Alright guys and gals. I have a 96 Blazer LS, 4 door, 4X4, manual shift transfer case, 4 wheel discs. Bla Bla Bla...... Anywho. It stalls out when you try to take off on a hill. This is according to my wife. In the driveway it revs very smoothly when you barely press the throttle, but at wide open throttle it studders above 3000 rpms. In may I replaced the fuel pressure regulator because the truck seemed to flood at Idle and would smooth out once you got it going. She also complains that when going down the road it will barely climb hills and has no passing power. I have only driven it a few times but I know there IS a problem, but what it is I'm not sure of. I have also changed plugs, wires, cap, and rotor button. I only have two codes which are both system too Rich bank one and two. I ordered an OBII to Bluetooth adapter in hopes of logging computer data to see whats going on. Suggestions

 

With those symptoms, the first step is check fuel pressure and leakdown. You'll need a fuel pressure tester. Most auto parts stores rent or loan them for free, and sell them for around $40. The test is quick & easy, takes about 15 minutes. Let us know when you have one available and we can explain how to do the tests.

 

I used to have a fuel pressure tester, but I think the garage trolls ate it. LOL I was going to rent one, but damn its 109 to rent up the street. I think I'll just buy one when I get a chance. Ever hear of a clogged fuel filter causing a problem? Just going over the different systems in my head at the moment trying to figure it out.

 

A restricted fuel filter can cause problems, and it would probably be a good idea to check & replace it if necessary. Usually doesn't cause symptoms like you're describing though. The pumps in these vehicles are capable of producing upwards of 100psi and regulated pressure is only ~63psi, so there is some room for error. A restricted filter will cause premature pump failure.

 

These are the two codes i'm getting, after clearing them, they constantly come back. I ordered a pressure tester, but it wont be here for a week. The thing is, it doesn't run rich till you get on the throttle. Has anyone over seen a regulator fail to properly regulate to the point that it was allowing the pressure to be too high but only under load. This thing is driving me crazy. I would think that a fuel pump would cause a low pressure or lean condition.

 

At idle, decel, & cruising, vacuum is high and fuel pressure is low. With the engine off or while accelerating, (WOT etc) vacuum is low and fuel pressure is high. Could be a regulator problem, or a leaky O ring in the fuel metering block.

If regulated pressure is too high, (out of spec) it's usually caused by a restricted fuel return line.

Checking fuel pressure and leakdown at the service port shows the lower of regulated pressure and maximum pump output pressure. For example: If the pump can only produce, lets say, 60psi, and the regulator is set for 62psi, your reading at the service port will be 60psi, which is within factory specs, but with only 60psi available from the pump, it's a serious problem. For that reason, it's best to check the maximum pressure that the pump can produce, along with testing at the service port. Pump max output is checked at the fuel filter outlet. All pressure and flow must end at the pressure tester, (no fuel allowed to the engine). Ideally, pressure and leakdown should be checked both places. Here's a parts list for building an adapter for checking max pump output:



You are correct that a failing fuel pump usually causes low fuel pressure and a lean condition.

 

I went through that same headache, all of the same symtoms and it ended up being the catylic converter clogged up. Check your back pressure for any restrictions. As the cat gets worst you will feel the difference in lack of power and even affecting your transmission shifting points in which are affected when the ecm is trying to compensate for all the back pressure build up which affects engine vacumn and fuel pressure. Alot of people start dumping money on new spiders and distributors do to multiple misfires and lack of power but it's the ecm simply trying to compensate. Good luck buddy.

 

I had wondered if it could be the cat, however, i had heard that they are self cleaning so i passed that up. How do you perform a back pressure test? Special tools?

 

Self cleaning? Absolutely not. Exhaust back pressure is checked at either upstream oxygen sensor. Remove the sensor, fabricate a fitting to go in the exhaust pipe, attach an accurate pressure gauge. Start the engine: pressure should not exceed .5 psi, (yes, one half pound). Check at idle and while briefly and rapidly opening and closing the throttle.

 

A far less accurate method would be to remove the O2 sensor before the cat, come-up with some kind of make-shift exhaust deflector for the open hole and then take Blazer out for a very short drive and see if problem is gone. This will set an error code, but if stumbling is gone...then the cat is plugged.

Captain's method is far better.