I have a 2001 Blazer 4x4 LT with 109,000 miles. I have owned it for 10 years. A few days ago, suddenly, it drastically lost power while going up a hill. I can back off the throttle and it the engine will smooth back up, running smoothly, but still can't give it much throttle or it will starve out again. It returns to perfect idle, you just can't give it much throttle.

I figured the fuel pump (only 2 years old (28,000 miles)) was losing it's ability, so I installed a new pump and filter with no change to the starving out of gas problem.

There are no trouble codes showing. Engine always starts and idles perfectly and you can drive around up to about 35 on flat road, but "runs out of gas" if you try to go faster, till you let off the throttle. Engine doesn't die, it returns to smooth idle.

Today I installed a new pressure regulator. It seems to have picked up a little power but far from normal. I did get it up to 50mph on flat road but on an incline you have to back off the throttle to keep it the engine from fading out and drop down to about 20-25 mph up hill to keep it running smoothly.

The static and idling fuel pressures are correct for the old pump and the new pump just installed. After shut down it will hold 59-60 pounds for 10 minutes and longer.

I took the gas cap off this evening and drove about a mile just to make sure the tank didn't have a venting problem. That made no difference, still same symptoms as above.

The blazer has never had any misfires or problems and has always ran perfectly. I have always consistently gotten 16.5-17.5 mpg around town and 20-22 mpg on the road.

What should the pressure gauge read while being driven? I'm thinking of removing the hood (or putting spacers under the hinges) so I can see the gauge and see if the pressure is drastically dropping off when it starts starving for gas.

Could the injector spider unit be the problem?
Still no trouble codes (the light does work).
Any ideas on what to check next?

 

Welcome to the forum!

On your 2001, in the underhood fuse panel there is a "pump prime terminal"




Connect the fuel pressure tester to the service port, just to the driver side of the distributor. Ignition OFF. Connect a fused jumper wire from battery positive to the pump prime terminal, this will activate the fuel pump. Pressure must be 60psi to 66psi while the pump is running. This is your regulated fuel pressure, it is the highest pressure the injectors will be exposed to. GM does not publish any "engine running" fuel pressure specs as there are far too many variables involved. Remove the jumper wire, fuel pressure will drop slightly but must remain above 55psi for at least 10 minutes. Post your results.


Have you checked exhaust backpressure? It could possibly be a restricted converter. Removing an upstream oxygen sensor, pressure must be less than 1.25psi at 2K rpm.

Edit: If the SES light does not come on or flash while driving, and no DTC's are in memory, the problem is something that the PCM does not monitor. The fuel delivery system and exhaust backpressure are not monitored by the PCM.

 

What about your MAF sensor? Have you tried cleaning it as well? How long has it been since you've had a full tune up?

 

Captain Hook, thanks for the photo showing the prime terminal. (I hadn't seen that anywhere else).

The pump pressure is 64 psi at constant on state, and the pump motor is pulling 8.4 -8.5 amps through the prime connection.

Engine idling up through 3000 rpm (no engine load) pressure is 57-58 psi.
After shutdown, pressure drops to 54 psi. After 10 minutes and 20 minutes the gauge still holds 54 psi.

Something strange. I just went out and checked the gauge again, about 45 minutes since shutdown and the pressure has gone up to 60 psi now.

The other pump (installed 29 months ago) was holding correct pressures and leak down was well within specs also.

I haven't checked the exhaust back pressure. I figured since it was running perfectly, with plenty of power, then suddenly has no power, that the cat wouldn't have developed a sudden problem. Am I thinking correctly?

But, it is definitely starving out of fuel if you give it too much throttle. If you get on the throttle a little more aggressively, it starves out quicker and takes longer to recover back to where you can get it back above 1500 rpm.


mrspeedy69, The last tune up was 28,000 miles ago (29 months ago at 82,000 miles) when I replaced the fuel pump for the first time.

 

mrspeedy69. I haven't cleaned the MAP sensor, but picked up a can of MAP sensor cleaner this evening.

 

It's been 90 minutes since shut down and the pressure has dropped down to 52 psi now.

 

That's the devil in this, great mpg and all of a sudden. I don't see were your at, could you have parked on some snow or hit a pothole and shattered up the ceramics in the cat.

Cheapest next I would do is pull the easiest upstream o2 and see if you have any more power.

 

yea,id call the pump fine.

Go adead and pull a o2 sensor and see if it runs better. Ive noticed alot of hesitation issues with corroded distributor caps. pop it off and look at it. clean em up with a wire brush and go to town. they can corrode fairly quickly.

 

spittybays, I'm in southern Ky and haven't seen an inch of snow yet. :-( It's not ran over anything or hit any potholes. We did have a lot of black ice and freezing rain all day Friday when the Blazer started acting up. I had been in and out with the Blazer most of the morning, probably 5-15 miles at a time. Got to love having 4 studded snow tires on an extra set of wheels for days like that. I had headed out again and got about 5 miles away when it lost all power when I started up a long hill. I got it back home, putting along about 15-20 mph, babying the throttle to keep it running smoothly. Too much throttle at it starts surging bad (leaning out), then back off the throttle till it smooths back out and keep going, just real slow.

 

Couple of things:

GM does not publish any "engine running" fuel pressure specs for this engine, there are far too many variables involved: engine condition, elevation above sea level, condition of fuel injectors, etc etc.

64psi KOEO is fine. Drop to 54psi "technically" is out of spec, but the fact that it holds solid, I don't think I'd worry about it. Your increase in fuel pressure, 45 minutes after the pump shut off, is due to engine heat transferring to the fuel lines under the hood. This is the reason for checking leakdown with the engine cold. If you've got heat increasing the pressure, you won't get an accurate reading of leakdown.

As mentioned, I'd remove the upstream oxygen sensors and take it for a short drive. If the converter is restricted, you'll notice an improvement in performance with the sensors removed.

Post your results.

Edit: Might be the ignition coil is "leaking" spark. More than likely it would set a P0300 series DTC, but worth checking.