More than likely the MAP sensor is bad. Early GM MAP sensors were prone to failure. They are cheap and easy to fix. Make sure you dont have a vacuum leak first, then try replacing it. Hope this helps...

 

MAP - Manifold Absolute Pressure if I remember correctly. I'm not that familiar, I've got the MAF.

Low reading could be grounded wire. If you don't see anything, change it out. I think about $30. Search the web for GM error codes or GM trouble codes and you should find more information.

 

Ya everything helps . I was just thinking if it was showing low due to some other component failure . It also showed a code 44 which is Lean Exhaust . Thanks


Jeff

 

The two codes could be correlated. The MAF/MAP sends information to the ECM about the engine load... how hard it's working. The ECM then leans or enriches the mixture to take into account the load. So, depending on what happened to the sensor, the engine could have been being trimmed too far back on gas and power loss and overheating could be the result until the sensor finally fails and is outside the ECM parameters and an error code is thrown showing two codes, not just a MAF/MAP sensor failure.

 

Typically if it was just a vacuum leak ..it would be accompanied by a high idle. If you unhook the PCV hose the idle will go high and you'll lose all your air doors inside. Swap out the MAP sensor.

Funny though ...I was unaware that a faulty MAP sensor totally disabled the vehicle.

 

I'm guessing that a bad MAP sensor will fool the computer into thinking there is no vacuum. Thus it thinks its WOT and floods the engine.

 

Leve , would a faulty MAP sensor make the vehicle not run at all ? What about a bad Oxygen sensor ? I`m thinking that the O sensor would just make the car run to lean/rich . I`m trying to do the best home work I can before going out and buying my armful of new sensors

. Thanks for the all the input guys ! If she ( my daughter) wasnt on the tight college budget I`d take her out and go (semi-new) car shopping . If you`ve had kids in college ( I think you have had , Larry ) you know what kind of extra money they have ( and thats including DAD`S help , hehe) .

Jeff

 

Jeff, don't discount there could be more than one problem contributing the overall "it ain't running" result. But try first to work on one at a time. I've seen MAP sensors foul up the EFI to the point the ECM is brain dead. It's a place to start. If the engine uses a two step process for setting the EFI, open and closed loop then in open loop the MAP and O2 sensor should be out of the loop. This condition is only when the engine's cold, like when you're trying to start it.

Does the engine cough or sputter? Is there spark? Are the plugs wet, fuel fouled?

More often a bad MAP can cause hard starting, stalling, and missing. In later model EFI even uses the MAP to help decide when to up and down shift the transmission as it is a fairly reliable indicator of manifold vacuum. This may be being used in Open Loop if the EFI's new enough.

As to the O2 sensor... heck you unhook it and the car should still start and run but like you said.. run rich. It's not a bad idea to take the O2 sensor out every now and then and wire brush the housing to free the vents. They can become clogged and then they're not able to sense the mixture and it drives the ECM nuts by sending it a false reading.

At this point I'm not thinking the 02 senosr is involved.

Drop back to basics... we need more input, again:

Do you have:
Spark
Fuel
Air
Timing

What's missing?

And you're right:

College + Kids = NO money. I've had kids in college the last 10 years and now you all know why my Jeep's the ugliest thing on 4 wheels... I think it still has four wheels... it's been a long time....

 

Larry

She is on her second computer in this car . Had a re-manufactured one put in last Christmas . I`m going to double/triple check the spark , fuel etc.. and report back tomorrow . I guess the codes I`m pulling from the comp. right now are saying what condition it was in last time it was actually running , correct ? OPEN Oxygen Sensor Circuit and LOW signal on the MAP sensor . That doesnt really mean that those components are bad , right ? I`ll have more info. tomorrow . Thanks again !

If I havent mentioned it , its like a good old motor with the distributor way to far advanced , you know like it really wants to catch , but just doesnt .


Jeff

 

My original post was based on the assumption that the ONLY code was the MAP. Get ALL the codes, write them down and give us the information. Then disconnect the battery to clear the codes.

Check the basic items in LEVE's list.

Check the plugs. Are they totally fouled? I had it happen.

A bad O2 sensor or MAP should not keep it from running.

If you get it to start, recheck the codes.

 

Well I finally got a couple days off work and played with the car yesterday . This is what I found .
1. Number one piston is at the right spot when the rotor is at # 1 under the cap and lines up perfect on the timing marks .
2. Plenty of fuel going down the TBI throat .
3. I charged up the battery and cleared all the codes and had it running yesterday , ran perfect for 10 minutes then stumbles bad and stalls .
4. I pulled a plug and it sparks good for about 4 revolutions then hardly anything at all . So tested the coil and cant see anything worng with it . So right now I`m thinking the module perhaps in the distributor is bad . This problem only happens when the car warms up .
5. I also tested the voltage values on the MAP sensor and they appear to be ok BUT the only code I`m pulling off the computer right now is a 34 ( MAP Sensor [low signal] ) ?????
after it stalls , no other codes present .

I un-hooked the O2 sensor and it runs richer but still runs ok , the O2 sensor isnt the problem .

When the motor does stall its like its dieseling too .

I`ll play around some more today with it .

Jeff

 

Sounds like a possible vacuum leak.

Run the engine with the MAP sensor disconnected. Do you still get the MAP low error?

Clear all the codes again. Reconnect the MAP sensor. When does the SES light come on? When you first start the engine, when it dies, other?

 

Well I was just out fiddling with it again and I`m almost convinced it`s the magnetic pick-up coil under the rotor inside the dist. It`s getting good spark from the coil ( and that eliminates a lot of other circuitry) but on the spark plug output its very intermittent , not what you should see out of a Hi energy ignition , sometimes it was so weak you couldnt see it at all . I`m going to go hunt for a used distributor and put that in and see . I still think there is a problem with the MAP sensor too , but it`s not the reason why its not running right . When I find some parts I`ll grab another MAP and put that in after I get the dist. in . That`s the update , thanks for help and opinions Taz . I`l let ya know how it goes .


TAZ . When it ran yesterday I had the volt meter on the MAP and it got the exact readings that it said it should have in the service manual . 5 volts , engine off . 2.0-2.5 volts with engine running , according to the book thats what it should be reading .

Jeff

 

For some reason ..I can't get away from EGR issues on the brain this week. The only reason that I mention it was because a friend of mine had a similar experience (exclusive of your "spark" problems) ..the car would start fine and drive okay ..until it warmed up and then would progressively stumble and die ...and not restart. It too had the "Chevy Chase Vacation Family Truckster" dieseling before giving up the ghost. This would also be independent of electronic problems. That is, it could create an anomoly without being indicated (not for cause only effect) by the OBD.

 

When I go to the auto wreckers for the distributor tomorrow I`ll grab another MAP and replace it anyways to be safe . The car has been running rich for some time and I still suspect the MAP has problems . When I tried to start it this morning (cold) it wouldnt run at all , thats when I did the more detailed spark tests . I`ll let you all know tomorrow how it went . I would just go and get a new pick up for the dist. if I hadnt of had this one in the vise a little crooked and broke the thing

.

Jeff