My wife's blazer has a horrible bog under certian conditions. If you ease into the gas, it runs great. If you try to open the throttle quickly, it will bog. If you slowly open the throttle you can get to WOT whith no problem. The blazer also has trouble with hills, so it appears to be an engine load issue. In park the engine will spin up with no issues.

I have replaced the following in order: Coil, ignition module, O2 sensors (something was rattling around in the sensors), fuel pressure regulator (it was leaking, the only clean spot in the intake was under the FPR), spark plugs (#6 was fouled from the leaky FPR), and MAP sensor. The only code that I have gotten recently was for the evap system. I disconnected the evap line and capped it off to verify that it was not causing the problem (I reconnected after the test).

I checked the fuel pressure, 60 psi with key on, no less than 50 psi running. The pressure will fluctuate rapidly between 50 and 52 at idle (I assumed due to the injectors opening and closing) and the fluctuation goes away off idle. The fuel pressure does not change when the engine bogs or when the engine gets in the upper RPMs. I replaced all of the questionable vacuum lines. I connected the vacuum gauge and it has 14" vacuum at idle, but when the engine bogs (throttle 1/4 open or less) the vacuum drops to 0. Not good! I checked the timing chain stretch by rotating the engine with my hand on the distributor rotor. There does not appear to be any stretch in the chain.

I have unplugged the EGR valve - no improvement.
I have used a length of hose to listen for a vacuum leak - can't find one.
I have tried unplugging the MAF - bad idea, could not even back out of the driveway.

My forehead hurts from banging my head on the wall, does anyone else have any ideas?

 

Have you cleaned the MAF sensor? Unplugging the MAF electrical connection should not cause it to run poorly...

 

Have not cleaned the MAF lately (last cleaned about 9 months ago). But since it got much worse with the MAF unplugged makes me believe that it is something mechanically wrong.

 

I just replaced my Injector unit, Fuel pressure was fine, and no leakes detected but the unit was bad started as rough idel ended at Enjine Bog and cutting out on acceleration so it could be a bad unit

 

That is what I was thinking, but I wanted to try and eliminate all the "cheaper" causes before I dropped a couple hundred into a new injector unit.

 

gscrippler has a very much different fuel system than you have ershealy. You really should not change the spider without first monitoring the sensor readings at the time of the bog. If, at the time of the bog, the fuel pressure remains relatively steady, but the O2 sensor value limits high or low, you may have a fuel problem. It could also be a problem with another sensor giving the PCM bad data.

 

I claim victory!

Replaced the SCFI unit with an MFI upgrade. Runs like the day we bought the thing except it starts quicker and idles smoother. There was no sign of leakage, so I can only assume that a) one of the poppets or injectors was extremely fouled (ran several bottles of techron through the engine with no improvement) or b) an injector coil was getting weak.

 

Glad you got it fixed. I had to replace the SCFI spider in my old Bravada due to three stuck injectors that were ruining my mileage and fouling plugs. I didn't have the symptoms that you had here though. Made a good bit of difference for sure.