97 blazer low fuel pressure

[tbnky]

My 97 Blazer has 186000 miles, 4.3L, W engine code, 4 door, 4x4, will run great for 10 - 12 miles. Then bogs down on acceleration. new egr valve, New fuel pump in Feb., new fuel filter, cleaned MAF, drove without cat, still having problems. Here are the results of the fuel pressure test:

ignition on/engine off 62 psi
engine runniing 52-54 psi
driving before problem 52-62 psi
driving after problem 52-46 psi
direct full fuel pressure at fuel filter 88-90 psi

Without throwing more money into this problem? What other tests can I perform to pinpoint faulty part? Any advice will be greatly appreciated. Thanks.

[MT-2500]

Fuel pressure is to low.
Specs are 60/66 lbs of pressure.
Check fuel pressure cold and then.
Recheck fuel pressure after hot or 30-45 minutes running.
After it gets hot block off or plug return line or check direct fuel pressure at in line to fuel filter.
Post back readings cold and hot.
Also recheck fuel filter and voltage and ground to fuel pump.
Was it a airtex pump?
MT

[tbnky]

I will recheck fuel pressure after engine gets hot. It is an Airtex fuel pump. By the way, I failed to mention that I did get two error codes a week ago P0171 and P0174. It is my belief that these error codes were the result of the low fuel pressure. Am I correct in my thinking?

[MT-2500]

Yes lean on both banks can be caused by low fuel pressure.
Also on a 97 make sure you run a voltage check on pump to.
97 is a bad year for ign switch problems.
And Airtex fuel pump is also bad news.
Carquest has droped them like a hot sput.
And other parts places are gettin a high come back rate on them.
Only replace with the AC Delco/delphi fuel pump.

If the airtex pump checks bad take it back and make them adjust it on a good AC Delco/delphi fuel pump.
Only about 25 dollars more.
Good Luck and let us know how it goes.
MT

[tbnky]

Originally Posted by MT-2500

Yes lean on both banks can be caused by low fuel pressure.
Also on a 97 make sure you run a voltage check on pump to.
97 is a bad year for ign switch problems.
And Airtex fuel pump is also bad news.
Carquest has droped them like a hot sput.
And other parts places are gettin a high come back rate on them.
Only replace with the AC Delco/delphi fuel pump.

If the airtex pump checks bad take it back and make them adjust it on a good AC Delco/delphi fuel pump.
Only about 25 dollars more.
Good Luck and let us know how it goes.
MT

Here are the results:

cold direct full fuel pressure at fuel filter 88-90 psi
hot fuel pressure with return line plugged 88-90 psi

voltage at fuel pump harness 11.37
voltage at fule pump harness\ground 11.45

After driving for 30 minutes, I noticed the following:

truck will accelerate if acceleration is ever so slightly fp holds at 52 psi

accelerate to much and fp will drop below 50 psi.

While testing fuel pressure, I noticed that I would have to turn ignition on\off a couple of times in order to energize fuel pump.

What is my next option?

[MT-2500]

Fuel pump is getting weak.
Recheck direct pressure when pump is hot.
Drop that airtex pump inthe trash can or take it back and make them adjust it on a ac delco/delphi pump
Time for a good ac delco/delphi fuel pump.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
Always check it cold and hot after a 30 minute run.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold and fuel pressure testing guide line.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.