's the opti? i also bought a mityvac so i'm going to check the map like don mentioned above.

car also has a brand new ram hdx clutch so i know it's not slipping that i'm feeling.

 

The pulley/damper hub is not keyed to the crank. It can (in extreme cases) rotate under heavy load, or may have simply been reinstalled incorrectly at some point in time.

Put a scanner on it and see what the MAP readings are under various engine operating conditons, UNDER LOAD.

 

I had the same problem it seems you are having, tried everything on the forum and some other stuff. Long story short it sounds like you have a small vacuum leak. Mine would show itself if i had to pick my daughter up from school or sit in traffic where I had to be on the brakes alot. I'm not a pro but I changed my intake gasket and never happened again.

 

how do you test for this?