I have been fighting a rough running engine for a while now. It all started after I replaced the intake gaskets and I also had to replace the MAP sensor because I damaged it when the intake was off. The MAP sensor I bought was a cheap china unit that I believe is the cause of my problem. I ordered another MAP sensor that is made in USA and it runs worse with that one than the first one I bought.


After looking online I am getting different information on what is the right part number for the jimmy. The ACDelco website says the right P/N is 12614973 but when I enter that in some websites it says that is NOT the right one.


Has anyone replaced their MAP sensor on there 1997 Jimmy or blazer and if so can you tell me what the part number was.


The readings on the scanner was very different from one another also.

 

Is the check engine light on? Are there any DTC's in memory? Did you replace the silicone seal in the plenum for the MAP sensor. They are one time use, if you remove the sensor, the seal needs to be replaced.

 

MIL is on with p0171 and p0174 codes. Before intake change there was no problem.

I did replace the silcone seal.

I have checked for vacuum leaks using carb cleaner while engine is running and I smoked the engine with smoke machine and did NOT find any leaks.

 

P0171 & P0174 indicate lean on both banks. If they set simultaneously, and you can't verify any vacuum leaks, low fuel pressure can set those DTC's. Here's a link: https://blazerforum.com/forum/2nd-ge...eakdown-88305/

 

I have checked the fuel pressure and it is good. I even replaced the fuel pump within this time due to the leakdown not passing even though I didn't think that would fix my stumbling problem but it did fix the leakdown problem.


Remember this only started after the intake was removed and replaced and at the same time I replaced the MAP sensor.


The codes do say it is running lean on both banks so I immediately thought I had a vacuum leak but I have not been able to find any evidence of a leak. I have had the upper intake off twice because I figured that is where it had to be. I smoked the engine and sprayed carb cleaner and can not find anything.


The puzzling part is how after the first 15 to 45 seconds of starting it smooth's out and runs fine.

 

If you damaged the MAP sensor, you may have also damaged the MAP sensor connector. I had to replace mine because it was kinda doing the same thing. It would idle rough for about 2-3 seconds then run normal but it did set the code for the MAP sensor. I know there is a flow chart in here somewhere to check this but I could not find it (maybe in the Tech Article DIY section).

 

If this happens on a warm restart, it makes perfect sense. On each start up, the PCM operates in open loop, and oxygen sensor data is ignored. If the engine is warm, it switches to closed loop very quickly, and the PCM uses the oxygen sensor data for fuel control.


After the engine sits for 10 to 12 hours, (without being started) and stabilizes with ambient temperature, connect your scan tool, turn the ignition to the RUN position, don't start the engine. Compare ECT, (engine coolant temperature) IAT, (inlet air temperature) and ambient temperature. Ideally they should all be the same, or within 2 or 3 degrees of each other. Post the results.

 

here are pics of the live data with key on engine off after sitting overnight.

 

Coolant at 37F
IAT at 42F

There's 5 degrees right there. The third temp reading will be the deciding factor... what was ambient temperature when these were taken?

 

Didn't measure temp when I got that data but I did check the IAT sensor with a chart from Mitchell and it showed to be within specs. The ECT sensor I didn't check but I will to see what it shows.

Something I did notice as I was checking the live data with scanner is with the engine off key on the MAF is showing 2.4gm/sec. Shouldn't that reading be 0gm/sec. I also thought the MAF reading rule of thumb was whatever your engine size in liters was is close to what the MAF should read at idle. So a 4.3 should be close to 4.3gm/sec and mine is around 5.7-6.0gm/sec at idle.

I was wondering what would a MAF reading of 2.4gm/sec high do to the fuel trims if the computer thought there was more air than there was coming in at idle.